This group of cells is found in the blood, spleen, intestines, liver, skin, fat-associated lymphoid clusters, and lymph nodes and is enriched in inflamed skin, nasal polyps, and lungs (data unpublished).1, 2, 4 Several previous studies have identified the innate epithelial cytokines IL-33, IL-25, and TSLP and the lipid mediator PGD2 as important stimulators for ILC2s.5, 7 Although cysLTs have been investigated in mice,8 in the current study we examined the previously unrecognized roles of cysLTs in human ILC2 activation. This evidence concerns the gene TSLP and Nasal polyposis.