Compared to SH, CD4 + T cells were significantly activated by periodontitis microbiota, with the accumulation of IFNγ+ CD4 (p < 0.05), IL17+ CD4 (p < 0.05), and IL22+ CD4 (p < 0.05) T cells in the small intestine (Figures 2D–F). This evidence concerns the gene IL17A and periodontitis.