Immunologically mediated signaling in basophils and mast cells: finding therapeutic targets for allergic diseases in the human FcvarepsilonR1 signaling pathway

Targeting spleen tyrosine kinase (SYK): structure, mechanisms and drug discovery

Spleen tyrosine kinase (SYK) is a crucial non-receptor tyrosine kinase involved in signaling pathways that regulate various cellular processes. It is primarily expressed in hematopoietic cells and myeloid cells, which are crucial for B-cell development, maturation and antibody production, and it is a key therapeutic target for autoimmune and allergic diseases. Overexpression of SYK is also associated with cancer and cardiovascular, cerebrovascular and neurodegenerative diseases, contributing to their initiation and progression. SYK is a promising target for drug development, and several inhibitors have already been reported. This review covers the structure and regulatory pathways of SYK, as well as its links to various diseases. It also highlights key small-molecule SYK inhibitors, their design strategies and their potential therapeutic benefits, aiming to enhance our understanding and aid in the discovery of more-effective SYK inhibitors.

Identification of a New and Effective Marker Combination for a Standardized and Automated Bin-Based Basophil Activation Test (BAT) Analysis

(1) Background: The basophil activation test (BAT) is a functional whole blood-based ex vivo assay to quantify basophil activation after allergen exposure by flow cytometry. One of the most important prerequisites for the use of the BAT in the routine clinical diagnosis of allergies is a reliable, standardized and reproducible data analysis workflow. (2) Methods: We re-analyzed a public mass cytometry dataset from peanut (PN) allergic patients (n = 6) and healthy controls (n = 3) with our binning approach "pattern recognition of immune cells" (PRI). Our approach enabled a comprehensive analysis of the dataset, evaluating 30 markers to achieve optimal basophil identification and activation through multi-parametric analysis and visualization. (3) Results: We found FcεRIα/CD32 (FcγRII) as a new marker couple to identify basophils and kept CD63 as an activation marker to establish a modified BAT in combination with our PRI analysis approach. Based on this, we developed an algorithm for automated raw data processing, which enables direct data analysis and the intuitive visualization of the test results including controls and allergen stimulations. Furthermore, we discovered that the expression pattern of CD32 correlated with FcεRIα, anticorrelated with CD63 and was detectable in both the re-analyzed public dataset and our own flow cytometric results. (4) Conclusions: Our improved BAT, combined with our PRI procedure (bin-BAT), provides a reliable test with a fully reproducible analysis. The advanced bin-BAT enabled the development of an automated workflow with an intuitive visualization to discriminate allergic patients from non-allergic individuals.

Caffeic acid methyl ester inhibits mast cell activation through the suppresion of MAPKs and NF-κB signaling in RBL-2H3 cells

Anti-inflammatory effects of caffeic acid derivatives have been widely reported. However, the effect of caffeic acid methyl ester (CAME) on the anti-allergic effect in mast cells has not been elucidated. The present study was aimed to investigate the anti-allergic properties of CAME and its underlying mechanism. Rat basophilic leukemia (RBL-2H3) cells were incubated withphorbol-12-myristate-13-acetate (PMA) and a calcium ionophore, A23187 to induce mast cell activation. Anti-allergic effect of CAME was examined by measuring cytokine, histamine and β-hexosaminidase release. Western blotting was conducted to determine cyclooxygenase-2 (COX-2) expression, Mitogen-activated protein kinases (MAPKs) activation and nuclear factor-κB (NF-κB) translocation. CAME significantly suppressed PMA/A23187-induced TNF-α secretion, and β-hexosaminidase and histamine release in a concentration-dependent manner. Furthermore, CAME significantly attenuated PMA/A23187-induced COX-2 expression and nuclear translocation of NF-κB. CAME significantly suppressed PMA/A23187-induced increased phosphorylation of p38, ERK and JNK RBL-2H3 cells. The results demonstrate that CAME significantly attenuates anti-allergic action by suppressing degranulation of mast cells through the suppression of MAPKs/NF-κB signaling pathway in RBL-2H3 cells.

Structures and Anti-Allergic Activities of Natural Products from Marine Organisms

In recent years, allergic diseases have occurred frequently, affecting more than 20% of the global population. The current first-line treatment of anti-allergic drugs mainly includes topical corticosteroids, as well as adjuvant treatment of antihistamine drugs, which have adverse side effects and drug resistance after long-term use. Therefore, it is essential to find alternative anti-allergic agents from natural products. High pressure, low temperature, and low/lack of light lead to highly functionalized and diverse functional natural products in the marine environment. This review summarizes the information on anti-allergic secondary metabolites with a variety of chemical structures such as polyphenols, alkaloids, terpenoids, steroids, and peptides, obtained mainly from fungi, bacteria, macroalgae, sponges, mollusks, and fish. Molecular docking simulation is applied by MOE to further reveal the potential mechanism for some representative marine anti-allergic natural products to target the H1 receptor. This review may not only provide insight into information about the structures and anti-allergic activities of natural products from marine organisms but also provides a valuable reference for marine natural products with immunomodulatory activities.

Brusatol Derivative-34 Attenuates Allergic Airway Inflammation Via Inhibition of the Spleen Tyrosine Kinase Pathway

Brusatol derivative-34 (Bru-34), a derivative of brusatol, has been shown significantly anti-inflammatory activity in mice in our previously work. However, to our knowledge, there were very limited studies on how Bru-34 affected airway inflammation. Thus, in this present study, the effects and potential mechanisms of Bru-34 on allergic airway inflammation were examined both in vivo and in vitro. The results showed that Bru-34 attenuated the allergic airway inflammation in mice, with significant decreasing of the inflammatory cells and mediators in bronchoalveolar lavage fluids and attenuation of the histopathological alterations in the lung tissues. In addition, Bru-34 significantly inhibited the release of inflammatory cytokines in antigen induced rat basophilic leukemia -2H3 (RBL-2H3) cells. What’s more, Bru-34 significantly decreased the expression of spleen tyrosine kinase (Syk), p-Syk, cytoplasmic phospholipase A2 (cPLA2), p-cPLA2, nuclear factor-κB (NF-κB) and p-NF-κB both in allergic mice lung tissue and antigen induced RBL-2H3 cells. Furthermore, the collaborative effects of Bru-34 with inhibitors against Syk, cPLA2, and NF-κB, showed that Syk was an important target of Bru-34, and cPLA2 and NF-κB played important roles in the coordinated inflammatory response. In conclusion, Bru-34 could significantly modulate the allergic airway inflammation, and its potential mechanism was revealed at least partially via down-regulating of Syk-cPLA2 -NF-κB signaling.

