DNA-mobility shift assay and the detection of anti-DNA IgG in systemic lupus erythematosus patients

Although the presence of antibodies against double-stranded (ds) DNA is highly specific of systemic lupus erythematosus (SLE), it is not detected in all SLE patients, perhaps due to a lack of sensitivity of the tests routinely used to assay anti-(ds) DNA. Looking for an alternative assay, this study explored the applicability of a DNA-mobility shift assay for the detection of anti-(ds) DNA; furthermore, the study compared the use of Salmonella typhimurium DNA with that of calf thymus DNA in the assay. After electrophoresis, samples containing S. typhimurium DNA and IgG from SLE sera showed marked alterations in DNA electrophoretic mobility when compared to DNA alone. In our sampling, SLE patients who tested negative for anti-(ds) DNA antibodies with routinely used assays such as Crithidia luciliae immunofluorescence test, radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA), tested positive for anti-(ds) DNA with the DNA mobility shift assay using S. typhimurium DNA. Incubation with IgG from control sera in the same proportions as above did not affect S. typhimurium DNA electrophoretic mobility. When S. typhimurium DNA was replaced by calf thymus DNA, the effect on the DNA mobility was less pronounced and less reliable. These results indicated that a DNA-mobility shift assay would be a useful alternative for the unequivocal detection of abnormal titers of anti-(ds) DNA antibodies. Furthermore, data indicated a greater ability of the IgG from SLE patients to form complexes with S. typhimurium DNA than with calf thymus DNA, suggesting an alternative testing DNA which may lead to a more sensitive anti-(ds) DNA detection.