SAT0024 Il-36 axis is an emerging therapeutic target in psoriatic arthritis synovial tissue
Authors: M.-A. Boutet, A. Nerviani, G. Lliso-Ribera, K. Goldmann, M. Lewis, C. Pitzalis
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> The IL-36 family of cytokines includes three agonists, IL-36α, IL-36β and IL-36γ, and two established or hypothetical antagonists, respectively IL-36Ra and IL-38. IL-36 agonists are pro-inflammatory cytokines highly expressed in skin and involved in the pathogenesis of psoriasis. A recent study demonstrated that only a subset of patients with rheumatoid arthritis (RA) had an elevated IL-36 agonists/antagonists ratio within the synovium and could potentially respond to IL-36 inhibition strategies but little is known about the expression and biologic functions of the IL-36 axis in synovial tissue of psoriatic arthritis (PsA) so far hardly been studied. <h3>Objectives</h3> In this study, we aimed to comparatively investigate the expression and role of IL-36 cytokines in synovial tissue of early RA and PsA patients. <h3>Methods</h3> Synovial tissue samples were collected from patients with early RA and PsA (disease duration &lt;12 months) DMARDs (Disease Modifying Anti-Rheumatic Drugs) and steroids-naïve. All patients underwent an ultrasound-guided synovial biopsy before starting the treatment; the procedure was repeated following six months of treatment with conventional DMARDs. The expression of IL-36 family members was investigated in synovial tissue at gene level by RNA-Sequencing (87 RA, 15 PsA), at protein level by immunohistochemistry (IHC) and immunofluorescence (IF) (20 RA, 26 PsA) and in plasma by ELISA (22 RA, 38 PsA). RA and PsA-fibroblasts-like-synoviocytes (FLS) and peripheral blood mononuclear cells (PBMCs) were treated <i>in vitro</i> to assess their response to IL-36 stimulation. <h3>Results</h3> Gene and protein expression of IL-36 agonists was comparable between RA and PsA synovial tissue; conversely, the antagonists IL-36Ra and IL-38 were significantly lower in PsA compared to RA. Accordingly, the agonists/antagonists ratio was considerably higher in PsA synovium, suggesting an activation of the IL36 pro-inflammatory pathway. Among the immune cells infiltrating the PsA synovium, macrophages (CD68+), T lymphocytes (CD3+) and plasma cells (CD138+) were the primary IL36α-expressing cells. At baseline, the synovial expression of IL-36α was significantly higher in PsA patients who did not respond to DMARDs treatment at 12 months; this differential synovial expression of IL-36α between responders and non-responders was also maintained at six months. In keeping with this observation, we showed that treatment with methotrexate or sulfasalazine did not reduce the expression of IL-36 in PsA cells <i>in vitro</i>. Finally, we observed that PsA-FLS and PsA-PBMCs produced significantly higher levels of IL-8 upon stimulation with IL-36α in comparison with cells isolated from RA patients. <h3>Conclusions</h3> The expression of the anti-inflammatory IL-36 cytokines antagonists are differently regulated in early RA and PsA, being significantly lower in the latter. Moreover, the pro-inflammatory IL-36α is up-regulated in synovial tissue of PsA non-responders to conventional DMARDs. The impaired balance between agonists and antagonists might contribute to the persistent inflammation characterising the diseased tissue. The exogenous replacement of the IL-36 antagonists may be a novel promising therapeutic target for PsA patients. <h3>Disclosure of Interest</h3> None declared