APC cleavage of factor Va on endothelium.

Endothelial cells were incubated with prothrombin, factor X, protein S, antithrombin III, and TFPI, along with 20 nM activated factor V. Accumulation of factor Va on the endothelial cells was detected by western blotting. The plot shows the density of the heavy chain band (measured as described in “Materials and methods”). Results are shown for the absence (●) or presence (▴) of 13 nM APC.