A novel human immunoglobulin Fc gamma Fc epsilon bifunctional fusion protein inhibits Fc epsilon RI-mediated degranulation

Generation of a virus-like particles based vaccine against IgE

BACKGROUND

Anti-IgE immunotherapy with monoclonal antibodies represents a breakthrough in treatment of severe allergic diseases. However, drawbacks such as short half-life and high price are not negligible. Our objective is to develop an anti-IgE vaccine based on virus-like particles (VLPs) which can induce long-lasting neutralizing IgG anti-IgE antibodies reducing allergic responses without causing intrinsic mast cell activation due to IgE cross-linking.

METHODS

The vaccines were made by chemically coupling three synthetic mouse IgE-Fc fragments to plant-derived immunologically optimized CuMVTT VLPs. The immunogenicity of the vaccines was tested by immunizing naive or allergic mice either with the coupled vaccines or the VLP control followed by systemic or local allergen challenge.

RESULTS

Mice immunized with the vaccines exhibited high titers of anti-IgE antibodies in the sera and high levels of anti-IgE secreting plasma cells in lymphoid organs. Moreover, free IgE in serum were reduced by the induced anti-IgE antibodies; therefore, less IgE was bound to FcεRI on the surface of basophils. In line with these reduced IgE levels on effector cells after vaccination, immunized mice were protected from challenge with allergens. Importantly, despite presence of anti-IgE antibodies, no signs of acute or chronic allergic response were seen in immunized allergic mice.

CONCLUSION

The generated vaccines can effectively induce anti-IgE antibodies that did not cause allergic responses in sensitized mice but were able to decrease the level of free and cell bound IgE and protected sensitized animals from allergic responses upon allergen challenge.

Research Advances in Mast Cell Biology and Their Translation Into Novel Therapies for Anaphylaxis

Anaphylaxis is an acute, potentially life-threatening systemic allergic reaction for which there are no known reliable preventative therapies. Its primary cell mediator, the mast cell, has several pathophysiologic roles and functions in IgE-mediated reactions that continue to be poorly understood. Recent advances in the understanding of allergic mechanisms have identified novel targets for inhibiting mast cell function and activation. The prevention of anaphylaxis is within reach with new drugs that could modulate immune tolerance, mast cell proliferation and differentiation, and IgE regulation and production. Several US Food and Drug Administration-approved drugs for chronic urticaria, mastocytosis, and cancer are also being repurposed to prevent anaphylaxis. New therapeutics have not only shown promise in potential efficacy for preventing IgE-mediated reactions, but in some cases, they are able to inform us about mast cell mechanisms in vivo. This review summarizes the most recent advances in the treatment of anaphylaxis that have arisen from new pharmacologic tools and our current understanding of mast cell biology.

Human Lung Mast Cells: Therapeutic Implications in Asthma

Mast cells are strategically located in different compartments of the lung in asthmatic patients. These cells are widely recognized as central effectors and immunomodulators in different asthma phenotypes. Mast cell mediators activate a wide spectrum of cells of the innate and adaptive immune system during airway inflammation. Moreover, these cells modulate the activities of several structural cells (i.e., fibroblasts, airway smooth muscle cells, bronchial epithelial and goblet cells, and endothelial cells) in the human lung. These findings indicate that lung mast cells and their mediators significantly contribute to the immune induction of airway remodeling in severe asthma. Therapies targeting mast cell mediators and/or their receptors, including monoclonal antibodies targeting IgE, IL-4/IL-13, IL-5/IL-5Rα, IL-4Rα, TSLP, and IL-33, have been found safe and effective in the treatment of different phenotypes of asthma. Moreover, agonists of inhibitory receptors expressed by human mast cells (Siglec-8, Siglec-6) are under investigation for asthma treatment. Increasing evidence suggests that different approaches to depleting mast cells show promising results in severe asthma treatment. Novel treatments targeting mast cells can presumably change the course of the disease and induce drug-free remission in bronchial asthma. Here, we provide an overview of current and promising treatments for asthma that directly or indirectly target lung mast cells.

Understanding human mast cells: lesson from therapies for allergic and non-allergic diseases

Mast cells have crucial roles in allergic and other inflammatory diseases. Preclinical approaches provide circumstantial evidence for mast cell involvement in many diseases, but these studies have major limitations - for example, there is still a lack of suitable mouse models for some mast cell-driven diseases such as urticaria. Some approaches for studying mast cells are invasive or can induce severe reactions, and very few mediators or receptors are specific for mast cells. Recently, several drugs that target human mast cells have been developed. These include monoclonal antibodies and small molecules that can specifically inhibit mast cell degranulation via key receptors (such as FcεRI), that block specific signal transduction pathways involved in mast cell activation (for example, BTK), that silence mast cells via inhibitory receptors (such as Siglec-8) or that reduce mast cell numbers and prevent their differentiation by acting on the mast/stem cell growth factor receptor KIT. In this Review, we discuss the existing and emerging therapies that target mast cells, and we consider how these treatments can help us to understand mast cell functions in disease.

Allergic rhinitis, allergic contact dermatitis and disease comorbidity belong to separate entities with distinct composition of T-cell subsets, cytokines, immunoglobulins and autoantibodies

Background

Allergic rhinitis (AR) and allergic contact dermatitis (ACD) are prevalent allergic diseases and have significant impacts on patients’ daily life. Despite many studies on AR or ACD have been conducted separately, little is known about the immune responses in patients of AR combined with ACD and the interplay between AR and ACD. Our study compared various aspects of immune elements in patients with AR or/and ACD, aiming to characterize the immune responses in AR, ACD, and AR combined with ACD.

Methods

A total of 57 patients diagnosed with AR or/and ACD and 28 healthy volunteers were included. AR patients were further divided into seasonal AR (SAR) and perennial AR (PAR). All subjects’ blood samples were taken to assess the concentration of immunoglobulins, complement C3, C4, autoantibodies and cytokines in serum by immunoturbidimetry, ELISA or Luminex200 platform. Peripheral blood mononuclear cells (PBMCs) were subjected to the analysis of lymphocyte subpopulations by flow cytometry.

Results

It indicated that AR disease caused elevated levels of IgE, IgA, IgG, IgG4, as well as IL-4, IL-15, IL-8 and IL-6 in serum. AR patients possessed a decreased CD4/CD8 ratio and an increased proportion of memory CD4 + T-cell subset, with a skewed Th2 response and an enhanced CD8 + T-cell activation. Compared with patients with sole AR or ACD condition, AR + ACD patients presented with a significantly increased proportion of memory CD8 + T-cell subset and were prone to autoimmune disorders as indicated by the increased autoantibodies. The immune elements in patients with ACD only were least affected compared with those in other conditions. Additionally, seasonal or perennial AR patients exhibited different cytokine profiles and proportions of memory T-cell subsets.

