An immunoglobulin E-reactive chimeric human immunoglobulin G1 anti-idiotype inhibits basophil degranulation through cross-linking of FcepsilonRI with FcgammaRIIb

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Flavoring agent dihydrocoumarin alleviates IgE-mediated mast cell activation and allergic inflammation

Mast cells (MCs) are the main effector cells in the onset of high-affinity receptor for IgE (FcεRI)-mediated allergic diseases. The aim of this study was to test whether dihydrocoumarin (DHC), a food flavoring agent derived from Melilotus officinalis, can block IgE-induced MC activation effects and to examine the potential molecular mechanisms by which DHC affects MC activation. Rat basophilic leukemia cells (RBLs) and mouse bone marrow-derived mast cells (BMMCs) were sensitized with anti-dinitrophenol (DNP) immunoglobulin (Ig)E antibodies, stimulated with DNP-human serum albumin antigen, and treated with DHC. Western blot analyses were performed to detect the expression of signaling proteins. Murine IgE-mediated passive cutaneous anaphylaxis (PCA) and ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) models were used to examine DHC effects on allergic reactions in vivo. DHC inhibited MC degranulation, as evidenced by reduced β-hexosaminidase activity and histamine levels, and reduced morphological changes associated with MC activation, namely cellular elongation and F-actin reorganization. DHC inhibited the activation of MAPK, NF-κB, and AP-1 pathways in IgE-activated MCs. Additionally, DHC could attenuate IgE/Ag-induced allergic reactions (dye extravasation and ear thickening) in PCA as well as OVA challenge-induced reactions in ASA mice (body temperature, serum histamine and IL-4 secretion changes). In conclusion, DHC suppressed MC activation. DHC may represent a new MC-suppressing treatment strategy for the treatment of IgE-mediated allergic diseases.

Bispecific T-Cell Engagers Targeting Membrane-Bound IgE

The increased incidence of allergies and asthma has sparked interest in IgE, the central player in the allergic response. Interaction with its high-affinity receptor FcεRI leads to sensitization and allergen presentation, extracellular membrane-proximal domain in membrane IgE can act as an antigen receptor on B cells, and the interaction with low-affinity IgE receptor CD23 additionally influences its homeostatic range. Therapeutic anti-IgE antibodies act by the inhibition of IgE functions by interfering with its receptor binding or by the obliteration of IgE-B cells, causing a reduction of serum IgE levels. Fusion proteins of antibody fragments that can act as bispecific T-cell engagers have proven very potent in eliciting cytotoxic T-lymphocyte-mediated killing. We have tested five anti-IgE Fc antibodies, recognizing different epitopes on the membrane-expressed IgE, for the ability to elicit specific T-cell activation when expressed as single-chain Fv fragments fused with anti-CD3ε single-chain antibody. All candidates could specifically stain the cell line, expressing the membrane-bound IgE-Fc and bind to CD3-positive Jurkat cells, and the specific activation of engineered CD3-overexpressing Jurkat cells and non-stimulated CD8-positive cells was demonstrated for 8D6- and ligelizumab-based bispecific antibodies. Thus, such anti-IgE antibodies have the potential to be developed into agents that reduce the serum IgE concentration by lowering the numbers of IgE-secreting cells.

"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.

Anti-ids in allergy: timeliness of a classic concept

Abstract:

Anti-idiotypic antibodies (anti-ids) are part of natural immune responses with regulatory capacity. Their effect on an antigen-specific, so-called Ab1 antibody response, is dependent on 1) the original antigen, which they mirror, being Ab2 antibodies, and 2) their isotype. In the case of IgE-mediated allergy, natural anti-ids against allergen-specific IgE represent internal images of allergen molecules. A key biologic feature of allergens is that they can crosslink IgE, expressed by B-lymphocytes or passively bound via high affinity receptors to effector cells, which renders cellular activation. Therefore, the IgE cross linking capability of anti-ids determines whether they dampen or enhance immediate-type hypersensitivity. Correspondingly to classic antiallergen blocking IgG antibodies, anti-ids may also interact with inhibitory FcγRIIb receptors and, thereby, down-regulate T_H2-type inflammation. Anti-ids and other B-cell epitope mimetics, like mimotopes and DARPins, represent antigen surrogates, which can be used for vaccination. Intriguingly, they may induce antibody responses without activating potentially proinflammatory, antiallergen T-lymphocytes. Taken together, collective evidence suggests that anti-ids, although representing immunologic classics, are a timeless concept in allergology.

