The Role of Nutrition in Enhancing Immunity in Aging

Aging Dis. 2012 February; 3(1): 91–129.

Published online 2011 September 30.

PMCID: PMC3320807

The Role of Nutrition in Enhancing Immunity in Aging

Munkyong Pae, Simin Nikbin Meydani, and Dayong Wu^*

Nutritional Immunology Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA

^*Correspondence should be addressed to: Dr. Dayong Wu, Nutritional Immunology Laboratory, Jean Mayer 91 USDA Human Nutrition Research Center on Aging at Tufts University, USA. Email: dayong.wu/at/tufts.edu

Received June 15, 2011; Revised August 22, 2011; Accepted September 25, 2011.

This article has been cited by other articles in PMC.

Abstract

Aging is associated with declined immune function, particularly T cell-mediated activity, which contributes to increased morbidity and mortality from infectious disease and cancer in the elderly. Studies have shown that nutritional intervention may be a promising approach to reversing impaired immune function and diminished resistance to infection with aging. However, controversy exists concerning every nutritional regimen tested to date. In this article, we will review the progress of research in this field with a focus on nutrition factor information that is relatively abundant in the literature. While vitamin E deficiency is rare, intake above recommended levels can enhance T cell function in aged animals and humans. This effect is believed to contribute toward increased resistance to influenza infection in animals and reduced incidence of upper respiratory infection in the elderly. Zinc deficiency, common in the elderly, is linked to impaired immune function and increased risk for acquiring infection, which can be rectified by zinc supplementation. However, higher than recommended upper limits of zinc may adversely affect immune function. Probiotics are increasingly being recognized as an effective, immune-modulating nutritional factor. However, to be effective, they require an adequate supplementation period; additionally, their effects are strain-specific and among certain strains, a synergistic effect is observed. Increased intake of fish or n-3 PUFA may be beneficial to inflammatory and autoimmune disorders as well as to several age-related diseases. Conversely, the immunosuppressive effect of fish oils on T cell-mediated function has raised concerns regarding their impact on resistance to infection. Caloric restriction (CR) is shown to delay immunosenescence in animals, but this effect needs to be verified in humans. Timing for CR initiation may be important to determine whether CR is effective or even beneficial at all. Recent studies have suggested that CR, which is effective at improving the immune response of unchallenged animals, might compromise the host’s defense against pathogenic infection and result in higher morbidity and mortality. The studies published thus far describe a critical role for nutrition in maintaining the immune response of the aged, but they also indicate the need for a more in-depth, wholestic approach to determining the optimal nutritional strategies that would maintain a healthy immune system in the elderly and promote their resistance to infection and other immune-related diseases

Keywords: Aging, Immunity, Infection, Nutrition

Aging is a complex process for living organisms. During the process of aging, the human body accumulates damage at the molecular, cellular, and organ levels, which results in diminished or dysregulated function and increased risk of disease and death. These age-related changes are well exemplified in the immune system. The immune system is a complex collection of different cells. Aging affects a majority of these cells to different degrees, often detrimentally; collectively, this is referred to as immunosenescence. While many aspects of immune function decline with aging, some become overactive, e.g., increased autoantibody production or upregulated inflammation state. Given that the main function of the immune system is to detect and guard the body against the invasion of foreign substances as well as the enemies within, e.g., neoplasia and autoimmunity, the consequences of immunosenescence are quite predictable. Indeed, it has been well-documented that the aged have increased susceptibility to and prolonged recovery from infectious disease, poor response to immunization, increased incidence of most types of cancers, and increased risk of developing certain autoimmune diseases.

Like the age-related changes that occur in other systems of the body, immunosenescence is a universal phenomenon, but there is considerable heterogeneity among individuals owing largely to the interaction of genetics, environment, life style, and nutrition. Nutrition as a modifiable factor in impacting immune function has been studied for a few decades, and this research has developed into a field called nutritional immunology. There is little argument that deficiency in both macronutrients and micronutrients can cause immune function impairment, which can be reversed by nutrient repletion. Nutritional deficiencies are prevalent among all age groups in less developed countries and are a main contributor to a high incidence of morbidity and mortality from infectious diseases. Even in developed countries, where general nutritional deficiencies are rare, specific nutrient deficiencies are observed among a significant portion of the elderly population. This is associated with a variety of factors seen more frequently in this population such as disability (physical, mental, dental), disease (digestive and metabolic disorders), disease and medicine-induced anorexia, poor food selection, and lower socio-economic status. Furthermore, the requirement for certain dietary components may need to be raised for the aged. For example, the elderly might need to consume more antioxidants to counteract increased oxidative stress and to compensate for reduced enzymatic antioxidant defense.

This review will examine the data representing the prominent nutritional approaches to delay/reverse immunosenescence and to improve the aged hosts’ resistance to infection. Immunosenescence as discussed in this review is focused on defense-related immunity relevant to infection. However, this review will not cover age-associated low grade inflammation and increased risk for autoimmune disease, which also pertain to immunosenescence. The discussion of nutritional modulation of immunosenescence will be preceded by a brief review of age-related changes in the immune system. This will not be, by any means, a comprehensive review of the topic, given the fact that all the important aspects of immunosenescence are already covered in great detail by other authors in this special issue.

Alterations in immune system during aging

Most of the components in the immune system experience different degrees of change with advancing age. These age-associated alterations involve both arms of the immune system, i.e., innate and adaptive immunity. A negative impact of advancing age has been well documented on the adaptive immune system, but there appears to be no consensus on whether, how, and to what extent aging impacts the innate immune system. Within the adaptive immune system, both cell-mediated (T cells) and humoral (B cells) immune responses are affected by aging, but the most striking change is observed in T cells. A decline in T cell function is known to be the central defect in immunosenescence as evidenced by numerous animal and human studies [1–3]. Age-associated impairment in T cells involves both their early development in the thymus and their continued expansion, differentiation, and function in the peripheral lymphoid tissue. Chronic involution of the thymus is thought to be one of the major contributing factors to the loss of immune function with aging. Thymic involution leads to impaired T cell differentiation and maturation with aging [4] resulting in a significant decline in the output of new T cells [4, 5]. This drives a shift towards greater numbers of antigen (Ag)-experienced memory T cells and a smaller proportion of naïve T cells [6–8]. It has been argued that despite drastic thymic involution and low output, the number of peripheral T cells is well-maintained with aging except for a moderate reduction in the population of naïve T cells. Recent research suggests that to maintain this relatively stabilized T cell population, naïve T cells in the aged must live longer, and as a result, they may accumulate defects that make their function less optimal [9, 10], and it also causes a reduced T cell receptor (TCR) diversity [11–13].

Age-related defects in T cell function have been repeatedly demonstrated, either determined in vitro as proliferative responses to stimulation with mitogens, Ag, and anti-CD3 antibody (Ab), or determined in vivo as T cell proliferation responding to immunization in adoptive transfer animal models, delayed-type hypersensitivity (DTH) response, Ab production to T cell-dependent Ag, and increased incidence of infectious disease. Aging is associated with declined interleukin (IL)-2 production and expression of its receptor, which often result in diminished proliferation of T cells [6, 14–16]. The defect in proliferation and IL-2 production appears more specific to naïve rather than to memory T cells [14]. Since IL-2 is essential to drive T cell expansion, which is required for mounting an effective immune response [17], the age-related defect in IL-2 production is probably a major contributing factor responsible for declined T cell function in aged mice [16, 18, 19]. T cell activation signaling through TCR is needed for IL-2 production and subsequent T cell expansion. Several age-related defects have been identified in the early signaling events of T cell activation including tyrosine and serine/threonine phosphorylation [20–22], calcium mobilization [21, 22], MAPK activity [23, 24], and activation of nuclear transcription factors NFAT [25], AP-1 [26, 27], and NF-κB [28, 29]. Ag engagement with T cells through formation of an immune synapse between Ag-presenting cells (APC) and T cells triggers redistribution of several signaling molecules to the proximity of TCR. An impaired immune synapse formation and reduced distribution of key signaling molecules including Zap70, LAT, Vav, Lck, and PLCγ have been reported in T cells from old compared to young mice [30–32]; this defect in immune synapse formation is more pronounced in naïve than in memory T cells [31]. Another important feature of T cell senescence is the loss of co-stimulation molecule CD28 expression. CD28 provides the major co-stimulatory signal that complements T cell receptors and is critical for T cell activation, proliferation, and survival. Thus, the loss of CD28 expression on T cells with aging is expected to significantly contribute to impaired T cell function. Indeed, CD28-T cells manifest defects in T helper (Th) cell function such as assisting B cell proliferation and immunoglobulin (Ig) production and Ag-specific cytotoxic CD8 T cell function. On the other hand, CD28-T cells are shown to promote the survival of autoreactive T cells, suppress APC function of dendritic cells (DC), and produce large amounts of interferon (IFN)-γ, which together seem to play a proinflammatory role (reviewed in [33, 34]).

In addition to intrinsic changes in T cells with aging, other non-T cell factors, particularly suppressive factors produced by macrophages (MΦ), have been shown to contribute indirectly to the decline of T cell function with aging. Among them, prostaglandin (PG)E₂ has been consistently shown to directly inhibit T cell proliferation. MΦ and spleen cells from old mice [35–37] and peripheral blood mononuclear cells (PBMC) from elderly human subjects [38] produce significantly more PGE₂ than their young counterparts. Increased PGE₂ production observed in MΦ from old compared to young mice is mainly caused by increased cyclooxygenage (COX)-2 mRNA and protein expression and thus, increased COX-2 activity when stimulated with lipopolysaccharide (LPS) [39, 40]. It has been suggested that ceramide mediates the age-associated increase in COX-2 expression and consequently, PGE₂ production [39]. In a subsequent study, Wu et al. have shown that ceramide-induced up-regulation of COX-2 in old MΦ was a result of its induction of NF-κB activation, a key transcription factor in COX-2 regulation [41].

B cell-mediated humoral immune response is believed to be compromised during aging. Age-related impairment in T cell helper function contributes to the compromised humoral immune response in the aged; however, studies have clearly shown that intrinsic defects occur in B cells during aging. Despite substantially decreased pro-B cells and pre-B cells exported from the bone marrow of aged mice [42, 43], the numbers of peripheral B cells remain relatively constant in a manner somewhat similar to what happens in T cell homeostasis during aging. This suggests increased longevity of peripheral B cells [44]. Although blood Ig concentrations generally remain unchanged or even increased, specific Ab response decreases with aging [45]. The quality of humoral immune response is less optimal in the aged as characterized by lower levels of effective and specific Ab, lower Ab affinity, higher levels of non-specific Ab, and decreased IgG isotype class switching in response to vaccination [46–48]. Furthermore, while specific Ab response declines with age, there is an increase in autoantibody levels [49, 50], which may explain the increased risk of developing autoimmune diseases in the elderly. No clear explanation exists presently for increased autoantibody levels with aging. One interesting theory proposes that increased autoantibody production with aging might be a consequence of the autoreactive recall response of memory B cells [51]. According to this theory, existing autoreactive memory B cells, which have been maintained in a tolerant state, become re-activated at a later age due to triggering events. These events include the change in B cell repertoires, reduced self-tolerance with a detection bias, loss of tissue integrity yielding neo-self antigens, and re-exposure to infectious agents that mimic the molecular composition of self tissues.

The innate immune system is the first line of defense for the host. It is composed of a variety of cell types and functional molecules produced by these cells. The impact of aging on the innate immune system is complex and has been discussed in several recent reviews [52–54]. While some innate immune responses are diminished with aging, others remain unchanged or even elevated. Unfortunately, there have been many discrepancies between studies on several aspects of innate immunity. As an example, the term “dysregulation” is often used to describe an altered innate immune response rather than “increase” or “decrease” given that some innate immune responses go down while others go up with aging. For instance, inflammation is a protective response to injury signals so that the body can eliminate the injury, whether it is an invading microorganism or dead tissue. However, excessive, long-lasting inflammation can be harmful. Although consensus has not yet been reached, some studies suggest that aging is associated with a chronically upregulated inflammation state, a phenomenon often called “inflammaging.” This theory is mainly supported by studies showing higher peripheral levels of inflammatory cytokines and acute-phase reaction proteins from the liver such as C-reactive protein in old compared to young subjects [1, 55–59]. It has been estimated that the aged have a 2–4-fold increase of these inflammatory mediators in their serum, which predicts mortality independent of pre-existing morbidity [3]. This inflammation state has been implicated in the pathogenesis of several common and disabling diseases, most of which have a clear connection to advancing age including cardiovascular disease, type 2 diabetes, Alzheimer’s disease, Parkinson’s disease, osteoporosis, and rheumatoid arthritis.

Natural killer (NK) cells, a key component of innate immunity, are involved in the recognition and lysis of tumors and virally-infected cells. NK cell numbers have been shown to remain unchanged or to increase with aging. However, evidence from animal and human studies indicates that NK cell cytotoxicity on a per cell basis and the cells’ ability to produce cytokines and chemokines are impaired with aging (reviewed in [53, 54, 60, 61]). Furthermore, aging can also affect NK cell activity indirectly via diminished production of NK cell-promoting Th1 cytokines (IL-2, IFN-α, and IFN-γ). Therefore, decreased NK activity with aging may contribute to a higher incidence of viral infection and cancer in the elderly.

Neutrophils are another primary innate immune defenses against pathogens, particularly bacteria, yeasts, and fungi. They function through phagocytosis and microbicidal mechanisms, which involve the generation of reactive oxygen and nitrogen species, proteolytic enzymes and anti-microbial peptides as well as the recruitment of other immune cells. While the total number of neutrophils remains constant, some studies have demonstrated that aging is associated with declined neutrophil activity including chemotaxis, phagocytosis, oxidative burst, and intracellular killing as summarized in several reviews [53, 54, 60].

DC, the major APC in the innate system, is present in peripheral tissue including epithelial tissues. They capture and process Ag, and they mature while migrating toward the lymphoid organs where they present Ag to T cells, initiating a specific immune response. By doing this, DC function as a bridge linking the innate to the adaptive immune response. Limited information in the literature indicates a lack of consensus regarding the changes in DC function with aging (reviewed in [53, 54, 60]).

Nutritional intervention to delay/reverse immunosenescence

Apart from genetics, environmental factors have a significant impact on the composition and function of the immune system. Nutrition is a well-recognized, modifiable factor in this regard. Nutritional interventions are an effective, logistically feasible, and cost-effective approach to tackle immunosenescence and its associated diseases. Compelling evidence suggests that a suboptimal status of essential nutrients contributes to the immunological defects observed with aging. Furthermore, evidence indicates that increased intake of some nutrients above the recommended levels is needed to maintain proper function of the immune system and to reduce the incidence of infection in the elderly. Also, a variety of non-nutrient, dietary components have been shown to affect immune cell function, though with varying qualitative and quantitative efficacy. In this section, we will discuss published studies on nutritional interventions involving macronutrients (dietary lipids such as n-3 polyunsaturated fatty acids, PUFA), micronutrients (vitamin E, zinc), functional foods (probiotics), and total calorie control (caloric restriction, CR). Some studies, such as those on vitamin E and zinc, provide information regarding nutrients’ effectiveness in the elderly, with or without comparison to their younger counterparts, whereas other studies, such as those on n-3 PUFA and CR, do not present much information focusing specifically on aged animals or elderly humans. Our discussion of each topic has been distributed according to the abundance and relevance of the information pertaining to the theme of this review: nutritional modulation of immunosenescence. While we have mainly focused on the studies that address the factor of age, we have also included some of the studies that do not since the immunologic changes reported in those studies have significant relevance to immunosenescence and age-related diseases and thus, deserve special attention for their potential applications in the elderly.

1. Vitamin E

1) Vitamin E and immune function

Vitamin E, a very effective chain-breaking, lipid-soluble antioxidant present in the membrane of all cells, is particularly enriched in the membrane of immune cells, which protects them from oxidative damage related to high metabolic activity, as well as high PUFA content in these cells [5, 62]. Vitamin E is considered one of the most effective nutrients enhancing immune function. A number of animal and human studies have indicated that vitamin E deficiency impairs both humoral and cell-mediated immune functions [63, 64]. Conversely, supplementation with vitamin E above recommended levels, especially in the aged, has been shown to enhance immune response, which is possibly associated with increased resistance against several pathogens [37, 38, 65, 66]. Vitamin E is a generic term for all tocopherols and tocotrienols that exhibit the biological activity of α-tocopherol. There are eight naturally occurring forms of vitamin E: α-, β-, γ-, and δ-tocopherols and α-, β-, γ-, and δ-tocotrienols. Chemically synthesized α-tocopherol contains eight stereoisomers and is designated all-rac-α-tocopherol (historically and incorrectly called dl-α-tocopherol), while the naturally-occurring stereoisomer of α-tocopherol is RRR-α-tocopherol (also called d-α-tocopherol). α- and γ-Tocopherols are the main forms of vitamin E in the common Western diet. α-Tocopherol is the most bioavailable and its plasma concentration is about 10-fold higher than γ-tocopherol, while other forms of vitamin E are very low or undetectable. α-Tocopherols, both synthetic and natural forms, are used in a majority of published studies (Table 1), and no consistent evidence suggests a difference in the immunologic effect between these two forms of α-tocopherol.

Table 1.

