The importance of lymphotoxin α (LTα) in lymphoid organogenesis is well established. Although LTα has been implicated in the pathogenesis of T-cell-mediated immunopathologies, the requirement for LTα in T-cell activation and effector function in vivo is not well understood. To determine the role of LTα in T-cell activation in vivo, we compared the generation of antigen-specific T-cell responses between wild type (+/+) and LTα-deficient (LTα−/−) mice during an acute infection with lymphocytic choriomeningitis virus (LCMV). Our studies showed that LCMV-infected LTα−/− mice had a profound impairment in the activation and expansion of virus-specific CD8 T cells in the spleen, as determined by cytotoxicity assays, intracellular staining for gamma interferon, and staining with major histocompatibility complex class I tetramers. Further, the nonlymphoid organs of LTα−/− mice also contained substantially lower number of LCMV-specific CD8 T cells than those of +/+ mice. Greatly reduced virus-specific CD8 T-cell responses in LTα−/− mice led to a defect in LCMV clearance from the tissues. In comparison to that in +/+ mice, the activation of LCMV-specific CD4 T cells was also significantly attenuated in LTα−/− mice. Adoptive transfer experiments were conducted to determine if abnormal lymphoid architecture in LTα−/− mice caused the impairment in the activation of LCMV-specific T-cell responses. Upon adoptive transfer into +/+ mice, the activation and expansion of LCMV-specific LTα−/− T cells were restored to levels comparable to those of +/+ T cells. In a reciprocal cell transfer experiment, activation of +/+ T cells was significantly reduced upon transfer into LTα−/− mice. These results showed that impairment in the activation of LCMV-specific T cells in LTα−/− mice may be due to abnormal lymphoid architecture and not to an intrinsic defect in LTα−/− T cells.
Respiratory challenge with murine gammaherpesvirus 68 (MHV-68) leads to an acute productive infection of the lung and a persistent latent infection in B lymphocytes, epithelia, and macrophages. The virus also induces splenomegaly and an increase in the number of activated CD8 T cells in the circulation. Lymphotoxin- α-deficient (LTα−/−) mice have no lymph nodes and have disrupted splenic architecture. Surprisingly, in spite of the severe defect in secondary lymphoid tissue, LTα−/− mice could clear a productive MHV-68 infection, although with delayed kinetics compared to wild-type mice, and could control latent infection. Cytotoxic T-cell activity was comparable in the lungs and spleens of LTα−/− and wild-type mice. However, splenic gamma interferon responses were substantially reduced in LTα−/− mice. Furthermore, LTα−/− mice failed to develop splenomegaly or lymphocytosis. Although germinal centers were absent, LTα−/− mice were able to class switch and showed significant virus-specific antibody titers. This work demonstrates that organized secondary lymphoid tissue is not an absolute requirement for the generation of immune responses to viral infections.
Although the essential role of tumor necrosis factor (TNF) in resistance to Listeria monocytogenes infection is well established, the roles of the related cytokines lymphotoxin alpha (LTα) and lymphotoxin beta (LTβ) are unknown. Using C57BL/6 mice in which the genes for these cytokines were disrupted, we examined the contributions of TNF, LTα, and LTβ in the host response to Listeria. To overcome the lack of peripheral lymph nodes in LTα−/− and LTβ−/− mice, bone marrow chimeras were constructed. TNF−/− and LTα−/− chimeras that lacked both secreted LTα3 and membrane-bound LTα1β2 and LTα2β1 were highly susceptible and succumbed 4.5 and 6 days, respectively, after a low-dose infection (200 CFU). LTβ−/− chimeras, which lacked only membrane-bound LT, controlled the infection in a manner comparable to wild-type (WT) chimeras. The Listeria-specific proliferative and gamma interferon T-cell responses were equivalent in all five groups of infected mice (LTα−/− and LTβ−/− chimeras, WT chimeras, and TNF−/− and WT mice). TNF−/− mice and LTα−/− chimeras, however, failed to generate the discrete foci of lymphocytes and macrophages that are essential for bacterial elimination. Rather, aberrant necrotic lesions comprised predominantly of neutrophils with relatively few lymphocytes and macrophages were observed in the livers and spleens of TNF−/− and LTα−/− chimeras. Therefore, in addition to TNF, soluble LTα3 plays a separate essential role in control of listerial infection through control of leukocyte accumulation and organization in infected organs.
