<qa>  What is a protease derived largely from neutrophils?Doxycycline is known to exhibit immune modulatory activities beyond its antibacterial effects. In particular, doxycycline is a potent inhibitor of matrix metalloproteinase 9, which is a protease derived largely from neutrophils. Recent studies demonstrate a significant correlation between pulmonary disease severity and sputum concentrations of MMP-9 in patients with CF. In addition, sputum MMP-9 levels are associated with airway remodeling in CF. 