IgE and FcepsilonRI regulation

SHIP-1 differentially regulates IgE-induced IL-10 and antiviral responses in human monocytes

IgE-mediated stimulation of monocytes regulates multiple cellular functions including cellular maturation, cytokine release, antiviral responses, and T cell priming and differentiation. The high affinity IgE receptor, FcεRI, is closely linked to serum IgE levels and atopic disease. The signaling molecules which regulate effector functions of this receptor have been well studied in mast cells and basophils, however, less is known about the signaling components, regulatory molecules, and mechanisms downstream of receptor activation in monocytes. This study sought to identify regulators of IgE-mediated cytokine release in human monocytes. SHIP-1 was identified as a negative regulator of IgE-induced IL-10 production. It was also determined that IgE-mediated stimulation and SHIP-1 inhibition decreased antiviral IP-10 production after liposomal poly(I:C) stimulation, indicating differential regulation by SHIP-1 in IgE-driven and antiviral response pathways. Both SHIP-1 and NF-κB were activated following IgE-mediated stimulation of primary monocytes, and NF-κB activation was related to both SHIP-1 and FcεRIα expression levels in monocytes. To our knowledge this is the first study to identify a role for SHIP-1 in regulating IgE-driven responses and antiviral responses in human monocytes. Given the importance of monocytes in inflammation and immune responses, a better understanding of the signaling and regulatory mechanisms downstream of FcεRI receptor could lead to new therapeutic targets in allergic disease.

FcεRI deficiency alleviates silica-induced pulmonary inflammation and fibrosis

Silicosis is one of the most important occupational diseases worldwide, caused by inhalation of silica particles or free crystalline silicon dioxide. As a disease with high mortality, it has no effective treatment and new therapeutic targets are urgently needed. Recent studies have identified FCER1A, encoding α-subunit of the immunoglobulin E (IgE) receptor FcεRI, as a candidate gene involved in the biological pathways leading to respiratory symptoms. FcεRI is known to be important in allergic asthma, but its role in silicosis remains unclear. In this study, serum IgE concentrations and FcεRI expression were assessed in pneumoconiosis patients and silica-exposed mice. The role of FcεRI was explored in a silica-induced mouse model using wild-type and FcεRI-deficient mice. The results showed that serum IgE concentrations were significantly elevated in both pneumoconiosis patients and mice exposed to silica compared with controls. The mRNA and protein expression of FcεRI were also significantly increased in the lung tissue of patients and silica-exposed mice. FcεRI deficiency significantly attenuated the changes in lung function caused by silica exposure. Silica-induced elevations of IL-1β, IL-6, and TNF-α were significantly attenuated in the lung tissue and bronchoalveolar lavage fluid (BALF) of FcεRI-deficient mice compared with wild-type controls. Additionally, FcεRI-deficient mice showed a significantly lower score of pulmonary fibrosis than wild-type mice following exposure to silica, with significantly lower hydroxyproline content and expression of fibrotic genes Col1a1 and Fn1. Immunofluorescent staining suggested FcεRI mainly on mast cells. Mast cell degranulation took place after silica exposure, as shown by increased serum histamine levels and β-hexosaminidase activity, which were significantly reduced in FcεRI-deficient mice compared with wild-type controls. Together, these data showed that FcεRI deficiency had a significant protective effect against silica-induced pulmonary inflammation and fibrosis. Our findings provide new insights into the pathophysiological mechanisms of silica-induced pulmonary fibrosis and a potential target for the treatment of silicosis.

The Effector Function of Allergens

Allergens are antigens that generate an IgE response (sensitization) in susceptible individuals. The allergenicity of an allergen can be thought of in terms of its ability to sensitize as well as its ability to cross-link IgE/IgE receptor complexes on mast cells and basophils leading to release of preformed and newly formed mediators (effector activity). The identity of the allergens responsible for sensitization may be different from those that elicit an allergic response. Effector activity is determined by (1) the amount of specific IgE (sIgE) and in some circumstances the ratio of sIgE to total IgE, (2) the number of high affinity receptors for IgE (FcεR1) on the cell surface, (3) the affinity of binding of sIgE for its epitope and, in a polyclonal response, the collective avidity, (4) the number and spatial relationships of IgE binding epitopes on the allergen and (5) the presence of IgG that can bind to allergen and either block binding of sIgE and/or activate low affinity IgG receptors that activate intracellular inhibitory pathways. This review will discuss these important immunologic and physical properties that contribute to the effector activity of allergens.

