The extent of emphysema (% LAA −950) was significantly associated with sputum MMP-9 protein concentration [r = 0.442 (0.171, 0.634), p = 0.020,)] (Figure 1) and MMP-9 activity [r = 0.447 (0.219, 0.643), p = 0.010]. Here, MMP9 is linked to pulmonary emphysema.