The role of algal fucoidans in potential anti-allergic therapeutics

Allergic diseases are among the commonest causes of chronic ill-health and are rapidly rising the prevalence and complexity. Although the current drugs are efficacy for treatment of allergic diseases, however the extensive clinical use of these drugs has led to the diverse and undesirable side effects. Thus, the extensive studies of alternative anti-allergic agents from natural products are essential for a long-term purpose. Marine environment covers a huge source of extremely potential secondary metabolites for drug discovery. Among them, fucoidans from brown seaweeds have been evidenced to possess various biological activities and health benefit effects. Notably, a great deal of interest has been expressed regarding anti-allergic activity of fucoidans. Consequently, this contribution presents an overview of potential anti-allergic therapeutics of fucoidans from brown seaweeds to emphasize its functions in prevention as well as treatment of allergic diseases.

Natural products targeting FcεRI receptor for anti-allergic therapeutics

Mast cells and basophils are important contributors for development of allergic reactions. The activation of these cells via cross-linking of IgE bound to FcεRI by allergen causes the generation of allergic mediators and the reaction of immediate hypersensitivity. Obviously, FcεRI is considered as a key trigger of acute allergic responses. Consequently, FcεRI is regarded as a potential target for downregulation of allergic diseases. So far, numerous synthetic agents have been reported for inhibition of FcεRI expression and FcεRI-IgE interaction. Meanwhile, natural products have received much attention due to their efficacy and safety. Recently, numerous anti-allergic agents from natural products have been revealed as promising inhibitors of allergic reactions via inhibiting the expression of FcεRI subunits as well as blocking FcεRI activation. Thus, the present contribution is mainly focused to describe natural products targeting FcεRI receptor and to emphasize their applicable potential as anti-allergic foods. PRACTICAL APPLICATIONS: Phlorotannins, epigallocatechin-3-gallate, peptides, chitooligosaccharides, and other natural products have been revealed as potential inhibitors of allergic responses. These bioactive agents target to FcεRI receptor by inhibiting expression of FcεRI and blocking interaction of FcεRI-IgE. Hence, these compounds could be applied as functional ingredients of anti-allergic foods.

Inhibitory effects of 2-oxo-2H-chromen-4-yl 4-methylbenzenesulfonate on allergic inflammatory responses in rat basophilic leukemia cells

Mast cells play crucial roles in the initiation of allergic inflammatory responses by releasing various mediators such as histamines, cytokines, and leukotrienes. In addition, signaling cascade pathways, such as the mitogen-activated protein kinase (MAPK) pathway, contribute to the regulation of mast cell degranulation. Accordingly, different research strategies have been pursued to develop anti-inflammatory and anti-allergic drugs by regulating these signaling pathways. The development of new drugs that inhibit mast cell degranulation may help in the treatment of allergies. In this study, we investigated the effects of coumarin derivatives on mast cell degranulation. The effect of coumarin derivatives on degranulation in rat basophilic leukemia (RBL)-2H3 cells was determined by a β-hexosaminidase assay and histamine assay. A coumarin derivative 1 (C1), 2-oxo-2H-chromen-4-yl 4-methylbenzenesulfonate, inhibited degranulation in a dose-dependent manner and demonstrated maximum therapeutic effect when used at 25μM. Additionally, these compounds inhibited the phosphorylation of the extracellular signal-regulated kinase (ERK) pathway. Taken together, these results indicate that 2-oxo-2H-chromen-4-yl 4-methylbenzenesulfonate inhibits mast cell degranulation by suppressing the activation of the ERK pathway and this inhibitory effect suggests potential therapeutic strategies towards the prevention of allergic disorders.

Peptide based immunotherapy: a pivotal tool for allergy treatment

Immunotherapies with T-cell epitope peptides have shown a promising impact over allergic diseases as a potential therapeutic tool in in vitro and in vivo conditions. It is recognized as an effective treatment with long lasting clinical effects and subsequent reduction of the allergic inflammatory reactions. In this review, we have summarized the role of peptide based immunotherapy and emphasis has been given to the recent advancement in pollen, cat, hymenoptera venom, and food allergy.

Transmembrane adaptor proteins in the high-affinity IgE receptor signaling

Aggregation of the high-affinity IgE receptor (FcεRI) initiates a cascade of signaling events leading to release of preformed inflammatory and allergy mediators and de novo synthesis and secretion of cytokines and other compounds. The first biochemically well defined step of this signaling cascade is tyrosine phosphorylation of the FcεRI subunits by Src family kinase Lyn, followed by recruitment and activation of spleen tyrosine kinase (Syk). Activity of Syk is decisive for the formation of multicomponent signaling assemblies, the signalosomes, in the vicinity of the receptors. Formation of the signalosomes is dependent on the presence of transmembrane adaptor proteins (TRAPs). These proteins are characterized by a short extracellular domain, a single transmembrane domain, and a cytoplasmic tail with various motifs serving as anchors for cytoplasmic signaling molecules. In mast cells five TRAPs have been identified [linker for activation of T cells (LAT), non-T cell activation linker (NTAL), linker for activation of X cells (LAX), phosphoprotein associated with glycosphingolipid-enriched membrane microdomains (PAG), and growth factor receptor-bound protein 2 (Grb2)-binding adaptor protein, transmembrane (GAPT)]; engagement of four of them (LAT, NTAL, LAX, and PAG) in FcεRI signaling has been documented. Here we discuss recent progress in the understanding of how TRAPs affect FcεRI-mediated mast cell signaling. The combined data indicate that individual TRAPs have irreplaceable roles in important signaling events such as calcium response, degranulation, cytokines production, and chemotaxis.

