Local Accumulation of Lymphocytes in the Intima of Human Aorta Is Associated with Giant Multinucleated Endothelial Cells: Possible Explanation for Mosaicism of Atherosclerosis

Abstract

Distribution of different types of atherosclerotic lesions in the arterial wall is not diffuse, but is characterized by mosaicism. The causes of such distribution remain to be established. At the early stages of atherogenesis, low-density lipoprotein (LDL) particles and immune cells penetrate into the intimal layer of the arterial wall through the endothelium. In adult humans, the luminal surface of the arterial wall is a heterogeneous monolayer of cells with varying morphology including typical endothelial cells (ECs) and multinucleated variant endothelial cells (MVECs). We hypothesized that distribution of MVECs in the endothelial monolayer can be related to the distribution pattern of early atherosclerotic lesions. We obtained en face preparations of intact adult (22-59 years old) aortic wall sections that allowed us to study the endothelial monolayer and the subendothelial layer. We compared the distribution of MVECs in the endothelial monolayer with the localization of early atherosclerotic lesions in the subendothelial layer, which were characterized by lipid accumulation and immune cell recruitment. In primary culture, MVECs demonstrated increased phagocytic activity compared to mononuclear ECs. Moreover, we have shown that unaffected aortic intima contained associates formed as a result of aggregation and/or fusion of LDL particles that are non-randomly distributed. This indicated that MVECs may be involved in the accumulation of LDL in the subendothelial layer through increased transcytosis. Interaction of LDL with subendothelial cells of human aorta in primary culture increased their adhesive properties toward circulating immune cells. Study of unaffected aortic intima revealed non-random distribution of leukocytes in the subendothelial layer and increased localization of CD45+ leukocytes in the subendothelial layer adjacent to MVECs. Together, our observations indicate that MVECs may be responsible for the distribution of atherosclerotic lesions in the arterial wall by participating in LDL internalization and immune cell recruitment.

Keywords: LDL; aortic intima; atherosclerosis; giant multinuclear endothelial cells; leukocytes; mosaicism.

Figure 1

Schematic presentation of the heterogeneous endothelium of the adult human arterial wall [3,4,5].

Figure 2

Fluorescence micrograph of LDL associates stained using ApoB-100 antibodies in the aortic intima. Image was taken with a Nikon C1 microscope, 20× lens. The size of the presented area is 100 × 140 µm.

Figure 3

Fluorescence micrograph of CD45+ leukocytes in the aortic intima. Image was taken with a Nikon C1 microscope, 10× lens. The size of the presented area is 390 × 520 µm.

Figure 4

Association of MVECs (giant endotheliocytes) with CD45+ cells in human aortic intima. *—statistically significant difference (p < 0.05).

Figure 5

Effect of LDL on the adhesion of human blood leukocytes to intimal subendothelial cells. (a) Average number of leukocytes associated with one subendothelial cell. (b) The proportion of subendothelial cells associated with at least one leukocyte. *—statistically significant difference (p < 0.05).

Figure 6

Average number of latex beads associated with one mononucleated or multinucleated EC in culture. *—statistically significant difference (p < 0.05).

Figure 7

Identification and counting of CD45+ leukocytes in the subendothelial intima co-localized with a giant endothelial cell (marked in green) in one field of view—a schematic example.