Active anaphylaxis in IgE-deficient mice

Essential Domain-Dependent Roles Within Soluble IgG for in vivo Superantigen Properties of Staphylococcal Protein A: Resolving the B-Cell Superantigen Paradox

Staphylococcus aureus is a common commensal and frequent opportunistic pathogen that causes invasive infections that often recur. Co-evolution with the host has led to the development of toxins that affect diverse immune cell types. Recent reports have highlighted the contributions of staphylococcal protein A (SpA). This small oligomeric secreted protein contains 4–5 homologous domains with two distinct immunoglobulin-binding sites; one for IgG Fc domains, while a separate site binds an evolutionarily conserved surface on Fab encoded by VHIII clan related genes. The Fab-binding site has been implicated in in vivo supraclonal VHIII-BCR targeted B-cell depletion by an activation induced death pathway. Yet the concept of a superantigen for B lymphocytes poses a seeming paradox. Unlike TCR that are expressed only in a membrane-associated form, BCR are expressed in both a membrane BCR form and in secreted Ig forms, which permeate virtually every part of the body at high levels. We therefore asked, why circulating immunoglobulin do not block the superantigen properties of SpA? Herein, we show that soluble IgG molecules are not in vivo inhibitors of these B-cell superantigen effects but are instead essential for potentiating these properties. We also show that the Fc subclass of circulating IgG is an indirect critical determinant of the B-cell superantigen effect. In contrast, host FcγR and complement are not required for SpA mediated in vivo B-cell depletion. Unexpectedly, after VHIII-IgG2a pretreatment SpA challenge resulted in fatal anaphylactic reactions, which we speculate may have involved FcγR interactions with mast cells and basophils. Cumulatively, our findings illuminate a cunning and potent molecular strategy by which a bacterial toxin effectively confounds the contributions of host B-lymphocytes to immune defenses.

Epithelial damage and tissue γδ T cells promote a unique tumor-protective IgE response

IgE is an ancient and conserved immunoglobulin isotype with potent immunological function. Nevertheless, the regulation of IgE responses remains an enigma, and evidence of a role for IgE in host defense is limited. Here we report that topical exposure to a common environmental DNA-damaging xenobiotic initiated stress surveillance by γδTCR+ intraepithelial lymphocytes that resulted in class switching to IgE in B cells and the accumulation of autoreactive IgE. High-throughput antibody sequencing revealed that γδ T cells shaped the IgE repertoire by supporting specific variable-diversity-joining (VDJ) rearrangements with unique characteristics of the complementarity-determining region CDRH3. This endogenous IgE response, via the IgE receptor FcεRI, provided protection against epithelial carcinogenesis, and expression of the gene encoding FcεRI in human squamous-cell carcinoma correlated with good disease prognosis. These data indicate a joint role for immunosurveillance by T cells and by B cells in epithelial tissues and suggest that IgE is part of the host defense against epithelial damage and tumor development.

Mast cells and basophils in allergic inflammation

Mast cells and basophils have similar characteristics in terms of their function and development. They both have detrimental functions, being implicated in pro-inflammatory responses to allergens, but can also provide protection against multicellular parasites such as parasitic worms (helminths). Both cell types express the high affinity Fc receptor for IgE, FcεRI, and allergen cross-linking of this receptor triggers degranulation and release a set of cytokines and biochemical mediators. Although mast cells and basophils are similar in many respects, newly developed antibody reagents and genetically modified mouse models that enable cell type-specific deletion have allowed us to appreciate their independent in vivo roles. This review focuses on recent advances in our understanding of the contribution of basophils and mast cells to innate and adaptive allergic responses.

Approaches to target IgE antibodies in allergic diseases

IgE is the antibody isotype found at the lowest concentration in the circulation. However IgE can undeniably play an important role in mediating allergic reactions; best exemplified by the clinical benefits of anti-IgE monoclonal antibody (omalizumab) therapy for some allergic diseases. This review will describe our current understanding of the interactions between IgE and its main receptors FcεRI and CD23 (FcεRII). We will review the known and potential functions of IgE in health and disease: in particular, its detrimental roles in allergic diseases and chronic spontaneous urticaria, and its protective functions in host defense against parasites and venoms. Finally, we will present an overview of the drugs that are in clinical development or have therapeutic potential for IgE-mediated allergic diseases.

Experimental Models for Studying Food Allergy

Immunoglobulin E-mediated food allergy is rapidly developing into a global health problem. Publicly available therapeutic intervention strategies are currently restricted to allergen avoidance and emergency treatments. To gain a better understanding of the disease pathophysiology so that new therapies can be developed, major research efforts have been put into studying food allergy in mice. Animal models should reflect the human pathology as closely as possible to allow for a rapid translation of basic science observations to the bedside. In this regard, experimental models of food allergy provide significant challenges for research because of discrepancies between the presentation of disease in humans and mice. The goal of this review is to give a summary of commonly used murine disease models and to discuss how they relate to the human condition. We will focus on epicutaneous sensitization models, on mouse strains that sensitize spontaneously to food as seen in humans, and on models in humanized animals. In summary, expanding the research toolbox of experimental food allergy provides an important step toward closing gaps in our understanding of the derailing immune mechanism that underlies the human disease. The availability of additional experimental models will provide exciting opportunities to discover new intervention points for the treatment of food allergies. (Cell Mol Gastroenterol Hepatol 2018;x:x).

Innate and adaptive type 2 immunity in lung allergic inflammation

Allergic inflammation is a type 2 immune disorder classically characterized by high levels of immunoglobulin E (IgE) and the development of Th2 cells. Asthma is a pulmonary allergic inflammatory disease resulting in bronchial hyper-reactivity. Atopic asthma is defined by IgE antibody-mediated mast cell degranulation, while in non-atopic asthma there is no allergen-specific IgE and more involvement of innate immune cells, such as basophils, group 2 innate lymphoid cells (ILC2), and eosinophils. Recently, protease allergens were shown to cause asthmatic responses in the absence of Th2 cells, suggesting that an innate cell network (IL-33/TSLP-basophil-ILC2-IL-5/IL-13 axis) can facilitate the sensitization phase of type 2 inflammatory responses. Recent evidence also indicates that in the chronic phase, these innate immune cells directly or indirectly contribute to the adaptive Th2 cell responses. In this review, we discuss the role of Th2 cytokines (IL-4 and IL-13) and innate immune cells (mast cells, basophils, ILC2s, and dendritic cells) in the cross-talk between innate and adaptive inflammatory responses.

Shuang-Huang-Lian injection induces an immediate hypersensitivity reaction via C5a but not IgE

Among traditional Chinese medicine injections, intravenous Shuang-Huang-Lian (IV-SHL) has the highest incidence of injection-induced immediate hypersensitivity reactions (IHRs). The precise mechanisms of IV-SHL-induced IHRs remain ambiguous. In this study, we investigated the mechanisms of SHL injection (SHLI)-induced IHRs. Our data showed that serum total IgE and mouse mast cell protease 1 (MMCP1) levels were higher in the SHLI antiserum; however, these effects of SHLI disappeared in the antibiotic-treated mice. SHLI caused intraplantar vasopermeability and shock during the first local or systemic injection. SHLI-induced nonallergic IHRs were attributed to its intermediate fraction F2 (the extract of Lonicerae Japonicae Flos and Fructus forsythiae), and could be blocked by antagonists for histamine or C5a, rather than PAF or C3a. Eight constituents of F2 were able to directly activate C5 to promote local vasopermeability at the mg/mL level. In conclusion, SHLI-induced IHRs are not mediated by IgE. SHLI or its F2 can directly activate blood C5. Subsequently, C5a is likely to provoke histamine release from its effector cells (e.g., mast cells and basophils), indicating that histamine is a principal effector of IHRs induced by SHLI.

IgE promotes type 2 innate lymphoid cells in murine food allergy

BACKGROUND

Mast cells serve an important sentinel function at mucosal barriers and have been implicated as key early inducers of type 2 immune responses in food allergy. The generation of Th2 and IgE following food allergen ingestion is inhibited in the absence of mast cells. Group 2 innate lymphoid cells are also thought to play an important early role in nascent allergic responses.