Conclusions

In this study, we illuminated the respective characteristics of immune responses in AR, ACD, and AR combined with ACD. Meanwhile, we discovered that the PAR and SAR patients possessed different cytokine profiles and T-cell compartments. It suggested that these allergic conditions belong to different disease entities. Characterizing the detailed immune changes in these allergic diseases would help to develop proper treatments targeting particular immune elements in different allergic diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13223-022-00646-6.

Allergen-specific IgG show distinct patterns in persistent and transient food allergy

BACKGROUND

Immediate food-allergic reactions are IgE-mediated, but many individuals with detectable allergen-specific IgE do not react to the food. Allergen-specific IgG may interfere with allergen-IgE interaction and/or through intracellular inhibitory signalling to suppress mast cell and basophil response to food allergens. We aimed to understand the role of allergen-specific IgG in food allergy and natural tolerance.

METHODS

IgG and IgG isotypes specific to peanut, cow's milk and egg were measured using ImmunoCAP and ELISA respectively in samples of children with suspected food allergies. Expression of IgE and IgG and their receptors and expression of activation markers following allergen stimulation were measured on basophils and mast cells by flow cytometry, with and without blockade of FcγRIIα or FcγRIIβ receptors.

RESULTS

The levels of peanut-specific IgG, IgG1, IgG2, IgG3 and IgG4 in ELISA were higher in peanut-allergic than in non-peanut-allergic children. No difference in allergen-specific IgG isotypes was observed between allergic and non-allergic children to milk or egg, except for milk-specific IgG4 that was higher in non-cow's milk-allergic than in cow's milk-allergic children. Basophils and LAD2 cells expressed IgG receptors, but IgG and IgA were not detected on the surface of either cell type and blocking FcγRIIα or FcγRIIβ did not modify basophil or mast cell activation in response to allergen in allergic or tolerant children.

CONCLUSION

Allergen-specific IgG patterns were distinct in persistent (peanut) versus transient (milk and egg) food allergies. We found no evidence that FcγRIIα or FcγRIIβ receptors affect allergen-induced activation of mast cells and basophils in food allergy or natural tolerance.

Novel Approaches in the Inhibition of IgE-Induced Mast Cell Reactivity in Food Allergy

Allergy is an IgE-dependent type-I hypersensitivity reaction that can lead to life-threatening systemic symptoms such as anaphylaxis. In the pathogenesis of the allergic response, the common upstream event is the binding of allergens to specific IgE, inducing cross-linking of the high-affinity FcεRI on mast cells, triggering cellular degranulation and the release of histamine, proteases, lipids mediators, cytokines and chemokines with inflammatory activity. A number of novel therapeutic options to curb mast cell activation are in the pipeline for the treatment of severe allergies. In addition to anti-IgE therapy and allergen-specific immunotherapy, monoclonal antibodies targeted against several key Th2/alarmin cytokines (i.e. IL-4Rα, IL-33, TSLP), active modification of allergen-specific IgE (i.e. inhibitory compounds, monoclonal antibodies, de-sialylation), engagement of inhibitory receptors on mast cells and allergen-specific adjuvant vaccines, are new promising options to inhibit the uncontrolled release of mast cell mediators upon allergen exposure. In this review, we critically discuss the novel approaches targeting mast cells limiting allergic responses and the immunological mechanisms involved, with special interest on food allergy treatment.

Mast Cells: A New Frontier for Cancer Immunotherapy

Mast cells are unique tissue-resident immune cells of the myeloid lineage that have long been implicated in the pathogenesis of allergic and autoimmune disorders. More recently, mast cells have been recognized as key orchestrators of anti-tumor immunity, modulators of the cancer stroma, and have also been implicated in cancer cell intrinsic properties. As such, mast cells are an underrecognized but very promising target for cancer immunotherapy. In this review, we discuss the role of mast cells in shaping cancer and its microenvironment, the interaction between mast cells and cancer therapies, and strategies to target mast cells to improve cancer outcomes. Specifically, we address (1) decreasing cell numbers through c-KIT inhibition, (2) modulating mast cell activation and phenotype (through mast cell stabilizers, FcεR1 signaling pathway activators/inhibitors, antibodies targeting inhibitory receptors and ligands, toll like receptor agonists), and (3) altering secreted mast cell mediators and their downstream effects. Finally, we discuss the importance of translational research using patient samples to advance the field of mast cell targeting to optimally improve patient outcomes. As we aim to expand the successes of existing cancer immunotherapies, focused clinical and translational studies targeting mast cells in different cancer contexts are now warranted.

Nanoparticles Displaying Allergen and Siglec-8 Ligands Suppress IgE-FcεRI-Mediated Anaphylaxis and Desensitize Mast Cells to Subsequent Antigen Challenge

Siglec-8 is an inhibitory receptor expressed on eosinophils and mast cells. In this study, we took advantage of a novel Siglec-8 transgenic mouse model to assess the impact of modulating IgE-dependent mast cell degranulation and anaphylaxis using a liposomal platform to display an allergen with or without a synthetic glycan ligand for Siglec-8 (Sig8L). The hypothesis is that recruitment of Siglec-8 to the IgE-FcεRI receptor complex will inhibit allergen-induced mast cell degranulation. Codisplay of both allergen and Sig8L on liposomes profoundly suppresses IgE-mediated degranulation of mouse bone marrow-derived mast cells or rat basophilic leukemia cells expressing Siglec-8. In contrast, liposomes displaying only Sig8L have no significant suppression of antigenic liposome-induced degranulation, demonstrating that the inhibitory activity by Siglec-8 occurs only when Ag and Sig8L are on the same particle. In mouse models of anaphylaxis, display of Sig8L on antigenic liposomes completely suppresses IgE-mediated anaphylaxis in transgenic mice with mast cells expressing Siglec-8 but has no protection in mice that do not express Siglec-8. Furthermore, mice protected from anaphylaxis remain desensitized to subsequent allergen challenge because of loss of Ag-specific IgE from the cell surface and accelerated clearance of IgE from the blood. Thus, although expression of human Siglec-8 on murine mast cells does not by itself modulate IgE-FcεRI-mediated cell activation, the enforced recruitment of Siglec-8 to the FcεRI receptor by Sig8L-decorated antigenic liposomes results in inhibition of degranulation and desensitization to subsequent Ag exposure.

