IL4R and chronic obstructive pulmonary disease: 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).