DsDNA autoantibodies

This autoantibody is associated with systemic lupus erythematosus (SLE) in which it is found in 50% of cases. Though less sensitive it is a more specific test than antinuclear factor, since it is seldom positive in other conditions (1).

It is associated with more severe disease, vasculitis and nephritis in SLE. The HLA-markers associated with SLE and anti-dsDNA are HLA-DR2 and HLA-DQB1.

Antiantibodies to double-stranded DNA (dsDNA) have also been reported as a consequence of medications such as minocycline and tumour necrosis factor-alpha inhibitors - thus their significance should be made in the context of the full clinical picture (2).

Laboratories may mention the Crithidia luciliae test (see notes for details)

• this haemoflagellate has giant mitochondria containing dsDNA (but not single-stranded DNA (ssDNA) - this lends itself to detection of dsDNA antibodies by immunofluorescence

Autoantibodies to ssDNA

• found in many connective tissue disorders and other conditions - are of little diagnostic use due to their lack of specificity (2)

Notes:

• dsDNA antibodies are excellent indicators of SLE disease activity and their elevated levels usually precede exacerbation of disease (sometimes by more than a year) (3)
  • anti-dsDNA levels rise during flares of SLE disease activity, especially in lupus nephritis (3)
• laboratory methods for detecting anti-dsDNA
  • anti-dsDNA antibodies are generally detected and quantified by commercially available kits for enzyme-linked immunosorbant assay (ELISA, also automated versions), Crithidia luciliae immunofluorescence assay (CLIFT), and radioimmunoassay methods developed according to Farr technique
    • different combinations of these methods are used in diagnostic laboratories worldwide, without a consensus on exclusive methods
    • an important cause of discrepancies between results obtained with different methods lies in the avidity of antibodies
      • ELISAs detect antibodies of both low and high avidity, whereas CLIFT and FARR-RIA assays predominantly detect antibodies of high avidity
  • for the diagnosis of SLE, it is crucial that the anti-dsDNA assay is highly specific for dsDNA, especially since elevated levels of anti-dsDNA antibodies can also be detected in other autoimmune diseases, as well as in blood donors, very much depending on the detection method used
    • FARR-RIA has the highest specificity for anti-dsDNA antibodies detection but a low sensitivity (3)
    • CLIFT detects both high and low avidity anti-dsDNA antibodies and may be used as a primary screen (3)
      • retesting of positive samples with FARR-RIA not only confirms the diagnosis but also provides the quantitative data allowing the monitoring of disease activity
    • problem with anti-dsDNA ELISAs is that they often give false-positive results due to binding of immune complexes (with negatively charged moieties) to the pre-coat intermediates
    • antibodies against single-stranded DNA only recognize single-stranded DNA and are specifically directed against purine and pyrimidine bases
      • observed not only in patients with SLE but also in other connective tissue diseases, such as systemic sclerosis and myositis

Reference:

• (1) Mills JA. Systemic lupus erythematosus. NEJM 1994; 330 (6):1871-1899.
• (2) Sherley-Dale A. Serum autoantibodies and connective tissue disorders. Dermatology in Practice (April 2008); 16(1).
• (3) Zigon P et al. Comparison and evaluation of different methodologies and tests for detection of anti-dsDNA antibodies on 889 Slovenian patients' and blood donors' sera. Croat Med J. 2011 Dec 15;52(6):694-702.