Two types of IL-4 receptor complexes have been described. The typeI IL-4 receptor complex is composed of a high-affinity IL-4-binding subunit (referred to as IL-4R or IL-4R alpha) and the common gamma chain that does not bind IL-4 by itself. The type II IL-4 receptor complex is composed of IL-4R and IL-13R alpha 1. Besides IL-4 signals, the type II IL-4 receptor complex can also transduce IL-13 signals. In the type II complex, IL-4R subunit binds only IL-4 and not IL-13. Similarly, the IL-13R alpha 1 subunit binds only IL-13 and not IL-4.