In conclusion, we have observed that IFN-γ production by CF PBMCs positively correlated with lung function, particularly in patients chronically infected with P. aeruginosa, while IL-17A levels tended to correlate negatively with lung function, with this trend becoming significant in patients chronically infected with P. aeruginosa. These results are in agreement with IFN-γ and IL-17A playing protective and detrimental roles, respectively, in CF. This evidence concerns the gene IL17A and cystic fibrosis.