An immunofluorescence assay for double-stranded DNA antibodies using the Crithidia luciliae kinetoplast as a double-stranded DNA substrate.

Circulating antibodies to dsDNA are found predominately in SLE and are seen most often in those patients with active systemic disease, particularly severe lupus glomerulonephritis. An IIF technique for measuring these antibodies has recently been described. This uncomplicated assay employs the kinetoplast of the nonpathogenic hemoflagellate Crithidia lucilliae as a dsDNA substrate. We herein report our experience with this assay, emphasizing the methodology and interpretation of results. Although slightly less sensitive than a radioimmunoassay, we find that this IF technique is a specific and reliable qualitative method for detecting anti-dsDNA. An estimate of the amount of DNA antibody present can be obtained by serum titration. The test was positive in only two patient groups tested, SLE (48%) and MCTD (20%).