Fibrinogen and flbrinogen/flbrin-related antigen (total FRA) was measured In human normal Intima and different types of atherosclerotic lesions and mural thrombi. The amount showed marked variation between groups of tissue samples, but within each group there was a significant correlation between levels of total FRA and low density llpoproteln (LDL), suggesting that some common factor must Influence their influx or retention. The total FRA were analyzed by gradient sodium dodecyl sutfate polyacrylamlde gel electrophoresis and ImmunoblottJng with antisera to whole fibrinogen and fragments D and E, and fibrinopeptlde A (FPA). All intimal samples (but not thrombi) contained fragment X, the first product of plasmln digestion of fibrinogen, but fragment Y was present In only half the samples, and no core-fragment E containing FPA was detected in any sample, suggesting that flbr/nogenolysis Is limited. By contrast, all samples contained fragment E, which was negative for FPA, so presumably derived from fibrin; they also contained fragments D-dlmer and DY, which are characteristic degradation products of cross-linked fibrin. There were no differences between samples obtained during reconstructive 1 The early proliferative lesions appear first as small translucent elevations but may progress to massive translucent proliferate mounds, up to 2500 tun In thickness, which are particularly characterized by their high water content; this gives them a soft and wobbly texture, and they are described as gelatinous lesions. 23 In a high proportion of these lesions, neither extracellular lipid nor lipid within fat-filled SMC or macrophages can be demonstrated in frozen microscopical sections, suggesting that lipid deposition cannot be the factor initiating SMC proliferation. These lesions contain large amounts of plasma macromolecules, including low density lipoprotein (LDL), fibrinogen and fibrin-related antigens (FRA), other components of the hemostatic system, and insoluble fibrins** In a preliminary study of the FRA fraction, Smith and Walker 6 found that about naff was comprised of intact fibrinogen, but the remainder consisted of fragments, mainly of high molecular mass, which showed characteristic patterns in different types of lesions. Different fibrin or fibrinogen degradation products have a wide range of pharmacobiological activities, including stimulation of growth of cultured cells; modification of clotting, vascular all of which might influence atherogenesis. In the present study we have attempted a detailed identification of the FRA present in lesions to relate them to particular biological activities, and, by determining if they are derived from fibrinogen or fibrin, to gain a better insight Into the handling of hemostatic factors in the arterial wall. Previously, we isolated the FRA from intimal extracts by affinity chromatography on Sepharose-antjfibrinogen columns, followed by elution with 8 M urea and separation by sodium dodecyl sutfate polyacrylamide gel electrophoresis (SDS-PAGE) and staining with Coomassie ...