Apoptosis assays. Apoptosis induction (% total annexin V positivity) of Ramos lymphoma cells after 24-hour incubation with: (A) increasing concentrations of mAb 37.1 in the absence of an IgG cross-linking Ab; (B) increasing concentrations of mAb 37.1 in the presence of an IgG cross-linking Ab; and (C) 100 μg/mL mAb 37.1 or rituximab in the absence (−) or presence (+) of an IgG cross-linking Ab. Bars represent mean of 4 experiments; SD is indicated. (D) apoptosis induction (% total annexin V positivity above spontaneous apoptosis) of primary CLL cells from 6 donors after 24-hour incubation with 30 μg/mL mAb 37.1, or rituximab in the absence or presence of an IgG cross-linking Ab. Bars represent mean of 6 donors; SD is indicated.