Immunofluorescent technique for the detection of antibodies to n-DNA: comparison with radioimmunoassay.

One hundred and six sera from patients with systemic lupus erythematosus (SLE), 20 from patients without SLE but with a positive FANA, and 50 controls were tested for the presence of antibodies to n-DNA, using an immunofluorescent technique with the kinetoplast of Crithidia luciliae as a substrate. A high degree of correlation existed between the results obtained with this technique and a Millipore radioimmunoassay method using a well characterized tritiated native human DNA. The result with the immunofluorescent method could be expressed semiquantitatively as a titer, if serial serum dilutions were used. Results in patients with SLE correlated well with disease activity. We conclude that the immunofluorescent technique can provide a useful alternative to a radioimmunoassay for the detection of antibodies to n-DNA. In addition, as this substrate is known to contain pure n-DNA, problems do not arise with contamination with singlestranded DNA as sometimes occurs with other test antigens. This avoids the detection of antibodies reacting only with single-stranded areas and consequently increased the specificity of the reaction.