Ultrastructural studies on the localization of IgG in the aortic endothelium and subendothelial intima of atherosclerotic and nonatherosclerotic rabbits

Immunoelectron microscopy with peroxidase-conjugated Fab fragments of anti-IgG was used for studying the localization of IgG in the aortic endothelium and subendothelial intima of atherosclerotic and nonatherosclerotic rabbits. Small amounts of IgG were found in the cell coat, in caveolae and vesicles, and also in intercellular clefts of endothelial cells from normocholesterolemic rabbits. Injured endothelial cells exhibited prominent accumulations of IgG in the cytoplasmic matrix, possibly due to leakage through plasma membrane defects. In atherosclerotic lesions from hypercholesterolemic rabbits, there was a striking increase in the amount of IgG-reactive material in the cell coat and vesicles of intact endothelial cells. Also in these animals, injured endothelial cells were characterized by a cytoplasmic IgG accumulation. There were prominent IgG depositions in the subendothelial zone of the lesions. IgG was adhering to collagen fibers, and also coating the surfaces of subendothelial foam cells. The pathophysiological significance of an interaction between such intimal IgG and phagocytes is discussed.