Anticardiolipin Antibodies in Infections are Heterogenous in Their Dependency on β 2-Glycoprotein I: Analysis of Anticardiolipin Antibodies in Leprosy

We studied the effect of β 2-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 β 2-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 β 2-GPI requirement for binding to CL.