At the initial stage of periodontitis, antigen‐presenting cells, such as macrophages and dendritic cells at the inflammatory site would activate naive T cells, and pro‐inflammatory T cells (Th1 and Th17) further secrete pro‐inflammatory cytokines (IFN‐γ, TNF‐α, IL‐17) to deteriorate the inflammatory response.[43] The polarization and proliferation of these cells may also be involved in the treatment of periodontitis. The gene discussed is IL17A; the disease is periodontitis.