Interleukin 2 (IL-2), a potent lymphoid cell growth factor, is a typical four α-helix bundle cytokine. IL-2 is produced by activated T cells, especially the CD4
+ T helper cell population. It plays an important role in both the activation and maintenance of immune responses and in lymphocyte development. IL-2 promotes proliferation and differentiation of T cells, NK cells, and B cells and is involved in the elimination of self-reactive T cells. IL-2 signals through a receptor complex consisting of IL-2 receptor α-chain (CD25), β- and common γ-chain. The latter two are also involved in IL-15 signaling.
