Exposure of fibrinogen-adherent platelets to plasma proteins: a new method for studying protein interactions with platelets

To understand the effects of mediators in coagulating blood at biomaterial surfaces, it is important to use methods that resemble the normal sequence of events in wound healing around implants. The initial adhesion of platelets from whole blood onto material surfaces is mediated by the fibrinogen receptor glycoprotein IIb/IIIa, as shown in a previous study (Broberg et al., J Lab Clin Med 2002; 139:163-172). In this study, isolated platelets were adhered to fibrinogen and exposed to IgG, von Willebrand factor, or thrombin. The response was detected as the number of adherent platelets, the spreading of platelets, the exposure of CD62P (P-selectin), and the release of platelet factor 4 (PF4), ADP, and ATP. These results were compared to the response of platelets adhering to surfaces coated with the same proteins. Fibrinogen-adherent platelets exposed to thrombin generated the significantly highest exposure of CD62P and release of PF4, ADP, and ATP. When platelets were adhered to different protein coatings, von Willebrand factor generated the most CD62P exposure, IgG generated the most PF4 release, and thrombin generated the highest concentration of ADP. These results indicate that protein interactions with platelets may generate different results, depending on the mode of protein exposure.