Characterization of a Platelet Membrane Protein of Low Molecular Weight Associated With Platelet Activation Following Binding by Monoclonal Antibody AG-i

With the exception of the major platelet glycoproteins llb/Illa and lb. which function as receptors for fibrinogen and von Willebrand factor, little is presently known regarding the possible role of other platelet surface proteins in mediating platelet aggregation. We report the production of a murine monoclonal antibody (AG-i ) recognizing human platelet membrane surface protein of relatively low molecular weight (mol wt) that may be involved in this process. AG-i added to human platelet-rich plasma induces dense granule secretion and aggregation, with lag phase and maximal extent of aggregation dependent on antibody concentration. Aggregation induced by AG-i is inhibited by AG-i Fab fragments, indicating that the response is not Fc receptor-mediated. Although AG-i continues to produce platelet shape change in the presence of EDTA. aggregation is fully inhibited and appears to be mediated by fibrinogen binding to glycoproteins llb/Illa. AG-i is a potent stimulus of thromboxane formation, but full inhibition of