The effect of C4BP and antibodies against protein S on thrombin generation in plasma with factor V_Leiden. (A) Thrombin generation curves in factor V_Leiden plasma without APC (▲), with 35 nM APC (△), and with 35 nM APC with 3.1 μM antibodies against protein S (●). Insets: percentage of endogenous thrombin potential (ETP) as a function of anti–protein S antibody concentration in factor V_Leiden plasma in the absence of APC (○) or in the presence of APC (●). (B) Thrombin generation curves in plasma with factor V_Leiden, without APC (▲), with 35 nM APC (△), and with 35 nM APC and 500 nM C4BP (●). Insets: percentage of ETP as a function of C4BP concentration in plasma with factor V_Leiden in the absence of APC (○) or in the presence of APC (●).