MMP-9 expression and activation levels have been shown to be elevated in lower airway secretions and/or serum of smokers and patients with chronic obstructive pulmonary disorder (COPD), emphysema, idiopathic pulmonary fibrosis (IPF), acute respiratory distress syndrome (ARDS), cystic fibrosis (CF), and asthma after allergen challenge [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Here, MMP9 is linked to pulmonary emphysema.