High-affinity Immunoglobulin E Receptor Research Articles

Modulation of the Fcepsilon receptor I signaling by tyrosine kinase inhibitors: search for therapeutic targets of inflammatory and allergy diseases.

Mast cells and basophils are major effector cells in the immunoglobulin E (IgE)-dependent allergic reactions as well as in the innate immunity. They are distributed throughout the body and, upon allergen exposure, are stimulated via the high affinity IgE receptor (FcepsilonRI) to release several pro-inflammatory mediators such as leukotrienes, immunoregulatory cytokines and histamine. FcepsilonRI-mediated signaling is initiated by tyrosine phosphorylation of FcepsilonRI subunits by Src family kinase Lyn, which is followed by an activation of Syk/Zap family kinase Syk. The activated kinases then in turn phosphorylate and activate other enzymes [phospholipase Cgamma (PLCgamma) isoforms, phosphatidylinositol-3 kinase (PI3K) isoforms, protein kinase C (PKC) isoforms, Bruton's tyrosine kinase (Btk) and others], adaptors [linker for activation of T cells (LAT), Cbl, Grb2 and others] and GTP exchange factors/GTPases (Vav, Ras, Rho, and others), and subsequently induce the mobilization of stored and extracellular Ca(2+). These and other biochemical events lead within seconds and minutes to the secretory response and later to the production of chemokines. This review is focused on the use of tyrosine kinase inhibitors specific for Src family kinases (PP1/PP2, SU6656 and CT5269), Syk kinase (piceatannol, ER-27319 and BAY 61-3606) and Btk (terreic acid and LFM-A13) for a modulation of FcepsilonRI-mediated signaling in mast cells. Potential use of the inhibitors in the treatment of inflammatory and allergy diseases as well as future directions in the development of highly specific tyrosine kinases inhibitors of new generations and their use in an intended modulation of mast cell signaling are discussed.

The role of human mast cell-derived cytokines in eosinophil biology.

Eosinophil-mediated diseases, such as allergic asthma, eosinophilic fasciitis, and certain hypersensitivity pulmonary disorders, are characterized by eosinophil infiltration and tissue injury. Mast cells and T cells often colocalize to these areas. Recent data suggest that mast cells can contribute to eosinophil-mediated inflammatory responses. Activation of mast cells can occur by antigen and immunoglobulin E (IgE) via the high-affinity receptor (FcepsilonRI) for IgE. The liberation of proteases, leukotrienes, lipid mediators, and histamine can contribute to tissue inflammation and allow recruitment of eosinophils to tissue. In addition, the synthesis and expression of a plethora of cytokines and chemokines (such as granulocyte-macrophage colony-stimulating factor [GM-CSF], interleukin-1 [IL-1], IL-3, IL-5, tumor necrosis factor-alpha [TNF-alpha], and the chemokines IL-8, regulated upon activation normal T cell expressed and secreted [RANTES], monocyte chemotactic protein-1 [MCP-1], and eotaxin) by mast cells can influence eosinophil biology. Stem cell factor (SCF)-c-kit, cytokine-cytokine receptor, and chemokine-chemokine receptor (CCR3) interactions leading to nuclear factor kappaB (NF-kappaB), mitogen-activated protein kinase (MAPK) expression, and other signaling pathways can modulate eosinophil function. Eosinophil hematopoiesis, activation, survival, and elaboration of mediators can all be regulated thus by mast cells in tissue. Moreover, because eosinophils can secrete SCF, eosinophils can regulate mast cell function in a paracrine manner. This two-way interaction between eosinophils and mast cells can pave the way for chronic inflammatory responses in a variety of human diseases. This review summarizes this pivotal interaction between human mast cells and eosinophils.

Rethinking the role of Src family protein tyrosine kinases in the allergic response: new insights on the functional coupling of the high affinity IgE receptor.