Although the essential role of tumor necrosis factor (TNF) in the control of intracellular bac-terial infection is well established, it is uncertain whether the related cytokines lymphotoxin-α (LTα3) and lymphotoxin-β (LTβ) have independent roles in this process. Using C57Bl/6 mice in which the genes for these cytokines have been disrupted, we have examined the relative contribution of secreted LTα3 and membrane-bound LTβ in the host response to aerosol Mycobacterium tuberculosis infection. To overcome the lack of peripheral lymph nodes in LTα−/− and LTβ−/− mice, bone marrow chimeric mice were constructed. LTα−/− chimeras, which lack both secreted LTα3 and membrane-bound LTβ (LTα1β2 and LTα2β1), were highly susceptible and succumbed 5 wk after infection. LTβ−/− chimeras, which lack only the membrane-bound LTβ, controlled the infection in a comparable manner to wild-type (WT) chimeric mice. T cell responses to mycobacterial antigens and macrophage responses in LTα−/− chimeras were equivalent to those of WT chimeras, but in LTα−/− chimeras, granuloma formation was abnormal. LTα−/− chimeras recruited normal numbers of T cells into their lungs, but the lymphocytes were restricted to perivascular and peribronchial areas and were not colocated with macrophages in granulomas. Therefore, LTα3 is essential for the control of pulmonary tuberculosis, and its critical role lies not in the activation of T cells and macrophages per se but in the local organization of the granulomatous response.
lymphotoxin; TNF; tuberculosis; granuloma; lung
Lymphotoxin alpha (LTα) can exist in soluble form and exert tumor necrosis factor (TNF)-like activity through TNF receptors. Based on the phenotypes of knockout (KO) mice, the physiological functions of LTα and TNF are considered partly redundant, in particular, in supporting the microarchitecture of the spleen and in host defense. We exploited Cre-LoxP technology to generate a novel neomycin resistance gene (neo) cassette-free LTα-deficient mouse strain (neo-free LTα KO [LTαΔ/Δ]). Unlike the “conventional” LTα−/− mice, new LTαΔ/Δ animals were capable of producing normal levels of systemic TNF upon lipopolysaccharide (LPS) challenge and were susceptible to LPS/d-galactosamine (D-GalN) toxicity. Activated neutrophils, monocytes, and macrophages from LTαΔ/Δ mice expressed TNF normally at both the mRNA and protein levels as opposed to conventional LTα KO mice, which showed substantial decreases in TNF. Additionally, the spleens of the neo-free LTα KO mice displayed several features resembling those of LTβ KO mice rather than conventional LTα KO animals. The phenotype of the new LTαΔ/Δ mice indicates that LTα plays a smaller role in lymphoid organ maintenance than previously thought and has no direct role in the regulation of TNF expression.
LTα-deficient (LTα−/−) mice show altered splenic microarchitecture. This includes loss of normal B cell–T cell compartmentalization, of follicular dendritic cell (FDC) clusters, and of ability to form germinal centers (GC). LTα−/− mice immunized with sheep red blood cells (SRBC) produced high levels of antigen-specific IgM but no IgG in either primary or secondary responses, demonstrating failure of Ig class switching. This inability to switch to IgG could have been due to the altered splenic microarchitecture in these mice. Alternatively, it could have been due directly to a requirement for LTα expression by lymphocytes cooperating in the antibody response. To investigate this, we performed reciprocal spleen cell transfers. When irradiated LTα−/− mice were reconstituted with wild-type splenocytes and immunized immediately with SRBC, splenic microarchitecture remained disturbed and there was no IgG response. In contrast, when irradiated wild-type animals received splenocytes from LTα−/− mice, follicle structure and a strong IgG response were retained. These data indicate that LTα-deficient B cells and T cells have no intrinsic defect in ability to generate an IgG response. Rather, the altered microenvironment characteristic of LTα−/− mice appears to result in impaired ability to switch to a productive IgG response. To investigate whether prolonged expression of LTα could alter the structure and function of spleen follicles, reciprocal bone marrow (BM) transplantation was performed. Six weeks after reconstitution of LTα−/− mice with wild-type BM, spleen follicle structure was partially restored, with return of FDC clusters and GC. B cell/T cell compartmentalization remained abnormal and white pulp zones were small. This was accompanied by restoration of IgG response to SRBC. Reconstitution of wild-type mice with LTα−/− BM resulted in loss of FDC clusters and GC, and loss of the IgG response, although compartmentalized B cell and T cell zones were largely retained. Thus, defective IgG production is not absolutely associated with abnormal B cell and T cell compartmentalization. Rather, expression of LTα supports the maturation of spleen follicle structure, including the development and maintenance of FDC clusters, which supports Ig class switching and an effective IgG response.
Nitrogen dioxide (NO2) is an air pollutant associated with poor respiratory health, asthma exacerbation, and an increased likelihood of inhalational allergies. NO2 is also produced endogenously in the lung during acute inflammatory responses. NO2 can function as an adjuvant, allowing for allergic sensitization to an innocuous inhaled antigen and the generation of an antigen-specific Th2 immune response manifesting in an allergic asthma phenotype. As CD11c+ antigen presenting cells are considered critical for naïve T cell activation, we investigated the role of CD11c+ cells in NO2-promoted allergic sensitization.
We systemically depleted CD11c+ cells from transgenic mice expressing a simian diphtheria toxin (DT) receptor under of control of the CD11c promoter by administration of DT. Mice were then exposed to 15 ppm NO2 followed by aerosolized ovalbumin to promote allergic sensitization to ovalbumin and were studied after subsequent inhaled ovalbumin challenges for manifestation of allergic airway disease. In addition, pulmonary CD11c+ cells from wildtype mice were studied after exposure to NO2 and ovalbumin for cellular phenotype by flow cytometry and in vitro cytokine production.
