Fc receptors as determinants of allergic reactions

Refinement of an ovine-based immunoglobulin therapy against SARS-CoV-2, with comparison of whole IgG versus F(ab')2 fragments

The development of new therapies against SARS-CoV-2 is required to extend the toolkit of intervention strategies to combat the global pandemic. In this study, hyperimmune plasma from sheep immunised with whole spike SARS-CoV-2 recombinant protein has been used to generate candidate products. In addition to purified IgG, we have refined candidate therapies by removing non-specific IgG via affinity binding along with fragmentation to eliminate the Fc region to create F(ab')2 fragments. These preparations were evaluated for in vitro activity and demonstrated to be strongly neutralising against a range of SARS-CoV-2 strains, including Omicron B2.2. In addition, their protection against disease manifestations and viral loads were assessed using a hamster SARS-CoV-2 infection model. Results demonstrated protective effects of both IgG and F(ab')2, with the latter requiring sequential dosing to maintain in vivo activity due to rapid clearance from the circulation.

Pathogenesis of allergic diseases and implications for therapeutic interventions

Allergic diseases such as allergic rhinitis (AR), allergic asthma (AAS), atopic dermatitis (AD), food allergy (FA), and eczema are systemic diseases caused by an impaired immune system. Accompanied by high recurrence rates, the steadily rising incidence rates of these diseases are attracting increasing attention. The pathogenesis of allergic diseases is complex and involves many factors, including maternal-fetal environment, living environment, genetics, epigenetics, and the body's immune status. The pathogenesis of allergic diseases exhibits a marked heterogeneity, with phenotype and endotype defining visible features and associated molecular mechanisms, respectively. With the rapid development of immunology, molecular biology, and biotechnology, many new biological drugs have been designed for the treatment of allergic diseases, including anti-immunoglobulin E (IgE), anti-interleukin (IL)-5, and anti-thymic stromal lymphopoietin (TSLP)/IL-4, to control symptoms. For doctors and scientists, it is becoming more and more important to understand the influencing factors, pathogenesis, and treatment progress of allergic diseases. This review aimed to assess the epidemiology, pathogenesis, and therapeutic interventions of allergic diseases, including AR, AAS, AD, and FA. We hope to help doctors and scientists understand allergic diseases systematically.

Natural isoflavone formononetin inhibits IgE-mediated mast cell activation and allergic inflammation by increasing IgE receptor degradation

Immunoglobulin (Ig)E-associated mast cell (MC) activation triggers pro-inflammatory signals that underlie type I allergic diseases. Here, we examined the effects of the natural isoflavone formononetin (FNT) on IgE-mediated MC activation and associated mechanisms of high-affinity IgE receptor (FcεRI) signal inhibition. The effects of FNT on the mRNA expression of inflammatory factors, release of histamine and β-hexosaminidase (β-hex), and expression of signaling proteins and ubiquitin (Ub)-specific proteases (USPs) were analyzed in two sensitized/stimulated MC lines. FcεRIγ-USP interactions were detected by co-immunoprecipitation (IP). FNT dose-dependently inhibited β-hex activity, histamine release, and inflammatory cytokine expression in FcεRI-activated MCs. FNT suppressed IgE-induced NF-κB and MAPK activity in MCs. The oral administration of FNT attenuated passive cutaneous anaphylaxis (PCA) reactions and ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) reactions in mice. FNT reduced the FcεRIγ chain expression, via increased proteasome-mediated degradation, and induced FcεRIγ ubiquitination by inhibiting USP5 and/or USP13. FNT and USP inhibition may be useful for suppressing IgE-mediated allergic diseases.

Micropatterned Ligand Arrays to Investigate Spatial Regulation of Cellular Signaling Initiated by Clustered Fc Receptors

Cell surface receptors that bind the Fc segment of antibodies to initiate signaling play fundamental roles in immune responses. Multiple, diverse Fc receptors (e.g., Fc gamma, Fc-alpha, and Fc-epsilon) are expressed on different immune cells, including natural killer cells, macrophages, mast cells, and neutrophils. Fc receptors bind particular antibody isotypes (e.g., IgG, IgA, IgE, respectively) thereby sensitizing the cells to their specific antigens. Receptor clustering by antigen or other multivalent ligands induces a signaling cascade that leads to targeted secretion of chemical mediators (e.g., histamine, cytokines, and chemokines) and other cell-specific responses. Spatial targeting and compartmentalization are common mechanisms for regulating Fc receptor signaling. However, the tools for studying these dynamic interactions at cellular levels have been limited due to the nanoscale dimensions of the signaling complexes and their dispersal across the cell surface. To overcome these limitations in our model system, we use microfabricated surfaces containing spatially defined ligands to cluster and activate IgE receptors (FcεRI), which initiate allergic responses by mast cells. Micron-scale control of receptor assemblies allows investigation with conventional fluorescence microscopy of spatially regulated redistributions of intracellular signaling components. This approach in conjunction with biochemical techniques has proven valuable for investigating immune receptor signaling.

