Platelet receptors for collagens

Collagens belong to the constituents that determine the thrombogenicity of the vessel wall. Seven genetically distinct collagens-type I, III, IV, V, VI, VIII and XIII-have been identified in the vessel wall. The interaction of platelets with collagens is a complex process since collagens are not only potent platelet agonists but also adhesive proteins. In recent years several platelet membrane glycoproteins have been shown to be involved in platelet-collagen interactions. The mechanisms of platelet-collagen interaction can be divided into primary, direct interactions and secondary, indirect interactions. A number of direct receptors for the collagens have been proposed. The glycoprotein complex Ia/IIa, also called VLA(2), α(2)β(1) integrin or CD49b/CD29, meets several criteria as the major platelet receptor for different types of collagens. There is some evidence that glycoprotein IIIb, also called glycoprotein IV or CD36, functions at the earliest stages of collagen adhesion as a platelet collagen receptor. CD36 seems to be essential for type V collagen-induced platelet aggregation and adhesion. Another putative platelet-collagen receptor is P62, a glycoprotein with a molecular weight of 62 kDa under reducing conditions.