Effect of fibrinogen γ′ peptides on the ETP-based APC response in normal and FV Leiden heterozygous plasma. Thrombin generation was initiated in normal plasma (A-C) with 10 pM TF in the presence of 0-4 nM APC in the absence (A) and presence of 250 μM SCR-S12 peptide (B) or WT-S12 peptide (C). The residual ETP (ETP_+APC/ETP_−APC) was plotted as a function of the APC concentration (D). Thrombin generation was initiated in FV Leiden heterozygous plasma (E-G) with 10 pM TF in the presence of 0-8 nM APC in the absence (E) and presence of 250 μM SCR-S12 peptide (F) or WT-S12 peptide (G). The residual ETP was plotted as a function of the APC concentration (H). Averages of triplicate experiments are shown. Error bars indicate the standard error of the mean.