Murine B-cell activation via CD38 and protein tyrosine phosphorylation.

CD38 has been implicated in the regulation of both proliferation and rescue from apoptosis of B cells. The signalling events associated with CD38-mediated activation of murine B cells are, as yet, not well defined but it is clear that ligation of CD38 by a mitogenic antibody, NIMR-5, induces a calcium influx in resting B cells. Interestingly, however, cross-linking of CD38 does not mobilize intracellular stores of calcium. We now provide a rationale for these findings by demonstrating that CD38 is not coupled to the generation of inositol phosphates in resting B cells. We do, however, show that CD38 ligation stimulates one, or more, protein tyrosine kinase activities which may play a central role in the transduction of CD38-mediated signals leading to B-cell activation.