Human Interleukin-13 (IL-13) is expressed by the IL13 gene located on the chromosome 5 and secreted by many cell types, especially T helper type 2 (Th2) cells. The high solution from of IL-13 reported to be a monomer with two internal disulfide bonds that contribute to a bundled four α-helix configuration. 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 exerts anti-inflammatory effects on monocytes and macrophages and it inhibits the expression of inflammatory cytokines such as IL-1beta, TNF-alpha, IL-6 and IL-8. IL-13 has also been shown to enhance B cell proliferation and to induce isotype switching resulting in increased production of IgE. Human, mouse and rat IL-3 share low homology, but have cross species activity.