Identification of macrophages and smooth muscle cells with monoclonal antibodies in the human atherosclerotic plaque.

Sections of human atherosclerotic plaques, obtained from 21 autopsy cases with various degrees of atherosclerosis, were stained with the indirect immunoperoxidase technique using specific monoclonal antibodies against macrophages and smooth muscle cells. Distinctive results were found in differing stages: Single blood monocytes were observed in diffuse intimal thickening and the foam cells seen in fatty streaks were mostly identified as mature tissue macrophages, while only very few blood monocytes were present. The spindle cells observed in fibroelastic plaques showed positive reactions to antibodies against desmin, which points to their derivation from smooth muscle cells, whereas only a few macrophage-derived foam cells were seen in these lesions. In the complicated lesions the majority of foam cells were macrophage-derived, but there was also a small number of foam cells positive to antibodies against desmin, suggesting a smooth muscle cell derivation. Our results confirm that in human atherosclerotic plaques the majority of the foam cells are obviously macrophage-derived, which emphasizes the important role of macrophages in the morphogenesis of these lesions.