IL17A and periodontitis: Th1 is involved in the developmental process of periodontitis, and osteoprotegerin ligands can be expressed in Th1 and then stimulate osteoclast differentiation[72]; the activated Th2 can secrete various cytokines, which in turn promote B cell activation and proliferation of B cells to mediate humoral immunity[73]; Th17 is an osteoclast T cell that exacerbates inflammation response by secreting the inflammatory factor IL-17.