Fc Epsilon RI Alpha Research Articles

Autoimmunity in chronic urticaria and urticarial vasculitis.

In contrast to acute urticaria, etiology cannot be identified in most cases of chronic urticaria. Recent evidence suggests that a subset of patients with chronic urticaria may have an autoimmune basis for their condition. The demonstration of antithyroid autoantibodies in some patients with chronic idiopathic urticaria (CIU) provides support for an association. However, the discovery of a positive skin test response to intradermal injection of autologous serum in as many as 60% of patients with CIU led to the identification of autoantibodies to IgE and the alpha-chain of the high-affinity IgE receptor, Fc epsilon RI alpha. Additional studies have demonstrated that some of these autoantibodies are capable of releasing histamine from donor basophils and mast cells. This article reviews the literature that addresses a possible autoimmune etiology in a subset of patients with CIU. Urticarial vasculitis is differentiated from chronic urticaria based on clinical features and biopsy findings of leukocytoclastic vasculitis. Most cases of urticarial vasculitis are secondary to an underlying systemic disease. The presence of autoantibodies has also been demonstrated in a subset of patients with primary urticarial vasculitis. This article briefly reviews some of this data.

Regulation of mouse mast cell surface Fc epsilon RI expression by dexamethasone.

It is now clear that the mast cell's functional response to IgE-dependent stimulation can be influenced significantly by the level of expression of the high-affinity IgE receptor (Fc epsilon RI) on the cell's surface. Thus, modulation of Fc epsilon RI surface expression represents a potentially important mechanism for regulating mast cell activity in allergic reactions. In this study, we examined whether a glucocorticoid, dexamethasone (DEX), can influence levels of mast cell Fc epsilon RI expression either in the presence or absence of IgE, an up-regulator of the mast cell surface Fc epsilon RI level. In the absence of IgE, DEX decreased the surface Fc epsilon RI levels in mouse peritoneal mast cells, mouse bone marrow-derived cultured mast cells and a mouse mast cell line, Cl.MC/C57.1. Moreover, DEX also partially suppressed the ability of IgE to enhance surface expression of Fc epsilon RI in these cells. Three different glucocorticoids, DEX, methylprednisolone and hydrocortisone, suppressed Fc epsilon RI expression in mast cells, whereas sex steroids, i.e. estradiol, progesterone and testosterone, did not, indicating that the Fc epsilon RI-suppressing effect is glucocorticoid specific. On the other hand, DEX did not affect levels of Fc epsilon RI alpha, beta or gamma mRNA, suggesting that its ability to decrease surface Fc epsilon RI reflects a post-transcriptional mechanism. Finally, DEX-treated mast cells showed a reduced degranulation response to antigenic stimulation through down-regulation of surface Fc epsilon RI expression in addition to DEX-induced changes in downstream signals. These results show that mast cell surface Fc epsilon RI expression is suppressed by glucocorticoids in both the presence and absence of IgE, and suggest that reduction of mast cell surface Fc epsilon RI levels may be one of the favorable anti-allergic actions of glucocorticoids.

GM-CSF downmodulates c-kit, Fc(epsilon)RI(alpha) and GM-CSF receptor expression as well as histamine and tryptase levels in cultured human mast cells.

GM-CSF is known primarily as a hematopoietic growth factor, but it has also been shown to inhibit mast cell differentiation in vitro. In order elucidate the mechanisms involved, we investigated the effects of GM-CSF in vitro on the differentiation of human leukemic mast cells (HMC-1 cells) and normal cord blood-derived mast cells (CBMC) under the influence of SCF, NGF, and fibroblast supernatant (FS). Under all culture conditions, GM-CSF induced a dose- and time-dependent reduction in intracellular histamine levels, tryptase activity, and numbers of cells immunoreactive for c-Kit and FcepsilonRIalpha. This effect leveled off between 10-100 ng/ml and after 4 days of culture. There was an associated decrease in mRNA expression for c-kit, FcepsilonRIalpha and tryptase. In contrast, no significant changes in the expression of the NGF receptor TrkA were noted under the same conditions. The GM-CSF receptor was found in HMC-1 cells and CBMC at both the mRNA and protein levels, but its expression decreased during culture with FS, and even more markedly during culture with GM-CSF. GM-CSF thus selectively inhibits in vitro induction and/or upregulation of all major mast cell characteristics in HMC-1 cells and CBMC irrespective of the growth factors present, and a concomitant downregulation of GM-CSF receptors can counteract these effects. GM-CSF may therefore function as a regulatory factor in mast cell growth and differentiation under normal and pathological conditions.

