Levels of the anaphylatoxin C3a are increased in patients with asthma compared with those in nonasthmatics and increase further still during asthma exacerbations. However, the role of C3a during sensitization to allergen is poorly understood. Sensitization to fungal allergens, such as Aspergillus fumigatus, is a strong risk factor for the development of asthma. Exposure to chitin, a structural polysaccharide of the fungal cell wall, induces innate allergic inflammation and may promote sensitization to fungal allergens. Here, we found that coincubation of chitin with serum or intratracheal administration of chitin in mice resulted in the generation of C3a. We established a model of chitin-dependent sensitization to soluble Aspergillus antigens to test the contribution of complement to these events. C3−/− and C3aR−/− mice were protected from chitin-dependent sensitization to Aspergillus and had reduced lung eosinophilia and type 2 cytokines and serum IgE. In contrast, complement-deficient mice were not protected against chitin-induced innate allergic inflammation. In sensitized mice, plasmacytoid dendritic cells from complement-deficient animals acquired a tolerogenic profile associated with enhanced regulatory T cell responses and suppressed Th2 and Th17 responses specific for Aspergillus. Thus, chitin induces the generation of C3a in the lung, and chitin-dependent allergic sensitization to Aspergillus requires C3aR signaling, which suppresses regulatory dendritic cells and T cells and induces allergy-promoting T cells.
Asthma is one of the fastest growing chronic illnesses worldwide. Chitin, a ubiquitous polymer in our environment and a key component in the cell wall of fungal spores and the exoskeletons of insects, parasites, and crustaceans, triggers innate allergic inflammation. However, there is little understanding of how chitin is initially recognized by mammals and how early recognition of chitin affects sensitization to environmental allergens and development of allergic asthma. The complement system is evolutionarily one of the oldest facets of the early or innate warning systems in mammals. We studied whether and how complement components influence the recognition of chitin and shape the downstream sensitization toward fungal allergens. We show here that complement recognition of chitin plays a critical role in shaping the behavior of dendritic cells, which in turn regulate the function of T cells that mediate allergic responses to fungi.
Activation of complement is one of the earliest immune responses to exogenous threats, resulting in various cleavage products including anaphylatoxin C3a. In addition to its contribution to host defense, C3a has been shown to mediate Th2 responses in animal models of asthma. However, the role of C3a on pulmonary Th17 responses during allergic inflammation remains unclear. Here, we show that mice deficient in C3a receptor (C3aR) exhibited (i) higher percentages of endogenous IL-17-producing CD4+ T cells in the lungs, (ii) higher amounts of IL-17 in the bronchoalveolar lavage fluid, and (iii) more neutrophils in the lungs than wild-type mice when challenged with intranasal allergens. Moreover, adoptive transfer experiments showed that the frequencies of antigen-specific IL-17-producing CD4+ T cells were significantly higher in the lungs and bronchial lymph nodes of C3aR-deficient recipients than those of wild-types recipients. Bone-marrow reconstitution study indicated that C3aR-deficiency on hematopoietic cells was required for the increased Th17 responses. Furthermore, C3aR-deficient mice exhibited increased percentages of Foxp3+ regulatory T cells; however, depletion of these cells minimally affected the induction of antigen-specific Th17 cell population in the lungs. Neutralization of IL-17 significantly reduced the number of neutrophils in bronchoalveolar lavage fluid of C3aR-deficient mice. Our findings demonstrate that C3a signals negatively regulate antigen-specific Th17 responses during allergic lung inflammation and the size of Foxp3+ regulatory T cell population in the periphery.