OBJECTIVE

To test whether IgE-mediated mast cell activation promotes intestinal ILC2 responses following ingestion of food allergens and whether ILC2 amplify food allergy.

METHODS

Two different mouse models of food allergy, one using intraperitoneally ovalbumin (OVA)-primed BALB/c animals and the other using enterally peanut-sensitized inherently atopic IL4raF709 mice, were applied to test the contributions of IgE antibodies and mast cells to ILC2 responses. The effect of ILC2 on mast cell activation and on anaphylaxis was tested.

RESULTS

ILC2 responses were significantly impaired in both models of food allergy in Igh7^-/- mice harbouring a targeted deletion of the gene encoding IgE. A similar reduction in food allergen-induced ILC2 was observed in mast cell-deficient Il4raF709 Kit^W-sh mice, and this was partially corrected by reconstituting these animals using cultured bone marrow mast cells. Mast cells activated ILC2 for IL-13 production in an IL-4Rα-dependent manner. Activated ILC2 amplified systemic anaphylaxis by increasing target tissue sensitivity to mast cell mediators.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings support an important role for IgE-activated mast cells in driving intestinal ILC2 expansion in food allergy and reveal that ILC2, in turn, can enhance responsiveness to the mediators of anaphylaxis produced by mast cells. Strategies designed to inhibit IgE signalling or mast cell activation are likely to inhibit both type 2 immunity and immediate hypersensitivity in food allergy.

Food allergy

Food allergies manifest in a variety of clinical conditions within the gastrointestinal tract, skin and lungs, with the most dramatic and sometimes fatal manifestation being anaphylactic shock. Major progress has been made in basic, translational and clinical research, leading to a better understanding of the underlying immunological mechanisms that lead to the breakdown of clinical and immunological tolerance against food antigens, which can result in either immunoglobulin E (IgE)-mediated reactions or non-IgE-mediated reactions. Lifestyle factors, dietary habits and maternal-neonatal interactions play a pivotal part in triggering the onset of food allergies, including qualitative and quantitative composition of the microbiota. These factors seem to have the greatest influence early in life, an observation that has led to the generation of hypotheses to explain the food allergy epidemic, including the dual-allergen exposure hypothesis. These hypotheses have fuelled research in preventive strategies that seek to establish desensitization to allergens and/or tolerance to allergens in affected individuals. Allergen-nonspecific therapeutic strategies have also been investigated in a number of clinical trials, which will eventually improve the treatment options for patients with food allergy.

Animal models of asthma: utility and limitations

Clinical studies in asthma are not able to clear up all aspects of disease pathophysiology. Animal models have been developed to better understand these mechanisms and to evaluate both safety and efficacy of therapies before starting clinical trials. Several species of animals have been used in experimental models of asthma, such as Drosophila, rats, guinea pigs, cats, dogs, pigs, primates and equines. However, the most common species studied in the last two decades is mice, particularly BALB/c. Animal models of asthma try to mimic the pathophysiology of human disease. They classically include two phases: sensitization and challenge. Sensitization is traditionally performed by intraperitoneal and subcutaneous routes, but intranasal instillation of allergens has been increasingly used because human asthma is induced by inhalation of allergens. Challenges with allergens are performed through aerosol, intranasal or intratracheal instillation. However, few studies have compared different routes of sensitization and challenge. The causative allergen is another important issue in developing a good animal model. Despite being more traditional and leading to intense inflammation, ovalbumin has been replaced by aeroallergens, such as house dust mites, to use the allergens that cause human disease. Finally, researchers should define outcomes to be evaluated, such as serum-specific antibodies, airway hyperresponsiveness, inflammation and remodeling. The present review analyzes the animal models of asthma, assessing differences between species, allergens and routes of allergen administration.

The pathophysiology of anaphylaxis

Anaphylaxis is a severe systemic hypersensitivity reaction that is rapid in onset; characterized by life-threatening airway, breathing, and/or circulatory problems; and usually associated with skin and mucosal changes. Because it can be triggered in some persons by minute amounts of antigen (eg, certain foods or single insect stings), anaphylaxis can be considered the most aberrant example of an imbalance between the cost and benefit of an immune response. This review will describe current understanding of the immunopathogenesis and pathophysiology of anaphylaxis, focusing on the roles of IgE and IgG antibodies, immune effector cells, and mediators thought to contribute to examples of the disorder. Evidence from studies of anaphylaxis in human subjects will be discussed, as well as insights gained from analyses of animal models, including mice genetically deficient in the antibodies, antibody receptors, effector cells, or mediators implicated in anaphylaxis and mice that have been "humanized" for some of these elements. We also review possible host factors that might influence the occurrence or severity of anaphylaxis. Finally, we will speculate about anaphylaxis from an evolutionary perspective and argue that, in the context of severe envenomation by arthropods or reptiles, anaphylaxis might even provide a survival advantage.

Increased malignancy incidence in IgE deficient patients not due to concomitant Common Variable Immunodeficiency

BACKGROUND

Immunoglobulin E (IgE) deficiency (<2.5 kU/L) has unclear clinical significance. Very little is known about the clinical characteristics of IgE deficiency in patients with Common Variable Immunodeficiency (CVID).

OBJECTIVE

To evaluate the clinical and laboratory differences between patients with IgE deficiency and those with non-IgE deficiency with and without CVID diagnosis.

METHODS

This is a retrospective study of adult patients who had total serum IgE levels measured at our facility from 2010 through 2015. Patients with IgE levels lower than 2.5 kU/L composed the IgE deficiency group. We used Clinical Looking Glass software to identify laboratory results and comorbid conditions including CVID and malignancy.

RESULTS

The IgE levels were measured in 2,339 patients and 63 (2.7%) had IgE deficiency. Of those with IgE deficiency, 14 of 63 (22%) had CVID diagnosis compared with only 62 of 2,276 patients (2.7%) with non-IgE deficiency and CVID. A significantly higher rate of prior malignancy was found in patients with IgE deficiency (21 of 63, 33%) compared with those with non-IgE deficiency (197 of 2,276, 8.7%; P = .001; odds ratio 5.51, 95% confidence interval 3.07-9.88). Six of 14 patients with CVID and IgE deficiency (43%) had a prior malignancy diagnosis compared with 8 of 62 patients (13%) with CVID and non-IgE deficiency (P = .009; odds ratio 10.65, 95% confidence interval 1.79-63.19). In addition to the higher rate of malignancy, patients with CVID and IgE deficiency did not have more severe disease than those with CVID and non-IgE deficiency.

CONCLUSION

The rate of prior malignancy is significantly higher in patients with IgE deficiency than in those without IgE deficiency. Similarly, patients with CVID and IgE deficiency have a higher frequency of prior malignancy than those with CVID and non-IgE deficiency. However, patients with IgE deficiency have higher frequency of malignancy than patients with normal IgE levels even in the absence of CVID.

Identification of IgE and IgG1 specific antigens in Echinococcus granulosus cyst fluid

Cystic echinococcosis (CE) is an anthropozoonotic disease with worldwide distribution and is caused by the cestode Echinococcus granulosus. Anaphylactic shock induced by CE rupture is a serious complication especially in patients with hydatid infections, as the resulting leakage of fluid contains highly toxic endogenous antigen. We aimed to isolate and identify the antigens of specific IgE and IgG1 (sIgE and sIgG1) in E. granulosus cyst fluid (EgCF). Crude antigen for EgCF was prepared from E. granulosus-infected sheep liver. Antigens were separated and identified by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1D SDS-PAGE), two-dimensional gel electrophoresis (2-DE), and immunoblotting. Results of 1D SDS-PAGE and immunoblotting showed that 40.5 kDa protein was the major antigen of sIgE, and 35.5 kDa protein was the major antigen of sIgG1 in EgCF. Results of 2-DE and immunoblotting showed that main antigens of sIgE in EgCF were four proteins with pI values ranging from 6.5 to 9.0 and a molecular weight of 40.5 kDa. Main antigens of sIgG1 in EgCF were five proteins with pI values ranging from 6.5 to 9.0 and a molecular weight of 35.5 kDa. The antigens identified for sIgE and sIgG1 can provide critical insights into cellular and molecular mechanisms underlying anaphylactic shock induced by CE.

