O72	Cellular origin of microparticles in human atherosclerotic plaques.
1A.Leroyer, 2G.Leseche, 1C.Nguyen, 1A.Tedgui, 1C.M.Boulanger
1Cardiovascular Research Center Inserm Lariboisiere, Paris, FR; 2Vascular Surgery Department, Hopital Beaujon, Clichy, FR.

Background : Human atherosclerotic plaques contain elevated levels of microparticles (MPs), which are submicron membrane vesicles released from many different cell types during cell activation or apoptosis. The aim of this study was to investigate the cellular origin and pro-inflammatory potential of MPs isolated from human atherosclerotic plaques. Methods and Results : Ten human atherosclerotic plaques (817±227 mg) obtained from patients undergoing carotid endarterectomy (77±2 years; 90% male) were minced in a volume of DMEM corresponding to the respective weight of each lesion. MPs were then purified by sequential centrifugations. Similar procedure was performed on apparently healthy vessel wall (n=3), which was adjacent to the lesion. Flow cytometry analysis demonstrated the presence of 355014±83593 annexinV+ MP/mg in the plaque, whereas apparently normal arterial walls only contained 31696±15482 annexinV+ MPs/mg tissue. The majority of the MPs present in human atherosclerotic plaque were of leukocyte origin (54±15%). Indeed, we detected 33±9% CD14+MP, 12±4% CD4+MP and 9±2% CD66b+MP per mg lesion, indicating of monocytes/macrophages, lymphocytes and granulocytes origin, respectively. Human atherosclerotic plaque also contained MPs derived from erythrocytes (30±6% CD235a+ MP/mg), smooth muscle cells (10±5% smooth muscle actin+ MP/mg) and from endothelial cells (6±2% CD144+ MP/mg). No CD41+ or CD62P+CD144- MPs were detected, indicating that if any, platelet-derived MP are present in very low levels in human atherosclerotic plaque. In addition, we investigated the pro-inflammatory potential of atherosclerotic plaques MPs by analyzing the presence of the major histo-compatibility complex II (MHCII) and that of CD40L on MPs. Flow cytometry analysis demonstrated that 48±9 % of plaques MPs express MHCII while 33±12 % were CD40L positives, thus reflecting the proinflammatory potential of these microparticles. Conclusion : These results indicate that MPs generated in atherosclerotic plaques are mainly derived from activated monocyte-macrophages and from erythrocytes. These MPs may contribute to the inflammatory process in the human atherosclerotic lesion and may be the determinants of plaque rupture.

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