Impaired platelet surface P-selectin expression is unlikely due to deficient cell surface P-selectin binding. (A) Fg^−/− platelets were incubated with either Fg^−/− or wild-type plasma 60 minutes before addition of TRAP. There was no significant difference in Fg^−/− platelet surface P-selectin expression in Fg^−/− plasma or wild-type plasma (n = 3; P > .05). (B) P-selectin expression on gel-filtered wild-type and GPIbα^−/− platelets was examined via flow cytometry. Higher expression of P-selectin on GPIbα^−/− platelets likely reflects the larger size of GPIbα^−/− platelets.