Patients without baseline antibody data or baseline data for any of the covariates used in the corresponding statistical models for each particular endpoint (SDAI and DAS28-hsCRP) and patients without both baseline and post-baseline radiographic data were excluded from statistical analysis. Statistical models Multivariable mixed-effect models for repeated measures (MMRM) [29] were used for the longitudinal analysis of Kynurenic acid treatment response (SDAI and DAS28-hsCRP). Disease Activity Index (SDAI) and Disease Activity Score for 28-joint count with serum high-sensitivity C-reactive protein (DAS28-hsCRP), and structural damage progression, assessed using CFB greater than the smallest detectable change in the van der Kynurenic acid Heijde-modified Total Sharp Score. The anti-CarbV and anti-MCV isotypes assessed were immunoglobulin (Ig) A, IgG, and IgM. Multivariable mixed-effect models for repeated steps (MMRMs) were used for the longitudinal analysis of treatment response, and multivariable logistic regression models were used for the analysis of structural damage progression at week 52. Results Analysis of the association between autoantibodies and treatment response showed that high titers of anti-CarbV (IgA and IgG) were associated with a greater clinical response as measured by SDAI and DAS28-hsCRP. Anti-CarbV IgA and IgG, but not IgM, exhibited an association after adjustment for other factors included in the MMRMs. High titers of anti-CarbV IgM were associated with a poor response to MTX monotherapy, whereas a nonsignificant pattern toward a better response to baricitinib and baricitinib plus MTX was observed. There was no association between anti-MCV antibodies and treatment response. High titers of anti-CarbV IgA were associated with a greater probability of radiographic progression, but no association between anti-MCV antibodies and radiographic progression was observed. Conclusions High titers of anti-CarbV IgA and IgG isotypes, but CFD1 not anti-MCV isotypes, may be useful prognostic biomarkers for identifying the likelihood of the response to treatment and structural damage progression in patients with RA. Keywords: Rheumatoid arthritis, Baricitinib, Autoantibodies, Anti-CarbV Introduction The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is known to be involved in the pathogenesis Kynurenic acid of the chronic inflammatory disease rheumatoid arthritis (RA) [1, 2]. Many proinflammatory cytokines signal through JAKs [2]; thus, JAK inhibitors represent an effective treatment option in patients with RA. There are four members of the JAK family: JAK1, JAK2, JAK3, and tyrosine kinase 2 (Tyk2) [1]; baricitinib is an oral selective inhibitor of JAK1 and JAK2, with less effect on JAK3 and Tyk2 [3, 4]. The efficacy and safety of baricitinib were established in four phase III, randomized, double-blind, multicenter studies in patients with active RA [5C8]; in these studies, baricitinib exhibited good clinical efficacy and clear inhibition of radiographic progression and was superior to methotrexate (MTX) and adalimumab with respect to treatment response [7, 8]. Baricitinib is currently approved in more than 65 countries worldwide, and over 100,000 patients with RA have been treated to date (Eli Lilly & Company, data on file). Autoantibodies are frequently involved in the pathogenesis of RA. The development of autoantibodies has been linked to a specific genetic background (the so-called shared epitope), and evidence Kynurenic acid also suggests they can be induced by environmental factors, such as smoking [9]. Often autoantibodies develop before the onset of RA symptoms and can serve as diagnostic markers [10, 11]. Patients with RA can generally be stratified into two subgroups (seropositive/seronegative) based on autoantibody prevalence, usually defined by the presence/absence of rheumatoid factor (RF) and/or anti-citrullinated protein antibody (ACPA) [12C14]; post-translational modification of proteins by citrullination has been linked to RA, and ACPA represents a highly specific marker for this disease [12, 13]. The targeted antigens of ACPA are altered autoantigens such as vimentin, alpha-enolase, and fibrinogen [12, 13, 15]. It has been reported that seropositive patients have a higher risk of severe and systemic disease than seronegative patients [16] and that these antibodies are also associated with certain comorbidities, such as coronary heart disease [17]. Therefore, treatment recommendations for seropositive patients with RA differ from those for seronegative patients, promoting earlier and more aggressive treatment [14]. Recently, an autoimmune response against other post-translational modifications, carbamylation (or homo-citrullination) and acetylation, has also been described in RA [18C21]. Of note, carbamylation has also been linked to environmental factors, such as exposure to cyanate through smoking, and to comorbidities, such as.