Effect of MCD on BCR-induced apoptosis. (A) WEHI-231 cells were left untreated, treated with 5 mM MCD for 25 minutes in lipid-free medium, or treated with 5 mM MCD for 25 minutes and allowed to recover for 4 hours. Cells were then left unstimulated (–) or were stimulated (+) for 5 minutes with 20 μg/mL anti-IgM Ab. Following lysis in 0.5% Triton X-100 and sucrose gradient ultracentrifugation, GEM fractions were blotted with CTB subunit and Abs against Lyn, IgM, and CD45. (B) WEHI-231 cells were incubated as in panel A and then either left unstimulated (–) or stimulated (+) for 24 hours with 20 μg/mL anti-IgM Ab and subjected to DNA fragmentation assays. (C) Effect of MCD on BCR-induced apoptosis. WEHI-231 cells treated as in panel B were labeled with FITC–annexin V and propidium iodide and subjected to flow cytometry. Cells that labeled positively for both were considered to be apoptotic. The results are expressed as means ± SEM of 3 independent experiments. *P < .005.