Advances in allergen-specific immune cell measurements for improved detection of allergic sensitization and immunotherapy responses

Over the past two decades, precision medicine has advanced diagnostics and treatment of allergic diseases. Component-resolved analysis of allergen sensitization facilitates stratification of patients. Furthermore, new formulations of allergen immunotherapy (AIT) products can more effectively deliver the relevant components. Molecular insights from the identification of allergen component sensitization and clinical outcomes of treatment with new AIT formulations can now be utilized for a deeper understanding of the nature of the pathogenic immune response in allergy and how this can be corrected by AIT. Fundamental in these processes are the allergen-specific B and T cells. Within the large B- and T-cell compartments, only those that specifically recognize the allergen with their immunoglobulin (Ig) or T-cell receptor (TCR), respectively, are of clinical relevance. With peripheral blood allergen-specific B- and T-cell frequencies below 1%, bulk cell analysis is typically insufficiently sensitive. We here review the latest technologies to detect allergen-specific B and T cells, as well as new developments in utilizing these tools for diagnostics and therapy monitoring to advance precision medicine for allergic diseases.

Expression of FcεRIα and tryptase in human lung tissue during drug-induced anaphylactic death

The diagnosis of drug-induced anaphylactic death is an important component of forensic medicine. The purpose of this study was to explore the expression of FcεRIα and tryptase in human lung tissue during drug-induced anaphylactic death and its value for forensic medicine. The expression of FcεRIα and tryptase in lung tissues of the drug-induced anaphylactic death group (n = 30) and control group (who died due to sudden cardiac death, falling from a height, or traffic accidents, n = 30) was detected by immunohistochemistry and immunofluorescence staining. The difference in FcεRIα and tryptase expression in the lung tissue between the drug-induced anaphylactic death group and the control group was statistically significant (p < 0.05). The levels of FcεRIα and tryptase expression greatly increased in the lung tissue of the drug-induced anaphylactic death group, which may provide morphological evidence and a reference for the diagnosis of drug-induced anaphylactic death in forensic medicine.

Enhanced plasmacytoid dendritic cell antiviral responses after omalizumab

BACKGROUND

Atopy and viral respiratory tract infections synergistically promote asthma exacerbations. IgE cross-linking inhibits critical virus-induced IFN-α responses of plasmacytoid dendritic cells (pDCs), which can be deficient in patients with allergic asthma.

OBJECTIVE

We sought to determine whether reducing IgE levels in vivo with omalizumab treatment increases pDC antiviral IFN-α responses in inner-city children with asthma.

METHODS

PBMCs and pDCs isolated from children with exacerbation-prone asthma before and during omalizumab treatment were stimulated ex vivo with rhinovirus and influenza in the presence or absence of IgE cross-linking. IFN-α levels were measured in supernatants, and mRNA expression of IFN-α pathway genes was determined by using quantitative RT-PCR (qRT-PCR) in cell pellets. FcεRIα protein levels and mRNA expression were measured in unstimulated cells by using flow cytometry and qRT-PCR, respectively. Changes in these outcomes and associations with clinical outcomes were analyzed, and statistical modeling was used to identify risk factors for asthma exacerbations.

RESULTS

Omalizumab treatment increased rhinovirus- and influenza-induced PBMC and rhinovirus-induced pDC IFN-α responses in the presence of IgE cross-linking and reduced pDC surface FcεRIα expression. Omalizumab-induced reductions in pDC FcεRIα levels were significantly associated with a lower asthma exacerbation rate during the outcome period and correlated with increases in PBMC IFN-α responses. PBMC FcεRIα mRNA expression measured on study entry significantly improved an existing model of exacerbation prediction.

CONCLUSIONS

These findings indicate that omalizumab treatment augments pDC IFN-α responses and attenuates pDC FcεRIα protein expression and provide evidence that these effects are related. These results support a potential mechanism underlying clinical observations that allergic sensitization is associated with increased susceptibility to virus-induced asthma exacerbations.

