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Background: In axial spondyloarthritis (axSpA), peripheral SpA (pSpA) and psoriatic arthritis (PsA), enthesitis is a hallmark clinical feature that can be assessed by the SPARCC index, LEI, MASES and MEI. These indices evaluate different locations, which may identify different numbers of patients with enthesitis among SpA subtypes. Thus, the aim of this study was to evaluate whether the proportion of patients with at least one enthesitis across these three most prevalent SpA subtypes differs according to the index used and to evaluate the level of agreement among indices in detecting patients with enthesitis., Methods: A total of 4185 patients (2719 axSpA, 433 pSpA and 1033 PsA) from the international and cross-sectional ASAS-PerSpA study were included. The proportion of patients with enthesitis identified by the indices was evaluated across the three diseases. Pairwise agreement between indices was computed using Cohen's kappa., Results: The prevalence rates of patients with at least one enthesitis according to the MEI, MASES, SPARCC index and LEI were 17.2%, 13.5%, 10.7%, and 8.3%, respectively. In axSpA, the indices that identified the most patients with enthesitis were the MEI and MASES (98.7% and 82.4%, respectively); in pSpA and PsA, the indices that identified the most patients with enthesitis were the MEI and SPARCC index (MEI: 100% and SPARCC: 84.6%; MEI: 97.3% and SPARCC: 77%, respectively). In the total population, the MASES vs. MEI showed the strongest agreement (absolute agreement 96.3%; kappa: 0.86); similar results were obtained in axSpA patients (97.3%; 0.90). In pSpA and PsA patients, the SPARCC vs. MEI (97.2%; 0.90 and 95.4%; 0.83, respectively) showed the strongest agreement., Conclusions: These results suggest that the prevalence of patients with enthesitis across SpA subtypes differs depending on the disease and the index used. The MEI and MASES appeared best for assessing enthesis in SpA and axSpA, while the MEI and SPARCC index appeared best for assessing enthesitis in pSpA and PsA., (© 2023. The Author(s).)

Background: Radiographic axial spondyloarthritis (r-axSpA) is a chronic inflammatory form of arthritis in which tumor necrosis factor (TNF)-α, a potent inducer of inflammatory response and a key regulator of innate immunity and of Th1 immune responses, plays a central role. NETosis is a mechanism of innate immune defense that is involved in diverse rheumatology diseases. Nevertheless, spontaneous NETosis generation in r-axSpA, its association to disease pathogenesis, and the NETosis involvement on anti-TNF-α therapy's effects has never been explored., Methods: Thirty r-axSpA patients and 32 healthy donors (HDs) were evaluated. Neutrophil extracellular trap (NET) formation, mediators of signal-transduction cascade required for NETosis induction and cell-free NETosis-derived products were quantified. An additional cohort of 15 r-axSpA patients treated with infliximab (IFX) for six months were further analyzed. In vitro studies were designed to assess the effects of IFX in NETosis generation and the inflammatory profile triggered., Results: Compared to HDs, neutrophils from r-axSpA patients displayed augmented spontaneous NET formation, elevated expression of NET-associated signaling components, nuclear peptidylarginine deiminase 4 translocation and increased citrullinated histone H3. Furthermore, patients exhibited altered circulating levels of cell-free NETosis-derived products (DNA, nucleosomes and elastase). Additional studies revealed that cell-free NETosis-derived products could be suitable biomarkers for distinguish r-axSpA patients from HDs. Correlation studies showed association between cell-free NETosis-derived products and clinical inflammatory parameters. Besides, nucleosomes displayed potential as a biomarker for discriminate patients according to disease activity. IFX therapy promoted a reduction in both NETosis generation and disease activity in r-axSpA patients. Mechanistic in vitro studies further unveiled the relevance of IFX in reducing NET release and normalizing the augmented inflammatory activities promoted by NETs in mononuclear cells., Conclusions: This study reveals that NETosis is enhanced in r-axSpA patients and identifies the NETosis-derived products as potential disease activity biomarkers. In addition, the data suggests the potential role of NET generation analysis for assessment of therapeutic effectiveness in r-axSpA.