Human peripheral basophils extended phenotype shows a high expression of CD244 immuno-regulatory receptor

INTRODUCTION

Basophils play a major physio-pathological role in hypersensitivity related diseases. Basophils express high affinity Immunoglobulin (Ig) E receptors (FcεRI), IgG and complement regulatory. Basophils also have immunoregulatory activity through interaction with T cells. The aim of this study was to look for the expression of markers reflecting the activation status of peripheral Basophil in healthy donors.

METHOD

the study was performed on 29 healthy donors, 62% females with a mean age of 50.1 + 17.0 years. Basophils were identified on their expression of CD123 without HLA-DR and/or CD193 in two 8 colors panels including CD46, CD55, CD59, CD203c, CD32 (FcγRII), CD64 (FcγRIII), CD163, CD137L (4-1BBL), CD252 (OX40L), CD244 (2B4) and CD3 on whole blood. Basophil activation with anti IgE was performed on 14 donors.

RESULTS AND DISCUSSION

Our results confirmed the Basophil expression of CD123, CD193 and CD203 (the latter is strongly increased under stimulation). Complement regulatory proteins (CD46, CD55, CD59) were expressed at the same levels as on other leukocytes; CD46, CD59 expression being slightly increased under stimulation. CD32 and CD163 scavenger were slightly higher than on lympho and not influenced by activation. CD252 or CD137L were expressed at low levels and significantly induced by stimulation. Most of all, CD244 was highly expressed on Basophils as compared to any other leukocytes in fresh peripheral blood.

CONCLUSIONS

Our study shows that human resting Basophils express IgE and IgG Fc receptors and check point receptor CD244 that could potentially play a role in their previously reported immunoregulatory activity in sensitization and even in tumor immune escape.

Canine immunoglobulin F(ab')2 fragments protect cats against feline parvovirus virus infection

Feline parvovirus virus (FPV) causes severe diarrhea and leukopenia in felines, and threatening the health of wild and domestic felines. Currently, specific drugs to treat FPV have not yet been developed. In this study, IgG was extracted from inactivated FPV-immunized dog sera. Canine F(ab')₂ fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. The results showed that canine immunoglobulin F(ab')₂ fragments showed efficient neutralizing activity in vitro against FPV and had therapeutic and prophylactic effects in FPV infected cats. The anti-FPV-specific F(ab')₂ fragment can significantly alleviate the clinical symptoms of FPV infected cats and reduce the viral loads of the intestinal tract. These results indicated that the F(ab')₂ fragment prepared from inactivated FPV-immunized felines may be used as a prophylactic and therapeutic agent for diseases caused by FPV.

Phellinus linteus Grown on Germinated Brown Rice Inhibits IgE-Mediated Allergic Activity through the Suppression of FcεRI-Dependent Signaling Pathway In Vitro and In Vivo

Phellinus linteus (PL) has been used as a traditional herbal medicine owing to its immune regulatory activity. Previous studies reported that PL grown on germinated brown rice (PBR) exerted immunomodulatory, anticancer, and anti-inflammatory activities. However, role of PBR on type I hypersensitive reactions has not been studied yet. We found that PBR contained more polyphenolic compounds than PL extract. Among fractions, PBR butanol fraction (PBR-BuOH) significantly contained the most amounts of total polyphenolic contents compared with all extracts or fractions. In this study, anti-allergic activity of PBR-BuOH was examined using in vitro and in vivo models of immunoglobulin E/antigen- (IgE/Ag-) stimulated allergy. The inhibitory activity of degranulation was higher in PBR-BuOH (IC₅₀ 41.31 ± 0.14 μg/mL) than in PL-BuOH (IC₅₀ 108.07 ± 8.98 μg/mL). We observed that PBR-BuOH suppressed calcium influx and the level of TNF-α and IL-4 mRNA expression in a dose-dependent manner. The phosphorylation of Fyn, Gab2, PI3K, Syk, and IκB protein is reduced by PBR-BuOH. Oral administration of PBR-BuOH inhibited allergic reactions including the extravasation of Evans blue dye, ear swelling, and infiltration of immune cells in mice with passive cutaneous anaphylaxis (PCA). These findings suggest that PBR-BuOH might be used as a functional food, a health supplement, or a drug for preventing type I hypersensitive allergic disease.