Effect of vitamin E on immune function

In an animal study testing vitamin E’s effect on immune response, Meydani et al. [37] fed young and old mice diets containing either 30 ppm (control) or 500 ppm (supplementation) vitamin E for 6 wk and found that vitamin E supplementation significantly enhanced DTH response, lymphocyte proliferation to concanavalin A (Con A), and IL-2 production in old mice. This effect of vitamin E was associated with a decrease in PGE₂ production. These findings were later confirmed in rats by Sakai and Moriguchi [67] who reported that vitamin E supplementation (585 mg/kg diet) for 12 mo significantly improved T cell-mediated function (proliferation and IL-2 production) compared with rats fed a control diet containing 50 mg vitamin E/kg.

This immuno-enhancing effect of vitamin E in aged animals is applicable to elderly humans as evidenced by several double blind, placebo controlled clinical trials. Meydani et al. [38] showed that healthy elderly (≥60 y) who received vitamin E supplementation (800 mg/d) for 1 mo displayed a significant improvement in DTH response, ex vivo T cell proliferation, IL-2 production, and a significant decrease in plasma lipid peroxide concentration and PGE₂ production compared to values before supplementation. These parameters remained unaltered in elderly subjects receiving a placebo. In a subsequent study by the same group [66], the authors tested whether lower doses of vitamin E could also be effective. They gave free-living elderly (≥65 y) 60, 200, or 800 mg/d of vitamin E, or a placebo for 4.5 mo. All three vitamin E groups showed a significant increase in DTH response after supplementation compared to their baseline levels. The subjects receiving 200 mg/d of vitamin E showed a significantly greater increase in median percent change of DTH compared to those receiving the placebo as well as a significant increase in Ab titers to hepatitis B and tetanus vaccines (T cell-dependent Ag) compared to their baseline. In a similar study, Pallast et al. [68] found that healthy elderly subjects (65–80 y) administered 50 or 100 mg/d of vitamin E for 6 mo had a significant increase in DTH (induration diameter and number of positive responses) compared with their own baseline values. Notably, a change in the number of positive DTH responses tended to be greater in the 100 mg/d group than in the placebo group (p=0.06). A significantly greater improvement in the cumulative DTH score and the number of positive DTH responses was observed in a subgroup of subjects who received 100 mg vitamin E and had a low baseline DTH reactivity. To this end, a more recent study [69] further supported this finding by showing that elderly subjects receiving 200 mg/d vitamin E for 3 mo had higher levels of lymphocyte proliferative response to phytohemagglutinin (PHA), Con A-stimulated IL-2 production, NK activity, and neutrophil chemotaxis and phagocytosis but lower levels of neutrophil adherence and superoxide anion production. Although this study was not placebo-controlled, this drawback is reduced by the fact that when the subjects were tested again 6 mo after ending supplementation, the majority of improvements were reduced to the baseline levels. Based on combined results from several studies, Meydani et al. proposed that changes in plasma vitamin E levels up to 25 μmol/L are linearly associated with a change in DTH and that further increase in plasma vitamin E levels does not seem to be associated with an additional improvement in DTH [70]. It is estimated that a 25 μmol/L increase in plasma vitamin E can be achieved by consuming 200 mg/d of vitamin E [70]. Thus, it appears that 200 mg/d is an optimal dose for improving T cell-mediated function in the elderly.

Results from animal studies have helped determine the mechanism by which vitamin E has an immune-enhancing effect in the aged. In general, vitamin E can enhance T cell-mediated function by directly influencing membrane integrity and signal transduction in T cells or indirectly, by reducing production of suppressive factors such as PGE₂ by MΦ as summarized in previous reviews [70, 71]. The direct effect of vitamin E on T cell response was examined in T cells purified from the spleens of young and old mice using in vitro and in vivo supplementation methods. The results indicate that vitamin E can reverse the age-associated reduction in activation-induced T cell division and IL-2 production in naïve but not memory T cells [14]. How vitamin E improves cell division and IL-2 production remains to be elucidated. The available information suggests that vitamin E may improve the early events in T cell activation including formation of effective immune synapses known to be impaired in aged animals and humans. For example, Marko et al. [31]showed that both in vivo and in vitro vitamin E supplementations improved effective immune synapse formation and restored defective redistribution of signaling molecules Zap70, LAT, Vav, and PLCγ in the immune synapse formed between APC and naïve CD4+ T cells from old mice. This effect of vitamin E was found in old naïve CD4+ T cells and not in old memory or young CD4+ T cells of either subset [31]. The phosphorylation of LAT is required for recruitment of adaptor and effector proteins including Grb2, Gads, SLP76, Vav1, PLCγ1, and phosphoinositide 3-kinase [72, 73]. In line with reduced LAT distribution in immune synapse in old mice [31], LAT phosphorylation was reduced in CD4+ T cells, and this was reversed by vitamin E supplementation [74].

In addition to its direct effect on T cells, vitamin E can enhance T cell function by reducing production of PGE₂, a well known potent T cell suppressor. Studies have shown that MΦ and spleen cells from old mice and PBMC from elderly human subjects synthesize significantly more PGE₂ than their young counterparts [35–38], which contributes to the age-associated decline in T cell function [75, 76]. Wu et al. [77] reported that dietary supplementation with 500 ppm of vitamin E for 30 d reduced LPS-stimulated PGE₂ production by MΦ from old mice to a level comparable to that which is seen in young MΦ. They further showed that vitamin E exerted its effect through inhibiting COX activity but without altering COX-1 or COX-2 expression at either protein or mRNA level, which was later confirmed by other investigators [78, 79]. While it is still not well understood how vitamin E inhibits COX activity, it has been suggested that it may occur through reduction of peroxynitrite production [80]. Peroxynitrite is a molecule that has been shown to upregulate COX-2 activity without changing its expression [81].

Although vitamin E generally improves cell-mediated immune function in the elderly, it has been well recognized that response to vitamin E supplementation varies among individuals depending on several factors, such as baseline levels of immune response and genetic background. For example, Belisle et al. examined the interaction between the response to vitamin E treatment (200 IU/d for 1 y) in cytokine production (IFN-γ, TNF-α, IL-1β, and IL-6) and the baseline levels of these cytokines in an elderly population. They concluded that the effect of vitamin E supplementation on cytokine production depended on pre-supplementation cytokine levels [82]. This group [83] also proposed that single nucleotide polymorphisms may influence how an individual responds to vitamin E treatment in terms of cytokine production. They found that only the participants with the A/A and A/G genotypes at TNF-α-308G > A who were treated with vitamin E had lower TNF-α production than those with the A allele treated with placebo. Since the A allele at TNF-α-308G>A has been shown to be associated with higher TNF-α levels [84, 85], these results suggest that the anti-inflammatory effect of vitamin E may be specific to those genetically predisposed to higher inflammation. Table 1 provides a summary for the effects of vitamin E supplementation on immune responses demonstrated in animal and human studies.

2) Vitamin E and infection

The elderly have not only an increased incidence of infection but also prolonged infection recovery times. These complications result in high mortality rates among the elderly [86–88], and one of the underlying causes might be their compromised immune response [89, 90]. Thus, it is anticipated that supplementing the elderly with vitamin E would be a useful strategy to enhance a human host’s resistance to infection by improving immune function. Indeed, several animal and human studies have reported a protective effect of vitamin E against infection (Table 2). Several of these studies have determined the effect of vitamin E on influenza infection in mice because host resistance to influenza infection has been used as a relevant outcome to test the changes in host immunity after nutrient intervention, especially those nutrients that affect T cell functions. As such, Hayek et al. [91]reported that old mice had higher viral titers after infection with influenza A/Port Chalmers/1/73 (H3N2) compared to young mice. Vitamin E supplementation (500 mg/kg diet) reduced viral titers in mice of both age groups but more significantly in old mice. Additionally, the authors noticed that the age-related decline in NK cell activity was restored by vitamin E, suggesting a possible mechanism for the protective effect of vitamin E in influenza infection. In a similar study, Han et al. [92] examined the involvement of cytokines in the effect of vitamin E on mouse influenza infection. They confirmed the protective effect of vitamin E in reducing viral titers in old mice and further showed that old mice, compared to young mice, produced less IL-2 and more PGE₂ before infection and had an impaired IFN-γ response to infection. All of these age-related changes were prevented by vitamin E supplementation. The authors also indicated that IL-4 production was not affected by age, infection, or vitamin E whereas the change in IFN-γ production significantly correlated with the decrease in viral titer. These results suggest that enhancement of the Th1 response is one of the mechanisms through which vitamin E provides protection against influenza infection in old mice.

Table 2.

Vitamin E in prevention and treatment of infections

Few investigators have directly examined the effect of vitamin E on resistance to infection in humans. While a majority of human studies have investigated the effect of nutritional intervention (including vitamin E) on immune response as primary outcome measures, these results are often used as surrogate markers for clinical endpoints. A retrospective study [93] in healthy persons (≥60 y) showed that plasma vitamin E levels were negatively related to the number of past infections in these subjects despite an absence of such a correlation between the vitamin status and the measurements of immune function indices (T cell subsets, PHA-induced lymphocyte proliferation, and DTH). In a study by Meydani et al. [66], vitamin E supplementation was shown to improve immune response (DTH and response to vaccines) in healthy elderly. In addition, the authors noticed a non-significant (p<0.09), 30% lower incidence of self-reported infections among the groups supplemented with vitamin E (60, 200, or 800 mg/d for 235 d) compared with the placebo group. Since infection was not the primary outcome, the study did not have enough power to detect significant differences in the incidence of infections. The research team later addressed this question in a larger, double-blind, placebo-controlled trial that determined the effect of one-year’s supplementation with 200 mg/d of vitamin E (optimal dose based on their previous study) on objectively recorded respiratory infections (RI) in 617 elderly nursing home residents (>65 y) [94]. Results showed significantly fewer participants acquiring one or more RI or upper RI in vitamin E-supplemented vs. the placebo-treated subjects and a lower incidence of common colds in the vitamin E group. These studies suggest that the immunostimulatory effect of vitamin E is associated with improved resistance to RI in the aged.

In contrast to this study, previous studies on vitamin E and infection in the elderly have demonstrated mixed results, largely owing to the various confounding factors present, particularly the difference in the health conditions of participants and the intervention protocols. For example, the results from the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) study showed a positive, no effect, or even a negative effect of vitamin E on pneumonia and the common cold depending on the age, smoking history, residence, and exercise, among other factors, of the subjects [95–97]. It is worth mentioning that the ATBC study used a small dose (50 mg/d) of vitamin E in combination with 20 mg/d of β-carotene, which makes it difficult to compare this study’s results with those reported by Meydani et al. Likewise, a double-blind trial in the Dutch elderly cohort living in the community reported no effect of 200 mg/d of vitamin E on the incidence of all RI and even reported a worsening in the severity of infections [98]. Notably, however, there are several differences in the study design and data analysis between this study, conducted with free living participants, and the one conducted in managed nursing homes by Meydani et al, which might have contributed to different outcomes of the two studies. Taken together, the data obtained thus far suggest that the immune-enhancing effect of vitamin E in the elderly might be associated with increased resistance to RI in nursing home residents. However, further studies are needed to confirm these results in elderly living independently.

2. Zinc

1) Zinc and immune function

Zinc is a trace element essential for the growth and development of all organisms, and its impact on immune system has been a topic of intensive study [99–101]. The importance of zinc to immune function has been well-documented in studies on zinc-deficient humans and experimentally-induced animal models. Zinc deficiency affects multiple immune cell types involved in both innate and adaptive immunity. For instance, zinc deficiency is known to cause thymus involution and reduction in Th1 cells leading to an imbalance of Th1/Th2. Further, this deficiency causes a reduction in an array of immune functions such as lymphocyte proliferation, IL-2 production, DTH response, Ab response, NK cell activity, MΦ phagocytic activity, and certain functions of neutrophils (reviewed in [61, 101–105]). One of the best demonstrated examples is acrodermatitis enterophathica, a rare, inheritable metabolic disorder in which zinc deficiency is caused by zinc-specific malabsorption. Patients of this disease have thymic atrophy and lymphopenia as well as intercurrent infection due to impaired cell-mediated immune function, which can be reversed by zinc supplementation [102, 106].These zinc-related impairments in immune function are similar to those observed in the elderly. Not surprisingly, like the elderly, zinc deficient subjects have greater susceptibility to a variety of pathogens (reviewed in [107]).

In contrast to the relatively clear association of zinc deficiency with impaired immune function, the beneficial effects of zinc supplementation on immune response has not been demonstrated in a consistent manner, particularly in human studies. In animal models, zinc supplementation can reverse thymic involution as demonstrated by an increase in thymulin activity, thymus weight, absolute number of T cells in thymocytes, and thymic output in middle-aged (12 mo) [108] or aged mice (22 mo) [109, 110]. In addition to its effect on the thymus, zinc supplementation can increase PHA- or Con A-stimulated lymphocyte proliferation and NK cell activity in old mice [109].

Several studies have investigated the efficacy of zinc supplementation on cell-mediated immunity and humoral response in the elderly human population. In some early studies, zinc supplementation was shown to improve DTH response [111–114]. In one of those studies [112], institutionalized healthy elderly (>70 y, n=30) receiving zinc supplements (440 mg of zinc sulfate/d) or control for 1 mo also had improved IgG Ab response to tetanus vaccine, along with an increased proportion of circulating T cells. More recently, Prasad et al. showed that the elderly who consumed 45 mg of zinc/d as gluconate for 6 mo had increased mRNA expression of IL-2 and IL-2 receptor (IL-2R)α mRNA in PBMC [115]. When interpreting the results from early studies, however, caution is needed since these studies were usually done on small numbers of subjects without a placebo control and thus, it is possible that the improved DTH response over time may be due to repeated DTH administration. The studies reported by Bogden et al. may exemplify this point [116, 117]. They gave healthy elderly (60–89 y) a placebo, 15 mg, or 100 mg of zinc/d in combination with multivitamin/mineral supplements for 12 mo, and tests were conducted every 3 mo. At 3 mo, they found increased serum zinc levels in only the 100 mg of zinc/d group, but observed no significant change in immune function including DTH and in vitro PBMC proliferation [117]. When this study ended at 12 mo, they found that zinc supplementation at 100 mg/d increased plasma zinc levels and in vitro PBMC proliferation, but the increased NK cell activity found at 3 mo was no longer present [116]. DTH response was progressively improved over time in all groups, but this increase was significantly greater in the placebo group than in zinc-supplemented groups [116]. The authors suggested that this might have been due to the multivitamins and minerals consumed by the placebo group.

Results on the effect of zinc supplementation on lymphocyte population are varied. For example, Fortes et al. [118] reported that institutionalized healthy elderly (≥65 y) showed increased numbers of activated (HLA-DR+) CD4+ and cytotoxic T lymphocytes (CTL) after 3 mo of zinc supplementation (25 mg/d as zinc sulfate), while Kanmann et al. [119] showed a reduction in activated (CD25+) CD4+ and no difference in Th2/Th1 (CCR4+/CCR5+) in the free-living elderly (65–82 y) who had been supplemented with zinc (10 mg/d as zinc aspartate for 7 wk).

Serum concentrations of active thymulin decline with aging as evidenced in both mice and humans [120, 121]. Thymulin, a zinc-containing thymic hormone, needs zinc to exert its biological activity [122]. Similar to the results obtained from animal studies [108, 109], the elderly who received zinc supplementation showed increased concentration of active thymulin [114, 123, 124]. In vitro administration of thymulin has been shown to improve the reduced NK cell activity of spleen cells from old mice [125]. In line with this, an observational study on healthy subjects (>90 y) found a strong association between serum zinc levels and the proportion of NK cells [126]; also, zinc supplementation increased NK cell cytotoxicity in healthy elderly (12 mg/d for 1 mo) [124] and in zinc-deficient elderly (10 mg/d for 7 wk) [127]. However, it is not certain that this effect of zinc is sustainable. Bogden et al. [117] reported that zinc supplementation at 100 mg of zinc/d enhanced NK activity transiently after 3 mo but this effect was no longer present at later time points (6 mo and 12 mo). Genetics may also influence an individual’s response to zinc supplementation, and this may possibly be one of the contributing factors to the discrepancies reported in the literature. As an example, a recent study showed that elderly carrying the GG genotype in the IL-6-174G/C locus displayed some differences in the relationship between zinc status (low plasma zinc, erythrocyte zinc, and nitric oxide-induced release of zinc in PBMC) and immune function (impaired NK cell cytotoxicity) when compared to those carrying GC and CC genotypes [127]. In a subgroup analysis based on plasma zinc levels, elderly with GC/CC alleles with plasma zinc >10.5 μmol/L had higher NK cell activity compared to those with GG allele, while subjects with plasma zinc ≤ 10.5 μmol/L showed the lowest NK cell cytotoxicity regardless of IL-6 polymorphism. Subjects with low zinc levels (≤10.5 μmol/L) benefited from zinc supplementation (10 mg of zinc/d for 7 wk) as demonstrated by improved plasma zinc levels and NK cell cytotoxicity. Among zinc-deficient elderly (60–83 y, serum zinc ≤11 μmol/L), those subjects receiving 10 mg of zinc/d for 7 wk and carrying MT1a+647GG and IL-6-174GC/CC alleles appeared to benefit more from zinc intervention than those bearing other genotypes as indicated by the largest elevation in plasma zinc and NK activity as well as reduction in plasma IL-6 and monocyte chemotactic protein-1 (MCP-1) levels in this group [128].

