A simple enzyme-linked immunosorbent assay for antibodies to native DNA

A simple and highly sensitive enzyme-linked immunosorbent assay (ELISA) has been developed for the measurement of anti-native DNA (anti-nDNA) antibodies in sera from patients with systemic lupus erythematosus (SLE). A solid-phase support for the assay was provided by coating wells of polystyrene microtiter plates with native salmon sperm DNA at a concentration of 1 microgram/ml. For standard determinations, test sera at a dilution of 1 : 100 were incubated in the DNA-coated wells which were then assayed for bound immunoglobulin using an alkaline phosphatase conjugated rabbit anti-human IgG reagent. The colorimetric yield at 400 nm was used as a measure of the content of anti-nDNA antibodies. Proof that the bound antibodies detected in this assay were directed toward native DNA was derived primarily from observations that: (1) purified native DNA blocked the binding of antibody from SLE sera; and (2) there was a correlation between determinations by the ELISA assay and a filter binding assay specific for anti-nDNA antibodies. Assay of serial samples from the same patient showed a close correlation between determinations by the ELISA and filter binding assays, suggesting the utility of the ELISA method as part of the evaluation of disease activity over time. The advantages of the ELISA methodology-sensitivity, convenience, speed, independence of radioactivity, and quantitative determination of antibody as opposed to protein-should make this assay a useful tool in clinical and experimental studies on SLE as well as the routine assay of anti-nDNA antibodies.