Background:Previous study evidenced a cross-reactivity between Sars-Cov-2 antibodies and autoimmune tissue antigen involved in connective tissue diseases, as nuclear antigen (NA), extractable nuclear antigen (ENA), histone and collagen (1). No study has been published about the titer of Sars-Cov-2 antibodies in non-infected patients with autoimmune disease.Objectives:To evaluate the titer of SARS-CoV-2 antibodies in non-COVID-19 patients and compare it between systemic sclerosis (SSc) patients and healthy controls (HC).Methods:A total of 58 patients with SSc (who fulfilled ACR/EULAR 2013 SSc classification criteria) and 18 HC were enrolled. Sera of all participants were collected, and SARS-CoV-2 antibodies (IgG and IgM) were evaluated by means ELISA. In all participants swabs for SARS-CoV-2 by real-time reverse-transcriptase-polymerase-chain-reaction assay were reported negative. Demographic, clinical, and autoimmune serological characteristics of SSc patients were recorded. The normal distribution was assessed using the Shapiro–Wilk’s test. Exclusion criteria was previous or actual Sars-Cov-2 infection. Comparisons between study groups of patients were evaluated by the Student’s t-test or Mann – Whitney U-test as appropriate. The differences between categorial variables were assessed by Pearson chi-square or Fisher’s exact test, as opportune. Statistical significance was set at p ≤ 0.05.Results:We observed significant differences between SSc patients and HC in serum levels of Sars-Cov-2 antibodies (IgG: 1,4±2,1 AU/ml vs 0,36±0,19 AU/ml respectively (p=0,001); and IgM: 2,5±3,1 AU/ml vs 0,8±0,7 AU/ml (p=0,022)). In 5 SSc patients was found titer of Sars-Cov-2 antibodies (IgG) exceeding the cut-off, but the control of swabs for SARS-CoV-2 by real-time reverse-transcriptase-polymerase-chain-reaction assay were negative. No significative differences in Sars-Cov-2 autoantibodies titer were found in subgroup of SSc patients with or without ILD or PAH, limited or diffuse skin subset, and different autoantibodies profile. Furthermore, antibodies titer was not associated with different drugs (steroid, methotrexate, mofetil-mycophenolate and bosentan) in use.Conclusion:A cross mimicking between Sars-Cov-2 antibodies and antinuclear antibodies or anti ENA could be hypothesized. Further studies are necessary to unravel the reliability of Sars-Cov-2 antibodies detection in autoimmune disease.References:[1]Vojdani, A., Vojdani, E., & Kharrazian, D. (2021). Reaction of human monoclonal antibodies to SARS-CoV-2 proteins with tissue antigens: Implications for autoimmune diseases. Frontiers in Immunology, 11, 3679Disclosure of Interests:None declared
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