IL-13 overexpression predisposes to anaphylaxis following antigen sensitization

Anaphylaxis represents an extreme form of allergic reaction. This acute-phase component of allergy and asthma is triggered by allergen-induced degranulation of mast cells following the cross-linking of cell surface-bound, allergen-specific IgE, resulting in the liberation of inflammatory mediators and the development of bronchoconstriction. We used IL-13 transgenic mice to investigate the role of this Th2 cell-derived cytokine in the onset of allergic disease. Strikingly, IL-13-transgenic mice were highly predisposed to fatal anaphylaxis following Ag sensitization. This response correlated with substantially elevated levels of circulating Ag-specific IgE, mast cell degranulation, and histamine release. Furthermore, allergen exposure also induced phenotypic changes typical of asthma, including pulmonary fibrosis, goblet cell hyperplasia, elevated Th2 cytokines, eosinophilia, and airways occluded by mucus and Charcot-Leyden crystals. Expression of IL-4 was not required for the induction of IgE-mediated responses. These data represent the first characterization of a functional role for IL-13-induced IgE in the generation of immediate hypersensitivity reactions and highlight the importance of IL-13 in the development of the symptoms of atopy. The systemic regulation of this response makes these mice an important resource for studying atopic responses.     

Dominant epitopes and allergic cross-reactivity: complex formation between a Fab fragment of a monoclonal murine IgG antibody and the major allergen from birch pollen Bet v 1

The symptoms characteristic of allergic hypersensitivity are caused by the release of mediators, i.e., histamine, from effector cells such as basophils and mast cells. Allergens with more than one B cell epitope cross-link IgE Abs bound to high affinity FcepsilonRI receptors on mast cell surfaces leading to aggregation and subsequent mediator release. Thus, allergen-Ab complexes play a crucial role in the cascade leading to the allergic response. We here report the structure of a 1:1 complex between the major birch pollen allergen Bet v 1 and the Fab fragment from a murine monoclonal IgG1 Ab, BV16, that has been solved to 2.9 A resolution by x-ray diffraction. The mAb is shown to inhibit the binding of allergic patients' IgE to Bet v 1, and the allergen-IgG complex may therefore serve as a model for the study of allergen-IgE interactions relevant in allergy. The size of the BV16 epitope is 931 A2 as defined by the Bet v 1 Ab interaction surface. Molecular interactions predicted to occur in the interface are likewise in agreement with earlier observations on Ag-Ab complexes. The epitope is formed by amino acids that are conserved among major allergens from related species within the Fagales order. In combination with a surprisingly high inhibitory capacity of BV16 with respect to allergic patients' serum IgE binding to Bet v 1, these observations provide experimental support for the proposal of dominant IgE epitopes located in the conserved surface areas. This model will facilitate the development of new and safer vaccines for allergen immunotherapy in the form of mutated allergens.     

Prostaglandin Production by Mast Cells and the Regulation of Airway Smooth Muscle Responses

The role of mast cell activation and the generation of mediator release are important factors in determining the reactivity of lung tissue during allergic reactions and asthma. In this article, the advantages of our procedure for isolating mast cells from lung tissue over other methods are discussed. Our studies have demonstrated the importance of cross talk between mast cells and other cell types that also release mediators of bronchoconstriction during activation, thus amplifying the response. In addition, it has been found that inositol phospholipid turnover in response to various mast cell mediators is enhanced in hyperresponsive lung tissue. The consequences to the contractility of the tissue of such alterations in the cellular signaling system in lung tissue are discussed.     

Mucosal injury and eicosanoid kinetics during hyperventilation-induced bronchoconstriction.

