Background and Objectives:Controversy exists about the characteristics of the lipid-oxidizing process, and the molecules in oxidized lipids that are involved in the binding and uptake to macrophages, in atherosclerosis. The aim of this study was to find answers to these questions using oxidized red blood cells (ox-RBCs). Materials and Methods:The RBCs were oxidized in the presence of various concentrations of CuSO4, and the degree of oxidation evaluated by the semiquantitative measurement of the thiobarbituric acid reactive substance (TBARS). The oxRBC was characterized using annexin-V and flow cytometry. The relationships between the CuSO4 concentration, the degree of oxidation, characteristics of the ox-RBC and it’s binding to macrophages transformed from THP-1 cells, were evaluated. Results:The RBCs were oxidized, not by their gradual changes, but by the sudden transformation of a proportion of the RBCs in relation to the CuSO4 concentration. There were few RBCs between oxidized and non-oxidized groups. The annexin-V bound only to the ox-RBC, with a similar degree of binding in all ox-RBCs. The binding of ox-RBC to macrophages was completely inhibited by oxidized low density lipoprotein, which was directly related to the CuSO4 concentration, the TBARS and the proportion of ox-RBC. Conclusion:These results suggest that the oxidation of lipids might be an on-off phenomenon process. Molecules that have the ability to bind annexin-V, presumptively phosphatidyl serine, may be involved in the process of binding the ox-lipids to macrophages. Further study will be needed to clarify these molecules. (Korean Circulation J 2003;33 (12):1174-1181)