Evaluation of the cross-reaction between anti-DNA and anti-cardiolipin antibodies in SLE and experimental animals.

The cross-reaction between anti-DNA and anti-cardiolipin IgG antibodies and its relation to the standard test for syphilis was studied with sera and monoclonal antibodies derived from human patients and mice with systemic lupus erythematosus (SLE). Syphilitic sera of humans and rabbits infected with the spirochete Treponema pallidum were also tested in this study. In addition, rabbits were immunized with ssDNA and cardiolipin and the cross-reactions of the induced antibodies were studied in two different assay systems. The results of these experiments suggest: that the anti-DNA and anti-cardiolipin IgG autoantibodies in SLE sera constitute separate antibody populations and, therefore, cardiolipin cannot play a role in the induction of immune response to DNA in SLE; that in immunized experimental animals there is a significant level of cross-reaction between anti-DNA and anti-cardiolipin-the detection of this cross-reaction depends on highly amplified solid phase assay systems which measure low affinity antibodies and that there is no correlation between the activity of syphilitic sera in the serologic test for syphilis and their binding to pure cardiolipin-this implies that cardiolipin may not be the dominant ingredient in this test as previously proposed.