Asthma is a common, disabling inflammatory respiratory disease that has increased in frequency and severity in developed nations. We review studies of murine allergic airway disease (MAAD2) and human asthma that evaluate the importance of Th2 cytokines, Th2 response-promoting cytokines, IL-17 and pro- and anti-inflammatory cytokines in MAAD and human asthma. We discuss murine studies that directly stimulate airways with specific cytokines or delete, inactivate, neutralize or block specific cytokines or their receptors, as well as controversial issues, including the roles of IL-5, IL-17 and IL-13Rα2 in MAAD and IL-4Rα expression by specific cell types. Studies of human asthmatic cytokine gene and protein expression, linkage of cytokine polymorphisms to asthma, cytokine responses to allergen stimulation and clinical responses to cytokine antagonists are discussed as well. Results of these analyses establish the importance of specific cytokines in MAAD and human asthma and have therapeutic implications.
The clinical manifestations of food allergy include diarrhea and systemic anaphylaxis (shock), which can occur together or by themselves in different individuals. Although ingested food antigens need to be absorbed to induce shock, it is not known whether they need to be absorbed to induce diarrhea.
Identify mechanisms that determine whether food allergy induces diarrhea versus shock and determine whether diarrhea requires absorption of ingested antigens. Methods: These issues were studied in mice in active, passive and hybrid immunization models. The active model was used to determine the allergic diarrhea susceptibility of J chain- and pIgR-deficient mice, which are unable to secrete IgA. The hybrid model was used to determine whether intravenously administered antigen-specific IgG antibody, which is not secreted into the gut, can protect against allergic diarrhea as well as shock.
Shock, but not diarrhea was induced in naïve mice by intravenous IgE anti-TNP antibody, followed by oral TNP-bovine serum albumin, whereas both were induced in mice presensitized with intraperitoneal ovalbumin/alum plus oral ovalbumin. More TNP-bovine serum albumin was required to induce shock than diarrhea in presensitized mice and intravenous IgG anti-TNP antibody, which is not secreted into the gut, protected these mice against both diarrhea and shock. Consistent with this, OVA-immunized J chain- and pIgR-deficient mice, which have high serum IgA but little intestinal IgA, resisted diarrhea induction.
Intestinal immunity and oral Ag dose determine whether diarrhea and/or systemic anaphylaxis are induced and ingested Ag must be absorbed to induce either response.
IgA; IgE; IgG; J chain; polymeric Ig receptor
The cytokine IL-9 has been implicated in allergic reactions, including food allergy, but its contribution to parenteral versus oral antigen–induced anaphylaxis remains unclear.
We sought to delineate the contribution of the IL-9/IL-9 receptor a-chain (IL-9R) pathway to parenteral and oral antigen–induced anaphylaxis.
Wild-type, IL-9–deficient (Il92/2), and IL-9R–deficient (Il9R2/2) mice were subjected to passive and active parenteral and oral antigen (ovalbumin [OVA])-induced anaphylaxis. Severity of systemic anaphylaxis was gauged by decreased body temperature; intestinal anaphylaxis was assessed based on secretory diarrhea, intestinal mastocytosis, and serum murine mast cell protease 1 level. Specific immunoglobulin isotypes or immunoglobulin receptor–blocking antibodies were administered before challenge to define the role of the IgE and IgG pathways.
Repeated oral antigen challenge of OVA-sensitized wild-type mice induced anaphylaxis with both systemic and intestinal involvement; both were IgE dependent and attenuated in Il92/2 and Il9R2/2 mice. In contrast, parenteral OVA challenge of OVA-sensitized wild-type mice induced systemic anaphylaxis, which was independent of the IL-9/IL-9R pathway. Strikingly, the IL-9/IL-9R pathway had no role in either the IgG or IgE component of parenteral antigen–induced or anti-IgE and anti-FcgRII/III mAb–induced systemic anaphylaxis.
Parenteral antigen–induced murine systemic anaphylaxis is mediated by both IgG- and IgE-dependent pathways, and both can occur independently of IL-9/IL-9R signaling. In contrast, oral antigen–induced intestinal and systemic anaphylaxis is strictly IgE mediated and requires IL-9/IL-9R signaling. These studies indicate differential involvement of the IL-9/IL-9R pathway in systemic and oral antigen–induced anaphylaxis.