Molecular allergy diagnostics using IgE singleplex determinations: methodological and practical considerations for use in clinical routine: Part 18 of the Series Molecular Allergology

Allergen molecules (synonyms: single allergens, allergen components) open up new horizons for the targeted allergen-specific diagnostics of immunoglobulin E (IgE) in singleplex determination. The following rationales support the targeted use of allergen molecules and, more importantly, improve test properties: (1) increased test sensitivity ("analytical sensitivity"), particularly when important allergens are under-represented or lacking in the extract; (2) improved test selectivity (analytical specificity), particularly when the selected IgE repertoire against an allergen yields additional information on: (a) potential risk, (b) possible cross-reactivity, or (c) primary (species-specific) sensitization. However, the appropriate indication for the use of single allergens can only be established on a case-by-case basis (depending on the clinical context and previous history) and in an allergen-specific manner (depending on the allergen source and the single allergens available), rather than in a standardized way. Numerous investigations on suspected food allergy, insect venom allergy, or sensitization to respiratory allergens have meanwhile demonstrated the successful use of defined molecules for allergen-specific singleplex IgE diagnosis. Specific IgE to single allergens is limited in its suitability to predict the clinical relevance of sensitivity on an individual basis. In food allergies, one can at best identify the relative risk of a clinical reaction on the basis of an IgE profile, but no absolutely reliable prediction on (future) tolerance can be made. Ultimately, the clinical relevance of all IgE findings depends on the presence of corresponding symptoms and can only be assessed on an individual basis (previous history, symptom log, and provocation testing with the relevant allergen source where appropriate). Thus, also in molecular allergology, the treating physician and not the test result should determine the clinical relevance of diagnostic findings.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available for this article at 10.1007/s40629-015-0067-z and is accessible for authorized users.

Clonal differences in IgE antibodies affect cutaneous anaphylaxis-associated thermal sensitivity in mice

Cellular and molecular mediators of immune responses are increasingly implicated in acute and chronic pain pathophysiologies. Here we demonstrate that passive cutaneous IgE/Ag anaphylaxis provokes increased thermal sensitivity in the hind paw tissue of mice. The murine anti-DNP IgE antibodies SPE-7 and ɛ26 are known to induce differential cytokine production in bone marrow cultured mast cells in vitro without antigen challenge. We found a novel, antigen-dependent heterogeneity in the thermal pain responses elicited in the hind paws between SPE-7 and ɛ26 sensitized DNP-challenged mice. Mice experienced pronounced hind paw thermal sensitivity lasting 6h after DNP challenge when sensitized with SPE-7 but not ɛ26 IgE. The two IgE clones induced equivalent hind paw edema, neutrophil influx, cytokine production, and reduction in tissue histamine content in vivo, and bound to the same or overlapping epitopes on the DNP antigen in vitro. Therefore IgE antibodies against the same antigen can induce comparable inflammation, yet contribute to markedly different anaphylaxis-associated pain within an allergic response, suggesting that non-canonical IgE binding partners such as sensory neurons may play a role in allergy-related pain responses.

Human FcR polymorphism and disease

Fc receptors play a central role in maintaining the homeostatic balance in the immune system. Our knowledge of the structure and function of these receptors and their naturally occurring polymorphisms, including single nucleotide polymorphisms and/or copy number variations, continues to expand. Through studies of their impact on human biology and clinical phenotype, the contributions of these variants to the pathogenesis, progression, and/or treatment outcome of many diseases that involve immunoglobulin have become evident. They affect susceptibility to bacterial and viral pathogens, constitute as risk factors for IgG or IgE mediated inflammatory diseases, and impact the development of many autoimmune conditions. In this chapter, we will provide an overview of these genetic variations in classical FcγRs, FcRLs, and other Fc receptors, as well as challenges in achieving an accurate and comprehensive understanding of the FcR polymorphisms and genomic architecture.

Cytokinergic IgE Action in Mast Cell Activation

Some 10 years ago it emerged that at sufficiently high concentrations certain monoclonal mouse IgEs exert previously unsuspected effects on mast cells. Thus they can both promote survival and induce activation of mast cells without the requirement for antigens. This was a wake up call that appears to have been missed (or dismissed) by the majority of immunologists. The structural attributes responsible for the potency of the so-called “highly cytokinergic” or HC IgEs have not yet been determined, but the events that ensue when such IgEs bind to the high-affinity receptor, FcεRI, on mast cells have been thoroughly studied, and are strikingly similar to those engendered by antigens when they form cross-linked complexes with the receptors. We review the evidence for the cytokinergic activity of IgE, and the structural features and known properties of immunoglobulins, and of IgE in particular, most likely to be implicated in the phenomenon. We suggest that IgEs with cytokinergic activity may be generated by local germinal center reactions in the target organs of allergy. We consider also the important implications that the existence of cytokinergic IgE may have for a fuller understanding of adaptive immunity and of the action of IgE in asthma and other diseases.

