IL26 and rheumatoid arthritis: Th1, Th17, and natural killer (NK) cells represent cellular sources of IL-26, with recent studies showing that IL-26 is also produced in various other cell types, including alveolar macrophages [7], fibroblast-like synoviocytes (FLSs), and macrophage-like synoviocytes in patients with RA [8] and myofibroblasts in patients with spondyloarthritis [9].