IL17A and periodontitis: Previous studies implicated that IL-17/IL23 pathway and TH17 cells play an important role in inflammation-related diseases [28], and several meta-analysis examined the relationship between IL-17A (rs2275913) and IL-17F (rs763780) gene polymorphisms and the risk of inflammatory diseases, including periodontitis, rheumatoid arthritis (RA), and inflammatory bowel disease, and all these documents demonstrate that IL-17 polymorphisms may increased the RA risk, but dependent with race and ethnic groups [29].