Cytokine; anaphylaxis; mast cells; IgE
In a manner partially independent of activating Fcγ receptors, antibody-mediated production of complement component C5a and recruitment of macrophages elicit transfusion-related acute lung injury in mice.
Transfusion-related acute lung injury (TRALI), a form of noncardiogenic pulmonary edema that develops during or within 6 h after a blood transfusion, is the most frequent cause of transfusion-associated death in the United States. Because development of TRALI is associated with donor antibodies (Abs) reactive with recipient major histocompatibility complex (MHC), a mouse model has been studied in which TRALI-like disease is caused by injecting mice with anti–MHC class I monoclonal Ab (mAb). Previous publications with this model have concluded that disease is caused by FcR-dependent activation of neutrophils and platelets, with production of reactive oxygen species that damage pulmonary vascular endothelium. In this study, we confirm the role of reactive oxygen species in the pathogenesis of this mouse model of TRALI and show ultrastructural evidence of pulmonary vascular injury within 5 min of anti–MHC class I mAb injection. However, we demonstrate that disease induction in this model involves macrophages rather than neutrophils or platelets, activation of complement and production of C5a rather than activation of FcγRI, FcγRIII, or FcγRIV, and binding of anti–MHC class I mAb to non-BM–derived cells such as pulmonary vascular endothelium. These observations have important implications for the prevention and treatment of TRALI.
IgE-mediated food allergy is a common cause of enteric disease and is responsible for approximately 100 systemic anaphylaxis deaths in the USA each year. IgG antibodies can protect against IgE-mediated systemic anaphylaxis induced by injected antigens by neutralizing antigens before they can bind to mast cell-associated IgE.
We have investigated whether IgA and IgG antibodies can similarly protect against systemic, IgE-mediated anaphylaxis induced by ingested antigens and, if so, whether IgA and IgG antibodies protect by neutralizing antigens before or after their systemic absorption.
Murine passive and active anaphylaxis models were used to study the abilities of serum vs. gut lumenal IgA antibodies and serum IgG antibodies to inhibit systemic anaphylaxis induced by ingested allergens in normal mice, mice deficient in the ability to secrete IgA into the intestines, and mice in which intestinal IL-9 overexpression has induced intestinal mastocytosis and increased intestinal permeability.
IgE-mediated systemic anaphylaxis and mast cell degranulation induced by antigen ingestion are suppressed by both serum antigen-specific IgA and IgG, but not by IgA within the gut lumen.
Systemic, rather than enteric antibodies protect against systemic anaphylaxis induced by ingested antigen. This implies that ingested antigens must be absorbed systemically to induce anaphylaxis and suggests that immunization protocols that increase serum levels of antigen-specific, non-IgE antibodies should protect against severe food allergy.
Induction of a systemic IgG or IgA antibody response against a food allergen should protect against induction of systemic anaphylaxis by ingestion of that allergen.
Mouse; food allergy; IgE; IgA; IgG; allergic diarrhea; blocking antibodies
IL-4Rα expression on airway smooth muscle cells is sufficient for the development of airway hyperresponsiveness.
Production of the cytokines IL-4 and IL-13 is increased in both human asthma and mouse asthma models, and Stat6 activation by the common IL-4/IL-13R drives most mouse model pathophysiology, including airway hyperresponsiveness (AHR). However, the precise cellular mechanisms through which IL-4Rα induces AHR remain unclear. Overzealous bronchial smooth muscle constriction is thought to underlie AHR in human asthma, but the smooth muscle contribution to AHR has never been directly assessed. Furthermore, differences in mouse versus human airway anatomy and observations that selective IL-13 stimulation of Stat6 in airway epithelium induces murine AHR raise questions about the importance of direct IL-4R effects on smooth muscle in murine asthma models and the relevance of these models to human asthma. Using transgenic mice in which smooth muscle is the only cell type that expresses or fails to express IL-4Rα, we demonstrate that direct smooth muscle activation by IL-4, IL-13, or allergen is sufficient but not necessary to induce AHR. Five genes known to promote smooth muscle migration, proliferation, and contractility are activated by IL-13 in smooth muscle in vivo. These observations demonstrate that IL-4Rα promotes AHR through multiple mechanisms and provide a model for testing smooth muscle–directed asthma therapeutics.