Suppression of IgE-mediated anaphylaxis and food allergy with monovalent anti-FcεRIα mAbs

BACKGROUND

Mast cell and basophil activation by antigen cross-linking of FcεRI-bound IgE is central to allergy pathogenesis. We previously demonstrated global suppression of this process by rapid desensitization with anti-FcεRIα mAbs.

OBJECTIVES

We sought to determine whether use of monovalent (mv) anti-FcεRIα mAbs increases desensitization safety without loss of efficacy.

METHODS

mv anti-human (hu) FcεRIα mAbs were produced with mouse-derived immunoglobulin variable regions and huIgG1 or huIgG4 C regions and were used to suppress murine IgE-mediated anaphylaxis and food allergy. mAbs were administered as a single dose or as serially increasing doses to mice that express hu instead of mouse FcεRIα; mice that additionally have an allergy-promoting IL-4Rα mutation; and hu cord blood-reconstituted immunodeficient, hu cytokine-secreting, mice that have large numbers of activated hu mast cells. Anaphylaxis susceptibility was sometimes increased by treatment with IL-4 or a β-adrenergic receptor antagonist.

RESULTS

mv anti-hu FcεRIα mAbs are considerably less able than divalent mAbs are to induce anaphylaxis and deplete mast cell and basophil IgE, but mv mAbs still strongly suppress IgE-mediated disease. The mv mAbs can be safely administered as a single large dose to mice with typical susceptibility to anaphylaxis, while a rapid desensitization approach safely suppresses disease in mice with increased susceptibility. Our huIgG4 variant of mv anti-huFcεRIα mAb is safer than our huIgG1 variant is, apparently because reduced interactions with FcεRs decrease ability to indirectly cross-link FcεRI.

CONCLUSIONS

mv anti-FcεRIα mAbs more safely suppress IgE-mediated anaphylaxis and food allergy than divalent variants of the same mAbs do. These mv mAbs may be useful for suppression of huIgE-mediated disease.

Ephedra Herb, Mao, Inhibits Antigen-Induced Mast Cell Degranulation by Induction of the Affinity Receptor for IgE Internalization

PURPOSE

Ephedra herb (Mao) exerts potent anti-allergic effects. This study aimed to examine the underlying mechanisms of Mao on allergic inflammation using in vitro cultured mast cells (MCs) and an in vivo model of MC-dependent anaphylaxis.

METHODS

Bone marrow-derived MCs (BMMCs) were presensitized with anti-2,4-dinitrophenol (DNP) immunoglobulin E (IgE) and challenged with antigens (Ag; DNP-human serum albumin). Degranulation responses and cell surface high-affinity receptor for IgE (FcεRI) expression were assessed with/without Mao treatment. Passive systemic anaphylaxis (PSA)-treated mice were administered Mao and the pathophysiological responses were evaluated.

RESULTS

Mao inhibited Ag-induced BMMC degranulation, but not polyclonal activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin, indicating that Mao inhibits IgE-dependent activation of BMMCs. Mao-treated BMMCs exhibited significant reductions in expression of surface IgE and its receptor FcεRI. Analysis of subcellular localization revealed that Mao induces FcεRI internalization in BMMCs without degranulation. In the PSA mouse model, Mao administration prevented antigen-induced hypothermia. Mao administration significantly reduced cell surface expression of IgE-bound FcεRI on peritoneal MCs.

CONCLUSIONS

Mao induced FcεRI internalization in MCs, thereby inhibiting Ag-induced IgE-dependent degranulation. The inhibitory effects of Mao on MC degranulation may offer a novel therapeutic approach for allergic diseases.

Targeting the FcεRI Pathway as a Potential Strategy to Prevent Food-Induced Anaphylaxis

Despite attempts to halt it, the prevalence of food allergy is increasing, and there is an unmet need for strategies to prevent morbidity and mortality from food-induced allergic reactions. There are no known medications that can prevent anaphylaxis, but several novel therapies show promise for the prevention of food-induced anaphylaxis through targeting of the high-affinity IgE receptor (FcϵRI) pathway. This pathway includes multiple candidate targets, including tyrosine kinases and the receptor itself. Small molecule inhibitors of essential kinases have rapid onset of action and transient efficacy, which may be beneficial for short-term use for immunotherapy buildup or desensitizations. Short courses of FDA-approved inhibitors of Bruton’s tyrosine kinase can eliminate IgE-mediated basophil activation and reduce food skin test size in allergic adults, and prevent IgE-mediated anaphylaxis in humanized mice. In contrast, biologics may provide longer-lasting protection, albeit with slower onset. Omalizumab is an anti-IgE antibody that sequesters IgE, thereby reducing FcϵRI expression on mast cells and basophils. As a monotherapy, it can increase the clinical threshold dose of food allergen, and when used as an adjunct for food immunotherapy, it decreases severe reactions during buildup phase. Finally, lirentelimab, an anti-Siglec-8 antibody currently in clinical trials, can prevent IgE-mediated anaphylaxis in mice through mast cell inhibition. This review discusses these and other emerging therapies as potential strategies for preventing food-induced anaphylaxis. In contrast to other food allergy treatments which largely focus on individual allergens, blockade of the FcϵRI pathway has the advantage of preventing clinical reactivity from any food.

Strategies for Mast Cell Inhibition in Food Allergy

Mast cells are tissue resident allergic effector cells that drive IgE-mediated food allergies. There are several steps leading to mast cell activation in the context of allergic disease that can be targeted to prevent mast cell activation and degranulation. These include blocking IgE-FcεRI crosslinking and type 2 cytokine receptor activation; modulating cell-surface neural chemical receptors; stabilizing mast cell membranes to prevent co-localization of activating receptors; impeding intracellular signaling; and engaging cell surface inhibitory receptors. This review highlights several ITIM-containing inhibitory mast cell surface receptors that could serve as pharmaceutical targets to prevent mast cell activation and degranulation in the context of food allergy. When activated, these ITIM-containing inhibitory receptors recruit the phosphatases SHP-1, SHP-2, and/or SHIP to dephosphorylate the tyrosine kinases responsible for activation signals downstream of the IgE-FcεRI complex. We describe several members of the Ig and Ig-like inhibitory receptor and C-type lectin inhibitory receptor superfamilies. Fundamental studies exploring the behavior of these receptors within the context of experimental food allergy models are needed. A deeper understanding of how these receptors modulate mast cell-driven food allergic responses will shape future strategies to harness these inhibitory receptors to treat food allergy.

