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Background: Myositis can be a clinical feature of several rheumatic diseases. In inflammatory idiopathic myopathies (IIM), such as Dermatomyositis (DM), Polymyositis (PM), Antisynthetase syndrome (ASS), muscular lesions are immune-mediated and may associate with skin, aesophagus, lung, heart and joint involvement. The role of myositis specific antibodies (MSA) and myositis associated antibodies (MAA) in determining the clinical phenotype is still unclear. Anti-dense fine speckled antibodies (anti-DFS70ab) show a low frequency in DM and are generally associated with DM-specific autoantibodies Objectives: to characterize antibodies in IIM and myositis related to other rheumatic diseases and to correlate them to clinical features, cancer history and anti-DFS70ab presence. Methods: 37 patients with myositis (including IIM, overlap syndrome and myositis related to other rheumatic diseases) were evaluated. Anti-DFS70ab pattern was determined by indirect immunofluorescence on HEp-2000 cells. Detection of anti-DFS70ab specificity (truncated sequence of the DFS70 antigen (residues 349-435)), of MSA (MDA-5, TIF 1-γ, SAE1, SAE2, NXP-2, Jo-1, PL-7, PL-12, EJ, OJ, KS, ZO, HA, SRP, Mi-2,), of MAA (U1-RNP, SSaRo52/60, PM-Scl100/75, Ku) and of other Scleroderma associated antibodies (Scl-70, CENP-A, CENP-B, RNA Polymerase III, Th/to, Fibrillarin) were performed using immunoblotting assay. Clinical, serological and instrumental data were recorded. Results: 15 patients had a diagnosis of DM, 8 of PM, 3 of ASS, 5 of overlap syndrome (3 with Systemic Sclerosis (SSc), 1 with Sjogren Syndrome (SS), 1 with cryoglobulinemia), 6 of myositis related to other rheumatic disease (1 SSc, 1 Rheumatoid Arthritis, 2 Undifferentiated Connective Tissue Disease, 2 Systemic Lupus Erithematosus). In IIM, overall frequencies of MSA and MAA were 46.1% (12/26) and 38.4% (10/26), respectively, with concomitant expression in 5/26 cases. The 30.7% (8/26) of patients was negative for any type of antibodies. Mi-2 (4/15=26.6%), NXP-2 (3/15=20%) and SRP (2/15=15.3%) were detected in DM subset and were associated with typical skin lesions, muscle weakness, dysphagia and microvascular damage on capillaroscopy, while no interstitial lung disease, cardiac and articular involvement were recorded. Jo-1 was positive in 5/26 patients (2 PM, 2 ASS, 1 DM=19.2%) characterized by interstitial lung disease, arthritis, skin involvement and muscle weakness and by pulmonary hypertension when associated with TIF1- γ (1 DM=6.6%). Autoantibodies profile in overlap syndrome and myositis related to other rheumatic diseases was characterized by prevalence of MAA, more frequently PM-Scl100/75, RNP, Ku, SSaRo52/60. Only in 1 patient with an overlap syndrome SSc/PM HMGCR reactivity was detected. As far as cancer association, a positive history was found in 8.1% (3/37), related more frequently to Jo-1 and SSaRo52. Anti-DFS70ab were positive in 2/26 patients with IIM (7.6%; 1 DM and 1 PM) and in 1 with SSaRo60. No cases of anti-DFS70ab positivity was found in other subsets. Conclusion: Prevalence of MSA and MAA and their clinical correlations in our population are comparable to data reported in literature. Mi-2, NXP-2 and SRP can be considered markers of DM, while Jo-1 a predictor of lung involvement. Jo1/SSaRo52 positivity is reported in association with lung cancer, but to our knowledge no data are present about melanoma. Our preliminary data confirm that, not only in DM but also in PM, anti-DFS70ab were observed with a low frequency; however more studies are needed to establish the pathogenetic role of these antibodies. Disclosure of Interests: carmela esposito: None declared, Teresa Carbone: None declared, Antonio Carriero: None declared, valentina picerno: None declared, Maria Carmela Padula: None declared, Angela Padula Speakers bureau: Lilly Italia EMS, vito pafundi: None declared, Salvatore D’Angelo: None declared

Background: anti-DFS70 antibodies (anti-DFS70ab) were recently described as biomarkers clinically useful to discriminate Systemic Autoimmune Rheumatic Diseases (SARD) from non-SARD patients, especially if no concomitant SARD-specific autoantibodies were found. Several unanswered questions concerning the biological significance of this autoantibodies still remain. Objectives: to evaluate the prevalence of anti-DFS70ab in Rheumatoid Arthritis (RA) and Spondyloarthritis (SpA) patients and the influence of anti-TNF therapy on their development. Methods: sera from adult RA (n= 100) and SpA (n= 105) patients, included psoriatic arthritis, fulfilling ACR/EULAR 2010 and ASAS 2011 criteria, respectively, were studied for anti-DFS70ab as measured by IIF, then confirmed by immunoblotting. Medical history, demographic and clinical data were collected at enrolment. Results: the prevalence of anti-DFS70ab was 4.00% (4/100) in the RA and 4.76% (5/105) in SpA cohort. All anti-DFS70ab in RA patients were monospecific, while only 1 sample in SpA showed concomitant anti-centromere positivity. The findings for the anti-DFS70ab positivity revealed no statistical differences between the groups (p>0.05). In RA cohort, there were no differences between anti-DFS70ab positive and negative patients regarding the F/M ratio (F/M, 3/1 vs 84/12, p>0.05), mean age (50.2±12.4 vs 55.6±11.7 yrs, p>0.05) and disease duration (18.2±15.2 vs 14.0±9.9 yrs, p>0.05). In SpA group, no significant differences were found between patients with and without anti-DFS70ab in F/M ratio (3/2 vs 43/57, p>0.05) and regarding disease duration (18.8±7.7 vs 19.0±20 yrs, p>0.05) while the mean age of anti-DFS70ab patients was significantly higher than the negatives (66.8±10.4 vs 53.5±15.0 yrs, p Conclusion: based on our findings, detection of anti-DFS70ab reactivity cannot completely exclude the suspicion of SARD, especially for RA and SpA. In addition, the rate of anti-DFS70ab positivity resulted higher in RA and SpA patients than previously observed in a cohort of samples from outpatients clinics (2.1%) [1]. Immunogenicity of anti-TNF therapy has been also addressed in this study, showing that all detected anti-DFS70ab were induced by anti-TNF therapy. Further studies are needed to support these preliminary data. References [1] Carbone T. et al. Prevalence and serological profile of anti-DFS70 positive subjects from a routine ANA cohort. Scientific Report. 2019, In press. Disclosure of Interests: Teresa Carbone: None declared, carmela esposito: None declared, ornella mercuro: None declared, Antonio Carriero: None declared, valentina picerno: None declared, Maria Carmela Padula: None declared, Angela Padula Speakers bureau: Lilly Italia EMS, vito pafundi: None declared, Salvatore D’Angelo: None declared