Transient depletion of CD11c+ cells during sensitization attenuated airway eosinophilia during allergen challenge and reduced Th2 and Th17 cytokine production. Lung CD11c+ cells from wildtype mice exhibited a significant increase in MHCII, CD40, and OX40L expression 2 hours following NO2 exposure. By 48 hours, CD11c+MHCII+ DCs within the mediastinal lymph node (MLN) expressed maturation markers, including CD80, CD86, and OX40L. CD11c+CD11b- and CD11c+CD11b+ pulmonary cells exposed to NO2 in vivo increased uptake of antigen 2 hours post exposure, with increased ova-Alexa 647+ CD11c+MHCII+ DCs present in MLN from NO2-exposed mice by 48 hours. Co-cultures of ova-specific CD4+ T cells from naïve mice and CD11c+ pulmonary cells from NO2-exposed mice produced IL-1, IL-12p70, and IL-6 in vitro and augmented antigen-induced IL-5 production.
CD11c+ cells are critical for NO2-promoted allergic sensitization. NO2 exposure causes pulmonary CD11c+ cells to acquire a phenotype capable of increased antigen uptake, migration to the draining lymph node, expression of MHCII and co-stimulatory molecules required to activate naïve T cells, and secretion of polarizing cytokines to shape a Th2/Th17 response.
Rotavirus is a major cause of pediatric diarrheal illness worldwide. To explore the role of organized intestinal lymphoid tissues in infection by and immunity to rotavirus, lymphotoxin alpha-deficient (LTα−/−) mice that lack Peyer's patches and mesenteric lymph nodes were orally infected with murine rotavirus. Systemic rotavirus was cleared within 10 days in both LTα−/− and wild-type mice, and both strains developed early and sustained serum antirotavirus antibody responses. However, unlike wild-type mice, which resolved the intestinal infection within 10 days, LTα−/− mice shed fecal virus for approximately 50 days after inoculation. The resolution of fecal virus shedding occurred concurrently with induction of intestinal rotavirus-specific IgA in both mouse strains. Induction of intestinal rotavirus-specific IgA in LTα−/− mice correlated with the (late) appearance of IgA-producing plasma cells in the small intestine. This, together with the absence of rotavirus-specific serum IgA, implies that secretory rotavirus-specific IgA was produced locally. These findings indicate that serum IgG responses are insufficient and imply that local intestinal IgA responses are important for the clearance of rotavirus from intestinal tissues. Furthermore, they show that while LTα-dependent lymphoid tissues are important for the generation of IgA-producing B cells in the intestine, they are not absolutely required in the setting of rotavirus infection. Moreover, the induction of local IgA-producing B cell responses can occur late after infection and in an LTα-independent manner.
Lymphotoxin (LT)α is expressed by activated T cells, especially CD4+ T helper type 1 cells, and by activated B and natural killer cells, but the functions of this molecule in vivo are incompletely defined. We have previously shown that follicular dendritic cell (FDC) clusters and germinal centers (GCs) are absent from the peripheral lymphoid tissues of LTα-deficient (LTα−/−) mice. LTα−/− mice produce high levels of antigen-specific immunoglobulin (Ig)M, but very low levels of IgG after immunization with sheep red blood cells. We show here that LTα-expressing B cells are essential for the recovery of primary, secondary, and memory humoral immune responses in LTα−/− mice. It is not necessary for T cells to express LTα to support these immune functions. Importantly, LTα-expressing B cells alone are essential and sufficient for the formation of FDC clusters. Once these clusters are formed by LTα-expressing B cells, then LTα-deficient T cells can interact with B cells to generate GCs and productive class-switched antibody responses. Thus, B cells themselves provide an essential signal that induces and maintains the lymphoid microenvironment essential for GC formation and class-switched Ig responses.
Chronic asthma is often associated with neutrophilic infiltration in the airways. Neutrophils contain elastase, a potent secretagogue in the airways, nonetheless the role for neutrophil elastase as well as neutrophilic inflammation in allergen-induced airway responses is not well defined. In this study, we have investigated the impact of neutrophil elastase inhibition on the development of allergic airway inflammation and airway hyperresponsiveness (AHR) in previously sensitized and challenged mice.
BALB/c mice were sensitized and challenged (primary) with ovalbumin (OVA). Six weeks later, a single OVA aerosol (secondary challenge) was delivered and airway inflammation and airway responses were monitored 6 and 48 hrs later. An inhibitor of neutrophil elastase was administered prior to secondary challenge.
Mice developed a two-phase airway inflammatory response after secondary allergen challenge, one neutrophilic at 6 hr and the other eosinophilic, at 48 hr. PAR-2 expression in the lung tissues was enhanced following secondary challenge, and that PAR-2 intracellular expression on peribronchial lymph node (PBLN) T cells was also increased following allergen challenge of sensitized mice. Inhibition of neutrophil elastase significantly attenuated AHR, goblet cell metaplasia, and inflammatory cell accumulation in the airways following secondary OVA challenge. Levels of IL-4, IL-5 and IL-13, and eotaxin in BAL fluid 6 hr after secondary allergen challenge were significantly suppressed by the treatment. At 48 hr, treatment with the neutrophil elastase inhibitor significantly reduced the levels of IL-13 and TGF-β1 in the BAL fluid. In parallel, in vitro IL-13 production was significantly inhibited in spleen cells from sensitized mice.