Peri-operative anaphylaxis

Peri-operative anaphylaxis is an important cause for mortality and morbidity associated with anaesthesia. The true incidence is unknown and is most likely under reported. Diagnosis can be difficult, particularly as a number of drugs are given simultaneously and any of these agents can potentially cause anaphylaxis. This review covers the clinical features, differential diagnosis and management of anaphylaxis associated with anaesthesia. The investigations to confirm the clinical suspicion of anaphylaxis and further tests to identify the likely drug(s) are examined. Finally the salient features of common and rare causes including non-drug substances are described.

Midostaurin (PKC412) inhibits immunoglobulin E-dependent activation and mediator release in human blood basophils and mast cells

BACKGROUND

KIT tyrosine kinase inhibitors (TKI), such as nilotinib or midostaurin (PKC412), are increasingly used in clinical trials to counteract neoplastic cell growth in patients with aggressive mast cell (MC) disorders. However, these patients suffer not only from MC infiltration and consecutive organ damage but also from MC mediator-related symptoms.

METHODS

We examined the effects of three KIT TKI, imatinib, nilotinib, and midostaurin, on IgE-dependent mediator release in normal human blood basophils and cultured cord blood cell-derived MC, and on spontaneous histamine secretion in the MC leukaemia cell line HMC-1 and the basophil cell line KU812.

RESULTS

The multi-kinase inhibitor midostaurin that interacts with KIT and protein kinase C was found to counteract anti-IgE-induced mediator release in blood basophils and cultured cord blood cell-derived MC in all samples examined. By contrast, no effects of imatinib or nilotinib on histamine secretion in basophils or MC were found. The effects of midostaurin on histamine release were dose-dependent and occurred at pharmacologic concentrations (IC(50) 10-100 nm). Midostaurin was also found to inhibit the IgE-dependent up-regulation of CD63 on cultured cord blood cell-derived human MC, but did not inhibit IgE-dependent up-regulation of CD63 or CD203c in human blood basophils.

CONCLUSION

Midostaurin may be a beneficial drug in aggressive systemic mastocytosis not only because of its growth-inhibitory effects but also because of its additional effects on activation and mediator release in MC and basophils.

Selective impairment of FcepsilonRI-mediated allergic reaction in Gads-deficient mice

Gads is a Grb2-like adaptor protein expressed in hematopoietic cells. We demonstrated that mast cells from Gads(-/-) mice have selective functional defects. Bone marrow-derived mast cells from Gads(-/-) mice failed to induce Ca(2+) mobilization, degranulation and cytokine production upon cross-linking of FcepsilonRI. In vivo passive cutaneous anaphylaxis was also greatly impaired in Gads(-/-) mice. In contrast, Gads was dispensable for Toll-like receptor-mediated cytokine production in mast cells. Accordingly, mast cell-dependent resistance to acute peritoneal bacterial infection is not reduced in Gads(-/-) mice in vivo. Moreover, mature T and B cell responses and antibody production upon immunization were apparently normal in Gads(-/-) mice. Thus, inhibition of Gads in vivo would suppress the IgE-mediated allergic reaction with minimum adverse effects on both innate and acquired immune responses, and Gads could be an ideal target for the control of allergic responses.

Defining targets for investigating the pharmacogenomics of adverse drug reactions to antifungal agents

Adverse drug reactions (ADRs) associated with antifungal therapy are major problems in patients with invasive fungal infections. Whether by clinical history or patterns of genetic variation, the identification of patients at risk for ADRs should result in improved outcomes while minimizing deleterious side effects. A major contributing factor to ADRs with antifungal agents relates to drug distribution, metabolism and excretion. Genetic variation in key genes can alter the structure and expression of genes and gene products (e.g., proteins). Thus far, the effort has focused on identifying polymorphisms with either empirical or predicted in silico functional consequences; the best candidate genes encode phase I and II drug-metabolizing enzymes (e.g., CYP2C19 and N-acetyltransferase), plasma proteins (albumin and lipoproteins) and drug transporters (P-glycoprotein and multidrug resistance proteins), which can affect the disposition of antifungal agents, eventually leading to dose-dependent (type A) toxicity. Less is known regarding the key genes that interact with antifungal agents, resulting in idiosyncratic (type B) ADRs. The possible role of certain gene products and genetic polymorphisms in the toxicities of antifungal agents are discussed in this review. The preliminary data address the following: low-density lipoproteins and cholesteryl ester transfer protein in amphotericin B renal toxicity; toll-like receptor 1 and 2 in amphotericin B infusion-related ADRs; phosphodiesterase 6 in voriconazole visual adverse events; flavin-containing monooxygenase, glutathione transferases and multidrug resistance proteins 1 and 2 in ketoconazole and terbinafine hepatotoxicity; CYP enzymes and P-glycoprotein in drug interactions between azoles and coadministered medications; multidrug resistance proteins 8 and 9 on 5-flucytosine bone marrow toxicity; and mast cell activation in caspofungin histamine release. This will focus on high-priority candidate genes, which could provide a starting point for molecular studies to elucidate the potential mechanisms for understanding toxicity associated with antifungal drugs as well as identifying candidate genes for large population prospective genetic association studies.

