Adhesive Protein Expression on Thrombin-Stimulated Platelets: Time-Dependent Modulation of Anti-Fibrinogen, -Fibronectin, and -von Willebrand Factor Antibody Binding

Platelets contain a pool of endogenous adhesive proteins that can be released and may bind to surface membrane receptors under appropriate conditions. Because the binding of exogenous fibrinogen to platelets was shown previously to be accompanied by a time-dependent decrease in fibrinogen accessibility t o antibody and enzymes, studies were performed t o evaluate changes in the expression of endogenous fibrinogen released from thrombin-stimulated platelets using monospecific polyclonal and monoclonal antibody F(ab'), fragments. Parallel studies were performed to compare the expression of released fibronectin and von Willebrand factor (vWF). Binding of polyclonal antibody F(ab'), fragments directed against individual adhesive proteins was inhibited by EDTA or the 10E5 monoclonal antibody, suggesting that fibrinogen, fibronectin, and vWF expression was mediated, in large part, by divalent cation-dependent interactions with the glycoprotein Ilb-llla complex. Interestingly, when polyclonal antibody F(ab'), fragments were added to platelet suspensions at discrete times after thrombin stimula-