These data indicate that neutrophil elastase plays an important role in the development of allergic airway inflammation and hyperresponsiveness, and would suggest that the neutrophil elastase inhibitor reduced AHR to inhaled methacholine indicating the potential for its use as a modulator of the immune/inflammatory response in both the neutrophil- and eosinophil-dominant phases of the response to secondary allergen challenge.
Neutrophil; Elastase; Airway; Hyperresponsiveness; Asthma
Lymphotoxin (LT) is widely regarded as a proinflammatory cytokine with activities equivalent to tumor necrosis factor (TNF). The contribution of LT to experimental autoimmune encephalomyelitis (EAE) was examined using TNF/LTα−/− mice, TNF−/− mice, and a new LTα−/− line described here. All mice were generated directly in the C57BL/6 strain and used for the preparation of radiation bone marrow chimeras to reconstitute peripheral lymphoid organs and restore immunocompetence. This approach overcame the problems related to the lack of lymph nodes that results from LTα gene targeting. We show here that when LT is absent but TNF is present, EAE progresses normally. In contrast, when TNF is absent but LT is present, EAE is delayed in onset and inflammatory leukocytes fail to move normally into the central nervous system parenchyma, even at the peak of disease. In the absence of both cytokines, the clinical and histological picture is identical to that seen when TNF alone is deficient, including demyelination. Furthermore, the therapeutic inhibition of TNF and LTα with soluble TNF receptor in unmanipulated wild-type or TNF−/− mice exactly reproduces these outcomes. We conclude from these studies that TNF and LT are functionally distinct cytokines in vivo, and despite sharing common receptors, show no redundancy of function nor mutual compensation.
Antigen-specific immunotherapy (SIT) has been widely practiced in treating allergic diseases such as asthma. However, this therapy may induce a series of allergic adverse events during treatment. Peptide immunotherapy (PIT) was explored to overcome these disadvantages. We confirmed that multiple antigen peptides (MAPs) do not cause autoimmune responses, which led to the presumption that MAPs intervention could alleviate allergic airway inflammation without inducing adverse effects.
In this study, synthesized OVA323-339MAP octamers were subcutaneously injected into ovalbumin (OVA)-sensitized and -challenged Balb/c mice to observe its effect on allergic airway inflammation, Th2 immune response, and immune regulating function. It was confirmed that OVA sensitization and challenge led to significant peritracheal inflammatory, cell infiltration, and intensive Th2 response. Treatment of OVA323-339MAP octomers in the airway inflammation mice model increased CD4+CD25+Foxp3+ T regulatory (Treg) cells and their regulatory function in peripheral blood, mediastinal draining lymph nodes, and the spleen. Furthermore, OVA323-339MAP increased IL-10 levels in bronchial alveolar lavage fluid (BALF); up-regulated the expression of IL-10, membrane-bound TGF-β1, as well as Foxp3 in lung tissues; and up-regulated programmed death-1 (PD-1) and cytotoxic T lymphocyte associated antigen 4 (CTLA-4) on the surface of Treg cells. These results were further correlated with the decreased OVA specific immunoglobulin E (sIgE) level and the infiltration of inflammatory cells such as eosinophils and lymphocytes in BALF. However, OVA323-339 peptide monomers did not show any of the mentioned effects in the same animal model.
Our study indicates that OVA323-339MAP had significant therapeutic effects on mice allergic airway inflammation by regulating the balance of Th1/Th2 response through Treg cells in vivo.
Allergic airway inflammation; Specific immunotherapy; Multiple antigen peptide
Secondary lymphoid tissue organogenesis requires tumor necrosis factor (TNF) and lymphotoxin α (LTα). The role of TNF in B cell positioning and formation of follicular structure was studied by comparing the location of newly produced naive recirculating and antigen-stimulated B cells in TNF−/− and TNF/LTα−/− mice. By creating radiation bone marrow chimeras from wild-type and TNF−/− mice, formation of normal splenic B cell follicles was shown to depend on TNF production by radiation-sensitive cells of hemopoietic origin. Reciprocal adoptive transfers of mature B cells between wild-type and knockout mice indicated that normal follicular tropism of recirculating naive B cells occurs independently of TNF derived from the recipient spleen. Moreover, soluble TNF receptor–IgG fusion protein administered in vivo failed to prevent B cell localization to the follicle or the germinal center reaction. Normal T zone tropism was observed when antigen-stimulated B cells were transferred into TNF−/− recipients, but not into TNF/LTα−/− recipients. This result appeared to account for the defect in isotype switching observed in intact TNF/LTα−/− mice because TNF/LTα−/− B cells, when stimulated in vitro, switched isotypes normally. Thus, TNF is necessary for creating the permissive environment for B cell movement and function, but is not itself responsible for these processes.
