The effect of Ac-DEVD-CHO (CPP32/Apopain-like protease inhibitor), Ac-YVAD-CHO (ICE-like protease inhibitor), and Z-VAD-FMK (pancaspase inhibitor) on induction of apoptosis by β₂m. (A) K562 cells were preincubated for 3 hours in the presence of 3 caspase inhibitors separately, each at 100 μmol/L. After that, these cells were exposed at 1 × 10⁵ cells/mL to 10 μg/mL of β₂m at 37°C for 48 hours. (B) CCRF-CEM cells were similarly preincubated with the 3 caspase inhibitors separately and exposed to β₂m. Control cells were cultured with the addition of 0.3% DMSO. Apoptotic cells were assayed by TUNEL. Data are expressed as the mean ± SE of 3 independent experiments.