Neutrophils in activate state produce several proteinases and oxidative enzymes which can degrade extracellular matrix components.27 In this study, we observed high expression of MMP-8 and neutrophil elastase (NE) in P + COPD group in both mRNA and protein level, while no significant expression in COPD group although there was a large number of neutrophils in the lung (Supplementary Fig. 3c and Fig. 3e). Here, ELANE is linked to chronic obstructive pulmonary disease.