Anti-FcγRIIB mAb suppresses murine IgG-dependent anaphylaxis by Fc domain targeting of FcγRIII

BACKGROUND

The inhibitory receptor FcγRIIB is expressed on human and murine bone marrow-derived cells and limits inflammation by suppressing signaling through stimulatory receptors.

OBJECTIVE

We sought to evaluate the effects of K9.361, a mouse IgG_2a alloantibody to mouse FcγRIIB, on murine anaphylaxis.

METHODS

Wild-type and FcγR-deficient mice were used to study anaphylaxis, which was induced by injection of 2.4G2 (rat IgG_2b mAb that binds both FcγRIIB and the stimulatory receptor FcγRIII), by actively immunizing IgE-deficient mice and then challenging with the immunizing antigen, and by passive immunization with IgG or IgE anti-2,4,6-trinitrophenyl mAb, followed by injection of 2,4,6-trinitrophenyl-ovalbumin. Pretreatment with K9.361 was assessed for its ability to influence anaphylaxis.

RESULTS

Unexpectedly, K9.361 injection induced mild anaphylaxis, which was both FcγRIIB and FcγRIII dependent and greatly enhanced by β-adrenergic blockade. K9.361 injection also decreased expression of stimulatory Fcγ receptors, especially FcγRIII, and strongly suppressed IgG-mediated anaphylaxis without strongly affecting IgE-mediated anaphylaxis. The F(ab')₂ fragment of K9.361 did not induce anaphylaxis, even after β-adrenergic blockade, and did not deplete FcγRIII or suppress IgG-mediated anaphylaxis but prevented intact K9.361-induced anaphylaxis without diminishing intact K9.36 suppression of IgG-mediated anaphylaxis.

CONCLUSION

Cross-linking FcγRIIB to stimulatory FcγRs through the Fc domains of an anti-FcγRIIB mAb induces and then suppresses IgG-mediated anaphylaxis without affecting IgE-mediated anaphylaxis. Because IgG- and IgE-mediated anaphylaxis can be mediated by the same cell types, this suggests that desensitization acts at the receptor rather than cellular level. Sequential treatment with the F(ab')₂ fragment of anti-FcγRIIB mAb followed by intact anti-FcγRIIB safely prevents IgG-mediated anaphylaxis.

Differences in the Importance of Mast Cells, Basophils, IgE, and IgG versus That of CD4+ T Cells and ILC2 Cells in Primary and Secondary Immunity to Strongyloides venezuelensis

There is evidence that mast cells, basophils, and IgE can contribute to immune responses to parasites; however, the relative levels of importance of these effector elements in parasite immunity are not fully understood. Previous work in Il3-deficient and c-kit mutant Kit^W/W-v mice indicated that interleukin-3 and c-Kit contribute to expulsion of the intestinal nematode Strongyloides venezuelensis during primary infection. Our findings in mast cell-deficient Kit^W-sh/W-sh mice and two types of mast cell-deficient mice that have normal c-kit ("Hello Kitty" and MasTRECK mice) confirmed prior work in Kit^W/W-v mice that suggested that mast cells play an important role in S. venezuelensis egg clearance in primary infections. We also assessed a possible contribution of basophils in immune responses to S. venezuelensis By immunohistochemistry, we found that numbers of basophils and mast cells were markedly increased in the jejunal mucosa during primary infections with S. venezuelensis Studies in basophil-deficient Mcpt8^DTR mice revealed a small but significant contribution of basophils to S. venezuelensis egg clearance in primary infections. Studies in mice deficient in various components of immune responses showed that CD4⁺ T cells and ILC2 cells, IgG, FcRγ, and, to a lesser extent, IgE and FcεRI contribute to effective immunity in primary S. venezuelensis infections. These findings support the conclusion that the hierarchy of importance of immune effector mechanisms in primary S. venezuelensis infection is as follows: CD4⁺ T cells/ILC2 cells, IgG, and FcRγ>mast cells>IgE and FcεRI>basophils. In contrast, in secondary S. venezuelensis infection, our evidence indicates that the presence of CD4⁺ T cells is of critical importance but mast cells, antibodies, and basophils have few or no nonredundant roles.

Lifelong memory responses perpetuate humoral TH2 immunity and anaphylaxis in food allergy

BACKGROUND

A number of food allergies (eg, fish, shellfish, and nuts) are lifelong, without any disease-transforming therapies, and unclear in their underlying immunology. Clinical manifestations of food allergy are largely mediated by IgE. Although persistent IgE titers have been attributed conventionally to long-lived IgE⁺ plasma cells (PCs), this has not been directly and comprehensively tested.

OBJECTIVE

We sought to evaluate mechanisms underlying persistent IgE and allergic responses to food allergens.

METHODS

We used a model of peanut allergy and anaphylaxis, various knockout mice, adoptive transfer experiments, and in vitro assays to identify mechanisms underlying persistent IgE humoral immunity over almost the entire lifespan of the mouse (18-20 months).

RESULTS

Contrary to conventional paradigms, our data show that clinically relevant lifelong IgE titers are not sustained by long-lived IgE⁺ PCs. Instead, lifelong reactivity is conferred by allergen-specific long-lived memory B cells that replenish the IgE⁺ PC compartment. B-cell reactivation requires allergen re-exposure and IL-4 production by CD4 T cells. We define the half-lives of antigen-specific germinal centers (23.3 days), IgE⁺ and IgG₁⁺ PCs (60 and 234.4 days, respectively), and clinically relevant cell-bound IgE (67.3 days).

CONCLUSIONS

These findings can explain lifelong food allergies observed in human subjects as the consequence of allergen exposures that recurrently activate memory B cells and identify these as a therapeutic target with disease-transforming potential.

Pathways of immediate hypothermia and leukocyte infiltration in an adjuvant-free mouse model of anaphylaxis

BACKGROUND

Conflicting results have been obtained regarding the roles of Fc receptors and effector cells in models of active systemic anaphylaxis (ASA). In part, this might reflect the choice of adjuvant used during sensitization because various adjuvants might differentially influence the production of particular antibody isotypes.

OBJECTIVE

We developed an "adjuvant-free" mouse model of ASA and assessed the contributions of components of the "classical" and "alternative" pathways in this model.

METHODS

Mice were sensitized intraperitoneally with ovalbumin at weekly intervals for 6 weeks and challenged intraperitoneally with ovalbumin 2 weeks later.

RESULTS

Wild-type animals had immediate hypothermia and late-phase intraperitoneal inflammation in this model. These features were reduced in mice lacking the IgE receptor FcεRI, the IgG receptor FcγRIII or the common γ-chain FcRγ. FcγRIV blockade resulted in a partial reduction of inflammation without any effect on hypothermia. Depletion of monocytes/macrophages with clodronate liposomes significantly reduced the hypothermia response. By contrast, depletion of neutrophils or basophils had no significant effects in this ASA model. Both the hypothermia and inflammation were dependent on platelet-activating factor and histamine and were reduced in 2 types of mast cell (MC)-deficient mice. Finally, engraftment of MC-deficient mice with bone marrow-derived cultured MCs significantly exacerbated the hypothermia response and restored inflammation to levels similar to those observed in wild-type mice.

CONCLUSION

Components of the classical and alternative pathways contribute to anaphylaxis in this adjuvant-free model, with key roles for MCs and monocytes/macrophages.

