Bcl-x(L) rescues WEHI 231 B lymphocytes from oxidant-mediated death following diverse apoptotic stimuli

Developing lymphocytes undergo extensive cell death during selection of the immune repertoire. We investigated the influence of bcl-x(L), a member of the bcl-2 family of apoptosis regulatory genes, on apoptosis in a model system for negative selection in the 8 lymphoid lineage. Overexpression of bcl-x(L) in WEHI 231 immature mouse B cells blocked apoptosis triggered by cross linking of surface IgM. bcl-x(L) transfected cells were also resistant to apoptosis following incubation in low serum medium or exposure to γ- irradiation, the sphingomyelin ceramide, or compounds that increase intracellular levels of oxidants. Remarkably, the addition of antioxidants (catalase, N-acetylcysteine, or pyruvate) alone rescued the native WEHI 231 cells from apoptosis while having only minor effects on the viability of cells overexpressing bcl-x(L). Anti-IgM cross-linking, ceramide, and γ- irradiation treatments elevated intracellular peroxide production, which was prevented by treatment with antioxidants. Cells overexpressing bcl-x(L) had a similar rise in intracellular oxidants as control cells, indicating that bcl- x(L) modifies the cell's response to oxidants while having no detectable influence on the endogenous production of oxidants following apoptotic stimuli. These data implicate bcl-x(L) as a potent death repressor in g lymphocytes and support the hypothesis that bcl-x(L) regulates survival decisions within susceptible cells by functioning downstream of oxidant production.