Allergic asthma is a chronic inflammatory disease of the upper airway. It is well appreciated that maladaptive Th2 immunity promotes the allergic phenotype, the underlying mechanisms of which remain elusive. The disease is associated with activation of complement, an ancient danger-sensing component of the innate immune system. Different models of experimental allergic asthma suggest that the small complement fragments of C3 and C5, the anaphylatoxins C3a and C5a, not only promote proallergic effector functions during the allergic effector phase but regulate the development of Th2 immunity during allergen sensitization. The available data support a concept in which C5a is dominant during allergen sensitization and protects against the development of maladaptive Th2 immunity. By contrast, C3a and C5a appear to act synergistically and drive allergic inflammation during the effector phase. In this article, we will review the recent findings in the field to judge the benefit of complement targeting in allergic asthma.
allergic asthma; anaphylatoxin; complement; dendritic cell; innate immunity; Th2 cytokine
Rationale: The factors that control the secretion of epithelial mucins are essential to understanding obstructive airway diseases such as asthma. Although the complement anaphylatoxin C3a and its receptor have been shown to promote many features of allergic lung inflammation, the contribution to mucin expression has not been elucidated.
Objectives: To determine if the C3a receptor with its ligand regulates airway epithelial mucin production.
Methods: Mice deficient in the C3a receptor were examined in a model of allergic airway disease for the presence of goblet cells and the gel-forming secreted mucin Muc5ac.
Measurements and Main Results: Lungs from antigen-challenged C3a receptor–deficient mice revealed a dramatic decrease in goblet cells and Muc5ac compared with challenged wild-type control animals. These differences were dependent on C3a binding to its receptor since intranasal challenge with C3a induced the formation of goblet cells only in wild-type but not C3a receptor–deficient mice. Increased numbers of goblet cells were also found in C3a-stimulated RAG-1–deficient mice demonstrating a mechanism independent of T lymphocytes and Th2 cytokines, mediators which have been shown to regulate mucin expression. A direct physiological role for C3a in these models was further demonstrated in cultures of airway epithelial Clara cells, which not only express the C3a receptor but also produce Muc5ac in response to C3a.
Conclusions: These studies identify a novel C3a receptor–dependent mechanism in the development of airway epithelial goblet cells and regulation of Muc5ac production and implicate C3a as a mediator of airway obstruction in asthma.
T cells; allergy; lung; inflammation
The complement system forms the central core of innate immunity but also mediates a variety of inflammatory responses. Anaphylatoxin C3a, which is generated as a byproduct of complement activation, has long been known to activate mast cells, basophils and eosinophils and to cause smooth muscle contraction. However, the role of C3a in the pathogenesis of allergic asthma remains unclear. In this review, we examine the role of C3a in promoting asthma. Following allergen challenge, C3a is generated in the lung of subjects with asthma but not healthy subjects. Furthermore, deficiency in C3a generation or in G protein coupled receptor for C3a abrogates allergen-induced responses in murine models of pulmonary inflammation and airway hyperresponsiveness. In addition, inhibition of complement activation or administration of small molecule inhibitors of C3a receptor after sensitization but before allergen challenge inhibits airway responses. At a cellular level, C3a stimulates robust mast cell degranulation that is greatly enhanced following cell-cell contact with airway smooth muscle (ASM) cells. Therefore, C3a likely plays an important role in asthma primarily by regulating mast cell-ASM cell interaction.
In six patients with extrinsic bronchial asthma the inhalation of prostaglandin (PG) F2 alpha in a small dosage produced significant bronchoconstriction, whereas PGE2 produced bronchodilatation. In these patients cholinergic blockade with atropine partially inhibited the PGF2 alpha-induced bronchoconstriction, but the alpha-receptor-blocking drug thymoxamine and sodium cromoglycate did not. These results suggest that the effect of PGF2 alpha is mediated through cholinergic receptors in the airways, and this effect is grossly exaggerated in asthma. The failure to inhibit PGF2 alpha-induced bronchoconstriction with sodium cromoglycate and the observation of an inhibitory effect of sodium cromoglycate in both allergic and exercise asthma suggest that locally formed PGF2 alpha may not be the main factor in the pathogenesis of bronchial asthma.
