IL-13 is a 10kD unglycosylated protein, secreted mainly by activated T helper 2 cells. IL-13 binds to IL-4Rα in addition to IL-13Rα1 and IL-13Rα2. And the function of IL-13 partially overlaps with IL-4. Both IL-4 and IL-13 link to signal transducer and activator of transcription 6 (STAT6) through the receptor activation. IL-13 can induce B-cell proliferation and IgE classs switching. However, IL-13 is less competent in this function comparing with IL-4. Unlike IL-4, IL-13 does not play an important role in hematopoietic cell shift, such as native T helper 0 differentiation to T helper 2. IL-I3 signaling is significant in inducing physiological changes to non-immuno cells in parasitized organs. For example, IL-13 induces enhanced gut contractions and glycoprotein hypersecretion which lead to the detachment of helminthes from gut wall. Eggs produced by Schistosoma mansoni can be limited inside granulomas formed through IL-13 induced cell changes. To organisms resided inside cells, IL-13 seemed to inhibit the clearance from host cell through antagonizing Th1 responses. IL-13 is also associated with many features of the allergic airway diseases, including mucus hypersecretion, goblet metaplasia, chemokine induction and recruitment of effector cells. All of them contribute to airway obstruction. Polymorphisms in IL-13 gene have been found to link to increased eosinophil count, serum total IgE and high risk of asthma.