In line with the general concept that the pro-fibrotic function of activated ILC2s is driven by their capacity to release high amounts of type-2 cytokines (35, 42), it has recently been postulated that ILC2-derived IL-9 might support pulmonary inflammation in CF patients via activation of mast cells and subsequent release of TGF-β (14). Here, IL9 is linked to cystic fibrosis.