IgE and IgG Antibodies as Regulators of Mast Cell and Basophil Functions in Food Allergy

Food allergy is a major health issue, affecting the lives of 8% of U.S. children and their families. There is an urgent need to identify the environmental and endogenous signals that induce and sustain allergic responses to ingested allergens. Acute reactions to foods are triggered by the activation of mast cells and basophils, both of which release inflammatory mediators that lead to a range of clinical manifestations, including gastrointestinal, cutaneous, and respiratory reactions as well as systemic anaphylaxis. Both of these innate effector cell types express the high affinity IgE receptor, FcϵRI, on their surface and are armed for adaptive antigen recognition by very-tightly bound IgE antibodies which, when cross-linked by polyvalent allergen, trigger degranulation. These cells also express inhibitory receptors, including the IgG Fc receptor, FcγRIIb, that suppress their IgE-mediated activation. Recent studies have shown that natural resolution of food allergies is associated with increasing food-specific IgG levels. Furthermore, oral immunotherapy, the sequential administration of incrementally increasing doses of food allergen, is accompanied by the strong induction of allergen-specific IgG antibodies in both human subjects and murine models. These can deliver inhibitory signals via FcγRIIb that block IgE-induced immediate food reactions. In addition to their role in mediating immediate hypersensitivity reactions, mast cells and basophils serve separate but critical functions as adjuvants for type 2 immunity in food allergy. Mast cells and basophils, activated by IgE, are key sources of IL-4 that tilts the immune balance away from tolerance and towards type 2 immunity by promoting the induction of Th2 cells along with the innate effectors of type 2 immunity, ILC2s, while suppressing the development of regulatory T cells and driving their subversion to a pathogenic pro-Th2 phenotype. This adjuvant effect of mast cells and basophils is suppressed when inhibitory signals are delivered by IgG antibodies signaling via FcγRIIb. This review summarizes current understanding of the immunoregulatory effects of mast cells and basophils and how these functions are modulated by IgE and IgG antibodies. Understanding these pathways could provide important insights into innovative strategies for preventing and/or reversing food allergy in patients.

IgE and mast cells: The endogenous adjuvant

Mast cells and IgE are most familiar as the effectors of type I hypersensitivity reactions including anaphylaxis. It is becoming clear however that this pair has important immunomodulatory effects on innate and adaptive cells of the immune system. In this purview, they act as endogenous adjuvants to ignite evolving immune responses, promote the transition of allergic disease into chronic illness and disrupt the development of active mechanisms of tolerance to ingested foods. Suppression of IgE-mediated mast cell activation can be exerted by molecules targeting IgE, FcɛRI or signaling kinases including Syk, or by IgG antibodies acting via inhibitory Fcγ receptors. In 2015 we reviewed the evidence for the adjuvant functions of mast cells. This update includes the original text, incorporates some important developments in the field over the past five years and discusses how interventions targeting these pathways might have promise in the development of strategies to treat allergic disease.

Past, present, and future of anti-IgE biologics

About 20 years after the identification of immunoglobulin E (IgE) and its key role in allergic hypersensitivity reactions against normally harmless substances, scientists have started inventing strategies to block its pathophysiological activity in 1986. The initial concept of specific IgE targeting through the use of anti-IgE antibodies has gained a lot of momentum and within a few years independent research groups have reported successful generation of first murine monoclonal anti-IgE antibodies. Subsequent generation of optimized chimeric and humanized versions of these antibodies has paved the way for the development of therapeutic anti-IgE biologicals as we know them today. With omalizumab, there is currently still only one therapeutic anti-IgE antibody approved for the treatment of allergic conditions. Since its application is limited to the treatment of moderate-to-severe persistent asthma and chronic spontaneous urticaria, major efforts have been undertaken to develop alternative anti-IgE biologicals that could potentially be used in a broader spectrum of allergic diseases. Several new drug candidates have been generated and are currently assessed in pre-clinical studies or clinical trials. In this review, we highlight the molecular properties of past and present anti-IgE biologicals and suggest concepts that might improve treatment efficacy of future drug candidates.

Nanotechnology-Based Vaccines for Allergen-Specific Immunotherapy: Potentials and Challenges of Conventional and Novel Adjuvants under Research

The increasing prevalence of allergic diseases demands efficient therapeutic strategies for their mitigation. Allergen-specific immunotherapy (AIT) is the only causal rather than symptomatic treatment method available for allergy. Currently, AIT is being administered using immune response modifiers or adjuvants. Adjuvants aid in the induction of a vigorous and long-lasting immune response, thereby improving the efficiency of AIT. The successful development of a novel adjuvant requires a thorough understanding of the conventional and novel adjuvants under development. Thus, this review discusses the potentials and challenges of these adjuvants and their mechanism of action. Vaccine development based on nanoparticles is a promising strategy for AIT, due to their inherent physicochemical properties, along with their ease of production and ability to stimulate innate immunity. Although nanoparticles have provided promising results as an adjuvant for AIT in in vivo studies, a deeper insight into the interaction of nanoparticle-allergen complexes with the immune system is necessary. This review focuses on the methods of harnessing the adjuvant effect of nanoparticles by detailing the molecular mechanisms underlying the immune response, which includes allergen uptake, processing, presentation, and induction of T cell differentiation.

Understanding of the Molecular Mechanisms of Allergy

The prevalence of allergic disease has dramatically increased over the past 30 years in Westernized countries. It is unlikely that the rapid increase in the prevalence of allergic disease is the result of genetic changes, which highlights the importance of environmental factors in the development of allergic disease. The "hygiene hypothesis" was put forward in 1989 and focused attention on the notion that exposure to microbes and their products in early life can modify the risk for development of allergic disease. Infections were thought to polarize the immunological response toward a Th2-mediated immune response causing allergic disease. However, it is likely that the Th1/Th2 imbalance is too simplistic to explain the increased prevalence of allergic disease. Current research is focusing on understanding the role of T-regulatory cells in inducing a state of tolerance and the resulting modified Th2 response observed in natural and induced tolerance.

Measurement of Specific IgG Anti-Fel d 1 Antibodies

There is currently considerable interest in the role of specific IgG antibodies in allergy. Several studies suggest that specific IgG antibodies may play a protective role in allergy. Successful immunotherapy is associated with increases in allergen-specific IgG antibodies which correlate with clinical outcome. Other studies have identified an inverse relationship between exposure to cat and sensitization, which was associated with high-titer-specific IgG and IgG₄. This immune response was described as a modified Th2 response, since both IgE and IgG₄ require Th2 cytokine IL-4 for their production. A modified Th2 response was described with laboratory animal allergy, where there was almost a twofold reduction in the risk of developing work-related chest symptoms.In this chapter, we review the major factors to be considered in the development of an ELISA for the determination of specific IgG and IgG₄ antibodies.

