B cell antigen receptor-mediated apoptosis. Importance of accessory molecules CD19 and CD22, and of surface IgM cross-linking.

Engagement of the B cell Ag receptor can induce a suicide pathway in various B cell types. Earlier studies showed that anti-IgM mAb treatment triggers apoptotic death in the Burkitt lymphoma-derived cell line, Ramos. We show that two B cell surface molecules, CD19 and CD22, which have been reported to interact either functionally or structurally with the B cell Ag receptor, also stimulate cell suicide when sufficiently aggregated, both in the Ramos and EBV-infected Ramos AW cell lines. In conditions of lower cross-linking, both molecules enhance the apoptotic response induced by a suboptimal dose of anti-IgM mAb in Ramos cells, reinforcing the notion that CD19 and CD22 may be involved in the death pathway and modulate Ag-induced B cell apoptosis. Similar outcomes were obtained with human tonsillar B cells, which enter the death program upon treatment with cross-linked anti-IgM, -CD19, or -CD22 mAbs. These results indicate that Ag-induced B cell suicide may affect mature B cells in the periphery and may be regulated via the interaction of CD19 and/or CD22 with their respective ligand(s). Early tyrosine phosphorylations were analyzed by Western blotting. The biologic outcome of these various treatments--cell survival or death--could not be related to any detectable new tyrosine-phosphorylated substrate, further questioning the biochemical basis of apoptosis signaling.