The cell surface receptor for IL-4 is composed of two polypeptide proteins that span the plasma membranes. One of these proteins chains, the IL-4R, binds to IL-4 with high affinity. Binding of IL-4 to the IL-4R on the cell surface results in its association with a second protein. In the type I IL-4 receptor complex the associating chain is the common chain. In the type II IL-4 receptor complex it is the IL-13R chain. Over the last 8 years, much work has focused on understanding the discrete signal transduction pathways activated by the IL-4 receptor and the coordination of these individual pathways in the
regulation of a final biological outcome. Experiments focused on signaling pathways have delineated the mechanism by which IL-4 regulates cell growth, survival, and gene expression. Strategies to block binding of IL-4 to its receptor and to target specific
signaling pathways are being tested to treat diseases associated with IL-4 such as allergy.