Bronchoalveolar lavage (BAL) of canine peripheral airways was performed at various times after hyperventilation, and BAL fluid (BALF) cell and mediator data were used to evaluate two hypotheses: 1) hyperventilation-induced mucosal injury stimulates mediator production, and 2) mucosal damage is correlated with the magnitude of hyperventilation-induced bronchoconstriction. We found that epithelial cells increased in BALF immediately after a 2- and a 5-min dry air challenge (DAC). Prostaglandins D(2) and F(2alpha) and thromboxane B(2) were unchanged immediately after a 2-min DAC but were significantly increased after a 5-min DAC. Leukotriene C(4), D(4), and E(4) did not increase until 5 min after DAC. Hyperventilation with warm moist air did not alter BALF cells or mediators and caused less airway obstruction that occurred earlier than DAC. BALF epithelial cells were correlated with mediator release, and mediator release and epithelial cells were correlated with hyperventilation-induced bronchoconstriction. These observations are consistent with the hypothesis that hyperventilation-induced mucosal damage initiates peripheral airway constriction via the release of biochemical mediators.     

Surfactant protein D decreases pollen-induced IgE-dependent mast cell degranulation

Mast cells play a key role in allergy and asthma. They reside at the host-environment interface and are among the first cells to make contact with inhaled microorganisms and particulate antigens. Pulmonary surfactant proteins A and D (SP-A and SP-D) function in lung host defense by enhancing microbe phagocytosis and mediating other immune cell functions, but little is known about their effects on mast cells. We hypothesized that SP-A and/or SP-D modulate IgE-dependent mast cell functions. Pollen starch granules (PSG) extracted from Dactylis glomerata and coated with trinitrophenol (TNP) were used as a model of an inhaled organic particulate allergen. Our data revealed that SP-D inhibited by 50% the release of beta-hexosaminidase by peritoneal mast cells sensitized with IgE anti-TNP and stimulated with TNP-PSG. In contrast, SP-A had no effect. Furthermore, SP-D aggregated PSG in a dose-dependent manner, and this aggregation was mediated by SP-D's carbohydrate recognition domain. A single arm SP-D mutant (RrSP-Dser15,20) neither aggregated PSG nor inhibited degranulation, suggesting that multimerization of SP-D is required for maximal PSG aggregation and inhibition of PSG-induced mast cell degranulation. This study is the first to demonstrate that SP-D modulates IgE-mediated mast cell functions, which are important in asthma and allergic inflammation.     

Rac and protein kinase C-delta regulate ERKs and cytosolic phospholipase A2 in FcepsilonRI signaling to cysteinyl leukotriene synthesis in mast cells

Although cysteinyl leukotrienes (cysLTs) are known to be principal inflammatory lipid mediators released from IgE-stimulated mast cells, the signaling mechanisms involved in the synthesis of cysLTs remain largely unknown. In the present study, therefore, we investigated the signaling pathway by which IgE induces cysLTs synthesis after binding to its high affinity receptor (FcepsilonRI) in RBL-2H3 mast cells. We found that IgE-induced cysLT synthesis is completely abolished in RBL-2H3(Rac-N17) cells, a stable cell line expressing Rac(N17), a dominant negative Rac1 mutant; conversely, synthesis was enhanced in cells expressing Rac(V12), a constitutively active Rac1 mutant, suggesting that Rac1 is a key mediator of IgE signaling to cysLT synthesis. Further analysis aimed at identifying mediators downstream of Rac1 revealed that pretreating cells with a protein kinase C-delta (PKC-delta) inhibitor or infection with an adenoviral vector harboring a dominant negative PKC-delta mutant significantly attenuates IgE-induced ERKs phosphorylation, cytosolic phospholipase A(2) phosphorylation/translocation, and cysLT synthesis. In addition, the expression of Rac(N17) blocked PKC-delta translocation and impaired the phosphorylation of ERKs and cytosolic phospholipase A(2) otherwise elicited by IgE stimulation. Taken together these results suggest that PKC-delta also plays a critical mediatory role in the IgE signaling pathway leading to cysLT synthesis, acting downstream of Rac1. Finally, the physiological significance of PKC-delta in the IgE signaling pathway was demonstrated in an Ag (OVA)-challenged in vivo mouse model, in which induced levels of cysLTs and airway responsiveness in lung airways were significantly diminished by prior i.p. injection of a PKC-delta inhibitor.     

