TLR4 and chronic obstructive pulmonary disease: IL-4 and IFN-γ were related with Th1/Th2 balance, IL-4 could act to promote lung-infiltrating monocytes differentiation into macrophages that produces MMP-12, resulting in the destruction of alveolar walls and emphysema development in COPD (Shibata et al., 2018), while IFN-γ synergistically enhanced TLR2 and TLR4 expressions and induced corticosteroid resistance in COPD patients (Southworth et al., 2012).