Time-course of mitochondrial damage and caspase-3 activation. B-CLL cells from one patient were cultured with 1000 ng/mL BL22 in the presence or absence of 100 μM Z-VAD.fmk, or, as a control, without immunotoxin. Cells were harvested after indicated time periods and were analyzed by flow cytometry. (A) After permeabilization of CLL cells, intracytoplasmic staining was performed with monoclonal antibody against the active form of caspase-3. (B) For analysis of the mitochondrial membrane potential Δψ_m, cells were incubated with DiOC6(3) for 30 minutes.