Antigen-induced cross-linking of immunoglobulin E (IgE) antibodies bound to the high-affinity IgE receptor (FcepsilonRI), on mast cells results in the release of mediators that initiate an inflammatory response. This normal immune response has been abducted by immunological adaptation, through the production of IgE antibodies to normally innocuous substances, to cause allergic disease. Therefore, understanding the molecular requirements in IgE-dependent mast-cell activation holds promise for therapeutic intervention in disease. Recent investigation on the functional coupling of FcepsilonRI to the intracellular signaling apparatus has provided paradigm-altering insights on the importance and function of Src family protein tyrosine kinases (Src PTK) in mast-cell activation. In this synopsis, we review the current knowledge on the role of the Src PTKs, Fyn and Lyn, in mast-cell activation and discuss the implications of our findings on allergic disease.

Role of immunoglobulin E and mast cells in murine models of asthma.

Immunoglobulin E (IgE) and mast cells are believed to play important roles in allergic inflammation. However, their contributions to the pathogenesis of human asthma have not been clearly established. Significant progress has been made recently in our understanding of airway inflammation and airway hyperresponsiveness through studies of murine models of asthma and genetically engineered mice. Some of the studies have provided significant insights into the role of IgE and mast cells in the allergic airway response. In these models mice are immunized systemically with soluble protein antigens and then receive an antigen challenge through the airways. Bronchoalveolar lavage fluid from mice with allergic airway inflammation contains significant amounts of IgE. The IgE can capture the antigen presented to the airways and the immune complexes so formed can augment allergic airway response in a high-affinity IgE receptor (FcepsilonRI)-dependent manner. Previously, there were conflicting reports regarding the role of mast cells in murine models of asthma, based on studies of mast cell-deficient mice. More recent studies have suggested that the extent to which mast cells contribute to murine models of asthma depends on the experimental conditions employed to generate the airway response. This conclusion was further supported by studies using FcepsilonRI-deficient mice. Therefore, IgE-dependent activation of mast cells plays an important role in the development of allergic airway inflammation and airway hyperresponsiveness in mice under specific conditions. The murine models used should be of value for testing inhibitors of IgE or mast cells for the development of therapeutic agents for human asthma.

Preferential signaling and induction of allergy-promoting lymphokines upon weak stimulation of the high affinity IgE receptor on mast cells.

Mast cell degranulation and de novo cytokine production is a consequence of antigen-aggregation of the immunoglobulin E (IgE)-occupied high affinity receptor for IgE (FcɛRI). Herein, we report that lymphokines that promote allergic inflammation, like MCP-1, were potently induced at low antigen (Ag) concentrations or at low receptor occupancy with IgE whereas some that down-regulate this response, like interleukin (IL)-10, required high receptor occupancy. Weak stimulation of mast cells caused minimal degranulation whereas a half-maximal secretory response was observed for chemokines and, with the exception of TNF-α, a weaker cytokine secretory response was observed. The medium from weakly stimulated mast cells elicited a monocyte/macrophage chemotactic response similar to that observed at high receptor occupancy. Weak stimulation also favored the phosphorylation of Gab2 and p38MAPK, while LAT and ERK2 phosphorylation was induced by a stronger stimulus. Gab2-deficient mast cells were severely impaired in chemokine mRNA induction whereas LAT-deficient mast cells showed a more pronounced defect in cytokines. These findings demonstrate that perturbation of small numbers of IgE receptors on mast cells favors certain signals that contribute to a lymphokine response that can mediate allergic inflammation.

Immunoglobulin E (IgE) containing complexes induce IL-4 production in human basophils: effect on Th1–Th2 balance in malaria

Human basophils are potent producers of IL-4 following cross-linking of the high affinity receptor for IgE (FcεR1). Elevated levels of both total- and malaria-specific IgE have been demonstrated in sera from people living in malaria-endemic regions. Whether or not these IgE antibodies are pathogenic is unclear. Serum containing high IgE levels obtained from malaria individuals was used to establish whether IgE-immune complexes could induce IL-4 production in human basophils. The basophils, obtained from healthy donors, were primed with 10 ng/ml of IL-3 before being transferred to wells containing goat anti-human IgE or human antimalarial IgE-immune complexes. IL-4 was induced upon stimulation of human basophils by plate bound IgE-containing immune complexes. Basophils treated similarly but with goat anti-IgG/human antimalarial- IgG-immune complexes did not secrete IL-4. Similarly mononuclear cells depleted of basophils in parallel culture did not secrete IL-4. Thus, human basophils may contribute to the polarization of T-helper type 2 in the (Th2) responses in malaria hosts via IgE-induced IL-4 production.

