ULTRASTRUCTURAL-LOCALIZATION OF TISSUE FACTOR ON MONOCYTE-DERIVED MACROPHAGES AND MACROPHAGE LOAM CELLS ASSOCIATED WITH ATHEROSCLEROTIC LESIONS

The expression of tissue factor (TF) antigen by circulating monocytes, cultured macrophages, and macrophages associated with atherosclerotic lesions was ultrastructurally analysed using immunogold labeling. A s ubpopulation of macrophages associated with the intimal surface overly ing lesions had a significant TF expression. Macrophages and macrophag e foam cells that projected from the intima into the arterial lumen al so expressed a high level of TF (14-fold increase over control). In co ntrast, circulating monocytes and macrophages in culture did not expre ss TF above background control levels. This TF expression by macrophag es in vivo but not by macrophages cultured from either normal or hyper cholesterolemic animals suggests that monocyte activation and macropha ge transition, as measured by TF expression, is lesion-dependent and n ot stimulated solely by intimal attachment, surface migration, or hype rcholesterolemia. These results further suggest that macrophages and f oam cells associated with early lesions of atherosclerosis can initiat e fibrin formation, which could contribute to lesion complications and transition to a fibromuscular stage.