Interleukin-13 (IL-13) is a Th2-type cytokine, secreted from CD4(+) T cells, mast cells, basophils and eosinophils. The human IL-13 gene locates at 5q31, generating a cluster with other Th2-type cytokines such as IL-4 and IL-5. Although the homology between IL-13 and IL-4 at the amino acid level is only about 25%, the IL-13 structure determined by NMR is very similar to that of IL-4. Both cytokines share their receptors and signal pathways, giving these two cytokines similar biological properties. However, the important role of IL-13 in the pathogenesis of bronchial asthma has recently been recognized, based mainly on analyses of mouse models. IL-13 and its signal pathway are thought to be promising targets to develop a therapeutic reagent for bronchial asthma. In this article, we summarize the signal transduction pathway of IL-13, the pathological roles of IL-13 in bronchial asthma and the reagents to inhibit IL-13 signals that are now under development.
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