Antibodies to Double-stranded DNA: A Comparison of the Indirect Immunofluorescent Test Using Crithidia luciliae and the DNA-binding Assay

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Abstract
Deegan, Michael J., Walker, Sara Ellen, and Lovell, Sharon E.: Antibodies to double-stranded DNA. A comparison of the indirect immunofluorescent test using Crithidia luciliae and the DNA-binding assay. Am J Clin Pathol 69: 599–604, 1978. A new indirect immunofluorescent test for detecting antidouble-stranded DNA (dsDNA) antibodies was evaluated and the results compared with those of the DNA-binding test (modified Farr assay). The substrate, Crithidia luciliae (CL), is a nonpathogenic trypanosome containing a kinetoplast of dsDNA. The test was performed with fluorescein-conjugated polyvalent (anti-IgG, -IgA and -IgM) and monospecific anti-immunoglobulin antisera. Sera from 57 patients (75 specimens) with systemic lupus erythematosus (SLE), 30 patients with rheumatoid arthritis, 31 patients with scleroderma, 59 patients with other rheumatic diseases and 31 normal individuals were studied. Thirty-three of the 51 SLE sera with positive DNA-binding tests (binding > 20%) also had positive CL tests. The 18 CL-negative, DNA-binding-positive sera had DNA-binding values between 20 and 45%. AntidsDNA were usually IgG, often accompanied by IgM and occasionally IgA antibodies. Sera of eight patients who had conditions other than SLE were CL-positive, DNA-binding-negative. The CL test is a simple and reproducible method for detecting anti-dsDNA antibodies, but in its present form is not as sensitive as the DNA-binding test.