Detection of dsDNA antibodies in diagnosis of systemic lupus erythematosus--comparative studies of diagnostic effectiveness of 3 ELISA methods with different antigens and a Crithidia luciliae immunofluorescence test

Abstract

Antibodies to double-stranded DNA (anti-dsDNA, dsDNA-Ab) are frequently found in systemic lupus erythematosus (SLE), especially during active disease and differ with respect to immunoglobulin class and avidity. The detection of anti-dsDNA is one of the diagnostic criteria for SLE according to the American College of Rheumatology (ACR). Most of the commercial ELISA test systems have great advantages in routine laboratory testing but often detect dsDNA-Ab which are not specific for SLE and therefore give false positive results for non-SLE patients. The newly developed ELISA presented here, using human recombinant dsDNA (h-Rek) is compared to two commercial ELISA tests with genomic dsDNA from salmon testes (L-dsDNA) or plasmid dsDNA (P-dsDNA) and to the Chrithidia luciliae immunofluorescence test (CLIF) as well. In this study 143 sera were tested, 48 derived from patients with SLE, 40 from rheumatoid arthritis patients, 26 from non-rheumatoid patients whose sera were ANA-negative but L-dsDNA-Ab-positive and 30 from healthy volunteers. All patients were followed and clinically defined by the rheumatology outpatient clinic of our hospital. The prevalence for SLE of all sera was 32%. The sensitivity was 0.73 (h-Rek), 0.83 (L-dsDNA), 0.81 (P-dsDNA) and 0.57 (CLIF); specificity was determined 0.84 (h-Rek), 0.62 (L-dsDNA), 0.63 (P-dsDNA) and 0.98 (CLIF). The diagnostic efficiency of the L-dsDNA- and P-dsDNA-assay was identical, 0.69, and amounted to 0.81 for the h-Rek and 0.84 for the CLIF. Comparing all the ELISA tests and CLIF, the human recombinant dsDNA ELISA is much more sensitive than the CLIF, but considerably more specific than the ELISA assays using genomic or plasmid DNA, whereas the diagnostic efficiency is very close to that of the CLIF. This new generation of anti-dsDNA ELISA using human recombinant dsDNA seems to be a much better diagnostic tool for the detection of highly specific anti-dsDNA antibodies in the diagnosis of SLE than other commercial ELISAs. These results can only be explained by the use of a human recombinant antigen instead of undefined genomic or recombinant plasmid DNA for immobilization.