CD33 recruitment inhibits IgE-mediated anaphylaxis and desensitizes mast cells to allergen

Allergen immunotherapy for patients with allergies begins with weekly escalating doses of allergen under medical supervision to monitor and treat IgE mast cell-mediated anaphylaxis. There is currently no treatment to safely desensitize mast cells to enable robust allergen immunotherapy with therapeutic levels of allergen. Here, we demonstrated that liposomal nanoparticles bearing an allergen and a high-affinity glycan ligand of the inhibitory receptor CD33 profoundly suppressed IgE-mediated activation of mast cells, prevented anaphylaxis in Tg mice with mast cells expressing human CD33, and desensitized mice to subsequent allergen challenge for several days. We showed that high levels of CD33 were consistently expressed on human skin mast cells and that the antigenic liposomes with CD33 ligand prevented IgE-mediated bronchoconstriction in slices of human lung. The results demonstrated the potential of exploiting CD33 to desensitize mast cells to provide a therapeutic window for administering allergen immunotherapy without triggering anaphylaxis.

Regulation of the pleiotropic effects of tissue-resident mast cells

Mast cells (MCs), which are best known for their detrimental role in patients with allergic diseases, act in a diverse array of physiologic and pathologic functions made possible by the plurality of MC types. Their various developmental avenues and distinct sensitivity to (micro-) environmental conditions convey extensive heterogeneity, resulting in diverse functions. We briefly summarize this heterogeneity, elaborate on molecular determinants that allow MCs to communicate with their environment to fulfill their tasks, discuss the protease repertoire stored in secretory lysosomes, and consider different aspects of MC signaling. Furthermore, we describe key MC governance mechanisms (ie, the high-affinity receptor for IgE [FcεRI]), the stem cell factor receptor KIT, the IL-4 system, and both Ca²⁺- and phosphatase-dependent mechanisms. Finally, we focus on distinct physiologic functions, such as chemotaxis, phagocytosis, host defense, and the regulation of MC functions at the mucosal barriers of the lung, gastrointestinal tract, and skin. A deeper knowledge of the pleiotropic functions of MC mediators, as well as the molecular processes of MC regulation and communication, should enable us to promote beneficial MC traits in physiology and suppress detrimental MC functions in patients with disease.

Current Strategies to Inhibit High Affinity FcεRI-Mediated Signaling for the Treatment of Allergic Disease

Allergies and asthma are a major cause of chronic disease whose prevalence has been on the rise. Allergic disease including seasonal rhinitis, atopic dermatitis, urticaria, anaphylaxis, and asthma, are associated with activation of tissue-resident mast cells and circulating basophils. Although these cells can be activated in different ways, allergic reactions are normally associated with the crosslinking of the high affinity Fc receptor for Immunoglobulin E, FcεRI, with multivalent antigen. Inflammatory mediators released from cytoplasmic granules, or biosynthesized de novo, following FcεRI crosslinking induce immediate hypersensitivity reactions, including life-threatening anaphylaxis, and contribute to prolonged inflammation leading to chronic diseases like asthma. Thus, inappropriate or unregulated activation of mast cells and basophils through antigenic crosslinking of FcεRI can have deleterious, sometimes deadly, consequences. Accordingly, FcεRI has emerged as a viable target for the development of biologics that act to inhibit or attenuate the activation of mast cells and basophils. At the forefront of these strategies are (1) Anti-IgE monoclonal antibody, namely omalizumab, which has the secondary effect of reducing FcεRI surface expression, (2) Designed Ankyrin Repeat Proteins (DARPins), which take advantage of the most common structural motifs in nature involved in protein-protein interactions, to inhibit FcεRI-IgE interactions, and (3) Fusion proteins to co-aggregate FcεRI with the inhibitory FcγRIIb. This review presents the published research studies that support omalizumab, DARPins, and fusion proteins as, arguably, the three most currently viable strategies for inhibiting the expression and activation of the high affinity FcεRI on mast cells and basophils.

Human mast cells and basophils-How are they similar how are they different?

Mast cells and basophils are key contributors to allergies and other inflammatory diseases since they are the most prominent source of histamine as well as numerous additional inflammatory mediators which drive inflammatory responses. However, a closer understanding of their precise roles in allergies and other pathological conditions has been marred by the considerable heterogeneity that these cells display, not only between mast cells and basophils themselves but also across different tissue locations and species. While both cell types share the ability to rapidly degranulate and release histamine following high-affinity IgE receptor cross-linking, they differ markedly in their ability to either react to other stimuli, generate inflammatory eicosanoids or release immunomodulating cytokines and chemokines. Furthermore, these cells display considerable pharmacological heterogeneity which has stifled attempts to develop more effective anti-allergic therapies. Mast cell- and basophil-specific transcriptional profiling, at rest and after activation by innate and adaptive stimuli, may help to unravel the degree to which these cells differ and facilitate a clearer understanding of their biological functions and how these could be targeted by new therapies.

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.

Mechanistic Insights of an Immunological Adverse Event Induced by an Anti-KIT Antibody Drug Conjugate and Mitigation Strategies

Purpose: Hypersensitivity reactions (HSRs) were observed in three patients dosed in a phase I clinical trial treated with LOP628, a KIT targeted antibody drug conjugate. Mast cell degranulation was implicated as the root cause for the HSR. Underlying mechanism of this reported HSR was investigated with an aim to identifying potential mitigation strategies.Experimental Design: Biomarkers for mast cell degranulation were evaluated in patient samples and in human peripheral blood cell-derived mast cell (PBC-MC) cultures treated with LOP628. Mitigation strategies interrogated include pretreatment of mast cells with small molecule inhibitors that target KIT or signaling pathways downstream of FcεR1, FcγR, and treatment with Fc silencing antibody formats.Results: Transient elevation of serum tryptase was observed in patients 1-hour posttreatment of LOP628. In agreement with the clinical observation, LOP628 and its parental antibody LMJ729 induced degranulation of human PBC-MCs. Unexpectedly, KIT small molecule inhibitors did not abrogate mast cell degranulation. By contrast, small molecule inhibitors that targeted pathways downstream of Fc receptors blunted degranulation. Furthermore, interference of the KIT antibody to engage Fc receptors by pre-incubation with IgG or using engineered Fc silencing mutations reduced or prevented degranulation. Characterization of Fcγ receptors revealed human PBC-MCs expressed both FcγRII and low levels of FcγRI. Interestingly, increasing the level of FcγRI upon addition of IFNγ, significantly enhanced LOP628-mediated mast cell degranulation.Conclusions: Our data suggest LOP628-mediated mast cell degranulation is the likely cause of HSR observed in the clinic due to co-engagement of the FcγR and KIT, resulting in mast cell activation. Clin Cancer Res; 24(14); 3465-74. ©2018 AACR.

