Interleukin 2 (IL 2), also termed T-cell growth factor, is a member of the cytokine family which includes IL-4, IL-7, IL-9, IL-15 and IL-21. Each member of this family has a four alpha helix bundle. IL-2 signals through the IL-2 receptor, a complex consisting of tree subunits, termed alpha, beta and gamma. The IL-2 R gamma is shared by cytokine receptors of all members of cytokine family. Mature mouse IL2 shares 56% and 73% aa sequence identity with human and rat IL2, respectively. IL-2 is produced by CD4+ T cell, CD8+ T cells, gamma δ T cells, B cells, dendritic cells and eosinophils, and plays a vital role in key function of the immune system, tolerance and immunity, primarily via its potent stimulatory activity for T cells.Thus, IL2 may be a key cytokine in the natural suppression of autoimmunity.