Functional role of the antigen recognized by an antiplatelet antibody specific for a putative collagen receptor in platelet-collagen interaction.

Collagen, a major component of blood vessels, mediates primary hemostasis brought about by platelets. The mechanism underlying platelet-collagen interaction is highly complicated and to date various molecules have been suggested to be platelet collagen receptors. We suggest that a platelet membrane protein with a molecular weight of 62 kDa in the reducing condition (P62) immunoprecipitated by the antibody of a patient with idiopathic thrombocytopenic purpura could be a platelet collagen receptor. The antibody was also primarily immunoreactive with P62 on immunoblotting. The patient's platelets, which were deficient in P62 and totally lacked collagen-induced platelet aggregation, showed normal platelet adhesion to collagen in the presence of Mg2+. However, the Fabs of the antibody, which completely abolished collagen-induced normal platelet aggregation, also had inhibitory effects on normal platelet adhesion to collagen. These results indicate that of the antigens recognized by this antibody, P62 could play an important role in platelet-collagen interaction mediating aggregation, and that multiple membrane molecules, including P62, may participate in platelet adhesion to collagen.