Immunoglobulin M type of autoantibodies to oxidized low-density lipoprotein has an inverse relation to carotid artery atherosclerosis

Background - Lipoprotein oxidation plays an important part in atherogenesis. Autoantibodies to oxidation-specific epitopes of LDL occur in plasma and atherosclerotic lesions of humans and animals. The potential role of these autoantibodies in atherogenesis still remains unsolved. We studied the relationship between different isotypes of autoantibodies to copper-oxidized LDL and malondialdehyde-modified LDL (MDA-LDL) and carotid artery intima-media thickness (IMT) in a population-based cohort of 1022 middle-aged men and women. In addition, we studied the relation of C-reactive protein (CRP) to IMT. Methods and Results - The levels of IgM, IgG, and IgG2 autoantibodies binding to MDA-LDL and copper-oxidized LDL were determined in plasma samples by chemiluminescence-based ELISA. IMT and the number of plaques were measured ultrasonographically. The subjects were divided into tertiles for antibody titers. We found an inverse association between IMT and IgM autoantibody titers to MDA-LDL that remained statistically significant after adjusting for age, gender, LDL cholesterol, systolic blood pressure, CRP, and smoking. CRP was not independently associated with IMT. Conclusions - These results show that IgM autoantibodies to MDA-LDL have an inverse association with carotid atherosclerosis. The possible implications of this finding are discussed.