Zinc supplementation has also been tested for its potential enhancement of low vaccination efficacy observed in the elderly; the results thus far are inconclusive. In an observational study [129] determining the effect of host immune responses and plasma micronutrient levels on vaccination efficacy of trivalent influenza vaccine, the authors found that the elderly subjects (mean 81 y, n=61) had a lower immune response, a lack of post-vaccination increase in immune response, and lower Ab titers compared to young subjects (mean 27 y, n=27) even though plasma zinc levels were similar in young and old subjects before and after vaccination. In a controlled clinical trial [130], the elderly (64–100 y, n=160) supplemented with 400 mg of zinc sulfate/d for 60 d starting 15 d before influenza vaccination did not show any difference in Ab titers compared to those receiving the placebo (n=190), and no change was found in lymphocyte phenotype (CD3+, CD4+, and CD8+) as a result of either vaccination or supplementation. Zinc’s lack of a positive effect cannot be clearly interpreted, but it might be related to the high dose used (zinc sulfate 400 mg/d is equal to element zinc 90 mg/d) compared to lower doses used in other studies. Of note, a previous study showed that oral zinc administration of 300 mg/d for 6 wk caused an inhibition in PHA-induced lymphocyte proliferation as well as chemotaxis and phagocytosis of bacteria by polymorphonuclear leukocytes (PMN) [131]. Results from some in vitro zinc supplementation studies support this speculation. For example, zinc supplementation at physiological concentration (15 µmol/L) boosts IFN-α production from leukocytes of elderly subjects [132], but zinc at higher concentrations (≥0.1 mmol/L) directly inhibits IL-1-dependent T cell proliferation through IL-1 receptor-associated protein kinase [133] and IL-2 production, expression of IL-2 and IL-2Rα mRNA, and NF-κB activation [134, 135]. The main findings from animal and human studies for zinc’s immunomodulating effect are summarized in Table 3. Taken together, the efficacy of zinc supplementation in enhancing vaccination response in the elderly needs further investigation. In future studies, researchers should use a multi-dose design given the dose-dependent, biphasic effect of zinc on immune responses.

Table 3.

Effect of zinc on immune function

2) Zinc and host resistance against infection

Several human studies have investigated zinc’s effect on infection (Table 4), and some of them indicate that zinc supplementation may provide protection against infection. Guatemalan children (6–9 mo) receiving 10 mg of zinc/d as sulfate for a mean of 7 mo had a reduced prevalence of diarrhea by 22% although no effect was observed in the incidence of RI [136]. In sickle-cell disease (SCD) patients, whose zinc status is commonly deficient, zinc supplementation (75 mg of zinc/d as acetate) for 3 mo reduced the total number of infections and upper RI, and it lowered the incidence of the common cold compared to those in the placebo group [137]. These SCD patients had a lower production of IFN-γ and a trend toward lower IL-2, but they had a higher production of TNF-α and IL-1β, compared to healthy subjects, representing a profile similar to that found in the elderly. Of note, zinc supplementation not only increased IL-2 and IFN-γ but also reduced TNF-α and IL-1β compared to the placebo group. These results might be relevant to zinc supplementation in the elderly.

Table 4.

Zinc in prevention and treatment of infections

Several studies have investigated the effect of zinc supplementation when it is started during the course of natural infection in the elderly population. In a controlled clinical trial (n=81) [138], institutionalized elderly (>65 y) had a significant decrease in the mean number of RI during a 2-y supplementation period with 20 mg of zinc and 100 μg of selenium. In a larger (n=725), controlled intervention trial [139], low-dose zinc and selenium supplementation (20 mg of zinc/d and 100 μg of selenium/d) for 2 y significantly increased humoral response (Ab titer and seroprotection) in institutionalized elderly (>65 y) after vaccination and tended to (p=0.06) reduce the incidence of RI, but these doses had no effect on DTH response during the 2-y period. Although these studies suggest a protective effect of zinc against RI, selenium’s contribution must be considered. In a controlled trial with elderly persons (55–87 y), of whom 35% were zinc-deficient [140], Prasad et al. found that zinc supplementation (45 mg of zinc/d) for 1 y significantly increased plasma zinc levels over time in the zinc group (n=24) but not in the placebo group (n=25), and the zinc group tended to have fewer common colds (p=0.067) as well as fewer infections and fevers during the study. Recently, an observational study by Meydani et al. [141] showed that 29% of nursing home residents (>65 y) had low serum zinc levels (<70 μg/dL) despite supplementation that included 7 mg of zinc/d for over one year. Subjects with normal serum zinc concentrations of >70 μg/dL had lower pneumonia incidence, reduced total antibiotic use (by almost 50%), and shorter duration of pneumonia and antibiotic use (by 3.9 and 2.6 d, respectively) compared to those with plasma zinc concentrations of <70 μg/dL. The authors suggested that a double-blind, placebo controlled study is needed to determine the efficacy of zinc supplementation on elderly immune response. Observations from a large controlled trial in children further supports this finding by showing that zinc supplementation (70 mg, weekly) in children (<2 y, n=706) reduced the incidence of pneumonia compared to the placebo group (n=768) [142].

In summary, zinc deficiency induces immunological changes similar to those observed in the elderly. A significant percentage of the elderly have low serum zinc levels due to inadequate intake, impaired metabolism, infection, inflammation, etc. Evidence from the literature indicates that the elderly, particularly those with low serum zinc levels, might benefit from optimizing their serum zinc status through adequate intake, but further studies to determine optimal zinc intake in the elderly are needed. These studies should consider variations in individual genetic background in order to maintain optimal immune response and to document the efficacy of zinc supplementation in reducing infection, particularly pneumonia in the elderly.

3. Probiotics

1) Probiotics and immune function

Probiotics are defined as live microorganisms that reach the intestinal tract in sufficient numbers and exert health benefits on the host [143]. Probiotic microorganisms are typically members of the genera Lactobacillus (L.), Bifidobacterium (B.), and Streptococcus (S.). Aging is associated with a reduction in 1) beneficial microbes in the colon including bifidobacteria, countered by a rise in proteolytic bacteria, 2) intestinal Ag-specific secretory IgA response, which is important in mucosal-associated immunity and helps protect the host by binding a variety of Ag from bacteria, viruses, and fungi [144–146], and 3) gut-associated lymphoreticular tissues as manifested by a size reduction in Peyer’s patches (PP), a decline in the number of lymphocytes in PP (especially, naïve CD4+ T cells and follicular DC) and mesenteric lymph nodes, a decreased ability of lamina propria T cells to proliferate and produce IL-2 [147], and an impaired T cell response such as Ag-specific Th function and CTL activity in PP (reviewed in [148]).

Probiotics are believed to modulate immune function in the gastrointestinal (GI) tract through interaction with intestinal epithelial cells [149, 150], M-cells in the PP [151, 152], and DC [153, 154]; thus, probiotics may affect other mucosal surfaces, including the upper respiratory tract, via mucosal immune systems. An increasing body of information now suggests that probiotics can also positively impact the systemic immune system [155–157]. Since mucosal and systemic immune functions are known to decline with aging, it is therefore expected that the aged would most likely benefit from consumption of probiotics. Indeed, studies have shown that splenocytes from old mice have a lower capacity to produce IFN-α and IFN-γ in response to mitogens, compared to splenocytes in young mice; this was reversed after administration of viable L. bulgaricus and S.thermophilus[8x10⁸ colony forming units (CFUs)/d] for 7 d [152]. Likewise, administration of B. bifidum (5x10⁸ CFUs/d) for 8 wk significantly increased Con A-induced IL-2 and IFN-γ production in splenocytes from old mice. Additionally, elevated serum levels of TNF-α and IL-6 in old mice were reduced by B. bifidum treatment, suggesting that it might be beneficial in reducing age-associated inflammation [158].

In addition to intrinsic age-related decline in immune response, malnutrition in the elderly can intensify compromised immune function, infection susceptibility, and ultimately, infection-related mortality [159, 160]. In aged mice with experimentally-induced protein-energy malnutrition (PEM) [161], it was evident that some immune responses were decreased compared to aged mice fed a complete diet. These compromised immune responses included diphtheria toxin (DT)-specific IgG in serum, lymphocytes’ proliferative response to Con A, and percentage of CD8+ cells; importantly, all of these parameters were improved after consumption of L. johnsonii La1 for 14 d. To a lesser extent, probiotics supplementation also increased DT-specific IgA and total IgA in fecal extract, and they decreased TNF-α production in LPS-induced splenocytes in old mice fed a complete diet [161]. While it is unclear how La 1 improved the impaired immune responses under PEM condition, it is noteworthy that La 1 consumption prevented the decrease in serum albumin levels and body weight in PEM mice, which the authors speculated was due to improved nutrient absorption by La 1 [161]. Thus improved nutritional status appeared to contribute to preserving positive immune responses seen in La 1 fed aged mice. Furthermore, studies have also suggested that probiotics may modulate innate immunity and DC APC function. Two B. strains isolated from healthy centenarians enhanced NK cell activity and phagocytic activity of MΦ in young mice [162]. Two other strains (L.fermentum strain PL9005 and L.plantarum strain PL9011) of probiotics were also shown to enhance the phagocytic capacity of peritoneal leukocytes [163].

Tsai et al. [164] showed that supplementing mice with L. paracasei NTU 101 (10⁸ CFUs/d) for 6 or 9 wk (but not 3 wk) upregulated expression of DC maturation markers (MHC-II^hi, CD80+, and CD86+) and NK group-2D (NKG2D) and promoted lymphocyte proliferation in response to L. paracasei Ag. These results suggest that probiotics may enhance specific immunity by promoting APC function. Indeed, Vidal et al. [157] showed that following a vaccination protocol with keyhole limpet hemocyanin (KLH), old mice supplemented with L. paracasei NCC2461 (1x10⁹ CFUs/d) for 44 d had an improved KLH-specific CD4+ T cell response including anti-KLH IgG2a production and DTH response, compared to the control aged mice. Since the proportions of lymphocytes including CD4+, CD44^high (memory T cells), CD44^low (naïve T cells) and NK cells remained unaltered [157], it is likely that probiotics administration improved the functionality of CD4+ T cells in response to Ag. Given the observed impairment in generating Ag-specific CD4+ T cell immunity in old mice [165, 166], probiotics could potentially be used as a practical strategy to boost protective immunity in the elderly.

Similar to animal study findings, certain strains of probiotics have been shown to influence innate immunity such as phagocytosis and cytotoxicity in humans. Administration of B. lactis (3x10¹¹ CFUs/d) to healthy elderly for 6 wk resulted in a significant increase in PMN cell phagocytic and bactericidal activity to Staphylococcus aureus challenge [167]. Dietary supplementation for 3 wk with L. rhamnosus HN001 (5x10¹⁰ CFUs/d) or B. lactis HN019 (5x10⁹ CFUs/d) in the elderly (60–84 y) increased both the peripheral blood proportion of NK cells and their tumoricidal activity. Of note, subjects over 70 y showed more pronounced improvement in tumoricidal activity [168]. In a subsequent study by the same group [169], healthy elderly were supplemented with two different doses of HN019 (low dose 5x10⁹ CFUs/d or typical dose 5x10¹⁰ CFUs/d) for 3 wk, and both doses were similarly effective in increasing phagocytic activity of PBMC and PMN cells as well as NK cell activity. The researchers also noticed a greater improvement in those subjects who had a lower pretreatment immune response. Furthermore, probiotics were shown to upregulate expression of the receptors in neutrophils important for their phagocytic activity including CR1, CR3, FcγRIII, and FcαR in healthy individuals [170, 171]. It appears that probiotics have a general immuno-enhancing effect irrespective of age: study participants who were selected from a broad range of ages (41–81 y [172]; 44–80 y [173]; 51–58 y [174]) all benefited from treatment with a variety of strains of probiotics (L. rhamnosus, 5x10¹⁰ CFUs/d [173]; L. casei DN114001 [174]; L. lactis, 3.4x10¹⁰ CFUs/d [170]; L. GG, 2.6x10⁸ CFUs/d [171]).

A striking feature of immunosenescence is inefficient response to vaccines, which reduces a vaccine’s protective effect against infections such as flu in the elderly. Based on a review of 48 studies [175], vaccine response in the elderly was about one-fourth to one half of the Ab response in young adults. Therefore, increasing vaccine efficacy through probiotics is one strategy that may enhance immunity to infectious diseases in the elderly. It has been reported that healthy elderly (>70 y) residing in nursing homes displayed improved humoral response (Ab titer against influenza vaccine and seroconversion) after 13 wk of supplementation with the daily consumption of a product containing L. casei DN114001 (2x10¹⁰ CFUs/d) and S. thermophilus and L. bulgaricus (2x10¹⁰ CFUs/d). However, a shorter time period of 7 wk of supplementation failed to induce this protective effect [176]. Similarly, 7 d supplementation with L. GG or L. lactis did not affect humoral response induced by Salmonella typhi oral vaccine in healthy adults [170]. Several studies have indicated that probiotics may induce production of proinflammatory cytokines, which support an adequate immune response against infection. On the other hand, anti-inflammatory cytokines are also induced, ameliorating excessive inflammatory reaction (reviewed in [145, 150, 177]). However, the immunomodulatory effects of probiotics on cytokine production appear to be strain-dependent. For example, probiotics taken orally induced IFN-α (B. lactis HN019, [167]), reduced TNF-α (L. rhamnosus GG, [178]) and IL-2 (B. animalis ssp. Lactis Bb12, [178]), and had no effect on IFN-γ, IL-1β, and IL-2 (L. casei, [179]). Immunomodulating effects of probiotics reported in the literature are summarized in Table 5. In short, studies thus far indicate that probiotics have the potential to modulate different aspects of immune function in the elderly. Whether this property of probiotics ultimately conveys a clinically-relevant benefit in terms of reducing infection in the elderly is summarized in Table 6 and discussed below.

Table 5.

Effect of probiotics on immune function

Table 6.

Probiotics in prevention and treatment of infections

2) Probiotics and resistance against infection

Several studies have demonstrated that probiotics administration could protect young mice from infection including Salmonella typhimurium [180, 181] and Listeria monocytogenes [182]. Results from these studies indicated that dietary probiotics reduced pathogen translocation to spleen and liver while increasing phagocytic activity, lymphocyte proliferation, and mucosal Ab response [180–182]. Data obtained from young mice raise the possibility that probiotics may exert a protective effect in the elderly population since they are more vulnerable to infection. In a study by Bunout et al. [183], free-living elderly (≥70 y) were provided with nutritional supplementation including L. paracasei (NCC 2461) and prebiotic (fructo-oligosaccharides) for 1 y and vaccinated against influenza and pneumococcus during the intervention period. The elderly receiving the nutritional supplementation (n=28) reported less infection, particularly RI, than those without supplementation (n=28). However, problems with the study design make it impossible to attribute the effect specifically to probiotics. First, the study was not blinded; further, the formulation contained several other active components such as protein, vitamin E, vitamin B12, folic acid, and a prebiotic (cited above) in addition to L. paracasei. Another study [184] reported that hospitalized enterally-fed elderly receiving L. johnsonii La1 and S. thermophilus for 12 wk had a significantly shorter duration of infection compared to the control group. Although these data suggest that probiotics may be able to modulate the risk of infection in the elderly, enterally-fed patients who are bed-ridden may not represent the general elderly population. In a larger controlled intervention [185], healthy, independently living elderly (≥70 y) who were supplemented with a fermented dairy drink (Actimel®) containing L. casei DN114001 as well as S. themophilus and L. bulgaricus for 3 mo (including the winter season) reported a shorter cumulative duration (7 vs 8 d in control group) and an average duration per episode (6.5 vs 8 d in control group) for all common infectious diseases (CID) compared to the placebo group, which consumed a non-fermented and acidified dairy drink. On average, probiotic supplementation reduced the duration of CID by 1–1.5 d. Reductions in both the number of episodes and cumulative duration were also significant for upper RI, accounting for 30.3% CID, and rhinopharyngitis, accounting for 50.3% CID. In contrast, probiotic consumption did not alter CID severity, fever, pathogen, medication, and immune parameters tested (oxidative burst activity in monocytes, cytotoxic activity and number of NK cells in blood, levels of serum cytokine including IL-1, IL-6, IFN-α, β, and γ, IL-12, IL-10, TNF-α, and IL-8). Similarly, Makino et al [186] reported that the elderly who were supplemented with yoghurt (fermented with L. bulgaricus and S. thermophilus) for 8 wk (Mar to May) or 12 wk (Nov to Feb) had a significant reduction in common cold or influenza virus infection compared to the placebo group consuming milk. Depending on the intervention period, NK cell cytotoxicity remained either unchanged (8 wk) or increased (12 wk), but both 8 wk and 12 wk interventions significantly improved NK cell cytotoxicity in the subjects with low basal NK cell activity. Again, as with immune response, the probiotics’ protective effect against infection is not limited to the elderly population. Healthy subjects (18–67 y) who received L. gasseri, B. longum, B. bifidum in addition to vitamins and minerals for 3 mo or 5.5 mo showed a 21.5% reduction in the mean duration of common cold episodes (1.9 d) along with increased CD8+ T cells, compared to the placebo group, which took only vitamins and minerals [187, 188]. Intake of L. plantarum HEAL9 and L. paracasei for 12 wk was shown to decrease incidence of acquiring one or more common colds in subjects aged 18–65 y [189].