A tea catechin suppresses the expression of the high-affinity IgE receptor Fc epsilon RI in human basophilic KU812 cells.

Human basophilic KU812 cells express the high-affinity IgE receptor Fc epsilon RI, which plays a central role in the IgE-mediated allergic response. The effect of several major tea catechins, (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate, and (-)-epigallocatechin gallate (EGCg), on the cell surface expression of Fc epsilon RI in KU812 cells was studied. Flow cytometric analysis showed that only EGCg was able to decrease the cell surface expression of Fc epsilon RI after a 24 h treatment in a dose-dependent manner. Moreover, immunoblot analysis revealed that the total cellular expression of the Fc epsilon RI alpha chain decreased upon treatment with EGCg. Fc epsilon RI 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. KU812 cells treated with EGCg expressed lower levels of Fc epsilon RI alpha and gamma mRNA than nontreated cells. These results suggest that EGCg has an ability to down-regulate Fc epsilon RI expression, and this suppressive effect may be due to the down-regulation of Fc epsilon RI alpha and gamma mRNA levels.

Human neutrophils express the high-affinity receptor for immunoglobulin E (Fc epsilon RI): role in asthma.

Polymorphonuclear neutrophils (PMNs) are important effector cells in host defense and the inflammatory response to antigen. The involvement of PMNs in inflammation is mediated mainly by the Fc receptor family, including IgE receptors. Recently, PMNs were shown to express two IgE receptors (CD23/Fc epsilon RII and galectin-3). In allergic diseases, the dominant role of IgE has been mainly ascribed to its high-affinity receptor, Fc epsilon RI. We have examined the expression of Fc epsilon RI by PMNS: mRNA and cell surface expression of Fc epsilon RI alpha chain was identified on PMNs from asthmatic subjects. Furthermore, preincubation with human IgE Fc fragment blocks completely the binding of anti-Fc epsilon RI alpha chain (mAb15--1) to human PMNS: Conversely, preincubation of PMNs with mAb15--1 inhibits significantly the binding of IgE Fc fragment to PMNs, indicating that IgE bound to the cell surface of PMNs mainly via the Fc epsilon RI. Peripheral blood and bronchoalveolar lavage (BAL) PMNs from asthmatic subjects also express intracellular Fc epsilon RI alpha and beta chain immunoreactivity. Engagement of Fc epsilon RI induces the release of IL-8 by PMNS: Collectively, these observations provide new evidence that PMNs express the Fc epsilon RI and suggest that these cells may play a role in allergic inflammation through an IgE-dependent activation mechanism.

A complex composed of USF1 and USF2 activates the human FcεRI α chain expression via a CAGCTG element in the first intron

The high-affinity IgE receptor, FcepsilonRI, is a key regulatory molecule in the allergic reaction. During the course of studies to find cis-acting elements for FcepsilonRI alpha chain gene expression, a CAGCTG sequence located in the first intron was revealed to serve as a crucial enhancer element. Electromobility shift assays using antibodies and in vitro translation products showed that the CAGCTG element was recognized by the USF1/USF2 complex. As was the case for other intronic cis-elements, the CAGCTG element regulated the promoter in an orientation- and position-dependent manner. Overexpression of USF2 antisense repressed the FcepsilonRI alpha chain gene promoter and decreased the amount of alpha chain mRNA in mast cell lines. All these results indicated that the USF1/USF2 complex activates the human FcepsilonRI alpha chain gene expression via the CAGCTG element in the first intron.

