IL17A and periodontitis: While clinical studies have noted elevated IL-17 levels in in GCF, saliva, and serum of periodontitis patients (Azman et al., 2014; Ohyama et al., 2009; Okui et al., 2012; Takahashi et al., 2005), other studies (Ay et al., 2012; Johannsen et al., 2015; Özçaka, Nalbantsoy & Buduneli, 2011; Vahabi, Yadegari & Pournaghi, 2020) observed lowered salivary IL-17 in periodontitis patient than control.