Antinuclear antibodies (ANA) are considered as a key serological feature of systemic autoimmune rheumatic diseases (SARD) which include syndromes like systemic lupus erythematodes (SLE), systemic sclerosis (SSc), mixed connective tissue disease (MCTD), Sjögren's syndrome (SS) or dermatomyositis/polymyositis (DM/PM). ANA, commonly detected by indirect immunofluorescence assays on HEp-2 cells (IF-ANA), recommended as the screening test of choice (ACR), comprise a plethora of antibody specificities, a part of which are important serological markers of the diagnostic armamentarium in SARD. However, the applicability of IF-ANA as global screening test is hampered by its limited diagnostic specificity for resulting positive in up to 20% of apparently healthy individuals. About half of IF-ANA in healthy individuals target the chromosome associated protein DFS70/LEDGF, which tethers transcriptional coactivators or lentiviral integrases to transcriptionally active chromatin moieties and induces pro-survival stress factor transcriptions. Because of their rare prevalence in SARD patients, isolated anti-DFS70 antibodies are being increasingly considered as important biomarker to exclude the diagnosis of SARD.
Scrutinizing the relevant articles cited in NCBI concerning the DFS70/LEDGF protein, the diverse methods of anti-DFS70 determination in human sera supplemented by own experiences and critical review of the complete literature relevant to anti-DFS70 and SARD.
Antibodies to DFS70/LEDGF (anti-DFS70), disclosed by IF-ANA, are characterized by a dense fine speckled (DFS) nucleoplasmic fluorescence pattern (DFS-ANA) accompanied by a striking staining of the condensed chromosomes in mitotic cells. By means of various methods anti-DFS70 may be found in 7.8 ± 6.2% (MD 7.6%) of apparently healthy individuals, may sometimes display rather high antibody titers and antibody carriers do not seem to manifest SARD symptoms within a five year interval. Their prevalence in non-selected cohorts originating from routine IF-ANA screenings (38643 tested individuals) fluctuates between 0.8 and 8.4% (MD 1.7%), depending on patient selection criteria and test performance. The proper appreciation of these data is hampered partially because of missing verification of antibody specificities partially by lack of specifications of associated disease or accompanying SARD specific marker antibodies. A metaanalysis of five studies including 1243 SARD patients confirms the rare mean prevalence of solitary anti-DFS70 (0.7 ± 0.9%, MD 0.45%) in SARD patients. The mean prevalence of anti-DFS70 accompanied by SARD specific markers is 3.8 ± 2.9% (MD 2.9%). In patients exclusively harbouring anti-DFS70 the likelihood ratio (LR+) for the absence of SARD approaches a significant value of 10.9.
Since anti-DFS70 according to the available data may being regarded as a possible biomarker for ruling out the diagnosis of a systemic autoimmune rheumatic disease, it seems to be indispensable to identify properly DFS-ANA patterns in the routine IF-ANA screening, to confirm the anti-DFS70 specificity by appropriate confirmation assays and to communicate the results with annotating comments to the clinician, in order to ameliorate the proper assessment of the pathological significance of serological results and the selection of adequate follow-up investigations.