IL17F and chronic obstructive pulmonary disease: In the submucosa, both IL-17A and IL-17F positive cells were observed (Figure 1A), and the absolute number of cells expressing both of these cytokines was higher in COPD subjects than in control subjects (IL-17A+: 199 (70-310) vs. 49 (0-150); IL-17F+: 287 (195-501) vs. 67 (0-203); P < 0.0001) (Figure 1C).