The cross-linking of IgE-bound FcεRI by Ags triggers mast cell activation leading to allergic reactions. The in vivo contribution of FcεRIγ signaling to IgE/FcεRI-mediated mast cell responses has not yet been elucidated. In this study FcεRIγ−/− mast cells were reconstituted with either wild-type or mutant FcεRIγ in transgenic mice and transfected mast cells in vitro. We demonstrate that FcεRIγ-immunoreceptor tyrosine-based activation motif is essential for degranulation, cytokine production, and PG synthesis as well as for passive systemic anaphylaxis. Recent reports have suggested that cell surface FcεRI expression and mast cell survival are regulated by IgE in the absence of Ag, although the molecular mechanism is largely unknown. We also found that the promotion of mast cell survival by IgE without Ags is mediated by signals through the FcεRIγ-immunoreceptor tyrosine-based activation motif. In contrast, the IgE-mediated up-regulation of FcεRI is independent of FcεRIγ signaling. These results indicate that FcεRIγ-mediated signals differentially regulate the receptor expression, activation, and survival of mast cells and systemic anaphylaxis.

We have investigated the effects of decreased levels of the complex between glycoprotein VI (GPVI) and the Fc receptor gamma-chain (FcRgamma) on responses to collagen and GPVI-specific ligands in murine platelets. We show that levels of GPVI-FcRgamma of the order of 50% and 20% of wild-type levels caused 2- and 5-fold shifts to the right respectively in the dose-response curve for aggregation in response to collagen, the snake toxin convulxin and the monoclonal antibody JAQ1. In addition, there is a delay in the onset of aggregation in response to collagen. In contrast, the stimulation of protein tyrosine phosphorylation by collagen (as measured after 150 s) and adhesion to a collagen-coated surface under static conditions were unaffected in platelets with 50% and 20% of wild-type levels of GPVI. In contrast, responses to a collagen-related peptide (CRP), made up of repeat glycine-proline-hydroxyproline motifs, were markedly inhibited and abolished in platelets expressing 50% and 20% of wild-type levels of GPVI respectively. We suggest that the marked effect of a reduction in GPVI levels on the CRP-induced activation of platelets is due to the multivalent nature of CRP and the fact that GPVI is its sole receptor on platelets. Thus it appears that the interaction of CRP with GPVI is determined by a combination of affinity and avidity. The observation that collagen does not behave like CRP in platelets expressing reduced levels of GPVI, even in the combined presence of blocking antibodies against integrin alpha2beta1 and GPV, suggests that collagen has a greater affinity than CRP for GPVI, and/or that other receptors are involved in its binding to platelets. The clinical significance of these results is discussed.

The gene for the beta-chain of the high-affinity receptor for IgE (Fc epsilon RI beta) has been proposed as a candidate gene for atopy. A coding variant Glu237Gly has been studied in various populations with asthma and atopy, and the results were controversial for association of the variant with atopy/asthma. Because nasal allergy is a more common atopic disease and shows less remission than asthma, we analyzed whether the Glu237Gly variant is correlated with nasal allergy. The study enrolled 233 patients with nasal allergy and 100 control subjects. Further, three subgroups were selected: patients with perennial nasal allergy (n=149), Japanese cedar pollinosis (n=189), and allergy to multiple allergens (n=45). The allele frequency of Gly237 in the controls and patients was 0.14 and 0.20, and the frequency of Gly237-positive subjects was 0.23 and 0.356, respectively. There was a significant association between Gly237-positivity and nasal allergy, perennial nasal allergy, Japanese cedar pollinosis, and allergy to multiple allergens. Among all 333 subjects we observed a significant relationship between Gly237 and elevated levels of serum total IgE (>250 IU/ml) and very high IgE (>1000 IU/ml). Among patients positive for a specific IgE, Gly237 was significantly associated with high IgE for house dust, mite, and Japanese cedar pollen. These results suggest that the Glu237Gly variant of the Fc epsilon RI beta gene is involved in the development of nasal allergy through the process for the production of both specific and nonspecific IgE antibodies.

The transgenic expression of a toxin gene or a thymidine kinase gene under the control of cell type-specific promoter͞enhancer has been shown to be useful for removing a specific cell population in mice. However, this approach requires extensive analysis of the control elements for gene expression in the preparation of the transgenic constructs, and furthermore, the toxin gene might be expressed ectopically because of random integration, resulting in aberrant depletion of unrelated cells. To avoid such difficulties with the transgenic approach, we established a method for the specific depletion of a cell population by replacing a uniquely expressed gene in the population with the diphtheria toxin gene by using homologous recombination. The NKR-P1 gene, a specific cell surface marker of natural killer (