Ultrastructural Aspects of Human Atherosclerosis; Role of the Foam Cells and Modified Smooth Muscle Cells

Abstract

With specimens of the human ascending aorta obtained from 10 cases ranging in age from 44 to 85, normal appearance, yellowish plaque and whitish plaque were studied electron microscopically. In yellowish plaques where foam cell infiltration is intensive, the infiltration of lipid–laden macrophages as well as non–lipid macrophages (monocytes), plasma cells and mast cells was seen. The lipid–laden macrophages resulted from phagocytosis in situ and resembled inflammatory reaction of the ecology against transintimal infusing substances having invaded by means of the rupture of blood barrier. Lipid metabolism in the foam cells originating in the smooth muscle cells was different morphologically from that in macrophages. Non–lipid intimal sclerosis (diffuse intimal thickening) was also seen widely in addition to the changes due to lipid insudation. These changes were the same electron microscopically as the intimal thickening of the peripheral small arteries. The nature of the modified smooth muscle cells in the lesions was understood as an accelerated state of protein synthesis consisting mostly of the synthesis of collagen fibers and elastic fibers, rather than as dedifferentiation.