Interleukin 2 was discovered through its function as a T cell growth factor (TCGF). IL-2 binds to IL-2 receptor which is expressed in T and B cells, thymocytes, and NK cells. The IL-2 receptor comprises three distinct components: the α-chain, which is cytokine specific, and the β- and γc-subunits which are share with the IL-15 receptor. In addition, the γc-subunit is a component of a series of other cytokine receptors, these being members of the γc cytokine receptor family (IL-4, IL-7, IL-9, and IL-21) (3). IL-2 signaling may play a major role in the differentiation of regulatory T cells (4). IL-2, IL-15, and IL-7 can all support NK cell differentiation; nevertheless, analyses of IL-2(-/-), IL-2Rα(-/-) mice fail to exhibit significant defects in NK cell development. This data suggest that IL-2 might have a redundant role in NK cell differentiation (4).