Effects of mAb against GPVI on collagen-induced aggregation of WT and GPV-deficient platelets.

Washed mouse platelets left untreated (CTRL) or preincubated with 2.5, 5, or 10 μg/mL JAQ1 against mouse GPVI were activated with 0.625 μg/mL collagen in the presence of fibrinogen. Amplitude of aggregation 3 minutes after the addition of collagen (percentage control) (A) and time to onset of aggregation (lag phase) (B) were determined in platelets from GPV null (−/−, open bars) and WT (+/+, black bars) mice. JAQ1 inhibited the collagen response of GPV null platelets to a greater extent than it did that of WT platelets, as shown by the smaller amplitude of aggregation and the increased lag time. Aggregation was significantly decreased (P ≤ .015, 2-tailed t test) in GPV null platelets than in WT platelets for 2.5 and 5 μg/mL JAQ1. The lag time was significantly increased (P ≤ .02, 2-tailedt test) in GPV null platelets than in WT platelets for control without JAQ1 and for 2.5 and 5 μg/mL JAQ1. No shape change was observed in −/− mice in the presence of 10 μg/mL JAQ1 (*). Results are expressed as mean ± SEM of 3 separate experiments.