Interleukin 13 (IL-13) is located on chromosome 5q31 and shares 30% homology and a similar structure to IL-4.IL-13 is secreted and produced by many cell types, particularly type 2 helper T cells (Th2). Similar to the closely related IL-4, IL-13 has multiple functions for immune cells. Although IL-13 is primarily associated with the induction of airway disease, it also has anti-inflammatory properties.IL-13 induces changes in hematopoietic cells, but these effects may be less important than those of IL-4.IL-13 specifically induces physiological changes in organs that host infections. It also induces many of the features of allergic lung disease, including airway hyperresponsiveness, cuprocyte proliferation, and mucus hypersecretion, all of which can lead to airway obstruction. In addition, IL-13 inhibits HIV-1 replication in primary culture-derived macrophages and may serve as a candidate cytokine for inhibiting HIV infection in monocytes and macrophages in vivo.