**3. Cellular composition of normal and atherosclerotic intima of the human aorta**

Cell numbers in the intimal layers of grossly normal areas and atherosclerotic lesions have been determined after alcohol-alkaline dissociation of tissue [26]. In the proteoglycan-rich layer of a fatty streak and an atherosclerotic plaque, the number of cells was found to be 1.5 and 2-fold higher than that in undiseased intima, while in the muscular-elastic layer of atherosclerotic lesions, the number of cells was found to remain practically unchanged in comparison with the normal intima [25].

Similar results were obtained during analysis of aortic cross sections [25]. Cell number in the muscular-elastic layer of uninvolved and atherosclerotic intima is similar, while the number of cells in the proteoglycan-rich layer of atherosclerotic lesions is twofold higher than in normal intima (Figure 2). Thus, atherosclerotic manifestations in the vascular wall coincide with an increase in the cell number of the proteoglycan-rich layer.

Cell number in the intimal layers was determined in suspension after alkali-alcohol dissociation on fixed tissue [25]. PG - proteoglycan-rich layer of the intima, ME - musculoelastic layer of the intima. \* - significant difference from normal, p<O.05

**Figure 2.** Cell number in different layers of the human aortic intima.

What are the cells populating different layers of the intima and what are the differences between these cells?

Cellular composition of the intima of human arteries has been studied for more than one century [27-30]. In classic works in this field, a special attention has been paid to the fact that the cell population inhabiting vascular walls is heterogeneous and consists of two subpopu‐ lations: resident vascular cells and round cells that are morphologically similar to peripheral blood monocytes and lymphocytes (inflammatory cells). In those studies, it was noted that resident subendothelial cells differ from typical smooth muscle cells of the media [28, 29]. These cells were referred to as intimal fibroblasts [27], mesenchymal reserve cells [28], pericytes or vascular cambium [30], etc. However, the application of electron microscopy studies led to the concept that *intimacytes* of major arteries are modified smooth muscle cells [31, 32]. Figure 3 shows typical ultrastructural features of cells that represent the main population among the subendothelial cells. The structural features of these cells include the presence of individual myofilaments and bundles of myofilaments in cell cytoplasm, the presence of "dense bodies" seen in the cytoplasm along the cell-surrounding membrane, and the presence of basal membrane surrounding the cell membrane extracellularly, a combination suggesting smooth muscle nature of these cells [31-33].

**3. Cellular composition of normal and atherosclerotic intima of the human**

Cell numbers in the intimal layers of grossly normal areas and atherosclerotic lesions have been determined after alcohol-alkaline dissociation of tissue [26]. In the proteoglycan-rich layer of a fatty streak and an atherosclerotic plaque, the number of cells was found to be 1.5 and 2-fold higher than that in undiseased intima, while in the muscular-elastic layer of atherosclerotic lesions, the number of cells was found to remain practically unchanged in

Similar results were obtained during analysis of aortic cross sections [25]. Cell number in the muscular-elastic layer of uninvolved and atherosclerotic intima is similar, while the number of cells in the proteoglycan-rich layer of atherosclerotic lesions is twofold higher than in normal intima (Figure 2). Thus, atherosclerotic manifestations in the vascular wall coincide with an

Cell number in the intimal layers was determined in suspension after alkali-alcohol dissociation on fixed tissue [25].

What are the cells populating different layers of the intima and what are the differences

Cellular composition of the intima of human arteries has been studied for more than one century [27-30]. In classic works in this field, a special attention has been paid to the fact that the cell population inhabiting vascular walls is heterogeneous and consists of two subpopu‐ lations: resident vascular cells and round cells that are morphologically similar to peripheral blood monocytes and lymphocytes (inflammatory cells). In those studies, it was noted that

PG - proteoglycan-rich layer of the intima, ME - musculoelastic layer of the intima.

**Figure 2.** Cell number in different layers of the human aortic intima.

\* - significant difference from normal, p<O.05

between these cells?

**aorta**

206 Muscle Cell and Tissue

comparison with the normal intima [25].

increase in the cell number of the proteoglycan-rich layer.

**Figure 3.** Electron micrographs showing ultrastructural appearance of *intimacytes* most frequently seen in the subendo‐ thelial space of undiseased aorta (**A**, **B**) (up to 90% of the total cells of the tunica intima of the undiseased aorta). Image (**A**): cell body; image (**B**): cell process. In (**A**, **B**), note the presence of myofilaments and the basal membrane; arrows show "dense bodies," a reliable ultrastructural criterion for the identification of smooth muscle cells. The presence of myofilaments and the basal membrane further supports the identification of the cells as smooth muscle cells.
