Mouse Interleukin 33 (IL-33) is a proinflammatory cytokine which may also regulates gene transcription inproducer cells. IL-33 is structurally related to IL-1, which induces helper T cells to produce type 2 cytokines andacts through the receptor IL1RL-1. BindingIL-33 to this receptor activates NF-kappa-B and MAP kinases andinduces in vitro Th2 cells to produce cytokines. In vivo, IL-33 induces the expression of IL-4, IL-5, IL-13 and alsoleads to severe pathological changes in mucosal organs.