Omalizumab. A review of the new treatment of allergic asthma and seasonal allergic rhinitis

The causal role of immunoglobulin E (IgE) in triggering the cascade of biochemical events leading to allergic disease is well established. Treatments that selectively inhibit IgE activity are a logical approach in managing the allergic response. Omalizumab is a recombinant humanised monoclonal antibody which specifically binds to the Cε3 domain of immunoglobulin (Ig) E, the site of high-affinity IgE receptor binding. The clinical benefit and steroid-sparing effect of treatment with the anti-immunoglobulin-E (IgE) antibody, Omalizumab, was assessed in patients with moderate-to-severe allergic asthma and seasonal allergic rhinitis. Intravenous and subcutaneous administration of anti-IgE mAb reduces circulating levels of IgE in atopic patients to low levels commonly seen in non-atopic individuals. Anti-IgE therapy offers protection against allergen-induced bronchoconstriction, reduces the need for short acting inhaled beta 2-agonist and corticosteroids among asthmatic patients and reduces severity of symptoms of allergic rhinitis. Adverse events were infrequent in clinical trials of omalizumab, and not significantly different from placebo. The most frequent drug-related event was mild to moderate urticaria. They do not induce anaphylaxis and the occurrence of antibodies against anti-IgE mAb is sporadic. The results of cited studies suggest that humanized anti-IgE monoclonal antibodies may have important immunotherapeutic benefit for treatment of allergic disorders.

Omalizumab: anti-IgE monoclonal antibody E25, E25, humanised anti-IgE MAb, IGE 025, monoclonal antibody E25, Olizumab, Xolair, rhuMAb-E25.

Omalizumab: anti-IgE monoclonal antibody E25, E25, humanised anti-IgE MAb, IGE 025, monoclonal antibody E25, Olizumab, Xolair, rhuMAb-E25.