Cyclical mechanical stretch enhances degranulation and IL‐4 secretion in RBL‐2H3 mast cells

Mast cells are widely distributed in the body and affect their surrounding environment through degranulation and secretion of cytokines. Conversely, mast cells are influenced by environmental stimuli such as cyclical mechanical stretch (CMS), such as that induced by heartbeat and respiration. Peripherally distributed mast cells are surrounded by extracellular matrix, where they bind IgE on their surface by expressing the high‐affinity Fc receptor for IgE (FcεRI), and they release mediators after cross‐linking of surface‐bound IgE by allergen. To analyse how CMS affects mast cell responses, we examined the effect of applying CMS on the behaviour of IgE‐bound mast cells (RBL‐2H3 cell line) adhering to fibronectin as a substitute for extracellular matrix. We found that CMS enhanced FcεRI‐mediated secretion in the presence of antigen (2,4‐dinitrophenol–bovine serum albumin). CMS increased expression of IL‐4 mRNA and secretion of IL‐4 protein. Western blot analysis showed that CMS changes the signal transduction in mitogen‐activated protein kinases and AKT, which in turn alters the regulation of IL‐4 and increases the secretion of IL‐4. These results suggest that CMS modulates the effect of mast cells on inflammation and resultant tissue remodelling. Understanding how CMS affects mast cell responses is crucial for developing therapies to treat mast cell‐related diseases. Copyright © 2013 John Wiley & Sons, Ltd.     

Role of histamine and platelet-activating factor in allergic rhinitis

This review is focused on the effects of histamine and platelet-activating factor (PAF) in allergic rhinitis and the plausible implications for therapy. Rhinitis is defined as a heterogeneous disorder resulting from an IgE-mediated reaction associated with nasal inflammation of variable intensity. Two phases of response are triggered by an IgE/allergen cross-linking event: the first is the release of preformed mediators such as histamine or interleukins from mast cells and basophils; the second begins when cells start producing lipid-derived mediators. One of these mediators is PAF. Apart from leukotrienes, PAF is perhaps the most potent inflammatory mediator in allergic rhinitis for inducing vascular leakage, a response that may contribute to the appearance of rhinorrhea and nasal congestion.     

Tolerization of a type I allergic immune response through transplantation of genetically modified hematopoietic stem cells

Allergy represents a hypersensitivity disease that affects >25% of the population in industrialized countries. The underlying type I allergic immune reaction occurs in predisposed atopic individuals in response to otherwise harmless Ags (i.e., allergens) and is characterized by the production of allergen-specific IgE, an allergen-specific T cell response, and the release of biologically active mediators such as histamine from mast cells and basophils. Regimens permanently tolerizing an allergic immune response still need to be developed. We therefore retrovirally transduced murine hematopoietic stem cells to express the major grass pollen allergen Phl p 5 on their cell membrane. Transplantation of these genetically modified hematopoietic stem cells led to durable multilineage molecular chimerism and permanent immunological tolerance toward the introduced allergen at the B cell, T cell, and effector cell levels. Notably, Phl p 5-specific serum IgE and IgG remained undetectable, and T cell nonresponsiveness persisted throughout follow-up (40 wk). Besides, mediator release was specifically absent in in vitro and in vivo assays. B cell, T cell, and effector cell responses to an unrelated control allergen (Bet v 1) were unperturbed, demonstrating specificity of this tolerance protocol. We thus describe a novel cell-based strategy for the prevention of allergy.     

