Increased IL-22-and IL-17A-Producing Mucosal-Associated Invariant T Cells in the Peripheral Blood of Patients With Ankylosing Spondylitis

The IL-23/T helper 17 (Th17) axis plays an important role in joint inflammation in ankylosing spondylitis (AS). Conventional CD4(+) Th17 cells are a major source of IL-17A. IL-22 is another cytokine implicated in AS pathophysiology and is produced by Th17 and Th22 cells. In this study, we aimed to analyze conventional and non-conventional T cell subsets producing IL-17A and IL-22 in patients with AS. We thus evaluated the intracellular staining for IL-17A, IL-22, and IFN-gamma in peripheral blood mononuclear cells of 36 patients with AS and 55 age-and sex-matched healthy controls (HC). Conventional CD4(+) and CD8(+) T cells, gamma delta T cells, and mucosal-associated invariant T (MAIT) cells were evaluated. In patients with AS, we found a decreased frequency and number of gamma delta T cells, of MAIT cells and of IFN-gamma(+) CD4(+) and CD8+ T cells. Th17-related IL-17A(+)/IFN-gamma(-) CD4(+) T cells were decreased in AS. The number of IL-22(+) MAIT cells was higher in AS compared with HC, as well as the number of IFN-gamma(+)/IL-17A(+) MAIT cells. The number of IFN-gamma(-)/IL-17A(+) MAIT cells was higher only in female patients with AS compared with female HC. The cellular source of IL-17A was thus not restricted to conventional Th17 CD4(+) T cells and might involve innate-like T cells, such as MAIT cells. Circulating MAIT cells producing IL-22 were increased in AS. These results strengthen the importance of innate and innate-like sources of IL-17A and/or IL-22.