IL17A and rheumatoid arthritis: Previous studies found that IL-17A could regulate MMPs, IL-1 and TNF in periodontitis [17], and found that IL-17 receptor deficiency results in impaired expression of IL-1 and MMP3/MMP9/MMP13 in rheumatoid arthritis [18], indicating that IL-17A also plays an important role in the regulation of MMPs.