Complement component 5 (C5) has been described as either promoting or protecting against airway hyperresponsiveness (AHR) in experimental allergic asthma, suggesting pleomorphic effects of C5. Here we report that local pharmacological targeting of the C5a receptor (C5aR) prior to initial allergen sensitization in murine models of inhalation tolerance or allergic asthma resulted in either induction or marked enhancement of Th2-polarized immune responses, airway inflammation, and AHR. Importantly, C5aR-deficient mice exhibited a similar, increased allergic phenotype. Pulmonary allergen exposure in C5aR-targeted mice resulted in increased sensitization and accumulation of CD4+CD69+ T cells associated with a marked increase in pulmonary myeloid, but not plasmacytoid, DC numbers. Pulmonary DCs from C5aR-targeted mice produced large amounts of CC chemokine ligand 17 (CCL17) and CCL22 ex vivo, suggesting a negative impact of C5aR signaling on pulmonary homing of Th2 cells. In contrast, C5aR targeting in sensitized mice led to suppressed airway inflammation and AHR but was still associated with enhanced production of Th2 effector cytokines. These data suggest a dual role for C5a in allergic asthma, i.e., protection from the development of maladaptive type 2 immune responses during allergen sensitization at the DC/T cell interface but enhancement of airway inflammation and AHR in an established inflammatory environment.
Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and a cellular infiltrate dominated by eosinophils. Numerous epidemiological studies have related the exacerbation of allergic asthma with an increase in ambient inhalable particulate matter from air pollutants. This is because inhalable particles efficiently deliver airborne allergens deep into the airways, where they can aggravate allergic asthma symptoms. However, the cellular mechanisms by which inhalable particulate allergens (pAgs) potentiate asthmatic symptoms remain unknown, in part because most in vivo and in vitro studies exploring the pathogenesis of allergic asthma use soluble allergens (sAgs). Using a mouse model of allergic asthma, we found that, compared with their sAg counterparts, pAgs triggered markedly heightened airway hyperresponsiveness and pulmonary eosinophilia in allergen-sensitized mice. Mast cells (MCs) were implicated in this divergent response, as the differences in airway inflammatory responses provoked by the physical nature of the allergens were attenuated in MC-deficient mice. The pAgs were found to mediate MC-dependent responses by enhancing retention of pAg/IgE/FcεRI complexes within lipid raft–enriched, CD63+ endocytic compartments, which prolonged IgE/FcεRI-initiated signaling and resulted in heightened cytokine responses. These results reveal how the physical attributes of allergens can co-opt MC endocytic circuitry and signaling responses to aggravate pathological responses of allergic asthma in mice.
Allergic diseases such as asthma result from inappropriate immunologic responses to common environmental allergens in genetically susceptible individuals. Following allergen exposure, interaction of dendritic cells (DC) with CD4+ T cells leads to the production of Th2 cytokines, which induce B cells to synthesize IgE molecules (sensitization phase). These IgE molecules bind to their high affinity receptors (FcεRI) on the surface of mast cells and basophils and their subsequent cross-linking by allergen results in the release of preformed and newly synthesized mediators, which cause bronchoconstriction, lung inflammation and airway hyperresponsiveness (AHR) in asthma (effector phase). The complement components C3a and C5a levels are increased in the lungs of patients with asthma and are likely generated via the actions of both allergen and mast cell proteases. In vivo studies with rodents have shown that while C3a facilitates allergen sensitization in some models C5a inhibits this response. Despite this difference, both anaphylatoxins promote lung inflammation and AHR in vivo indicating that cells other than DC and T cells likely mediate the functional effects of C3a and C5a in asthma. This review focuses on the contribution of C3a and C5a in the pathogenesis of asthma with a particular emphasis on mast cells and basophils. It discusses the mechanisms by which anaphylatoxins activate mast cells and basophils and the associated signaling pathways via which their receptors are regulated by priming and desensitization.