tumor necrosis factor; lymphotoxin; B cell movement; germinal center; follicular structure
Vitamin D may be essential for restricting the development and severity of allergic diseases and asthma, but a direct causal link between vitamin D deficiency and asthma has yet to be established. We have developed a ‘low dose’ model of allergic airway disease induced by intraperitoneal injection with ovalbumin (1 µg) and aluminium hydroxide (0.2 mg) in which characteristics of atopic asthma are recapitulated, including airway hyperresponsiveness, antigen-specific immunoglobulin type-E and lung inflammation. We assessed the effects of vitamin D deficiency throughout life (from conception until adulthood) on the severity of ovalbumin-induced allergic airway disease in vitamin D-replete and -deficient BALB/c mice using this model. Vitamin D had protective effects such that deficiency significantly enhanced eosinophil and neutrophil numbers in the bronchoalveolar lavage fluid of male but not female mice. Vitamin D also suppressed the proliferation and T helper cell type-2 cytokine-secreting capacity of airway-draining lymph node cells from both male and female mice. Supplementation of initially vitamin D-deficient mice with vitamin D for four weeks returned serum 25-hydroxyvitamin D to levels observed in initially vitamin D-replete mice, and also suppressed eosinophil and neutrophil numbers in the bronchoalveolar lavage fluid of male mice. Using generic 16 S rRNA primers, increased bacterial levels were detected in the lungs of initially vitamin D-deficient male mice, which were also reduced by vitamin D supplementation. These results indicate that vitamin D controls granulocyte levels in the bronchoalveolar lavage fluid in an allergen-sensitive manner, and may contribute towards the severity of asthma in a gender-specific fashion through regulation of respiratory bacteria.
Airway hyperresponsiveness (AHR) is one of the most prominent features of asthma, however, precise mechanisms for its induction have not been fully elucidated. We previously reported that systemic antigen sensitization alone directly induces AHR before development of eosinophilic airway inflammation in a mouse model of allergic airway inflammation, which suggests a critical role of antigen-specific systemic immune response itself in the induction of AHR. In the present study, we examined this possibility by cell transfer experiment, and then analyzed which cell source was essential for this process.
BALB/c mice were immunized with ovalbumin (OVA) twice. Spleen cells were obtained from the mice and were transferred in naive mice. Four days later, AHR was assessed. We carried out bronchoalveolar lavage (BAL) to analyze inflammation and cytokine production in the lung. Fluorescence and immunohistochemical studies were performed to identify T cells recruiting and proliferating in the lung or in the gut of the recipient. To determine the essential phenotype, spleen cells were column purified by antibody-coated microbeads with negative or positive selection, and transferred. Then, AHR was assessed.
Transfer of spleen cells obtained from OVA-sensitized mice induced a moderate, but significant, AHR without airway antigen challenge in naive mice without airway eosinophilia. Immunization with T helper (Th) 1 elicited antigen (OVA with complete Freund's adjuvant) did not induce the AHR. Transferred cells distributed among organs, and the cells proliferated in an antigen free setting for at least three days in the lung. This transfer-induced AHR persisted for one week. Interleukin-4 and 5 in the BAL fluid increased in the transferred mice. Immunoglobulin E was not involved in this transfer-induced AHR. Transfer of in vitro polarized CD4+ Th2 cells, but not Th1 cells, induced AHR. We finally clarified that CD4+CD62Llow memory/effector T cells recruited in the lung and proliferated, thus induced AHR.
These results suggest that antigen-sensitized memory/effector Th2 cells themselves play an important role for induction of basal AHR in an antigen free, eosinophil-independent setting. Therefore, regulation of CD4+ T cell-mediated immune response itself could be a critical therapeutic target for allergic asthma.
Background and Aims
Specific hyper-responsiveness towards an allergen and non-specific airway hyperreactivity both impair quality of life in patients with respiratory allergic diseases. We aimed to investigate cellular responses following specific and non-specific airway challenges locally and systemically in i) sensitized BALB/c mice challenged with grass pollen allergen Phl p 5, and in ii) grass pollen sensitized allergic rhinitis subjects undergoing specific airway challenge in the Vienna Challenge Chamber (VCC).
Methods and Results
BALB/c mice (n = 20) were intraperitoneally immunized with grass pollen allergen Phl p 5 and afterwards aerosol challenged with either the specific allergen Phl p 5 (n = 10) or the non-specific antigen ovalbumin (OVA) (n = 10). A protocol for inducing allergic asthma as well as allergic rhinitis, according to the united airway concept, was used. Both groups of exposed mice showed significantly reduced physical activity after airway challenge. Specific airway challenge further resulted in goblet cell hyperplasia, enhanced mucous secretion, intrapulmonary leukocyte infiltration and lymphoid follicle formation, associated with significant expression of IL-4, IL-5 and IL-13 in splenocytes and also partially in lung tissue. Concerning circulating blood cell dynamics, we observed a significant drop of erythrocyte counts, hemoglobin and hematocrit levels in both mouse groups, challenged with allergen or OVA. A significant decrease in circulating erythrocytes and hematocrit levels after airway challenges with grass pollen allergen was also found in grass pollen sensitized human rhinitis subjects (n = 42) at the VCC. The effects on peripheral leukocyte counts in mice and humans however were opposed, possibly due to the different primary inflammation sites.
