IL-25 (also known as IL-17E) is a member of the IL-17 family, which includes IL-17A, IL-17B, IL-17C, IL-17F, and IL-17A/F. The primary sequence homology differs between family members, with mouse IL-17A and IL-17F having the highest homology (49%), while mouse IL-17A and IL-25 have the lowest (28%). IL-25 induces gene expression of IL-4, IL-5, and IL-13 in multiple tissues, and this induction results in T helper 2?(TH2)-type immune responses; this is characterized by an increase in serum IgE levels, pathologic changes in the lungs and digestive tract with eosinophilic infiltrates, an increase in mucus production, epithelial cell hyperplasia, and overall amplified allergic inflammation. IL-25 shares the receptor IL-17RB with IL-17B, although it binds with much higher affinity than IL-17B.