AbstractOxidized low-density lipoproteins (ox-LDLs) and their autoantibodies (OLAB) are involved in the development of atherosclerosis in animal models, but their role in humans is still not clear. For this reason we studied 54 patients with β-thalassemia major (TM), as a model of chronically low circulating LDLs with a high level of oxidation; 44 patients with primary hypercholesterolemia, as model of chronically high circulating LDLs; 24 type 2 diabetic mellitus patients (T2DM) before and after 3 months of atorvastatin treatment (20 mg/day), as a model of acute changes in circulating LDLs; and 41 normolipidemic subjects as a control group. ox-LDLs were measured by the determination of baseline diene concentration in the plasma LDL lipidic fraction after 12 hours fasting and were expressed as the amount of conjugated dienes/liter (BDC/l) or BDC/LDL-cholesterol (LDL-C), which indicate respectively LDL oxidation degree and status. OLABwere determined using an enzyme immunoassay and related to LDL oxidation degree (BDC/l). In TM, BDC/l was lower, while BDC/LDL-C was significantly higher, compared to both hypercholesterolemia and normolipidemic subjects. Patients with hypercholesterolemia had higher BDC/l, but lower BDC/LDL-C and OLAB/BDC-l, than normolipidemic subjects. In T2DM patients at diet, BDC/LDL-C and OLAB/BDC-l were lower than in normolipidemic subjects. After 3 months of atorvastatin treatment, BDC/LDL-C and OLAB/BDC-l ratios increased. When all patients were evaluated together, a significant inverse correlation was evident between OLABand either LDL or BDC/l. Our findings suggest that a relationship between OLABtiter and oxidation indices (BDC/l and BDC/LDL-C) does exist and we may speculate that an increase in OLAB/BDC-l ratio might be protective against the risk of atherosclerosis.