Complement; Anaphylatoxin; C3a; C5a; Mast cell; Basophil; G protein; Priming; Desensitization; Signal Transduction; Asthma
The cysteinyl leukotrienes, LTC4, LTD4, and LTE4, play an integral role in the pathophysiology of asthma. Acting via the type 1 leukotriene (CysLT1) receptor, these proinflammatory mediators have numerous effects in the lungs, including decreased activity of respiratory cilia, increased mucus secretion, increased venopermeability, and promotion of eosinophil migration into airway mucosa. Blocking studies show that Cys-LTs are pivotal mediators in the pathophysiology of asthma. Cys-LTs are key components in the early and late allergic airway response and also contribute to bronchial obstruction after exercise and hyperventilation of cold, dry air in asthmatics. Effects of the cysteinyl leukotrienes are blocked by leukotriene receptor antagonists; these agents inhibit bronchoconstriction in normal subjects provoked with inhaled cysteinyl leukotrienes, as well as in patients with asthma undergoing allergen, exercise, cold air, or aspirin challenge. Montelukast is a potent and selective blocker of the CysLT1 receptor. For treatment of chronic asthma, montelukast is administered once daily to adults as a 10-mg film-coated tablet, to children aged 6–14 years as a 5-mg chewable tablet, and to children aged 2–5 years as a 4-mg chewable tablet form. Given their efficacy, antiinflammatory activity, oral administration, and safety, leukotriene modifiers will play an important role in the treatment of asthmatic children.
montelukast; asthma; children; efficacy
Rationale: Reports from our laboratory, as well as those from others, have documented the importance of complement activation, the C3a anaphylatoxin, and its receptor, C3aR, in promoting Th2 effector functions in a mouse model of bronchopulmonary allergy. Although deficiency in the fifth complement component (C5) has been linked to enhanced airway hyperresponsiveness in mice, the contribution of C5 to other major biological hallmarks of asthma has not been evaluated.
Objective: Accordingly, congenic C5-sufficient and C5-deficient mice were subjected to a mouse model of bronchopulmonary allergy to assess the impact of C5 on pulmonary inflammation and Th2 effector functions in experimental asthma.
Methods and Main Results: In contrast to observations reported for C3- and C3aR-deficient animals, C5-deficient mice exhibited significantly increased airway hyperresponsiveness relative to wild-type congenic control mice after antigen challenge. Moreover, challenged C5-deficient mice had a 3.4-fold and 2.7-fold increase in the levels of airway eosinophils and lung interleukin (IL)-4–producing cells, respectively, compared with challenged wild-type mice. Consistent with the numbers of IL-4–producing cells, C5-deficient mice also had increased bronchoalveolar lavage levels of the Th2 cytokines IL-5 and IL-13 and elevated serum levels of total and antigen-specific IgE.
Conclusions: These data indicate that C5 plays an important protective role in allergic lung disease by suppressing inflammatory responses and Th2 effector functions observed in this experimental model. The protection provided by the presence of C5 is likely mediated by C5a, suggesting that C5a may play a significant role in tempering inflammation in Th2-driven diseases such as asthma.
allergy; complement; lung; Th1/Th2 cells; T lymphocytes
We identify the tumor necrosis factor receptor superfamily 25 (TNFRSF25)/TNFSF15 pair as critical trigger for allergic lung inflammation, which is a cardinal feature of asthma. TNFRSF25 (TNFR25) signals are required to exert T helper cell 2 (Th2) effector function in Th2-polarized CD4 cells and co-stimulate interleukin (IL)-13 production by glycosphingolipid-activated NKT cells. In vivo, antibody blockade of TNFSF15 (TL1A), which is the ligand for TNFR25, inhibits lung inflammation and production of Th2 cytokines such as IL-13, even when administered days after airway antigen exposure. Similarly, blockade of TNFR25 by a dominant-negative (DN) transgene, DN TNFR25, confers resistance to lung inflammation in mice. Allergic lung inflammation–resistant, NKT-deficient mice become susceptible upon adoptive transfer of wild-type NKT cells, but not after transfer of DN TNFR25 transgenic NKT cells. The TNFR25/TL1A pair appears to provide an early signal for Th2 cytokine production in the lung, and therefore may be a drug target in attempts to attenuate lung inflammation in asthmatics.
