Abstract-Monocyte/macrophage infiltration to the arterial wall is an initial step in atherosclerosis, and monocyte chemoattractant protein-1 (MCP-1) is thought to play a central role in the recruitment of these cells. In the present study, we examined the role of local expression of MCP-1 at the vessel wall in the initiation and development of atherosclerosis. We transfected the cDNA encoding rat MCP-1 into the vessel wall of the rabbit carotid artery with the use of the hemagglutinating virus of Japan (HVJ)-liposome method. The rabbits were divided into the following groups:(1) those fed normal chow and transfected with MCP-1-HVJ, (2) those fed a high cholesterol diet (1% cholesterol) and transfected with MCP-1-HVJ, and (3) those fed a high cholesterol diet and transfected with control-HVJ. Prescribed diets were started 2 weeks before transfection and were continued for another 2 weeks. In group 1, vascular lesion formation was not found, and anti-rabbit monocyte/macrophage antibody (RAM-11) staining for monocytes/macrophages was negative, although anti-rat MCP-1 antibody (R-17) staining for rat MCP-1 was positive mainly in endothelial cells. Cholesterol feeding increased plasma cholesterol levels to 1801Ϯ444 mg/dL in group 2. In group 2, all rabbits displayed neointimal formation with infiltration of RAM-11-positive cells, and a part of the lesion was also positive for Sudan III lipid staining. In group 3, hypercholesterolemia did not induce the infiltration of monocytes/ macrophages and subsequent lesion formation in the vessel wall despite definite upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 on the endothelium. To initiate atherosclerotic changes, local MCP-1 overexpression at the vessel is not sufficient, and activation of other factors induced by hypercholesterolemia is required. Key Words: monocyte chemoattractant protein-1 Ⅲ hypercholesterolemia Ⅲ atherosclerosis M onocytes/macrophages play an essential role in the initiation and progression of atherosclerosis. Foam cells accumulating cholesterol ester are found in early atherosclerotic lesions, and these cells are believed to be derived mainly from circulating monocytes/macrophages. 1,2 Among many factors involved in the recruitment of monocytes/macrophages, recent studies have highlighted monocyte chemoattractant protein-1 (MCP-1). 3,4 MCP-1 is highly expressed in the macrophage-rich area of the atherosclerotic lesions in human and animal models. 3 MCP-1 is induced by oxidized lipoproteins and proinflammatory cytokines, such as interleukin-1 and tumor necrosis factor-␣, 5,6 and its expression and secretion from vascular cells have been demonstrated to account for the increased monocyte chemotactic activity. 7 These findings suggest that MCP-1 plays an important role in the initiation of atherosclerotic lesion formation. However, chemotactic factors other than MCP-1 are also involved in monocyte recruitment and the subsequent lesion formation in atherogenesis. 8 On the other hand, MCP-1 in transgenic mice in ...