In summary, probiotics are an active food component, and interest in determining their impact on the immune response of the elderly has grown in recent years. The research to date suggests a potential for using probiotics to improve age-related defects in the immune system and to reduce the high incidence and severity of infectious diseases in the elderly. However, studies in this field have presented many inconsistent and discrepant results. The possible reasons include: unequal baseline conditions between treatment and control groups, short intervention periods, underpowered designs, and lack of precise documentation of infections. In addition, it is important to note that there are many different probiotics, and their effects may be strain specific. Furthermore, interaction among probiotics occurs so that it is possible to obtain various synergistic effects by combining different strains.

4. Fish oil and n-3 PUFA

1) N-3 PUFA and immune function

Dietary lipids are not only fundamental energy-providing nutrients, but also greatly impact specific cell functions. There are different classifications and categorizations for dietary fatty acids (FA) including: essential (further divided into n-3 and n-6 families), saturated, monounsaturated, and PUFA. Mammals depend on food to obtain essential FA from plants or animals, and each source has a unique FA composition. Most plants and land animals provide us with n-6 PUFA, some plants are sources of shorter chain n-3 PUFA, and marine animals are virtually the sole source of long chain n-3 PUFA. Marine animal-derived n-3 PUFA (mainly eicosapentaenoic acid or EPA, and docosahexaenoic acid or DHA) have the most significant effect on immune cell functions compared to other FA. In fact, n-6 FA are often used as the control fat in studies determining the effect of n-3 PUFA. Consumption of long chain n-3 PUFA or fish oil has been shown to have beneficial effects on several prevalent, age-related diseases such as cardiovascular disease, degenerative neurological diseases, inflammatory and autoimmune diseases, and age-related macular degeneration. A common mechanism of the beneficial effect of n-3 PUFA on these diseases is their anti-inflammatory property. Although still controversial, n-3 PUFA are largely known to suppress both innate (mainly inflammation) and adaptive (mainly T cell-mediated) immune responses, and thus may impair the host’s defense against infectious and neoplastic diseases. Given that aged individuals already have impaired immune responses, it is important to carefully assess the advantages and drawbacks of n-3 PUFA supplementation in the elderly population. To date, however, only a very limited number of studies have compared the effect of dietary supplementation with fish oil on immune responses of young and aged animals or humans. We are therefore not limiting our literature review to only those studies that address the age issue but rather, we will also discuss the effect of n-3 PUFA on immune functions that are known to change with age. This evaluation has potential clinical relevance for the elderly since they are the population that is particularly encouraged to, and in fact do take more n-3 PUFA to mitigate age-related diseases.

There are a number of recent excellent reviews on the effect of n-3 PUFA on inflammatory and immune responses [190–196]. In general, n-3 PUFA are anti-inflammatory, having been shown repeatedly to inhibit production of inflammatory mediators including eicosanoids (PGE₂, 4-series leukotrienes), proinflammatory cytokines (IL-1β, TNF-α, IL-6), chemokines (IL-8, MCP-1), adhesion molecules (ICAM-1, VCAM-1, selectins), platelet activating factor, and reactive oxygen and nitrogen species. In addition, more recent work indicates that n-3 PUFA have a pro-resolution effect by serving as precursors for the production of pre-resolving mediators resolvins, protectins, and marensins [197, 198]. These effects of n-3 PUFA apparently contribute to their efficacy in alleviating inflammatory and autoimmune diseases, some of which have an increased incidence with aging.

It is widely agreed that the most dramatic, consistently observed change in the immune system during aging is defective T cell response. A majority of work on the immunomodulating effect of n-3 PUFA has focused on T cell-mediated immunity, but the research on this topic has not reached a clear consensus. In general, the results from animal studies are relatively less discrepant, which is mainly due to the ability to control genetic background, habitual diet, and feeding regimen. Further, high doses of n-3 PUFA can be used in animal models. Although some studies have reported no significant effect [199, 200] or even an enhancing effect [201–203] of n-3 PUFA supplementation on immune response, more studies have shown a suppression in cell-mediated immune function resulting from n-3 PUFA supplementation as summarized in the reviews mentioned above. Consumption of fish oil or n-3 PUFA has been shown to inhibit ex vivo T cell mitogen- or TCR activation-induced lymphocyte and CD4+ T cell proliferation, IL-2 production, and IL-2R expression, or specific Ag-driven CD4+ T cell expansion both ex vivo and in vivo [204, 205], as well as the in vivo immune response indicated by DTH skin test [206]. Mechanistic studies have revealed the cellular and molecular basis for n-3 PUFA-induced effects. For example, n-3 PUFA can inhibit several important events in the TCR activation cascade including phosphorylation of signaling molecules and their translocation in the immunologic synapse [194, 195, 207]. This proposed association between n-3 PUFA and T cell function is further reinforced by the recent work using fat-1 mice, a transgenic mouse model that can endogenously synthesize n-3 PUFA [208, 209].

Few studies have particularly examined how n-3 PUFA supplementation affects immune response in aged persons with respect to their young counterparts. Meydani et al. [210] reported that n-3 PUFA supplementation (1.68 g EPA and 0.72 g DHA/d) for 3 mo significantly inhibited T cell mitogen-induced PBMC proliferation and IL-2 production in older (51–68 y), but not young (23–33 y), female subjects. They also observed a decreased production of inflammatory cytokines (L-1β, IL-6, TNF-α) in both age groups, but the effect was larger in older than in young subjects. In another study, Bechoua et al. [211] showed that elderly subjects (70–83 y) consuming habitual amounts of n-3 PUFA (30 mg EPA and 150 mg DHA/d) for 6 wk had decreased lymphocyte proliferation in response to Con A, PHA, and OKT3. In a later study, Rees et al. [212] compared the change in innate immune function in young and older men after they consumed 1.35, 2.7, or 4.05 g EPA/d for 12 wk. They found that EPA treatment dose-dependently decreased neutrophil respiratory burst in only the older men. These results suggest that elderly individuals are more sensitive to the immunologic effects of n-3 PUFA, which can be an advantage (in the case of inflammatory and autoimmune disorders) or a disadvantage (in the case of combating pathogens and cancers). Future studies should be designed to address the clinical relevance of the differential effect of n-3 PUFA in different age groups.

2) N-3 PUFA and infection

Since n-3 PUFA can attenuate inflammatory and T cell-mediated immune responses, which are key components in the body’s defense against microbial infection, it is important to know if increased intake of n-3 PUFA can actually compromise the host’s defense against infection. Because data from human studies are very limited, preliminary knowledge is largely from animal studies utilizing a variety of infection models or from very limited epidemiological studies. Of relevance to this issue, a prospective study of 83,165 participants (27–44 y) in the Nurses’ Health Study II showed that women in the highest quintile of EPA and DHA intake had a 24% greater risk of community-acquired pneumonia than did those in the lowest quintile [213]. However, the Health Professionals Follow-Up Study cohort of 38,378 men (44–79 y) found no association between EPA and DHA intakes and pneumonia risk [214]. It is not clear if and how much the difference in age and gender is attributable to the discrepancy between the two studies. Regarding animal studies, although information is relatively more abundant, the picture is not much more explicit. Outcomes are roughly even between reported adverse effects, no effects, or even beneficial effects of n-3 PUFA intake on the host’s resistance to infections. As summarized by Anderson and Fritsche [215], many animal studies have shown both improved and impaired host’s resistance to a number of pathogens following increased consumption of n-3 PUFA. Importantly, studies have shown impaired host’s resistance to several infectious pathogens that are prevalent in infections in the elderly. For example, fish oil fed mice infected with influenza had a higher lung viral load, more weight loss, lower cytotoxicity of lung virus-specific T cells, and reduced production of lung IFN-γ, serum IgG, and lung IgA-specific Ab [216, 217]. These results were confirmed by a more recent study showing that feeding fish oil to mice resulted in higher mortality, higher lung viral load, and longer recovery period after influenza infection, and all these changes were at least in part associated with fewer CD8 T cells and inflammatory cytokine expression in lungs [218]. n-3 PUFA is also related to lower host resistance to infection from mycobacterium tuberculosis (TB). As another example, n-3 PUFA fed to guinea pigs [219, 220], mice [221], and transgenic fat-1 mice, which can endogenously synthesize n-3 PUFA [222], have reduced survival and impaired bacterial clearance after TB infection. Impaired resistance to TB infection is associated with reduced oxidative burst, less robust inflammatory response manifested by lower production of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6, and diminished Ag-specific T cell function in response to TB infection. Likewise, n-3 PUFA supplementation was also shown to impair infection resistance in mice infected with several other pathogens such as Listeria monocytogenes [223] and Salmonella typhimurium [224]. In both cases, the animals fed fish oil had much lower survival rates and delayed bacterial clearance from spleens. Conversely, some studies have reported a beneficial effect of n-3 PUFA against infection by increasing host survival after infection. In those cases, it is possible that the overwhelming inflammation induced by pathogens or pathogen-released endotoxin is the major cause of fatality; therefore, n-3 PUFA could be protective given their ability to inhibit production of PGE₂ and pro-inflammatory cytokines [196].

Given all the potential beneficial and adverse effects of n-3 PUFA reported in the literature, the data suggest that n-3 PUFA do not improve immunosenescence in defense of the host against pathogens. Although this might discourage the elderly from taking advantage of the beneficial effects of n-3 PUFA, the advantages of taking n-3 PUFA may outweigh the potential adverse effects under certain circumstances. For example, increasing n-3 PUFA intake might be beneficial to treat inflammatory and autoimmune diseases such as inflammatory bowel disease and rheumatoid arthritis or diseases in which inflammation is an underlying factor of pathogenesis such as cardiovascular disease, type 2 diabetes, and Alzheimer’s disease. In addition, dose and adequate provision of other nutrients such as vitamin E can influence the nature and magnitude of the effect of n-3 PUFA on immune response.

5. Caloric restriction (CR)

1) CR and immune function

In the 1930’s, McCay et al. [225] presented the first evidence suggesting that long term CR increases life span. Since then, compelling, supporting evidence has accumulated to show that reduced caloric intake without malnutrition not only extends average and maximum life spans in a wide array of species (from yeast to rodents, and possibly non-human primates, NHP) [226–228], but also preserves a variety of body functions at a youthful age and delays the onset or decreases the severity of several age-associated diseases. Importantly, we have learned that CR can intervene in the body’s age-related changes that come with immunosenescence. The majority of studies related to CR and immune response have been conducted in rodents, particularly mice. These investigations show that CR can reverse most of the manifestations of immunosenescence including defects in hematopoietic stem cells [229], decreased naïve T cell and increased memory T cell population [230], reduced T cell proliferative response to mitogens or Ag, decreased IL-2 production, NK activity, and CTL generation [230–234], age-related increase in serum levels of TNF-α and IL-6 [235], and in autoimmune diseases [236, 237]. More recently, the impact of CR has been studied in NHP. These studies take advantage of their higher degree of similarity to humans and serve as an alternative to long term CR tests on humans. For the most part, CR studies in NHP have generated similar results to those seen in the rodent studies [238–241] regarding effect on immune response and several other age-related disorders [226]. Since conducting long term CR to determine its effect on human longevity is not feasible, many surrogate outcome measures on a variety of body functions have been used to assess CR’s health benefit. Recently, Ahmed et al. [242] reported the first human study determining the effect of CR on immune response. In this study, a small number of overweight men and women (20–40 y) were subjected to 10% or 30% CR for 6 months. The authors found that CR at both levels enhanced T cell-mediated immune response, which was measured in vivo by DTH and ex vivo by T cell proliferation. Also, 30% CR reduced LPS-stimulated ex vivo production of T cell-suppressive eicosanoid PGE₂. While these results still need to be confirmed in larger human trials, current observations strongly suggest that CR’s beneficial effects on immune function in experimental animal models may also apply to humans.

Although animal studies and limited human studies indicate a positive effect of CR on immunosenescence, many questions remain. Apart from needing more human studies, the issues of when to initiate CR and how long to maintain it still must be addressed. It is generally agreed that CR should not be recommended for individuals in growing and developmental stages, but there is no agreement on when to initiate CR during adult years. To this end, a recent study by Messaoudi et al. [239] has provided interesting, valuable information. In their study, the authors started CR at early, adult, and late life stages in primates and found that CR induced beneficial effects in maintaining youthful T cell function in the adult-onset animals, but this benefit was lost in both early- and late-onset animals. These findings caution us about the importance of timing since there might be window of time when initiating CR might be ineffective or even harmful. These results need to be verified and, if confirmed, we will need to learn if and to what extent this phenomenon is applicable to humans.

2) CR and infection

Resistance to infection is one of the most important outcomes for testing the efficacy of an intervention on a host’s immune function. The question that logically follows is: are all the reported beneficial effects of CR on selected parameters of immune function sufficient to afford a host, in particular an aged one, better protection from pathogenic infection? It is well known that the elderly have a particularly higher rate of morbidity and mortality from influenza infection; therefore, influenza infection and vaccination are commonly used outcomes to determine the efficacy of immune enhancing interventions. An early study by Effros et al. [243] showed that aged CR mice had an improved immune response to influenza infection with enhancement in Ag presentation, T cell proliferation, and Ab production compared to the control mice. Since no information on the clinical signs of the disease or viral titer was provided, it is not clear if CR-induced enhancements were associated with better resistance to influenza infection. However, a recent study by Gardner et al. [244] reported that after influenza infection, aged CR mice had lower NK activity, decreased survival, and delayed viral clearance (higher viral titers) compared to ad-libitum fed mice. The same CR effect was also reported by this group in a later study of young adult mice [245] suggesting that this effect of CR is independent of age. Further, this group showed that short-term re-feeding of the young adult mice, after they had been subjected to CR regimen, restored their body weight and improved their survival and NK cell function [246]. There are only two other reported studies that have examined how CR impacts the host’s response to infection by intact pathogen. One study showed that adult CR mice had a higher mortality from polymicrobial sepsis induced by cecal ligation and puncture [247]. The CR mice had impaired MΦ function, indicated by lower production of inflammatory cytokines IL-6 and IL-12, lower expression of toll like receptor (TLR)2 and TLR4 mRNA, reduced phagocytic capacity, and diminished class II (I-A(b)) expression compared to the control mice [247]. In the other study [248], the author initially hypothesized that CR mice would be less susceptible to the intestinal parasite heligmosomoides bakeri (a rodent model for human hookworm infection) through enhancing both innate and adaptive immune responses. However, contrary to the predictions, CR mice not only had more worms, but the worms from the CR mice produced more eggs compared to the control mice. This occurred even though CR caused no change in the number of eosinophils and even increased serum IgG1 levels. These studies indicate that further investigation is needed to more precisely delineate the overall impact of CR on infection. In the meantime, caution should be taken before recommending CR to the frail elderly, and those who are at high risk of infection.

Concluding remarks

Since human lifespan and the proportion of elderly are increasing worldwide, immunosenescence has become an increasingly prominent topic given its relationship to increased incidence of infectious disease and cancer. The intrinsic defects that develop in the immune system during aging are further intensified by the absolute or relative deficiency in the elderly of several nutrients with known immune-enhancing properties. Therefore, nutritional intervention has been recognized as a practical, cost-effective approach to attenuating age-associated decline in immune function, vaccination efficiency, and resistance to infectious and neoplastic diseases. Although research in this field has continued to make significant progress, the impact of virtually all the nutritional agents studied on both immune response and related clinical endpoints remains controversial. It is well-acknowledged that being able to favorably modulate immune cell functions would not necessarily translate into a corresponding change in clinical outcome. Further, for those nutrients or food components with a relatively strong clinical efficacy, reproducibility continues to be a significant issue. The literature review summarized above indicates that substantial variation exists among nutritional interventions in the nature and relative potency of their immunomodulating activity. For nutrients like vitamin E, increased intake at 5–10 folds above recommended levels may be needed for optimal effect, whereas for others such as zinc, increased intake above recommended levels might not be beneficial and even might cause harm due to the narrow range of safe doses. For probiotics, strain, dose, and combined use of different strains are all important in determining their immunomodulatory effect. While some nutrients clearly benefit one aspect of immune function, they may adversely affect another. As an example, increased intake of n-3 PUFA is recommended to prevent and ameliorate inflammatory and autoimmune diseases as well as several age-related diseases in which inflammation plays a role; however, the reported immunosuppressing effect on T cells and increased risk of certain infections cautions against a general “one-fits-all” recommendation. Similarly, CR, an intervention shown to have broad health benefits including immunoenhancement, still needs further study in humans since it may be ineffective or even harmful under certain circumstances. Taken altogether, strong evidence generally supports the notion that proper nutrition is critical for optimal immune response and host defense against infection. Future studies are needed to determine the effectiveness and optimal conditions for various nutritional intervention regimens to improve the function of the aged immune system. In designing these studies, the following factors need to be considered: 1) optimal dose, 2) characteristics of targeted populations including their nutritional status, health condition, and genetic background, and 3) selection of clinically relevant, sensitive, reproducible, and feasible endpoints or surrogate readouts for reliable assessments of intervention efficacy. It is hoped that future studies will further enrich our knowledge to help us develop more effective and directed nutritional strategies to undertake the challenges of immunosenescence.

