Determination of anti-DNA antibodies by a modified 125I-labelled DNA-binding test. Elimination of non-specific binding of DNA to non-immunoglobulin basic proteins by using an anionic detergent.

A modified 125I-labelled DNA-binding test was developed. By using an anionic detergent, 0-025% sodium dodecyl sulphate, the non-specific binding of DNA by basic proteins was completely eliminated, while the specific binding of DNA by anti-DNA antibodies was not interfered with. The level of DNA-binding activity in normal human sera was decreased in the modified DNA-binding test, while its sensitivity was similar to that of the Farr assay in presence of sera from SLE patients.