IL17A and periodontitis: Activated by IL-1β, IL-6, and IL-23, TH17 cells produce IL-17 family cytokines including IL-17A, which is demonstrated to be the primary mediator of immunopathology in the context of periodontitis and periodontitis-related systemic diseases (Moutsopoulos et al., 2012; Dutzan et al., 2018; Samuel et al., 2019), while IL-17E, another subtype of IL-17, may play an opposite role in the occurrence and development of periodontitis (Awang et al., 2014).