Complement activation by antibodies to DNA in systemic lupus erythematosus measured by enzyme immunoassay.

An enzyme immunoassay to detect complement-fixing antibodies to DNA (CF-antiDNA) was developed. Of SLE sera, 64% had these antibodies as did 6% of 50 rheumatoid arthritis and 3.2% of 93 normal human sera. The mean CF-antiDNA level was higher in the sera of SLE patients with renal disease than those SLE patients who had no renal disease (P less than 0.0001), and higher in those SLE patients with active rather than inactive renal disease (P = 0.006). CF-antiDNA was more closely associated with renal activity than total IgG-antiDNA or CH50. These observations suggest that both the quality and quantity of anti-DNA antibodies play a role in the pathogenesis of renal disease, and that modern enzyme immunoassays help distinguish the relative importance of complement-fixing antibodies to anti-DNA from that of total anti-DNA.

Enzyme immunoassay for antibodies to native DNA. Specificity and quality of antibodies.

An enzyme immunoassay was developed to detect antibodies to native DNA; DNA coating conditions that maximized sensitivity, specificity, and reproducibility were selected. Sera of patients with systemic lupus erythematosus (SLE) were positive more frequently by this immunoassay than by the Crithidia luciliae assay or by counterimmunoelectrophoresis. By enzyme immunoassay, 94% of sera with active SLE and 70% of sera from patients with inactive SLE were positive, as were 16% from those suspected of having SLE, and 2.5% of normal persons. Specificity for native DNA was shown for both SLE and normal sera by inhibition studies and by S1 nuclease treatment of polystyrene-bound native DNA. The enzyme immunoassay correlated more with serum hemolytic complement levels that did the other 2 assays, suggesting that it detects biologically more relevant anti-DNA antibodies than do the other 2 tests.