In patients with periodontitis, lower levels of pro-inflammatory factors IFN-γ, IL-1β, IL-2, IL-6, IL-7, IL-21, TNF-αand higher levels of anti-inflammatory factors IL-4 and IL-5 in gingival crevicular fluid in the Sp group were identified than those in the Dp group. The gene discussed is IL21; the disease is periodontitis.