Murine Interleukin-13 (IL-13) is expressed by the IL13 gene located on the chromosome 11 and secreted by many cell types, especially T helper type 2 (Th2) cells. Targeted deletion of IL-13 in mice resulted in impaired Th2 cell development and indicated an important role for IL-13 in the expulsion of gastrointestinal parasites. IL-13 has been implicated as a key factor in asthma, allergy, atopy and inflammatory response, establishing the protein as a valuable therapeutic target. Human, mouse and rat IL-3 share low homology, but have cross species activity.