NEW AND ALTERNATIVE PHARMACOLOGIC THERAPY IN ASTHMA

Much has been learned about the inflammatory response in the lung, but many of the immunologic and molecular details still are not understood completely. The inflammatory response in the lung is a mechanism by which the body responds to and protects itself from infectious and noninfectious events. In the lung, the mechanism may be nonspecific or antigen specific. The inflammatory response is usually protective, but inflammation has the potential to injure tissue including the airways and lead to chronic irreversible changes. New approaches to therapy are based on understanding the pathophysiology of asthma and are directed toward blocking the inflammation. What is known about the inflammatory response in the lung is that histologically it starts with increased vascular permeability, followed by accumulation of granulocytes initially and monocytes and phagocytes later, and eventual resolution.24 Permeability changes occur within minutes after allergen exposure, and influx of inflammatory cells develop over the next several hours. Eosinophils predominate as the time after the allergic challenge passes. Monocytes and phagocytes appear in 24 to 48 hours and persist for days even without further allergen exposure. Mediators, such as histamine and the products of arachidonic acid metabolism (prostaglandins, leukotrienes), which are produced by mast cells and other inflammatory cells, produce and regulate most of the characteristic features of inflammation. Cytokines are low-molecular-weight proteins that regulate immunologic inflammation and are secreted by a variety of cells in response to specific stimuli. Cytokines function as immune mediators and originally were named on the basis of the cell origin or biologic activity. Monokines are produced by monocytes, and lymphokines are released by lymphocytes. The chemoattractant cytokines are called chemokines. Cytokines involved in stimulating growth often are designated to be growth factors. The cytokine system is redundant, and there is cross reactivity. Over 100 cytokines have been identified so far. Many cytokines have been implicated in the pathophysiology of atopic disease, although certain cytokines play a more critical role in atopic inflammation. The synthesis of many cytokines is down-regulated by corticosteroids.3, 26, 41 In asthma, the immunologic response begins with allergen sensitization leading to the production of allergen-specific immunoglobulin E (IgE).32 In genetically susceptible persons, naïve CD4+ T-helper cells (Th0) with receptors to offending antigens become activated when they come into contact with that antigen in the presence of MHC Class II and other proteins. Th0 cells can differentiate into Th1 and Th2 cells. Differentiation into Th2 cells is a key step in IgE production. Th2 lymphocytes develop from Th0 cells in the presence of interleukin 4 (IL-4). Th2 cells then produce additional cytokines, including IL-4, IL-5, IL-9, and IL-13, eventually leading to the production of IgE by B cells.32 Allergen-specific IgE antibodies bind to the high-affinity IgE receptors on the surface of mast cells and basophils and to low-affinity receptors on B cells, monocytes, and other inflammatory cells.41 When the IgE receptors are bridged by allergen, the mast cells degranulate and release histamine, cytokines, and other chemical mediators of inflammation. Histamine is primarily responsible for the early phase response that occurs within minutes after allergen exposure. Other mast-cell mediators include leukotrienes, interleukins, proteases, and platelet-activating factor. Leukotrienes increase vascular permeability and mucus production and cause bronchoconstriction. Leukotriene B4 (LTB4) is a powerful chemokine for eosinophils and neutrophils. IL-3, IL-4, and IL-5 also are produced by mast cells. IL-3 is chemotactic for basophils. IL-4 stimulates IgE formation and the differentiation of Th2 from Th0 cells. IL-5 attracts eosinophils and basophils, stimulates eosinophil proliferation and differentiation, and possibly slows eosinophils apoptosis. Other cytokines released from mast cells include tumor necrosis factor α (TNF α), granulocyte-macrophage colony-stimulating factor (GM-CSF), and platelet-activating factor (PAF).42 Mast-cell mediators initiate the early phase response that includes increased vascular permeability, bronchoconstriction, edema, increased mucus secretion, and activation of the chemical cascades that attract eosinophils and other granulocytes to the area. The late phase reaction occurs about 4 to 8 hours after allergen exposure with influx of eosinophils, neutrophils, and other inflammatory cells in the mucosa and submucosa. Eosinophils release a variety of chemical products, including major basic protein and eosinophilic cationic protein, that produce epithelial damage. Constant and repeated inflammatory reactions in the lungs may produce permanent changes and airway remodeling.9, 16 Many different treatments are available for managing asthma, and there are many new therapeutic approaches that are possible. Therapy that changes or controls the basic immunologic processes discussed previously will be a more easily available option in the near future for many patients who are not controlled with presently available medications. Several if not all of the following new therapeutic agents will definitely play important roles in the treatment of asthma in the new millennium.

Measurement of canine IgE using the alpha chain of the human high affinity IgE receptor

In vitro assays for allergen specific immunoglobulin E (IgE) are a convenient and reproducible alternative to intradermal skin testing in dogs. Such tests may be used to support a diagnosis of atopic dermatitis and to define appropriate allergens for immunotherapy. Current in vitro assays rely upon monoclonal or polyclonal antibodies as IgE detection reagents. However, in sera where allergen-specific IgG occurs in great excess, any IgE:IgG cross-reactivity of the detection reagent may result in lowered assay specificity. Therefore, we have developed an assay for canine IgE which uses a recombinant form of the extracellular part of the alpha chain of the human high affinity IgE receptor (FcεRIα). Biotinylated FcεRIα shows no significant binding to purified canine IgG, and recognizes a heat labile antibody in serum, with a detection limit of 73–146 pg/ml. Comparison of assay signals using the labeled FcεRIα and a highly specific anti-canine IgE monoclonal antibody (MAb) shows good agreement. The FcεRIα is therefore a sensitive and specific alternative to polyclonal or monoclonal antibodies for canine serum IgE measurement.

Antibody cross-linking of human CD9 and the high-affinity immunoglobulin E receptor stimulates secretion from transfected rat basophilic leukaemia cells.

