IL17A and periodontitis: found a Th17/Treg imbalance in patients with chronic periodontitis, in which the Th17 ratio was upregulated and the Treg ratio was downregulated, and the expression level of the pro-inflammatory factor IL-17 was significantly increased while the expression of the anti-inflammatory factor IL-10 was decreased, and this imbalance ultimately led to the resorption of alveolar bone (Zheng et al., 2019).