IL-13 is an immunoregulatory cytokine produced primarily by activated Th2 cells, and also by mast cells and NK 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 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.Blocking of IL-13 activity inhibits the pathophysiology of asthma.Human and murine IL-13 is cross-species reactive.Recombinant rat IL-13 is a 12.3kD protein consisting of 113 amino acid residues.