MMP9 and chronic obstructive pulmonary disease: The expression of MMP-9 increased with COPD severity (GOLD II; mean 137 (range 17.7–301), GOLD III; 833 (50–5360) and GOLD IV; 1127 (88.6–8820) ng/mL with a significant increase observed in GOLD IV vs. GOLD II (p<0.05, Figure 2B).