MMP9 and chronic obstructive pulmonary disease: In contrast, there were no significant differences in the mean serum levels of MMP-9/TIMP1 and MMP-9/TIMP2 between the COPD patients and controls, except a significant difference between COPD patients and total controls in levels of MMP-9/TIMP1 complex (3146.8 pg/ml versus 2970.1 pg/ml, p = 0.04).