Acknowledgments

Supported by the US Department of Agriculture, Agriculture Research Service under contract number 58-1950-7-707. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the US Department of Agriculture. The authors would like to thank Stephanie Marco for her assistance in the preparation of the manuscript and Maria Carlota Dao for her critical comments.

Abbreviations


Ab	antibody

Ag	antigen

APC	antigen-presenting cells

Con A	concanavalin A

CR	caloric restriction

CTL	cytotoxic T lymphocytes

DHA	docosahexaenoic acid

DTH	delayed-type hypersensitivity

EPA	eicosapentaenoic acid

Ig	immunoglobulin

IL	interleukin

IL-2R	IL-2 receptor

LPS	lipopolysaccharide

MΦ	macrophages

PBMC	peripheral blood mononuclear cells

PHA	phytohemagglutinin

PMN	polymorphonuclear leukocytes

PUFA	polyunsaturated fatty acids

RI	respiratory infections

TB	mycobacterium tuberculosis

TCR	T cell receptor

Th	T helper

TLR	toll like receptor

TNF	tumor necrosis factor

References

[1] Krabbe KS, Pedersen M, Bruunsgaard H. Inflammatory mediators in the elderly. Exp Gerontol. 2004;39:687–699. [PubMed]

[2] Sarkar D, Fisher PB. Molecular mechanisms of aging-associated inflammation. Cancer Lett. 2006;236:13–23. [PubMed]

[3] Vasto S, Candore G, Balistreri CR, Caruso M, Colonna-Romano G, Grimaldi MP, Listi F, Nuzzo D, Lio D, Caruso C. Inflammatory networks in ageing, age-related diseases and longevity. Mech Ageing Dev. 2007;128:83–91. [PubMed]

[4] Webster RG. Immunity to influenza in the elderly. Vaccine. 2000;18:1686–1689. [PubMed]

[5] Coquette A, Vray B, Vanderpas J. Role of vitamin E in the protection of the resident macrophage membrane against oxidative damage. Arch Int Physiol Biochim. 1986;94:S29–34. [PubMed]

[6] Nagel JE, Chopra RK, Chrest FJ, McCoy MT, Schneider EL, Holbrook NJ, Adler WH. Decreased proliferation, interleukin 2 synthesis, and interleukin 2 receptor expression are accompanied by decreased mRNA expression in phytohemagglutinin-stimulated cells from elderly donors. J Clin Invest. 1988;81:1096–1102. [PMC free article] [PubMed]

[7] Roberts-Thomson IC, Whittingham S, Youngchaiyud U, Mackay IR. Ageing, immune response, and mortality. Lancet. 1974;2:368–370. [PubMed]

[8] Wayne SJ, Rhyne RL, Garry PJ, Goodwin JS. Cell-mediated immunity as a predictor of morbidity and mortality in subjects over 60. J Gerontol. 1990;45:M45–48. [PubMed]

[9] Jones SC, Clise-Dwyer K, Huston G, Dibble J, Eaton S, Haynes L, Swain SL. Impact of Post-Thymic Cellular Longevity on the Development of Age-Associated CD4+ T Cell Defects. J Immunol. 2008;180:4465–4475. [PMC free article] [PubMed]

[10] Swain S, Clise-Dwyer K, Haynes L. Homeostasis and the age-associated defect of CD4 T cells. Semin Immunol. 2005;17:370–377. [PMC free article] [PubMed]

[11] Goronzy JJ, Lee WW, Weyand CM. Aging and T-cell diversity. Exp Gerontol. 2007;42:400–406. [PMC free article] [PubMed]

[12] Goronzy JJ, Weyand CM. T cell development and receptor diversity during aging. Curr Opin Immunol. 2005;17:468–475. [PubMed]

[13] Nikolich-Zugich J, Slifka MK, Messaoudi I. The many important facets of T-cell repertoire diversity. Nat Rev Immunol. 2004;4:123–132. [PubMed]

[14] Adolfsson O, Huber BT, Meydani SN. Vitamin E-enhanced IL-2 production in old mice: naive but not memory T cells show increased cell division cycling and IL-2-producing capacity. J Immunol. 2001;167:3809–3817. [PubMed]

[15] Larbi A, Douziech N, Dupuis G, Khalil A, Pelletier H, Guerard KP, Fulop T., Jr Age-associated alterations in the recruitment of signal-transduction proteins to lipid rafts in human T lymphocytes. J Leukoc Biol. 2004;75:373–381. [PubMed]

[16] Thoman ML, Weigle WO. Lymphokines and aging: interleukin-2 production and activity in aged animals. J Immunol. 1981;127:2102–2106. [PubMed]

[17] Smith KA. Interleukin-2: inception, impact, and implications. Science. 1988;240:1169–1176. [PubMed]

[18] Haynes L, Linton PJ, Eaton SM, Tonkonogy SL, Swain SL. Interleukin 2, but not other common gamma chain-binding cytokines, can reverse the defect in generation of CD4 effector T cells from naive T cells of aged mice. J Exp Med. 1999;190:1013–1024. [PMC free article] [PubMed]

[19] Linton PJ, Li SP, Zhang Y, Bautista B, Huynh Q, Trinh T. Intrinsic versus environmental influences on T-cell responses in aging. Immunol Rev. 2005;205:207–219. [PubMed]

[20] Grossmann A, Rabinovitch PS, Kavanagh TJ, Jinneman JC, Gilliland LK, Ledbetter JA, Kanner SB. Activation of murine T-cells via phospholipase-C gamma 1-associated protein tyrosine phosphorylation is reduced with aging. J Gerontol A Biol Sci Med Sci. 1995;50:B205–212. [PubMed]

[21] Miller RA, Garcia G, Kirk CJ, Witkowski JM. Early activation defects in T lymphocytes from aged mice. Immunol Rev. 1997;160:79–90. [PubMed]

[22] Pahlavani MA. T cell signaling: effect of age. Front Biosci. 1998;3:D1120–1133. [PubMed]

[23] Kirk CJ, Miller RA. Analysis of Raf-1 activation in response to TCR activation and costimulation in murine T-lymphocytes: effect of age. Cellular Immunology. 1998;190:33–42. [PubMed]

[24] Pahlavani MA, Harris MD, Richardson A. Activation of p21ras/MAPK signal transduction molecules decreases with age in mitogen-stimulated T cells from rats. Cell Immunol. 1998;185:39–48. [PubMed]

[25] Pahlavani MA, Harris MD, Richardson A. The age-related decline in the induction of IL-2 transcription is correlated to changes in the transcription factor NFAT. Cell Immunol. 1995;165:84–91. [PubMed]

[26] Whisler RL, Beiqing L, Chen M. Age-related decreases in IL-2 production by human T cells are associated with impaired activation of nuclear transcriptional factors AP-1 and NF-AT. Cell Immunol. 1996;169:185–195. [PubMed]

[27] Whisler RL, Chen M, Beiqing L, Carle KW. Impaired induction of c-fos/c-jun genes and of transcriptional regulatory proteins binding distinct c-fos/c-jun promoter elements in activated human T cells during aging. Cell Immunol. 1997;175:41–50. [PubMed]

[28] Trebilcock GU, Ponnappan U. Evidence for lowered induction of nuclear factor kappa B in activated human T lymphocytes during aging. Gerontology. 1996;42:137–146. [PubMed]

[29] Trebilcock GU, Ponnappan U. Nuclear factor-kappaB induction in CD45RO+ and CD45RA+ T cell subsets during aging. Mech Ageing Dev. 1998;102:149–163. [PubMed]

[30] Garcia GG, Miller RA. Single-cell analyses reveal two defects in peptide-specific activation of naive T cells from aged mice. J Immunol. 2001;166:3151–3157. [PubMed]

[31] Marko MG, Ahmed T, Bunnell SC, Wu D, Chung H, Huber BT, Meydani SN. Age-associated decline in effective immune synapse formation of CD4(+) T cells is reversed by vitamin E supplementation. J Immunol. 2007;178:1443–1449. [PubMed]

[32] Tamir A, Eisenbraun MD, Garcia GG, Miller RA. Age-dependent alterations in the assembly of signal transduction complexes at the site of T cell/APC interaction. J Immunol. 2000;165:1243–1251. [PubMed]

[33] Vallejo AN. CD28 extinction in human T cells: altered functions and the program of T-cell senescence. Immunol Rev. 2005;205:158–169. [PubMed]

[34] Weng NP, Akbar AN, Goronzy J. CD28(−) T cells: their role in the age-associated decline of immune function. Trends Immunol. 2009;30:306–312. [PMC free article] [PubMed]

[35] Bartocci A, Maggi FM, Welker RD, Veronese F. Age-related immunossuppresion: putative role of prostaglandins. In: Powles TJ, Backman RS, Honn KV, Ramwell P, editors. Prostaglandins and Cancer. Alan R. Liss; New York: 1982. pp. 725–730.

[36] Hayek MG, Meydani SN, Meydani M, Blumberg JB. Age differences in eicosanoid production of mouse splenocytes: effects on mitogen-induced T-cell proliferation. J Gerentol. 1994;49:B197–B207. [PubMed]

[37] Meydani SN, Meydani M, Verdon CP, Shapiro AA, Blumberg JB, Hayes KC. Vitamin E supplementation suppresses prostaglandin E1(2) synthesis and enhances the immune response of aged mice. Mech Ageing Dev. 1986;34:191–201. [PubMed]

[38] Meydani SN, Barklund MP, Liu S, Meydani M, Miller RA, Cannon JG, Morrow FD, Rocklin R, Blumberg JB. Vitamin E supplementation enhances cell-mediated immunity in healthy elderly subjects. Am J Clin Nutr. 1990;52:557–563. [PubMed]

[39] Claycombe KJ, Wu D, Nikolova-Karakashian M, Palmer H, Beharka A, Paulson KE, Meydani SN. Ceramide mediates age-associated increase in macrophage cyclooxygenase-2 expression. J Biol Chem. 2002;277:30784–30791. [PubMed]

[40] Hayek MG, Mura C, Wu D, Beharka AA, Han SN, Paulson KE, Hwang D, Meydani SN. Enhanced expression of inducible cyclooxygenase with age in murine macrophages. J Immunol. 1997;159:2445–2451. [PubMed]

[41] Wu D, Marko M, Claycombe K, Paulson KE, Meydani SN. Ceramide-induced and age-associated increase in macrophage COX-2 expression is mediated through up-regulation of NF-kappa B activity. J Biol Chem. 2003;278:10983–10992. [PubMed]

[42] Miller JP, Allman D. The decline in B lymphopoiesis in aged mice reflects loss of very early B-lineage precursors. J Immunol. 2003;171:2326–2330. [PubMed]

[43] Min H, Montecino-Rodriguez E, Dorshkind K. Effects of aging on the common lymphoid progenitor to pro-B cell transition. J Immunol. 2006;176:1007–1012. [PubMed]

[44] Kline GH, Hayden TA, Klinman NR. B cell maintenance in aged mice reflects both increased B cell longevity and decreased B cell generation. J Immunol. 1999;162:3342–3349. [PubMed]

[45] Rajczy K, Vargha P, Beregi E. Relationship between immunoglobulin levels and specific antibody titers in the elderly. Z Gerontol. 1986;19:158–161. [PubMed]

[46] Weksler ME, Szabo P. The effect of age on the B-cell repertoire. J Clin Immunol. 2000;20:240–249. [PubMed]

[47] Howard WA, Gibson KL, Dunn-Walters DK. Antibody quality in old age. Rejuvenation Res. 2006;9:117–125. [PubMed]

[48] Gibson KL, Wu YC, Barnett Y, Duggan O, Vaughan R, Kondeatis E, Nilsson BO, Wikby A, Kipling D, Dunn-Walters DK. B-cell diversity decreases in old age and is correlated with poor health status. Aging Cell. 2009;8:18–25. [PMC free article] [PubMed]

[49] Hijmans W, Radl J, Bottazzo GF, Doniach D. Autoantibodies in highly aged humans. Mech Ageing Dev. 1984;26:83–89. [PubMed]

[50] Silvestris F, Anderson W, Goodwin JS, Williams RC., Jr Discrepancy in the expression of autoantibodies in healthy aged individuals. Clin Immunol Immunopathol. 1985;35:234–244. [PubMed]

[51] Stacy S, Krolick KA, Infante AJ, Kraig E. Immunological memory and late onset autoimmunity. Mech Ageing Dev. 2002;123:975–985. [PubMed]

[52] Gomez CR, Nomellini V, Faunce DE, Kovacs EJ. Innate immunity and aging. Exp Gerontol. 2008;43:718–728. [PMC free article] [PubMed]

[53] Kovacs EJ, Palmer JL, Fortin CF, Fulop T, Jr, Goldstein DR, Linton PJ. Aging and innate immunity in the mouse: impact of intrinsic and extrinsic factors. Trends Immunol. 2009;30:319–324. [PMC free article] [PubMed]

[54] Shaw AC, Joshi S, Greenwood H, Panda A, Lord JM. Aging of the innate immune system. Curr Opin Immunol. 2010;22:507–513. [PubMed]

[55] Bruunsgaard H, Pedersen M, Pedersen BK. Aging and proinflammatory cytokines. Curr Opin Hematol. 2001;8:131–136. [PubMed]

[56] Ershler WB. Interleukin-6: a cytokine for gerontologists. J Am Geriatr Soc. 1993;41:176–181. [PubMed]

[57] Fagiolo U, Cossarizza A, Scala E, Fanales-Belasio E, Ortolani C, Cozzi E, Monti D, Franceschi C, Paganelli R. Increased cytokine production in mononuclear cells of healthy elderly people. Eur J Immunol. 1993;23:2375–2378. [PubMed]

[58] Forsey RJ, Thompson JM, Ernerudh J, Hurst TL, Strindhall J, Johansson B, Nilsson BO, Wikby A. Plasma cytokine profiles in elderly humans. Mech Ageing Dev. 2003;124:487–493. [PubMed]

[59] Franceschi C, Bonafe M, Valensin S, Olivieri F, De Luca M, Ottaviani E, De Benedictis G. Inflamm-aging. An evolutionary perspective on immunosenescence. Ann N Y Acad Sci. 2000;908:244–254. [PubMed]

[60] Panda A, Arjona A, Sapey E, Bai F, Fikrig E, Montgomery RR, Lord JM, Shaw AC. Human innate immunosenescence: causes and consequences for immunity in old age. Trends Immunol. 2009;30:325–333. [PubMed]

[61] Mocchegiani E, Malavolta M. NK and NKT cell functions in immunosenescence. Aging Cell. 2004;3:177–184. [PubMed]

[62] Hatam LJ, Kayden HJ. A high-performance liquid chromatographic method for the determination of tocopherol in plasma and cellular elements of the blood. J Lipid Res. 1979;20:639–645. [PubMed]

[63] Gebremichael A, Levy EM, Corwin LM. Adherent cell requirement for the effect of vitamin E on in vitro antibody synthesis. J Nutr. 1984;114:1297–1305. [PubMed]

[64] Kowdley KV, Mason JB, Meydani SN, Cornwall S, Grand RJ. Vitamin E deficiency and impaired cellular immunity related to intestinal fat malabsorption. Gastroenterology. 1992;102:2139–2142. [PubMed]

[65] Han SN, Meydani SN. Vitamin E and infectious diseases in the aged. Proc Nutr Soc. 1999;58:697–705. [PubMed]

[66] Meydani SN, Meydani M, Blumberg JB, Leka LS, Siber G, Loszewski R, Thompson C, Pedrosa MC, Diamond RD, Stollar BD. Vitamin E supplementation and in vivo immune response in healthy elderly subjects. A randomized controlled trial. Jama. 1997;277:1380–1386. [PubMed]

[67] Sakai S, Moriguchi S. Long-term feeding of high vitamin E diet improves the decreased mitogen response of rat splenic lymphocytes with aging. J Nutr Sci Vitaminol (Tokyo) 1997;43:113–122. [PubMed]

[68] Pallast EG, Schouten EG, de Waart FG, Fonk HC, Doekes G, von Blomberg BM, Kok FJ. Effect of 50- and 100-mg vitamin E supplements on cellular immune function in noninstitutionalized elderly persons. Am J Clin Nutr. 1999;69:1273–1281. [PubMed]

[69] De la Fuente M, Hernanz A, Guayerbas N, Victor VM, Arnalich F. Vitamin E ingestion improves several immune functions in elderly men and women. Free Radic Res. 2008;42:272–280. [PubMed]

[70] Meydani SN, Han SN, Wu D. Vitamin E and immune response in the aged: molecular mechanisms and clinical implications. Immunol Rev. 2005;205:269–284. [PubMed]

[71] Wu D, Meydani SN. Age-associated changes in immune and inflammatory responses: impact of vitamin E intervention. J Leukoc Biol. 2008;84:900–914. [PubMed]

[72] Zhang W, Trible RP, Zhu M, Liu SK, McGlade CJ, Samelson LE. Association of Grb2, Gads, and phospholipase C-gamma 1 with phosphorylated LAT tyrosine residues. Effect of LAT tyrosine mutations on T cell angigen receptor-mediated signaling. J Biol Chem. 2000;275:23355–23361. [PubMed]

