Yan Jiang et al. have reported that PM2.5 induced airway inflammation, compromised lung function, emphysematous lesions, and deleterious airway remodeling in chronic obstructive pulmonary disease (COPD) through inducing the M2 polarization of AMs and upregulating transforming growth factor-β, matrix metallopeptidase (MMP)-9, and MMP-12 [19]. The gene discussed is MMP12; the disease is chronic obstructive pulmonary disease.