IL-17E, also known as IL-25, shares the least structural homology with other IL-17 family members and is also functionally distinct from other IL-17 familiy members. IL-17E is primarily involved in type 2 immune response. IL-17E can induce Th2 cytokines, including IL-4, IL-5, IL-9 and IL-13, in multiple tissues. IL-17E can also inhibit pro-inflammatory Th1 and Th17 cytokine response. It has been well established that IL-17E plays an important role in allergy and asthma. Blocking IL-25 has been a therapeutic option. IL-25 is also required for protection against gastrointestinal helminth infections. IL-17E-deficient mice exihibit impaired Th2 immune response. Exclusion of helminth parasites was delayed in IL-17E-deficient mice. Recently, the potential neuroprotective effect of IL-17E is also being explored. IL-17E can regulate the development of autoimmune inflammation mediated by IL-17-prodcuing T cells. IL-17E-deficient mice are highly susceptible to experimential autoimmune encephalomyelitis. Interestingly, in vivo antitumor activity of IL-17E has also been reported.