Increased synovial expression of IL-27 by IL-17 in rheumatoid arthritis

Interleukin (IL) 17 plays an important role in synovial inflammation and bone destruction in rheumatoid arthritis (RA), while IL-27 exerts a regulatory role in T cell-mediated immune responses. Our aim was to study the influence of IL-17 on IL-27 production in RA. Following injection of IL-17 in the knee joint of CIA mice, synovium was examined for IL-17 and IL-27 expression by western blot, real-time PCR, and immunohistochemistry. IL-17 and IL-27 levels were measured by ELISA in mouse bone marrow-derived dendritic cells (BM-DCs) and in synovial fluid (SF) macrophages from RA patients. IL-17 exacerbated disease progression in CIA mice. Histological analysis showed increased pannus formation associated with cartilage and bone erosion following injection with IL-17. The expression of IL-27 was increased in CIA mice. The expression of IL-17 and IL-27 was increased more in IL-17-injected CIA mice than in control mice. The majority of cells expressing IL-27 were co-localized with synovial macrophages. Increased expression of IL-27 by application of recombinant IL-17 was confirmed in CIA BM-DCs and in SF macrophages from RA patients. IL-17 enhanced expression of IL-27 in synovial macrophages from RA patients and CIA mice, indicating an interaction between IL-17 and IL-27 as an autoregulatory mechanism.