COLLAGEN-PLATELET INTERACTIONS - EVIDENCE FOR A DIRECT INTERACTION OF COLLAGEN WITH PLATELET GPIA/IIA AND AN INDIRECT INTERACTION WITH PLATELET GPIIB/IIIA MEDIATED BY ADHESIVE PROTEINS

  • 1 July 1989
    • journal article
    • research article
    • Vol. 74  (1) , 182-192
Abstract
Using intact human platelets as the immunogen and a functional, collagen-coated bead agglutination assay, we have produced a murine monoclonal antibody (6F1) that blocks the interaction between platelets and collagen in the presence of Mg++. 6F1 affinity-purified the platelt glycoprotein Ia/IIa complex, and approximately 800 molecules of 6F1 bound per platelet as saturation. 6F1 nearly completely inhibited collagen-induced platelet aggregation and inhibited platelet adhesion to collagen by >95% when plasma proteins were absent. Antibody 10E5, which blocks the binding of adhesive glycoproteins to GPIIb/IIIa, produced only minor inhibition (.apprx.25%) of adhesion under the same circumstances. In contrast, when tested in platelet-rich plasma (PRP), 6F1 had only a minor effect on collagen-induced platelet aggregation, prolonging the lag phase but not the slope or maximum aggregation. Similarly, when collagen was precoated with plasma, 6F1 caused less inhibition of platelet adhesion (53%) than without the precoating (>95%). Antibody 10E5 inhibited this adhesion by 32%, and the combination of 6F1 and 10E5 was more effective than either alone, inhibiting it by 90%. Time course studies of platelet agglutination of collagen-coated beads using PRP containing physiologic concentrations of divalent cations showed early inhibition of 6F1, indicating that the GPIa/IIa receptor operators in this environment. With more prolonged incubation, however, 6F1 was less effective; this later agglutination could be partailly prevented by adding 10E5 or PGE1 to the 6F1. These data support a model wherein collagen can directly interact with GPIa/IIa and can indirectly interact with GpIIb/IIIa via intermediary adhesive proteins. The physiological significance of these interactions, and potential interactions with other receptors, remains to be established.