IL-13 receptor alpha2 (IL-13Rα2) binds IL-13 with high affinity and modulates IL-13 responses. There are soluble and membrane forms of IL-13Rα2 generated by alternative splicing in mice but humans express only the membrane form (memIL-13Rα2).
We determined the role of memIL-13Rα2 in development of allergic inflammation in mouse models of asthma.
IL-13Rα2-deficient and memIL-13Rα2 lung epithelium-specific transgenic mice were challenged with house dust mite (HDM). Airway hyperresponsiveness (AHR) and inflammation were assessed by airway pressure time index, bronchoalveolar lavage (BAL) cell counts and lung histology. The mucus production was determined by periodic acid-Schiff (PAS) staining of lung sections, western blot analysis of chloride channel calcium activated 3 (CLCA3) expression in lung homogenates, and ELISA of Muc5ac in BAL fluid (BALF). The expression of cytokines and chemokines was determined by RT-quantitative PCR.
In IL-13Rα2-deficient mice, AHR and airway inflammation were attenuated compared to wild type mice following HDM challenge. Lung epithelium overexpression of memIL-13Rα2 in the IL-13Rα2-deficient mice reconstituted AHR and inflammation to levels similar to those observed in HDM-challenged wild type mice. Mucus production was attenuated in lungs from HDM-treated IL-13Rα2-deficient mice while lung epithelium overexpression of memIL-13Rα2 increased mucus production. Lung epithelium overexpression of memIL-13Rα2 had no effect on the levels of sIL-13Rα2 in the serum or BALF and did not affect IL-13-dependent STAT6 activation in the lungs.
These data collectively support a distinct role for memIL-13Rα2 in lung, and suggest that memIL-13Rα2 may contribute to allergic inflammation.
IL-13; IL-13 receptor; lung; airway hyperresponsiveness; airway inflammation
Intestinal anaphylaxis (manifested by acute diarrhea) is dependent on IgE and mast cells.
We aimed to define the respective roles of IL-4 and IL-13 and their receptors in disease pathogenesis.
Wild-type mice and mice deficient in IL-4, IL-13, and IL-13Rα1 (part of the type 2 IL-4R) were sensitized with ovalbumin (OVA)/alum and subsequently given repeated intragastric OVA exposures. IL-4Rα chain was targeted with anti-IL-4Rα mAb prior to or after intragastric OVA exposures.
IL-4−/− (and IL-4/13−/−) mice produced almost no IgE and were highly resistant to OVA-induced diarrhea, whereas allergic diarrhea was only partially impaired in IL-13−/− and IL-13Rα1−/− mice. IL-13Rα1-deficient mice developed decreased IgE despite having normal baseline IL-4 levels. Intestinal mast cell accumulation and activation also depended mainly on IL-4 and to a lesser extent on IL-13. Prophylactic anti-IL-4Rα mAb treatment, which blocks all IL-4 and IL-13 signaling, suppressed development of allergic diarrhea. However, treatment with anti-IL-4Rα mAb for 7 days only partially suppressed IgE and did not prevent intestinal diarrhea.
Endogenously-produced IL-13 supplements the ability of IL-4 to induce allergic diarrhea by promoting oral allergen sensitization rather than the effector phase of intestinal anaphylaxis.
