Essential role of the prosurvival bcl-2 homologue A1 in mast cell survival after allergic activation

Mast cells reside in tissues, where upon activation through the high-affinity-IgE-receptor (FcΕRI) they degranulate and orchestrate the allergic reaction. Mast cells survive this activation and can thus be reactivated. In this study we demonstrate that this process depends on the prosurvival gene Al. Activation of mast cells through FcΕRI resulted in degranulation, strong induction of A1 mRNA and protein, and cell survival. In contrast, Al-deficient mast cells released granule mediators similar to the wild-type control, but the cells did not survive an allergic activation. Furthermore, A1^-/- mice that had been sensitized and provocated with allergen exhibited a lower number of mast cell compared with littermate controls. The induction of A1 was dependent on calcium, as EDTA prevented A1 expression. The calcium ionophore, ionomycin, induced A1 expression and mast cell survival, whereas compound 48/80, a well-known mast cell secretagogue, did not. This study uncovers the importance of A1 for mast cell survival in allergic reactions, and it proposes A1 as a potential target for the treatment of allergic diseases.