[73] Paz PE, Wang S, Clarke H, Lu X, Stokoe D, Abo A. Mapping the Zap-70 phosphorylation sites on LAT (linker for activation of T cells) required for recruitment and activation of signalling proteins in T cells. Biochem J. 2001;356:461–471. [PubMed]

[74] Marko MG, Pang HJ, Ren Z, Azzi A, Huber BT, Bunnell SC, Meydani SN. Vitamin E reverses impaired linker for activation of T cells activation in T cells from aged C57BL/6 mice. J Nutr. 2009;139:1192–1197. [PubMed]

[75] Beharka AA, Wu D, Han SN, Meydani SN. Macrophage PGE₂ production contributes to the age-associated decrease in T cell function which is reversed by dietary antioxidants. Mech Ageing Dev. 1997;93:59–77. [PubMed]

[76] Franklin RA, Arkins S, Li YM, Kelley KW. Macrophages suppress lectin-induced proliferation of lymphocytes from aged rats. Mech Ageing Dev. 1993;67:33–46. [PubMed]

[77] Wu D, Mura C, Beharka AA, Han SN, Paulson KE, Hwang D, Meydani SN. Age-associated increase in PGE2 synthesis and COX activity in murine macrophages is reversed by vitamin E. Am J Physiol. 1998;275:C661–668. [PubMed]

[78] Jiang Q, Elson-Schwab I, Courtemanche C, Ames BN. gamma-tocopherol and its major metabolite, in contrast to alpha-tocopherol, inhibit cyclooxygenase activity in macrophages and epithelial cells. Proc Natl Acad Sci U S A. 2000;97:11494–11499. [PubMed]

[79] O'Leary KA, de Pascual-Tereasa S, Needs PW, Bao YP, NM OB, Williamson G. Effect of flavonoids and vitamin E on cyclooxygenase-2 (COX-2) transcription. Mutat Res. 2004;551:245–254. [PubMed]

[80] Beharka AA, Wu D, Serafini M, Meydani SN. Mechanism of vitamin E inhibition of cyclooxygenase activity in macrophages from old mice: role of peroxynitrite. Free Radic Boil Med. 2002;32:503–511. [PubMed]

[81] Landino LM, Crews BC, Timmons MD, Morrow JD, Marnett LJ. Peroxynitrite, the coupling product of nitric oxide and superoxide, activates prostaglandin biosynthesis. Proc Natl Acad Sci U S A. 1996;93:15069–15074. [PubMed]

[82] Belisle SE, Leka LS, Dallal GE, Jacques PF, Delgado-Lista J, Ordovas JM, Meydani SN. Cytokine response to vitamin E supplementation is dependent on pre-supplementation cytokine levels. Biofactors. 2008;33:191–200. [PMC free article] [PubMed]

[83] Belisle SE, Leka LS, Delgado-Lista J, Jacques PF, Ordovas JM, Meydani SN. Polymorphisms at cytokine genes may determine the effect of vitamin E on cytokine production in the elderly. J Nutr. 2009;139:1855–1860. [PubMed]

[84] Louis E, Franchimont D, Piron A, Gevaert Y, Schaaf-Lafontaine N, Roland S, Mahieu P, Malaise M, De Groote D, Louis R, Belaiche J. Tumour necrosis factor (TNF) gene polymorphism influences TNF-alpha production in lipopolysaccharide (LPS)-stimulated whole blood cell culture in healthy humans. Clin Exp Immunol. 1998;113:401–406. [PubMed]

[85] Wilson AG, Symons JA, McDowell TL, McDevitt HO, Duff GW. Effects of a polymorphism in the human tumor necrosis factor alpha promoter on transcriptional activation. Proc Natl Acad Sci U S A. 1997;94:3195–3199. [PubMed]

[86] Crossley KB, Peterson PK. Infections in the elderly. Clin Infect Dis. 1996;22:209–215. [PubMed]

[87] Farber BF, Brennen C, Puntereri AJ, Brody JP. A prospective study of nosocomial infections in a chronic care facility. J Am Geriatr Soc. 1984;32:499–502. [PubMed]

[88] Mehr DR, Foxman B, Colombo P. Risk factors for mortality from lower respiratory infections in nursing home patients. J Fam Pract. 1992;34:585–591. [PubMed]

[89] Ely KH, Roberts AD, Kohlmeier JE, Blackman MA, Woodland DL. Aging and CD8+ T cell immunity to respiratory virus infections. Exp Gerontol. 2007;42:427–431. [PMC free article] [PubMed]

[90] Gavazzi G, Krause KH. Ageing and infection. Lancet Infect Dis. 2002;2:659–666. [PubMed]

[91] Hayek MG, Taylor SF, Bender BS, Han SN, Meydani M, Smith DE, Eghtesada S, Meydani SN. Vitamin E supplementation decreases lung virus titers in mice infected with influenza. J Infect Dis. 1997;176:273–276. [PubMed]

[92] Han SN, Wu D, Ha WK, Beharka A, Smith DE, Bender BS, Meydani SN. Vitamin E supplementation increases T helper 1 cytokine production in old mice infected with influenza virus. Immunology. 2000;100:487–493. [PubMed]

[93] Chavance M, Herbeth B, Fournier C, Janot C, Vernhes G. Vitamin status, immunity and infections in an elderly population. Eur J Clin Nutr. 1989;43:827–835. [PubMed]

[94] Meydani SN, Leka LS, Fine BC, Dallal GE, Keusch GT, Singh MF, Hamer DH. Vitamin E and respiratory tract infections in elderly nursing home residents: a randomized controlled trial. Jama. 2004;292:828–836. [PMC free article] [PubMed]

[95] Hemila H, Kaprio J. Subgroup analysis of large trials can guide further research: a case study of vitamin E and pneumonia. Clin Epidemiol. 2011;3:51–59. [PMC free article] [PubMed]

[96] Hemila H, Virtamo J, Albanes D, Kaprio J. Vitamin E and beta-carotene supplementation and hospital-treated pneumonia incidence in male smokers. Chest. 2004;125:557–565. [PubMed]

[97] Hemila H, Virtamo J, Albanes D, Kaprio J. The effect of vitamin E on common cold incidence is modified by age, smoking and residential neighborhood. J Am Coll Nutr. 2006;25:332–339. [PubMed]

[98] Graat JM, Schouten EG, Kok FJ. Effect of daily vitamin E and multivitamin-mineral supplementation on acute respiratory tract infections in elderly persons: a randomized controlled trial. Jama. 2002;288:715–721. [PubMed]

[99] Prasad AS. Zinc: role in immunity, oxidative stress and chronic inflammation. Curr Opin Clin Nutr Metab Care. 2009;12:646–652. [PubMed]

[100] Haase H, Rink L. Functional significance of zinc-related signaling pathways in immune cells. Annu Rev Nutr. 2009;29:133–152. [PubMed]

[101] Mitchell WA, Meng I, Nicholson SA, Aspinall R. Thymic output, ageing and zinc. Biogerontology. 2006;7:461–470. [PubMed]

[102] Haase H, Rink L. The immune system and the impact of zinc during aging. Immun Ageing. 2009;6:9. [PMC free article] [PubMed]

[103] Keen CL, Gershwin ME. Zinc deficiency and immune function. Annu Rev Nutr. 1990;10:415–431. [PubMed]

[104] Prasad AS. Effects of zinc deficiency on Th1 and Th2 cytokine shifts. J Infect Dis. 2000;182(Suppl 1):S62–68. [PubMed]

[105] Prasad AS. Zinc in human health: effect of zinc on immune cells. Mol Med. 2008;14:353–357. [PMC free article] [PubMed]

[106] Fraker PJ, King LE, Laakko T, Vollmer TL. The dynamic link between the integrity of the immune system and zinc status. J Nutr. 2000;130:1399S–1406S. [PubMed]

[107] Fischer Walker C, Black RE. Zinc and the risk for infectious disease. Annu Rev Nutr. 2004;24:255–275. [PubMed]

[108] Dardenne M, Boukaiba N, Gagnerault MC, Homo-Delarche F, Chappuis P, Lemonnier D, Savino W. Restoration of the thymus in aging mice by in vivo zinc supplementation. Clin Immunol Immunopathol. 1993;66:127–135. [PubMed]

[109] Mocchegiani E, Santarelli L, Muzzioli M, Fabris N. Reversibility of the thymic involution and of age-related peripheral immune dysfunctions by zinc supplementation in old mice. Int J Immunopharmacol. 1995;17:703–718. [PubMed]

[110] Wong CP, Song Y, Elias VD, Magnusson KR, Ho E. Zinc supplementation increases zinc status and thymopoiesis in aged mice. J Nutr. 2009;139:1393–1397. [PubMed]

[111] Cossack ZT. T-lymphocyte dysfunction in the elderly associated with zinc deficiency and subnormal nucleoside phosphorylase activity: effect of zinc supplementation. Eur J Cancer Clin Oncol. 1989;25:973–976. [PubMed]

[112] Duchateau J, Delepesse G, Vrijens R, Collet H. Beneficial effects of oral zinc supplementation on the immune response of old people. Am J Med. 1981;70:1001–1004. [PubMed]

[113] Wagner PA, Jernigan JA, Bailey LB, Nickens C, Brazzi GA. Zinc nutriture and cell-mediated immunity in the aged. Int J Vitam Nutr Res. 1983;53:94–101. [PubMed]

[114] Prasad AS, Fitzgerald JT, Hess JW, Kaplan J, Pelen F, Dardenne M. Zinc deficiency in elderly patients. Nutrition. 1993;9:218–224. [PubMed]

[115] Prasad AS, Bao B, Beck FW, Sarkar FH. Correction of interleukin-2 gene expression by in vitro zinc addition to mononuclear cells from zinc-deficient human subjects: a specific test for zinc deficiency in humans. Transl Res. 2006;148:325–333. [PubMed]

[116] Bogden JD, Oleske JM, Lavenhar MA, Munves EM, Kemp FW, Bruening KS, Holding KJ, Denny TN, Guarino MA, Holland BK. Effects of one year of supplementation with zinc and other micronutrients on cellular immunity in the elderly. J Am Coll Nutr. 1990;9:214–225. [PubMed]

[117] Bogden JD, Oleske JM, Lavenhar MA, Munves EM, Kemp FW, Bruening KS, Holding KJ, Denny TN, Guarino MA, Krieger LM, et al. Zinc and immunocompetence in elderly people: effects of zinc supplementation for 3 months. Am J Clin Nutr. 1988;48:655–663. [PubMed]

[118] Fortes C, Forastiere F, Agabiti N, Fano V, Pacifici R, Virgili F, Piras G, Guidi L, Bartoloni C, Tricerri A, Zuccaro P, Ebrahim S, Perucci CA. The effect of zinc and vitamin A supplementation on immune response in an older population. J Am Geriatr Soc. 1998;46:19–26. [PubMed]

[119] Kahmann L, Uciechowski P, Warmuth S, Malavolta M, Mocchegiani E, Rink L. Effect of improved zinc status on T helper cell activation and TH1/TH2 ratio in healthy elderly individuals. Biogerontology. 2006;7:429–435. [PubMed]

[120] Bach JF, Papiernik M, Levasseur P, Dardenne M, Barois A, Le Brigand H. Evidence for a serum-factor secreted by the human thymus. Lancet. 1972;2:1056–1058. [PubMed]

[121] Iwata T, Incefy GS, Tanaka T, Fernandes G, Menendez-Botet CJ, Pih K, Good RA. Circulating thymic hormone levels in zinc deficiency. Cell Immunol. 1979;47:100–105. [PubMed]

[122] Dardenne M, Pleau JM, Nabarra B, Lefrancier P, Derrien M, Choay J, Bach JF. Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proc Natl Acad Sci U S A. 1982;79:5370–5373. [PubMed]

[123] Boukaiba N, Flament C, Acher S, Chappuis P, Piau A, Fusselier M, Dardenne M, Lemonnier D. A physiological amount of zinc supplementation: effects on nutritional, lipid, and thymic status in an elderly population. Am J Clin Nutr. 1993;57:566–572. [PubMed]

[124] Mocchegiani E, Muzzioli M, Giacconi R, Cipriano C, Gasparini N, Franceschi C, Gaetti R, Cavalieri E, Suzuki H. Metallothioneins/PARP-1/IL-6 interplay on natural killer cell activity in elderly: parallelism with nonagenarians and old infected humans. Effect of zinc supply Mech Ageing Dev. 2003;124:459–468. [PubMed]

[125] Muzzioli M, Mocchegiani E, Bressani N, Bevilacqua P, Fabris N. In vitro restoration by thymulin of NK activity of cells from old mice. Int J Immunopharmacol. 1992;14:57–61. [PubMed]

[126] Ravaglia G, Forti P, Maioli F, Bastagli L, Facchini A, Mariani E, Savarino L, Sassi S, Cucinotta D, Lenaz G. Effect of micronutrient status on natural killer cell immune function in healthy free-living subjects aged >/=90 y. Am J Clin Nutr. 2000;71:590–598. [PubMed]

[127] Mocchegiani E, Giacconi R, Costarelli L, Muti E, Cipriano C, Tesei S, Pierpaoli S, Giuli C, Papa R, Marcellini F, Gasparini N, Pierandrei R, Piacenza F, Mariani E, Monti D, Dedoussis G, Kanoni S, Herbein G, Fulop T, Rink L, Jajte J, Malavolta M. Zinc deficiency and IL-6 -174G/C polymorphism in old people from different European countries: effect of zinc supplementation. ZINCAGE study Exp Gerontol. 2008;43:433–444. [PubMed]

[128] Mariani E, Neri S, Cattini L, Mocchegiani E, Malavolta M, Dedoussis GV, Kanoni S, Rink L, Jajte J, Facchini A. Effect of zinc supplementation on plasma IL-6 and MCP-1 production and NK cell function in healthy elderly: interactive influence of +647 MT1a and −174 IL-6 polymorphic alleles. Exp Gerontol. 2008;43:462–471. [PubMed]

[129] Gardner EM, Bernstein ED, Popoff KA, Abrutyn E, Gross P, Murasko DM. Immune response to influenza vaccine in healthy elderly: lack of association with plasma beta-carotene, retinol, alpha-tocopherol, or zinc. Mech Ageing Dev. 2000;117:29–45. [PubMed]

[130] Provinciali M, Montenovo A, Di Stefano G, Colombo M, Daghetta L, Cairati M, Veroni C, Cassino R, Della Torre F, Fabris N. Effect of zinc or zinc plus arginine supplementation on antibody titre and lymphocyte subsets after influenza vaccination in elderly subjects: a randomized controlled trial. Age Ageing. 1998;27:715–722. [PubMed]

[131] Chandra RK. Excessive intake of zinc impairs immune responses. Jama. 1984;252:1443–1446. [PubMed]

[132] Cakman I, Kirchner H, Rink L. Zinc supplementation reconstitutes the production of interferon-alpha by leukocytes from elderly persons. J Interferon Cytokine Res. 1997;17:469–472. [PubMed]

[133] Wellinghausen N, Martin M, Rink L. Zinc inhibits interleukin-1-dependent T cell stimulation. Eur J Immunol. 1997;27:2529–2535. [PubMed]

[134] Bao B, Prasad A, Beck FW, Suneja A, Sarkar F. Toxic effect of zinc on NF-kappaB, IL-2, IL-2 receptor alpha, and TNF-alpha in HUT-78 (Th(0)) cells. Toxicol Lett. 2006;166:222–228. [PubMed]

[135] Tanaka S, Akaishi E, Hosaka K, Okamura S, Kubohara Y. Zinc ions suppress mitogen-activated interleukin-2 production in Jurkat cells. Biochem Biophys Res Commun. 2005;335:162–167. [PubMed]

[136] Ruel MT, Rivera JA, Santizo MC, Lonnerdal B, Brown KH. Impact of zinc supplementation on morbidity from diarrhea and respiratory infections among rural Guatemalan children. Pediatrics. 1997;99:808–813. [PubMed]

[137] Bao B, Prasad AS, Beck FW, Snell D, Suneja A, Sarkar FH, Doshi N, Fitzgerald JT, Swerdlow P. Zinc supplementation decreases oxidative stress, incidence of infection, and generation of inflammatory cytokines in sickle cell disease patients. Transl Res. 2008;152:67–80. [PubMed]

[138] Girodon F, Lombard M, Galan P, Brunet-Lecomte P, Monget AL, Arnaud J, Preziosi P, Hercberg S. Effect of micronutrient supplementation on infection in institutionalized elderly subjects: a controlled trial. Ann Nutr Metab. 1997;41:98–107. [PubMed]

[139] Girodon F, Galan P, Monget AL, Boutron-Ruault MC, Brunet-Lecomte P, Preziosi P, Arnaud J, Manuguerra JC, Herchberg S. Impact of trace elements and vitamin supplementation on immunity and infections in institutionalized elderly patients: a randomized controlled trial. MIN VIT AOX geriatric network Arch Intern Med. 1999;159:748–754. [PubMed]

[140] Prasad AS, Beck FW, Bao B, Fitzgerald JT, Snell DC, Steinberg JD, Cardozo LJ. Zinc supplementation decreases incidence of infections in the elderly: effect of zinc on generation of cytokines and oxidative stress. Am J Clin Nutr. 2007;85:837–844. [PubMed]

[141] Meydani SN, Barnett JB, Dallal GE, Fine BC, Jacques PF, Leka LS, Hamer DH. Serum zinc and pneumonia in nursing home elderly. Am J Clin Nutr. 2007;86:1167–1173. [PMC free article] [PubMed]

