MMP9 and chronic obstructive pulmonary disease: Active MMP-9 quantified using flourescein conjugated gelatin as a substrate also showed an increase in MMP-9 activity with COPD severity (GOLD II; mean 0.43 (range 0.21–0.81), GOLD III; 4.78 (0.21–30.4) and GOLD IV; 8.96 (0.17–27.4)×104 RFU, with a significant increase observed in GOLD IV vs. GOLD II (p<0.05, Figure 2C).