Lack of cross-reaction between antibodies to beta2-glycoprotein-I and oxidized low-density lipoprotein in patients with antiphospholipid syndrome.

Previous studies have shown a cross-reaction between anticardiolipin and anti-oxidized low-density lipoprotein (LDL) antibodies in patients with the antiphospholipid syndrome (APS). The aim was to investigate the existence of a cross-reaction between anti-beta2-glycoprotein-I (beta2-GP-I) and anti-oxidized LDL antibodies in a group of APS patients. Ninety-three patients with APS were included in the study; 47 of these patients were diagnosed as primary APS, while the rest (46 patients) fulfilled criteria for the classification of systemic lupus erythematosus (SLE). All patients were positive for the IgG isotype of anticardiolipin antibodies (aCL). Twelve (26%) SLE-associated APS and 14 (29.7%) primary APS patients had raised concentrations of IgG antibodies to oxidized LDL. There was no correlation between anti-beta2-GP-I and anti-oxidized LDL antibodies. Inhibition experiments showed no cross-reaction either between anti-beta2-GP-I and anti-oxidized LDL antibodies, or between anti-beta2-GP-I and anti-native LDL antibodies. Our study suggests that the presence of both anti-beta2-GP-I and anti-oxidized LDL antibodies in patients with APS is not due to the structural similarity and consequent cross-reaction, and that they are two different populations of antibodies directed against different antigens.