allergy; anaphylaxis; IL-4; IL-13; IL-13Ralpha1; intestine; mast cell
IL 4 receptor α (IL-4Rα) expression by non-bone marrow (BM)-derived cells is required to protect hosts against several parasitic helminth species. In contrast, we demonstrate that IL-4Rα expression by BM-derived cells is both necessary and sufficient to prevent Schistosoma mansoni-infected mice from developing severe inflammation directed against parasite ova, whereas IL-4Rα expression by non-BM-derived cells is neither necessary nor sufficient. Chimeras that express IL-4Rα only on non-BM-derived cells still produce Th2 cytokines, but overproduce IL-12p40, TNF, and IFN-γ, fail to generate alternatively activated macrophages, and develop endotoxemia and severe hepatic and intestinal pathology. In contrast, chimeras that express IL-4Rα only on BM-derived cells have extended survival, even though the granulomas that they develop around parasite eggs are small and devoid of collagen. These observations identify distinct roles for IL-4/IL-13 responsive cell lineages during schistosomiasis: IL-4Rα-mediated signaling in non-BM-derived cells regulates granuloma size and fibrosis, whereas signaling in BM-derived cells suppresses parasite egg-driven inflammation within the liver and intestine.
Th2 cells drive protective immunity against most parasitic helminths, but few mechanisms have been demonstrated that facilitate pathogen clearance. We show that IL-4 and IL-13 protect against intestinal lumen-dwelling worms primarily by inducing intestinal epithelial cells (IECs) to differentiate into goblet cells that secrete resistin-like molecule (RELM) β. RELM-β is essential for normal spontaneous expulsion and IL-4–induced expulsion of Nippostrongylus brasiliensis and Heligmosomoides polygyrus, which both live in the intestinal lumen, but it does not contribute to immunity against Trichinella spiralis, which lives within IEC. RELM-β is nontoxic for H. polygyrus in vitro but directly inhibits the ability of worms to feed on host tissues during infection. This decreases H. polygyrus adenosine triphosphate content and fecundity. Importantly, RELM-β–driven immunity does not require T or B cells, alternative macrophage activation, or increased gut permeability. Thus, we demonstrate a novel mechanism for host protection at the mucosal interface that explains how stimulation of epithelial cells by IL-4 and IL-13 contributes to protection against parasitic helminthes that dwell in the intestinal lumen.
Peanut allergy is the most common food-related cause of lethal anaphylaxis and, unlike other food allergies, typically persists into adulthood. Resistance to digestion and dendritic cell activation by the major peanut allergen, Ara h1, are reported to contribute to its allergenicity.
Evaluate whether peanut molecules may also promote anaphylaxis through an innate immune mechanism.
Naïve mice were treated with a β-adrenergic receptor antagonist and long-acting IL-4 to increase sensitivity to vasoactive mediators and injected with peanut extract (PE). Shock was detected and quantified by rectal thermometry. Gene-deficient mice and specific antagonists were used to determine the roles of specific cell types, complement, Fc receptors, and vasoactive mediators in shock pathogenesis.
1) PE induces dose-dependent shock; 2) PE activates complement in vivo in mice and in vitro in mice and humans; 3) C3a, and, to a lesser extent, stimulatory immunoglobulin (Ig) receptors contribute to PE-induced shock; 4) PE-induced shock depends more on macrophages and basophils than on mast cells; 5) platelet activating factor and, to a lesser extent, histamine contribute to PE-induced shock; 6) PE induces shock in the absence of the adaptive immune system; 7) LPS contamination is not responsible for PE-induced shock; 8) PE and IgE-mediated mast cell degranulation synergistically induce shock; and 9) Tree nuts have similar effects to PE; skim milk and egg white do not.
Peanuts can contribute to shock by causing production of C3a, which stimulates macrophages, basophils and mast cells to produce PAF and histamine.
peanut; C3a; complement; anaphylaxis; shock; macrophages; mast cells; basophils; PAF; histamine
A food-induced anaphylactic reaction can occur within seconds to a few hours following exposure to the causal food allergen and often affects multiple organ systems including gastrointestinal (GI), cutaneous, respiratory and cardiovascular. A conundrum in the allergy field is that consumption of the same allergen can cause reactions of vastly different severity in separate individuals; one patient may experience a mild non-life-threatening reaction characterized by pruritis of lips or urticaria whereas another may experience a life-threatening reaction that involves respiratory and cardiovascular compromise leading to loss of consciousness and sometimes death. While there are tests available to determine the predictive risk value of a positive food challenge test or clinical reactivity, there is currently no reliable method to distinguish between individuals who are at risk of mild non-life-threatening versus life-threatening reaction. Recent research has significantly advanced our understanding of the involvement of immune pathways in the effector phase of food-induced anaphylaxis, a void remains regarding our understanding of the contribution of these pathways to severity of disease. In this review, we discuss mild, non-life-threatening versus life-threatening food-induced anaphylaxis and factors (co-morbidities and immune-activation) that predispose individuals to more severe disease. Furthermore, we summarize recent advancements in our understanding of the involvement of underlying immune pathways in systemic and food-induced anaphylaxis in mouse systems and discuss how these pathways may contribute to more severe disease phenotype.
