IL17A and periodontitis: found that P. gingivalis in periodontitis stimulates CD4+ T cell responses and increases the Th17/Treg ratio in the intestinal lamina propria, upregulates Th17-related transcription factor expression and production of the pro-inflammatory factors IL-17 and IL-6 through the TLR4 pathway, and downregulates the expression of the Treg transcription factor Foxp3 and production of the anti-inflammatory factors TGF-β and IL-10, thereby exacerbating intestinal inflammation (Jia et al., 2020).