A Novel Model of IgE-Mediated Passive Pulmonary Anaphylaxis in Rats

Mast cells are central effector cells in allergic asthma and are augmented in the airways of asthma patients. Attenuating mast cell degranulation and with it the early asthmatic response is an important intervention point to inhibit bronchoconstriction, plasma exudation and tissue oedema formation. To validate the efficacy of novel pharmacological interventions, appropriate and practicable in vivo models reflecting mast cell-dependent mechanisms in the lung, are missing. Thus, we developed a novel model of passive pulmonary anaphylaxis in rats. Rats were passively sensitized by concurrent intratracheal and intradermal (ear) application of an anti-DNP IgE antibody. Intravenous application of the antigen, DNP-BSA in combination with Evans blue dye, led to mast cell degranulation in both tissues. Quantification of mast cell degranulation in the lung was determined by (1) mediator release into bronchoalveolar lavage, (2) extravasation of Evans blue dye into tracheal and bronchial lung tissue and (3) invasive measurement of antigen-induced bronchoconstriction. Quantification of mast cell degranulation in the ear was determined by extravasation of Evans blue dye into ear tissue. We pharmacologically validated our model using the SYK inhibitor Fostamatinib, the H₁-receptor antagonist Desloratadine, the mast cell stabilizer disodium cromoglycate (DSCG) and the β₂-adrenergic receptor agonist Formoterol. Fostamatinib was equally efficacious in lung and ear. Desloratadine effectively inhibited bronchoconstriction and ear vascular leakage, but was less effective against pulmonary vascular leakage, perhaps reflecting the differing roles for histamine receptor sub-types. DSCG attenuated both vascular leakage in the lung and bronchoconstriction, but with a very short duration of action. As an inhaled approach, Formoterol was more effective in the lung than in the ear. This model of passive pulmonary anaphylaxis provides a tissue relevant readout of early mast cell activity and pharmacological benchmarking broadly reflects responses observed in patients with asthma.     

Allergome: the characterization of allergens based on a 2D gel electrophoresis approach

Type I hypersensitivity reactions are in constant progression in industrialized countries. The physiopathologic mechanism of these diseases implicates the production of specific immunoglobulin (Ig)E to allergenic molecules, their binding to the Fcepsilon receptor on the surface of mast cells and basophils, and the release of inflammatory mediators when allergens are introduced into the body and crosslink with the IgE bound to the cell surface. An allergen is defined as a molecule that induces the production of, and binds to, IgE. The identification of the allergenic molecules is an important goal to improve diagnosis and treatment of allergy. This characterization aims to extract proteins from the allergenic source, to analyze IgE specificity by immunoblotting and to identify the proteins that bind IgE.     

IgE production in CD40/CD40L cross-talk of B and mast cells and mediator release via TGase 2 in mouse allergic asthma

TGase 2 is over-expressed in a variety of inflammatory diseases including allergic asthma. This study aimed to investigate the role of TGase 2 on IgE production and signaling pathways in mast cell activation related to OVA-induced allergic asthma. Bone marrow-derived mast cells (BMMCs) isolated from WT or TGase 2^?/? mice were activated with Ag/Ab (refer to act-WT-BMMCs and act-KO-BMMCs, respectively). B cells isolated from splenocytes were activated with anti-mouse IgM (act-B cells), and B cells were co-cultured with BMMCs. WT and TGase 2^?/? mice were sensitized and challenged with OVA adsorbed in alum hydroxide. Intracellular Ca^2 + ([Ca^2 +]_i) levels were determined by fluorescence intensity; IgE, mediators and TGase 2 activity by ELISA; the CD138 expression by FACS analyzer; cell surface markers and signal molecules by Western blot; NF-κB by EMSA; co-localization of mast cells and B cells by immunohistochemistry; Fcε RI-mediated mast cell activation by PCA test; expression of cytokines, MMPs, TIMPs, TLR2 and Fc?RI by RT-PCR. In vitro, act-KO-BMMCs reduced the [Ca^2 +]i levels, NF-κB activity, expression of CD40/CD40L, plasma cells, total IgE levels and TGase 2 activity in act-B cells co-cultured with act-BMMCs, expression of inflammatory cytokines and MMPs2/9, release of mediators (TNF-α, LTs and cytokines), and activities of signal molecules (PKCs, MAP kinases, I-κB and PLA2), which were all increased in act-WT-BMMCs. TGase 2 siRNA transfected/activated-BMMCs reduced all responses as same as those in act-KO-BMMCs. In allergic asthma model, TGase 2^?/? mice protected against PCA reaction, OVA-specific IgE production and AHR, and they reduced co-localization of mast cells and B cells or IgE in lung tissues, expression and co-localization of surface molecules in mast cells (c-kit and CD40L) and B cells (CD23 and CD40), inflammatory cells including mast cells, goblet cells, amounts of collagen and mediator release in BAL fluid and/or lung tissues, which were all increased in WT mice. TLR expression in TGase 2^?/? mice did not differ from those in WT mice. Our data suggest that TGase 2 expression and Ca^2 + influx required by bidirectional events in mast cell activation facilitate IgE production in B cells via up-regulating mast cell CD40L expression, and induce the expression of numerous signaling molecules associated with airway inflammation and remodeling in allergic asthma.     