IL-4 Haploinsufficiency Specifically Impairs IgE Responses against Allergens in Mice

Polymorphisms in genes involved in IL-4 responses segregate with allergic disease risk and correlate with IgE levels in humans, and IL-4 promotes IgE and IgG1 Ab production against allergens in mice. We report that mice with only one intact Il4 gene copy are significantly impaired in their ability to make specific IgE responses against allergens, whereas IgG1 responses to allergens remain unaffected. Il4-hemizygosity also resulted in a modest but detectable drop in IL-4 production by CD4⁺ T cells isolated from lymph nodes and prevented IgE-dependent oral allergen-induced diarrhea. We conclude that a state of haploinsufficiency for the Il4 gene locus is specifically relevant for IL-4-dependent IgE responses to allergens with the amount of IL-4 produced in the hemizygous condition falling close to the threshold required for switching to IgE production. These results may be relevant for how polymorphisms in genes affecting IL-4 responses influence the risk of IgE-mediated allergic disease in humans.

Mechanisms of anaphylaxis in human low-affinity IgG receptor locus knock-in mice

BACKGROUND

Anaphylaxis can proceed through distinct IgE- or IgG-dependent pathways, which have been investigated in various mouse models. We developed a novel mouse strain in which the human low-affinity IgG receptor locus, comprising both activating (hFcγRIIA, hFcγRIIIA, and hFcγRIIIB) and inhibitory (hFcγRIIB) hFcγR genes, has been inserted into the equivalent murine locus, corresponding to a locus swap.

OBJECTIVE

We sought to determine the capabilities of hFcγRs to induce systemic anaphylaxis and identify the cell types and mediators involved.

METHODS

hFcγR expression on mouse and human cells was compared to validate the model. Passive systemic anaphylaxis was induced by injection of heat-aggregated human intravenous immunoglobulin and active systemic anaphylaxis after immunization and challenge. Anaphylaxis severity was evaluated based on hypothermia and mortality. The contribution of receptors, mediators, or cell types was assessed based on receptor blockade or depletion.

RESULTS

The human-to-mouse low-affinity FcγR locus swap engendered hFcγRIIA/IIB/IIIA/IIIB expression in mice comparable with that seen in human subjects. Knock-in mice were susceptible to passive and active anaphylaxis, accompanied by downregulation of both activating and inhibitory hFcγR expression on specific myeloid cells. The contribution of hFcγRIIA was predominant. Depletion of neutrophils protected against hypothermia and mortality. Basophils contributed to a lesser extent. Anaphylaxis was inhibited by platelet-activating factor receptor or histamine receptor 1 blockade.

CONCLUSION

Low-affinity FcγR locus-switched mice represent an unprecedented model of cognate hFcγR expression. Importantly, IgG-related anaphylaxis proceeds within a native context of activating and inhibitory hFcγRs, indicating that, despite robust hFcγRIIB expression, activating signals can dominate to initiate a severe anaphylactic reaction.

The Mast Cell-IgE Paradox: From Homeostasis to Anaphylaxis

Mast cells and IgE are so inextricably linked to the pathology of allergic disorders, including fatal anaphylaxis, that it can be difficult to think of them in other contexts. Surely, we do not have mast cells and IgE so that we can eat a peanut and die! It is thought that mast cells and IgE and basophils (circulating granulocytes, whose functions partially overlap with those of mast cells) can contribute to host defense as components of adaptive T helper cell type 2 immune responses to helminths, ticks, and certain other parasites. Accordingly, it was suggested that allergies are misdirected type 2 immune responses in which IgE antibodies are produced against any of a broad variety of apparently harmless antigens. However, components of animal venoms also can sensitize individuals to develop severe IgE-associated allergic reactions, including fatal anaphylaxis, on subsequent venom exposure. Here, I describe evidence that mast cells can enhance innate host resistance to reptile or arthropod venoms during responses to an initial exposure to such venoms and that acquired type 2 immune responses, IgE antibodies, the high-affinity IgE receptor FcεRI, and mast cells can contribute toward acquired resistance in mice to the lethal effects of honeybee or Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against noxious substances.

Human IgE-independent systemic anaphylaxis

Anaphylaxis is a rapidly developing, life-threatening, generalized or systemic allergic reaction that is classically elicited by antigen crosslinking of antigen-specific IgE bound to the high-affinity IgE receptor FcεRI on mast cells and basophils. This initiates signals that induce cellular degranulation with release and secretion of vasoactive mediators, enzymes, and cytokines. However, IgE-independent mechanisms of anaphylaxis have been clearly demonstrated in experimental animals. These include IgG-dependent anaphylaxis, which involves the triggering of mediator release by IgG/antigen complex crosslinking of FcγRs on macrophages, basophils, and neutrophils; anaphylaxis mediated by binding of the complement-derived peptides C3a and C5a to their receptors on mast cells, basophils, and other myeloid cells; and direct activation of mast cells by drugs that interact with receptors on these cells. Here we review the mechanisms involved in these IgE-independent forms of anaphylaxis and the clinical evidence for their human relevance. We conclude that this evidence supports the existence of all 3 IgE-independent mechanisms as important causes of human disease, although practical and ethical considerations preclude their demonstration to the degree of certainty possible with animal models. Furthermore, we cite evidence that different clinical situations can suggest different mechanisms as having a primal role in anaphylaxis and that IgE-dependent and distinct IgE-independent mechanisms can act together to increase anaphylaxis severity. As specific agents become available that can interfere with mechanisms involved in the different types of anaphylaxis, recognition of specific types of anaphylaxis is likely to become important for optimal prophylaxis and therapy.

Local IgE in non-allergic rhinitis

Local allergic rhinitis (LAR) is characterized by the presence of a nasal Th2 inflammatory response with local production of specific IgE antibodies and a positive response to a nasal allergen provocation test (NAPT) without evidence of systemic atopy. The prevalence has been shown to be up to 25% in subjects affected with rhinitis with persistence, comorbidity and evolution similar to allergic rhinitis. LAR is a consistent entity that does not evolve to allergic rhinitis with systemic atopy over time although patients have significant impairment in quality of life and increase in the severity of nasal symptoms over time. Lower airways can be also involved. The diagnosis of LAR is based mostly on demonstration of positive response to NAPT and/or local synthesis of specific IgE. Allergens involved include seasonal or perennial such as house dusts mites, pollens, animal epithelia, moulds (alternaria) and others. Basophils from peripheral blood may be activated by the involved allergens suggesting the spill over of locally synthesized specific IgE to the circulation. LAR patients will benefit from the same treatment as allergic patients using antihistamines, inhaled corticosteroids and IgE antagonists. Studies on immunotherapy are ongoing and will determine its efficacy in LAR in terms of symptoms improvement and evolution of the natural course of the disease.

Mast cells and IgE in defense against venoms: Possible "good side" of allergy?

Physicians think of mast cells and IgE primarily in the context of allergic disorders, including fatal anaphylaxis. This 'bad side' of mast cells and IgE is so well accepted that it can be difficult to think of them in other contexts, particularly those in which they may have beneficial functions. However, there is evidence that mast cells and IgE, as well as basophils (circulating granulocytes whose functions partially overlap with those of mast cells), can contribute to host defense as components of adaptive type 2 immune responses to helminths, ticks and certain other parasites. Accordingly, allergies often are conceptualized as "misdirected" type 2 immune responses, in which IgE antibodies are produced against any of a diverse group of apparently harmless antigens, as well as against components of animal venoms. Indeed, certain unfortunate patients who have become sensitized to venoms develop severe IgE-associated allergic reactions, including fatal anaphylaxis, upon subsequent venom exposure. In this review, we will describe evidence that mast cells can enhance innate resistance to reptile or arthropod venoms during a first exposure to such venoms. We also will discuss findings indicating that, in mice which survive an initial encounter with venom, acquired type 2 immune responses, IgE antibodies, the high affinity IgE receptor (FcɛRI), and mast cells can contribute to acquired resistance to the lethal effects of both honeybee venom and Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against venoms and perhaps other noxious substances.

