FIG 4.

Increased caspase-3/7 activity in ricin- and TRAIL-treated Calu-3 cells. For the quantification of caspase-3/7 activity, Calu-3 cells were treated with ricin (0.25 µg/ml) or TRAIL (0.1 µg/ml) or ricin and TRAIL with or without caspase 3 inhibitor Z-DEVD-FMK(62.5 nM) for 24 h or with medium only (negative control). The caspase-3/7 activity levels were determined by flow cytometry as described in Materials and Methods. Caspase-3/7 activity was expressed as a percentage of total cells. The results are presented as means ± SD of three independent experiments. ***, P  < 0.001 (versus control cells).