Effect of anti-TRAIL antibody on TTP plasma–mediated apoptosis. Aliquots of 5 different acute TTP plasmas were incubated with control rabbit serum (1:500 dilution) or polyclonal rabbit anti–human TRAIL IgG (1:500 dilution) for 2 hours at 4°C. Final concentrations (1% vol/vol) of the TTP plasmas were then incubated with dermal MVECs for 18 hours at 37°C. Apoptosis was assessed as in the legend to Figure 1. Anti-TRAIL Ab decreased TTP plasma–mediated apoptosis (P = .02). Standard deviations are noted for the mean values.