CHARACTERIZATION OF ADHESION OF RESTING AND STIMULATED PLATELETS TO FIBRINOGEN AND ITS FRAGMENTS

Adhesion of resting and stimulated platelets to immobilized fibrinogen (Fg) was characterized using various forms of Fg, receptor peptide mi mics, and antibodies to glycoprotein (GP) IIb/IIIa and Fg. Resting pla telets adhered to Fg, but to less than half the extent of the same pla telets stimulated with epinephrine/ADP. The adhesion of resting and st imulated platelets to Fg was inhibited by a receptor peptide mimic (G1 3, a peptide corresponding to residues 300-312 of GPIIb), anti-GPIIb/I IIa antibodies, and a monoclonal antibody (4A5) against the carboxyl t erminus of the gamma chain of Fg. The results presented here demonstra te that the alpha chain RGD platelet recognition sites are not require d to mediate the adhesion of either stimulated or resting platelets to immobilized Fg. Although stimulated platelets can adhere extensively to monomeric Fg containing one functional gamma chain, resting platele ts require bivalent Fg containing two functional gamma chains to media te irreversible adhesion to Fg.