IMMUNOLOGY
PAGE EXPIRES: June 2000
SYNONYM: Native double-stranded DNA
COMPONENT TESTS: none (single test)
SCHEDULE: Reference Lab turnaround time: 7 working days
SPECIMEN AND COLLECTION REQUIREMENTS:
CAUSES FOR REJECTION: Improperly labeled specimen; hemolysis, lipemia or turbidity
STORAGE AND SHIPPING: Maintain at 4° C
USES: Detect and monitor disease activity in Systemic Lupus Erythematosus (SLE)
NORMAL VALUES: Negative (titer < 1:10)
METHOD: Indirect immunofluorescence
DESCRIPTION AND COMMENTS:
Antibodies to DNA were initially detected in sera of patients with Systemic Lupus Erythematosus (SLE). However, DNA is a molecule with multiple epitopes and antibodies to DNA may include a heterogeneous group of immunoglobulins with a variety of specificities. The most common antibodies reactive with DNA are those directed against antigenic determinants found on single-stranded DNA. Detection of such antibodies provides little diagnostic specificity since they are found in a wide variety of autoimmune and connective tissue diseases. In contrast, antibodies reactive primarily or exclusively with native, double- stranded DNA (anti-nDNA) are found in up to 60% of patients with SLE, in almost all cases of lupus nephritis, and can be found in rheumatic diseases. Compared to the fluorescent antinuclear-antibody (ANA) test, which has a high degree of sensitivity but much lower specificity for SLE, the anti-nDNA test has a very high degree of specificity for SLE and therefore provides confirmation in patients for whom this diagnosis is clinically suspected.
A good source of native DNA is found within the hemoflagellate Crithidia luciliae. This organism contains a modified giant mitochondrion, the kinetoplast, which contains a large concentration of well characterized, double-stranded DNA in a stable, circular configuration. The test is positive for anti-nDNA antibody if there is an apple-green fluorescence concentrated in the kinetoplast of C. luciliae. Fluorescence of the kinetoplast and the nucleus is also a positive reaction.