Activation of platelet-derived TAFI. (A) Gel-filtered platelets (3 × 10⁸) were either incubated with thrombin (50 nM), thrombomodulin (10 nM), and/or CPI (10 μg/mL) as indicated. As a control, platelets were removed by centrifugation before addition of thrombin-thrombomodulin to the supernatant (SUP). The inactivation of platelet-derived TAFIa was analyzed by incubation of the activated platelet mixture for 30 minutes at 37°C after the addition of PPACK but before addition of the substrate (hippuryl-Arg). (B) Thrombin (50 nM)-thrombomodulin (10 nM), activated platelets (2 × 10⁸) or plasma TAFI were incubated for 1 hour at room temperature with immobilized minimally degraded fibrin (Desafib X), after which binding of plasminogen was determined. In both panels, each bar represents the mean ± SEM of 3 independent experiments.