Effect of modulation of c-FLIP expression in pulmonary and dermal MVECs on their sensitivity to TTP plasma–mediated apoptosis. (A) Representative immunoblot for c-FLIP in pulmonary MVECs 18 hours after culture with 100 nM of control or 50 nM or 100 nM of anti-FLIP siRNA. (B) Effect of anti-FLIP siRNA on susceptibility of pulmonary MVECs to TTP plasma. Cells were exposed to siRNAs for 18 hours followed by addition of TTP plasma (2% vol/vol) and an additional 18-hour culture. Apoptosis was assessed by ELISA-based quantitation of DNA-histone complexes in cell lysates. The apoptotic index was significantly increased over baseline (MVECs treated with control siRNA) when pulmonary MVEC were treated with either 50 nM (P < .001) or 100 nM (P < .001) of anti-FLIP siRNA, then exposed to 2 different TTP plasmas. (C) Dermal MVECs were infected with adenovirus-bearing null or c-FLIP-coding sequences for 18 hours, followed by addition of control or TTP plasmas (2% vol/vol) and an additional 18 hours of incubation. Apoptosis, assessed as in panel B, was significantly reduced by AdFLIP treatment (P = .01). Buffer alone gave an index of 0.4. Standard deviations for mean values are provided.