Background

The IL-2 receptor is a multicomponent complex consisting of three subunits, α,β and γ, each of which is required for high affinity binding of IL-2. The α chainfunctions primarily in binding IL-2, whereas the β and γ chains contribute toIL-2 binding and are essential to IL-2-induced activation of signaling pathwaysleading to T cell growth. Both IL-4R and IL-7R were initially described as single chain, high-affinity ligand-binding cytokine receptors. However, it is nowwell established that the IL-2Rγ chain functions as a second subunit of thehigh affinity IL-4R and IL-7R receptors. Consequently, the originally describedsubunits of these latter receptors are now referred to as IL-4Rα and IL-7Rα,respectively, while the common subunit is referred to as γc. Although the common γ chain enhances ligand binding in these three cytokine receptors, ithas no capacity to bind these ligands on its own. There is evidence that theγc chain is also a subunit of IL-13R.