HTLV-1–infected cells are resistant to CD95-mediated apoptosis. (A) HuT-102, MT-2, and SLB-1 cells were incubated with the indicated concentrations of LZ-CD95L for 16 hours. CD95-sensitive CEM and H9 cells were used as positive control. Apoptosis was determined by analyzing subdiploid DNA by fluorescence-activated cell sorter (FACS). Specific apoptosis was calculated as described in “Materials and methods.” The experiment shown is representative of 3 independent experiments. (B) Expression levels of Tax in HTLV-1–infected cells. Lysates of noninfected (CEM, H9) and HTLV-1–infected (HuT-102, MT-2, and SLB-1) cells were subjected to sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis with antibodies against Tax. Analysis of Erk expression served as control for equal protein loading. An additional anti-Tax–reactive band specifically expressed in MT-2 cells is marked with an asterisk.