Interleukin 13 (IL-13), also known as ALRH, is a single-chain, glycosylated polypeptide and a cytokine that is critical in regulating inflammatory and immune responses (1). It is produced primarily by activated Th2 cells, as well as mast cells and NK cells (1). The functions of IL-13 overlap considerably with those of IL-4 but these effects are probably less important given the more potent role of IL-4 (2). IL-13 exerts its effects through a multi-subunit receptor comprising the alpha chain of the IL-4 receptor (IL-4Rα), and at least one of two known IL-13-specific binding chains (IL13 Rα1 and IL13 Rα2). Most of the biological effects of IL-13, like those of IL-4, are linked to signal transducer and activator of transcription 6 (STAT6) (2). Although IL-13 is associated primarily with the induction of airway disease, it also has anti-inflammatory properties. It exerts these anti-inflammatory effects on monocytes and macrophages, and 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 (3). Blocking of IL-13 activity inhibits the pathophysiology of asthma (4). Targeted deletion of IL-13 in mice results in impaired Th2 cell development and indicates an important role for IL-13 in the expulsion of gastrointestinal parasites (5). In addition, studies have identified IL-13 expression as a common feature of cHL (classical Hodgkin lymphoma) (6). Human and murine IL-13 are cross-species reactive.

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