Expression of humanized Fab fragments that recognize the IgE-binding domain of human Fc(epsilon)RIalpha in COS and CHO cells.

Interfering with the binding of IgE to high-affinity IgE receptor alpha chain (Fc(epsilon)RIalpha) is a straightforward strategy for the specific prevention of the IgE-mediated allergic reaction specifically. A Fab fragment (Fab) of a humanized antibody against the membrane proximal IgE-binding domain of human Fc(epsilon)RIalpha inhibits the release of histamine from human basophils. We established an efficient expression system in which to produce directly the humanized anti-human Fc(epsilon)RIalpha Fabs without papain-digestion of the whole antibody. Four Fabs with different C-termini of CH1 were expressed directly in COS-7 cells transfected with expression vectors with or without the Fc gene downstream of a stop codon inserted within the hinge gene. The secretion of Fabs when transfected without the Fc gene was remarkably enhanced compared to that when transfected with the Fc gene. The ability of Fabs to inhibit IgE-Fc(epsilon)RIalpha binding when transfected without the Fc gene was equivalent to that of purified Fab prepared by papain-digestion of the whole antibody. No significant differences among the four Fabs were observed in secretion or activity. Clones of CHO-transfectant cells that secreted the Fabs constitutively were acclimatized to a serum-free medium. Analysis of the binding interface between the Fab and human Fc(epsilon)RIalpha will provide useful information for the design of therapeutic reagents for allergy and asthma.

Production of humanized antibody against human high-affinity IgE receptor in a serum-free culture of CHO cells, and purification of the Fab fragments.

We describe the preparation of Fab fragments of a humanized anti-human high-affinity IgE receptor (Fc epsilonRIalpha) antibody potentially useful for treatment of IgE-mediated allergic diseases. IgE-binding capacities of sixteen combinations of light and heavy chains of four recombinant anti-Fc epsilonRIalpha antibodies, chimeric CRA2, humanized CRA2, chimeric CRA4, and humanized CRA4, were compared. A combination in which both chains were of humanized CRA2 had the highest activity. Stable transfectant clones of four kinds of host cells expressing recombinant antibodies were established. CHO-K1 cells were the most productive. Serum-free media suitable for culture of the stable CHO-transfectant clones were screened. The concentration of the humanized CRA2, which the most productive clone secreted into the chosen serum-free medium, was approximately 100 microg/ml. A procedure for the purification of the antibody, papain-digestion, and purification of Fab fragments was established. The highly purified humanized Fab fragments are suitable for use to examine their in vivo activity and immunogenicity in primates.

Molecular cloning of rat USF2 cDNA and characterization of splicing variants.

The complete nucleotide sequence of rat USF2 cDNA was determined. In addition to the full length clone (USF2FL), four isoforms (delta1, delta2, delta3, and delta4) suggested to be generated by alternative splicing were isolated. USF2delta1 and delta2 lacked 27 and 67 internal amino acid residues, respectively. USF2delta3 and delta4 lacked most of the entire sequence but encoded short peptides of an N-terminal portion of USF2FL. Overexpression of USF2FL increased the transcription of the human high affinity IgE receptor (FcepsilonRI) alpha chain gene through specific binding to the CAGCTG motif in the first intron. On the other hand, overexpression of USF2delta1 or delta2 reduced the transcription of the human FcepsilonRI alpha chain gene. Both USF2FL and USF2delta1 bound to CACGTG as well as CAGCTG, while USF2delta2 bound to CACGTG but not to CAGCTG. These results suggested the presence of a different and definitive role of each variant in the expression of the alpha chain gene.

Structure of the Fc fragment of human IgE bound to its high-affinity receptor Fc epsilonRI alpha.

