Studies on autoantibodies to deoxyribonucleic acid and deoxyribonucleoprotein with enzyme-immunoassay (ELISA)

Simple, rapid, quantitative, and reproducible ELISA procedures were developed for the determination of antibodies to DNA and NP in human sera. The results are reported in International Units per milliliter, based on the WHO reference preparation of anti-nuclear factor serum. The results of both tests are significantly correlated with anti-dsDNA values obtained by an RIA (Farr technic) and by the Crithidia luciliae IF assay. The anti-DNA and anti-NP ELISA test results were more frequently positive in SLE sera than were screening tests for anti-dsDNA by the Crithidia procedure or anti-NP detection by a latex agglutination test. Parallel tests in 284 sera from patients for anti-DNA and anti-NP by ELISA showed a significant correlation between the two antibody values. However, 17% of the specimens were positive for antibodies to one antigen but not the other, whereas other specimens showed a strong predominance of one antibody over the other. Absorption studies confirmed the differing antibody specificities measured by the two assays. The ELISA anti-DNA results were inhibited by native DNA, NP, and denatured DNA in increasing order of efficiency. In contrast, the antibodies against NP were strongly inhibited by NP but only very slightly by dsDNA or denatured DNA. Other antigens, including histones, ribonucleic acid, extractable nuclear antigens, and aggregated human IgG, inhibited only slightly or not at all in either assay.