Ultrastructural localization of apolipoprotein B in human aortic and coronary atherosclerotic plaques

Abstract

The ultrastructural localization of apolipoprotein B (apo B), the major protein in human plasma low (LDL) and very low density lipoproteins (VLDL), was determined in advanced atherosclerotic plaques from human coronary arteries and aorta using an immunoperoxidase procedure. Positive regions were most predominant in the lipid core at the base of the plaque. Apo B was localized on the surface of circular structures, presumably spheres, ranging in size from 250 to 2000 Å diameters. These spheres were found either free, attached to collagen and elastic fibers, or bound to extracellular lipid droplets and crystals. Smaller apo B-positive spheres (250 to 1000 Å diameters) frequently surrounded the larger spheres (1000 to 2000 Å). Saline extracts as well as homogenates of plaques contained particles of 250 to 800 Å diameters after negative staining. It is suggested that the smaller spheres are intact LDL and VLDL, whereas the larger ones may either represent lipid-free apo B attached to cell debris, or the ultrastructural morphology of denatured lipoproteins.