Genetic and biochemical evidence for a critical role of Janus kinase (JAK)-3 in mast cell-mediated type I hypersensitivity reactions

We investigated the role of JAK3 in IgE receptor/FcepsilonRI-mediated mast cell responses. IgE/antigen induced degranulation and mediator release were substantially reduced with Jak3-/- mast cells from JAK3-null mice that were generated by targeted disruption of Jak3 gene in embryonic stem cells. Further, treatment of mast cells with 3'bromo-4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P154), a potent inhibitor of JAK3, inhibited degranulation and proinflammatory mediator release after IgE receptor/ FcepsilonRI crosslinking. Thus, JAK3 plays a pivotal role in IgE receptor/ FcepsilonRI-mediated mast cell responses and targeting JAK3 may provide the basis for new and effective treatment as well as prevention programs for mast cell-mediated allergic reactions.     

Allergome: the characterization of allergens based on a 2D gel electrophoresis approach

Type I hypersensitivity reactions are in constant progression in industrialized countries. The physiopathologic mechanism of these diseases implicates the production of specific immunoglobulin (Ig)E to allergenic molecules, their binding to the Fcε receptor on the surface of mast cells and basophils, and the release of inflammatory mediators when allergens are introduced into the body and crosslink with the IgE bound to the cell surface. An allergen is defined as a molecule that induces the production of, and binds to, IgE. The identification of the allergenic molecules is an important goal to improve diagnosis and treatment of allergy. This characterization aims to extract proteins from the allergenic source, to analyze IgE specificity by immunoblotting and to identify the proteins that bind IgE.     

Mast cell alpha-chymase reduces IgE recognition of birch pollen profilin by cleaving antibody-binding epitopes.

In sensitized individuals birch pollen induces an allergic response characterized by IgE-dependent mast cell degranulation of mediators, such as alpha-chymase and other serine proteases. In birch and other plant pollens, a major allergen is profilin. In mammals, profilin homologues are found in an intracellular form bound to cytoskeletal or cytosolic proteins or in a secreted form that may initiate signal transduction. IgE specific to birch profilin also binds human profilin I. This cross-reactivity between airborne and endogenous proteins may help to sustain allergy symptoms. The current work demonstrates that cultured mast cells constitutively secrete profilin I, which is susceptible to degranulation-dependent proteolysis. Coincubation of chymase-rich BR mastocytoma cells with Ala-Ala-Pro-Phe-chloromethylketone (a chymase inhibitor) blocks profilin cleavage, which does not occur in degranulated HMC-1 mast cells, which are rich in tryptase, but chymase deficient. These data implicate chymase as the serine protease cleaving secreted mast cell profilin. Sequencing of chymase-cleaved profilins reveals hydrolysis at Tyr(6)-Val(7) and Trp(35)-Ala(36) in birch profilin and at Trp(32)-Ala(33) in human profilin, with all sites lying within IgE-reactive epitopes. IgE immunoblotting studies with sera from birch pollen-allergic individuals demonstrate that cleavage by chymase attenuates binding of birch profilin to IgE. Thus, destruction of IgE-binding epitopes by exocytosed chymase may limit further mast cell activation by this class of common plant allergens, thereby limiting the allergic responses in sensitized individuals.     

Drastic up-regulation of Fcepsilonri on mast cells is induced by IgE binding through stabilization and accumulation of Fcepsilonri on the cell surface.