Our data revealed that, besides significant leukocyte dynamics, particularly erythrocytes are involved in acute hypersensitivity reactions to respiratory allergens. A rapid recruitment of erythrocytes to the lungs to compensate for hypoxia is a possible explanation for these findings.
Both nature and induced regulatory T (Treg) lymphocytes are potent regulators of autoimmune and allergic disorders. Defects in endogenous Treg cells have been reported in patients with allergic asthma, suggesting that disrupted Treg cell-mediated immunological regulation may play an important role in airway allergic inflammation. In order to determine whether adoptive transfer of induced Treg cells generated in vitro can be used as an effective therapeutic approach to suppress airway allergic inflammation, exogenously induced Treg cells were infused into ovalbumin-sensitized mice prior to or during intranasal ovalbumin challenge. The results showed that adoptive transfer of induced Treg cells prior to allergen challenge markedly reduced airway hyperresponsiveness, eosinophil recruitment, mucus hyper-production, airway remodeling, and IgE levels. This effect was associated with increase of Treg cells (CD4+FoxP3+) and decrease of dendritic cells in the draining lymph nodes, and with reduction of Th1, Th2, and Th17 cell response as compared to the controls. Moreover, adoptive transfer of induced Treg cells during allergen challenge also effectively attenuate airway inflammation and improve airway function, which are comparable to those by natural Treg cell infusion. Therefore, adoptive transfer of in vitro induced Treg cells may be a promising therapeutic approach to prevent and treat severe asthma.
Cysteinyl leukotrienes (cys-LTs) are very important factors in the pathophysiology of bronchial asthma. Cys-LT receptor antagonists (LTRAs) decrease allergic airway inflammation. The aim of the present study was to determine the differential effects of LTRAs and corticosteroids on allergic airway inflammation and allergen-specific cytokine production from lymphoid tissues using a murine model of asthma.
Four groups of female BALB/c mice [control (Cont); Dermatophagoides farinae allergen-sensitized (AS); pranlukast (Prl), an LTRA-treated AS; and dexamethasone (Dex)-treated AS] were examined. Lung pathology and cytokine production by prepared mononuclear cells isolated from mediastinal lymph nodes (MLNs) and spleen were compared among these groups.
AS mice exhibited allergic airway inflammation and significant increases in allergen-specific Th1 and Th2 cytokines in MLNs and spleen. Prl-treated mice showed significant attenuation of allergic airway inflammation concomitant with reduction of Th2 cytokines and IFN-γ in MLNs but not in spleen. In contrast, Dex significantly decreased Th1 and Th2 cytokines in MLNs and also decreased them (except IL-13 and IL-2) in spleen.
The inflammatory effects of cys-LTs could differ in lymphoid organs. LTRAs potentially regulate allergic airway inflammation in an organ- and cytokine-specific manner, while systemic corticosteroid shows nonspecific effects.
Leukotriene Antagonists; Lymphoid Tissue; Pranlukast; Asthma
Mice deficient in the cytokines tumor necrosis factor (TNF) or lymphotoxin (LT) α/β lack polarized B cell follicles in the spleen. Deficiency in CXC chemokine receptor 5 (CXCR5), a receptor for B lymphocyte chemoattractant (BLC), also causes loss of splenic follicles. Here we report that BLC expression by follicular stromal cells is defective in TNF-, TNF receptor 1 (TNFR1)-, LTα- and LTβ-deficient mice. Treatment of adult mice with antagonists of LTα1β2 also leads to decreased BLC expression. These findings indicate that LTα1β2 and TNF have a role upstream of BLC/CXCR5 in the process of follicle formation. In addition to disrupted follicles, LT-deficient animals have disorganized T zones. Expression of the T cell attractant, secondary lymphoid tissue chemokine (SLC), by T zone stromal cells is found to be markedly depressed in LTα-, and LTβ-deficient mice. Expression of the SLC-related chemokine, Epstein Barr virus–induced molecule 1 ligand chemokine (ELC), is also reduced. Exploring the basis for the reduced SLC expression led to identification of further disruptions in T zone stromal cells. Together these findings indicate that LTα1β2 and TNF are required for the development and function of B and T zone stromal cells that make chemokines necessary for lymphocyte compartmentalization in the spleen.