Innate myeloid cells under the control of adaptive immunity: the example of mast cells and basophils

Mast cells and basophils are mostly known as the initiators of IgE-dependent allergic reactions. They, however, contribute to innate immunity against pathogens and venoms. Like other myeloid cells, they also express receptors for the Fc portion of IgG antibodies. These include activating receptors and inhibitory receptors. Because IgG antibodies are produced in exceedingly higher amounts than IgE antibodies, IgG receptors are co-engaged with IgE receptors under physiological conditions. Mast cells and basophils are examples of the many innate myeloid cells whose effector functions are used and finely tuned by antibodies. They can be thus enrolled in a variety of adaptive immune responses, their activation can be regulated, positively and negatively and their biological responses can be modulated qualitatively by antibodies.

Pathophysiology of Food Allergy

Food allergy is a growing public health problem that is estimated to affect 4% to 8% of children and 5% of adults. In this review, we discuss our current understanding of the pathophysiology of food allergy, from oral tolerance, to sensitization, and lastly the elicitation of an allergic response. As much of the existing evidence for the mechanisms of food allergy is derived from animal models, we include these studies where relevant. In addition, whenever possible, we review similar evidence involved in human disease and provide applications for consideration in clinical practice.

Immunogenicity of infliximab and adalimumab: what is its role in hypersensitivity and modulation of therapeutic efficacy and safety?

INTRODUCTION

TNF-α inhibitors have demonstrated efficacy both as monotherapy and in combination with disease-modifying antirheumatic drugs (DMARDs) in the treatment of chronic inflammatory immune-mediated diseases such as rheumatoid arthritis, Crohn's disease, ankylosing spondylitis, psoriasis and/or psoriatic arthritis, and may be administered off-label to treat disseminated granuloma annulare systemic lupus erythematosus and systemic sclerosis. There are several TNF-α inhibitors available for clinical use including infliximab, adalimumab, golimumab, certolizumab pegol and etanercept.

AREAS COVERED

infliximab and adalimumab can induce the development of anti-infliximab (anti-IFX) and anti-adalimumab (anti-ADA) monoclonal antibodies (mAbs). In this review, we discuss the impact of anti-IFX and anti-ADA mAbs upon efficacy and safety of these biological agents.

EXPERT OPINION

IgG/IgE neutralizing antibodies against infliximab and adalimumab decrease the possibility of achieving a minimal disease activity state or clinical remission, decrease drug survival, increase the need for doctors to prescribe a higher drug dosage and, finally, favor the occurrence of adverse events. Concomitant administration of DMARDs such as methotrexate or leflunomide prevents the development of neutralizing Abs against infliximab and adalimumab.

The Extracellular Domains of IgG1 and T Cell-Derived IL-4/IL-13 Are Critical for the Polyclonal Memory IgE Response In Vivo

IgE-mediated activation of mast cells and basophils contributes to protective immunity against helminths but also causes allergic responses. The development and persistence of IgE responses are poorly understood, which is in part due to the low number of IgE-producing cells. Here, we used next generation sequencing to uncover a striking overlap between the IgE and IgG1 repertoires in helminth-infected or OVA/alum-immunized wild-type BALB/c mice. The memory IgE response after secondary infection induced a strong increase of IgE⁺ plasma cells in spleen and lymph nodes. In contrast, germinal center B cells did not increase during secondary infection. Unexpectedly, the memory IgE response was lost in mice where the extracellular part of IgG1 had been replaced with IgE sequences. Adoptive transfer studies revealed that IgG1⁺ B cells were required and sufficient to constitute the memory IgE response in recipient mice. T cell-derived IL-4/IL-13 was required for the memory IgE response but not for expansion of B cells from memory mice. Together, our results reveal a close relationship between the IgE and IgG1 repertoires in vivo and demonstrate that the memory IgE response is mainly conserved at the level of memory IgG1⁺ B cells. Therefore, targeting the generation and survival of allergen-specific IgG1⁺ B cells could lead to development of new therapeutic strategies to treat chronic allergic disorders.

This study reveals that repertoires of IgE—the class of antibody that mediates allergic reactions—closely resemble those of IgG1, suggesting that the memory IgE response unfolds from IgG1-switched B cells (and not from IgM-expressing B cells) in response to T cell-derived cytokines.

Allergic inflammation is initiated when IgE antibodies bind to high-affinity receptors on the cell surface of mast cells and basophils, thereby triggering the release of proinflammatory mediators. The development and persistence of IgE responses in vivo is poorly characterized because of the low number of IgE-producing B cells and plasma cells. Naïve mature B cells produce IgM antibodies. Upon activation, they “switch” class to produce IgG, IgA, or IgE antibodies. It is currently highly debated whether IgE-expressing B cells are generated by direct switching from IgM-expressing B cells or by sequential switching via IgG1-expressing B cells. Using next generation sequencing, we compared thousands of IgE, IgG1, and IgM sequences after immunization of mice with parasitic worms and found a striking overlap between the IgE and IgG1 repertoires. We further show that the memory IgE response to a secondary encounter with the same parasitic worms was dependent on T cell-derived cytokines. Genetically modified mice and adoptive transfers of B cells revealed that the memory IgE response is conserved at the level of IgG1-expressing B cells. These results favor the concept that bona fide IgE-expressing B cells do not exist, and memory IgE responses unfold from IgG1-expressing B cells, which undergo a secondary switch reaction and differentiation to plasma cells.

IgE antibodies, FcεRIα, and IgE-mediated local anaphylaxis can limit snake venom toxicity

BACKGROUND

Type 2 cytokine-related immune responses associated with development of antigen-specific IgE antibodies can contribute to pathology in patients with allergic diseases and to fatal anaphylaxis. However, recent findings in mice indicate that IgE also can enhance defense against honeybee venom.

OBJECTIVE

We tested whether IgE antibodies, IgE-dependent effector mechanisms, and a local anaphylactic reaction to an unrelated antigen can enhance defense against Russell viper venom (RVV) and determined whether such responses can be influenced by immunization protocol or mouse strain.

METHODS

We compared the resistance of RVV-immunized wild-type, IgE-deficient, and Fcer1a-deficient mice after injection of a potentially lethal dose of RVV.

RESULTS

A single prior exposure to RVV enhanced the ability of wild-type mice, but not mice lacking IgE or functional FcεRI, to survive challenge with a potentially lethal amount of RVV. Moreover, IgE-dependent local passive cutaneous anaphylaxis in response to challenge with an antigen not naturally present in RVV significantly enhanced resistance to the venom. Finally, we observed different effects on resistance to RVV or honeybee venom in BALB/c versus C57BL/6 mice that had received a second exposure to that venom before challenge with a high dose of that venom.

CONCLUSION

These observations illustrate the potential benefit of IgE-dependent effector mechanisms in acquired host defense against venoms. The extent to which type 2 immune responses against venoms can decrease pathology associated with envenomation seems to be influenced by the type of venom, the frequency of venom exposure, and the genetic background of the host.

Airway fibrinogenolysis and the initiation of allergic inflammation

The past 15 years of allergic disease research have produced extraordinary improvements in our understanding of the pathogenesis of airway allergic diseases such as asthma. Whereas it was previously viewed as largely an immunoglobulin E-mediated process, the gradual recognition that T cells, especially Type 2 T helper (Th2) cells and Th17 cells, play a major role in asthma and related afflictions has inspired clinical trials targeting cytokine-based inflammatory pathways that show great promise. What has yet to be clarified about the pathogenesis of allergic inflammatory disorders, however, are the fundamental initiating factors, both exogenous and endogenous, that drive and sustain B- and T-cell responses that underlie the expression of chronic disease. Here we review how proteinases derived from diverse sources drive allergic responses. A central discovery supporting the proteinase hypothesis of allergic disease pathophysiology is the role played by airway fibrinogen, which in part appears to serve as a sensor of unregulated proteinase activity and which, when cleaved, both participates in a novel allergic signaling pathway through Toll-like receptor 4 and forms fibrin clots that contribute to airway obstruction. Unresolved at present is the ultimate source of airway allergenic proteinases. From among many potential candidates, perhaps the most intriguing is the possibility such enzymes derive from airway fungi. Together, these new findings expand both our knowledge of allergic disease pathophysiology and options for therapeutic intervention.

