Matrix metalloproteinase 12 (MMP12) is a matrix metalloproteinase with elastolytic capacity [48] that is secreted by activated macrophages and has been implicated in emphysema pathogenesis in mouse models of COPD and asthma via several independent mechanisms including (i) degradation of the extracellular matrix, (ii) proteolytic inactivation of antiproteases such as α1-antitrypsin, and (iii) proteolytic activation of proinflammatory cytokines including TNFα [10, 21, 60]. Here, MMP12 is linked to asthma.