It has been shown that IgE binding to FcepsilonRI on mast cells results in increased FcepsilonRI expression, which in turn enhances IgE-dependent chemical mediator release from mast cells. Therefore, prevention of the IgE-mediated FcepsilonRI up-regulation would be a promising strategy for management of allergic disorders. However, the mechanism of IgE-mediated FcepsilonRI up-regulation has not been fully elucidated. In this study, we analyzed kinetics of FcepsilonRI on peritoneal mast cells and bone marrow-derived mast cells. In the presence of brefeldin A, which prevented transport of new FcepsilonRI molecules to the cell surface, levels of IgE-free FcepsilonRI on mast cells decreased drastically during culture, whereas those of IgE-bound FcepsilonRI were stable. In contrast, levels of FcgammaRIII on the same cells were stable even in the absence of its ligand, indicating that FcepsilonRI alpha-chain, but not beta- and gamma-chains, was responsible for the instability of IgE-free FcepsilonRI. As far as we analyzed, there was no evidence to support the idea that IgE binding to FcepsilonRI facilitated synthesis and/or transport of FcepsilonRI to the cell surface. Therefore, the stabilization and accumulation of FcepsilonRI on the cell surface through IgE binding appears to be the major mechanism of IgE-mediated FcepsilonRI up-regulation.     

IgE enhances Fc epsilon receptor I expression and IgE-dependent release of histamine and lipid mediators from human umbilical cord blood-derived mast cells: synergistic effect of IL-4 and IgE on human mast cell Fc epsilon receptor I expression and mediator release

We investigated the effects of IgE versus IL-4 on Fc epsilon RI surface expression in differentiated human mast cells derived in vitro from umbilical cord blood mononuclear cells. We found that IgE (at 5 micrograms/ml) much more strikingly enhanced surface expression of Fc epsilon RI than did IL-4 (at 0.1-100 ng/ml); similar results were also obtained with differentiated mouse mast cells. However, IL-4 acted synergistically with IgE to enhance Fc epsilon RI expression in these umbilical cord blood-derived human mast cells, as well as in mouse peritoneal mast cells derived from IL-4-/- or IL-4+/+ mice. We also found that: 1) IgE-dependent enhancement of Fc epsilon RI expression was associated with a significantly enhanced ability of these human mast cells to secrete histamine, PGD2, and leukotriene C4 upon subsequent passive sensitization with IgE and challenge with anti-IgE; 2) preincubation with IL-4 enhanced IgE-dependent mediator secretion in these cells even in the absence of significant effects on Fc epsilon RI surface expression; 3) when used together with IgE, IL-4 enhanced IgE-dependent mediator secretion in human mast cells to levels greater than those observed in cells that had been preincubated with IgE alone; and 4) batches of human mast cells generated in vitro from umbilical cord blood cells derived from different donors exhibited differences in the magnitude and pattern of histamine and lipid mediator release in response to anti-IgE challenge, both under baseline conditions and after preincubation with IgE and/or IL-4.     

Why do asthmatic subjects respond so strongly to inhaled adenosine?

Bronchospasm induced by adenosine is blocked by representatives of all the major classes of drugs used in the treatment of asthma. Understanding the mechanism of this bronchospasm may help understand the way these drugs work. Clinical studies have suggested involvement of neural pathways, mast-like cells and mediators such as histamine, serotonin and lipoxygenase products. There is a strong link between responsiveness to adenosine and eosinophilia. In different animal models A1, A2b and A3 adenosine receptor subclasses have all been implicated in inducing bronchospasm. whilst occupation of the A2a receptor generally has no, or the opposite effect. At least two different mechanisms, both involving neural pathways, exist. One, involving the adenosine A1 receptor, functions in mast cell depleted animals; the other requires interaction with a population of mast-like cells activated over A2b or A3 receptors. Not only histamine but also serotonin and lipoxygenase products released from the mast-like cells are potential mediators. In animal models good reactivity to adenosine receptor agonists is generally only found when the animals are first sensitized and exposed to allergen in ways likely to induce an allergic inflammation. An exception is the BDE rat, which reacts to adenosine receptor agonists such as APNEA or NECA even without allergen exposure. This rat strain does however show evidence of spontaneous eosinophilic inflammation in the lung even without immunization. As mast cells both release adenosine and respond to adenosine, adenosine provides a non-specific method of amplifying specific signals resulting from IgE/antigen interaction. This mechanism may not only have a pathological significance in asthma; it may be part of a normal bodily defense response that in asthmatic subjects is inappropriately activated.