Topographic Analysis of Proliferative Activity in Carotid Endarterectomy Specimens by Immunocytochemical Detection of the Cell Cycle–Related Antigen Ki-67

Abstract

Background On the basis of contradictory results found in animal experiments and coronary atherectomy tissue, there is an ongoing debate about the significance of cellular proliferation in human atherosclerosis. In the present prospective study, the cell cycle–related antigen Ki-67 was detected for topographic determination of cell turnover in distinct regions of human carotid endarterectomy specimens harvested en bloc by surgical biopsy. Methods and Results After en bloc resection, serial sections of 26 consecutive carotid lesions were analyzed by histomorphological examination and immunohistochemistry. Thereby, 319 high-power fields were attributed to separate plaque regions defined as follows: distal boundary of the lesion with normal intima, plaque shoulder, core region, and diffuse intimal thickening. Endothelial cells, smooth muscle cells, T cells, and macrophages were identified by immunostaining of factor VIII–related protein, α-actin, CD68, and CD45R0. An overall proliferation index of 0.49±1.05% was yielded by positive anti–Ki-67 immunolabeling, predominantly in macrophage-rich areas characterized by high cell density (>1000 cells/mm 2 ) as well as in reparative sites in the perimeter of atheroma, intramural thrombosis, plaque hemorrhage, and neovascularization (P<.01). Few or no signs of proliferation activity were found in normal intima, in areas of dense α-actin positivity, or adjacent media. As shown by double immunostaining, macrophages and unspecified mesenchymal cells represented the prevailing proliferating cell type. Conclusions Our results suggest that proliferation in advanced human carotid lesions is confined to the intima and focally concentrated in central plaque regions negative for α-actin. Furthermore, it apparently occurs primarily as part of inflammatory processes and structural repair predominantly involving macrophages, as well as unspecific mesenchymal cells.