The localization pattern of low-density lipoproteins in atherosclerotic arteries from normolipemic humans has been determined employing immunofluorescent techniques. Goat antiserum was prepared against delipidated human low-density lipoproteins (apo low-density lipoproteins) and conjugated with fluorescein isothiocyanate. A monospecific antibody was isolated by affinity chromatography using low-density lipoproteins attached to a column of Sepharose 4B. This antibody reacted with both low-density lipoproteins and apo low-density lipoproteins, and the fluorescence localization experiments did not distinguish between the lipoprotein and apoprotein. Sections of uninvolved areas, fatty streaks, and fibrous plaques from aorta, coronary, carotid and cerebral arteries from 20 normolipemics were studied following incubation with the purified antiserum. Uninvolved segments demonstrated no specific fluorescence. Fatty streaks and the fibromuscular caps of fibrous plaques demonstrated specific fluorescence to collagen and elastic fibers. Specific fluorescence was seen in fibrous plaques in large bands of collagen, in acellular areas as well as in the atheromatous core. Although this localization pattern was found consistently in arteries from normolipemics, not all atheromas or collagen and elastic fibers from these subjects were positive. By contrast, incubation of serial sections with fluorescein isothiocyanate-conjugated non-immune globulins resulted in non-specific fluorescence to only the cytoplasm of all intimal and medial cells. This non-specific pattern was present in both non-involved and involved segments of arteries.
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