Modified Allergens for Immunotherapy

PURPOSE OF REVIEW

During the past few decades, modified allergens have been developed for use in allergen-specific immunotherapy (AIT) with the aim to improve efficacy and reduce adverse effects. This review aims to provide an overview of the different types of modified allergens, their mechanism of action and their potential for improving AIT.

RECENT FINDINGS

In-depth research in the field of allergen modifications as well as the advance of recombinant DNA technology have paved the way for improved diagnosis and research on human allergic diseases. A wide range of structurally modified allergens has been generated including allergen peptides, chemically altered allergoids, adjuvant-coupled allergens, and nanoparticle-based allergy vaccines. These modified allergens show promise for the development of AIT regimens with improved safety and long-term efficacy. Certain modifications ensure reduced IgE reactivity and retained T cell reactivity, which facilities induction of immune tolerance to the allergen. To date, multiple clinical trials have been performed using modified allergens. Promising results were obtained for the modified cat, grass and birch pollen, and house dust mite allergens. The use of modified allergens holds promise for improving AIT efficacy and safety. There is however a need for larger clinical studies to reliably assess the added benefit for the patient of using modified allergens for AIT.

Basophils from allergic patients are neither hyperresponsive to activation signals nor hyporesponsive to inhibition signals

BACKGROUND

Basophil activation contributes to inflammatory reactions, especially in allergy. It is controlled, both positively and negatively, by several mechanisms. High-affinity IgE receptors (FcεRI) generate a mixture of activation and inhibition signals when aggregated, the ratio of which depends on the concentration of allergen recognized by receptor-bound IgE. Low-affinity IgG receptors (FcγRIIA/B) generate inhibition signals when coengaged with FcεRI by allergen-antibody immune complexes. Commensal and probiotic bacteria, such as Lactobacillus paracasei, generate inhibition signals through still unclear mechanisms.

OBJECTIVE

We sought to investigate whether mechanisms that control, both positively and negatively, basophil activation, which were unraveled and studied in basophils from healthy donors, are functional in allergic patients.

METHODS

FcεRI and FcγRIIA/B expression, FcεRI-dependent activation, FcεRI-dependent inhibition, and FcγRIIB-dependent inhibition were examined in blood basophils incubated overnight with or without L paracasei and challenged under 10 experimental conditions. Basophils from healthy donors were compared with basophils from patients who consulted an allergology outpatient clinic over a period of 3 months with respiratory allergy, anaphylaxis antecedents, chronic urticaria, and/or atopic dermatitis.

RESULTS

Patients' basophils expressed neither more FcεRI nor less FcγRIIB than basophils from healthy donors. They were neither hyperreactive to positive regulation nor hyporeactive to negative regulation, irrespective of the receptors or mechanisms involved and the allergic manifestations of the patients.

CONCLUSION

Regulatory mechanisms that control basophil activation are fully functional in allergic patients. Intrinsic defects in these mechanisms do not explain allergic manifestations. Based on these mechanisms, immune checkpoint modifiers can be developed as novel therapeutic tools for allergy.

Davallia mariesii Moore Improves FcεRI-Mediated Allergic Responses in the Rat Basophilic Leukemia Mast Cell Line RBL-2H3 and Passive Cutaneous Anaphylaxis in Mice

Davallia mariesii Moore (Drynaria rhizome extract (DRE)) is widely known for its efficacy in treating inflammation, arteriosclerosis, and bone injuries. This study evaluated whether treatment with DRE inhibited FcɛRI-mediated allergic responses in the RBL-2H3 mast cells and investigated the early- and late-phase mechanisms by which DRE exerts its antiallergic effects. IgE anti-DNP/DNP-HSA-sensitized RBL-2H3 mast cells were tested for cytotoxicity to DRE, followed by the assessment of β-hexosaminidase release. We measured the amounts of inflammatory mediators (e.g., histamine, PGD₂, TNF-α, IL-4, and IL-6) and examined the expression of genes involved in arachidonate and FcεRI signaling pathways. In addition, we confirmed the antiallergic effects of DRE on passive cutaneous anaphylaxis (PCA) in mice. DRE inhibited RBL-2H3 mast cell degranulation and production of allergic mediators in them. In early allergic responses, DRE reduced expression of FcεRI signaling-related genes (e.g., Syk, Lyn, and Fyn) and extracellular signal-regulated kinase phosphorylation in mast cells. In late allergic responses, DRE reduced PGD₂ release and COX-2 expression and cPLA₂ phosphorylation in FcɛRI-mediated mast cells. Lastly, 250-500 mg/kg DRE significantly attenuated the IgE-induced PCA reaction in mice. These findings provide novel information on the molecular mechanisms underlying the antiallergic effects of DRE in FcɛRI-mediated allergic responses.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

A novel bispecific DARPin targeting FcγRIIB and FcεRI-bound IgE inhibits allergic responses

BACKGROUND

Binding of allergen-specific IgE to its high-affinity receptor FcεRI on basophils and mast cells is a central event in the development of allergies. Exposure of these cells to allergens induces the release of soluble mediators causing allergic symptoms. The inhibitory low-affinity IgG Fc-receptor FcγRIIB is co-expressed on allergic effector cells and has been implicated in negative regulation of immediate hypersensitivity responses. In order to harvest the inhibitory function of this receptor, we aimed to select specific binders against FcγRIIB and to generate a bispecific molecule simultaneously targeting FcγRIIB and FcεRI-bound IgE on the surface of allergic effector cells.

METHODS

We selected FcγRIIB-specific binding molecules from a library of designed ankyrin repeat proteins using ribosome display technology. The bispecific binding modality was generated by molecular cloning and recombinant protein expression. We determined binding characteristics on molecular and cellular levels using SPR, ELISA, and flow cytometry. The inhibitory potential of the newly described molecules was assessed in different cellular degranulation assays ex vivo and in a mouse model of passive systemic anaphylaxis.

RESULTS

We demonstrate that the selected DARPin^® proteins recognize FcγRIIB with high affinity. Furthermore, the bispecific binding protein successfully interferes with allergen-induced cell degranulation and efficiently inhibits systemic anaphylaxis in vivo. Mechanistically, we report that FcγRIIB-mediated inhibition of effector cell activation requires direct ligation to an activating FcεRI receptor.

CONCLUSION

The described bispecific DARPin protein has the ability to co-ligate FcγRIIB with FcεRI-bound IgE on allergic effector cells and represents an efficient dual-modality to interfere with allergic hypersensitivity reactions.