Equine immunoglobulin F(ab')2 fragments protect cats against feline calicivirus infection

Feline calicivirus (FCV) causes upper respiratory tract infections in felines and threatens the health of wild and domestic felines. Clinically, specific drugs to treat FCV have not yet been developed. Here, IgG was extracted from inactivated FCV-immunized horse sera. Equine F(ab')₂ fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. In our study, equine immunoglobulin F(ab')₂ fragments showed efficient neutralizing activity in vitro against FCV and had therapeutic and prophylactic effects in FCV-infected cats. The anti-FCV-specific F(ab')₂ fragment can significantly alleviate the clinical symptoms of FCV-infected cats and reduce the viral loads of the trachea, lung and spleen. These results indicate that the F(ab')₂ fragment prepared from inactivated FCV-immunized horses may be used as a prophylactic and therapeutic agent for diseases caused by FCV.

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High-purity anti-FCV F(ab')₂ fragments were prepared from equine IgG.

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F(ab')₂ fragments can bind to FCV both in vivo and in vitro.

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F(ab')₂ fragments can reduce the clinical symptoms in kittens infected with FCV.

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Passive transfer of equine immune antibodies significantly reduced virus titers in the lungs and trachea of kittens.

Characterizing Antibodies

Perhaps because they are such commonly used tools, many researchers view antibodies one-dimensionally: Antibody Y binds antigen X. Although few techniques require a comprehensive understanding of any particular antibody's characteristics, well-executed experiments do require a basic appreciation of what is known and, equally as important, what is not known about the antibody being used. Ignorance of the relevant antibody characteristics critical for a particular assay can easily lead to loss of precious resources (time, money, and limiting amounts of sample) and, in worst-case scenarios, erroneous conclusions. Here, we describe various antibody characteristics to provide a more well-rounded perspective of these critical reagents. With this information, it will be easier to make informed decisions on how best to choose and use the available antibodies, as well as knowing when it is essential and how to determine a particular as yet-undefined characteristic.

A Reliable Method for the Evaluation of the Anaphylactoid Reaction Caused by Injectable Drugs

Adverse reactions of injectable drugs usually occur at first administration and are closely associated with the dosage and speed of injection. This phenomenon is correlated with the anaphylactoid reaction. However, up to now, study methods based on antigen detection have still not gained wide acceptance and single physiological indicators cannot be utilized to differentiate anaphylactoid reactions from allergic reactions and inflammatory reactions. In this study, a reliable method for the evaluation of anaphylactoid reactions caused by injectable drugs was established by using multiple physiological indicators. We used compound 48/80, ovalbumin and endotoxin as the sensitization agents to induce anaphylactoid, allergic and inflammatory reactions. Different experimental animals (guinea pig and nude rat) and different modes of administration (intramuscular, intravenous and intraperitoneal injection) and different times (15 min, 30 min and 60 min) were evaluated to optimize the study protocol. The results showed that the optimal way to achieve sensitization involved treating guinea pigs with the different agents by intravenous injection for 30 min. Further, seven related humoral factors including 5-HT, SC5b-9, Bb, C4d, IL-6, C3a and histamine were detected by HPLC analysis and ELISA assay to determine their expression level. The results showed that five of them, including 5-HT, SC5b-9, Bb, C4d and IL-6, displayed significant differences between anaphylactoid, allergic and inflammatory reactions, which indicated that their combination could be used to distinguish these three reactions. Then different injectable drugs were used to verify this method and the results showed that the chosen indicators exhibited good correlation with the anaphylactoid reaction which indicated that the established method was both practical and reliable. Our research provides a feasible method for the diagnosis of the serious adverse reactions caused by injectable drugs which could be used in the clinical practice.

The inhibitory effect of piperine from Fructus piperis extract on the degranulation of RBL-2H3 cells

Allergy is an abnormal immune response to an allergen. Type I hypersensitivity is an immunoglobulin (Ig) E-mediated allergic disorder. Fructus piperis is derived from the ripe fruit of the pepper, which is widely used as a spice in human diets and is also administered as a medicine in many countries. Piperine has been shown to have anti-oxidant, anti-depressant, anti-tumor, and anti-inflammatory activities. However, the effect of piperine on IgE-mediated allergic responses has not been reported. Here, the rat basophilic leukemia cells by membrane chromatography (RBL-2H3/CMC) coupled to high performance liquid chromatography/mass spectrometry (HPLC/MS) to discover and identify piperine can bind to RBL-2H3 cell membranes. Piperine inhibited the expression of cytokines, and the release of both β-hexosaminidase and histamine, which could be stimulated by antigen in RBL-2H3 mast cells. We found that the levels of intracellular Ca(2+) also decreased. Furthermore, RT-PCR showed that the mRNA expression levels of IL-4, IL-13, and TNF-α were significantly suppressed by piperine. The inhibitory effect of piperine on IgE-mediated degranulation and cytokine production by RBL-2H3 cells may be caused by the inhibition of IgE-mediated signaling pathways, including the phosphorylation of Lyn, p38, Erk, and Ras. In summary, piperine can inhibit antigen-induced allergic reactions that control degranulation.

