Circulating DNA-anti-DNA complexes in lupus nephritis and idiopathic nephritis

Although DNA and anti-DNA antibodies have been eluted from diseased tissues in systemic lupus erythematosus (SLE) it is uncertain whether DNA and anti-DNA comprise circulating antigen-antibody complexes in SLE. Cryoglobulins from 20 patients with SLE were examined for (i) DNA, using a radioimmunoassay and an ethidium bromide assay, (ii) anti-DNA activity of IgG and IgM, isolated from the cryoglobulins by ultracentrifugation at pH 3.5, by a modified Farr assay (anti-dsDNA) and a solid phase ELISA (anti-ssDNA). DNA was found in each of the 20 cryoglobulins by both methods. Isolated IgG had anti-DNA activity in 14 cryoglobulins: 5 anti-dsDNA, 5 anti-ssDNA and 4 anti-ds- and ssDNA; isolated IgM had anti-dsDNA activity in 3 cryoglobulins. Isolated IgG/IgM had no anti-DNA activity in 6 of the 20 cryoglobulins. In controls with idiopathic nephritis (11 membranous, 13 mesangio-capillary) DNA was detected in cryoglobulins, but no ati-DNA activity was found. It is concluded that circulating dsDNA-anti-dsDNA complexes are present in SLE, but some patients have SLE without these complexes. Our failure to find dsDNA-anti-dsDNA complexes in nephritis not due to SLE indicates the specificity of such complexes for SLE.