GP VI cleavage down-regulates receptor platelet aggregation to collagen and convulxin. Washed platelets (3 × 10⁸/mL) were aggregated following preincubation with monoclonal IV.3 (25 μg/mL) in the presence or absence of 9012.2 (25 μg/mL) using collagen (10 μg/mL), convulxin (10 ng/mL), or TRAP (10 μM). (A) Mean aggregation to collagen and TRAP in the presence of IV.3 and IV.3 + 9012.2. (B) Mean aggregation to convulxin in the presence of IV.3 and IV.3 + 9012.2. Data are expressed as mean ± SEM. (C) Platelet aggregations in response to collagen following preincubation at 37°C for 5 minutes in the presence of IV.3 and IV.3 + 9012.2. (D) Platelet aggregations under control and collagen-stimulated conditions. Platelet aggregation to E, collagen, and F, TRAP following 45 minutes' preincubation with antibodies. Results shown are representative of 3 independent experiments.