Mast cells are required for full expression of allergen/SEB-induced skin inflammation

Atopic dermatitis is a chronic pruritic inflammatory skin disease. We recently described an animal model in which repeated epicutaneous applications of a house dust mite extract and staphylococcal enterotoxin B induced eczematous skin lesions. In this study we showed that global gene expression patterns are very similar between human atopic dermatitis skin and allergen/staphylococcal enterotoxin B-induced mouse skin lesions, particularly in expression of genes related to epidermal growth/differentiation, skin-barrier, lipid/energy metabolism, immune response, or extracellular matrix. In this model, mast cells and T cells, but not B cells or eosinophils, were shown to be required for the full expression of dermatitis, as revealed by reduced skin inflammation and reduced serum IgE levels in mice lacking mast cells or T cells (TCRβ^−/− or Rag1^−/−). The clinical severity of dermatitis correlated with the numbers of mast cells, but not eosinophils. Consistent with the idea that Th2 cells play a predominant role in allergic diseases, the receptor for the Th2-promoting cytokine thymic stromal lymphopoietin and the high-affinity IgE receptor, FcεRI, were required to attain maximal clinical scores. Therefore, this clinically relevant model provides mechanistic insights into the pathogenic mechanism of human atopic dermatitis.

Prevention and treatment of allergic inflammation by an Fcγ-Der f2 fusion protein in a murine model of dust mite-induced asthma

The immunoglobulin E (IgE) high-affinity receptor FcεRI expressed on mast cells and basophils plays a critical role in triggering allergic disease. The co-aggregation of the FcεRI and FcγRIIb receptors is inhibitory to FcεRI signaling and holds great potential for the treatment of IgE-mediated allergies. In China, Dermatophagoides farinae is a common anaphylaxis trigger. Therefore, in this study, the FcγRIIb-mediated immunomodulating activity of recombinant Fcγ-Der f2 fusion protein was tested in a Der f2-allergic murine model. Following the treatment, bronchoalveolar lavage fluid (BALF) was collected to measure the expression of several Th1/Th2-type cytokines (IL-5, TNF-α, IL-12p70, IL-4, IL-10, IFN-γ and IL-18) and histamine, while blood was used to detect the specific IgE and IgG-types anti-Der f2 antibodies, for measurement. In contrast to the saline-treated allergic mice, the levels of Der f2-specific IgE, cytokines and histamine were lowered in the Fcγ-Der f2-treated allergic mice, in addition to the rare inflammatory cell infiltration in the airways and blood vessels revealed by histopathological examination. The recombinant Fcγ-Der f2 protein was demonstrated to function as an effective immunotherapeutic agent, suggesting that chimeric human Fcγ-allergen proteins could be used in the development of antigen-specific immunotherapy for human allergic diseases.

An involvement of neurokinin-1 receptor in FcεRΙ-mediated RBL-2H3 mast cell activation

OBJECTIVE AND DESIGN

To determine whether the neurokinin-1 receptor (NK1R) plays a role in the activation of RBL-2H3 mast cells after FcεRΙ aggregation.

MATERIALS AND METHODS

NK1R expression in RBL-2H3 cells was inhibited by small hairpin RNA (shRNA) against NK1R, and determined by western blotting. For activation, both NK1R knockdown and control RBL-2H3 cells were sensitized by dinitrophenol (DNP)-specific IgE and stimulated with the antigen DNP-bovine serum albumin (BSA). Following the activation of RBL-2H3 cells, monocyte chemoattractant protein (MCP-1) production and intracellular calcium flux were monitored by ELISA and confocal microscopy assay, respectively. For investigation of the signaling mechanism, phosphorylation of mitogen-activated protein kinases (MAPKs) after RBL-2H3 cell activation was assessed by western blotting.

RESULTS

shRNA-NK1R mediated an effective inhibition of NK1R expression in RBL-2H3 cells. Protein production of MCP-1 was reduced by more than 55 % in NK1R knockdown RBL-2H3 cells compared with control RBL-2H3 cells. In addition, both calcium mobilization and phosphorylation levels of MAPKs (Erk1/2, JNK, and p38) after DNP-BSA stimulation (via FcεRΙ) were decreased due to the inhibition of NK1R expression.

CONCLUSION

NK1R is required for the activation of RBL-2H3 cells following FcεRΙ engagement and involved in the regulation of MAPK signaling pathways.

