[Leukocytes and arteriosclerosis]

Human atherosclerotic plaques contain two type of leucocytes: 1. Monocytes/macrophages comprise almost two thirds of the cells in the center of the lesion (lipid core), and a quarter of the cells in its periphery (fibrous cap); 2. T lymphocytes comprise 10 to 15% of the plaque cells. Polymorphonuclear granulocytes are only present in very small number. The abundance of leucocytes, together with sclerosis and proliferation of mesenchymatous cells (arterial smooth muscle cells), confer to atherosclerosis the aspect of a chronic inflammatory reaction, a fact which has been recognised for a long time. Monocytes/macrophages may contribute to the development of atherosclerosis in several ways: stimulation of the fibro-muscular reaction, endothelial injury, accumulation of intimal lipids. The role of T lymphocytes is still poorly understood. According to some observations, they might be involved in an immunological reaction of the arterial wall which could be determinant in the evolution of the lesion. Arterial leucocytes have somewhat complicated, but also widened our pathogenic hypotheses of atherosclerosis. A major issue now is to identify the nature of the arterial aggressions which provoke the involvement of leucocytes, and the reasons why the defences they oppose are overwhelmed to result eventually in severe thrombo-occlusive events. Recent evidence has strengthened the possibility that viral infection plays a role in atherosclerosis. Beyond their pathogenic interest, these acquisitions might soon provide interesting therapeutic approaches.