Previous studies have shown that antibody cross-linking of the tetraspanin protein CD9 stimulates the degranulation of platelets and eosinophils, although the mechanism of activation is unclear. In this work we transfected human CD9 into the rat basophilic leukaemia (RBL-2H3) cell line and studied the stimulation of secretion from these cells in response to a panel of anti-CD9 antibodies. Intact immunoglobulin G1 (IgG1) antibodies activated transfected cells whereas F(ab')2 fragments of antibody and an intact IgG2a did not. Stimulation of secretion was inhibited by co-incubation with monomer murine immunoglobulin E (IgE) but not with an IgG1 isotype control, indicating that the response involves the endogenous high-affinity IgE receptor (FcepsilonRI). The anti-CD9 antibody activation curve was biphasic, and supraoptimal antibody concentrations stimulated little or no degranulation, indicating that multivalent binding of human CD9 molecules is necessary for the formation of an active complex with rat FcepsilonRI. Immunoprecipitation of FcepsilonRI under mild detergent conditions co-precipitated CD9, suggesting the presence of pre-existing complexes of CD9 and FcepsilonRI that could be activated by antibody cross-linking. These data are further evidence that tetraspanins are involved in FcepsilonRI signalling and may reflect the participation of tetraspanins in the formation of complexes with other membrane proteins that use components of Fc receptors for signal transduction.

Detection of Basophil Activation by Flow Cytometry in Patients with Allergy to Muscle-relaxant Drugs

ALLERGIC or pseudoallergic reactions that occur during anesthesia have been increasing over the last few years. 1 Muscle-relaxant drugs are responsible for at least half of these life-threatening adverse reactions. 1,2 The diagnosis of drug allergy is mainly based on a detailed clinical history, positive skin tests, and detection of specific immunoglobulin E (IgE). Nevertheless, the biologic results are not always closely correlated with clinical assessment of the disease, and discrepancies between skin tests and specific IgE are reported, 2,3 In these cases, in vitro investigations to identify the responsible drug are needed, and the histamine release (HR) test is usually performed. 2 HR reflects basophil degranulation, but the very small number of circulating basophils is a limitation to this test, and its clinical benefit remains controversial. Because flow cytometry is a valuable tool for identifying cell populations even at low concentrations, we developed a tricolor flow cytometric method (FCM) for the study of allergen-induced basophil activation. 4 Briefly, identification of basophils is based both on CD45 expression (a common leukocyte antigen) and on the presence of IgE on the cell surface, because basophils express high-affinity receptor for IgE. Cell activation on allergen or drug challenge is assessed by the expression of CD63 on the plasma membrane. 5 After the publication of preliminary data (only focused on usual allergens), we initiated studies to evaluate the usefulness of the method in the diagnosis of drug allergy. We report here results of the first four cases of allergy to muscle-relaxant drugs since this FCM was introduced in our laboratory. The patients were recruited from different associated hospitals in Lyon, France, and rapidly developed clinical features evocative of anaphylactic reaction after induction of anesthesia, e.g., hypotension, bronchospasm, and cutaneous signs. Investigations of the responsible drug were performed in the outpatient unit of the Department of Anesthesia (screening for drug allergy unit) at least 2 months after the allergic reaction. Skin prick and intradermal reaction (IDR) tests 3 were performed using various dilutions of drug solutions, specific IgE antibodies (against ammonium group) were measured using radioallergosorbent techniques (Capsystem; Pharmacia, Uppsala, Sweden), histamine was measured using a radioimmunoassay (Immunotech, Marseille, France), and HR test was considered positive when superior to 10% of total HR. Basophil degranulation by FCM was detected by CD63 expression on the cell surface. A positive threshold is defined with a negative control without any drug. Results are positive when > 10% of basophils express CD63.

Signalling through the high-affinity IgE receptor Fc epsilonRI.

The Fc epsilonRI complex forms a high-affinity cell-surface receptor for the Fc region of antigen-specific immunoglobulin E (IgE) molecules. Fc epsilonRI is multimeric and is a member of a family of related antigen/Fc receptors which have conserved structural features and similar roles in initiating intracellular signalling cascades. In humans, Fc epsilonRI controls the activation of mast cells and basophils, and participates in IgE-mediated antigen presentation. Multivalent antigens bind and crosslink IgE molecules held at the cell surface by Fc epsilonRI. Receptor aggregation induces multiple signalling pathways that control diverse effector responses. These include the secretion of allergic mediators and induction of cytokine gene transcription, resulting in secretion of molecules such as interleukin-4, interleukin-6, tumour-necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor. Fc epsilonRI is therefore central to the induction and maintenance of an allergic response and may confer physiological protection in parasitic infections.

