**11. Proliferation (hypercellularity)**

Cell number estimated on cross sections and in the suspensions obtained by alcohol-alkaline dissociation is twofold higher in atherosclerotic lesions compared to uninvolved intima [25]. The maximum cell number was revealed in lipid-rich lesions. In pronounced lipidrich lesions (fatty streaks and fibrolipid plaques), where the cell number is maximal, the number of both resident and inflammatory cells is increased. As the bulk of the intimal cell population (84-93%) is made of resident cells, the changes in the number of resident cells determine the increase in the cell content in atherosclerotic lesions. It should be noted that the cell number of fibrotic plaque is significantly lower than that of lipidrich atherosclerotic lesions.

For the identification of proliferating cells antibody to cyclin (proliferating cell nuclear antigen - PCNA), a protein expressed in the S-phase of cell cycle was used [74]. The number of proliferating cells in the lipidrich atherosclerotic lesions (fatty streak and fibrolipid plaques) is 10- to 20-fold higher than in uninvolved intima. The number of proliferating cells in fibrous plaques was found to be lower than in fatty lesions, being significantly higher than in unin‐ volved intima (Figure 7).

The proliferative index (the ratio between proliferating cells and the total cell number) for resident cells was considerably higher in all atherosclerotic lesions than in uninvolved intima [9, 74]. The maximum proliferative index (eight times as high as that in uninvolved intima) was recorded for fibrous plaques. Proliferative index of inflammatory cells is higher than that for resident cells; however, it is similar in uninvolved intima and atherosclerotic lesions and is comparable to that of peripheral blood leukocytes [9, 74]. From these findings, it can be suggested that the changes in cellularity of arterial intima is the result of resident cell prolif‐ eration and, probably, the migration of inflammatory cells. A "splash" of proliferative activity of resident cells takes place in lipid-rich lesions (fatty streaks and fibrolipid plaques). Prolif‐ eration of inflammatory cells was observed in the vascular wall too; however, proliferative index of inflammatory cells does not change in atherosclerotic lesions. Presumably, prolifer‐ ative activity of inflammatory cells is a background process in atherosclerotic lesions and reflects the changes in the number of inflammatory cells as a result of their migration into subendothelial intima from blood stream. In contrast to resident cells, proliferative activity of inflammatory cells is not stimulated in atherosclerosis.

laden cells (up to 25%); these cells are located in the upper part of the proteoglycan-rich layer, comprising approximately two-thirds of it. By contrast, in atherosclerotic plaques, most of the cells with lipid inclusions are located in one-third of the proteoglycan-rich layer adjacent to the internal limiting membrane. In the muscular-elastic layer, the proportion of lipid-laden cells is the highest in atherosclerotic plaques, remaining not higher than 5%. Cells with lipid inclusions were found among all cell types of the aortic intima; however, their proportion among stellate cells reaches 30%, which is considerably higher than that among other cell types.

Cell number estimated on cross sections and in the suspensions obtained by alcohol-alkaline dissociation is twofold higher in atherosclerotic lesions compared to uninvolved intima [25]. The maximum cell number was revealed in lipid-rich lesions. In pronounced lipidrich lesions (fatty streaks and fibrolipid plaques), where the cell number is maximal, the number of both resident and inflammatory cells is increased. As the bulk of the intimal cell population (84-93%) is made of resident cells, the changes in the number of resident cells determine the increase in the cell content in atherosclerotic lesions. It should be noted that the cell number of fibrotic

For the identification of proliferating cells antibody to cyclin (proliferating cell nuclear antigen - PCNA), a protein expressed in the S-phase of cell cycle was used [74]. The number of proliferating cells in the lipidrich atherosclerotic lesions (fatty streak and fibrolipid plaques) is 10- to 20-fold higher than in uninvolved intima. The number of proliferating cells in fibrous plaques was found to be lower than in fatty lesions, being significantly higher than in unin‐

The proliferative index (the ratio between proliferating cells and the total cell number) for resident cells was considerably higher in all atherosclerotic lesions than in uninvolved intima [9, 74]. The maximum proliferative index (eight times as high as that in uninvolved intima) was recorded for fibrous plaques. Proliferative index of inflammatory cells is higher than that for resident cells; however, it is similar in uninvolved intima and atherosclerotic lesions and is comparable to that of peripheral blood leukocytes [9, 74]. From these findings, it can be suggested that the changes in cellularity of arterial intima is the result of resident cell prolif‐ eration and, probably, the migration of inflammatory cells. A "splash" of proliferative activity of resident cells takes place in lipid-rich lesions (fatty streaks and fibrolipid plaques). Prolif‐ eration of inflammatory cells was observed in the vascular wall too; however, proliferative index of inflammatory cells does not change in atherosclerotic lesions. Presumably, prolifer‐ ative activity of inflammatory cells is a background process in atherosclerotic lesions and reflects the changes in the number of inflammatory cells as a result of their migration into subendothelial intima from blood stream. In contrast to resident cells, proliferative activity of

plaque is significantly lower than that of lipidrich atherosclerotic lesions.

inflammatory cells is not stimulated in atherosclerosis.

**11. Proliferation (hypercellularity)**

216 Muscle Cell and Tissue

volved intima (Figure 7).

0 – grossly normal (4), I – initial lesions (5), II – fatty streaks (4), Va - fibrolipid plaques (5), Vc - fibrotic plaques (6). The number of autopsy cases is indicated in the brackets. \*- significant difference from 0, p<0.05.

**Figure 7.** PCNA-positive cells in human aortic intima. On cross sections of human aortic intima, immunocytochemical identification of PCNA-positive cells was performed. Total cell number and number of cells with positively stained nuclei were calculated on each tissue section and the data from the same atherosclerotic lesions combined. Reproduced from Orekhov AN, Andreeva ER, Mikhailova IA, Gordon D. Cell proliferation in normal and atherosclerotic human aorta: proliferative splash in lipid-rich lesions. Atherosclerosis 1998;139(1):41-8 [74], with permission from Elsevier.