The prevalence of peanut allergies is rising. Peanuts and many other allergen sources contain significant amounts of triglycerides, which affect absorption of antigens but have unknown effects on sensitization and anaphylaxis. We recently reported that dietary medium-chain triglycerides (MCT), which bypass mesenteric lymph and directly enter portal blood, reduce intestinal antigen absorption into blood compared to long-chain triglycerides (LCT), which stimulate mesenteric lymph flow and are absorbed in chylomicrons via mesenteric lymph.
Test how dietary MCT affect food allergy.
C3H/HeJ mice were fed peanut butter protein in MCT, LCT (peanut oil), or LCT plus an inhibitor of chylomicron formation (Pluronic L81; “PL81”). Peanut-specific antibodies in plasma, responses of the mice to antigen challenges, and intestinal epithelial cytokine expression were subsequently measured.
MCT suppressed antigen absorption into blood, but stimulated absorption into Peyer's patches. A single gavage of peanut protein with MCT as well as prolonged feeding in MCT-based diets caused spontaneous allergic sensitization. MCT-sensitized mice experienced IgG-dependent anaphylaxis upon systemic challenge and IgE-dependent anaphylaxis upon oral challenge. MCT feeding stimulated jejunal-epithelial TSLP, IL-25 and IL-33 expression compared to LCT, and promoted Th2 cytokine responses in splenocytes. Moreover, oral challenges of sensitized mice with antigen in MCT significantly aggravated anaphylaxis compared to challenges with LCT. Importantly, effects of MCT could be mimicked by adding PL81 to LCT, and in vitro assays indicated that chylomicrons prevent basophil activation.
Dietary MCT promote allergic sensitization and anaphylaxis by affecting antigen absorption and availability and by stimulating Th2 responses.
Peanut allergy; triglycerides; TSLP; adjuvant; chylomicrons; intestinal epithelium; Th2 responses
Although it has long been hypothesized that allergen immunotherapy inhibits allergy, in part, by inducing production of IgG Abs that intercept allergens before they can cross-link mast cell FcεRI-associated IgE, this blocking Ab hypothesis has never been tested in vivo. In addition, evidence that IgG-allergen interactions can induce anaphylaxis by activating macrophages through FcγRIII suggested that IgG Ab might not be able to inhibit IgE-mediated anaphylaxis without inducing anaphylaxis through this alternative pathway. We have studied active and passive immunization models in mice to approach these issues and to determine whether any inhibition of anaphylaxis observed was a direct effect of allergen neutralization by IgG Ab or an indirect effect of cross-linking of FcεRI to the inhibitory IgG receptor FcγRIIb. We demonstrate that IgG Ab produced during the course of an immune response or administered passively can completely suppress IgE-mediated anaphylaxis; that these IgG blocking Abs inhibit IgE-mediated anaphylaxis without inducing FcγRIII-mediated anaphylaxis only when IgG Ab concentration is high and challenge allergen dose is low; that allergen epitope density correlates inversely with the allergen dose required to induce both IgE- and FcγRIII-mediated anaphylaxis; and that both allergen interception and FcγRIIb-dependent inhibition contribute to in vivo blocking Ab activity.