Shp2 activates Fyn and Ras to regulate RBL-2H3 mast cell activation following FcεRI aggregation

The protein-tyrosine phosphatase (PTP) Shp2 has been implicated in many immunoreceptor signaling pathways, but its role in immunoreceptor FcεRI signaling, which leads to the activation of mast cells and blood basophils, is still largely undefined. Using Shp2 knockdown RBL-2H3 (RBL) mast cells, we here reported that Shp2 is required for the activation of RBL cells induced by FcεRI. FcεRΙ-evoked degranulation, calcium mobilization, and synthesis of cytokine transcripts (IL-1β, IL-10, and monocyte chemoattractant protein 1 (MCP-1)) were reduced in Shp2 knockdown RBL cells. Signaling regulatory mechanism investigation using immunoblotting, immunoprecipitation, and GST pull-down assay reveals that the down-regulation of Shp2 expression in RBL cells leads to decreased activities of Fyn, PLCγ, JNK, p38MAPK, and Ras/Erk1/2 after FcεRΙ aggregation. Further studies suggest that Paxillin phosphoryaltion was also impaired, but PAG phosphorylation was normal after FcεRΙ stimulation as a consequence of the inhibition of Shp2 expression in RBL cells. Collectively, our data strongly indicate that Shp2 is essential for the activation of RBL cells in response to FcεRΙ aggregation. Shp2 regulates this process through Fyn and Ras with no involvement of PAG. In addition, we identify Paxillin as an indirect substrate of Shp2 in FcεRΙ-initiated signaling of RBL cells.

Micropatterned ligand arrays to study spatial regulation in Fc receptor signaling

Fc receptor signaling plays a fundamental role in immune responses. A plethora of Fc -receptors (e.g., Fc gamma, Fc-alpha, and Fc-epsilon) are expressed on different immune cells, including natural killer cells, macrophages, mast cells, and neutrophils. Receptor clustering and activation by multivalent ligands or opsonized particles induce a signaling cascade that leads to targeted secretion of chemical mediators (i.e., histamine, cytokines, and chemokines) and phagocytosis, among other responses. Spatial targeting and compartmentalization are common mechanisms of regulation in Fc receptor signaling. However, the tools for studying these dynamic interactions have been limited. To overcome these limitations in our model system, microfabricated surfaces containing spatially defined ligands are used to cluster- and activate IgE receptors (FcεRI), involved in allergic responses by mast cells. Micron-scale control of cell activation allows investigation of spatially regulated mechanisms for intracellular signaling with -fluorescence microscopy. This approach in conjunction with biochemical techniques has proven to be valuable for investigating immune receptor signaling.

Immunoglobulin E-binding autoantigens: biochemical characterization and clinical relevance

Although immediate-Type I skin reactions to human dander have been described six decades ago, only the recent application of molecular biology to allergology research allowed fast and detailed characterization of IgE-binding autoantigens. These can be functionally subdivided into three classes: (1) self-antigens with sequence homology to environmental allergens belonging to the class of phylogenetically conserved proteins, (2) self-antigens without sequence homology to known environmental allergens, and (3) chemically modified self-antigens deriving from workplace exposure. As environmental allergens, also IgE-binding autoantigens belong to different protein families without common structural features that would explain their IgE-binding capability. Many of the self-antigens showing sequence homology to environmental allergens, are phylogenetically conserved proteins like manganese dependent superoxide dismutase, thioredoxin or cyclopilin. Their IgE-binding capability can be explained by molecular mimicry resulting from shared B-cell epitopes. A common factor of IgE-binding self-antigens without sequence homology to known environmental allergens is that they elicit IgE responses only in individuals suffering from long-lasting atopic diseases. In contrast, IgE-mediated reactions to modified self-antigens might be explained with the generation of novel B-cell epitopes. Chemically modified self-antigens are likely to be recognized as non-self by the immune system. The clinical relevance of IgE responses to self-antigens remains largely unclear. Well documented is their ability to induce immediate Type I skin reactions in vivo, and to induce mediator release from effector cells of sensitized individuals in vitro. Based on these observations it is reasonable to assume that IgE-mediated cross-linking of FcRIε receptors on effector cells can elicit the same symptoms as those induced by environmental allergens, and this could explain exacerbations of chronic allergic diseases in the absence of external exposure. However, because most of the described IgE-binding self-antigens are intracellular proteins normally not accessible for antigen-antibody interactions, local release of the antigens is required to explain the induction of symptoms.

