Platelet adhesion to immobilized rFVIIa is dependent on negatively charged phospholipids and GPIbα. (A) Washed platelets were stimulated with collagen (4 μg/mL) or a combination of collagen (4 μg/mL) and thrombin (1 U/mL). Subsequently, platelets were allowed to adhere under static conditions for 60 minutes at 37°C to immobilized rFVIIa at the concentrations indicated. (B) Washed platelets were pretreated with annexin A5 (30 μg/mL, AnnA5), OSE (80 μg/mL), an inhibitory antibody against TF (0.5 mg/mL, anti-TF), sTF (10 μg/mL), or vehicle (−) before stimulation with a combination of collagen (4 μg/mL) and thrombin (1 U/mL) and subsequently allowed to adhere to rFVIIa. Adhesion of stimulated platelets to rFVIIa (5 μg/mL) is indicated as 100% platelet adhesion. Graph shows mean platelet adhesion of at least 2 independent experiments performed in triplicate. *P < .05 compared with control.