Effect of PECAM-1 interactions in collagen-induced platelet aggregation.

(A) Washed platelets were pre-incubated with FcγRIIA-blocking antibody IV.3 Fab (10 μg/mL) followed by recombinant human PECAM-1–immunoglobulin chimera (0-100 μg/mL) for 5 minutes with stirring. Platelet aggregation was initiated by the addition of collagen (5 μg/mL), and the percentage change in light transmission was monitored. Aggregation traces from 1 of 3 representative experiments are shown. (B) Washed platelets were pre-incubated with increasing doses of recombinant human PECAM-1–immunoglobulin chimera (0-100 μg/mL) (white bars) or mutant K89A human PECAM-1–immunoglobulin chimera (0-100 μg/mL) (black bars) or human IgG (0-100 μg/mL) (gray bars) before stimulation with collagen (5 μg/mL). These results are expressed as mean ± SD of percentage of controls (0 μg/mL recombinant protein) from 3 separate experiments with different blood donors. **Significantly differentP < .0001, according to Student unpaired ttest from 3 separate experiments.