ANTI-DNA ANTIBODIES

CLINICAL UTILITY:

Antibodies form against native, or double stranded (ds) DNA in patients with systemic lupus erythematosus (SLE), but not in other rheumatic diseases. The titer of the antibodies is helpful in monitoring treatment of SLE. High titers usually are associated with acute flares of naturally occurring SLE, especially in association with diffuse proliferative lupus nephritis. Titers often decrease with successful treatment.

The antibodies may play a significant role in the pathogenesis of the disease. Deposition of DNA-anti-DNA immune complexes in the kidney and other tissues is thought to be responsible for clinical manifestations of SLE.

METHOD DESCRIPTION:

The two methods used for detecting anti-dsDNA antibodies are the radioimmunoassay DNA-Binding test, and an indirect immunofluorescence screening test, using the protozoa Crithidia luciliae as substrate. In the DNA-binding test (Farr assay), the patient’s serum is incubated with 125-I-labeled dsDNA. The immunoglobulin fraction is precipitated with ammonium sulfate, and radiolabeled DNA bound to DNA antibodies appears in the precipitate. The amount of anti-DNA antibody present is expressed as the percent of radioactivity in the precipitate.

In the Crithidia screen, anti-dsDNA antibodies in the patient’s serum attach to the substrate, a non-pathogenic hemoflagellate, Crithidia luciliae, on a microscope slide. Crithidia possess a kinetoplast in which is concentrated a large network of dsDNA. Antibodies to dsDNA are detected by fluorescence of the kinetoplast. Occasionally false positive Crithidia tests may occur due to the presence of antibodies to histone.

REFERENCE RANGE:

Anti-DNA Binding: <20% Binding is Normal. Crithidia screen: Negative

SPECIMEN REQUIREMENTS:

Anti-DNA Binding: 0.5 ml serum, frozen. Crithidia screen: 0.5 ml serum, frozen.