Molecular mechanisms of IgE mediated food allergy

The purpose of this review is to collate current knowledge and recent advances in molecular mechanism behind the immediate type hypersensitivity of foods. Food allergy is a growing concern of human health in developed as well as developing countries now days. Food allergic reactions are mostly IgE mediated and also known as immediate type hypersensitivity or type I reaction. This review encompasses a wide range of molecular events during IgE mediated reactions like primary exposure of allergens, processing of allergens by antigen presenting cells, role of transcription factors like GATA-3, STAT-6, NF-AT, c-maf, c-kit and NF-κB, Treg cells, toll like receptors, cytokines and chemokines, class switch to IgE, FcεR1 receptor, priming of IgE on mast cells or basophils, signaling events followed by secondary exposure of allergens, degranulation and release of mediators like leukotrienes, histamines, prostaglandins, β-hexosaminidase and ultimately anaphylaxis. This review may be helpful to beginners as well as experts working in the field of allergy and immunology because of the stepwise explanations of molecular mechanisms involved in IgE mediated reactions.

Omalizumab-induced decrease of FcξRI expression in patients with severe allergic asthma

BACKGROUND

It is documented that omalizumab treatment reduces the cell surface expression of immunoglobulin E high-affinity receptor (FcɛRI) on several cell types. This has not been investigated in patients with uncontrolled severe persistent allergic asthma.

METHODS

In a double-blind, randomized, placebo-controlled study, patients with severe allergic asthma uncontrolled by high dose inhaled corticosteroids and long-acting β(2)-agonist received either omalizumab (n = 20) or placebo (n = 11) over 16 weeks at appropriate doses and frequencies. Baseline and end of study (week 16) FcɛRI expression on basophils and plasmacytoid dendritic cells was determined by flow cytometry for the primary endpoint. Secondary efficacy endpoints included asthma control and lung function as part of an initial investigation into the use of FcɛRI expression as a marker of response.

RESULTS

In the omalizumab group, and with respect to placebo, FcɛRI expression was significantly reduced at end of study on basophils (-82.6%, p < 0.01) and plasmacytoid dendritic cells (-44.2%, p = 0.029). FcɛRI expression reduction was not found to be correlated with clinical response.

CONCLUSIONS

Long-term omalizumab treatment induced reduction of FcɛRI expression on circulating basophils and plasmacytoid dendritic cells. These changes were not associated with those of clinical features related to severe asthma, which does not support further investigation into its use as a predictive marker of response.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov (identifier: NCT00454051) and the European Clinical Trials Database, EudraCT (identifier: 2006-003591-35).

Development of an inhaled endotoxin challenge protocol for characterizing evoked cell surface phenotype and genomic responses of airway cells in allergic individuals

BACKGROUND

Environmental exposure to endotoxin is a known cause of exacerbation of asthma. Inhaled endotoxin protocols have been used to evaluate airway cell surface phenotypes associated with antigen presentation and innate immunity in healthy volunteers, but not in allergic volunteers.

OBJECTIVES

To establish the safety of challenge with low-dose endotoxin (10,000 endotoxin units) (lipopolysaccharide [LPS]) inhalation in allergic individuals, to measure airway cell surface phenotypes associated with antigen presentation and innate immunity in induced sputum (IS) after LPS challenge, and to conduct gene expression profiling in IS cells to determine which host genetic networks are modified by LPS inhalation.

METHODS

Induced sputum was obtained before and 6 hours after LPS inhalation in 10 allergic volunteers (8 with asthma and 2 with rhinitis). Flow cytometry was used to examine cell surface phenotypes on IS cells. Genomic expression was analyzed on a subset of IS samples (n = 10) using microarray and ingenuity pathway analysis.

