Immunohistochemical double labeling of macrophages, smooth muscle cells, and apolipoprotein E in the atherosclerotic plaque.

To find out which cell types in the atherosclerotic plaque are actively involved in apolipoprotein-secretion, we stained tissue samples from the ascending aorta of patients undergoing coronary bypass surgery. We used monoclonal antibodies against macrophages, smooth muscle cells and apolipoprotein E. The present in situ-study of the atherosclerotic plaque has shown that apolipoprotein synthesis is predominantly secreted by macrophages transformed into foam cells. Besides this, there are obviously some smooth muscle cells equally transformed to foam cells, which also carry apolipoprotein E in their cytoplasm. Our data suggest that both cell types in the atherosclerotic plaque are actively involved in apolipoprotein secretion.