Roos et al., showed that numbers of IL-17A-, IL-17F-, IL-17RA-, and IL-17RC-expressing cells are increased in lung samples obtained from stable COPD patients with mast and T cells being the primary source of IL-17A in end-stage COPD and that the expression of IL-17A correlates with disease progression [96,97]. Here, IL17RA is linked to chronic obstructive pulmonary disease.