Evaluation of 125I-DNA for detecting anti-DNA antibodies in the diagnosis of systemic lupus erythematosus.

A 125I-DNA preparation for the detection of human anti-DNA antibodies (ADA) was evaluated as a diagnostic test for systemic lupus erythematosus (SLE). A normal range of 0-25 U/ml was established. Serum ADA level greater than 110 U/ml were diagnostic in clinically active SLE and levels greater than 45 U/ml were found in 75% of patients with inactive disease. This value was significantly greater than that found in rheumatoid arthritis, renal disease caused by non-immune mechanisms, post-streptococcal glomerulonephritis and a miscellaneous group of disorders comprising connective tissue diseases, auto-immune disorders and chronic active hepatitis. Anti-nuclear factor (ANF) titres greater than 1/160 and LE cells were found in 85% of these patients. In inactive disease the ADA levels ranged between 25 and 98 U/ml, ANF titres varied from 1/40 to 1/640, and LE cells were detected in only 20% of the cases. In 3 patients investigated during the course of the disease, the ADA levels correlated best with clinical improvement. Two patients with apparent active lupus nephritis showed intermediate ADA levels, which were probably caused by antigen-antibody formation and immune complex deposition in the kidneys.