The SCHOOL of nature: III. From mechanistic understanding to novel therapies

Protein-protein interactions play a central role in biological processes and thus represent an appealing target for innovative drug design and development. They can be targeted by small molecule inhibitors, modulatory peptides and peptidomimetics, which represent a superior alternative to protein therapeutics that carry many disadvantages. Considering that transmembrane signal transduction is an attractive process to therapeutically control multiple diseases, it is fundamentally and clinically important to mechanistically understand how signal transduction occurs. Uncovering specific protein-protein interactions critical for signal transduction, a general platform for receptor-mediated signaling, the signaling chain homooligomerization (SCHOOL) platform, suggests these interactions as universal therapeutic targets. Within the platform, the general principles of signaling are similar for a variety of functionally unrelated receptors. This suggests that global therapeutic strategies targeting key protein-protein interactions involved in receptor triggering and transmembrane signal transduction may be used to treat a diverse set of diseases. This also assumes that clinical knowledge and therapeutic strategies can be transferred between seemingly disparate disorders, such as T cell-mediated skin diseases and platelet disorders or combined to develop novel pharmacological approaches. Intriguingly, human viruses use the SCHOOL-like strategies to modulate and/or escape the host immune response. These viral mechanisms are highly optimized over the millennia, and the lessons learned from viral pathogenesis can be used practically for rational drug design. Proof of the SCHOOL concept in the development of novel therapies for atopic dermatitis, rheumatoid arthritis, cancer, platelet disorders and other multiple indications with unmet needs opens new horizons in therapeutics.

The SCHOOL of nature: I. Transmembrane signaling

Receptor-mediated transmembrane signaling plays an important role in health and disease. Recent significant advances in our understanding of the molecular mechanisms linking ligand binding to receptor activation revealed previously unrecognized striking similarities in the basic structural principles of function of numerous cell surface receptors. In this work, I demonstrate that the Signaling Chain Homooligomerization (SCHOOL)-based mechanism represents a general biological mechanism of transmembrane signal transduction mediated by a variety of functionally unrelated single- and multichain activating receptors. within the SCHOOL platform, ligand binding-induced receptor clustering is translated across the membrane into protein oligomerization in cytoplasmic milieu. This platform resolves a long-standing puzzle in transmembrane signal transduction and reveals the major driving forces coupling recognition and activation functions at the level of protein-protein interactions-biochemical processes that can be influenced and controlled. The basic principles of transmembrane signaling learned from the SCHOOL model can be used in different fields of immunology, virology, molecular and cell biology and others to describe, explain and predict various phenomena and processes mediated by a variety of functionally diverse and unrelated receptors. Beyond providing novel perspectives for fundamental research, the platform opens new avenues for drug discovery and development.

Targeting allergen to Fc gammaRI: a strategy to treat allergic disease?

PURPOSE OF REVIEW

Targeting allergens to surface receptors on antigen presenting cells may provide a therapeutic strategy for allergic disease. This article discusses the immunomodulatory capacity of a molecule (H22-Fel d 1), which targets the major cat allergen, Fel d 1, to the high affinity IgG receptor, Fc gammaRI, on human dendritic cells.

RECENT FINDINGS

The fusion protein, H22-Fel d 1, induced a semi-mature phenotype in dendritic cells characterized by production of inflammatory cytokines with no change in surface markers, suggesting tolerogenic capacity. At the T-cell level, H22-Fel d 1 stimulated increased proliferation coupled with amplification of T cells expressing IL-5 and IL-10. Further analysis revealed induction of diverse T cell subtypes characteristic of Th0, regulatory Th1 and regulatory Th2 cells. Notably, this effect was restricted to T cells isolated from cat-allergic patients. Despite the increase in IL-5-expressing T cells, responses induced by H22-Fel d 1 appeared to be regulated by IL-10. Comparison with nonreceptor-targeted allergens from cat and house dust mite confirmed that qualitative T-cell changes induced by H22-Fel d 1 were unique.

SUMMARY

H22-Fel d 1 induces a novel variation of the Th2 response, which incorporates elements of a protective T-cell response. Exploiting Fc gammaRI-mediated pathways for allergen delivery may offer a new approach for treatment.

New insights into the mechanism and management of allergic diseases: atopic dermatitis

Rapidly increasing knowledge on the complex background of atopic dermatitis (AD) on the genetic, immunological and environmental level in combination with the continuous improvement in our diagnostic options has initiated an ongoing discussion on factors, which primarily promote the disease on one hand and mechanisms which emerge rather secondarily as a consequence of disease-specific modifications, on the other hand. Beside a sustained search for reliable and meaningful diagnostic tools for elicitors of the disease, novel therapeutic approaches are required, as most of the treatments of AD are limited to symptomatic therapies. In contrast, therapeutic approaches selectively regulating aberrant pathophysiological mechanisms in AD itself would be much more effective and promising.