Inhibitory effects of thunberginols A and B isolated from Hydrangeae Dulcis Folium on mRNA expression of cytokines and on activation of activator protein-1 in RBL-2H3 cells

Previously, thunberginols A and B from the processed leaves of Hydrangeae macrophylla var. thunbergii (Hydrangea dulcis folium) substantially inhibited the degranulation caused by antigen and calcium ionophore A23187, and the release of tumor necrosis factor (TNF)-alpha and interleukin (IL)-4 by antigen in RBL-2H3 cells. In the present study, we examined the effect of thunberginol B on the expression of mRNA of several cytokines [ILs-2, 3, 4 and 13, TNF-alpha and granulocyte/macrophage-colony stimulating factor (GM-CSF)] and effects of thunberginols A and B on activator protein (AP)-1 composed of c-jun and c-fos, which is essential for the expression of the cytokine mRNA, in RBL-2H3 cells. Thunberginol B inhibited up-regulated genes of all cytokines, and thunberginols A and B (30 microM) inhibited the phosphorylation of c-jun and expression of c-fos mRNA and phosphorylation of extracellular signal-regulated kinases (ERK1/2). In addition, the profile of gene expression by thunberginol B was similar to that by luteolin, a natural flavone with a potent anti-allergic effect.

Role of IgE receptors in IgE antibody-dependent cytotoxicity and phagocytosis of ovarian tumor cells by human monocytic cells

Antibodies directed against tumor-associated antigens are emerging as effective treatments for a number of cancers, although the mechanism(s) of action for some are unclear and still under investigation. We have previously examined a chimeric IgE antibody (MOv18 IgE), against the ovarian tumor-specific antigen, folate binding protein (FBP), and showed that it can direct human PBMC to kill ovarian cancer cells. We have developed a three-color flow cytometric assay to investigate the mechanism by which IgE receptors on U937 monocytes target and kill ovarian tumor cells. U937 monocytes express three IgE receptors, the high-affinity receptor, FcepsilonRI, the low-affinity receptor, CD23, and galectin-3, and mediate tumor cell killing in vitro by two mechanisms, cytotoxicity, and phagocytosis. Our results suggest that CD23 mediates phagocytosis, which is enhanced by upregulation of CD23 on U937 cells with IL-4, whereas FcepsilonRI mediates cytotoxicity. We show that effector : tumor cell bridging is associated with both activities. Galectin-3 does not appear to be involved in tumor cell killing. U937 cells and IgE exerted ovarian tumor cell killing in vivo in our xenograft model in nude mice. Harnessing IgE receptors to target tumor cells suggests the potential of tumor-specific IgE antibodies to activate effector cells in immunotherapy of ovarian cancer.

The effects of dasatinib on IgE receptor-dependent activation and histamine release in human basophils

Dasatinib is a multitargeted drug that blocks several tyrosine kinases. Apart from its well-known antileukemic activity, the drug has attracted attention because of potential immunosuppressive and anti-inflammatory effects. We report that dasatinib at 1 microM completely blocks anti-IgE-induced histamine release in blood basophils in healthy donors, and allergen-induced release of histamine in sensitized individuals. In addition, dasatinib inhibited FcepsilonRI-mediated release of IL-4 and IgE-mediated up-regulation of CD13, CD63, CD164, and CD203c in basophils. The effects of dasatinib were dose-dependent (IC(50): 50-500 nM) and specific for FcepsilonRI activation in that the drug failed to inhibit C5a-induced or Ca-ionophore-induced histamine release. Interestingly, at lower concentrations, dasatinib even promoted FcepsilonRI-dependent histamine release in basophils in allergic subjects. In consecutive studies, dasatinib was found to interact with and block several FcepsilonRI downstream targets in basophils, including Btk. Correspondingly, FcepsilonRI-mediated histamine secretion in basophils was markedly reduced in Btk knockout mice and in a patient with Btk deficiency. However, the remaining "low-level" mediator secretion in Btk-deficient cells was fully blocked down again by 1 muM dasatinib. Together, these data suggest that dasatinib inhibits FcepsilonRI-mediated activation of basophils through multiple signaling molecules including Btk. Dasatinib may be an interesting agent for immunologic disorders involving Btk-dependent responses or/and FcepsilonRI activation of basophils.

"Accentuate the negative, eliminate the positive": engineering allergy therapeutics to block allergic reactivity through negative signaling

By targeting the dominant-negative signaling receptor FcgammaRIIb expressed on proallergic cells, we have developed 2 novel platforms for the treatment of IgE-mediated allergic disease. First is a genetically engineered bifunctional human fusion protein GE2, which is comprised of the Fc portions of human IgE and IgG1 with an interposed flexible linker designed as a long-term parenteral allergen-nonspecific therapy. GE2 blocks the effector phase of the IgE response in vitro in mice and human subjects and in vivo in the skin and airway and systemically in mice and monkeys. Whether reactivity against human GE2 in human subjects will limit its applicability remains to be determined. The second platform is designed to provide a safer form of allergen-specific immunotherapy and consists of genetically engineered chimeric human Fcgamma-allergen proteins, with Fcgamma-Fel d 1 as the prototype. The allergen portion binds to specific IgE on FcepsilonRs, whereas the Fcgamma portion coaggregates inhibitory FcgammaRIIb and drives inhibition of allergic reactivity. Fcgamma-Fel d 1 blocked human mast cell Fel d 1-induced allergic reactivity in vitro and in vivo in murine models while functioning as an immunogen but not as an allergen.

Inhibition of IgE-mediated phosphorylation of FcεRIγ protein by antiallergic drugs in rat basophilic leukemia (RBL-2H3) cells: A novel action of antiallergic drugs

We examined the effect of antiallergic drugs, azelastine and epinastine, on the expression of FcepsilonRIalpha, beta, and gamma chains and phosphorylation of the gamma chains in rat basophilic leukemia (RBL-2H3) cells. The cells were cultured for 24 h with IgE treatment in the presence of azelastine or epinastine at the concentration of 10(-5) M. The FcepsilonRIalpha mRNA expression was determined by northern blot analysis. The protein level of FcepsilonRI expressed on the plasma membrane was examined following IgE treatment by immunoprecipitation with anti-IgE light chain, followed by western blot analysis with anti-gamma chain of FcR. Azelastine and epinastine had no effect on the FcepsilonRIalpha, beta and gamma mRNA levels. Although the amount of gamma chain assembled into IgE-bound FcepsilonRI was not changed by treatment with azelastine nor epinastine, phosphorylation levels of gamma chains of IgE-bound FcepsilonRI were inhibited by azelastine. The inhibitory effect of azelastine on the IgE-mediated expression of FcepsilonRIgamma protein is not due to their inhibition of mRNA and protein expression, but due to abrogating phosphorylation of the gamma chains, which is important for initiation of FcepsilonRI signaling cascade elicited by IgE interaction.

