A double antibody solid phase assay for DNA autoantibodies for clinical use.

DNA antoantibodies in serum will bind to antigen-coated polystyrene tubes and can be detected by radiolabelled anti-immunoglobulin. The method is quantitative, gives information on the antibody class and is not readily subject to interference by factors such as the size of the DNA, minor contamination of double-stranded with single-stranded DNA and the presence of materials which can combine "non-specifically" with the antigen. Double-stranded DNA gave good discrimination between SLE and rheumatoid arthritis but with single-stranded preparations approximately 40% of the RA patients showed elevated antibody values. Individual results obtained with the two antigens were compared and correlated with the Farr test and ANA titres. Surprisingly, a proportion of the SLE sera gave high background binding to tubes coated with gelatine.