Immunoglobulin E and Allergy: Antibodies in Immune Inflammation and Treatment

The pathogenic role of immunoglobulin E (IgE) antibodies in triggering and maintaining allergic inflammation in response to allergens is due to the binding of multivalent allergens to allergen-specific IgEs on sensitized effector cells. These interactions trigger effector cell activation, resulting in release of potent inflammatory mediators, recruitment of inflammatory cells, antigen presentation, and production of allergen-specific antibody responses. Since its discovery in the 1960s, the central role of IgE in allergic disease has been intensively studied, placing IgE and its functions at the heart of therapeutic efforts for the treatment of allergies. Here, we provide an overview of the nature, roles, and significance of IgE antibodies in allergic diseases, infections, and inflammation and the utility of antibodies as therapies. We place special emphasis on allergen-IgE-Fcε receptor complexes in the context of allergic and inflammatory diseases and describe strategies, including monoclonal antibodies, aimed at interrupting these complexes. Of clinical significance, one antibody, omalizumab, is presently in clinical use and works by preventing formation of IgE-Fcε receptor interactions. Active immunotherapy approaches with allergens and allergen derivatives have also demonstrated clinical benefits for patients with allergic diseases. These treatments are strongly associated with serum increases of IgE-neutralizing antibodies and feature a notable redirection of humoral responses towards production of antibodies of the IgG4 subclass in patients receiving immunotherapies. Lastly, we provide a new perspective on the rise of recombinant antibodies of the IgE class recognizing tumor-associated antigens, and we discuss the potential utility of tumor antigen-specific IgE antibodies to direct potent IgE-driven immune responses against tumors.

Disease associated cellular machinery in anaphylaxis - And the de novo paradigm shift

Anaphylaxis is a sudden immune reaction against an allergen that can potentially lead to Anaphylactic Shock (AS). This immune reaction is characterized by an increase in Immunoglobulin-E (IgE) type of antibodies that bind with FcεRI receptors on mast cells to release inflammatory mediators. Various intracellular signaling molecules downstream of IgE/ FcεRI axis play a potential role in cytokine, chemokine and eicosanoid secretion as well as degranulation of immune cells causing vasodilation, vascular permeability, and reduction of intravascular volume leading to cardiovascular collapse. Here, we discuss the cellular machinery of anaphylaxis and the de novo paradigm shift in the cellular aspects of AS.

Basophil-mediated protection against gastrointestinal helminths requires IgE-induced cytokine secretion

Basophils orchestrate protection against reinfections with gastrointestinal helminths and ticks, but the underlying mechanisms remain elusive. We investigated the role of Fc receptors on basophils, the antibody isotypes IgG1 and IgE, and basophil-derived IL-4/IL-13 during challenge infections with Heligmosomoides polygyrus and Nippostrongylus brasiliensis. Using mixed bone marrow chimeras, we found that activating Fc receptors on basophils were required for protective immunity but not for regulation of basophil homeostasis. Furthermore, rapid worm expulsion was impaired in IgE-deficient but not in IgG1-deficient mice. Basophils promoted the recruitment of other effector cells into the small intestine and induced expression of the antihelminthic proteins resistin-like molecule β and mucin 5ac. Selective deletion of IL-4/IL-13 in basophils resulted in impaired worm expulsion. Collectively, our results indicate that IgE-mediated activation of basophils and the release of basophil-derived IL-4/IL-13 are critical steps in protective immunity against helminths. Therefore, development of effective vaccines against helminths should consider boosting the IL-4/IgE/basophil axis of the immune system.

Immunoglobulin E plays an immunoregulatory role in lupus

The (patho)physiological role of IgE in nonallergic inflammatory diseases is not well understood. Here, we explored the effect of IgE deficiency on the inflammatory response in FcγRIIB-deficient mice as well as in mice carrying both a deletion of FcγRIIB and the chromosomal translocation of Y-linked autoimmune acceleration (Yaa) that hastens and results in a more aggressive lupuslike disease in these mice. The findings show that deficiency of IgE delays disease development and severity as demonstrated by reduced autoantibody production and amelioration of organ pathologies. This was associated with decreased numbers of plasma cells and reduced levels of IgG2b and IgG3. Unexpectedly, the loss of IgE also caused a striking decrease of immune cell infiltration in secondary lymphoid organs with a marked effect on the presence of dendritic cells, monocytes, neutrophils, and eosinophils in these organs and decreased activation of basophils. The presence of autoreactive IgE in human systemic lupus erythematosus subjects was also associated with increased basophil activation and enhanced disease activity. These findings argue that IgE facilitates the amplification of autoimmune inflammation.

Rethinking the role of immunoglobulin E and its high-affinity receptor: new insights into allergy and beyond

Immunoglobulin E (IgE) and its high-affinity receptor (FcεRI) are well-known participants in the allergic response. The interaction of allergens with FcεRI-bound IgE antibodies is an essential step in mast cell/basophil activation and the subsequent release of allergic mediators. It is known that the affinity of the interaction between an IgE antibody and an allergen may differ, raising the question of whether FcεRI can decipher these differences. If so, do the cellular and physiological outcomes vary? Are the molecular mechanisms initiated by FcεRI similarly under low- or high-affinity interactions? Could the resulting inflammatory response differ? Recent discoveries summarized herein are beginning to shed new light on these important questions. What we have learned from them is that IgE and FcεRI form a complex regulatory network influencing the inflammatory response in allergy and beyond.

Immunoglobulin E signal inhibition during allergen ingestion leads to reversal of established food allergy and induction of regulatory T cells

Immunoglobulin E (IgE) antibodies are known for triggering immediate hypersensitivity reactions such as food anaphylaxis. In this study, we tested whether they might additionally function to amplify nascent antibody and T helper 2 (Th2) cell-mediated responses to ingested proteins and whether blocking IgE would modify sensitization. By using mice harboring a disinhibited form of the IL-4 receptor, we developed an adjuvant-free model of peanut allergy. Mast cells and IgE were required for induction of antibody and Th2-cell-mediated responses to peanut ingestion and they impaired regulatory T (Treg) cell induction. Mast-cell-targeted genetic deletion of the FcεRI signaling kinase Syk or Syk blockade also prevented peanut sensitization. In mice with established allergy, Syk blockade facilitated desensitization and induction of Treg cells, which suppressed allergy when transferred to naive recipients. Our study suggests a key role for IgE in driving Th2 cell and IgE responses while suppressing Treg cells in food allergy.

IgG-mediated anaphylaxis to a synthetic long peptide vaccine containing a B cell epitope can be avoided by slow-release formulation

Synthetic long peptides (SLP) are a promising vaccine modality to induce therapeutic T cell responses in patients with chronic infections and tumors. We studied different vaccine formulations in mice using SLP derived from carcinoembryonic Ag. We discovered that one of the SLP contains a linear Ab epitope in combination with a CD4 epitope. Repeated vaccination with this carcinoembryonic Ag SLP in mice shows improved T cell responses and simultaneously induced high titers of peptide-specific Abs. These Abs resulted in unexpected anaphylaxis after a third or subsequent vaccinations with the SLP when formulated in saline. Administration of low SLP doses in the slow-release vehicle IFA prevented the anaphylaxis after repeated vaccination. This study underscores both the immunogenicity of SLP vaccination, for inducing T cell as well as B cell responses, and the necessity of safe administration routes.

