Polymorphism in rs2069885 (c.350 C>T) in IL9 (5q31.1) has an opposite effect on the risk of severe respiratory syncytial virus infection in boys and girls (116), as well as on Aspergillus fumigatus-induced allergic lung inflammation estimated as IgE level and IL9/IL9R mRNA ratio in lung expectorates in males and females suffering by cystic fibrosis (117). Here, IL9 is linked to cystic fibrosis.