TNF and inflammatory response: Cigarette smoking is considered the major cause of COPD, which can induce oxidative stress, trigger pulmonary inflammation and immune dysregulation, followed by activating epithelial cells and macrophages, releasing inflammatory mediators such as tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6) and matrix metallo-peptidases (MMPs), and finally leading to inflammatory processes in airways, progressive airflow limitation and cell injury and apoptosis [8,9,10,11,12].