Allergen recognition by innate immune cells: critical role of dendritic and epithelial cells

Allergy is an exacerbated response of the immune system against non-self-proteins called allergens and is typically characterized by biased type-2 T helper cell and deleterious IgE mediated immune responses. The allergic cascade starts with the recognition of allergens by antigen presenting cells, mainly dendritic cells (DCs), leading to Th2 polarization, switching to IgE production by B cells, culminating in mast cell sensitization and triggering. DCs have been demonstrated to play a crucial role in orchestrating allergic diseases. Using different C-type lectin receptors DCs are able to recognize and internalize a number of allergens from diverse sources leading to sensitization. Furthermore, there is increasing evidence highlighting the role of epithelial cells in triggering and modulating immune responses to allergens. As well as providing a physical barrier, epithelial cells can interact with allergens and influence DCs behavior through the release of a number of Th2 promoting cytokines. In this review we will summarize current understanding of how allergens are recognized by DCs and epithelial cells and what are the consequences of such interaction in the context of allergic sensitization and downstream events leading to allergic inflammation. Better understanding of the molecular mechanisms of allergen recognition and associated signaling pathways could enable developing more effective therapeutic strategies that target the initial steps of allergic sensitization hence hindering development or progression of allergic diseases.

Immunology in the Clinic Review Series; focus on allergies: basophils as biomarkers for assessing immune modulation

Allergen-specific immunotherapy is an effective clinical treatment for hypersensitivity to many allergens. Studies of basophils during immunotherapy have provided insight into underlying immune mechanisms and support the potential use of basophil activation as a biomarker of clinical outcomes. This review examines the evidence for different pathways of basophil modulation associated with various forms of immunotherapy. Better understanding the molecular mechanisms of basophil activation and desensitization and the relationship between suppression of these effector cells to clinical outcomes holds promise for further development and improvement in potential therapies for allergic diseases.

Pathophysiology of asthma: what has our current understanding taught us about new therapeutic approaches?

Current asthma therapy is based on the use of adrenergic bronchodilator and anti-inflammatory drugs the specificity, efficacy, duration of action, and safety of which have been derived through classical pharmacology and medicinal chemistry. That asthma is a T(H)2-type inflammatory disorder frequently associated with atopy and allergic comorbidities has led to a concentrated effort to find treatments that act selectively on this pathway. A systematic literature review was undertaken, as well as a review of the Web site Clinicaltrials.gov for ongoing trials. Targets have included T cells themselves and their associated cytokines, chemokines, and receptors mostly targeted with biological agents. With the exception of anti-human IgE, none of these have met the expectations predicted from animal models and human in vitro tests. For most of these new therapies, only a very small subpopulation appears to respond. A case is made for a different approach to drug discovery based on acquiring a greater understanding of asthma stratification, the relevant pathways involved, and the development of appropriate diagnostic tests enabling the targeting of selective treatments to those asthmatic phenotypes most likely to respond. The recognition that asthma is more than allergy mandates improved predictive animal models and an appreciation that many of the environmental insults that initiate, consolidate, and exacerbate asthma operate through an epithelium functioning in a disorderly fashion. An integrated model that places the epithelium at the forefront of asthma pathogenesis suggests that greater emphasis should be placed on therapeutics that increase the airways' resistance against the inhaled environment rather than focusing only on suppression of inflammation.

Inhibition of ongoing allergic reactions using a novel anti-IgE DARPin-Fc fusion protein

BACKGROUND

Aggregation of the high-affinity IgE receptor (FcεRI) with the low-affinity IgG receptor (FcγRIIb) on basophils or mast cells has been shown to inhibit allergen-induced cell degranulation. Molecules cross-linking these two receptors might therefore be of interest for the treatment of allergic disorders. Here, we demonstrate the generation of a novel bispecific fusion protein efficiently aggregating FcεRI-bound IgE with FcγRIIb on the surface of basophils to prevent pro-inflammatory mediator release.

METHODS

Alternative binding molecules recognizing receptor-bound human IgE were selected from DARPin (designed ankyrin repeat protein) libraries. One of the selected DARPins was linked to the Fc-part of a human IgG(1) antibody for binding to FcγRIIb.

RESULTS

The resulting anti-IgE DARPin-Fc fusion protein was not anaphylactogenic and inhibited allergen-induced basophil activation in whole blood assays. Both binding moieties of the fusion protein, namely the anti-IgE DARPin as well as the IgG(1) Fc-part, were required to achieve this inhibitory effect. Most importantly, inhibition was faster and more efficient than with Omalizumab, a humanized anti-IgE antibody currently used for the treatment of severe asthma.

