Fibrinogen.
Fibrinogen is a blood-borne glycoprotein comprised of three pairs of nonidentical polypeptide chains. Following vascular injury, fibrinogen is cleaved by thrombin to form fibrin which is the most abundant component of blood clots. As well as controlling blood loss at sites of tissue damage, other properties of fibrinogen have recently been discovered. For example, various cleavage products of fibrinogen and fibrin, released during coagulation and fibrinolysis, respectively, regulate cell adhesion and spreading, display vasoconstrictor and chemotactic activities, and are mitogens for several cell types including fibroblasts, endothelial and smooth muscle cells. Current research aims to define the bioactive fibrinogen molecule moieties and cellular receptors involved in these processes. Future studies may provide us with new opportunities to develop agents which are useful in promoting tissue repair or conversely in inhibiting fibrosis in inflammatory and fibroproliferative diseases where endothelial cell damage or chronic leakage of blood proteins is a feature.