Activation and migration of marginal zone B (MZB) cells into follicular (FO) regions of the spleen has been proposed as one of the mechanisms that regulate the development of autoreactive B cells. The mer receptor tyrosine kinase (Mertk) mediates apoptotic cell clearance and regulates activation and cytokine secretion. In the well-studied class II chronic GVH model of bm12 cells into B6 hosts, we observed that Mertk deficient B6 mice did not generate autoantibodies in response to this allogeneic stimulus. We posited that Mertk is important in MHC-II-mediated B-cell signaling. In the present study, we show that B cells from Mertk-/- mice but not WT B6 mice exhibited decreased calcium mobilization and tyrosine phosphorylation when stimulated by MHC-II cross-linking. The finding that Mertk was important for class II signaling in B cells was further supported by the preponderance of a-allotype autoantibodies in cGVH in RAG-KO mice reconstituted with a mixture of bone marrow from Mertk-/- mice (b-allotype) and C20 mice (a-allotype). MZB cells from Mertk-/- mice were unable to down regulate surface CD1d expression and subsequent inclusion in the MZ, associated with significantly lower germinal center responses compared to MZB cells from WT. Moreover, Mertk-/- mice treated with an anti-CD1d down-regulating antibody responded significantly to bm12 cells, while no response was observed in Mertk-/- mice treated with control antibodies. Taken together, these findings extend the role of Mertk to include CD1d down regulation on MZB cells, a potential mechanism limiting B-cell activation in cGVH.
MZ B cell; cGVH; CD1d; GC; MHC II
The CD40 gene, an important immune regulatory gene, is also expressed and functional on non-myeloid derived cells, many of which are targets for tissue specific autoimmune diseases, including beta cells in type 1 diabetes, intestinal epithelial cells in Crohn’s disease, and thyroid follicular cells in Graves’ disease (GD). Whether target tissue CD40 expression plays a role in autoimmune disease etiology has yet to be determined. Here we show, that target-tissue over-expression of CD40 plays a key role in the etiology of autoimmunity. Using a murine model of GD, we demonstrated that thyroidal CD40 over-expression augmented the production of thyroid specific antibodies, resulting in more severe experimental autoimmune Graves’ disease (EAGD), whereas deletion of thyroidal CD40 suppressed disease. Using transcriptome and immune-pathway analyses we showed that in both EAGD mouse thyroids and human primary thyrocytes, CD40 mediates this effect by activating downstream cytokines and chemokines, most notably IL-6. To translate these findings into therapy, we blocked IL-6 during EAGD induction in the setting of thyroidal CD40 over-expression, and showed decreased levels of TSHR stimulating antibodies and frequency of disease. We conclude that target tissue over-expression of CD40 plays a key role in the etiology of organ specific autoimmune disease.
Eosinophilic esophagitis (EE) is an emerging disease associated with both food and respiratory allergy characterized by extensive esophageal tissue remodeling and abnormal esophageal gene expression including increased IL-13. We investigated the ability of increased airway IL-13 to induce EE-like changes. Mice that overexpress an IL-13 transgene in the lung (but not esophagus) accumulated esophageal IL-13 and developed prominent esophageal remodeling with epithelial hyperplasia, angiogenesis, collagen deposition and increased circumference. IL-13-induced marked changes in esophageal transcripts overlapped with the human EE esophageal transcriptome. IL-13-induced esophageal eosinophilia was eotaxin-1 (but not eotaxin-2) dependent but remodeling occurred independent of eosinophils, as demonstrated by studying eosinophil lineage-deficient IL-13 transgenic mice. IL-13-induced remodeling was significantly enhanced by IL-13Rα2 gene deletion, indicating an inhibitory effect of IL-13Rα2. In the murine system, there was partial overlap between IL-13-induced genes in the lung and esophagus, yet the transcriptomes were also divergent at the tissue level. In human esophagus, IL-13 levels correlated with the magnitude of the EE transcriptome. In conclusion, inducible airway expression of IL-13 results in an esophageal gene expression and extensive tissue remodeling pattern that resembles human EE. Notably, we have identified a pathway for inducing EE-like changes that is IL-13-driven, eosinophil-independent and suppressed by IL-13Rα2.
