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. Primary sequence homology differs between family members, with hIL-17 and hIL-17F having the highest homology (44%), while hIL-17 and hIL-25 have the lowest (15%). IL-25 induces elevated gene expression of IL-4, IL-5 and IL-13 in multiple tissues and results in T helper 2(TH2)-type immune responses (increased serum IgE levels) and pathologic changes in the lungs and digestive tract with eosinophilic infiltrates, increased 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.