Effect of aspirin on normal PBMCs and B cells. (A) Dose-response of the cytotoxic effect of aspirin on normal PBMCs. Cells from 6 normal donors were incubated with various concentrations of aspirin as indicated for 48 hours. Data are presented as the means ± SD of 3 experiments each for all 6 normal donors and compared with the means of the 5 B-CLL patients represented in Fig 1A. Cell viability was determined by the MTT assay as described in the Materials and Methods and is expressed as a percentage of the viability of control cells at the beginning of the culture. (B) Comparison between the induction of apoptosis in B cells and T cells from B-CLL patients and normal donors. Cells were incubated with 1 to 10 mmol/L aspirin for 24 hours and phosphatidylserine exposure was measured by binding of annexin V to CD19⁺ or CD2⁺ cells as described in the Materials and Methods. Statistical significance was determined using the t-test for nonpaired samples. *P < .05; **P < .01; ***P < .001.