lymphoid tissue; follicle; lymphocyte; follicular dendritic cell; dendritic cell
Severe, glucocorticoid-resistant asthma comprises 5-7% of patients with asthma. IL-17 is a biomarker of severe asthma, and the adoptive transfer of Th17 cells in mice is sufficient to induce glucocorticoid-resistant allergic airway disease. Nitrogen dioxide (NO2) is an environmental toxin that correlates with asthma severity, exacerbation, and risk of adverse outcomes. Mice that are allergically sensitized to the antigen ovalbumin by exposure to NO2 exhibit a mixed Th2/Th17 adaptive immune response and eosinophil and neutrophil recruitment to the airway following antigen challenge, a phenotype reminiscent of severe clinical asthma. Because IL-1 receptor (IL-1R) signaling is critical in the generation of the Th17 response in vivo, we hypothesized that the IL-1R/Th17 axis contributes to pulmonary inflammation and airway hyperresponsiveness (AHR) in NO2-promoted allergic airway disease and manifests in glucocorticoid-resistant cytokine production. IL-17A neutralization at the time of antigen challenge or genetic deficiency in IL-1R resulted in decreased neutrophil recruitment to the airway following antigen challenge but did not protect against the development of AHR. Instead, IL-1R-/- mice developed exacerbated AHR compared to WT mice. Lung cells from NO2-allergically inflamed mice that were treated in vitro with dexamethasone (Dex) during antigen restimulation exhibited reduced Th17 cytokine production, whereas Th17 cytokine production by lung cells from recipient mice of in vitro Th17-polarized OTII T-cells was resistant to Dex. These results demonstrate that the IL-1R/Th17 axis does not contribute to AHR development in NO2-promoted allergic airway disease, that Th17 adoptive transfer does not necessarily reflect an endogenously-generated Th17 response, and that functions of Th17 responses are contingent on the experimental conditions in which they are generated.
The lymphotoxin system (LT) regulates interactions between lymphocytes and stromal cells to maintain lymphoid microenvironmental homeostasis. Soluble LT beta-receptor-Ig (LTβRIg) blocks lymphocyte LTα1β2-stromal cell LTβR signaling. In a model of costimulatory blockade induced tolerance, LTβRIg caused accelerated inflammation and fibrosis in cardiac allografts, and this effect was specific for LTα1β2-LTβR interactions. LTβRIg treatment decreased PD-L1 expression by blood endothelial cells, and decreased VCAM-1 while increasing CXCL1, CXCL2, CXCL12, CCL5, CCL21, and IL-6 expression in fibroblastic reticular cells. In secondary lymphoid organs these effects caused T and B cell zone disruption, loss of CD35+ follicular dendritic cells, and abnormal recruitment of CD11b+Ly6G+ neutrophils. These disruptions correlated with increased numbers of CD8+ T cells and CD11b+Ly6G+ neutrophils, and decreased numbers of CD4+ T cells and Foxp3+ regulatory T cells in the grafts. Depleting neutrophils or blocking neutrophil-attracting chemokines restored normal histology in lymph node, spleen and grafts. Taken together, LTβRIg treatment altered stromal subset, particularly fibroblastic reticular cell, production of cytokines and chemokines, resulting in changes in neutrophil recruitment in spleen, lymph node, and grafts, and inflammation and fibrosis associated with decreased Foxp3+ regulatory T cells and increased CD8+ T cell infiltration of grafts.
lymphotoxin beta receptor; lymph node stromal cells; and neutrophils
Offspring of asthmatic mothers have increased risk of developing asthma, based on human epidemiologic data and experimental animal models. The objective of this study was to determine whether maternal allergy at non-pulmonary sites can increase asthma risk in offspring.
BALB/c female mice received 2 topical applications of vehicle, dinitrochlorobenzene, or toluene diisocyanate before mating with untreated males. Dinitrochlorobenzene is a skin-sensitizer only and known to induce a Th1 response, while toluene diisocyanate is both a skin and respiratory sensitizer that causes a Th2 response. Both cause allergic contact dermatitis. Offspring underwent an intentionally suboptimal protocol of allergen sensitization and aerosol challenge, followed by evaluation of airway hyperresponsiveness, allergic airway inflammation, and cytokine production. Mothers were tested for allergic airway disease, evidence of dermatitis, cellularity of the draining lymph nodes, and systemic cytokine levels. The role of interleukin-4 was also explored using interleukin-4 deficient mice.
Offspring of toluene diisocyanate but not dinitrochlorobenzene-treated mothers developed an asthmatic phenotype following allergen sensitization and challenge, seen as increased Penh values, airway inflammation, bronchoalveolar lavage total cell counts and eosinophilia, and Th2 cytokine imbalance in the lung. Toluene diisocyanate treated interleukin-4 deficient mothers were able to transfer asthma risk to offspring. Mothers in both experimental groups developed allergic contact dermatitis, but not allergic airway disease.
Maternal non-respiratory allergy (Th2-skewed dermatitis caused by toluene diisocyanate) can result in the maternal transmission of asthma risk in mice.
Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a multienzyme complex, is the major source for production of reactive oxygen species (ROS). ROS are increased in allergic diseases, such as asthma, but the role of ROS in disease pathogenesis remains uncertain. We hypothesized that mice unable to generate ROS via the NADPH oxidase pathway would have decreased allergic airway inflammation. To test this hypothesis, we studied gp91phox−/− mice in a model of allergic airway inflammation after sensitization and challenge with ovalbumin. Serum, bronchoalveolar lavage fluid, and lungs were then examined for evidence of allergic inflammation. We found that mice lacking a functional NADPH oxidase complex had significantly decreased ROS production and allergic airway inflammation, compared with wild-type (WT) control animals. To determine the mechanism by which allergic inflammation was inhibited by gp91phox deficiency, we cultured bone marrow–derived dendritic cells from WT and gp91phox−/− mice and activated them with LPS. IL-12 expression was significantly increased in the gp91phox−/− bone marrow–derived dendritic cells, suggesting that the cytokine profile produced in the absence of gp91phox enhanced the conditions leading to T helper (Th) type 1 differentiation, while inhibiting Th2 polarization. Splenocytes from sensitized gp91phox−/− animals produced significantly less IL-13 in response to ovalbumin challenge in vitro compared with splenocytes from sensitized WT mice, suggesting that NADPH oxidase promotes allergic sensitization. In contrast, inflammatory cytokines produced by T cells cultured from WT and gp91phox−/− mice under Th0, Th1, Th2, and Th17 conditions were not significantly different. This study demonstrates the importance of NADPH oxidase activity and ROS production in a murine model of asthma.
asthma; allergic airway inflammation; gp91phox; reactive oxygen species; NADPH oxidase
Although several cytokines, including tumor necrosis factor (TNF), can promote the growth of dendritic cells (DCs) in vitro, the cytokines that naturally regulate DC development and function in vivo have not been well defined. Here, we report that membrane lymphotoxin (LT), instead of TNF, regulates the migration of DCs in the spleen. LTα−/− mice, lacking membrane LTα/β and LTα3, show markedly reduced numbers of DCs in the spleen. Unlike wild-type mice and TNF−/− mice that have densely clustered DCs in the T cell zone and around the marginal zone, splenic DCs in LTα−/− mice are randomly distributed. The reduced number of DCs in lymphoid tissues of LTα−/− mice is associated with an increased number of DCs in nonlymphoid tissues. The number of splenic DCs in LTα−/− mice is restored when additional LT-expressing cells are provided. Blocking membrane LTα/β in wild-type mice markedly diminishes the accumulation of DCs in lymphoid tissues. These data suggest that membrane LT is an essential ligand for the presence of DCs in the spleen. Mice deficient in TNF receptor, which is the receptor for both soluble LTα3 and TNF-α3 trimers, have normal numbers of DCs. However, LTβR−/− mice show reduced numbers of DCs, similar to the mice lacking membrane LT α/β. Taken together, these results support the notion that the signaling via LTβR by membrane LTα/β is required for the presence of DCs in lymphoid tissues.
membrane lymphotoxin; tumor necrosis factor; dendritic cells; lymphotoxin receptor; migration
Efficient immune defenses are facilitated by the organized microarchitecture of lymphoid organs, and this organization is regulated by the compartmentalized expression of lymphoid tissue chemokines. Mouse cytomegalovirus (MCMV) infection induces significant remodeling of splenic microarchitecture, including loss of marginal zone macrophage populations and dissolution of T and B cell compartmentalization. MCMV preferentially infected the splenic stroma, targeting endothelial cells (EC) as revealed using MCMV-expressing green fluorescent protein. MCMV infection caused a specific, but transient transcriptional suppression of secondary lymphoid chemokine (CCL21). The loss of CCL21 was associated with the failure of T lymphocytes to locate within the T cell zone, although trafficking to the spleen was unaltered. Expression of CCL21 in lymphotoxin (LT)-α–deficient mice is dramatically reduced, however MCMV infection further reduced CCL21 levels, suggesting that viral modulation of CCL21 was independent of LTα signaling. Activation of LTβ-receptor signaling with an agonistic antibody partially restored CCL21 mRNA expression and redirected transferred T cells to the splenic T cell zone in MCMV-infected mice. These results indicate that virus-induced alterations in lymphoid tissues can occur through an LT-independent modulation of chemokine transcription, and targeting of the LT cytokine system can counteract lymphoid tissue remodeling by MCMV.
The architecture of the spleen and lymph nodes is organized into discrete compartments that promote the immune system's ability to capture pathogens and mount protective defenses. The white blood cells that fill these compartments are positioned in discrete regions by chemoattractants produced by the cells that form the architecture of the spleen (stroma). The white blood cells must be positioned to interact with each other to mount effective host defense. Benedict and colleagues demonstrate that cytomegalovirus, a β herpesvirus, can remodel the architecture of the spleen by specifically inhibiting a key chemoattractant produced by the stromal cells, the chemokine CCL21. This action by the virus impedes efficient contact between cells by altering the movement of T lymphocytes to their correct position within the spleen. However, as a counter strategy, activating the lymphotoxin-β receptor pathway, a cytokine known to control the embryonic development of lymphoid organs, partially restored CCL21 and the ability of T lymphocytes to find their correct position. Thus, infection with this herpesvirus selectively remodels the structure of lymphoid tissues perhaps aiding in the formation of a portal though host defenses.