Allergen-specific IgG antibody signaling through FcγRIIb promotes food tolerance

BACKGROUND

Patients with food allergy produce high-titer IgE antibodies that bind to mast cells through FcεRI and trigger immediate hypersensitivity reactions on antigen encounter. Food-specific IgG antibodies arise in the setting of naturally resolving food allergy and accompany the acquisition of food allergen unresponsiveness in oral immunotherapy.

OBJECTIVE

In this study we sought to delineate the effects of IgG and its inhibitory Fc receptor, FcγRIIb, on both de novo allergen sensitization in naive animals and on established immune responses in the setting of pre-existing food allergy.

METHODS

Allergen-specific IgG was administered to mice undergoing sensitization and desensitization to the model food allergen ovalbumin. Cellular and molecular mechanisms were interrogated by using mast cell- and FcγRIIb-deficient mice. The requirement for FcγRII in IgG-mediated inhibition of human mast cells was investigated by using a neutralizing antibody.

RESULTS

Administration of specific IgG to food allergy-prone IL4raF709 mice during initial food exposure prevented the development of IgE antibodies, T_H2 responses, and anaphylactic responses on challenge. When given as an adjunct to oral desensitization in mice with established IgE-mediated hypersensitivity, IgG facilitated tolerance restoration, favoring expansion of forkhead box protein 3-positive regulatory T cells along with suppression of existing T_H2 and IgE responses. IgG and FcγRIIb suppress adaptive allergic responses through effects on mast cell function.

CONCLUSION

These findings suggest that allergen-specific IgG antibodies can act to induce and sustain immunologic tolerance to foods.

IgE-Related Chronic Diseases and Anti-IgE-Based Treatments

IgE is an immunoglobulin that plays a central role in acute allergic reactions and chronic inflammatory allergic diseases. The development of a drug able to neutralize this antibody represents a breakthrough in the treatment of inflammatory pathologies with a probable allergic basis. This review focuses on IgE-related chronic diseases, such as allergic asthma and chronic urticaria (CU), and on the role of the anti-IgE monoclonal antibody, omalizumab, in their treatment. We also assess the off-label use of omalizumab for other pathologies associated with IgE and report the latest findings concerning this drug and other new related drugs. To date, omalizumab has only been approved for severe allergic asthma and unresponsive chronic urticaria treatments. In allergic asthma, omalizumab has demonstrated its efficacy in reducing the dose of inhaled corticosteroids required by patients, decreasing the number of asthma exacerbations, and limiting the effect on airway remodeling. In CU, omalizumab treatment rapidly improves symptoms and in some cases achieves complete disease remission. In systemic mastocytosis, omalizumab also improves symptoms and its prophylactic use to prevent anaphylactic reactions has also been discussed. In other pathologies such as atopic dermatitis, food allergy, allergic rhinitis, nasal polyposis, and keratoconjunctivitis, omalizumab significantly improves clinical manifestations. Omalizumab acts in two ways: by sequestering free IgE and by accelerating the dissociation of the IgE-Fcε receptor I complex.

Human Helminths and Allergic Disease: The Hygiene Hypothesis and Beyond

There is much debate about the interaction between helminths and allergic disease. The "Hygiene Hypothesis," a very popular concept among scientists and the lay public, states that infections, especially during childhood, can protect against allergic diseases. Indeed, helminth infections are known to induce regulatory responses in the host that can help the control of inflammation (including allergic inflammation). However, these infections also induce type-2-associated immune responses including helminth-specific IgE that can cross-react against environmental allergens and mediate IgE-driven effector responses. Thus, it is the delicate balance between the parasites' anti- and pro-allergenic effects that define the helminth/allergy interface.

Allergen Immunotherapy: Past, Present, and Future

Allergen-specific immunotherapy (AIT), although in clinical use for more than a century, is still the only causal treatment of allergic diseases. The safety and efficacy of AIT has been demonstrated in a large number of clinical trials. In addition to allergy symptom reduction AIT plays an essential role in preventing new allergies and asthma and shows long-term effects after discontinuation of treatment. Ideally, it is capable of curing allergy. However, AIT is not effective in all allergic individuals and is not equally effective in the treatment of various hypersensitivities to different allergens. For many years, the route of administration and the vaccine compositions have been evolving. Still there is a strong need for research in the field of new AIT modalities to increase its effectiveness and safety. Growing evidence on immunological effects of AIT, especially new T cell subsets involved in antigen/allergen tolerance, provides novel concepts for safer and more effective vaccination. Pharmacoeconomic studies have demonstrated a clear advantage of AIT over pharmacologic therapies.

Fc Receptors and Fc Receptor-Like Molecules within the Immunoreceptor Family

Receptors for the Fc portion of immunoglobulins (FcRs) account for most cell-mediated biological activities of antibodies. The majority of FcRs are encoded by a set of genes, clustered in the fcr locus, on chromosome 1 in humans and on chromosome 1 and 3 in mice. Eight (in humans) and six (in mice) new genes were found, intermixed with FcR genes in corresponding fcr loci, which encode FcR-like molecules (FcRLs). FcRs and FcRLs are genetically, phylogenetically, structurally, and functionally related. FcRs and FcRLs, however, markedly differ by their ligands, their tissue distribution, and, therefore, by the biological functions they control. A systematic comparison of their biological properties leads to the conclusion that FcRLs are not like FcRs. They altogether form a single family within the immunoreceptor family, whose members fulfill distinct but complementary roles in immunity by differentially controlling innate and adaptive responses.

Novel immunotherapy vaccine development

PURPOSE OF REVIEW

Allergen-specific immunotherapy is the only curative treatment for allergic diseases. In spite of the great progress in both vaccine development and the methods of allergen immunotherapy (AIT) in recent years, several key problems related to limited efficacy, side-effects, low patient adherence and the relatively high costs due to the long duration (3-5 years) remain to be solved. The current approaches aiming at optimization of AIT are reviewed, including both conceptual studies in experimental models and proof-of-concept - as well as large, multicenter clinical studies.

RECENT FINDINGS

The most promising approaches to improve efficacy and safety of vaccine-based AIT include bypassing IgE binding and targeting allergen-specific T cells using hypoallergenic recombinant allergen derivatives and immunogenic peptides, the use of new adjuvants and stimulators of the innate immune response, the fusion of allergens to immune modifiers and peptide carrier proteins and new routes of vaccine administration.

SUMMARY

The cloning of allergen proteins and genetic engineering enabled the production of vaccines that have well defined molecular, immunologic and biologic characteristics as well as modified molecular structure. These new compounds along with new immunization protocols can bring us closer to the ultimate goal of AIT, that is, complete cure of a large number of allergic patients.

