Periodontal tissue destruction in periodontitis is primarily caused by the immunoresponse and inflammation toward bacterial challenge. T helper(Th) cells are important for the cellular immunity of T cells. In particular, Th2 cells are important for the humoral immunity of B cells. Th1/Th2 is a pair of important effector T cells, which inhibit each other in function by the different cytokines they secrete and keep balance in normal conditions. Previous findings demonstrate that the different clinical manifestations of periodontitis at different periods are associated with Th1/Th2 imbalance. The early and stable period of periodontitis is dominated by Th1 immunoresponses, whereas the progressive period of the disease is dominated by Th2 immunoresponses. The recently found Th17 and regulatory T cell(Treg) are new T helper cell subsets. Th17 cells are associated with chronic periodontal inflammation and tissue destruction, whereas Tregcells are associated with the inhibition of inflammation. Similar to the case of Th1/Th2 balance pattern, Th17 and Tregare also closely related, and they balance each other both in terms of differentiation and functions. Th17/Tregand Th1/Th2 and their cytokines constitute a complicated cytokine network at the periodontal tissue. Their relationship with the progression and tissue destruction of periodontitis is currently undergoing extensive research.
