Detection by flow cytometry of AP-2 binding to platelets after their incubation with abciximab for 30 minutes in vitro. In (A), AP-2 binding to untreated and unstimulated platelets was considered as 100%. This value increased twofold after incubation of the platelets with 0.5 U/mL thrombin for 10 minutes. In (B), AP-2 binding to unstimulated platelets was again considered as 100%. AP-2 binding was severely decreased after a 30-minute preincubation with 10 μg/mL of abciximab. In (C), AP-2 binding to untreated thrombin-stimulated platelets was now taken as 100%; when platelets were incubated with c7E3 Fab before stimulation with thrombin, AP-2 binding was 33.8 ± 10.9% of that obtained in the absence of drug. Tests were performed on platelets from five donors.