Interleukin-4 Receptor, also known as IL-4RA and CD124, is a transmembrane glycoprotein belonging to the class I receptor family. It is highly expressed by activated T-cells. IL-4RA couples with ? chain to form the type I receptor for IL-4. The extracellular domain of IL-4RA binds to IL-4 and antagonizes its activity. IL-4RA plays an important role in Th2 cell differentiation, Ig class switching and alternative macrophage activation. It has also been implicated in allergic inflammation, tumor progression and atherogenesis.