Inhaled short acting β2-agonists (SABA), e.g. albuterol, are used for quick reversal of bronchoconstriction in asthmatics. While SABA are not recommended for maintenance therapy, it is not uncommon to find patients who frequently use SABA over a long period of time and there is a suspicion that long term exposure to SABA could be detrimental to lung function. To test this hypothesis we studied the effect of long-term inhaled albuterol stereoisomers on immediate allergic response (IAR) and airway hyperresponsiveness (AHR) in mouse models of asthma.
Balb/C mice were sensitized and challenged with ovalbumin (OVA) and then we studied the IAR to inhaled allergen and the AHR to inhaled methacholine. The mice were pretreated with nebulizations of either racemic (RS)-albuterol or the single isomers (S)- and (R)-albuterol twice daily over 7 days prior to harvest.
We found that all forms of albuterol produced a significant increase of IAR measured as respiratory elastance. Similarly, we found that AHR was elevated by albuterol. At the same time a mouse strain that is intrinsically hyperresponsive (A/J mouse) was not affected by the albuterol isomers nor was AHR induced by epithelial disruption with Poly-L-lysine affected by albuterol.
We conclude that long term inhalation treatment with either isomer of albuterol is capable of precipitating IAR and AHR in allergically inflamed airways but not in intrinsically hyperresponsive mice or immunologically naïve mice. Because (S)-albuterol, which lacks affinity for the β2-receptor, did not differ from (R)-albuterol, we speculate that isomer-independent properties of the albuterol molecule, other than β2-agonism, are responsible for the effect on AHR.
Allergic asthma is a complex disease characterized by eosinophilic pulmonary inflammation, mucus production and reversible airway obstruction1. Exposure to indoor allergens is a clear risk factor for asthma, but this disease is also associated with high household levels of total and Gram-negative bacteria2. The ability of bacterial products to act as adjuvants3 suggests they might promote asthma by priming allergic sensitization to inhaled allergens. In support of this idea, house dust extracts (HDEs) can activate antigen presenting dendritic cells (DC) in vitro and promote allergic sensitization to inhaled innocuous proteinsin vivo4. It is unknown which microbial products provide most of the adjuvant activity in HDEs. A screen of microbial products for their adjuvant activity in the airway revealed that the bacterial protein, flagellin (FLA) stimulated strong allergic responses to an innocuous inhaled protein. Moreover, toll-like receptor (TLR)5, the mammalian receptor for FLA5,6, was required for priming strong allergic responses to natural indoor allergens present in HDEs. In addition, the incidence of human asthma was associated with high serum levels of FLA-specific antibodies. Together, these findings suggest that household FLA promotes the development of allergic asthma by TLR5-dependent priming of allergic responses to indoor allergens.
Phagocytosis is a key process in protection of the host against pathogens and in provision of antigens for the immune response. Synergism between C3b and IgG and their receptors in promoting adherence to and then ingestion of an antigen has been recognized for decades. Only more recently, however, has cross-talk between another complement activation fragment, the anaphylatoxin C5a, and Fcγ receptors (FcγRs) been defined. In this issue of the JCI, C5a is shown to signal, via its receptor, the upregulation of activating (proinflammatory-type) FcγRs. Moreover, engagement of FcγRs by the IgG-bearing immune complex instructs the cell to synthesize more C5, from which C5a is derived. Thus, this work establishes a feedback loop whereby FcγR expression and function are enhanced, a very desirable event in concert with an infection but potentially deleterious in autoimmunity.
Immunized mice after inhalation of specific antigen have the following characteristic features of human asthma: airway eosinophilia, mucus and Th2 cytokine release, and hyperresponsiveness to methacholine. A model of late-phase allergic pulmonary inflammation in ovalbumin-sensitized mice was used to address the role of the alpha4 integrin (CD49d) in mediating the airway inflammation and hyperresponsiveness. Local, intrapulmonary blockade of CD49d by intranasal administration of CD49d mAb inhibited all signs of lung inflammation, IL-4 and IL-5 release, and hyperresponsiveness to methacholine. In contrast, CD49d blockade on circulating leukocytes by intraperitoneal CD49d mAb treatment only prevented the airway eosinophilia. In this asthma model, a CD49d-positive intrapulmonary leukocyte distinct from the eosinophil is the key effector cell of allergen-induced pulmonary inflammation and hyperresponsiveness.
