Objective To study the role of natural antiox-LDL subclass IgM antibodies in formation of atherclerosis.Methods The macrophages from mice were divded into LDL group,Cuox-LDL group and control group.The macrophages in LDL group and Cuox-LDL group were precultured with LDL and Cuox-LDL.Adhesion experiment was performed in control group.3A6,5G8 and 2H7 were incubated.The macrophages were divided into 3A6 group,5G8 group and 2H7 group.Adhesion experiment was performed by adding the pretreated 125I Cuox-LDL.The binding parameters of macrophages and 125I Cuox-LDL in different groups were recorded.Foam cells were analyzed by cell lipid analysis with oil red O staining.Results The bound 125I Cuox-LDL level was significantly lower in Cuox-LDL group than in control group and LDL group (P＜0.01).No significant difference was found in bound 125I Cuox-LDL level between 5G3 group and 2H7 group (P＞0.05).The bound 125I Cuox-LDL level was significantly lower in 3A6 group than in control group,5G8 group and 2H7 group (P＜0.01).Oil red O staining showed no oil drop in macrophages,but a small number of oil drops in 3A6 group and a large number of oil drops in control group.The cholesterol and TG in macrophages reduced 45％ and the TG reduced 170％ in 3A6 group,which were significantly lower than those in control group (P＜0.01).Conclusion Antiox-LDL IgM subclass antibody 3A6 can effectively prevent the binding of unactivated macrophages to ox-LDL,reduce the occurrence and progression of atherosclerosis.