Atherosclerosis-prone branch regions in human aorta: microarchitecture and cell composition of intima

The microarchitecture and cell composition of intima were studied at the macroscopically unaffected branch regions of human thoracic aorta using en face preparations, scanning and transmission electron microscopy, and immunohistochemistry. The endothelial lining showed a heterogeneous pattern and altered morphology including the areas of deendothelialization covered with platelets and dilated intercellular clefts. Leukocyte adhesion, accumulation of subendothelial macrophages and lymphocytes were characteristic of proximal and lateral zones, while the flow divider showed no significant accumulation of blood cells. Smooth muscle cells (SMCs) on the flow divider were elongated, in a contractile state, contacted side-by-side and did not contain lipid inclusions. In the lateral and proximal zones, intima appeared to be a network of stellate SMCs which were in contact through their processes. Most of the SMCs were in a synthetic state and many of them contained small lipid droplets. The number of procollagen I positive cells and the volume of extracellular components were most significant at the lateral zones rather than at the flow divider. We did not observe any difference in the rate of proliferation. Our results suggest that the intimal layer at the lateral and proximal zones has some distinct structural peculiarities, which provoke the development of initial atherosclerotic lesions at these sites. Such an intimal structure is probably caused by different flow patterns at these zone. However, only the totality of different morphological features exhibited in the area of altered vascular wall shear stress may be considered as a prerequisite for atherosclerotic lesions.