Chimeric human fcgamma-allergen fusion proteins in the prevention of allergy

Allergic responses are strongly associated with Th2-type immune responses, and modulation of the skewed Th2 response toward a more balanced response is the major goal of allergen immunotherapy (IT) in allergic disorders. To achieve this goal, several approaches have been tested. The authors previously showed that a human immunoglobulin (Ig) Fcgamma-Fcvarepsilon fusion protein (GE2) that directly cross-links FcvarepsilonRI and FcgammaRIIb on human mast cells and basophils was able to inhibit degranulation, and they reasoned that human gamma-allergen fusion protein would achieve a similar inhibitory effect in an allergen-specific fashion while preserving the immunogenicity of the allergen component. Therefore, the authors constructed and developed a human-cat chimeric fusion protein composed of the human Fcgamma1 and the cat allergen Fel d1 (Felis domesticus) for cat allergen-specific IT. This article summarizes the therapeutic features and potential of this novel fusion protein for allergic IT.

Flotillin-1 regulates IgE receptor-mediated signaling in rat basophilic leukemia (RBL-2H3) cells

Cross-linking of high-affinity IgE receptors by multivalent Ag on mast cells (rat basophilic leukemia (RBL)-2H3) induces the phosphorylation of ITAM motifs of an IgE receptor by Src family tyrosine kinase, Lyn. The phosphorylation of IgE receptors is followed by a series of intracellular signals, such as Ca(2+) mobilization, MAPK activation, and degranulation. Therefore, Lyn is a key molecule in the activation of mast cells, but the molecular mechanisms for the activation of Lyn are still unclear. Recently, it is suggested that the localization of Lyn in lipid rafts is critical for its activation in several cell lines, although the precise mechanism is still unknown. In this study, we found that flotillin-1, which is localized in lipid rafts, is involved in the process of Lyn activation. We obtained flotillin-1 knockdown (KD)(2) rat basophilic leukemia (RBL)-2H3 cells, which express a low level of flotillin-1. In the flotillin-1 KD cells, we observed a significant decrease in Ca(2+) mobilization, the phosphorylation of ERKs, tyrosine phosphorylation of the gamma-subunit of IgE receptor, and IgE receptor-mediated degranulation. We also found that flotillin-1 is constitutively associated with Lyn in lipid rafts in RBL-2H3 cells, and Ag stimulation induced the augmentation of flotillin-1 binding to Lyn, resulting in enhancement of kinase activity of Lyn. These results suggest that flotillin-1 is an essential molecule in IgE receptor-mediated mast cell activation, and regulates the kinase activity of Lyn in lipid rafts.

Diagnostic tests based on human basophils: potentials, pitfalls and perspectives

Human basophils are important tools for studying immediate-type hypersensitivity reactions since they release a variety of mediators (e.g., histamine, leukotriene C4, IL-4 and IL-13) following allergen triggering. Several diagnostic tools have been introduced that measure either leukotriene production or the upregulation of surface markers (CD63 and CD203c) from these cells after antigen stimulation. However, a broad variability in basophil activity exists between different basophil donors and different antigens within one donor. This manifests itself in terms of their reactivity (maximum secretory response), based on the intracellular signaling of the basophils studied, and in terms of their sensitivity. The latter is governed by the number of IgE receptors per basophil, the ratio of antigen-specific IgE to total IgE, and by the number of cell surface antigen-specific IgE molecules for half-maximal responses, termed 'intrinsic sensitivity'. These variables give rise to shifts in the dose-response curves which, in a diagnostic setting where only a single antigen concentration is employed, may produce false-negative data. Thus, in order to meaningfully utilize the current basophil activation tests for diagnostic purposes, each allergen should be pre-evaluated separately in order to determine a suitable stimulation range. Additionally, anti-IgE or anti-FcepsilonRIalpha antibodies should serve as positive controls, bearing in mind that 10-20% of basophil donors are not responsive to IgE-mediated stimulation. Diagnostic studies using CD63 or CD203c in hymenoptera, food and drug allergy are critically discussed. Basophil-based tests are indicated for allergy testing in selected cases but should only be performed by experienced laboratories.

Requirements for effective IgE cross-linking on mast cells and basophils

This article reviews the characteristics of high affinity IgE receptors (FcepsilonRI) and their role in the response to allergenic proteins. The requirements for successful cross-linking of FcepsilonRI on basophils and mast cells and subsequent degranulation by allergenic proteins will be explained in detail. Methods for in vitro analysis of allergen-induced mast cell and basophil degranulation will be described and issues/problems in applying these methods will be discussed. Finally, implications for manipulation of protein allergens will be discussed.

Differential expression of spleen tyrosine kinase Syk isoforms in tissues: effects of the microbial flora

Spleen tyrosine kinase (Syk) is expressed widely in hematopoietic and non-hematopoietic cells. The widespread distribution of Syk and its involvement in host defense and allergic reactions, prompted us analyze the influence of microbial exposure on Syk expression. We compared the distribution of Syk in various tissues of germ-free and conventional mice using immunohistochemistry, Western blot analysis and real time RT-PCR. Total Syk expression was similar between germ-free and conventional mice. Since it has been claimed that Syk isoforms are differentially expressed, we studied the distribution and abundance of Syk (L) and Syk (S) isoforms in tissues from these mice. In contrast to previous reports, we found broad tissue expression of Syk (S). Interestingly, in germ-free mice the amount of Syk (S) but not Syk L protein was selectively increased in lung and spleen. In summary, our study reveals new and broad tissue expression of both Syk isoforms and demonstrates that lack of microbial flora results in selectively increased expression of Syk (S) isoform in lung and spleen.

