MONOCYTE-MACROPHAGE ACCUMULATION AND SMOOTH-MUSCLE CELL PHENOTYPES INEARLY ATHEROSCLEROTIC LESIONS OF HUMAN AORTA

In a search for early atherosclerotic lesions, we have investigated gr ossly normal areas of human thoracic aortas taken at autopsy from 40 t rauma victims aged from 3 to 40 years. Two areas of aorta were compare d: lesion predisposed to atherosclerosis (LP) area localized on the do rsal aspect of the vessel along the row of intercostal branching sites , and lesion resistant (LR) area located on the ventral aspect of the vessel. Accumulation of apolipoprotein B (apo B) was found in LP aorti c area of each child older than 6 years. Similar retention of apo B in LR area appeared only in aortas of teenagers. The apo B staining incr eased with age in both areas tested but was usually of a greater exten t in LP area than in LR area. Typical smooth muscle cells (SMCs) and a few monocytes/macrophages (Mn/Mph) were revealed in the intimal layer of all aortas examined. The number of Mn/Mph dramatically increased i n LP areas of individuals over 17 years. Quantitative study of double stained sections has shown a 2- to 6-fold enhanced number of Mn/Mph in LP area compared with LR aortic area of 10 men over 21 years. Focal i nfiltration of Mn/Mph in aortas of young adults occurred without endot helial denudation. In addition, some intimal SMCs in LP area of 12 aor tas out of 29 expressed desmin and contained well-developed endoplasmi c reticulum, while such cells were seldom detected in LP area of the v essels. Thus, focal accumulation of apo B with subsequent Mn/Mph infil tration and SMC phenotypic modulation in LP aortic area of young adult s may be causally involved in fatty streak and atherosclerotic plaque formation.