The initiation of immunoglobulin-E (IgE)-mediated allergic responses requires the binding of IgE antibody to its high-affinity receptor, Fc epsilonRI. Crosslinking of Fc epsilonRI initiates an intracellular signal transduction cascade that triggers the release of mediators of the allergic response. The interaction of the crystallizable fragment (Fc) of IgE (IgE-Fc) with Fc epsilonRI is a key recognition event of this process and involves the extracellular domains of the Fc epsilonRI alpha-chain. To understand the structural basis for this interaction, we have solved the crystal structure of the human IgE-Fc-Fc epsilonRI alpha complex to 3.5-A resolution. The crystal structure reveals that one receptor binds one dimeric IgE-Fc molecule asymmetrically through interactions at two sites, each involving one C epsilon3 domain of the IgE-Fc. The interaction of one receptor with the IgE-Fc blocks the binding of a second receptor, and features of this interaction are conserved in other members of the Fc receptor family. The structure suggests new approaches to inhibiting the binding of IgE to Fc epsilonRI for the treatment of allergy and asthma.

Splice isoforms of transcription factor Elf-1 affecting its regulatory function in transcription-molecular cloning of rat Elf-1.

To elucidate the role of Elf-1 in Fc epsilonRI alpha chain expression, rat Elf-1 cDNAs were isolated and characterized. The rat Elf-1 cDNA of 2744 bp contained an open reading frame of 1848 bp. In addition to the full length rat Elf-1 cDNA (named type 1), two splice isoforms were isolated. One of the two isoforms lacked the amino acid residues from 85th to 120th (type 2), and the other from 85th to 175th (type 3). Similar isoforms were also observed in human tissue. Overexpression of rat Elf-1 (type 1) using a transient coexpression system inhibited of the alpha chain promoter activity. The inhibition activity was different between the isoforms; the inhibition activity of type 2 was lower than that of type 1, and type 3 did not have an inhibitory effect. This observation suggested that each Elf-1 isoform played a different role in the gene expression under its control.

Structural Aspects of the Association of FcεRI with Detergent-resistant Membranes

We recently showed that aggregation of the high affinity IgE receptor on mast cells, FcepsilonRI, causes this immunoreceptor to associate rapidly with specialized regions of the plasma membrane, where it is phosphorylated by the tyrosine kinase Lyn. In this study, we further characterize the detergent sensitivity of this association on rat basophilic leukemia-2H3 mast cells, and we compare the capacity of structural variants of FcepsilonRI and other receptors to undergo this association. We show that this interaction is not mediated by the beta subunit of the receptor or the cytoplasmic tail of the gamma subunit, both of which are involved in signaling. Using chimeric receptor constructs, we found that the extracellular segment of the FcepsilonRI alpha subunit was not sufficient to mediate this association, implicating FcepsilonRI alpha and/or gamma transmembrane segments. To determine the specificity of this interaction, we compared the association of several other receptors. Interleukin-1 type I receptors on Chinese hamster ovary cells and alpha4 integrins on rat basophilic leukemia cells showed little or no association with isolated membrane domains, both before and after aggregation on the cells. In contrast, interleukin-2 receptor alpha (Tac) on Chinese hamster ovary cells exhibited aggregation-dependent membrane domain association similar to FcepsilonRI. These results provide insights into the structural basis and selectivity of lipid-mediated interactions between certain transmembrane receptors and detergent-resistant membranes.

Most chronic urticaria is food-dependent, and not idiopathic.

Although chronic urticaria is generally thought to be mostly idiopathic, we have recently provided convincing evidence that in the majority of patients, food ingredients provoke the symptoms and sustain the disease. On a diet largely avoiding preservatives, dyes and natural pseudoallergens, 73% of patients experienced remission of more than 6 months duration, starting within the first 3 weeks after initiation of the diet. This response rate is clearly higher than the reported 24% spontaneous remission rate over the same time period. The specificity of the dietary effect was proven 1) by double-blind provocation with pureed pseudoallergen-low versus -rich food and 2) by induction of a clinical response to a 3-week diet low in pseudoallergens, but not to a standard diabetes diet in 3 patients studied in a double-blind crossover design. On double-blind, placebo controlled oral provocation, only 18% of diet-responsive patients reacted to known food preservatives and dyes, but 71% to pureed tomatoes and 44% to their steam extracts. These findings identify naturally occurring pseudoallergens in food as major elicitors of chronic urticaria. In contrast, autoantibodies against Fc epsilonRIalpha have been identified in only about 30% of chronic urticaria patients, and evidence for their truly causative role is still lacking since therapeutic measures work in patients irrespective of the presence or absence of the autoantibodies. For both food intolerance and Fc epsilonRIalpha-autoantibodies in chronic urticaria, the associated pathomechanisms are however still in need of clarification. Meanwhile, the diet-responsiveness in the majority of patients opens new perspectives for the management of chronic urticaria.