An IgE receptor mimetic peptide (PepE) protects mice from IgE mediated anaphylaxis

Crosslinking of receptor-bound Immunoglobulin E (IgE) triggers immediate hypersensitivity reactions including anaphylaxis. Blocking the interaction of IgE with its high-affinity receptor, FcεRI, on mast cells and basophils is an attractive strategy for the treatment of allergies. This approach has seen clinical success using the anti-IgE monoclonal antibody, omalizumab. We recently designed and characterized a novel FcεRI-mimetic peptide (PepE) which contains the two key FcεRI α-chain receptor loops known to interact with the ε-heavy chain of IgE, C'-E and B-C, with an optimized linker for joining them. PepE has high specificity and affinity for IgE, blocks IgE binding to FcεRI and prevents IgE-induced mediator release from RBL2H3 cells. We have now investigated the biological effects of this peptide in vivo using a line of mice (BALB/c Il4raF709) very sensitive to IgE-mediated systemic anaphylaxis. IgE-deficient (IgE-/-) Il4raF709 mice were passively sensitized with the anti-DNP IgE monoclonal antibody (SPE-7) and subsequently challenged i.v. with DNP-BSA. Mice receiving a single dose of PepE prior to sensitization with SPE-7 IgE were fully protected from anaphylaxis while vehicle control-treated mice displayed strong reactions with significant core body temperature drops and elevated levels of mouse mast cell protease-1 (mMCP-1) in the serum. However, PepE had no effect on IgE-mediated anaphylaxis if given after IgE administration in IgE-/- mice, suggesting that PepE can block binding of free IgE to FcεRI but cannot compete with the receptor for already bound IgE in vivo. A single dose of PepE treatment did not protect IgE sufficient mice from IgE mediated anaphylaxis. However, a 3 week long course of PepE treatment protected IgE sufficient Il4raF709 mice from body temperature drops and elevation of serum mMCP-1. Our findings establish the potential of this type of structure for blocking IgE binding to mast cells in vivo and suggest that related peptides might have the potential to attenuate clinical allergic reactions.

Lymphocyte-based model systems for allergy research: a historic overview

During the last decades, a multitude of studies applying distinct in vitro and in vivo model systems have contributed greatly to our better understanding of the initiation and regulation of inflammatory processes leading to allergic diseases. Over the years, it has become evident that among lymphocytes, not only IgE-producing B cells and allergy-orchestrating CD4(+) helper cells but also cytotoxic CD8(+) T cells, γδ-T cells and innate lymphoid cells, as well as regulatory lymphocytes, might critically shape the immune response towards usually innocuous allergens. In this review, we provide a historic overview of pioneering work leading to the establishment of important lymphocyte-based model systems for allergy research. Moreover, we contrast the original findings with our currently more refined knowledge to appreciate the actual validity of the respective models and to reassess the conclusions obtained from them. Conflicting studies and interpretations are identified and discussed. The tables are intended to provide an easy overview of the field not only for scientists newly entering the field but also for the broader readership interested in updating their knowledge. Along those lines, herein we discuss in vitro and in vivo approaches to the investigation of lymphocyte effector cell activation, polarization and regulation, and describe depletion and adoptive transfer models along with gene knockout and transgenic (tg) methodologies. In addition, novel attempts to establish humanized T cell antigen receptor tg mouse models for allergy research are described and discussed.

Anaphylaxis caused by repetitive doses of a GITR agonist monoclonal antibody in mice

Immunotherapy for cancer using antibodies to enhance T-cell function has been successful in recent clinical trials. Many molecules that improve activation and effector function of T cells have been investigated as potential new targets for immunomodulatory antibodies, including the tumor necrosis factor receptor superfamily members GITR and OX40. Antibodies engaging GITR or OX40 result in significant tumor protection in preclinical models. In this study, we observed that the GITR agonist antibody DTA-1 causes anaphylaxis in mice upon repeated intraperitoneal dosing. DTA-1-induced anaphylaxis requires GITR, CD4(+) T cells, B cells, and interleukin-4. Transfer of serum antibodies from DTA-1-treated mice, which contain high levels of DTA-1-specific immunoglobulin G1 (IgG1), can induce anaphylaxis in naive mice upon administration of an additional dose of DTA-1, suggesting that anaphylaxis results from anti-DTA-1 antibodies. Depletion of basophils and blockade of platelet-activating factor, the key components of the IgG1 pathway of anaphylaxis, rescues the mice from DTA-1-induced anaphylaxis. These results demonstrate a previously undescribed lethal side effect of repetitive doses of an agonist immunomodulatory antibody as well as insight into the mechanism of toxicity, which may offer a means of preventing adverse effects in future clinical trials using anti-GITR or other agonist antibodies as immunotherapies.

Antigen-specific human monoclonal antibodies from transgenic mice

Due to the difficulties found when generating fully human monoclonal antibodies (mAbs) by the traditional method, several efforts have attempted to overcome these problems, with varying levels of success. One approach has been the development of transgenic mice carrying immunoglobulin (Ig) genes in germ line configuration. The engineered mouse genome can undergo productive rearrangement in the B cell population, with the generation of mouse B lymphocytes expressing human Ig (hIg) chains. To avoid the expression of mouse heavy or light chains, the endogenous mouse Ig (mIg) loci must be silenced by gene-targeting techniques. Subsequently, to obtain antigen-specific mAbs, conventional immunization protocols can be followed and the mAb technique used (fusion of activated B cells with mouse myeloma cells, screening, cloning, freezing, and testing) with these animals expressing human Ig genes. This chapter describes the type of transgenic knockout mice generated for various research groups, provides examples of human mAbs developed by research groups and companies, and includes protocols of immunization, generation, production, and purification of human mAbs from such mice. In addition, it also addresses the problems detected, and includes some of the methods that can be used to analyze functional activities with human mAbs.

Anaphylaxis: opportunities of stratified medicine for diagnosis and risk assessment

The risk to develop anaphylaxis depends on the sensitization pattern, the proportion of the involved immunoglobulin classes, the avidity and affinity of immunoglobulins to bind an allergen, characteristics of the allergen, the route of allergen application, and, last but not least, the presence of cofactors of anaphylaxis. To be able to calculate the risk to develop anaphylaxis and to anticipate the severity of the reactions under certain conditions, it is necessary to understand how all these factors interact with each other. Important progress for risk assessment in anaphylaxis is based on component-resolved stratified diagnostics, which allow to (i) determine a patient's sensitization pattern on a molecular basis, (ii) correlate clinical responses to defined sensitization patterns, and (iii) better identify cross-reactive allergens. Together with the increasing knowledge regarding the role and mode of action of cofactors of anaphylaxis, these data pave the way to unscramble the complex interactions determining the clinical relevance of sensitizations, the risk of anaphylaxis, and the severity of reactions. As a consequence, this understanding allows to better determine the individual risk in response to an identified allergen and results in more specific advices and education for our patients to prevent further life-threatening anaphylactic reactions.

A beneficial role for immunoglobulin E in host defense against honeybee venom

Allergies are widely considered to be misdirected type 2 immune responses, in which immunoglobulin E (IgE) antibodies are produced against any of a broad range of seemingly harmless antigens. However, components of insect venoms also can sensitize individuals to develop severe IgE-associated allergic reactions, including fatal anaphylaxis, upon subsequent venom exposure. We found that mice injected with amounts of honeybee venom similar to that which could be delivered in one or two stings developed a specific type 2 immune response that increased their resistance to subsequent challenge with potentially lethal amounts of the venom. Our data indicate that IgE antibodies and the high affinity IgE receptor, FcεRI, were essential for such acquired resistance to honeybee venom. The evidence that IgE-dependent immune responses against venom can enhance survival in mice supports the hypothesis that IgE, which also contributes to allergic disorders, has an important function in protection of the host against noxious substances.

