TNF and chronic obstructive pulmonary disease: Similarly, smoke exposure increased serum levels of IL-1β (p < 0.001), CXCL1 (p < 0.01), IL-17 (p < 0.001), and TNF-α (p < 0.001) in the COPD animals (Figures 2(e), 2(f), 2(g), and 2(h)).