IL17A and periodontitis: Previous studies found that MMPs, IL-1 and TNF are regulated by IL-17 in periodontitis [30], and found that IL-17 receptor deficiency results in impaired expression of IL-1 and MMP-3/MMP-9/MMP-13 in rheumatoid arthritis [31], indicating that IL-17 also plays an important role in the regulation of MMPs.