Background Antinuclear antibodies (ANA) positivity with a dense fine speckled (DFS) pattern by indirect immunofluorescence (IIF), as per the definition of the International Consensus on ANA Patterns (ICAP), is not uncommon and is linked to the presence of anti-DFS70 antibodies. These antibodies, in the absence of others, are very valuable as biomarkers of exclusion of a systemic autoimmune disease (SAD).

Objectives To evaluate anti-DFS70 antibody detection by two different laboratory techniques and its relation with different IIF patterns, including DFS pattern.

Methods During three months, the serum of patients with positive ANA was consecutively collected. Three groups of patients were established according to their IIF pattern: a first group (D) with a DFS pattern as per ICAP; a second group (M) with other speckled with positive mitosis patterns; and a third group (C), as a control, with well defined homgeneous and speckled patterns.

In order to perform a preliminary analysis, 10 serum samples were randomly selected from each group. In each serum sample, an ANA screening by IIF on Hep-2000 cells (Fluorescent IgG ANA-Ro Test System – Immunoconcepts) using an AP-16 Elite/Zenit-Up/GSight system from Menarini, and an anti-DFS70 antibodies detection by two different laboratory techniques (IIF on Hep-2 cells [Hep-2/DFS70 Knock-out - Immco Diagnostics] and inmunoblot [ANA+DFS70 Dot Blot – Alphadia]) were performed. Simultaneously, antibodies against extractable nuclear antigens (ENA), nucleosomes (NUS) and histones (HIS) were tested.

Results In group D, positivity for anti-DFS70 antibodies was confirmed in 7/10 cases, all of them being negative for other ANA. In group M, 2/10 serum samples were positive for anti-DFS70 and 2/10 were positive for anti- NUS antibodies, none of them being positive for anti-ENA. In group C, no sample was positive for anti-DFS70 antibodies, while all of them showed positivity for antibodies against ENA, NUS and HIS.

The detection of anti-DFS70 was found to be equal by the two methods in 8 of the 9 positive cases, being both negative in the others. In no case the presence of anti-DFS70 was associated with a diagnosis of SAD.

Conclusions Both IIF and immunoblot are suitable methods for detecting anti-DFS70 antibodies. We propose to determine anti-DFS70 and to perform an ENA screening in case of finding a DFS pattern of ANA by IIF, and to investigate anti-DFS70 in other speckled patterns with positive mitosis if no other specificities have been previously found.

Disclosure of Interest None declared