IL17A and periodontitis: In addition, during the development of periodontitis, the expression levels of IFN-γ (linked to Th cell polarization toward the Th1 cells), IL-17A, IL-17F, IL-1β, IL-6, IL-23 (linked to Th cell polarization toward the Th17 cells), TNF-α, RANKL, glucocorticoid-induced TNFR-related gene (GITR), T-bet, and GATA-3 are all highly increased (92–94).