INDUCTION OF B-CELL APOPTOSIS BY CO-CROSS-LINKING CD23 AND SIG INVOLVES ABERRANT REGULATION OF C-MYC AND IS INHIBITED BY BCL-2

A novel system to study the effects of cc-cross-linking CD23/Fc epsilo n RII and sig on murine B lymphocytes utilizes a highly multivalent fo rm of anti-lg prepared by covalently linking anti-Ig antibodies to a D NP-dextran backbone. CD23-slg co-cross-linking is accomplished by the addition of DNP-specific monoclonal IgE, Previous studies demonstrated that co-cross-linking CD23 and sig significantly inhibited mouse B ce ll proliferation, especially at high doses of the multivalent anti-tg. interestingly examination of early activation signals reveals no diff erence in a cells subjected to cc-cross-linking conditions as compared to B cells activated with anti-lg alone, Total cellular protein tyros ine phosphorylation levels are unchanged by co-cross-linking. Analysis of B cell mRNA reveals that co-cross-linking the receptors does not a lter the expression levels of ornithine decarboxylase 8 h after stimul ation as compared to the controls, In contrast, revels of the protoonc ogene c-myc were significantly elevated 1 h after inducing a cell acti vation under co-crosslinking conditions, However, it remains unclear w hether this aberrant c-myc regulation plays any role in inducing apopt osis. In addition, on day 3 after stimulation, the co-cross-linking of CD23 and sig resulted in the formation of apoptotic a cells, determin ed by both photomicroscopy of the B cell cultures and FAGS analysis of B cell nuclei. B cells obtained from bcl-2 transgenic mice proliferat ed as well as controls, and failed to undergo apoptosis when CD23 and sig were co-crosslinked on their surface, These studies indicate that co-cross-linking of CD23 with a cell sig inhibits B cell proliferation by a mechanism that is distinct from that seen by co-cross-linking of the Fc gamma RII and sig, In addition, these results suggest a means by which antigen-specific IgE can downregulate additional B cell activ ation and IgE synthesis.