[142] Brooks WA, Santosham M, Naheed A, Goswami D, Wahed MA, Diener-West M, Faruque AS, Black RE. Effect of weekly zinc supplements on incidence of pneumonia and diarrhoea in children younger than 2 years in an urban, low-income population in Bangladesh: randomised controlled trial. Lancet. 2005;366:999–1004. [PubMed]

[143] Guarner F, Schaafsma GJ. Probiotics. Int J Food Microbiol. 1998;39:237–238. [PubMed]

[144] de Moreno de LeBlanc A, Chaves S, Carmuega E, Weill R, Antoine J, Perdigon G. Effect of long-term continuous consumption of fermented milk containing probiotic bacteria on mucosal immunity and the activity of peritoneal macrophages. Immunobiology. 2008;213:97–108. [PubMed]

[145] Delcenserie V, Martel D, Lamoureux M, Amiot J, Boutin Y, Roy D. Immunomodulatory effects of probiotics in the intestinal tract. Curr Issues Mol Biol. 2008;10:37–54. [PubMed]

[146] Mazanec MB, Nedrud JG, Kaetzel CS, Lamm ME. A three-tiered view of the role of IgA in mucosal defense. Immunol Today. 1993;14:430–435. [PubMed]

[147] Beharka AA, Paiva S, Leka LS, Ribaya-Mercado JD, Russell RM, Nibkin Meydani S. Effect of age on the gastrointestinal-associated mucosal immune response of humans. J Gerontol A Biol Sci Med Sci. 2001;56:B218–223. [PubMed]

[148] Fujihashi K, Kiyono H. Mucosal immunosenescence: new developments and vaccines to control infectious diseases. Trends Immunol. 2009;30:334–343. [PubMed]

[149] Galdeano CM, Perdigon G. Role of viability of probiotic strains in their persistence in the gut and in mucosal immune stimulation. J Appl Microbiol. 2004;97:673–681. [PubMed]

[150] Thomas CM, Versalovic J. Probiotics-host communication: Modulation of signaling pathways in the intestine. Gut Microbes. 2010;1:1–16. [PMC free article] [PubMed]

[151] Macpherson AJ, Uhr T. Induction of protective IgA by intestinal dendritic cells carrying commensal bacteria. Science. 2004;303:1662–1665. [PubMed]

[152] Muscettola M, Massai L, Tanganelli C, Grasso G. Effects of lactobacilli on interferon production in young and aged mice. Ann N Y Acad Sci. 1994;717:226–232. [PubMed]

[153] Baba N, Samson S, Bourdet-Sicard R, Rubio M, Sarfati M. Selected commensal-related bacteria and Toll-like receptor 3 agonist combinatorial codes synergistically induce interleukin-12 production by dendritic cells to trigger a T helper type 1 polarizing programme. Immunology. 2009;128:e523–531. [PubMed]

[154] Rescigno M, Urbano M, Valzasina B, Francolini M, Rotta G, Bonasio R, Granucci F, Kraehenbuhl JP, Ricciardi-Castagnoli P. Dendritic cells express tight junction proteins and penetrate gut epithelial monolayers to sample bacteria. Nat Immunol. 2001;2:361–367. [PubMed]

[155] Davidson LE, Fiorino AM, Snydman DR, Hibberd PL. Lactobacillus GG as an immune adjuvant for live-attenuated influenza vaccine in healthy adults: a randomized double-blind placebo-controlled trial. Eur J Clin Nutr. 2011;65:501–507. [PMC free article] [PubMed]

[156] Elmadfa I, Klein P, Meyer AL. Immune-stimulating effects of lactic acid bacteria in vivo and in vitro. Proc Nutr Soc. 2010;69:416–420. [PubMed]

[157] Vidal K, Benyacoub J, Moser M, Sanchez-Garcia J, Serrant P, Segura-Roggero I, Reuteler G, Blum S. Effect of Lactobacillus paracasei NCC2461 on antigen-specific T-cell mediated immune responses in aged mice. Rejuvenation Res. 2008;11:957–964. [PubMed]

[158] Fu YR, Yi ZJ, Pei JL, Guan S. Effects of Bifidobacterium bifidum on adaptive immune senescence in aging mice. Microbiol Immunol. 2010;54:578–583. [PubMed]

[159] Bouillanne O, Morineau G, Dupont C, Coulombel I, Vincent JP, Nicolis I, Benazeth S, Cynober L, Aussel C. Geriatric Nutritional Risk Index: a new index for evaluating at-risk elderly medical patients. Am J Clin Nutr. 2005;82:777–783. [PubMed]

[160] Chandra RK. Nutritional regulation of immunity and risk of infection in old age. Immunology. 1989;67:141–147. [PubMed]

[161] Kaburagi T, Yamano T, Fukushima Y, Yoshino H, Mito N, Sato K. Effect of Lactobacillus johnsonii La1 on immune function and serum albumin in aged and malnourished aged mice. Nutrition. 2007;23:342–350. [PubMed]

[162] Yang HY, Liu SL, Ibrahim SA, Zhao L, Jiang JL, Sun WF, Ren FZ. Oral administration of live Bifidobacterium substrains isolated from healthy centenarians enhanced immune function in BALB/c mice. Nutr Res. 2009;29:281–289. [PubMed]

[163] Lee Y, Lee TS. Enhancement in ex vivo phagocytic capacity of peritoneal leukocytes in mice by oral delivery of various lactic-acid-producing bacteria. Curr Microbiol. 2005;50:24–27. [PubMed]

[164] Tsai YT, Cheng PC, Fan CK, Pan TM. Time-dependent persistence of enhanced immune response by a potential probiotic strain Lactobacillus paracasei subsp paracasei NTU 101 Int J Food Microbiol. 2008;128:219–225. [PubMed]

[165] Fernandez-Gutierrez B, Jover JA, De Miguel S, Hernandez-Garcia C, Vidan MT, Ribera JM, Banares A, Serra JA. Early lymphocyte activation in elderly humans: impaired T and T-dependent B cell responses. Exp Gerontol. 1999;34:217–229. [PubMed]

[166] Linton PJ, Haynes L, Klinman NR, Swain SL. Antigen-independent changes in naive CD4 T cells with aging. J Exp Med. 1996;184:1891–1900. [PMC free article] [PubMed]

[167] Arunachalam K, Gill HS, Chandra RK. Enhancement of natural immune function by dietary consumption of Bifidobacterium lactis (HN019) Eur J Clin Nutr. 2000;54:263–267. [PubMed]

[168] Gill HS, Rutherfurd KJ, Cross ML. Dietary probiotic supplementation enhances natural killer cell activity in the elderly: an investigation of age-related immunological changes. J Clin Immunol. 2001;21:264–271. [PubMed]

[169] Gill HS, Rutherfurd KJ, Cross ML, Gopal PK. Enhancement of immunity in the elderly by dietary supplementation with the probiotic Bifidobacterium lactis HN019. Am J Clin Nutr. 2001;74:833–839. [PubMed]

[170] Fang H, Elina T, Heikki A, Seppo S. Modulation of humoral immune response through probiotic intake. FEMS Immunol Med Microbiol. 2000;29:47–52. [PubMed]

[171] Pelto L, Isolauri E, Lilius EM, Nuutila J, Salminen S. Probiotic bacteria down-regulate the milk-induced inflammatory response in milk-hypersensitive subjects but have an immunostimulatory effect in healthy subjects. Clin Exp Allergy. 1998;28:1474–1479. [PubMed]

[172] Chiang BL, Sheih YH, Wang LH, Liao CK, Gill HS. Enhancing immunity by dietary consumption of a probiotic lactic acid bacterium (Bifidobacterium lactis HN019): optimization and definition of cellular immune responses. Eur J Clin Nutr. 2000;54:849–855. [PubMed]

[173] Sheih YH, Chiang BL, Wang LH, Liao CK, Gill HS. Systemic immunity-enhancing effects in healthy subjects following dietary consumption of the lactic acid bacterium Lactobacillus rhamnosus HN001. J Am Coll Nutr. 2001;20:149–156. [PubMed]

[174] Parra MD, Martinez de Morentin BE, Cobo JM, Mateos A, Martinez JA. Daily ingestion of fermented milk containing Lactobacillus casei DN114001 improves innate-defense capacity in healthy middle-aged people. J Physiol Biochem. 2004;60:85–91. [PubMed]

[175] Goodwin K, Viboud C, Simonsen L. Antibody response to influenza vaccination in the elderly: a quantitative review. Vaccine. 2006;24:1159–1169. [PubMed]

[176] Boge T, Remigy M, Vaudaine S, Tanguy J, Bourdet-Sicard R, van der Werf S. A probiotic fermented dairy drink improves antibody response to influenza vaccination in the elderly in two randomised controlled trials. Vaccine. 2009;27:5677–5684. [PubMed]

[177] Borchers AT, Keen CL, Gershwin ME. The influence of yogurt/Lactobacillus on the innate and acquired immune response. Clin Rev Allergy Immunol. 2002;22:207–230. [PubMed]

[178] Kekkonen RA, Lummela N, Karjalainen H, Latvala S, Tynkkynen S, Jarvenpaa S, Kautiainen H, Julkunen I, Vapaatalo H, Korpela R. Probiotic intervention has strain-specific anti-inflammatory effects in healthy adults. World J Gastroenterol. 2008;14:2029–2036. [PMC free article] [PubMed]

[179] Spanhaak S, Havenaar R, Schaafsma G. The effect of consumption of milk fermented by Lactobacillus casei strain Shirota on the intestinal microflora and immune parameters in humans. Eur J Clin Nutr. 1998;52:899–907. [PubMed]

[180] Gill HS, Shu Q, Lin H, Rutherfurd KJ, Cross ML. Protection against translocating Salmonella typhimurium infection in mice by feeding the immuno-enhancing probiotic Lactobacillus rhamnosus strain HN001. Med Microbiol Immunol. 2001;190:97–104. [PubMed]

[181] Shu Q, Lin H, Rutherfurd KJ, Fenwick SG, Prasad J, Gopal PK, Gill HS. Dietary Bifidobacterium lactis (HN019) enhances resistance to oral Salmonella typhimurium infection in mice. Microbiol Immunol. 2000;44:213–222. [PubMed]

[182] de Waard R, Garssen J, Vos JG, Claassen E. Modulation of delayed-type hypersensitivity and acquired cellular resistance by orally administered viable indigenous lactobacilli in Listeria monocytogenes infected Wistar rats. Lett Appl Microbiol. 2002;35:256–260. [PubMed]

[183] Bunout D, Barrera G, Hirsch S, Gattas V, de la Maza MP, Haschke F, Steenhout P, Klassen P, Hager C, Avendano M, Petermann M, Munoz C. Effects of a nutritional supplement on the immune response and cytokine production in free-living Chilean elderly. JPEN J Parenter Enteral Nutr. 2004;28:348–354. [PubMed]

[184] Fukushima Y, Miyaguchi S, Yamano T, Kaburagi T, Iino H, Ushida K, Sato K. Improvement of nutritional status and incidence of infection in hospitalised, enterally fed elderly by feeding of fermented milk containing probiotic Lactobacillus johnsonii La1 (NCC533) Br J Nutr. 2007;98:969–977. [PubMed]

[185] Guillemard E, Tondu F, Lacoin F, Schrezenmeir J. Consumption of a fermented dairy product containing the probiotic Lactobacillus casei DN-114001 reduces the duration of respiratory infections in the elderly in a randomised controlled trial. Br J Nutr. 2010;103:58–68. [PubMed]

[186] Makino S, Ikegami S, Kume A, Horiuchi H, Sasaki H, Orii N. Reducing the risk of infection in the elderly by dietary intake of yoghurt fermented with Lactobacillus delbrueckii ssp bulgaricus OLL1073R-1. Br J Nutr. 2010;104:998–1006. [PubMed]

[187] de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, Ott S, Hampe J, Schreiber S, Heller K, Schrezenmeir J. Effect of Lactobacillus gasseri PA 16/8, Bifidobacterium longum SP 07/3, B. bifidum MF 20/5 on common cold episodes: a double blind, randomized, controlled trial. Clin Nutr. 2005;24:481–491. [PubMed]

[188] de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, Ott S, Hampe J, Schreiber S, Heller K, Schrezenmeir J. Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial. Vaccine. 2006;24:6670–6674. [PubMed]

[189] Berggren A, Lazou Ahren I, Larsson N, Onning G. Randomised, double-blind and placebo-controlled study using new probiotic lactobacilli for strengthening the body immune defence against viral infections. Eur J Nutr. 2011;50:203–210. [PubMed]

[190] Galli C, Calder PC. Effects of fat and fatty acid intake on inflammatory and immune responses: a critical review. Ann Nutr Metab. 2009;55:123–139. [PubMed]

[191] Fernandes G. Progress in nutritional immunology. Immunol Res. 2008;40:244–261. [PubMed]

[192] Fritsche K. Important differences exist in the dose-response relationship between diet and immune cell fatty acids in humans and rodents. Lipids. 2007;42:961–979. [PubMed]

[193] Sijben JW, Calder PC. Differential immunomodulation with long-chain n-3 PUFA in health and chronic disease. Proc Nutr Soc. 2007;66:237–259. [PubMed]

[194] Shaikh SR, Edidin M. Polyunsaturated fatty acids, membrane organization, T cells, and antigen presentation. Am J Clin Nutr. 2006;84:1277–1289. [PubMed]

[195] Kim W, Khan NA, McMurray DN, Prior IA, Wang N, Chapkin RS. Regulatory activity of polyunsaturated fatty acids in T-cell signaling. Prog Lipid Res. 2010;49:250–261. [PMC free article] [PubMed]

[196] Calder PC. The 2008 ESPEN Sir David Cuthbertson Lecture: Fatty acids and inflammation--from the membrane to the nucleus and from the laboratory bench to the clinic. Clin Nutr. 2010;29:5–12. [PubMed]

[197] Serhan CN, Chiang N, Van Dyke TE. Resolving inflammation: dual anti-inflammatory and pro-resolution lipid mediators. Nat Rev Immunol. 2008;8:349–361. [PMC free article] [PubMed]

[198] Kohli P, Levy BD. Resolvins and protectins: mediating solutions to inflammation. Br J Pharmacol. 2009;158:960–971. [PubMed]

[199] Kew S, Banerjee T, Minihane AM, Finnegan YE, Muggli R, Albers R, Williams CM, Calder PC. Lack of effect of foods enriched with plant- or marine-derived n-3 fatty acids on human immune function. Am J Clin Nutr. 2003;77:1287–1295. [PubMed]

[200] Wallace FA, Miles EA, Calder PC. Comparison of the effects of linseed oil and different doses of fish oil on mononuclear cell function in healthy human subjects. Br J Nutr. 2003;89:679–689. [PubMed]

[201] Fowler KH, Chapkin RS, McMurray DN. Effects of purified dietary n-3 ethyl esters on murine T lymphocyte function. J Immunol. 1993;151:5186–5197. [PubMed]

[202] Payan DG, Wong MY, Chernov-Rogan T, Valone FH, Pickett WC, Blake VA, Gold WM, Goetzl EJ. Alterations in human leukocyte function induced by ingestion of eicosapentaenoic acid. J Clin Immunol. 1986;6:402–410. [PubMed]

[203] Wu D, Meydani SN, Meydani M, Hayek MG, Huth P, Nicolosi RJ. Immunologic effects of marine- and plant-derived n-3 polyunsaturated fatty acids in nonhuman primates. Am J Clin Nutr. 1996;63:273–280. [PubMed]

[204] Pompos LJ, Fritsche KL. Antigen-driven murine CD4+ T lymphocyte proliferation and interleukin-2 production are diminished by dietary (n-3) polyunsaturated fatty acids. J Nutr. 2002;132:3293–3300. [PubMed]

[205] Zhang P, Kim W, Zhou L, Wang N, Ly LH, McMurray DN, Chapkin RS. Dietary fish oil inhibits antigen-specific murine Th1 cell development by suppression of clonal expansion. J Nutr. 2006;136:2391–2398. [PubMed]

[206] Meydani SN, Lichtenstein AH, Cornwall S, Meydani M, Goldin BR, Rasmussen H, Dinarello CA, Schaefer EJ. Immunologic effects of national cholesterol education panel step-2 diets with and without fish-derived N-3 fatty acid enrichment. J Clin Invest. 1993;92:105–113. [PMC free article] [PubMed]

[207] Chapkin RS, Kim W, Lupton JR, McMurray DN. Dietary docosahexaenoic and eicosapentaenoic acid: emerging mediators of inflammation. Prostaglandins Leukot Essent Fatty Acids. 2009;81:187–191. [PMC free article] [PubMed]

[208] Kim W, Fan YY, Barhoumi R, Smith R, McMurray DN, Chapkin RS. n-3 polyunsaturated fatty acids suppress the localization and activation of signaling proteins at the immunological synapse in murine CD4+ T cells by affecting lipid raft formation. J Immunol. 2008;181:6236–6243. [PMC free article] [PubMed]

[209] Yog R, Barhoumi R, McMurray DN, Chapkin RS. n-3 polyunsaturated fatty acids suppress mitochondrial translocation to the immunologic synapse and modulate calcium signaling in T cells. J Immunol. 2010;184:5865–5873. [PubMed]

