Isoform-specific functions of phosphoinositide 3-kinases:: p110δ but not p110γ promotes optimal allergic responses in vivo

The leukocyte-enriched p110 gamma and p110 delta isoforms of PI3K have been shown to control in vitro degranulation of mast cells induced by cross-linking of the high affinity receptor of IgE (Fc epsilon RI). However, the relative contribution of these PI3K isoforms in IgE-dependent allergic responses in vivo is controversial. A side-by-side comparative analysis of the role of p110 gamma and p110 delta in mast cell function, using genetic approaches and newly developed isoform-selective pharmacologic inhibitors, confirms that both PI3K isoforms play an important role in Fc epsilon RI-activated mast cell degranulation in vitro. In vivo, however, only p110 delta was found to be required for optimal IgE/Ag-dependent hypersensitivity responses in mice. These observations identify p110 delta as a key therapeutic target among PI3K isoforms for allergy- and mast cell-related diseases.