Redistribution of Activation-Dependent Antigens on the Platelet Surface In Vivo and In Vitro.

Platelets play a crucial role in thrombosis, platelet activation induces an alteration of platelet membrane glycoproteins between the platelet surface and surface connected canalicular system (SCCS). In an attempt to better understand this process and assess its significance in the study of thrombosis disease, we used flowcytometry for detecting the redistribution of antigens on the platelet surface following activation. The expression of platelet membrane glycoproteins (GP) Ib, IIIa and P-selectin as well as the platelet agglutination induced by ristocetin were measured in 20 normal subjects, whose platelets were stimulated by the peptide SFLLRNP(TRAP, thrombin receptor activated peptide) at different time points (0~30minute). The same antigens were also analyzed in whole blood in 30 patients with cerebral infarction. As expected, a stable increase of P-selectin was obtained from 2 minute upon TRAP activation, while a reversible reduction of GPIbα and agglutinability by ristocetin were showed at the same time, with a maximum decrease at 2 minute, then followed by a return of GP Ibα to platelet surface. In addition, the platelet membrane GPIIIa was not significantly changed in the initial stage after platelet stimulation and increased by degrees 10 minutes later. Compared with those in normal group, there was an apparent increase of P-selectin and a lower expression of GPIb in the patients with cerebral infarction, while GPIIIa was not significantly changed in all the samples. In summary, TRAP can mediate platelet activation, which leads to the redistribution of GPIb and GPIIIa in a time-dependent manner, together with the release of P-selectin. Meanwhile, the change of activation-dependent antigens on the platelet surface could be an important index reflecting the platelet activation in vivo.