TNF and chronic obstructive pulmonary disease: In the initial immune response of COPD, cigarette smoke and other irritants stimulate the airway epithelial cells and alveolar macrophages to secrete pro-inflammatory cytokines/chemokines such as tumor necrosis factor (TNF)-α, IL-1β, IL-6, CXCL8, and granulocyte macrophage colony-stimulating factor (GM-CSF), which recruit and activate IL-17A-secreting helper T (TH17) cells [23].