Figure 4.

Th17/Treg imbalance during periodontitis. During periodontal health, there is a balance between the Th17- and Treg-pattern of the immune response, which determines the molecularly mediated cellular coupling between osteoclasts and osteoblasts and thus the consequent physiological process of bone remodeling. However, during periodontitis, there is a Th17/Treg imbalance that favors the Th17-pattern of immune response and leads to osteoclast/osteoblast uncoupling. Remarkably, this Th17/Treg imbalance provokes an increased differentiation and activation of osteoclast caused by the production of elevated levels of pro-osteoclastogenic mediators, such as receptor–activator of NF-κB ligand (RANKL), interleukin (IL)-17A, IL-17F, IL-21, IL-22, and tumor necrosis factor (TNF)-α, which finally lead to irreversible tooth-supporting alveolar bone loss.