Left-handed "Z" DNA antibodies in rheumatoid arthritis and systemic lupus erythematosus.

A solid phase radioimmunoassay was used to evaluate antibodies to 13 nucleic acid antigens for their ability to distinguish between systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and control sera. The antigens included 5 synthetic duplex DNA, several single-stranded nucleic acids and 2 left-handed "Z" DNA. Many of the 45 SLE patients' sera showed distinctive patterns of binding to the various antigens, but this could not be correlated with disease type or activity. In general, the duplex DNA antigens gave the best sensitivity and specificity for the detection of SLE but the antigen poly(dA) may be superior. Antibodies to "Z" DNA were found in some SLE patients but surprisingly, the binding was significantly higher in the RA group than in the SLE group. This is the first nucleic acid antigen to show more specificity for RA than for SLE.