BACKGROUND: Interleukin 40 (IL-40) is a cytokine implicated in malignancies and rheumatic disorders. Its association with fibrotic mediators has been previously described. Since inflammation and fibrosis are hallmarks of systemic sclerosis (SSc), we aimed to analyze the role of IL-40 in SSc. METHODS: IL-40 levels were analyzed in the serum of 90 SSc patients and 75 healthy controls (HCs). IL-40 expression in dermal biopsies from 5 SSc patients and 5 HCs was assessed via immunohistochemistry. IL-40 was analyzed in 39 SSc patients with interstitial lung disease treated with cyclophosphamide (CPA) and in 24 SSc patients with active progressive disease treated with rituximab (RTX). SSc activity was assessed by the European Scleroderma Study Group (ESSG) index. The effect of recombinant IL-40 on peripheral blood mononuclear cells (PBMCs) from 10 SSc patients was determined in vitro. IL-40 was analyzed in 24 individuals at risk of developing SSc (VEDOSS), who were categorized as progressors (n = 11) and nonprogressors (n = 13). RESULTS: IL-40 expression was elevated in the skin of SSc patients compared to HCs, particularly in fibroblasts and immune infiltrates. Serum IL-40 was increased in SSc compared to HCs (p < 0.0001) and was associated with ESSG (r = 0.372, p = 0.0005) and gastrointestinal involvement (p < 0.05). IL-40 correlated with serum IL-8 (r = 0.270, p = 0.019) and TGF-β1 (r = 0.301, p = 0.024) levels. In the CPA and RTX cohort, no significant changes in the serum IL-40 were observed upon treatment. Baseline and changes in IL-40 levels were associated with changes in several clinical parameters. IL-40 was elevated in patients at risk of SSc compared to HCs (p = 0.0003). No significant changes were observed in progressors vs. nonprogressors; however, IL-40 was associated with capillaroscopy findings (p < 0.05). IL-40 induced the upregulation of IL-6 (p = 0.002), MCP-1 (p = 0.002) and IL-10 (p = 0.002) in PBMCs from SSc patients in vitro. CONCLUSIONS: IL-40 was upregulated in the skin and serum of SSc patients and was associated with disease activity, gastrointestinal involvement and fibrotic mediators. Our in vitro findings indicate that IL-40 might be involved in the immune response and fibrotic processes in SSc.

• Keywords
• Biomarkers, Interleukin 40, Systemic sclerosis,
• MeSH
• Adult MeSH
• Fibrosis MeSH
• Gastrointestinal Diseases * blood   immunology   MeSH
• Immunohistochemistry MeSH
• Skin pathology   metabolism   MeSH
• Leukocytes, Mononuclear metabolism   drug effects   immunology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Aged MeSH
• Scleroderma, Systemic * blood   immunology   pathology   MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH

INTRODUCTION: IL-40 is a novel cytokine associated with autoimmune connective tissue disorders such as rheumatoid arthritis (RA) or Sjögren syndrome. We have previously shown an accumulation of IL-40 in the RA joint and its expression by immune cells and fibroblasts. Therefore, we aimed to assess the role of IL-40 in association with hyaline cartilage and chondrocyte activity. METHODS: Immunohistochemistry was employed to detect IL-40 in paired samples of loaded and unloaded regions of osteoarthritis (OA) cartilage (n=5). Synovial fluid IL-40 was analysed by ELISA in OA (n=31) and control individuals after knee injury (n=34). The impact of IL-40 on chondrocytes was tested in vitro. RESULTS: IL-40 was found in chondrocytes of the superficial zone of the OA cartilage, both in loaded and unloaded explants. Additionally, only biopsies from loaded explants showed significant IL-40 positivity in transitional zone chondrocytes. Levels of IL-40 were significantly elevated in the synovial fluid from OA patients compared to controls (p<0.0009) and correlated with synovial fluid leukocyte counts in OA (r=0.444, p=0.014). Chondrocytes exposed to IL-40 dose dependently increased in the secretion of pro-inflammatory cytokines IL-6 (p<0.0001) and IL-8 (p=0.004). Moreover, a dose dependent up-regulation of matrix degrading metalloproteinases MMP-1 (p=0.004), MMP-3 (p=0.031) and MMP-13 (p=0.0002) upon IL-40 treatment was observed in contrast to untreated chondrocytes. CONCLUSION: This study is the first to demonstrate the accumulation of IL-40 in OA cartilage and its up-regulation in the synovial fluid of OA patients compared to controls. In addition, extracellular IL-40 appears to play a role in promoting inflammation and cartilage destruction by driving chondrocyte behaviour towards a more aggressive phenotype.

• Keywords
• Cartilage, Chondrocytes, Interleukin 40, Osteoarthritis,
• MeSH
• Chondrocytes * metabolism   pathology   MeSH
• Adult MeSH
• Enzyme-Linked Immunosorbent Assay MeSH
• Phenotype MeSH
• Immunohistochemistry MeSH
• Interleukins * metabolism   MeSH
• Cartilage, Articular metabolism   pathology   MeSH
• Cells, Cultured MeSH
• Middle Aged MeSH
• Humans MeSH
• Osteoarthritis * metabolism   pathology   MeSH
• Aged MeSH
• Synovial Fluid * metabolism   MeSH
• Up-Regulation MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• C17orf99 protein, human MeSH Browser
• Interleukins * MeSH