RESULTS

A total of 10,000 endotoxin units of LPS induced significant up-regulation of membrane CD14, CD11b, CD16, HLA-DR, CD86, and Fcepsilon receptor 1 on sputum phagocytes and increased expression of genes that influence antigen-presenting surface molecules (HLA-DR, chemokine ligand 2 or monocyte chemoattractant protein 1, v-rel reticuloendotheliosis viral oncogene homolog, prostaglandin-endoperoxide synthase 2 or cyclooxygenase 2, and transforming growth factor beta), immune activation (CD14, interleukin 1beta, and regulated upon activation, normal T cell expressed and secreted), and inflammation (intracellular adhesion molecule 1 and inhibitory kappaBalpha). Gene profiles for nuclear factor kappaB, interleukin 1, and tumor necrosis factor pathways were also significantly affected.

CONCLUSIONS

Low-dose inhaled endotoxin challenge is safe in allergic individuals with mild to moderate disease. It enhances airway cell surface phenotypes and expression of genes associated with antigen presentation, innate immunity, and inflammation. Microarray with ingenuity pathway analysis can be successfully applied to sputum cells to characterize genetic responses to inhaled exacerbants.

Inhibition of FcepsilonRI-dependent mediator release and calcium flux from human mast cells by sialic acid-binding immunoglobulin-like lectin 8 engagement

BACKGROUND

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are a family of glycan-binding inhibitory receptors, and among them, Siglec-8 is selectively expressed on human eosinophils, basophils, and mast cells. On eosinophils, Siglec-8 engagement induces apoptosis, but its function on mast cells is unknown.

OBJECTIVE

We sought to study the effect of Siglec-8 engagement on human mast cell survival and mediator release responses.

METHODS

Human mast cells were generated from CD34+ precursors. Apoptosis was studied by using flow cytometry. Mast cell mediator release or human lung airway smooth muscle contraction was initiated by FcepsilonRI cross-linking with or without preincubation with Siglec-8 or control antibodies, and release of mediators was analyzed along with Ca++ flux. RBL-2H3 cells transfected with normal and mutated forms of Siglec-8 were used to study how Siglec-8 engagement alters mediator release.

RESULTS

Siglec-8 engagement failed to induce human mast cell apoptosis. However, preincubation with Siglec-8 mAbs significantly (P < .05) inhibited FcepsilonRI-dependent histamine and prostaglandin D(2) release, Ca++ flux, and anti-IgE-evoked contractions of human bronchial rings. In contrast, release of IL-8 was not inhibited. Siglec-8 ligation was also shown to inhibit beta-hexosaminidase release and Ca++ flux triggered through FcepsilonRI in RBL-2H3 cells transfected with full-length human Siglec-8 but not in cells transfected with Siglec-8 containing a tyrosine to phenylalanine point mutation in the membrane-proximal immunoreceptor tyrosine-based inhibitory motif domain.

CONCLUSION

These data represent the first reported inhibitory effects of Siglec engagement on human mast cells.

Gene expression analysis illuminates the transcriptional programs underlying the functional activity of ex vivo-expanded granulocytes

Global gene expression analysis established the temporal expression patterns and programs underlying the development of functional activity of ex vivo-expanded (EXE) human granulocytes, as well as differences compared with peripheral blood (PB) granulocytes. CD34(+) progenitor cells were cultured for 3 wk to induce rapid expansion and granulocytic differentiation, with 40% CD15(+) cells by day 3 and 90% by day 12. Phagocytic and respiratory burst activity increased with the fraction of CD15(++)CD11b(+) cells (myelocytes to segmented) and peaked by day 17. However, only 25% of CD15(++)CD11b(+) cells were phagocytic, and respiratory burst activity was one-third that of PB granulocytes. EXE granulocytes from later days and PB granulocytes showed similar expression of Fc gamma receptors (-1A, -2A, -2C, -3A) and complement receptors (-1, -3, -4). Later downregulation of CD36 (expressed by macrophages) suggests lineage plasticity early in granulocytic differentiation. Expression in mature EXE and PB granulocytes was similar for most Fc gamma receptor-mediated phagocytosis signaling proteins, including high-level expression of Hck, Fgr, and the actin-related protein 2/3 complex. Lower expression of Lyn, Cdc42, pleckstrin, and PKC beta(I) by EXE granulocytes may explain decreased phagocytosis. PB and mature EXE granulocytes expressed similar levels of NADPH oxidase complex genes and receptors for fMLP-mediated respiratory burst. Lower burst activity by EXE granulocytes may result from lower expression of Raf1 and PKC zeta. Elevated expression of toll-like receptor (TLR)2, TLR1, and CD14 in mature EXE and PB granulocytes supports a role for the TLR2 and CD14 pathway in zymosan-mediated respiratory burst activity. Lower activity in EXE granulocytes may be due to greater expression of IRAK3, which inhibits TLR-mediated signaling.

