Interleukin-2 (IL-2) is a T cell stimulatory cytokine best known for inducing T cell proliferation and NK cell proliferation and activation. IL-2 also promotes peripheral development of regulatory T cells (Tregs). Conversely, IL-2 is involved in the activation-induced cell death (AICD) that is observed post T cell expansion by increasing levels of Fas on CD4+ T cells. The effects of IL-2 are mediated through a trimeric receptor complex consisting of IL-2R?, IL-2R?, and the common gamma chain, ?c. IL-2R? binds exclusively to IL-2 with low affinity and increases the binding affinity of the whole receptor complex including IL-2R? and ?c subunits. IL-15 also binds to IL-2R?. ?c is used by other cytokines including IL-4, IL-7, IL-9, IL-15, and IL-21. Binding of IL-2 initiates signaling cascades involving Jak1, Jak3, Stat5, and the PI3K/Akt pathways.