CXCL9 and chronic obstructive pulmonary disease: CXCR3 binds to three distinct ELR negative ligands, CXCL9 (monokine induced by interferon γ (IFNγ); MIG), CXCL10 (interferon inducible protein of 10 kDa; IP10) and CXCL11 (interferon inducible T-cell α chemoattractant; ITAC) [10], all of which are elevated in the airways of patients with COPD [11] with CXCL10 being elevated in both sputum and serum during a viral exacerbation [12, 13] Although all three of these chemokines bind to the CXCR3 receptor, however CXCL11 has increased affinity and CXCL9 the least, implying a hierarchy of activity [9].