Fig. 6. Caspase 8, caspase 9 and caspase 3 are activated in human ESCs upon apoptotic Fas signaling. Human ESCs treated with 50 ng/ml IFN- and 25 ng/ml TNF- for 24 hours (black dots) before stimulating the cells with 100 ng/ml of an activating anti-Fas antibody for the indicated time periods were compared to ESCs without pre-treatment with cytokines (white dots). The enzymatic activity of caspase 8 (A), caspase 9 (B) and caspase 3 (C) was measured using specific luminescent activity assays [**P<0.01: ESCs with cytokine pre-treatment versus cells without pre-treatment; values of control (0 hours) were set 1].