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 B 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 B lymphocytes and support the hypothesis that bcl-x_L regulates survival decisions within susceptible cells by functioning downstream of oxidant production.