Thermodynamics of the interaction of human immunoglobulin E with its high-affinity receptor Fc epsilon RI.

We have employed isothermal titration calorimetry (ITC) and circular dichroism (CD) spectroscopy to characterize the binding of soluble fragments of IgE (IgE-Fc and Fc epsilon 3-4) to a soluble fragment of the high-affinity receptor Fc epsilon RI alpha-chain (sFc epsilon RI alpha). The thermodynamic parameters for the interaction of IgE-Fc and Fc epsilon 3-4 with sFc epsilon RI alpha, determined using ITC, confirm the earlier conclusion that the C epsilon 2 domain is not involved in the interaction and that the stoichiometry of both complexes is 1:1. For both IgE-Fc and Fc epsilon 3-4, the value of Delta H degrees is -36.9 +/- 4.6 kcal mol-1 at 37.3 degreesC and Delta Cp degrees is -820 +/- 120 cal mol-1 K-1. The temperature at which DeltaS degrees is zero is 284 +/- 1 K, indicating that the entropy contribution to the thermodynamics of association is unfavorable at physiological temperature. Of particular interest is the large value of Delta Cp degrees. The large surface area of IgE and Fc epsilon RI alpha that is implicated in complex formation from previous mutagenesis studies on the two proteins may account in part for the magnitude of Delta Cp degrees. Additional contributions may arise from hydration within the binding site and changes in tertiary structure of the individual components of the complex. However, the CD spectra of IgE, IgE-Fc, and Fc epsilon 3-4 complexes with sFc epsilon RI alpha are merely the sum of the spectra of their individual components, indicating that the secondary structure of the immunoglobulin domain folds are preserved on complex formation. Thus, any change in tertiary structure must be limited to the relative disposition of the immunoglobulin domains C epsilon 3 and C epsilon 4 in IgE and the two immunoglobulin-like domains in the alpha-chain of Fc epsilon RI.

Specific inhibition of immunoglobulin E-mediated allergic reaction using antisense Fc epsilon RI alpha oligodeoxynucleotides.

We have investigated the ability of an antisense immunoglobulin E (IgE) receptor alpha-subunit oligodeoxynucleotide (Fc epsilon RI alpha ODN) specifically to inhibit IgE-mediated allergic reactions in the mouse. Synthetic antisense Fc epsilon RI alpha ODN dose-dependently inhibited passive cutaneous anaphylaxis and histamine release from the mouse peritoneal mast cells (MPMC) activated by anti-dinitrophenyl (DNP) IgE. Northern blot analysis showed that the mast cells treated with antisense Fc epsilon RI alpha ODN exhibited no detectable levels of L-histidine decarboxylase mRNA after anti-DNP IgE stimulation, whereas the cells treated with sense Fc epsilon RI alpha ODN possessed significant amounts of this mRNA. Examination of the elevation of cAMP levels in MPMC following the activation with anti-DNP IgE demonstrated a significant rise in activated cells, but not in the antisense Fc epsilon RI alpha ODN-treated cells. Moreover, antisense Fc epsilon RI alpha ODN had a significant inhibitory effect on anti-DNP IgE-induced tumour necrosis factor-alpha production. Our results demonstrated that antisense Fc epsilon RI alpha ODN inhibited the IgE-mediated allergic reaction in vivo and in vitro.

