Apoptosis of Fas-positive and Fas-negative ATL cells induced by monoclonal antibody against Fas antigen and adriamycin. Fas-positive (•, ▴) and Fas-negative (○, ▵) ATL cells were cultured with antibody against Fas antigen (CH11; ▴, ▵) or adriamycin (4 μmol/L; •, ○). Apoptosis was detected by uptake of propidium iodide at 0, 2, and 6 hours after incubation. Specific cell death was calculated as described in the Materials and Methods.