Association of FcepsilonR1-beta polymorphisms with asthma and associated traits in Australian asthmatic families.

Asthma is a genetically complex disease, and is characterized by elevated serum immunoglobulin E (IgE) levels, elevated blood eosinophil counts and increased airway responsiveness. Polymorphisms in the beta subunit of the high affinity receptor for IgE (FcepsilonR1-beta) have been previously associated with these phenotypes and with an increased risk of asthma. To investigate the association of all known bi-allelic polymorphisms in FcepsilonR1-beta to asthma and quantitative traits associated with asthma in a selected sample of Australian asthmatic children and their nuclear families. Australian Caucasian nuclear families (n = 134 subjects) were recruited on the basis of a child proband with current, severe, symptomatic asthma. The quantitative traits assessed included serum levels of total IgE and specific IgE to house dust mite and mixed grass, blood eosinophil counts and the dose-response slope of the forced expiratory volume in 1 s to histamine provocation. Neither the Leu181 nor the E237G mutations were detected in this population. Allele B of RsaI intron 2 (RsaI_in2*B) was significantly associated with physician-diagnosed asthma (ever) (P = 0.002). Alleles of both the RsaI_in2 and RsaI exon 7 (RsaI_ex7) polymorphisms were significantly associated with loge total serum IgE levels and the combined RAST index. RsaI_ex7 was also associated with loge blood eosinophil counts. These associations were independent of age, sex and familial correlations. This study supports a role for the FcepsilonR1-beta gene or a nearby gene in the pathogenesis of asthma.

Role of IgE in the development of allergic airway inflammation and airway hyperresponsiveness--a murine model.

The importance of IgE in airway inflammation and development of AHR in allergen-sensitized mice has been compared and contrasted in different models of sensitization and challenge. Using different modes of sensitization in normal and genetically manipulated mice after anti-IgE treatment, we have been able to distinguish the role of IgE under these different conditions. Striking differences in the three sensitization protocols were delineated in terms of the role of allergen-specific IgE, extent of eosinophilic airway inflammation, and development of AHR (Table 1). The highest levels of IgE and eosinophil infiltration (approximately 20-fold increases) were achieved after systemic sensitization with allergen (plus adjuvant) followed by repeated airway challenge. Passive sensitization with allergen-specific IgE followed by limited airway challenge induced a modest eosinophilic inflammatory response in the airways despite high levels of serum IgE. Exposure to allergen exclusively via the airways also resulted in a modest serum IgE response and a limited eosinophilic inflammatory response (approximately fourfold increases). Under all of these conditions, inhibition of IL-5-mediated eosinophilic airway inflammation was associated with attenuation of AHR. In contrast, the differences in the responses to the different modes of allergen exposure were associated with differences in the requirements for IgE in the development of AHR (Table 1). In the two models associated with mild eosinophil infiltration (passive sensitization and exclusive airway exposure), IgE was required for the development of AHR but did not substantially enhance airway inflammation on its own. However, IgE-allergen interaction was able to enhance T-cell function in vitro and induce T-cell expansion in vivo. In mice systemically sensitized and challenged via the airways, IgE (or IgE-mediated mast-cell activation) was not required for T-cell activation, eosinophilic inflammation and activation in the airways, or development of AHR. This was most clearly seen in B-cell-deficient and mast-cell-deficient, low-IgE-responder mouse strains (B6, B10) and in anti-IgE-treated high-IgEresponder mice (BALB/c). At the same time, we confirmed the importance of IgE in the induction of immediate-type hypersensitivity (mast-cell activation, immediate cutaneous hypersensitivity, passive cutaneous and systemic anaphylaxis). These differences were also highlighted by the means used to detect altered airway function. Passive sensitization and limited airway challenge or exclusive airway exposure to allergen over 10 days elicited changes in airway function that could be detected only in tracheal smooth-muscle preparations exposed to EFS. In contrast, systemic sensitization followed by repeated airway challenge resulted not only in changes in the contractile response to EFS but also in increased responsiveness to inhaled MCh. Thus, these results distinguish not only the differential involvement of IgE and eosinophil numbers but also their contribution to the readouts used to monitor airway function. Based on these studies, we conclude that IgE plays an important role in the development of airway inflammation and AHR under conditions in which limited IL-5-mediated eosinophilic airway infiltration is induced. In conditions where a robust eosinophilic inflammation of the airways is elicited, IgE (and IgE-mediated mast-cell activation) does not appear to be essential for airway inflammation and the development of AHR, detected as increased responsiveness to inhaled MCh. These findings reveal the potential importance of differential targeting in the treatment of allergic diseases with a predominance of IgE-mediated symptoms, e.g., allergic rhinitis and conjunctivitis, where anti-IgE may be an effective therapy, compared to those diseases with a predominant inflammatory component, e.g., AHR in atopic bronchial asthma, where anti-inflammatory or anti-IL-5 therapy may be more beneficial.

