MMP9 and periodontitis: In COPD BALF samples containing the periodontal pathogenic bacteria P. gingivalis, the levels of IL 17 and IFN γ and the gene expressions of IL 17, IFN γ, and M2 polarization associated genes, including ARG1, CD206, MMP9, MMP12, TGF β, IL 4, and IL10, were significantly upregulated (Fig. 6), indicating the important roles of IL 17 and IFN γ and M2 macrophages in periodontitis-aggravated COPD in the clinical samples.