TIMP-1 is crucial to the balance of increased MMP-9 activity, and cigarette smoke exposure among smokers without COPD could be implicated in the activation of several pro-inflammatory signally pathways, including oxidative stress, pro-inflammatory cells, and alveolar macrophages, which results in the activation of several proteases, especially MMP-9. Here, MMP9 is linked to chronic obstructive pulmonary disease.