Defective degranulation and calcium mobilization of bone-marrow derived mast cells from Xid and Btk-deficient mice

Regulation of adhesion and degranulation of mast cells plays an important r ole in allergy and inflammation. We investigated a possible role of Bruton' s tyrosine kinase (Btk) in the regulation of adhesion and degranulation by using bone marrow-derived mast cells from X-linked immunodeficiency (Xid) a nd Btk-deficient mice. Cross-linking of the high affinity IgE receptor (Fc epsilon RI) and steel factor (SLF) induced indistinguishable adhesive respo nses of mast cells to fibronectin in kinetics, and these adhesive responses were comparable among wild type, Xid, and Btk-deficient mast cells. Cross- linking of Fc epsilon RI, but not SLF triggered degranulation of bone marro w-derived mast cells. However, Fc epsilon RI-induced degranulation was impa ired in Xid and Btk-deficient mast cells. Calcium influx induced by Fc epsi lon RI cross-linking and SLF were also reduced in Xid and Btk-deficient mas t cells. Degranulation and calcium influx were reduced more severely in Btk -deficient than in Xid mast cells. Consistently, cross-linking Fc epsilon R I and SLF augmented Btk kinase activities transiently. Inositol triphosphat e (IP3) production was also severely reduced in Btk-deficient mast cells, i ndicating Btk play a critical role of Fc epsilon RI-induced IP3 production. The differential sensitivity of wortmannin on calcium influx in wild type and Xid mast cells suggested that the activation of phosphatidylinositol 3 kinase (PI 3-kinase) was required in calcium influx. Furthermore, abnormal secretory granules with translucent contents and variable in size were obse rved both in Xid and Btk-deficient mast cells. Our study demonstrated a cri tical role of Btk in regulating intracellular calcium and granule exocytosi s. (C) 1998 Elsevier Science B.V. All rights reserved.