CONCLUSION

This novel anti-IgE DARPin-Fc fusion protein might represent a potential drug candidate for preventive or immediate treatment of allergic reactions.

The inhibitory effects of intravenous administration of rabbit immunoglobulin G on airway inflammation are dependent upon Fcγ receptor IIb on CD11c(+) dendritic cells in a murine model

Immunoglobulins (Igs) play important immunomodulatory effects on allergic asthma. Among these, IgG has been reported to regulate allergic inflammation in previous studies about immunotherapy and intravenous immunoglobulin therapy. In this study, to examine the immunomodulatory mechanisms of IgG and FcRs we evaluated the effects of intravenous (i.v.) rabbit IgG administration (IVIgG) on allergic airway inflammation and lung antigen-presenting cells (APCs) in a murine model of ovalbumin (OVA) sensitization and challenge. In OVA-challenged mice, IVIgG attenuated airway eosinophilia, airway hyperresponsiveness and goblet cell hyperplasia and also inhibited the local T helper type (Th) 2 cytokine levels. Additionally, IVIgG attenuated the proliferation of OVA-specific CD4(+) T cells transplanted into OVA-challenged mice. Ex vivo co-culture with OVA-specific CD4(+) cells and lung CD11c(+) APCs from mice with IVIgG revealed the attenuated transcription level of Th2 cytokines, suggesting an inhibitory effect of IVIgG on CD11c(+) APCs to induce Th2 response. Next, to analyse the effects on Fcγ receptor IIb and dendritic cells (DCs), asthmatic features in Fcγ receptor IIb-deficient mice were analysed. IVIgG failed to attenuate airway eosinophilia, airway inflammation and goblet cell hyperplasia. However, the lacking effects of IVIgG on airway eosinophilia in Fcγ receptor IIb deficiency were restored by i.v. transplantation of wild-type bone marrow-derived CD11c(+) DCs. These results demonstrate that IVIgG attenuates asthmatic features and the function of lung CD11c(+) DCs via Fcγ receptor IIb in allergic airway inflammation. Targeting Fc portions of IgG and Fcγ receptor IIb on CD11c(+) DCs in allergic asthma is a promising therapeutic strategy.

Sensitization of skin mast cells with IgE antibodies to Culicoides allergens occurs frequently in clinically healthy horses

IgE antibodies are mediators of mast cell degranulation during allergic diseases. The binding of IgE to its high-affinity IgE receptor on mast cell surfaces is called "sensitization" and precedes the development of clinical allergy. Previously, intradermal injection of anti-IgE or the anti-IgG(T) antibody CVS40 induced immediate skin reactions in horses. This suggested that both IgE and IgG(T) sensitize equine skin mast cells. Here, we investigated sensitization to allergen and with IgE or IgG(T) in clinically healthy horses of different age groups. In addition, immediate skin reactions to Culicoides were determined by intradermal testing in non-allergic horses. A total of 14% of the young horses 1-3 years old and 38% of the adult animals showed skin reaction to Culicoides allergen extract. Sensitization with IgE and IgG(T) was evaluated in skin mast cells and peripheral blood basophils to determine whether sensitization with IgG(T) preceded that with IgE in young horses. Anti-IgE stimulated immediate skin reactions in 18 of 21 young horses, but only 7 of them reacted to the anti-IgG(T) antibody CVS40. The equine IgG(T) fraction is composed of IgG3 and IgG5. We used several newly developed monoclonal antibodies to IgG3 and IgG5 for intradermal testing to improve our understanding about the mast cell reaction induced by the anti-IgG(T) antibody CVS40. None of these antibodies induced a skin reaction in young or adult horses. To determine sensitization with IgE in neonates and foals at 6 and 12 weeks of age an in vitro histamine release assay was performed using peripheral blood cells. The histamine concentration released by anti-IgE stimulation from foal basophils increased between birth and 12 weeks of age, while almost no histamine release was observed after anti-IgG(T) treatment of the cells. In summary, IgE was the major immunoglobulin involved in the sensitization of mast cells and basophils in horses at various ages. IgG(T) antibodies did not play a major role in the activation of mast cells or basophils in young horses and their role in the sensitization of adult horses remains unclear. Sensitization to Culicoides allergen in the absence of clinical disease was frequently found in horses of all age groups. Because many clinically healthy horses developed skin reactions to this allergen, sensitization results are useful to diagnose Culicoides-induced allergy only in horses with allergic conditions.