[Studies on anti-DNA antibodies associated with renal involvement by enzyme-linked immunosorbent assay in patients with systemic lupus erythematosus].

It has been reported that a significantly higher incidence of lupus nephritis was found in patients with high avidity anti-DNA antibodies. Radioimmunoassay (Farr's assay) is a method which enables to detect high avidity anti-DNA antibodies, whereas enzyme-linked immunosorbent assay (ELISA) can detect anti-DNA antibodies from low to high avidity. There are, however some patients who had high levels of anti-DNA antibodies by Farr's assay without renal involvement. In this study, ELISA was developed to detect IgG anti-DNA antibodies highly associated with lupus nephritis by changing salt concentration of reaction buffer solution. Levels of a fraction, we call [0.1 M - 0.3 M] fraction, which was obtained from the antibody levels measured under 0.1 molar of sodium chloride (NaCl) subtracted by antibodies levels under 0.3 molar of NaCl solution were found to be significantly higher in patients with urinary protein (p = 0.0074) and low serum complement (C 3 less than 50 mg/dl; p = 0.0026, C 4 less than 10 mg/dl; p = 0.0280 and CH 50 less than 30 U/mL; p = 0.0662). Among the patients with hypocomplementemia, levels of [0.1 M - 0.3 M] fraction were significantly higher in patients with urinary protein than in patients without renal involvement. This fraction might be consistent with anti-DNA antibodies with intermediate avidity that are related to lupus nephritis. The ELISA procedure established in this study is showed to be a available method to detect anti-DNA antibodies associated with renal disease in patients with systemic lupus erythematosus.