Viral illnesses are important factors in both asthma inception and exacerbations, and allergic sensitization in early life further enhances asthma risk through unclear mechanisms. Cellular damage due to infection or allergen inhalation increases ATP in the airways with subsequent purinergic receptor activation. The purinergic receptor P2X7 may enhance airway leukocyte recruitment to the airways and P2X7 knockout mice display a reduced asthma-like phenotype.
Based upon the P2X7 knockout mouse, we hypothesized that children with low functioning P2X7 would have decreased rates of asthma.
We utilized a functional assay to determine P2X7 pore-producing capacity in whole blood samples in a birth cohort study at high risk for asthma development. The P2X7 assay was validated with known loss-of-function alleles in humans. P2X7 pore status categorization was used to assess asthma and allergy status in the cohort.
Attenuated P2X7 function was associated with lower asthma rates at ages 6 and 8 and the greatest effects were observed in boys. Children with asthma at age 11 who had low P2X7 capacity had less severe disease in the previous year. Attenuated P2X7 function was also associated with sensitization to fewer aeroallergens.
P2X7 functional capacity is associated with asthma risk or disease severity and these relationships appear to be age-related.
asthma; allergy; children; P2X7; ATP
Atopic dermatitis (AD) is characterized by local and systemic Th2 responses to cutaneously introduced allergens and is a risk factor for asthma. Blockade of Th2 cytokines has been suggested as therapy for AD.
To examine the effect of the absence of IL-4 and IL-13 on the Th-17 response to epicutaneous (EC) sensitization in a mouse model of allergic skin inflammation with features of AD.
Wild-type (WT), IL-4KO, IL-13KO and IL-4/13 double KO (DKO) mice were subjected to EC sensitization with ovalbumin (OVA) or saline and airway challenged with OVA. Systemic immune responses to OVA, skin and airway inflammation, and airway hyperresponsiveness (AHR) were examined.
OVA sensitized DKO mice exhibited impaired Th2 driven responses with undetectable OVA specific IgE and severely diminished eosinophil infiltration at sensitized skin sites, but intact dermal infiltration with CD4+ cells. DKO mice mounted an exaggerated IL-17A, but normal IFN-γ and IL-5 systemic responses. Airway challenge of these mice with OVA caused marked upregulation of IL-17 mRNA expression in the lungs, increased neutrophilia in bronchoalveolar lavage fluid (BALF), airway inflammation characterized by mononuclear cell infiltration with no detectable eosinophils, and bronchial hyperresponsiveness to methacholine that were reversed by IL-17 blockade. IL-4, but not IL-13, was identified as the major Th2 cytokine that downregulates the IL-17 response in EC sensitized mice.
EC sensitization in the absence of IL-4/IL-13 induces an exaggerated Th17 response systemically, and in lungs following antigen challenge that results in airway inflammation and AHR.
Blockade of IL-4 may promote IL-17-mediated airway inflammation in AD.
IL-17; Th2 cytokines; atopic dermatitis; asthma
Mechanical injury to the skin results in activation of the complement component C3 and release of the anaphylatoxin C3a. C3a binds to a seven-transmembrane G protein–coupled receptor, C3aR. We used C3aR–/– mice to examine the role of C3a in a mouse model of allergic inflammation induced by epicutaneous sensitization with OVA. C3aR–/– mice exhibited an exaggerated Th2 response to epicutaneous but not to intraperitoneal sensitization with OVA, as evidenced by significantly elevated levels of serum OVA-specific IgG1 and significantly increased secretion of the Th2 cytokines IL-4, IL-5, and IL-10 by antigen-stimulated splenocytes. Presentation of OVA peptide by C3aR–/– APCs caused significantly more IL-4 and IL-5 secretion by T cells from OVA–T cell receptor (OVA-TCR) transgenic mice compared with presentation by WT APCs. C3a inhibited the ability of splenocytes, but not of highly purified T cells, to secrete Th2 cytokines in response to TCR ligation. This inhibition was mediated by IL-12 secreted by APCs in response to C3a. These results suggest that C3a-C3aR interactions inhibit the ability of APCs to drive Th2 cell differentiation in response to epicutaneously introduced antigen and may have important implications for allergic skin diseases.
