Research progress on the role of T helper cells 17 and interleukin 17 in oral mucosal diseases

T helper 17 (Th17) cells are a new type of CD4⁺ T helper cell. They participate in the immune and inflammatory response by secreting specific interleukin-17 (IL-17). In oral mucosal diseases, oral lichen planus (OLP), recurrent aphthous ulcer (RAU) and Behcet′s disease (BD) are associated with Th17 cells and IL-17. There were 17 kinds of proteins in the saliva of patients with OLP that could upregulate the expression of Th17 cells and induce the secretion of IL-17. IL-17 can stimulate epithelial cells, endothelial cells and fibroblasts to produce a variety of cytokines, such as IL-6, IL-8, granulocyte macrophage colony-stimulating factor and cell adhesion molecule-1, leading to the production and aggravation of inflammation. Th17/Tc17 cell-targeted therapy can significantly improve the clinical symptoms of OLP patients′ mucosa and skin. IL-17 can stimulate oral keratinocytes through the IL-17RA or IL-17RE receptor and produce proinflammatory effects in RAU. Th17 cells in the peripheral blood of BD patients are significantly increased, while Treg cells are significantly decreased.