Circulating DNA:anti-DNA complexes in systemic lupus erythematosus. Detection and characterization by ultracentrifugation.

Although it is generally accepted that DNA:anti-DNA immune complexes play a significant role in the pathogenesis of tissue injury in systemic lupus erythematosus, their presence in the circulation is still a matter of controversy. In this study, we detected DNA:anti-DNA compexes by identification of both the antigen and(or) the antibody, the necessary requisites for immune complex definition, in 14 of 24 plasmas (7 of 11 patients). These antibodies were specific for native DNA and could be adsorbed by anti-immunoglobulin (Ig)G antisera. The DNA recovered was, at least in part, of low molecular weight. The presence of DNA:anti-DNA compexes was not related to high molecular weight IgG, cryoprecipitins, positive polyethylene glycol precipitation, or low plasma C3 levels. It was related significantly to low plasma C4 levels and to the presence of diffuse proliferative nephritis. The lack of correlation with other methods of detection of immune complexes and with the presence of heavy IgG (above 13 S) is in favor of the existence of other antigen-antibody systems (or aggregated immunoglobulins) in systemic lupus erythematosus plasmas. From the results, it appears that methods directed towards the demonstration of specific immune complexes are more informative than those detecting heavy or altered immunoglobulins.