An improved ELISA for anti-native DNA by elimination of interference by anti-histone antibodies

We evaluated an enzyme-linked immunosorbent assay (ELISA) for antibodies to native DNA (nDNA) in which protamine was used to link DNA to polystyrene. Elevated anti-nDNA was largely restricted to patients with systemic lupus erythematosus (SLE), and within this group good correlation between ELISA and the ammonium sulfate assay was obtained. However, substantial background immunoglobulin binding to protamine coated wells was commonly observed, and it was necessary to subtract this activity from each anti-DNA determination. Many of the SLE sera also contained anti-histone antibodies, and this antibody activity showed significant correlation with the binding to protamine. In contrast, methylated bovine serum albumin (mBSA) did not bind anti-histone antibodies and provided a substrate for coupling nDNA to polystyrene. This modified ELISA allowed the quantitation of antibodies to native DNA without the simultaneous binding of anti-histone antibodies.