[Platelet structure and function: immunocytochemical localizations of membrane glycoprotein and alpha-granule...

The platelet membrane glycoproteins (GPs) are receptors or binding sites for adhesive proteins. GPIb and GPIIb/IIIa complex are major glycoproteins and have important roles, functionally. GPIb plays an essential role in primary hemostasis as receptor for the von Willebrand factor. The GPIIb/IIIa complex acts as the binding site for adhesive proteins on activated platelets and, as such, is essential for platelet aggregation. On the other hand, four adhesive proteins (fibrinogen, fibronectin, thrombospondin and von Willebrand factor), which are present not only in plasma but also in alpha-granules, mediate or modulate the platelet adhesive response. The interaction between these adhesive proteins and platelet membrane GPs are essential for platelet adhesion and aggregation. The present report will focus on the localization of GPIb and GPIIb/IIIa on the platelet surface and that of adhesive proteins in alpha-granules in both resting and activated human platelets.