Among the CD4+ T-cell subsets, TH17 cells exclusively accumulated in the oral mucosa and draining lymph nodes during oral infection (Fig. 2a–c, Supplementary Fig. 2), consistent with high expression of TH17-related cytokines Il17a and Il6 in the oral mucosa of periodontitis-induced mice (Fig. 1d). This evidence concerns the gene IL6 and periodontitis.