Identification of TAFI in platelets. TAFI was identified in cytospins of gel-filtered platelets by immunofluorescence confocal microscopy (A), using a monoclonal antibody against TAFI (9H10) and an FITC-labeled secondary antibody. The scale bar represents 5 μm. TAFI secretion by stimulated platelets (B). Gel-filtered platelets (2.8 × 10⁷) were incubated with a high (dark bars) or a low (light bars) concentration of platelet agonist for 15 minutes at 37°C, and the secretion of TAFI was determined by ELISA. The agonists used were thrombin (IIa; 5 or 0.5 U/mL), thrombin receptor–activating peptide (TRAP; 100 or 10 μM), adenosine 5′-diphosphate (ADP; 20 or 2 μM), collagen (COL; 10 or 1 μg/mL), and epinephrine (EPI; 10 or 1 μM). Each bar represents the mean ± SEM of 5 independent experiments using different donors.