MMP9 and chronic obstructive pulmonary disease: In addition, the total number of macrophages in the airway lumen (Kuschner et al., 1996; Kaku et al., 2014) and in the BALF (Lacoste et al., 1993; Traves et al., 2002; Profita et al., 2010) is increased in smokers and COPD patients, likely playing a role in emphysema by releasing elastolytic enzymes such as MMP-9, elastase (MMP-12), and cathepsins (Russell et al., 2002).