Effect of cyclosporin and tacrolimus (FK506) on the antigen-induced mediator release, membrane potential and 86Rb+/K+ and Ca2+ fluxes in the RBL-2H3 cell line

The immunosuppressants cyclosporin A (CsA) and tacrolimus (FK506) inhibit the activation by antigen of T-lymphocytes as well as mast cells. The mechanism of their action on mast cells has yet to be elucidated. We, therefore, assessed their effect on antigen-induced histamine and beta-hexosaminidase release, membrane potential changes (bis-oxonol fluorescent probe), 86RB+ (marker for K+)-efflux, the intracellular free calcium concentration ([Ca2+]i in single cells) and 45Ca2+ uptake (CsA only) in RBL-2H3 cells, a mucosal-type mast cell line, passively sensitized with monoclonal mouse IgE antibody. Antigen addition induced depolarization within 1-2 min, followed by slower repolarization, reaching a steady state (approximately 90% repolarization) after 7-9 min. CsA and FK506 each dose-dependently inhibited antigen-induced histamine and beta-hexosaminidase secretion and the membrane repolarization phase, with similar IC50s for both actions, approximately 20 nM for CsA and approximately 2 nM for FK506. Antigen-induced 86Rb+-efflux was also significantly inhibited. Antigen-evoked increase in [Ca2+]i (area under the curve, AUC) was reduced by 35% and 52% in the presence of CsA or FK506 (1 microM each), respectively. However, 45Ca2+-uptake was not inhibited by CsA. These results suggest that both CsA and FK506 may inhibit mediator release from mast cells via blocking two interrelated processes, which are involved in the secretory process: 1. Membrane repolarization phase, which is essential for optimal mediator secretion and is mediated by a Ca2+-sensitive K+-efflux, yet to be further characterized, and (2) Increase in [Ca2+]i, probably via reduction of Ca(+2)-release from intracellular stores, [Ca2+]s.

Protein Flexibility and Ligand Rigidity: A Thermodynamic and Kinetic Study of ITAM-Based Ligand Binding to Syk Tandem SH2

The Syk tandem Src homology 2 domain (Syk tSH2) constitutes a flexible protein module involved in the regulation of Syk kinase activity. The Syk tSH2 domain is assumed to function by adapting the distance between its two SH2 domains upon bivalent binding to diphosphotyrosine ligands. A thermodynamic and kinetic analysis of ligand binding was performed by using surface plasmon resonance (SPR). Furthermore, the effect of binding on the Syk tSH2 structural dynamics was probed by hydrogen/deuterium exchange and electrospray mass spectrometry (ESI-MS). Two ligands were studied: 1, a flexible peptide derived from the tSH2 recognition ITAM sequence at the gamma chain of the FcepsilonRI-receptor, and 2, a ligand in which the amino acids between the two SH2 binding motifs in ligand 1 have been replaced by a rigid linker of comparable length. Both ligands display comparable affinity for Syk tSH2 at 25 degrees C, yet a major difference in thermodynamics is observed. Upon binding of the rigid ligand, 2, the expected entropy advantage is not realized. On the contrary, 2 binds with a considerably higher entropy price of approximately 9 kcal mol-1, which is attributed to a further decrease in protein flexibility upon binding to this rigid ligand. The significant reduction in deuterium incorporation in the Syk tSH2 protein upon binding of either 1 or 2, as monitored by ESI-MS, indicates a major reduction in protein dynamics upon binding. The results are consistent with a two-step binding model: after an initial binding step, a rapid structural change of the protein occurs, followed by a second binding step. Such a bivalent binding model allows high affinity and fast dissociation kinetics, which are very important in transient signal-transduction processes.

A chimeric human-cat fusion protein blocks cat-induced allergy

Animal allergens are an important cause of asthma and allergic rhinitis. We designed and tested a chimeric human-cat fusion protein composed of a truncated human IgG Fcgamma1 and the major cat allergen Fel d1, as a proof of concept for a new approach to allergy immunotherapy. This Fcgamma-Fel d1 protein induced dose-dependent inhibition of Fel d1-driven IgE-mediated histamine release from cat-allergic donors' basophils and sensitized human cord blood-derived mast cells. Such inhibition was associated with altered Syk and ERK signaling. The Fcgamma-Fel d1 protein also blocked in vivo reactivity in FcepsilonRIalpha transgenic mice passively sensitized with human IgE antibody to cat and in Balb/c mice actively sensitized against Fel d1. The Fcgamma-Fel d1 protein alone did not induce mediator release. Chimeric human Fcgamma-allergen fusion proteins may provide a new therapeutic platform for the immune-based therapy of allergic disease.

Mast cells are involved in inflammatory reactions during Complex Regional Pain Syndrome type 1

BACKGROUND

The Complex Regional Pain Syndrome type 1 (CRPS1) is a complication of surgery or trauma but spontaneous development is also described. Although the pathogenesis remains debatable, afferent, efferent and central nervous system mechanisms are proposed. Recently we showed involvement of the proinflammatory cytokines IL-6 and TNFalpha which is direct evidence for an inflammatory process. Many types of cells, such as activated T lymphocytes, monocytes, macrophages and skin resident cells like mast cells, could contribute to the production of cytokines. Involvement of mast cells is relatively easy to detect by measurement of tryptase.

AIM

To establish whether mast cells are involved in the inflammatory reactions during CRPS1.

