IL-6 activates pathologic Th17 cell via STAT 3 phosphorylation in inflammatory joint of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease, which is characterized by inflammation of the axial skeleton and the peripheral arthritis. An increase in the number of Th17 cells in patients with AS has been reported. Although Th17 cells have been involved in the induction of inflammation, recent data suggest that not all Th17 cells are pathogenic, showing regulatory function of Th17 cell. Cells producing both interferon-gamma (IFN-γ) and interleukin (IL)-17 have been reported to be the main pathologic Th17 (pTh17) cells that induce inflammation at sites of joint. Emerging evidence demonstrated that IL-6 has a main role in regulating the balance between inflammatory and regulatory T cells. However, there is no direct study to assess pTh17 cell with IL-6 in AS. Therefore, we evaluated the effect of IL-6 on pTh17 cell activation, and it's mechanism, using ex vivo and mouse model of AS. As a result, we found that pTh17 cell is dependent on the cytokine milieu with IL-6. We confirmed pTh17 cells play a pathogenic role at sites of inflammation. As a mechanism, it was revealed that IL-6 induced STAT 3 phosphorylation contributes to the increased pTh17 responses in AS patients with peripheral arthritis. Though validation of our results is required, IL-6 inhibitor can be a promising treatment for inflammation in AS patients with peripheral arthritis.