Resistin-like molecule α (Relm-α) is one of the most up-regulated gene products in allergen- and parasite-associated Th2 responses. Localized to alternatively activated macrophages, Relm-α was shown to exert an anti-inflammatory effect in parasite-induced Th2 responses, but its role in experimental asthma remains unexplored. Here, we analyzed the cellular source, the IL-4 receptors required to stimulate Relm-α production, and the role of Relm-α after experimental asthma induction by IL-4, IL-13, or multiple experimental regimes, including ovalbumin and Aspergillus fumigatus immunization. We demonstrate that Relm-α was secreted into the airway lumen, dependent on both the IL-13 receptor–α1 chain and likely the Type I IL-4 receptor, and differentially localized to epithelial cells and myeloid cells, depending on the specific cytokine or aeroallergen trigger. Studies performed with Retnla gene–targeted mice demonstrate that Relm-α was largely redundant in terms of inducing the infiltration of Th2 cytokines, mucus, and inflammatory cells into the lung. These results mirror the dispensable role that other alternatively activated macrophage products (such as arginase 1) have in allergen-induced experimental asthma and contrast with their role in the setting of parasitic infections. Taken together, our findings demonstrate the distinct utilization of IL-4/IL-13 receptors for the induction of Relm-α in the lungs. The differential regulation of Relm-α expression is likely determined by the relative expression levels of IL-4, IL-13, and their corresponding receptors, which are differentially expressed by divergent cells (i.e., epithelial cells and macrophages.) Finally, we identify a largely redundant functional role for Relm-α in acute experimental models of allergen-associated Th2 immune responses.
resistin-like molecule–α; asthma; IL-4; IL-13Rα1
Anaphylaxis is a rapid, life-threatening hypersensitivity reaction. Until recently, it was mainly attributed to histamine released by mast cells activated by allergen crosslinking (XL) of FcεRI-bound allergen-specific IgE. However, recent reports established that anaphylaxis could also be triggered by basophil, macrophage and neutrophil secretion of platelet activating factor subsequent to FcγR stimulation by IgG/Ag complexes. We have investigated the contribution of Fyn and Lyn tyrosine kinases to FcγRIIb and FcγRIII signaling in the context of IgG-mediated passive systemic anaphylaxis (PSA). We found that mast cell IgG XL induced Fyn, Lyn, Akt, Erk, p38 and JNK phosphorylation. Additionally, IgG XL of mast cells, basophils and macrophages resulted in Fyn- and Lyn-regulated mediator release in vitro. FcγR–mediated activation was enhanced in Lyn-deficient (KO) cells, but decreased in Fyn KO cells, compared to wild type cells. More importantly, Lyn KO mice displayed significantly exacerbated PSA features while no change was observed for Fyn KO mice, compared to wild type littermates. Intriguingly, we establish that mast cells account for the majority of serum histamine in IgG-induced PSA. Taken together, our findings establish pivotal roles for Fyn and Lyn in the regulation of PSA and highlight their unsuspected functions in IgG-mediated pathologies.
Mechanistic understanding of RP105 has been confounded by the fact that this TLR homolog has appeared to have opposing, cell type-specific effects on TLR4 signaling. While RP105 inhibits TLR4-driven signaling in cell lines and myeloid cells, impaired LPS-driven proliferation by B cells from RP105−/− mice has suggested that RP105 facilitates TLR4 signaling in B cells. We show here that modulation of B cell proliferation by RP105 is not a function of B cell-intrinsic expression of RP105, and identify a mechanistic role for dysregulated BAFF expression in the proliferative abnormalities of B cells from RP105−/− mice: serum BAFF levels are elevated in RP105−/− mice, and partial BAFF neutralization rescues aberrant B cell proliferative responses in such mice. These data indicate that RP105 does not have dichotomous effects on TLR4 signaling, and emphasize the need for caution in interpreting the results of global genetic deletion.