Chimeric immunoglobulin E reactive with tumor-associated antigen activates human FcεRI bearing cells

Crosslinking of immunoglobulin E molecules that are bound to the Fc epsilon receptors expressed on mast cells or basophils triggers activation of these cells, resulting in the development of a type I hypersensitivity. Targeting this potent immune reaction towards tumors by using IgE that reacts with a tumor-associated antigen, may induce a local inflammation at the tumor site, and may therefore promote tumor regression. We have previously shown that murine IgE bound to tumor cells can activate murine mast cells to release TNF-alpha and histamine. To further investigate the therapeutic potential of IgE-mediated immunotherapy of carcinomas, we have developed human/murine chimeric versions, containing the murine variable regions and human constant regions, of both G250 and 323/A3 IgE. These chimeric IgEs are reactive respectively with the G250 renal cell carcinoma antigen and the Ep-CAM molecule, which is highly expressed by most carcinomas. Transfection of the respective chimeric heavy and light chain genes into recipient Sp2/0 myeloma cells yielded chimeric IgE-producing clones. Chimeric G250 and 323/A3 IgE reacted with tumor cells expressing the G250 antigen or Ep-CAM, respectively. To generate a cell line that expresses Fc receptors for human or chimeric IgE, the rat basophilic leukemia cell line RBL-7 was transfected with the human Fc epsilon RI alpha chain (RBL-7TZ) and subsequently tested for binding of chimeric IgE. Functional assays showed that both chimeric IgEs activated RBL-7TZ cells to release TNF-alpha when cultured with tumor cells that express the respective specific antigen. Furthermore, both chimeric IgEs were able to activate freshly isolated human basophils.

Effect of recombinant human IL-4 on tryptase, chymase, and Fc epsilon receptor type I expression in recombinant human stem cell factor-dependent fetal liver-derived human mast cells.

The effect of recombinant human IL-4 (rhIL-4) on the development of recombinant human stem cell factor-dependent fetal liver-derived mast cells was examined. RhIL-4 attenuates the number of mast cells that develop, preferentially affecting the MC(T) type of mast cell. Cellular levels of tryptase and chymase mRNA normalized to that of glyceraldehyde-3-phosphate dehydrogenase were not appreciably affected. Tryptase mRNA levels peaked at least 2 wk before tryptase protein and before chymase mRNA and protein, indicating that tryptase mRNA expression is an early marker of commitment to a mast cell lineage. In contrast, alpha-tryptase and beta-tryptase mRNA levels increased and decreased in parallel. The most dramatic effect of rhIL-4 was to induce expression of functional surface Fc epsilonRI. Expression was maximal by 21 days with 20 ng/ml of rhIL-4 and reached a plateau by 2 ng/ml of rhIL-4 at 4 wk. Fc epsilonRI+ cells increased modestly when myeloma IgE was added to the developing mast cells, but increased synergistically when both myeloma IgE and rhIL-4 were present together. Delayed addition of rhIL-4 progressively diminished Fc epsilonRI expression, as did withdrawal of rhIL-4 during the first 2 wk of culture. RhIL-4 selectively increased Fc epsilonRI alpha mRNA levels at least 10-fold. Mast cells developed in the presence of rhIL-4 released tryptase when exposed to anti-Fc epsilonRI alpha. In conclusion, induction of functional Fc epislonRI on recombinant human stem cell factor-dependent human fetal liver-derived mast cells by rhIL-4 harmonizes with the well-accepted ability of this cytokine to enhance IgE production by B cells.

Allergen-induced recruitment of Fc epsilon RI+ eosinophils in human atopic skin.

