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.
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 platelet glycoprotein Ia/IIa complex, and approximately 800 molecules of 6F1 bound per platelet at saturation. 6F1 nearly completely inhibited collagen-induced platelet aggregation and inhibited platelet adhesion to collagen by greater than 95% when plasma proteins were absent. Antibody 10E5, which blocks the binding of adhesive glycoproteins to GPIIb/IIIa, produced only minor inhibition (approximately 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 (greater than 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 by 6F1, indicating that the GPIa/IIa receptor operates in this environment. With more prolonged incubation, however, 6F1 was less effective; this later agglutination could be partially 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.
Coller
B S
BS
Department of Medicine, State University of New York Stony Brook 11794.
Beer
J H
JH
Scudder
L E
LE
Steinberg
M H
MH
D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000502:physiology*; D002448:Cell Adhesion; D002846:Chromatography, Affinity; D003094:Collagen / Q000502:physiology*; D005434:Flow Cytometry; D006801:Humans; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000302:isolation & purification / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology
D000911:Antibodies, Monoclonal; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D003094:Collagen