BCR triggering protects CLL cells from spontaneous apoptosis. (A) The bars display increases in mean relative viability of CLL cells cultured in medium supplemented with 10 μg/mL anti-IgM, when assessed after 24 and 48 hours, and compared with CLL cells cultured in medium without anti-IgM. Displayed are the mean (± SEM) viabilities of 15 different CLL patient samples, and the asterisks indicate significant increases in viability with P < .05. (B-C) Increased viability of CLL cells after culture with anti-IgM in the subsets of ZAP-70–positive (●, n = 9) or ZAP-70–negative CLL samples (○, n = 6). After 24 (B) and 48 hours (C) of stimulation with anti-IgM, ZAP-70–positive CLL cells displayed higher levels of cell viability than ZAP-70–negative cells; however, these differences did not reach statistical significance.