We have attempted to identify Fc epsilon RI+ eosinophils in cutaneous late-phase reaction in atopic subjects biopsied at 6, 24 and 48 h after the injection of either allergen or a diluent control. Compared to the diluent sites, allergen-injected sites had significantly increased numbers of eosinophils, peaking between 6 and 24 h, of which approximately 20-30% expressed mRNA for the alpha, beta, and gamma chains of Fc epsilon RI, as shown by in situ hybridization. Using either a monoclonal or a polyclonal anti-alpha chain antibody, the Fc epsilon RI alpha protein also co-localized to approximately 50-80% of eosinophils at all time points studied. We also observed a significant correlation (r = 0.89; p = 0.02) between the numbers of Fc epsilon RI+ (997+)/EG2+ eosinophils and the magnitude of the late-phase reaction. Thus, a significant proportion of eosinophils infiltrating the site of allergen-induced allergic tissue reactions in atopic subjects express Fc epsilon. RI. The findings show that high-affinity IgE receptors may play a role in eosinophil secretory processes in vivo.

Nasal mast cells in perennial allergic rhinitics exhibit increased expression of the Fc epsilonRI, CD40L, IL-4, and IL-13, and can induce IgE synthesis in B cells.

Cross-linking of allergen specific IgE bound to the high affinity IgE receptor (FC epsilonRI) on the surface of mast cells with multivalent allergens results in the release of both pre-formed and newly generated mediators, and in the manifestation of allergic symptoms. The expression of Fc epsilonRI, and the synthesis of IgE are therefore critical for the development of allergic diseases. In this study, we report that nasal mast cells (NMC) from patients with perennial allergic rhinitis (PAR) expressed significantly greater levels of the Fc epsilonRI, CD40L, IL-4, and IL-13 as compared to NMC from patients with chronic infective rhinitis (CIR). The level of Fc epsilonRI expression in NMC of PAR patients strongly correlated with the levels of serum total (r = 0.8, P < 0.003) and specific IgE (r = 0.89, P < 0.0004) antibodies. In addition, stimulation of NMC with IL-4, upregulated the Fc epsilonRIalpha chain expression both at the protein and mRNA levels, as detected by flow cytometry and reverse transcriptase-polymerase chain reaction. Furthermore, NMC from PAR, but not CIR, patients induced IgE synthesis by purified B cells in the presence of Der fII (mite antigen). These results suggest novel and critical roles for mast cells in promoting the allergic reaction through the increased expression of Fc epsilonRI and by enhancing and amplifying the IgE production, within the local microenvironment.

Absence of Fc epsilonRI alpha chain results in upregulation of Fc gammaRIII-dependent mast cell degranulation and anaphylaxis. Evidence of competition between Fc epsilonRI and Fc gammaRIII for limiting amounts of FcR beta and gamma chains.

In mouse mast cells, both Fc epsilonRI and Fc gammaRIII are alpha beta gamma2 tetrameric complexes in which different alpha chains confer IgE or IgG ligand recognition while the signaling FcR beta and gamma chains are identical. We used primarily noninvasive techniques (changes in body temperature, dye extravasation) to assess systemic anaphylactic responses in nonanesthetized wild-type, Fc epsilonRI alpha chain -/- and FcR gamma chain -/- mice. We confirm that systemic anaphylaxis in mice can be mediated largely through IgG1 and Fc gammaRIII and we provide direct evidence that these responses reflect activation of Fc gammaRIII rather than Fc gammaRI. Furthermore, we show that Fc gammaRIII-dependent responses are more intense in normal than in congenic mast cell-deficient KitW/KitW-v mice, indicating that Fc gammaRIII responses have mast cell-dependent and -independent components. Finally, we demonstrate that the upregulation of cell surface expression of Fc gammaRIII seen in Fc epsilonRI alpha chain -/- mice corresponds to an increased association of Fc gammaRIII alpha chains with FcR beta and gamma chains and is associated with enhanced Fc gammaRIII-dependent mast cell degranulation and systemic anaphylactic responses. Therefore, the phenotype of the Fc epsilonRI alpha chain -/- mice suggests that expression of Fc epsilonRI and Fc gammaRIII is limited by availability of the FcR beta and gamma chains and that, in normal mice, changes in the expression of one receptor (Fc epsilonRI) may influence the expression of functional responses dependent on the other (Fc gammaRIII).