Complement is an ancient danger sensing system playing critical roles in host defense, immune surveillance and homeostasis1. C5a and its G-Protein-coupled receptor mediate many of the pro-inflammatory properties of complement2. Despite its critical role in allergic asthma3, autoimmune arthritis4, sepsis5 and cancer6, our knowledge about C5a regulation is limited. Here we demonstrate an unexpected link through which IgG1 immune complexes (IC), the inhibitory IgG receptor FcγRIIB and the C-type lectin-like receptor Dectin-1 suppress C5a receptor (C5aR) functions. Specifically, we found that IgG1 IC associate FcγRIIB with Dectin-1, resulting in phosphorylation of spleen tyrosine kinase (Syk) downstream of Dectin-1 and Src homology 2 domain containing inositol phosphatase (SHIP) downstream of FcγRIIB. This pathway blocks C5a receptor-mediated ERK1/2 phosphorylation and C5a effector functions in vitro and C5a-dependent inflammatory responses in vivo including the development of skin blisters in experimental epidermolysis bullosa acquisita (EBA), an autoimmune skin disorder. Notably, high galactosylation of IgG N-glycan is critical for this inhibitory property of IgG1 IC as it promotes the association between FcγRIIB and Dectin-1. Thus, galactosylated IgG1 and FcγRIIB exert immunoregulatory properties beyond their impact on activating FcγRs that may control allergy, autoimmunity and cancer.
The repair protein trefoil factor 2 promotes Th2 responses to helminth infection and allergens in part by inducing IL-33.
The molecular mechanisms that drive mucosal T helper type 2 (TH2) responses against parasitic helminths and allergens remain unclear. In this study, we demonstrate in mice that TFF2 (trefoil factor 2), an epithelial cell–derived repair molecule, is needed for the control of lung injury caused by the hookworm parasite Nippostrongylus brasiliensis and for type 2 immunity after infection. TFF2 is also necessary for the rapid production of IL-33, a TH2-promoting cytokine, by lung epithelia, alveolar macrophages, and inflammatory dendritic cells in infected mice. TFF2 also increases the severity of allergic lung disease caused by house dust mite antigens or IL-13. Moreover, TFF2 messenger RNA expression is significantly increased in nasal mucosal brushings during asthma exacerbations in children. These experiments extend the biological functions of TFF2 from tissue repair to the initiation and maintenance of mucosal TH2 responses.
Genome-wide screening and positional cloning have linked neuropeptide S receptor 1 (NPSR1) with asthma and airway hyperresponsiveness. However, the mechanism by which NPSR1 regulates pulmonary responses remains elusive. Because neuropeptide S and its receptor NPSR1 are expressed in brain regions that regulate respiratory rhythm, and Npsr1-deficient mice have impaired stress and anxiety responses, we aimed to investigate whether neuropeptide S and NPSR1 regulate respiratory function through a central-mediated pathway. After neuropeptide S intracerebroventricular administration, respiratory responses of wildtype and Npsr1-deficient mice were monitored by whole-body or invasive plethysmography with or without serial methacholine inhalation. Airway inflammatory and hyperresponsiveness were assessed in allergen-challenged (ovalbumin or Aspergillus fumigatus) Npsr1-deficient mice. Analysis of breathing patterns by whole-body plethysmography revealed that intracerebroventricular neuropeptide S, as compared with the artificial cerebral spinal fluid control, increased respiratory frequency and decreased tidal volume in an NPSR1-dependent manner but did not affect enhanced pause. Following serial methacholine inhalation, intracerebroventricular neuropeptide S increased respiratory frequency in wildtype mice, but not Npsr1-deficient mice, and had no effect on tidal volume. Intracerebroventricular neuropeptide S significantly reduced airway responsiveness to methacholine as measured by whole-body plethysmography. Npsr1 deletion had no impact on airway inflammation or hyperresponsiveness in ovalbumin- or Aspergillus fumigatus-induced experimental asthma. Our results demonstrate that neuropeptide S and NPSR1 regulate respiratory function through a central nervous system-mediated pathway.
Respiration; brain; neuropeptide S; neuropeptide S receptor 1; panting; stress
A defining feature of inflammation is the accumulation of innate immune cells in the tissue that are thought to be recruited from the blood. We reveal that a distinct process exists in which tissue macrophages undergo rapid in situ proliferation in order to increase population density. This inflammatory mechanism occurred during T helper 2 (Th2)-related pathologies under the control of the archetypal Th2 cytokine interleukin-4 (IL-4), and was a fundamental component of Th2 inflammation because exogenous IL-4 was sufficient to drive accumulation of tissue macrophages through self-renewal. Thus, expansion of innate cells necessary for pathogen control or wound repair can occur without recruitment of potentially tissue-destructive inflammatory cells.