Interleukin 17E (IL-17E), also known as IL-25, is a cytokine that belongs to the IL-17 cytokine family and is secreted by type 2 helper T cells (Th2) and mast cells. It shares the sequence similarity with IL-17. This cytokine can induce NF-κB activation, and stimulate the production of IL-8. Both this cytokine and IL-17B are ligands for the cytokine receptor IL-17RB. Studies in mice suggested that this cytokine may be a proinflammatory cytokine favoring Th2-type immune response. IL-17E induces the production of other cytokines, including IL-4, IL-5 and IL-13 in multiple tissues, which stimulate the expansion of eosinophils. This cytokine is an important molecule controlling immunity of the gut and has been implicated in chronic inflammation associated with the gastrointestinal tract. IL-17E can kill some types of breast cancer cells.