Asthma is a chronic inflammatory disease of the airways characterized by variable airway obstruction and airway hyperresponsiveness (AHR). The T regulatory (Treg) cell subset is critically important for the regulation of immune responses. Adoptive transfer of Treg cells has been shown to be sufficient for the suppression of airway inflammation in experimental allergic asthma. Intervention strategies aimed at expanding the Treg cell population locally in the airways of sensitized individuals are therefore of high interest as a potential therapeutic treatment for allergic airway disease. Here, we aim to test whether long-term suppression of asthma manifestations can be achieved by locally expanding the Treg cell subset via intranasal administration of a TLR-2 agonist. To model therapeutic intervention aimed at expanding the endogenous Treg population in a sensitized host, we challenged OVA-sensitized mice by OVA inhalation with concomitant intranasal instillation of the TLR-2 agonist Pam3Cys, followed by an additional series of OVA challenges. Pam3Cys treatment induced an acute but transient aggravation of asthma manifestations, followed by a reduction or loss of AHR to methacholine, depending on the time between Pam3Cys treatment and OVA challenges. In addition, Pam3Cys-treatment induced significant reductions of eosinophils and increased numbers of Treg cells in the lung infiltrates. Our data show that, despite having adverse acute effects, TLR2 agonist treatment as a therapeutic intervention induces an expansion of the Treg cell population in the lungs and results in long-term protection against manifestation of allergic asthma upon subsequent allergen provocation. Our data indicate that local expansion of Tregs in allergic airway disease is an interesting therapeutic approach that warrants further investigation.
Severe asthma is associated with interleukin 17A (IL-17A) production. The exact role of IL-17A in severe asthma and the factors driving its production are unknown. Here we have demonstrated that IL-17A mediated severe airway hyperresponsiveness (AHR) in susceptible strains of mice by enhancing IL-13-driven responses. Mechanistically, we have demonstrated that IL-17A and AHR were regulated by allergen-driven production of anaphylatoxins, as complement factor 5 (C5) and C5aR-deficient strains mounted robust IL-17A responses, while C3aR-deficient mice had reduced TH17 cells and AHR following allergen challenge. The opposing effects of C3a and C5a were mediated through their reciprocal regulation of IL-23 production. These data demonstrate a critical role for complement-mediated regulation of the IL-23–TH17 axis in severe asthma.
airway hyperresponsiveness; asthma; IL-17A; anaphylatoxins; IL-23
The role of complement in the development of maladaptive immunity in experimental allergic asthma is unclear. In this study, we show that C3a receptor (C3aR)-deficient mice are protected from the development of Th2 immunity in a model of house dust mite-induced asthma. C5a receptor (C5aR)-targeting of C3aR-deficient mice during allergen sensitization not only reversed the protective effect but enhanced Th2 cytokine production, airway inflammation, and airway responsiveness, suggesting that the reduced allergic phenotype in C3aR-deficient mice results from protective C5aR signaling. In support of this view, C5aR expression in C3aR-deficient pulmonary dendritic cells (DCs) was increased when compared with wild-type DCs. Moreover, C5aR targeting regulated the frequency of pulmonary plasmacytoid DCs expressing costimulatory molecules B7-H1 and B7-DC. Ex vivo targeting of B7-H1 and B7-DC increased Th2 cytokine production from T cells of wild-type but not of C5aR-targeted mice, suggesting a protective role for C5a through regulation of B7 molecule expression on plasmacytoid DCs.
