CXCL9 and chronic obstructive pulmonary disease: A series of cytokines and chemokines modulate COPD, including IL-8, TNF-α, IFN-γ, TGF-β, CCL-2, CXCL1, CXCL9, CXCL10, and CXCL11; these are related to the changes typically observed in COPD [15].