Laboratory screening of anti-nuclear antibodies (ANAs) by indirect immunofluorescence method (IIF) is often positive in patients without proven autoimmune pathologies. The most frequent pattern, which is detected is a « dense fine speckled » (DFS) pattern (AC-2), characterized by the fine-granular fluorescence of the nuclei in the chromatin interphase and metaphase, and could occur in 2-22% of healthy individuals, infection, cancer and inflammatory conditions. However, there is still need for information about its clinical significance. This study aimed to investigate the performance of available routine screening methods for detection of ANAs and anti-DFS70 antibodies, and the clinical significance of anti-DFS70 autoantibodies using remaining patient samples, which were sent to laboratory for ANA detection.
Material and Methods:
31 serum samples routinely requested for ANAs screening were analyzed using IIF on HEp-2 cell substrates (Euroimmun, Germany). The semi-quantitative determination of the anti-histone autoantibodies in the patient's serum was carried out using an enzyme immunoassay (Euroimmun, Germany). For detecting autoantibodies against dsDNA, U1RNP, Sm, Ro/SSA, La/SSB, Scl-70, Pm-scl, Jo-1 and CENP a quantitative fluorescence enzyme immunoassay for extractable nuclear antigen screen was performed (Thermo Fisher Scientific, Germany). Immunoblot (Euroimmun, Germany) enabled the detection of 14 autoantibodies against EJ, Jo1, Ku, MDA5, Mi-2α, Mi-2β, NXP2, OJ, PL-7, PL-12, PMScl100, PMScl75, Ro-52, SAE1, SRP and TIF1γ. The quantitative in-vitro measurement of antibodies of the IgG class against DFS70 in serum was performed using a quantitative fluorescence enzyme immunoassay (Thermo Fisher Scientific, Germany). Demographic and clinical data were analyzed from the medical records.
Among the 31 samples, which were tested for ANA, 20 (64.5%) were ANA positive by IIF. The frequency of AC-2 immunofluorescence pattern by ANA-IIF was 16.2% (5/31), of these only four samples contained antibodies against DFS70 in serum. No significant differences were observed between anti-DFS70 positive and anti-DFS70 negative patients concerning age, gender, symptoms, clinical signs or other disease-specific antibodies. 75% of the patients with positive DFS70 antibody was without proven autoimmune pathologies. However, of the four anti-DFS70 positive patients, only one patient had accompanying autoantibodies (anti-histone and anti-dsDNA).
Autoantibodies against DFS70 are less prevalent in patients with proven autoimmune pathologies. Monospecific anti-DFS70 antibodies are significant in excluding ANA-associated rheumatic disease in patients presented with an AC-2 pattern. It has been observed that anti-DFS70 autoantibodies may be associated with non-ANA-associated rheumatic diseases and in many diseases related to other systems. Therefore, it is essential to evaluate these pathologies in patients positive for anti-DFS70 antibodies.