METHODS

Twenty patients fulfilling the Bruehl criteria with CRPS1 in one extremity were studied. Impairment was assessed by registration of pain and measurement of differences in temperature, volume and mobility between the involved and uninvolved extremity. Blisters were made with a suction method in order to determine cytokines and mast cell derived tryptase in the involved and uninvolved extremity.

RESULTS

In the blister fluid a significant difference (median +/- interquartile range, Wilcoxon signed-ranks test P < 0.05) was found between the involved and uninvolved extremity in IL-6 [53.5 (17.3-225) versus 6.2 (2-20.3) pg/ml], TNFalpha [31 (15.5-131.5) versus 8 (4-39) pg/ml], and tryptase [37 (20.5-62.3) versus 12.5 (6.7-23.5) ng/ml]. There was a significant correlation (0.455) between the intensity of pain and tryptase levels in the involved extremity (Spearman's test, P < 0.05).

CONCLUSION

Mast cells are involved in inflammatory reactions during the CRPS1. Mast cells could play a role in the production of cytokines such as TNFalpha.

Inhibition of the antigen-induced activation of RBL-2H3 cells by charybdotoxin and cetiedil

Quinidine and Ba(2+), non-selective K(+)-channel blockers, have previously been shown to inhibit antigen-induced mediator (beta-hexosaminidase) release from RBL-2H3 cells, a mucosal-type mast cell line. We therefore used selective blockers of Ca(2+)-activated and other K(+) channels to determine if there was a role for these channels in antigen-induced mediator release. Charybdotoxin and cetiedil dose-dependently inhibited beta-hexosaminidase release with IC(50) values of 133 nM and 84 microM, respectively. Charybdotoxin also inhibited the repolarization phase of the antigen-induced biphasic change in the membrane potential (IC(50) 84 nM), antigen-stimulated 86Rb(+)-efflux and increase in free intracellular calcium, [Ca(2+)](i). Iberiotoxin, margatoxin, apamin and tetraethylammonium had no effect on beta-hexosaminidase release. These results suggest that K(+) conductances play a significant role in mediator release from RBL-2H3, that these conductances are of the intermediate conductance Ca(2+)-activated K(+) channel (IK(Ca)) type, and that they are somewhat similar to those which have been described in red blood cells, though they are much less sensitive to clotrimazole.

Differential regulation of IL-4 expression and degranulation by anti-allergic olopatadine in rat basophilic leukemia (RBL-2H3) cells

Olopatadine hydrochloride (olopatadine) is an anti-allergic drug that functions as a histamine H(1) antagonist and inhibits both mast cell degranulation and the release of arachidonic acid metabolites in various types of cells. In this study, we examined the ability of olopatadine to inhibit the expression of cytokine genes in vitro via high-affinity receptors for immunoglobulin E in mast cells, using a rat basophilic leukemia (RBL-2H3) cell line and an in vivo mouse model. Levels of gene expression in RBL-2H3 cells were determined by semi-quantitative RT-PCR, and serum interleukin-4 (IL-4) level in mice was quantified by ELISA. Olopatadine inhibited significantly the induction of IL-4 expression by mast cells both in vivo and in vitro. Olopatadine inhibited Ca(2+) influx through receptor-operated channels (ROC) without affecting Ca(2+) release from intracellular stores. Comparative analysis of olopatadine with other anti-allergic drugs and the ROC blocker SKF-96365 demonstrated that the potency of inhibition of Ca(2+) influx correlated with the degree of suppression of degranulation and arachidonic acid release. Inhibition of Ca(2+) influx decreased phosphorylation of p38 mitogen-activated protein kinase and c-Jun NH(2)-terminal kinase, which participate in regulation of cytokine (e.g. IL-4) gene expression. However, the rank order of inhibition of Ca(2+) influx did not correspond to reduction of IL-4 expression, suggesting that an unknown mechanism(s) of action, in addition to inhibition of Ca(2+) influx, is involved in the expression of cytokines in mast cells.

Unraveling the mission of FcepsilonRI on antigen-presenting cells

A decade ago, the discovery of the high-affinity receptor for IgE (FcepsilonRI) on epidermal Langerhans cells documented the end of the dogma that FcepsilonRI is only expressed on effector cells of anaphylaxis. Since then, the functional significance of this receptor on antigen-presenting cells (APCs) has been an area of intense research work. Scientists have focused on a better understanding of the molecular structure, regulation, and role of FcepsilonRI on APCs in the human immune system. Insights into the cellular events linked to the activation of APCs on ligation of FcepsilonRI by IgE and allergens might provide the basis for new aspects in the pathophysiology of allergic diseases and the design of future diagnostic and therapeutic strategies. This review is dedicated to the 10th anniversary of the discovery of FcepsilonRI on APCs and describes the numerous areas of research in this field.

Antiallergic tea catechin, (-)-epigallocatechin-3-O-(3-O-methyl)-gallate, suppresses FcepsilonRI expression in human basophilic KU812 cells

We previously found that the O-methylated derivative of (-)-epigallocatechin-3-O-gallate (EGCg), (-)-epigallocatechin-3-O-(3-O-methyl)-gallate (EGCG' '3Me), has potent antiallergic activity. The high-affinity IgE receptor, FcepsilonRI, is found at high levels on basophils and mast cells and plays a key role in a series of acute and chronic human allergic reactions. To understand the mechanism of action for the antiallergic EGCG' '3Me, the effect of EGCG' '3Me on the cell surface expression of FcepsilonRI in human basophilic KU812 cells was examined. Flow cytometric analysis showed that EGCG' '3Me was able to decrease the cell surface expression of FcepsilonRI. Moreover, immunoblot analysis revealed that total cellular expression of the FcepsilonRI alpha chain decreased upon treatment with EGCG' '3Me. FcepsilonRI is a tetrameric structure comprising one alpha chain, one beta chain, and two gamma chains. The level of mRNA production of each subunit in KU812 cells was investigated. EGCG' '3Me reduced FcepsilonRI alpha and gamma mRNA levels. The cross-linkage of FcepsilonRI causes the activation of basophils, which leads to the secretion of inflammatory mediators including histamine. EGCG' '3Me treatment inhibited the FcepsilonRI cross-linking-induced histamine release. These results suggested that EGCG' '3Me can negatively regulate basophil activation through the suppression of FcepsilonRI expression.