Molecular Characterization of Trimellitic Anhydride–induced Respiratory Allergy in Brown Norway Rats

To contribute to the hazard identification of low molecular weight (LMW) respiratory allergens, respiratory allergy induced by trimellitic anhydride (TMA) was characterized by whole genome analysis of lung tissue and blood proteomics in Brown Norway rats. Dermal sensitization (50% and 25% w/v) with TMA and an inhalation challenge of 15 mg/m3 TMA-induced apneas, laryngeal inflammation, increased numbers of eosinophils, neutrophils and macrophages in bronchoalveolar lavage (BAL), and increased immunoglobulin E levels in serum and lung tissue. Whole genome analysis of lung, sampled 24 hours after challenge, showed expression changes of not only genes belonging to several Gene Ontology groups with up-regulation of inflammatory-associated genes and those associated with lung remodeling but also genes involved in downsizing these processes. Blood proteomics reflected activation of inflammation-inhibiting pathways. Unsensitized animals challenged with TMA exhibited also an increased number of macrophages in BAL, but gene expression in the above-mentioned gene pathways was unchanged or down-regulated. The authors conclude that parameters for lung remodeling can be a valuable tool in hazard identification of LMW respiratory allergens.

Systemic administration of an Fcgamma-Fc(epsilon)-fusion protein in house dust mite sensitive nonhuman primates

Crosslinking Fc(epsilon)RI and FcgammaRIIB receptors inhibits mast cell and basophil activation, decreasing mediator release. In this study, a fusion protein incorporating human Fcgamma and Fc(epsilon) domains, hGE2, was shown to inhibit degranulation of human mast cells and basophils, and to exhibit efficacy in a nonhuman primate model of allergic asthma. hGE2 increased the provocative concentration of dust mite aeroallergen that induced an early phase asthmatic response. The treatment effect lasted up to 4 weeks and was associated with reduction in the number of circulating basophils and decreased expression of Fc(epsilon)RI on repopulating basophils. Repeat hGE2 dosing induced production of serum antibodies against human Fcgamma and Fc(epsilon) domains and acute anaphylaxis-like reactions. Immune serum induced histamine release from human IgE or hGE2-treated cord blood-derived mast cells and basophils in vitro. These results indicate that repeat administration with hGE2 induced an antibody response to the human molecule that resulted in activation rather than inhibition of allergic responses.

A high-affinity monoclonal anti-IgE antibody for depletion of IgE and IgE-bearing cells

BACKGROUND

We have identified a monoclonal anti-human immunoglobulin E (IgE) antibody, which recognizes FcepsilonRI-bound IgE and prevents binding of IgE to FcepsilonRI. In this study, we assessed the binding kinetics and affinity of monoclonal antibody 12 (mAb12) for IgE and investigated whether mAb12 can be used for depletion of IgE and isolation of IgE-bearing cells from peripheral blood.

METHODS

Binding kinetics and affinity for IgE were studied using Biacore surface plasmon resonance technique experiments. IgE antibodies were depleted from serum using sepharose-coupled mAb12 and IgE-bearing cells were enriched from heparinized blood samples with mAb12. The extent and biological relevance of IgE depletion were studied by quantitative IgE measurements and basophil histamine release experiments. Specific binding of mAb12 to IgE-bearing cells (basophils, mast cells, IgE-secreting plasma cells) was demonstrated by FACS.

RESULTS

Monoclonal antibody 12 shows rapid association (k(a) = 5.46e5/Ms) with IgE, almost no dissociation (k(d) = 8.8e-5/s) and an affinity for IgE (K(D) = 1.61e-10 M), which is as high as that of FcepsilonRI. Immobilized mAb12 could be used to deplete IgE antibodies and isolate IgE-bearing cells from peripheral blood in a single-step procedure.

CONCLUSIONS

Monoclonal antibody 12 is a high affinity anti-human IgE antibody, which efficiently removes IgE and IgE-bearing cells from peripheral blood and may thus be used for extracorporeal depletion of IgE and IgE-bearing cells.

The immune privilege of the oral mucosa

Despite high bacterial colonization and frequent allergen contact, acute inflammatory and allergic reactions are rarely seen in the oral mucosa. Therefore we assert that immune tolerance predominates at this site and antigen presenting cells, such as dendritic cells and different T cell subtypes, serve as key players in oral mucosal tolerance induction. In this article we describe the mechanisms that lead to tolerance induced in the oral mucosa and how they differ from tolerance induced in the lower gastrointestinal tract. Furthermore we discuss ways in which novel nonparenteral approaches for immune intervention, such as allergen-specific immunotherapy applied by way of the sublingual route, might be improved to target the tolerogenic properties of the sophisticated oral mucosal immune network.

