Recent reports have shown that IL-17 is produced by mainly T helper (Th) 17 cells (Abe et al., 2012; Eskan et al., 2012; Gaffen & Hajishengallis, 2008; Takahashi et al., 2014) and interferon (IFN)-γ produced by Th1 cells (Teng, 2006) may play an important destructive role in periodontitis. This evidence concerns the gene IFNG and periodontitis.