Association of the Src homology 2 domain-containing inositol 5' phosphatase (SHIP) to releasability in human basophils

During the study of the biology of the Human recombinant Histamine Releasing Factor (HrHRF), we uncovered a hyperreleasable phenotype of basophils from HrHRF-responder donors. Basophils from these donors released histamne to HrHRF, IL-3 and D(2)O. While there has been a significant amount of work elucidating signal transduction events in human basophils, the reason for this hyperreleasable phenotype remained illusive. A clue to the releasability of these highly allergic, asthmatic HrHRF-responder donor basophils was demonstrated in studies using SHIP knockout mice. Bone marrow-derived mast cells from the SHIP knockout mice demonstrated hyperreleasability to stimuli through the IgE receptor and alteration of subsequent signal transduction events. We have demonstrated a highly significant negative correlation between the amount of SHIP protein per cell equivalent and maximum histamine release to HrHRF. These results provide a clue to the hyperreleasable phenotype and implicate SHIP as an additional regulator of secretion in human basophils.

Piceatannol, a Syk-selective tyrosine kinase inhibitor, attenuated antigen challenge of guinea pig airways in vitro

Activation of nontransmembrane protein tyrosine kinases, such as Lyn and Syk, has been shown to be the earliest detectable signaling response to Fc receptor (Fc epsilon RI) cross-linking on mast cells leading to mast cell degranulation. The present study examined the effects of piceatannol (3,4,3',5'-tetrahydroxy-trans-stilbene, 10-100 microM), a Syk-selective tyrosine kinase inhibitor, on ovalbumin-induced anaphylactic contraction of isolated guinea pig bronchi and release of histamine and peptidoleukotrienes from chopped lung preparations. Pretreatment with piceatannol slightly suppressed ovalbumin-induced peak anaphylactic bronchial contraction but markedly (P<0.05) facilitated relaxation of the anaphylactically contracted bronchi. Piceatannol did not inhibit direct histamine-, leukotriene D(4)- or KCl-induced bronchial contraction, nor revert an existing anaphylactic bronchial contraction. Piceatannol, at 30 microM and above, significantly (P<0.05) prevented ovalbumin-induced release of both histamine and peptidoleukotrienes from lung fragments. Piceatannol did not inhibit exogenous arachidonic acid-induced release of peptidoleukotrienes from lung fragments. Our data show for the first time that inhibition of Syk tyrosine kinase can attenuate anaphylactic bronchial contraction in vitro, probably via inhibition of mast cell degranulation.

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

Human mast cells and basophils that express the high-affinity immunoglobulin E (IgE) receptor, Fc epsilon receptor 1 (Fc epsilon RI), have key roles in allergic diseases. Fc epsilon RI cross-linking stimulates the release of allergic mediators. Mast cells and basophils co-express Fc gamma RIIb, a low affinity receptor containing an immunoreceptor tyrosine-based inhibitory motif and whose co-aggregation with Fc epsilon RI can block Fc epsilon RI-mediated reactivity. Here we designed, expressed and tested the human basophil and mast-cell inhibitory function of a novel chimeric fusion protein, whose structure is gamma Hinge-CH gamma 2-CH gamma 3-15aa linker-CH epsilon 2-CH epsilon 3-CH epsilon 4. This Fc gamma Fc epsilon fusion protein was expressed as the predicted 140-kappa D dimer that reacted with anti-human epsilon- and gamma-chain specific antibodies. Fc gamma Fc epsilon bound to both human Fc epsilon RI and Fc gamma RII. It also showed dose- and time-dependent inhibition of antigen-driven IgE-mediated histamine release from fresh human basophils sensitized with IgE directed against NIP (4-hydroxy-3-iodo-5-nitrophenylacetyl). This was associated with altered Syk signaling. The fusion protein also showed increased inhibition of human anti-NP (4-hydroxy-3-nitrophenylacetyl) and anti-dansyl IgE-mediated passive cutaneous anaphylaxis in transgenic mice expressing human Fc epsilon RI alpha. Our results show that this chimeric protein is able to form complexes with both Fc epsilon RI and Fc gamma RII, and inhibit mast-cell and basophil function. This approach, using a Fc gamma Fc epsilon fusion protein to co-aggregate Fc epsilon RI with a receptor containing an immunoreceptor tyrosine-based inhibition motif, has therapeutic potential in IgE- and Fc epsilon RI-mediated diseases.

IgE receptors

IgE receptors are implicated as important components of the immunological pathway in allergic and inflammatory diseases. Recent investigations have begun to unravel the structure, signal transduction and function of IgE receptors from different cell types in rodent and human systems. Studies of the mechanisms involved might provide opportunities for therapeutic intervention strategies in the treatment of allergic and hypersensitivity reactions.

Fc-signalling in the modulation of immune responses by passive antibody

Passive antibody can both suppress and augment immune responses. Until recently, there was virtual unanimity on the importance of the interaction of the Fc portion of modulating antibody with Fc-receptors (Fc-signalling), especially in experiments involving the suppression by antibody. Experiments reported in the last few years, that do not demonstrate the range of Fc-portion/Fc-receptor influences on the suppression of immune responses by passive antibody, have introduced new uncertainty into this field. The purpose of this paper is to review how the initial controversy on the influence of Fc-signalling in inhibition by passive antibody was resolved. Old and new approaches are suggested that may help in resolving the current uncertainty engendered by recent experimental results that were interpreted to mean that passive suppressive antibody does not utilize the inhibitory FcgammaRIIB receptor. An understanding of the factors that influence negative Fc-signalling is needed in order to optimize clinical therapies whose action depends on the suppressive property of antibody.