Since the polarization of AMs plays a significant role in the progression of COPD, fine particulate matter, with aerodynamic diameter ≤ 2.5 μm (PM2.5) stimulated the high expression of IL-4 in mouse BALF, which a key inducer of M2 polarization, acting on the IL-4R on the surface of AM cells, inducing downstream STAT6 phosphorylation and nuclear translocation, binding to the Matrix Metalloproteinase -12 (MMP12) promoter region and promoting the expression of MMP12, causing excessive degradation of extracellular matrix (ECM), which is related to the destruction of lung tissue in COPD (42). The gene discussed is MMP12; the disease is chronic obstructive pulmonary disease.