MMP9 and chronic obstructive pulmonary disease: The activation of peripheral and lung neutrophils causes the release of a number of mediators, including neutrophil elastase, MMP-9, IL-8, IL-1β and reactive oxygen species (ROS) that induce lung structural changes, including mucus secretion, bronchial smooth muscle hypertrophy and fibrosis in asthma and COPD, and emphysema in COPD, characterized by loss of respiratory bronchioles, alveolar ducts, and alveoli7 contributing to bronchial obstruction and irreversibility.