ELN and Airway obstruction: An important example is chronic obstructive pulmonary disease (COPD), in which neutrophils colonize the airways and release high amounts of proteases including neutrophil elastase (NE) and matrix metalloproteinase, which then digest extracellular matrix proteins including collagen, elastin and fibronectin, thereby causing alveolar destruction, mucous secretion and airway obstruction [44,45].