GPIIb/IIIa is the main receptor for initial platelet adhesion to glass and titanium surfaces in contact with whole blood

Platelets are the first cells to adhere to a surface in contact with blood and are capable of mediating several different responses after contact with different protein-coated surfaces. They are the main source of growth factors such as platelet-derived growth factor and are therefore important in the healing process. In this study, initial platelet adhesion to and spread on hydrophilic and hydrophobic (methylized) glass and titanium with similar wettability were investigated. Whole coagulating blood was used to simulate the in vivo situation shortly after implantation, in which bleeding precedes inflammation and wound healing. Several different antibodies directed against platelet integrins and receptors (CD9, FcgammaRII, GPIIb/IIIa, vitronectin receptor, GPIb/V/IX) were used in an attempt to block platelet adhesion to the surfaces. Immunofluorescence results show that initial platelet adhesion to all the surfaces we investigated can be almost completely inhibited (approximately 95%) by clone M148, an antibody against the GPIIb/IIIa complex (integrin alpha(IIbbeta)3; CD41/CD61), but not with other antibodies to the separate parts of the integrin. Antibodies known to inhibit fibrinogen binding to GPIIb/IIIa after adenosine diphosphate- and collagen-induced aggregation had very little effect on initial platelet adhesion. None of the other integrins were found to have such an effect on initial platelet adhesion. Antibody clone M148 was furthermore found to inhibit platelet spreading. This study shows that regardless of wettability and the biomaterial used, initial adhesion of platelets appears to be mediated by GPIIb/IIIa binding to surface adsorbed fibrinogen.