Human platelet specific antigens and their importance.

Platelets are metabolically very active cells which support primary hemostasis and blood coagulation. Their glycocalyx layer on the external membrane contains a series of complex glycoprotein molecules, which are classified from glycoprotein-I to glycoprotein-X. The platelet membrane glycoproteins act as receptors for many adhesive proteins such as collagen, von-Willebrand factor, fibronectin, ADP, thrombin, etc. which bring about platelet aggregation. These glycoproteins express several polymorphic antigenic determinants on their surface, which are called human platelet specific antigens (HPA) (Figs. 1a, 1b).