Anti-IgE as novel therapy for the treatment of asthma.

Immunoglobulin-E (IgE) is believed to be the central effector antibody reacting to allergen in patients with allergic asthma. Clinical manifestations of allergic asthma result from the release of chemical mediators from mast cells and basophils on exposure to allergen. A humanized murine monoclonal antibody to IgE, rhuMAb-E25, recognizes the specific Fc epsilon3 portion of circulating IgE that binds to the high-affinity IgE receptor, Fc epsilonRI. In clinical studies, single and multiple doses of subcutaneous and intravenous rhuMAb-E25 have been shown to reproducibly reduce the serum free IgE concentrations in a dose-dependent manner. Clinical trials conducted in aeroallergen bronchoprovocation laboratories demonstrated that decreasing circulating IgE resulted in significant attenuation of the early and late asthmatic responses. Studies completed in moderate to severe allergic asthmatics have extended the safety and efficacy of rhuMAb-E25. Significant improvements in asthma symptoms, meaningful reductions in corticosteroid agents while decreasing reliance on bronchodilator rescue drugs, decreased asthma exacerbations, and improved quality of life have been documented. Because of the remarkable protein engineering and the humanization technology now available, rhuMAb-E25 therapy has elicited no antibody responses and has been safely administered to atopic subjects. rhuMAb-E25 as a novel monoclonal antibody, the first to be applied to lung diseases, holds promise for the control of many IgE-mediated diseases.

Protein and cell engineering of components of the human immunoglobulin E receptor/effector system: applications for therapy and diagnosis

Adaptive immune responses characterised by the synthesis of antibodies of the immunoglobulin E (IgE) isotype play an important role in type I hypersensitivity disorders and parasitic infestations, diseases which have an significant socioeconomic impact world-wide. This paper considers potential applications of recent advances in our understanding of the origin of isotype specific immune responses which emerged as a result of cell and protein engineering studies on components of the human IgE/receptor/effector system. Furthermore, the identification of the receptor binding regions in IgE as a result of the development of a stable assay system has important applications for the design of rational therapeutic interventions in allergy and asthma, the treatment of mast cell tumours, and the establishment of procedures for the selective isolation of cells expressing the high-affinity receptor for IgE for functional studies.

IgE enhances mouse mast cell Fc(epsilon)RI expression in vitro and in vivo: evidence for a novel amplification mechanism in IgE-dependent reactions.

