FIBRINOGEN, FIBRIN AND THE ARTERIAL-WALL

Virtually all plasma proteins, including fibrinogen, low density lipoprotein and lipoprotein(a), are present in normal arterial intima and in atherosclerotic lesions, and their concentrations are related to plasma concentrations. Fibrin is also a significant component of many lesions, particularly early proliferative (gelatinous) lesions, where it may be present both in the deep layers and on the intimal surface. The fibrin strands provide a scaffold along which smooth muscle cells migrate and proliferate, bind thrombin, and are a source of fibrin degradation products (FDPs), which are mitogenic. Very recent studies suggest that free alpha-thrombin may be present in lesions despite an apparent excess of antithrombin III, so this may promote fibrin formation within the lesion. Furthermore, fibrinolysis and FDP generation may be mediated by catheptic enzymes in addition to plasmin.