In periodontal lesions, Th17 cell-related cytokines (IL-17A, IL-6, IL-23, and IL-21) and osteoclastogenic mediators (RANKL) are significantly increased.44 Treg cells are an important subpopulation of immunosuppressive CD4 + T cells; they secrete anti-inflammatory cytokines (IL-10, IL-4, TGF-β) and downregulate RANKL expression, inhibiting alveolar bone resorption in periodontitis.45 Th17 cells and Treg cells have opposite immune regulation functions on bone metabolism. This evidence concerns the gene IL4 and periodontitis.