IL17A and rheumatoid arthritis: Interestingly, we observed that (i) IL-26 is expressed in the sublining layer of synovium and in T cell-rich areas, (ii) that myeloid cells infiltrating RA joints are sensitive to IL-26, and (iii) that IL-26 in RA fluids is biologically active and in sufficient concentrations to induce the production of proinflammatory cytokines by monocytes and of IL-17A by memory T cells.