CD23-mediated transport of IgE/immune complexes across human intestinal epithelium: role of p38 MAPK

We previously reported that CD23/FcepsilonRII (low-affinity IgE receptor) is expressed on human intestinal epithelial cells and is responsible for transepithelial transport of IgE. In this study, we compared the transport of IgE with that of immune complexes in both the apical-to-serosal and the serosal-to-apical directions across HT29 epithelial cell layers and examined the effects of two p38 MAPK inhibitors, SKF86002 and SB203580, on the expression and function of CD23. Our study showed that both p38 MAPK inhibitors at 10 microM significantly inhibited constitutive and IL-4-upregulated CD23 protein expression in epithelial cells. Both inhibitors, in a concentration-dependent manner, also significantly reduced IgE binding and uptake into cells. Transepithelial transport of IgE and immune complexes across the epithelial barrier were similarly inhibited. IL-4 upregulated the phosphorylation and activity of p38 MAPK and the phosphorylation of the downstream substrate MAPKAPK-2 (MK-2). The inhibitors exerted effects in the pathway post the p38 MAPK; SB203580 significantly inhibited the phosphorylation of MK-2. Our results indicate that CD23 expression in these human intestinal epithelial cells is mediated through the p38 MAPK pathway and that inhibition of p38 MAPK consequently interferes with the transport of IgE and immune complexes across the intestinal epithelial barrier.

An intermediate pH unfolding transition abrogates the ability of IgE to interact with its high affinity receptor FcepsilonRIalpha

The interaction between IgE-Fc (Fcepsilon) and its high affinity receptor FcepsilonRI on the surface of mast cells and basophils is a key event in allergen-induced allergic inflammation. Recently, several therapeutic strategies have been developed based on this interaction, and some include Fcepsilon-containing moieties. Unlike well characterized IgG therapeutics, the stability and folding properties of IgE are not well understood. Here, we present comparative biophysical analyses of the pH stability and thermostability of Fcepsilon and IgG1-Fc (Fcgamma). Fcepsilon was found to be significantly less stable than Fcgamma under all pH and NaCl conditions tested. Additionally, the Cepsilon3Cepsilon4 domains of Fcepsilon were shown to become intrinsically unfolded at pH values below 5.0. The interaction between Fcepsilon and an Fcgamma-FcepsilonRIalpha fusion protein was studied between pH 4.5 and 7.4 using circular dichroism and a combination of differential scanning calorimetry and isothermal titration calorimetry. Under neutral pH conditions, the apparent affinity of Fcepsilon for the dimeric fusion protein was extremely high compared with published values for the monomeric receptor (KD < 10(-12) m). Titration to pH 6.0 did not significantly change the binding affinity, and titration to pH 5.5 only modestly attenuated affinity. At pH values below 5.0, the receptor binding domains of Fcepsilon unfolded, and interaction of Fcepsilon with the Fcgamma-FcepsilonRIalpha fusion protein was abrogated. The unusual pH sensitivity of Fcepsilon may play a role in antigen-dependent regulation of receptor-bound, non-circulating IgE.

Fc receptors as determinants of allergic reactions

Activation of the high-affinity receptor for IgE (FcepsilonRI) on allergic effector cells induces a multitude of positive signals via immunoreceptor tyrosine-based activation motifs, which leads to the rapid manifestation of allergic inflammatory reactions. As a counterbalance, the coaggregation of the IgG receptor FcgammaRIIB mediates inhibitory signals via immunoreceptor tyrosine-based inhibition motifs. Advances in the positive and negative regulation of Fc receptor expression and signaling have shed light on the role of Fc receptors in our immune system, indicating them to be bifunctional, inhibitory and activating structures. Based on these findings, exciting new therapeutic strategies have been developed, such as the use of chimeric fusion proteins, which concomitantly activate FcepsilonRI and FcgammaRIIB. These new approaches successfully take advantage of the bivalent character of Fc receptors and pave the way for innovative strategies to modulate allergic immune reactions.