[The Crithidia Luciliae Immunofluorescence Test for Detection of Antibodies to Double-stranded DNA (author's Transl)]

For measurement of antibodies of double-stranded DNA (ds DNA) the Crithidia luciliae immunofluorescence test (C1-IFT) was compared with the Farr precipitation technique in diagnosis and management of systemic lupus erythematosus (SLE). The C1-IFT proved to be less sensitive in SLE patients without clinical disease activity, but the sensitivity of the test in those with active disease was comparable to that of the Farr test. In 76.9% of the patients' sera identical test results were obtained by both assays. In some sera antibodies were detected only by the C1-IFT. Positive test results in patients with diseases other than SLE were found more often with the Farr test. Thus, The C1-IFT seemed to be more specific for diagnosis of SLE. Measurement of titers using the C1-IFT provides a simple method to survey SL E disease activity. It allows to analyze the immunoglobulin classes of the reacting antibodies and their complement fixation ability in vitro. All three major immunoglobulin classes (IgG, IgM, IgA) were found to be present in the sera with high antibody titers, complement fixation in the C1-IFT could predominantly be detected is sera with high antibody titers.