IL17A and chronic obstructive pulmonary disease: In lung tissue from COPD subjects, a significant increase in IL-17A/F expression was observed at 6 h with 10% of CSE (IL-17A: 4.2 ± 0.8 fold increase; IL-17 F: 3.3 ± 0.8 fold increase, P < 0.05, Figure 1B).