C3a and C5a anaphylatoxins are proinflammatory polypeptides released during complement activation. They exert their biological activities through interaction with two G protein-coupled receptors named C3aR and C5aR, respectively. In the brain, these receptors are expressed on glial cells, and some recent data have suggested that anaphylatoxins could mediate neuroprotection. In this study, we used RT-PCR and ribonuclease protection assays (RPA) to investigate the role of anaphylatoxins on neurotrophin expression by the human glioblastoma cell line T98G and by rat astrocytes. Our data show that for both cell types, anaphylatoxins upregulate expression of NGF mRNA. This response depended on a G protein-coupled pathway since pre-treatment of cells with pertussis toxin (PTX) completely blocked NGF mRNA increases. This effect was anaphylatoxin-specific since pre-incubation with anti-C3a or anti-C5aR antibodies abolished the effects of C3a and C5a, respectively. The regulation of NGF mRNA by anaphylatoxins was not accompanied by translation into protein expression, but there was a significant synergic effect of anaphylatoxins/IL-1b costimulation. Our demonstration of involvement of anaphylatoxins in the NGF release process by astrocytes suggests that C3a and C5a could modulate neuronal survival in the CNS.
Asthma, allergic rhinitis (AR), and atopic dermatitis (AD) are the most prevalent allergic diseases and number of studies has shown an increase in prevalence of both all over the world in recent years. Although little about the prevalence of asthma, AR, and AD in Korean adults. And the incident sensitization to common allergens in the setting of sensitization to an occupational allergen has not been described. Our aim was to determine the prevalence of living and working place in adults. And also, determines the sensitization to common allergens in subjects with incident sensitization to a work-related allergen.
We performed questionnaire survey and allergy skin prick test with 27 common inhalant allergens among 294 subjects (response rate, 94.9%, n = 279) age 19 to 54 years in Seoul and forest service workers. One hundred thirty four subjects were forest service workers and 145 subjects were urban office workers.
The mean age was 33.7 ± 7.6 years. There were 141 man and 138 women. A history of asthma was noted in 3.8% and a history of AR was noted in 28.7%. And a history of AD was noted 21.3%. The each group of sensitization to allergen were 40.3% (urban) and 60.0% (forest), (P = 0.002). The most common allergen was mites. The sensitization to birch allergen were more high in urban office workers (P = 0.01).
The prevalence of allergic rhinitis in urban areas was high. And urban officer workers were also high with sensitization rate compare to forest workers. The interesting results were the pollen sensitization rate in urban areas showed higher tendencies. More research will be needed in futures.
Toll-like receptor (TLR) ligands and other allergen nonspecific immunostimulatory molecules are ubiquitous in ambient air and have profound modulatory activities in animal models of allergic asthma. However, several of these molecules have been shown to promote exaggerated Th2 biased airway hypersensitivity responses (AHRs), while others attenuate the asthmatic phenotype. Therefore, it has proven difficult to extrapolate experimental results with purified molecules towards a more general understanding of the allergen nonspecific immunomodulatory influence of living environments on the natural history of allergic asthma. These investigations determined how regular and intermittent airway exposures to an unpurified but sterile house dust extract standard (HDEst) affected the ovalbumin (OVA) specific AHR and immune status of previously Th2 sensitized mice. Low dose daily and high dose intermittent HDEst exposures modulated ongoing airway hypersensitivity responses considerably, reducing eosinophil recruitment and methacholine responsiveness, while increasing neutrophilic inflammation. However, only daily airway delivery of low dose HDEst attenuated OVA specific Th2 cytokine production and Th2 biased AHRs to allergen challenge a month later. Finally, while LPS mimicked many of the immunomodulatory characteristics of HDEst in this murine asthma model, daily airway HDEst delivery was highly effective in attenuating the AHR of OVA/alum sensitized TLR4 deficient mice. Taken together, these investigations provide direct evidence that living environments contain allergen nonspecific immunostimulatory molecules that influence the airway hypersensitivity status of allergen-sensitized mice by TLR4 dependent and independent mechanisms.
Allergy; Lung; T cells; Rodent