Circulating DNA-antibodies in systemic lupus erythematosus.

Sera from 57 patients with systemic lupus erythematosus (SLE) were tested for DNA-antibodies by three different methods: a radioimmunological test using the Farr technique, the Crithidia luciliae immunofluorescence assay for anti-double-stranded (native) DNA (anti-ds-DNA), and a solid-phase immunoenzymatic assay for anti-single-stranded (denatured) DNA (anti-ss-DNA) of IgG and IgM classes. There was a positive correlation between the activity of the disease and the levels of ds-DNA-antibodies and IgG anti-ss-DNA. Patients with active nephritis had a higher amount of anti-ds-DNA and anti-ss-DNA of IgG class than patients with inactive nephritis (P less than 0.05 and 0.01, respectively). Patients with SLE nephritis had lower levels of ss-DNA-antibodies of IgM class than patients without nephritis (P less than 0.02). There was a positive correlation between the IgG-anti-ss-DNA/IgM-anti-ss-DNA ratio and the activity score of the disease. These results suggest that the anti-ss-DNA assay may be useful in the follow-up of SLE. Complement fixing anti-ds-DNA and the highest levels of anti-ds-DNA by Farr assay were usually associated with an active disease, especially nephritis and joint involvement.