Localization of tissue factor in the normal vessel wall and in the atherosclerotic plaque

Tissue factor (TF)-producing cells were identified in normal human vessels and atherosclerotic plaques by in situ hybridization and immunohistochemistry using a specific riboprobe for TF mRNA and a polyclonal antibody directed against human TF protein. TF mRNA and protein were absent from endothelial cells lining normal internal mammary artery and saphenous vein samples. In normal vessels TF was found to be synthesized in scattered cells present in the tunica media as well as fibroblast-like adventitial cells surrounding vessels. Atherosclerotic plaques contained many cells synthesizing TF mRNA and protein. Macrophages present as foam cells and monocytes adjacent to the cholesterol clefts contained TF mRNA and protein, as did mesenchymal-appearing intimal cells. Significant TF protein staining was found deposited in the extracellular matrix surrounding mRNA-positive cells adjacent to the cholesterol clefts and within the necrotic cores. These results suggest that deposition of TF protein in the matrix of the necrotic core of the atherosclerotic plaque may contribute to the hyperthrombotic state of human atherosclerotic vessels.