In a study comparing COPD patients exposed to woodsmoke and tobacco smoke with controls for matrix metalloproteinase (MMP) activity and expression, researchers found significant increases in MMP-2 and MMP-9 in both exposed groups and concluded that such increased activity from wood smoke exposure could produce lung damage similar to COPD associated with tobacco smoke (Montaño et al. 2004). Here, MMP9 is linked to chronic obstructive pulmonary disease.