Antibodies trap tissue migrating helminth larvae and prevent tissue damage by driving IL-4Rα-independent alternative differentiation of macrophages

Approximately one-third of the world's population suffers from chronic helminth infections with no effective vaccines currently available. Antibodies and alternatively activated macrophages (AAM) form crucial components of protective immunity against challenge infections with intestinal helminths. However, the mechanisms by which antibodies target these large multi-cellular parasites remain obscure. Alternative activation of macrophages during helminth infection has been linked to signaling through the IL-4 receptor alpha chain (IL-4Rα), but the potential effects of antibodies on macrophage differentiation have not been explored. We demonstrate that helminth-specific antibodies induce the rapid trapping of tissue migrating helminth larvae and prevent tissue necrosis following challenge infection with the natural murine parasite Heligmosomoides polygyrus bakeri (Hp). Mice lacking antibodies (J_H^−/−) or activating Fc receptors (FcRγ^−/−) harbored highly motile larvae, developed extensive tissue damage and accumulated less Arginase-1 expressing macrophages around the larvae. Moreover, Hp-specific antibodies induced FcRγ- and complement-dependent adherence of macrophages to larvae in vitro, resulting in complete larval immobilization. Antibodies together with helminth larvae reprogrammed macrophages to express wound-healing associated genes, including Arginase-1, and the Arginase-1 product L-ornithine directly impaired larval motility. Antibody-induced expression of Arginase-1 in vitro and in vivo occurred independently of IL-4Rα signaling. In summary, we present a novel IL-4Rα-independent mechanism of alternative macrophage activation that is antibody-dependent and which both mediates anti-helminth immunity and prevents tissue disruption caused by migrating larvae.

Intestinal helminths present a pressing problem in developing countries with approximately 2 billion people suffering from chronic infection. To date no successful vaccines are available and a detailed mechanistic understanding of anti-helminth immunity is urgently needed to improve strategies for prevention and therapy. Antibodies form a crucial component of protective immunity against challenge infections with intestinal helminths. However, the exact mechanisms by which antibodies target these large multi-cellular parasites have remained obscure. We now demonstrate that helminth-specific antibodies induce the rapid trapping of tissue migrating helminth larvae by activating phagocytes. In the absence of antibodies or their receptors, helminth-infected mice developed extensive tissue damage, revealing a novel role for antibodies in limiting parasite-caused tissue disruption. Furthermore, helminth-specific antibodies reprogrammed macrophages to express wound-healing factors such as the arginine-metabolizing enzyme Arginase-1. Interestingly, the Arginase-1 product L-ornithine directly impaired the motility of helminth larvae. In summary, our study provides detailed mechanistic insights into how antibodies can modulate phagocyte function to provide protection against a large multi-cellular parasite. Our findings suggest that novel anti-helminth vaccines should target the larval surface and activate wound-healing macrophages to provide rapid protection against tissue-disruptive larvae.

Epicutaneous sensitization results in IgE-dependent intestinal mast cell expansion and food-induced anaphylaxis

BACKGROUND

Sensitization to food antigen can occur through cutaneous exposure.

OBJECTIVE

We sought to test the hypothesis that epicutaneous sensitization with food antigen predisposes to IgE-mediated anaphylaxis on oral allergen challenge.

METHODS

BALB/c mice were epicutaneously sensitized by repeated application of ovalbumin (OVA) to tape-stripped skin over 7 weeks or orally immunized with OVA and cholera toxin (CT) weekly for 8 weeks and then orally challenged with OVA. Body temperature was monitored, and serum mouse mast cell protease 1 levels were determined after challenge. Tissue mast cell (MC) counts were examined by using chloroacetate esterase staining. Levels of serum OVA-specific IgE and IgG(1) antibodies and cytokines in supernatants of OVA-stimulated splenocytes were measured by means of ELISA. Serum IL-4 levels were measured by using an in vivo cytokine capture assay.

RESULTS

Epicutaneously sensitized mice exhibited expansion of connective tissue MCs in the jejunum, increased serum IL-4 levels, and systemic anaphylaxis after oral challenge, as evidenced by decreased body temperature and increased serum mouse mast cell protease 1 levels. Intestinal MC expansion and anaphylaxis were IgE dependent because they did not occur in epicutaneously sensitized IgE(-/-) mice. Mice orally immunized with OVA plus CT did not have increased serum IL-4 levels, expanded intestinal MCs, or anaphylaxis after oral challenge, despite OVA-specific IgE levels and splenocyte cytokine production in response to OVA stimulation, which were comparable with those of epicutaneously sensitized mice.

CONCLUSION

Epicutaneously sensitized mice, but not mice orally immunized with antigen plus CT, have expansion of intestinal MCs and IgE-mediated anaphylaxis after single oral antigen challenge. IgE is necessary but not sufficient for food anaphylaxis, and MC expansion in the gut can play an important role in the development of anaphylaxis.

Rapid polyclonal desensitization with antibodies to IgE and FcεRIα

BACKGROUND

Rapid desensitization, a procedure in which persons allergic to an antigen are treated at short intervals with increasing doses of that antigen until they tolerate a large dose, is an effective, but risky, way to induce temporary tolerance.

OBJECTIVE

We wanted to determine whether this approach can be adapted to suppress all IgE-mediated allergies in mice by injecting serially increasing doses of monoclonal antibodies (mAbs) to IgE or FcεRIα.

METHODS

Active and passive models of antigen- and anti-IgE mAb-induced IgE-mediated anaphylaxis were used. Mice were desensitized with serially increasing doses of anti-IgE mAb, anti-FcεRIα mAb, or antigen. Development of shock (hypothermia), histamine and mast cell protease release, cytokine secretion, calcium flux, and changes in cell number and FcεRI and IgE expression were evaluated.

RESULTS

Rapid desensitization with anti-IgE mAb suppressed IgE-mediated immediate hypersensitivity; however, some mice developed mild anaphylaxis during desensitization. Rapid desensitization with anti-FcεRIα mAb that only binds FcεRI that is not occupied by IgE suppressed both active and passive IgE-mediated anaphylaxis without inducing disease. It quickly, but temporarily, suppressed IgE-mediated anaphylaxis by decreasing mast cell signaling through FcεRI, then slowly induced longer lasting mast cell unresponsiveness by removing membrane FcεRI. Rapid desensitization with anti-FcεRIα mAb was safer and longer lasting than rapid desensitization with antigen.

CONCLUSION

A rapid desensitization approach with anti-FcεRIα mAb safely desensitizes mice to IgE-mediated anaphylaxis by inducing mast cell anergy and later removing all mast cell IgE. Rapid desensitization with an anti-human FcεRIα mAb may be able to prevent human IgE-mediated anaphylaxis.

IL-33-dependent induction of allergic lung inflammation by FcγRIII signaling

Atopic asthma is a chronic inflammatory disease of the lungs generally marked by excessive Th2 inflammation. The role of allergen-specific IgG in asthma is still controversial; however, a receptor of IgG-immune complexes (IgG-ICs), FcγRIII, has been shown to promote Th2 responses through an unknown mechanism. Herein, we demonstrate that allergen-specific IgG-ICs, formed upon reexposure to allergen, promoted Th2 responses in two different models of IC-mediated inflammation that were independent of a preformed T cell memory response. Development of Th2-type airway inflammation was shown to be both FcγRIII and TLR4 dependent, and T cells were necessary and sufficient for this process to occur, even in the absence of type 2 innate lymphoid cells. We sought to identify downstream targets of FcγRIII signaling that could contribute to this process and demonstrated that bone marrow-derived DCs, alveolar macrophages, and respiratory DCs significantly upregulated IL-33 when activated through FcγRIII and TLR4. Importantly, IC-induced Th2 inflammation was dependent on the ST2/IL-33 pathway. Our results suggest that allergen-specific IgG can enhance secondary responses by ligating FcγRIII on antigen-presenting cells to augment development of Th2-mediated responses in the lungs via an IL-33-dependent mechanism.

Protective and pathological roles of mast cells and basophils

Mast cells and basophils are potent effector cells of the innate immune system, and they have both beneficial and detrimental functions for the host. They are mainly implicated in pro-inflammatory responses to allergens but can also contribute to protection against pathogens. Although both cell types were identified more than 130 years ago by Paul Ehrlich, their in vivo functions remain poorly understood. The precursor cell populations that give rise to mast cells and basophils have recently been characterized and isolated. Furthermore, new genetically modified mouse strains have been developed, which enable more specific targeting of mast cells and basophils. Such advances offer new opportunities to uncover the true in vivo activities of these cells and to revisit their previously proposed effector functions.