Effects of mAbs against GPV on collagen- and vWF-induced aggregation of human platelets.

In panels A and B, washed human platelets incubated with MOPC21 IgG1 (control), mAb V.1 (●), or V.3 (○) against human GPV, or mAb ALMA.16 against human GPIX (▵) (all 20 μg/mL) were activated by the addition of collagen (2.5, 1.2, 0.8, or 0.6 μg/mL) in the presence of fibrinogen. The amplitude of aggregation at 3 minutes (A) and lag phase (B) were expressed as the percentages of the values for MOPC-treated platelets. Treatment with V.3 decreased the amplitude of aggregation for 0.6 μg/mL collagen (P = .02; 2-tailed ttest, A) and increased the lag phase for all collagen concentrations (P ≤ .01, 2-tailed t test, B), whereas V.1 and ALMA.16 had no effect on the collagen response. In panel C, washed human platelets incubated with MOPC21 (control) or mAb V.3 (both 20 μg/mL) were activated with 10 μg/mL human vWF and 5 μg/mL botrocetin or 0.7 μg/mL human vWF and 50 μg/mL ristocetin. Treatment with V.3 had no effect on vWF-dependent aggregation. Results are the mean ± SEM from 3 separate experiments (A, B), and tracings are representative of 3 experiments (C).