Identification of foam cells in human atherosclerotic lesions as macrophages using monoclonal antibodies

Four monoclonal antibodies against human monocyte/macrophage epitopes were used in an immunoperoxidase procedure to identify foam cells in atherosclerotic plaques from human aortas and coronary arteries. All antibodies gave positive reactions with the majority of foam cells observed in fatty streaks and advanced atheromas. Immunoperoxidase staining correlated with oil red O and nonspecific esterase-positive areas. Use of the immunohistochemical technique on Bouin's-fixed, paraffin-embedded tissue gave good results that afforded better localization and cell morphology than observed with frozen sections. In addition to the identification of the majority of foam cells as monocytic in origin, the technique described allowed visualization of membrane-bound extracellular droplets that were monocyte derived within necrotic cores of atheromas, indicating a contribution by dead macrophages to the lipid of atherosclerotic plaques.