IFNG and chronic obstructive pulmonary disease: For all subjects combined (COPD patients and controls), IL-1β, IL-1RA, IL-2, IL-4, IL-6, IL-8, IL-17A, G-CSF, IFN-γ, IP-10, MIP-1α, MIP-1β and TNF-α were significantly correlated with sputum neutrophil percentage (Table 5).