CD2 LIGATION ABROGATES ANTIGEN-INDEPENDENT APOPTOSIS IN B-CELLS

We have described recently the prevention of apoptosis by CDS-soluble CD48 interaction on antigen B cell receptor occupancy. Here, we show t hat CD2 ligation is also able to interfere with B cell receptor-indepe ndent apoptosis pathways such as spontaneous death in spleen B cells o r serum deprivation and hydrogen peroxide exposure in the BAL-17 cell line. In all cases, CD2 ligation induces a signal that prevents the do wnregulation of Bcl-2 expression. The specific CD2 signal pathway invo lved in this phenomenon is still unknown. As reported, CD2 did not app ear to induce Ca2+ mobilization, phosphatidylinositol turnover, or PKC translocation in B cells. Nevertheless, we show that CD2 receptor lig ation is coupled to the tyrosine phosphorylation pathway in B cells. T hese observations indicate that CD2 is functionally able to trigger at least an early signal that could play a role in apoptosis blockage B cells in addition to the adhesion one. The results suggest the partici pation of cellular membrane receptors other that CD40 in apoptosis res cue, not only in the antigen-dependent but also in the antigen-indepen dent phases of B cell lymphopoiesis. (C) 1996 Academic Press, Inc.