Role of caspase-8 and caspase-3 in Fas-mediated apoptotic and proliferative signaling of IL-7–treated T cells. T cells of noninfected individuals, pretreated by 25 ng/mL IL-7, were activated using 1 μg/mL coated anti-Fas and anti-CD3 mAbs. Caspase-8 and caspase-3 activation was measured by flow cytometry in the course of the 24-hour activation period (A). The association of caspase-8 and caspase-3 activation with annexin-V binding was monitored (B). Inhibitors of caspase-3 (Z-DEVD-FMK) and caspase-8 (Z-IETD-FMK) were added to T cells at different doses, and 30 minutes later the cells were activated with 1 μg/mL coated anti-Fas and anti-CD3 mAbs. The ratio of apoptotic cells was determined in the cultures after 24 hours using annexin-V staining; proliferation was measured after 4 days of activation using CFSE staining (C). A representative experiment of 3 is shown.