In rats: a ligature-induced (Lig) periodontitis model and Aβ25-35-induced model of Alzheimer’s disease (AD) were established; tumor necrosis factor-α (TNF-α), interleukin 1 (IL-1), interleukin 6 (IL-6), and C-reactive protein levels in the hippocampus and cerebral cortex were detected. The gene discussed is IL6; the disease is periodontitis.