[210] Meydani SN, Endres S, Woods MM, Goldin BR, Soo C, Morrill-Labrode A, Dinarello CA, Gorbach SL. Oral (n-3) fatty acid supplementation suppresses cytokine production and lymphocyte proliferation: comparison between young and older women. J Nutr. 1991;121:547–555. [PubMed]

[211] Bechoua S, Dubois M, Vericel E, Chapuy P, Lagarde M, Prigent AF. Influence of very low dietary intake of marine oil on some functional aspects of immune cells in healthy elderly people. Br J Nutr. 2003;89:523–531. [PubMed]

[212] Rees D, Miles EA, Banerjee T, Wells SJ, Roynette CE, Wahle KW, Calder PC. Dose-related effects of eicosapentaenoic acid on innate immune function in healthy humans: a comparison of young and older men. Am J Clin Nutr. 2006;83:331–342. [PubMed]

[213] Alperovich M, Neuman MI, Willett WC, Curhan GC. Fatty acid intake and the risk of community-acquired pneumonia in U.S. women. Nutrition. 2007;23:196–202. [PMC free article] [PubMed]

[214] Merchant AT, Curhan GC, Rimm EB, Willett WC, Fawzi WW. Intake of n-6 and n-3 fatty acids and fish and risk of community-acquired pneumonia in US men. Am J Clin Nutr. 2005;82:668–674. [PubMed]

[215] Anderson M, Fritsche KL. (n-3) Fatty acids and infectious disease resistance. J Nutr. 2002;132:3566–3576. [PubMed]

[216] Byleveld M, Pang GT, Clancy RL, Roberts DC. Fish oil feeding enhances lymphocyte proliferation but impairs virus-specific T lymphocyte cytotoxicity in mice following challenge with influenza virus. Clin Exp Immunol. 2000;119:287–292. [PubMed]

[217] Byleveld PM, Pang GT, Clancy RL, Roberts DC. Fish oil feeding delays influenza virus clearance and impairs production of interferon-gamma and virus-specific immunoglobulin A in the lungs of mice. J Nutr. 1999;129:328–335. [PubMed]

[218] Schwerbrock NM, Karlsson EA, Shi Q, Sheridan PA, Beck MA. Fish oil-fed mice have impaired resistance to influenza infection. J Nutr. 2009;139:1588–1594. [PubMed]

[219] Paul KP, Leichsenring M, Pfisterer M, Mayatepek E, Wagner D, Domann M, Sonntag HG, Bremer HJ. Influence of n-6 and n-3 polyunsaturated fatty acids on the resistance to experimental tuberculosis. Metabolism. 1997;46:619–624. [PubMed]

[220] McFarland CT, Fan YY, Chapkin RS, Weeks BR, McMurray DN. Dietary polyunsaturated fatty acids modulate resistance to Mycobacterium tuberculosis in guinea pigs. J Nutr. 2008;138:2123–2128. [PubMed]

[221] Jordao L, Lengeling A, Bordat Y, Boudou F, Gicquel B, Neyrolles O, Becker PD, Guzman CA, Griffiths G, Anes E. Effects of omega-3 and -6 fatty acids on Mycobacterium tuberculosis in macrophages and in mice. Microbes Infect. 2008;10:1379–1386. [PubMed]

[222] Bonilla DL, Fan YY, Chapkin RS, McMurray DN. Transgenic mice enriched in omega-3 fatty acids are more susceptible to pulmonary tuberculosis: impaired resistance to tuberculosis in fat-1 mice. J Infect Dis. 2010;201:399–408. [PubMed]

[223] Fritsche KL, Shahbazian LM, Feng C, Berg JN. Dietary fish oil reduces survival and impairs bacterial clearance in C3H/Hen mice challenged with Listeria monocytogenes. Clin Sci (Lond) 1997;92:95–101. [PubMed]

[224] Chang HR, Dulloo AG, Vladoianu IR, Piguet PF, Arsenijevic D, Girardier L, Pechere JC. Fish oil decreases natural resistance of mice to infection with Salmonella typhimurium. Metabolism. 1992;41:1–2. [PubMed]

[225] McCay CM, Crowell MF, Maynard LA. The effect of retarded growth upon the length of the life span and upon the ultimate body size. J Nutr. 1935;10:63–79. [PubMed]

[226] Anderson RM, Shanmuganayagam D, Weindruch R. Caloric restriction and aging: studies in mice and monkeys. Toxicol Pathol. 2009;37:47–51. [PubMed]

[227] Fontana L, Partridge L, Longo VD. Extending healthy life span--from yeast to humans. Science. 2010;328:321–326. [PMC free article] [PubMed]

[228] Heilbronn LK, Ravussin E. Calorie restriction and aging: review of the literature and implications for studies in humans. Am J Clin Nutr. 2003;78:361–369. [PubMed]

[229] Chen J, Astle CM, Harrison DE. Hematopoietic senescence is postponed and hematopoietic stem cell function is enhanced by dietary restriction. Exp Hematol. 2003;31:1097–1103. [PubMed]

[230] Chen J, Astle CM, Harrison DE. Delayed immune aging in diet-restricted B6CBAT6 F1 mice is associated with preservation of naive T cells. J Gerontol A Biol Sci Med Sci. 1998;53:B330–337. discussion B338–339. [PubMed]

[231] Walford RL, Liu RK, Gerbase-Delima M, Mathies M, Smith GS. Longterm dietary restriction and immune function in mice: response to sheep red blood cells and to mitogenic agents. Mech Ageing Dev. 1973;2:447–454. [PubMed]

[232] Weindruch R, Devens BH, Raff HV, Walford RL. Influence of dietary restriction and aging on natural killer cell activity in mice. J Immunol. 1983;130:993–996. [PubMed]

[233] Weindruch R, Gottesman SR, Walford RL. Modification of age-related immune decline in mice dietarily restricted from or after midadulthood. Proc Natl Acad Sci U S A. 1982;79:898–902. [PubMed]

[234] Weindruch R, Walford RL. Dietary restriction in mice beginning at 1 year of age: effect on life-span and spontaneous cancer incidence. Science. 1982;215:1415–1418. [PubMed]

[235] Spaulding CC, Walford RL, Effros RB. Calorie restriction inhibits the age-related dysregulation of the cytokines TNF-alpha and IL-6 in C3B10RF1 mice. Mech Ageing Dev. 1997;93:87–94. [PubMed]

[236] Fernandes G, Friend P, Yunis EJ, Good RA. Influence of dietary restriction on immunologic function and renal disease in (NZB x NZW) F1 mice. Proc Natl Acad Sci U S A. 1978;75:1500–1504. [PubMed]

[237] Friend PS, Fernandes G, Good RA, Michael AF, Yunis EJ. Dietary restrictions early and late: effects on the nephropathy of the NZB X NZW mouse. Lab Invest. 1978;38:629–632. [PubMed]

[238] Jankovic V, Messaoudi I, Nikolich-Zugich J. Phenotypic and functional T-cell aging in rhesus macaques (Macaca mulatta): differential behavior of CD4 and CD8 subsets. Blood. 2003;102:3244–3251. [PubMed]

[239] Messaoudi I, Fischer M, Warner J, Park B, Mattison J, Ingram DK, Totonchy T, Mori M, Nikolich-Zugich J. Optimal window of caloric restriction onset limits its beneficial impact on T-cell senescence in primates. Aging Cell. 2008;7:908–919. [PMC free article] [PubMed]

[240] Messaoudi I, Warner J, Fischer M, Park B, Hill B, Mattison J, Lane MA, Roth GS, Ingram DK, Picker LJ, Douek DC, Mori M, Nikolich-Zugich J. Delay of T cell senescence by caloric restriction in aged long-lived nonhuman primates. Proc Natl Acad Sci U S A. 2006;103:19448–19453. [PubMed]

[241] Nikolich-Zugich J, Messaoudi I. Mice and flies and monkeys too: caloric restriction rejuvenates the aging immune system of non-human primates. Exp Gerontol. 2005;40:884–893. [PubMed]

[242] Ahmed T, Das SK, Golden JK, Saltzman E, Roberts SB, Meydani SN. Calorie restriction enhances T-cell-mediated immune response in adult overweight men and women. J Gerontol A Biol Sci Med Sci. 2009;64:1107–1113. [PMC free article] [PubMed]

[243] Effros RB, Walford RL, Weindruch R, Mitcheltree C. Influences of dietary restriction on immunity to influenza in aged mice. J Gerontol. 1991;46:B142–147. [PubMed]

[244] Gardner EM. Caloric restriction decreases survival of aged mice in response to primary influenza infection. J Gerontol A Biol Sci Med Sci. 2005;60:688–694. [PubMed]

[245] Ritz BW, Aktan I, Nogusa S, Gardner EM. Energy restriction impairs natural killer cell function and increases the severity of influenza infection in young adult male C57BL/6 mice. J Nutr. 2008;138:2269–2275. [PubMed]

[246] Clinthorne JF, Adams DJ, Fenton JI, Ritz BW, Gardner EM. Short-term re-feeding of previously energy-restricted C57BL/6 male mice restores body weight and body fat and attenuates the decline in natural killer cell function after primary influenza infection. J Nutr. 2010;140:1495–1501. [PubMed]

[247] Sun D, Muthukumar AR, Lawrence RA, Fernandes G. Effects of calorie restriction on polymicrobial peritonitis induced by cecum ligation and puncture in young C57BL/6 mice. Clin Diagn Lab Immunol. 2001;8:1003–1011. [PMC free article] [PubMed]

[248] Kristan DM. Chronic calorie restriction increases susceptibility of laboratory mice (Mus musculus) to a primary intestinal parasite infection. Aging Cell. 2007;6:817–825. [PubMed]

[249] Han SN, Adolfsson O, Lee CK, Prolla TA, Ordovas J, Meydani SN. Age and vitamin E-induced changes in gene expression profiles of T cells. J Immunol. 2006;177:6052–6061. [PubMed]

[250] Ren Z, Pae M, Dao MC, Smith D, Meydani SN, Wu D. Dietary supplementation with tocotrienols enhances immune function in C57BL/6 mice. J Nutr. 2010;140:1335–1341. [PubMed]

[251] Lee C-Y, Wan F. Vitamin E supplementation improves cell-mediated immunity and oxidative stress of Asian men and women. J Nutr. 2000;130:2392–2397. [PubMed]

[252] Radhakrishnan AK, Lee AL, Wong PF, Kaur J, Aung H, Nesaretnam K. Daily supplementation of tocotrienol-rich fraction or alpha-tocopherol did not induce immunomodulatory changes in healthy human volunteers. Br J Nutr. 2009;101:810–815. [PubMed]

[253] Mahalingam D, Radhakrishnan AK, Amom Z, Ibrahim N, Nesaretnam K. Effects of supplementation with tocotrienol-rich fraction on immune response to tetanus toxoid immunization in normal healthy volunteers. Eur J Clin Nutr. 2011;65:63–69. [PubMed]

[254] Gay R, Han SN, Marko M, Belisle S, Bronson R, Meydani SN. The effect of vitamin E on secondary bacterial infection after influenza infection in young and old mice. Ann N Y Acad Sci. 2004;1031:418–421. [PubMed]

[255] Hemila H, Kaprio J, Albanes D, Heinonen OP, Virtamo J. Vitamin C, vitamin E, and beta-carotene in relation to common cold incidence in male smokers. Epidemiology. 2002;13:32–37. [PubMed]

[256] Hemila H. Vitamin E supplementation and respiratory infections in older people. J Am Geriatr Soc. 2007;55:1311–1313. author reply 1313–1314. [PubMed]

[257] Hemila H, Kaprio J. Vitamin E supplementation may transiently increase tuberculosis risk in males who smoke heavily and have high dietary vitamin C intake. Br J Nutr. 2008;100:896–902. [PubMed]

[258] Hemila H, Kaprio J. Vitamin E supplementation and pneumonia risk in males who initiated smoking at an early age: effect modification by body weight and dietary vitamin C. Nutr J. 2008;7:33. [PMC free article] [PubMed]

[259] Belisle SE, Hamer DH, Leka LS, Dallal GE, Delgado-Lista J, Fine BC, Jacques PF, Ordovas JM, Meydani SN. IL-2 and IL-10 gene polymorphisms are associated with respiratory tract infection and may modulate the effect of vitamin E on lower respiratory tract infections in elderly nursing home residents. Am J Clin Nutr. 2010;92:106–114. [PubMed]

[260] Hodkinson CF, Kelly M, Alexander HD, Bradbury I, Robson PJ, Bonham MP, O'Connor JM, Coudray C, Strain JJ, Wallace JM. Effect of zinc supplementation on the immune status of healthy older individuals aged 55–70 years: the ZENITH Study. J Gerontol A Biol Sci Med Sci. 2007;62:598–608. [PubMed]

[261] Bose A, Coles CL, Gunavathi, John H, Moses P, Raghupathy P, Kirubakaran C, Black RE, Brooks WA, Santosham M. Efficacy of zinc in the treatment of severe pneumonia in hospitalized children <2 y old. Am J Clin Nutr. 2006;83:1089–1096. quiz 1207. [PubMed]

[262] Coles CL, Bose A, Moses PD, Mathew L, Agarwal I, Mammen T, Santosham M. Infectious etiology modifies the treatment effect of zinc in severe pneumonia. Am J Clin Nutr. 2007;86:397–403. [PubMed]

[263] Lawson L, Thacher TD, Yassin MA, Onuoha NA, Usman A, Emenyonu NE, Shenkin A, Davies PD, Cuevas LE. Randomized controlled trial of zinc and vitamin A as co-adjuvants for the treatment of pulmonary tuberculosis. Trop Med Int Health. 2010;15:1481–1490. [PubMed]

[264] Pakasi TA, Karyadi E, Suratih NM, Salean M, Darmawidjaja N, Bor H, van der Velden K, Dolmans WM, van der Meer JW. Zinc and vitamin A supplementation fails to reduce sputum conversion time in severely malnourished pulmonary tuberculosis patients in Indonesia. Nutr J. 2010;9:41. [PMC free article] [PubMed]

[265] Takamura T, Harama D, Fukumoto S, Nakamura Y, Shimokawa N, Ishimaru K, Ikegami S, Makino S, Kitamura M, Nakao A. Lactobacillus bulgaricus OLL1181 activates the aryl hydrocarbon receptor pathway and inhibits colitis. Immunol Cell Biol 2011 [PMC free article] [PubMed]

[266] Paineau D, Carcano D, Leyer G, Darquy S, Alyanakian MA, Simoneau G, Bergmann JF, Brassart D, Bornet F, Ouwehand AC. Effects of seven potential probiotic strains on specific immune responses in healthy adults: a double-blind, randomized, controlled trial. FEMS Immunol Med Microbiol. 2008;53:107–113. [PubMed]

[267] Ouwehand AC, Bergsma N, Parhiala R, Lahtinen S, Gueimonde M, Finne-Soveri H, Strandberg T, Pitkala K, Salminen S. Bifidobacterium microbiota and parameters of immune function in elderly subjects. FEMS Immunol Med Microbiol. 2008;53:18–25. [PubMed]

[268] Ouwehand AC, Tiihonen K, Saarinen M, Putaala H, Rautonen N. Influence of a combination of Lactobacillus acidophilus NCFM and lactitol on healthy elderly: intestinal and immune parameters. Br J Nutr. 2009;101:367–375. [PubMed]

[269] Schiffrin EJ, Parlesak A, Bode C, Bode JC, van't Hof MA, Grathwohl D, Guigoz Y. Probiotic yogurt in the elderly with intestinal bacterial overgrowth: endotoxaemia and innate immune functions. Br J Nutr. 2009;101:961–966. [PubMed]

[270] Turchet P, Laurenzano M, Auboiron S, Antoine JM. Effect of fermented milk containing the probiotic Lactobacillus casei DN-114001 on winter infections in free-living elderly subjects: a randomised, controlled pilot study. J Nutr Health Aging. 2003;7:75–77. [PubMed]

[271] Tubelius P, Stan V, Zachrisson A. Increasing work-place healthiness with the probiotic Lactobacillus reuteri: a randomised, double-blind placebo-controlled study. Environ Health. 2005;4:25. [PMC free article] [PubMed]

[272] Winkler P, de Vrese M, Laue C, Schrezenmeir J. Effect of a dietary supplement containing probiotic bacteria plus vitamins and minerals on common cold infections and cellular immune parameters. Int J Clin Pharmacol Ther. 2005;43:318–326. [PubMed]

[273] Pregliasco F, Anselmi G, Fonte L, Giussani F, Schieppati S, Soletti L. A new chance of preventing winter diseases by the administration of synbiotic formulations. J Clin Gastroenterol. 2008;42(Suppl 3 Pt 2):S224–233. [PubMed]

[274] Mukerji SS, Pynnonen MA, Kim HM, Singer A, Tabor M, Terrell JE. Probiotics as adjunctive treatment for chronic rhinosinusitis: a randomized controlled trial. Otolaryngol Head Neck Surg. 2009;140:202–208. [PubMed]

[275] Hojsak I, Abdovic S, Szajewska H, Milosevic M, Krznaric Z, Kolacek S. Lactobacillus GG in the prevention of nosocomial gastrointestinal and respiratory tract infections. Pediatrics. 2010;125:e1171–1177. [PubMed]

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