Potential effector and immunoregulatory functions of mast cells in mucosal immunity

Mast cells (MCs) are cells of hematopoietic origin that normally reside in mucosal tissues, often near epithelial cells, glands, smooth muscle cells, and nerves. Best known for their contributions to pathology during IgE-associated disorders such as food allergy, asthma, and anaphylaxis, MCs are also thought to mediate IgE-associated effector functions during certain parasite infections. However, various MC populations also can be activated to express functional programs--such as secreting preformed and/or newly synthesized biologically active products--in response to encounters with products derived from diverse pathogens, other host cells (including leukocytes and structural cells), damaged tissue, or the activation of the complement or coagulation systems, as well as by signals derived from the external environment (including animal toxins, plant products, and physical agents). In this review, we will discuss evidence suggesting that MCs can perform diverse effector and immunoregulatory roles that contribute to homeostasis or pathology in mucosal tissues.

IgE immunotherapy against cancer

The success of antibody therapy in cancer is consistent with the ability of these molecules to activate immune responses against tumors. Experience in clinical applications, antibody design, and advancement in technology have enabled antibodies to be engineered with enhanced efficacy against cancer cells. This allows re-evaluation of current antibody approaches dominated by antibodies of the IgG class with a new light. Antibodies of the IgE class play a central role in allergic reactions and have many properties that may be advantageous for cancer therapy. IgE-based active and passive immunotherapeutic approaches have been shown to be effective in both in vitro and in vivo models of cancer, suggesting the potential use of these approaches in humans. Further studies on the anticancer efficacy and safety profile of these IgE-based approaches are warranted in preparation for translation toward clinical application.

Regulation of IgE-mediated signalling in human basophils by CD32b and its role in Syk down-regulation: basic mechanisms in allergic disease

BACKGROUND

CD32b has been previously demonstrated to modulate IgE-mediated secretion from human basophils. However, exploration of the implications of this regulation has been limited. One unstudied area is whether regulation of signalling by CD32 also alters some of the phenotypic changes induced by IgE-mediated activation. The reported character of CD32-mediated signal transduction is not clear for human basophils and the two primary mechanisms considered important in this reaction predict different long-term outcomes, notably predicting different outcomes for down-regulation of syk expression.

OBJECTIVE

Syk expression was considered a unique point of phenotypic control in human basophils and the role of CD32b in its regulation is explored in this study. However, initial pilot studies discovered that IL-3 could markedly up-regulate CD32 expression and first describing the consequences of this up-regulation became an additional focus of this study.

METHODS

Human basophils were examined for the changes in IgE-mediated signalling during simultaneous engagement of CD32b.

RESULTS

Preliminary experiments noted that CD32b could be up-regulated by IL-3 (3- to 12-fold). Both natural variation and induced up-regulation of CD32b modulated the efficacy of this receptor to inhibit IgE-mediated release. Signalling induced by engagement of CD32b (lyn, syk, SHP-1, or SHIP1 phosphorylation) was more consistent with a mode of action involving SHIP1 rather than SHP-1. IgE-mediated down-regulation of syk expression was not altered by co-engagement of CD32b, a result also consistent with a SHIP1-dependent mechanism of inhibition.

CONCLUSIONS

Taken together these results suggest that the combined action of IgE and IgG could generate a natural mechanism, whereby the significant variation in syk expression in allergic subjects occurs without necessarily also inducing mediator release.

Targeting the Fc receptor in autoimmune disease

INTRODUCTION

The Fc receptors (FcRs) and their interactions with immunoglobulin and innate immune opsonins, such as C-reactive protein, are key players in humoral and cellular immune responses. As the effector mechanism for some therapeutic monoclonal antibodies, and often a contributor to the pathogenesis and progression of autoimmunity, FcRs are promising targets for treating autoimmune diseases.

AREAS COVERED

This review discusses the nature of different FcRs and the various mechanisms of their involvement in initiating and modulating immunocyte functions and their biological consequences. It describes a range of current strategies in targeting FcRs and manipulating their interaction with specific ligands, while presenting the pros and cons of these approaches. This review also discusses potential new strategies including regulation of FcR expression and receptor crosstalk.

EXPERT OPINION

FcRs are appealing targets in the treatment of inflammatory autoimmune diseases. However, there are still knowledge limitations and technical challenges, the most important being a better understanding of the individual roles of each of the FcRs and enhancement of the specificity in targeting particular cell types and specific FcRs.

New treatments for allergen immunotherapy

Allergen-specific immunotherapy (SIT) represents the only curative and specific way for the treatment of allergic diseases, which have reached a pandemic dimension in industrial countries affecting up to 20-30% of the population. Although applied for 100 years to cure allergy, SIT still faces several problems related to side effects and limited efficacy. Currently, allergen-SIT is performed with vaccines based on allergen extracts that can cause severe, often life threatening, anaphylactic reactions as well as new IgE sensitization to other allergens present in the extract. Low patient adherence and high costs due to long duration (3 to 5 years) of treatment have been commonly reported. Several strategies have been developed to tackle these issues and it became possible to produce recombinant allergen-SIT vaccines with reduced allergenic activity.

"Auto-anti-IgE": naturally occurring IgG anti-IgE antibodies may inhibit allergen-induced basophil activation

Background

Naturally occurring IgE-specific IgG autoantibodies have been identified in patients with asthma and other diseases, but their spectrum of functions is poorly understood.

Objective

Address the hypothesis that: (i) IgG anti-IgE autoantibodies are detectable in the serum of all subjects but elevated in asthmatic patients regardless of atopic status as compared with controls; (ii) some activate IgE-sensitized basophils; and (iii) some inhibit allergen-induced basophil activation.

Methods

IgE-specific IgG autoantibodies were detected and quantified in sera using ELISA. Sera were examined for their ability to activate IgE-sensitized human blood basophils in the presence and absence of allergen using a basophil activation test, and to inhibit allergen binding to specific IgE on a rat basophilic cell line stably expressing human FcεRI.

Results

IgG autoantibodies binding to both free and FcεRI-bound IgE were detected in patients with atopic and non-atopic asthma, as well as controls. While some were able to activate IgE-sensitised basophils, others inhibited allergen-induced basophil activation, at least partly by inhibiting binding of IgE to specific allergen.

Conclusion

Naturally occurring IgG anti-IgE autoantibodies may inhibit, as well as induce, basophil activation. They act in a manner distinct from therapeutic IgG anti-IgE antibodies such as omalizumab. They may at least partly explain why atopic subjects who make allergen-specific IgE never develop clinical symptoms, and why omalizumab therapy is of variable clinical benefit in severe atopic asthma.