Abstract
Mast cells are major effectors in high-affinity IgE receptor (FcɛRI)-dependent allergic reactions. Here we show that phospholipase C (PLC)-β3 is crucial for FcɛRI-mediated mast cell activation. Plcb3(-/-) mice showed blunted FcɛRI-dependent late-phase, but not acute, anaphylactic responses and airway inflammation. Accordingly, FcɛRI stimulation of Plcb3(-/-) mast cells exhibited reduced cytokine production but normal degranulation. Reduced cytokine production in Plcb3(-/-) cells could be accounted for by increased activity of the negative regulatory Src family kinase Lyn and reduced activities of the positive regulatory protein kinases MAPKs. Mechanistically, PLC-β3 constitutively interacts with FcɛRI, Lyn, and SHP-1 (protein phosphatase). SHP-1 probably recognizes its substrates Lyn and MAPKs via the recently described kinase tyrosine-based inhibitory motif, KTIM. Consistent with PLC-β3- and SHP-1-mediated repression of Lyn activity by dephosphorylation at Tyr396, FcɛRI-mediated phenotypes were similar in Plcb3(-/-) and SHP-1 mutant mast cells. Thus, we have defined a PLC-β3- and SHP-1-mediated signaling pathway for FcɛRI-mediated cytokine production.