Interleukin 2 was initially identified as a T cell growth factor that is produced by T cells following activation by mitogens or antigens. IL-2 has since been found to also stimulate the growth and differentiation of B cells, natural killer (NK) cells, lymphocyte activated killer (LAK) cells, monocytes/macrophages and oligodendrocytes.The biological activity of IL-2 is mediated by the binding of IL-2 to cell surface receptor complexes. The functional high-affinity receptor that mediate IL‑2 signals is composed of three polypeptide chains, the IL-2 receptor alpha, beta and gamma subunits. IL-2 also signals via the intermediate affinity receptor complex of the beta and gamma subunits. In T cells, the beta and gamma subunits are shared with the IL-15 receptor complex. The gamma subunit of the IL-2 receptor complex has also been shown to be a subunit of the receptor complexes of IL-4, IL-7, IL-9 and IL-21.