Cofactor-dependent IgG anti-cardiolipin antibodies (ACA) were examined in sera from various connective tissue diseases by ELISA using purified human β2-glycoprotein I. The frequency and titer of cofactor-dependent IgG ACA were higher in patients with SLE than in those with other diseases, such as RA, SSc, PM/DM, overlap syndrome, and MCTD. The predictive value for SLE was 95%. However, all of the ACA were not cofactor-dependent in SLE patients. These results indicated that cofactor-dependent IgG ACA were specific for SLE patients, but the epitopes of ACA were heterogenous, depending on various clinical manifestations.
