Biology of the vessel wall and atherosclerosis

Langhans cells of human arterial intima: uniform by stellate appearance but different by nature

The stellate cells in human arterial intima known as Langhans cells were investigated. Arterial specimens were obtained during carotid endarterectomy and aortic reconstruction and included atherosclerotic lesions as well as areas of the adjacent normal appearing arterial wall. Following immunohistochemical and electron microscopic analysis, most of the stellate cells were found to inhabit the elastic-hyperplastic layer of the intima in the normal arterial wall but in atherosclerotic lesions, stellate cells were distributed throughout all intimal layers. Immunohistochemical examination revealed that different types of intimal cells, including smooth muscle cells (HHF-35; smooth muscle alpha-actin +) and vascular dendritic cells (CD1a+, S-100+), exhibited a typical stellate appearance but the cell processes of macrophages (HAM56+, CD68+) were too short for macrophages to be considered as stellate. No other intimal cells formed processes which could be detected under immunohistochemical examination. In atherosclerotic lesions, some smooth muscle cells transforming to foam cells retained their stellate shape. Smooth muscle cells interacted with each other through gap junctions while other intimal cells including vascular dendritic cells contacted each other without forming any specialized structures. We conclude that Langhans cells comprise two histological types of intimal cells, namely, smooth muscle cells and vascular dendritic cells.

Heterogeneity of smooth muscle cells in embryonic human aorta

Cellular composition of aortas from 5- to 12-week and 18- to 28-week-old human embryos were investigated using immunocytochemistry, scanning and transmission electron microscopy. The aorta of the 5- to 12-week-old embryos consisted of three sublayers differing in cellular composition. The inner sublayer adjacent to the endothelium contained round and ovoid cells with synthetic phenotype. In the intermediate sublayer, spindle-like cells ultrastructurally similar to smooth muscle cells were found. Cells of the outer sublayer resembled fibroblasts or poorly differentiated mesenchymal cells. There were not definite morphological borders between sublayers. In the 18- to 28-week-old embryo aorta the intima was separated from media by internal elastic lamina. Intimal and innermost medial cells had predominately stellate shape and synthetic phenotype. The outer part of media contained spindle-like cells that had well developed contractile structures. Both the 5- to 12-week-old and the 18- to 28-week-old embryo aortic cells were positively stained for alpha-actin and myosin and negatively stained for macrophage antigens. Thus, the majority of embryo aortic cells appeared smooth muscle cells, however there was a regional difference in shape and synthetic state of these cells.

Characterization of atherosclerosis with a 1.5-T imaging system

It is shown that a conventional 1.5-T magnetic resonance (MR) imaging system can help characterize some of the key components of atherosclerotic plaque ex vivo. Fresh human aorta with atheromata was suspended in solutions of agarose and manganese chloride and heated to body temperature. The specimens were imaged with modified Dixon and projection-reconstruction imaging sequences. The specimens were then examined histologically to obtain direct correlation between images, spectra, and histologic characteristics. The results show that vessel wall and plaque components can be identified by means of their MR characteristics and correlated with their histologic appearance. The authors were able to identify normal vessel wall components, such as adventitial lipids and smooth muscle. They were also able to identify and localize plaque components such as fibrous tissue, calcification, lipids, and possible areas of hemorrhage and hemosiderin deposition.

Coagulation factors X, Xa, and protein S as potent mitogens of cultured aortic smooth muscle cells

Smooth muscle cells (SMCs) in the rat carotid artery leave the quiescent state and proliferate after balloon catheter injury. The precise signals responsible for this SMC mitogenesis need to be elucidated. Although platelet-derived growth factor (PDGF), a potent SMC mitogen, is released from activated platelets, damaged endothelium, and macrophages, it cannot be solely responsible for this proliferation. In search of other SMC growth factors, we have examined several proteins of the coagulation cascade. At nanomolar concentrations, factors X, Xa, and protein S promote cultured rat aortic SMC mitosis. In contrast, factor IX is only weakly mitogenic, whereas factor VII and protein C fail to stimulate SMC division. Protein S, the most mitogenic of these coagulation cascade factors, stimulates DNA synthesis in cultured SMCs with a time course similar to that of PDGF-AA and without the delay observed for transforming growth factor beta. Antistasin and tick anticoagulant peptide, two specific factor Xa inhibitors, inhibit SMC mitogenesis due to Xa and protein S. Coagulation factors that possess mitogenic activity may contribute to intimal SMC proliferation after vascular injury as a result of angioplasty or vascular compromise during atherogenesis.

Stellate cells of aortic intima: I. Human and rabbit

Stellate cells hitherto accounted exclusively in the innermost elastic-hyperplastic layer were already reported to inhabit human aortic intima. The present paper shows that most of these cells are situated just beneath the endothelium. Stellate cells also appear in the deendothelialization-induced myointimal thickening of rabbit aorta. In the myointimal thickening these cells were revealed in the direct proximity to the endothelium. A conclusion is available that the previously demonstrated polymorphism of human aortic intimal cells may be reproduced in a simple experimental model, which gives new possibilities for the study of the cellular polymorphism in the vessel wall.