COLLAGEN-PLATELET INTERACTION - SEPARATE RECEPTOR-SITES FOR TYPE-I AND TYPE-III COLLAGEN

We have isolated a platelet membrane protein of M(r) 47 kDa which is r esponsible for the interaction of platelets with type III collagen. Th e 47 kDa protein was purified to apparent homogeneity by type III coll agen-Sepharose 2B column chromatography and preparative slab gel elect rophoreses. The 47 kDa protein blocked the adhesion of platelets to ty pe III but not to type I collagen. Polyclonal antibodies were obtained from rabbits immunized with the purified 47 kDa protein emulsified in complete Freund's adjuvant. The polyclonal antibodies inhibited the t ype III collagen but not type I collagen-induced platelet aggregation. The inhibitory effect of the antibodies on type III collagen-induced platelet aggregation was dose-dependent. Cross-inhibition on platelet aggregation studies showed that type I collagen receptor antibodies (M (r) 65 kDa) did not inhibit type III collagen-induced platelet aggrega tion and type III collagen receptor antibodies did not inhibit type I collagen induced platelet aggregation. These results suggest that type I and type IH collagens interact with platelets at separate sites.