TNF and chronic obstructive pulmonary disease: In addition to IFN-γ, other major cytokines expressed in COPD are IL-1, IL-8 (also known as CXCL8), leukotriene B4, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-α (TNF-α) (Kim and Rhee, 2010; Athanazio, 2012).