Anti-DFS70 antibodies detected by immunoblot methods: A reliable tool to confirm the dense fine speckles ANA pattern.

Background: Autoantibodies to the DFS70 (dense fine speckles 70) protein have been identified among the antinuclear antibodies (ANA) in patients with various disorders. However, the ANA test in indirect immunofluorescence (IIF) is not a reliable method to identify anti-DFS70 antibodies. We undertook this study to evaluate the diagnostic performance of two new immunoblot methods for the detection of anti-DFS70 antibodies and to investigate whether their different DFS70 antigen composition could affect diagnostic accuracy in detecting anti-DFS70 antibodies.

Methods: 62 samples showing a DFS70 staining pattern by IIF were tested by dot blot (Alphadia) and line blot (Euroimmun) methods. The dot blot method employs a truncated sequence of the DFS70 antigen (residues 349-435), while the line blot uses the full-length protein (aa 1-530). The 62 samples were previously assayed by a chemoluminescent (CLIA) method also using a truncated antigen (aa 349-435): 27 were CLIA positive and 35 were CLIA negative. 120 sera from subjects with infectious diseases were used as controls.

Result: Both immunoblot methods were positive in the 27 IIF/CLIA positive samples; in addition, the Alphadia dot blot identified another seven DFS70 samples and the Euroimmun line blot was positive in five samples that were negative by CLIA. Among the 120 control samples, two false positives were recorded for the CLIA method, six for the Alphadia method and four for the Euroimmun method. Therefore, in this selected series of samples, sensitivity and specificity were 43.5% and 98.3% for the CLIA method, 54.8% and 95% for the dot blot and 51.6% and 96.6% for the line blot, respectively.

Conclusions: Because of great inconsistency in assessing the DFS70 pattern using the ANA-IIF test, specific assays should be used to confirm anti-DFS70 antibodies. The results of this study show that there is no difference in the overall diagnostic accuracy among methods that use the truncated or the full-length DFS70 antigenic sequence and that it is likely that antibodies directed against antigens other than DFS70 may be responsible for producing a DFS70-like ANA-IIF pattern.