Platelet aggregation induced by cross-linked peptides. Aggregation of human platelets in citrated PRP (A,B) and murine washed platelets (C,D) induced by cross-linked peptides. Peptide concentration in panels C,D was 100 μg/mL in all cases. FcRγ−/− platelets did not respond to any of the collagen peptides; however, they did respond normally to the TxA2 analog U46619 (D inset). CRP was more potent in humans than in the mouse. III-30 in human platelets and III-30 and III-30b in murine platelets showed similar levels of reactivity, whereas III-30b was less potent in the human. III-01a induced aggregation in human platelets at high concentrations. Although III-01a showed a similar extent of aggregation to the other active peptides, the response was much slower as indicated by the lower rate of aggregation. III-01a did not induce aggregation in murine platelets. Monomeric peptides induced no aggregation (data not shown). Extent of aggregation was determined 6 minutes after addition of agonist. Data shown are mean plus or minus SE (n = 3 or 4).
