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Melis L.,Laboratory for Molecular Immunology and Inflammation | Van Praet L.,Laboratory for Molecular Immunology and Inflammation | Van Praet L.,Ghent University | Pircher H.,Institute of Medical Microbiology and Hygiene | And 3 more authors.
Annals of the Rheumatic Diseases

Objectives: Killer cell lectin-like receptor G1 (KLRG1) is an NK cell marker also expressed on T cells showing an immunosenescent phenotype. KLRG1 binding to its ligand E-cadherin inhibits functional responses. It was recently shown that soluble E-cadherin (sE-cadherin) also influences KLRG1 signalling, although its involvement in arthritis is unknown. Our goal was to evaluate the contribution of KLRG1+ T cells to synovitis. Methods: Paired peripheral blood (PB) and synovial fluid (SF) mononuclear cells from 21 patients with spondyloarthritis (SpA) or rheumatoid arthritis (RA), eight with crystal-induced arthritis and 10 controls were obtained. T cells were characterised for KLRG1 expression directly ex vivo, while TNF-α/IFN- γ production was assessed after polyclonal stimulation. Assays of chemotaxis response towards SF were conducted. Additionally, sE-cadherin levels in our paired samples were determined. Moreover, TNF-α/IFN-γ production by antigen-specific T cells was evaluated in the presence of sE-cadherin. Results: KLRG1+ T cells were enriched in SF as opposed to PB of SpA and RA patients, which contrasts with results obtained in crystal-induced arthritides. KLRG1+ T cells were more functionally active as opposed to KLRG1- T cells and migrated preferentially towards SpA and RA SF. sE-cadherin levels were higher in SF versus plasma. The presence of sE-cadherin enhanced the number of KLRG1+ CD4+ T cells able to produce TNF-α but not IFN-γ. Conclusions: sE-cadherin contributes to the local proinflammatory environment in the joint by favouring TNF-α production by KLRG1+ CD4+ T cells. This pathway seems to be operational in both SpA and RA, but not in crystal-induced arthritis. Source

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