IL17F and chronic obstructive pulmonary disease: Similarly there was greater number of cells positive for both IL-17A and IL-17F in COPD subjects compared to controls (IL-17A: 8 (6-14) % vs. 3 (0-7) %, P < 0.0001; IL-17F: 10 (4-28) % vs. 4 (0-14) %, P < 0.0001) (Figure 2B).