Cross-disease immunological comparison reveals shared systemic immune activation across the broader spondyloarthritis...

To perform cross-disease immunological comparison across the broader spondyloarthritis (SpA) spectrum and examine their association with disease activity. We analyzed 111 patients with active broader SpA spectrum (ankylosing spondylitis, inflammatory bowel disease-associated SpA, psoriatic arthritis, pustulotic arthro-osteitis, and chronic non-bacterial osteitis) and 24 age- and sex-matched healthy controls (HC). Serum IL-17A, IL-17F, TNFα, and Oncostatin M levels were higher in the broader SpA spectrum than in HC. These cytokines levels did not differ among the broader SpA spectrum. Activated Th17, activated Th1-17, classical and intermediate monocytes were increased in the broader SpA spectrum compared with HC. Although Kruskal-Wallis test showed differences among the spectrum for activated Th17, activated Th1-17, and classical monocytes, post hoc analyses did not identify a specific disease driving these differences. Intermediate monocytes positively correlated with CRP and MMP-3 levels. Circulating immune subsets remained unchanged following DMARDs treatment despite clinical improvement. Systemic immune alterations, including activation of IL-17 axis, elevated Oncostatin M, and expansion of intermediate monocytes, are broadly shared across the broader SpA spectrum. Although global differences among the spectrum were observed for some immune cell populations, post hoc analyses did not identify disease-specific enrichment.