IL17A and periodontitis: In the presence of periodontitis, the severity of COPD disease was much greater, the proportion of γδ T/IL17+ γδ T/IFN γ+ γδ T cells in COPD lung tissue was significantly up-regulated, and the contents of IL 17 and IFN γ were also significantly increased (Fig. 3; Fig. S1 and S2).