Fc-receptors as regulators of immunity

Receptors for immunoglobulins [Fc-receptors (FcRs)] are widely expressed throughout the immune system. By binding to the antibody Fc-portion, they provide a link between the specificity of the adaptive immune system and the powerful effector functions triggered by innate immune effector cells. By virtue of coexpression of activating and inhibitory FcRs on the same cell, they set a threshold for immune cell activation by immune complexes (ICs). Besides their involvement in the efferent phase of an immune response, they are also important for modulating adaptive immune responses by regulating B cell and dendritic cell (DC) activation. Deletion of the inhibitory FcR leads to the loss of tolerance in the humoral immune system and the development of autoimmune disease. Uptake of ICs by FcRs on DCs and the concommitant triggering of activating and inhibitory signaling pathways will determine the strength of the initiated T-cell response. Loss of this balanced signaling results in uncontrolled responses that can lead to the damage of healthy tissues and ultimately to the initiation of autoimmune processes. In this chapter, we will discuss how coexpression of different activating and inhibitory receptors on different immune cells of the innate and adaptive immune system modulates cell activity. Moreover, we will focus on exogenous factors that can influence the balanced triggering of activating and inhibitory FcRs, such as the cytokine milieu and the role of differential antibody glycosylation.

A mouse Fcgamma-Fcepsilon protein that inhibits mast cells through activation of FcgammaRIIB, SH2 domain-containing inositol phosphatase 1, and SH2 domain-containing protein tyrosine phosphatases

BACKGROUND

A human Fcgamma-Fcepsilon fusion protein (GE2) designed to inhibit FcepsilonRI signaling by coaggregating FcepsilonRI with the inhibitory receptor FcgammaRIIB has been shown to inhibit mast cell activation and block cutaneous anaphylaxis. A critical issue remained as to whether the mechanism of GE2 inhibition is competition for IgE binding or inhibitory signaling through FcgammaRIIB.

OBJECTIVE

Our aim was to define the in vitro and in vivo mechanism of action of a mouse homolog of GE2 (mGE) and to assess the potential of human GE2 (hGE2) for therapeutic administration.

METHODS

The in vitro activity of mGE on mediator release and signaling pathways was characterized in IgE-sensitized bone marrow-derived mast cells (BMMCs). The in vivo activity of mGE was examined in mouse passive cutaneous and passive systemic anaphylaxis models, and the therapeutic activity of hGE2 was evaluated in Ascaris suum-sensitized cynomolgus monkeys.

RESULTS

mGE inhibited release of histamine and cytokines by BMMCs from wild-type mice but not by BMMCs from FcgammaRIIB-deficient mice. In mice mGE blocked IgE-dependent anaphylaxis mediated by mast cells with sustained efficacy. In BMMCs mGE decreased spleen tyrosine kinase and extracellular signal-regulated kinases 1/2 phosphorylation and induced FcgammaRIIB phosphorylation and the subsequent recruitment of SH2 domain-containing inositol polyphosphate 5' phosphatase (SHIP) 1 and SH2 domain-containing protein tyrosine phosphatase (SHP) 1/2 phosphatases. When administered therapeutically, hGE2 protected sensitized monkeys from local anaphylaxis for 3 weeks.

CONCLUSION

mGE-mediated inhibition of mast cell activation is associated with inhibitory signaling through FcgammaRIIB that results from activation of SHIP-1 and SHP-1/2 phosphatases.

New developments in FcepsilonRI regulation, function and inhibition

The high-affinity Fc receptor for IgE (FcepsilonRI), a multimeric immune receptor, is a crucial structure for IgE-mediated allergic reactions. In recent years, advances have been made in several important areas of the study of FcepsilonRI. The first area relates to FcepsilonRI-mediated biological responses that are antigen independent. The second area encompasses the biological relevance of the distinct signalling pathways that are activated by FcepsilonRI; and the third area relates to the accumulated evidence for the tight control of FcepsilonRI signalling through a broad array of inhibitory mechanisms, which are being developed into promising therapeutic approaches.

Activating and inhibitory FcγRs in autoimmune disorders

Autoimmune disorders are characterized by the destruction of self-tissues by the immune system. Multiple checkpoints are in place to prevent autoreactivity under normal circumstances. Coexpression of activating and inhibitory Fc receptors (FcR) represents such a checkpoint by establishing a threshold for immune cell activation. In many human autoimmune diseases, however, balanced FcR expression is disturbed. Analysis of murine model systems provides strong evidence that aberrant FcR expression can result in uncontrolled immune responses and the initiation of autoimmune disease. This review will summarize this data and explain how this information might be used to better understand human autoimmune diseases and to develop novel therapeutic strategies.