The binding of immunoglobulin E (IgE) to high affinity IgE receptors (Fc(epsilon)RI) expressed on the surface of mast cells primes these cells to secrete, upon subsequent exposure to specific antigen, a panel of proinflammatory mediators, which includes cytokines that can also have immunoregulatory activities. This IgE- and antigen-specific mast cell activation and mediator production is thought to be critical to the pathogenesis of allergic disorders, such as anaphylaxis and asthma, and also contributes to host defense against parasites. We now report that exposure to IgE results in a striking (up to 32-fold) upregulation of surface expression of Fc(epsilon)RI on mouse mast cells in vitro or in vivo. Moreover, baseline levels of Fc(epsilon)RI expression on peritoneal mast cells from genetically IgE-deficient (IgE -/-) mice are dramatically reduced (by approximately 83%) compared with those on cells from the corresponding normal mice. In vitro studies indicate that the IgE-dependent upregulation of mouse mast cell Fc(epsilon)RI expression has two components: an early cycloheximide-insensitive phase, followed by a later and more sustained component that is highly sensitive to inhibition by cycloheximide. In turn, IgE-dependent upregulation of Fc(epsilon)RI expression significantly enhances the ability of mouse mast cells to release serotonin, interleukin-6 (IL-6), and IL-4 in response to challenge with IgE and specific antigen. The demonstration that IgE-dependent enhancement of mast cell Fc(epsilon)RI expression permits mast cells to respond to antigen challenge with increased production of proinflammatory and immunoregulatory mediators provides new insights into both the pathogenesis of allergic diseases and the regulation of protective host responses to parasites.

Anti-ganglioside monoclonal antibody AA4 selectively inhibits IgE-induced signal transduction pathways in rat basophilic leukemia cells

In rat basophilic leukemia 2H3 (RBL-2H3) cells, mAb AA4 binds to two derivatives of ganglioside GD 1b that associate with the Src family kinase p53 56 lyn and a serine kinase. Pre-incubation of cells with mAb AA4 blocks immunoglobulin E (IgE) mediated histamine release. In the present study we investigated the effect of incubation with mAb AA4 on signal transduction events. In addition to stimulation of the high affinity IgE receptor (FcεRI), cells were also activated by the calcium ionophore A23187 and the acetylcholine agonist carbachol in RBL-2H3 cells transfected with the G protein-coupled m3 muscarinic receptor. Incubation of cells with mAb AA4 in a dose-dependent manner inhibited the following FcεRI-induced signal transduction events: the increase of intracellular free calcium, phosphoinositol breakdown, tyrosine phosphorylation of proteins including the β- of FcεRI and secretion. However, there was no inhibition of degranulation or of these biochemical events when cells were stimulated with calcium ionophore or activated via a G protein-coupled pathway. Our results demonstrate that mAb AA4 selectively blocks FcεRI-induced cell activation at a very early step upstream of receptor tyrosine phosphorylation. As mAb AA4 has previously been found to bind to gangliosides associated with FcεRI, inhibition of very early biochemical events may be due to interaction of mAb AA4 with the FcεRI induced signal transduction cascade at the receptor level.

Allelic association of gene markers on chromosomes 5q and 11q with atopy and bronchial hyperresponsiveness.

To investigate genetic factors in asthma and atopy, we sought allelic associations for 12 markers near candidate loci for serum total, immunoglobulin E (IgE), and bronchial hyperresponsiveness (BHR) to inhaled histamine in 131 families comprising 685 individuals, selected randomly without regard to atopy or asthma. Nonparametric linkage and association analyses were performed with the Nonparametric Analysis of Lineage and Association (NOPAR) program, and parametric analyses were performed with the Complex Inheritance with Diathesis and Severity (COMDS) program on an ordered polychotomy of ranked scores. On chromosome 11q, allele 168 at the D11S527 locus was significantly associated with BHR (p<0.0003) but not with log IgE. At the D11S534 locus, allele 235 was significantly associated with log IgE (p = 0.007) but not with BHR. Both D11S527 and D11S534 were too distant from the gene encoding the high-affinity IgE receptor FcepsilonRIbeta to account for the association. At the interleukin-9 (IL-9) locus, the 118 allele showed significant association with serum total IgE (p<0.003) but not with histamine BHR. Parametric tests are more conservative, perhaps because they demand consistency with mendelian inheritance and tight linkage. These findings provide support for the view that both chromosomes 5 and 11 may contain genes relevant to asthma and atopy, a possible candidate being the interleukin-4 (IL-4) gene cluster. Because these associations are extremes in a large number of tests, they require confirmation in other samples.