Induction of BIM phosphorylation after stimulation with anti-IgM. (A) CLL samples were treated with 20 μg/mL anti-IgM for the indicated times, and expression of BIM and β-actin was analyzed by immunoblotting. BIM_EL and BIM_L isoforms are indicated by closed arrowheads. Open arrowheads indicate phosphorylated forms. Data are representative of a total of 28 samples analyzed and illustrate the various patterns of BIM_EL/BIM_L phosphorylation observed in this cohort. For example, CLL 376 shows > 5% increased phosphorylation of both BIM_EL and BIM_L, whereas CLL 363 shows increased > 5% phosphorylation of BIM_EL only. CLL 251 shows no response and CLL 291 has > 5% basal phosphorylation of Bim_EL and Bim_L, which increased after stimulation. (B) Correlation between maximum anti-IgM–induced BIM_EL phosphorylation and BIM_L phosphorylation. Results of linear regression are shown. (C) Correlation between maximum anti-IgM–induced BIM_EL/BIM_L phosphorylation and intracellular Ca²⁺ responses. (D) Normal B cells were treated with anti-IgM for half an hour or 1 hour, and expression of BIM and β-actin was analyzed by immunoblotting. Results are representative of 3 different B-cell preparations.