Anticardiolipin antibodies in infections are heterogenous in their dependency on β₂-glycoprotein I: Analysis of anticardiolipin antibodies in leprosy

We studied the effect of β₂-GPI on binding of antibodies in sera from patients with leprosy and patients with the antiphospholipid syndrome (APS) to CL in enzyme-linked immunosorbent assays (ELISAs). Increased levels of IgG aCL were detected in 59 of 61 leprosy patients' sera by the standard aCL-ELISA in the presence of bovine β₂-GPI and in 60 of the 61 leprosy patients' sera by the modified aCL-ELISA without β₂-GPI. When tested by both aCL-ELISAs on the same plate, 10/31 leprosy sera and 9/10 APS sera bound better in the standard aCL-ELISA, 16/31 leprosy sera bound better in the modified aCL-ELISA and in five leprosy and one APS sera the difference was not significant. A dose-dependent enhancing effect of β₂-GPI on the leprosy and APS sera binding to CL was confirmed using purified human β₂-GPI. Enhanced binding was seen if β₂-GPI was added either before or together with the test serum. In 11/61 leprosy sera increased levels of IgG antibodies against β₂-GPI were found by ELISA. Leprosy anti-β₂-GPI antibodies appear to be a separate antibody population recognizing only β₂-GPI adsorbed on the ELISA plate. These results demonstrate heterogeneity of leprosy aCL with respect to their β₂-GPI requirement for binding to CL.