Interleukin 25 (IL25) is also known as Interleukin-17E (IL-17E), is a distinct member of the IL17 cytokine family comprised of at least six members sharing a conserved cysteine-knot structure but divergent at the N-terminus. IL-25 is secreted by type 2 helper T cells (Th2) and mast cells. IL25 can induce NF-κB activation, and stimulate the production of IL8. Both this cytokine and IL17B are ligands for the cytokine receptor IL17RB. IL-25 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-25 can kill some types of breast cancer cells.