Coaggregation of FcεRI with FcγRIIB inhibits degranulation but not induction of Bcl-2 family members A1 and Bim in mast cells

The aggregation of high-affinity immunoglobulin E (IgE) receptors (FcεRI) on mast cells is a critical event in the initiation of an allergic reaction. Coengagement of FcεRI with immunoglobulin G (IgG) low-affinity receptor FcγRIIB/CD32 inhibits degranulation and the release of inflammatory mediators from mast cells and has therefore been proposed as a new therapeutic approach for the treatment of allergies. In this study, we investigated whether FcγRIIB, besides inhibiting degranulation, negatively regulates other signalling pathways downstream of FcεRI. For this, we determined the phosphorylation and/or expression of proteins involved in the regulation of mast-cell apoptosis. Coaggregation led to an attenuation of Akt phosphorylation but did not inhibit phosphorylation of transcription factor Foxo3a or its proapoptotic target, Bim. Similarly, FcεRI-dependent expression of the prosurvival gene A1 was not affected by coaggregation. Our data demonstrate that coengagement of FcεRI and FcγRIIB inhibits degranulation but not the signalling pathways regulating Bcl-2 family members Bim and A1.