Interleukin-2 (IL2) is a secreted immunomodulatory cytokine that is essential in regulation and proliferation of T and B lymphocytes, and other activities crucial to regulation of the immune response. The receptor of this cytokine (the IL-2R receptor) is a heterotrimeric protein complex whose gamma chain is also shared by interleukin 4 (IL4) and interleukin 7 (IL7). The expression of this gene in mature thymocytes is monoallelic, which represents an unusual regulatory mode for controlling the precise expression of a single gene. The targeted disruption of a similar gene in mice leads to ulcerative colitis like disease, which suggests an essential role of this gene in the immune response to antigenic stimuli. IL2 has been shown to have antitumor effects in some studies. This is probably mediated by cytotoxic effector cells. Produced by T-cells in response to antigenic or mitogenic stimulation, this protein can stimulate B-cells, monocytes, lymphokine-activated killer cells, natural killer cells, and glioma cells. Recombinant IL-2 produced in E. coli is a single, non-glycosylated polypeptide chain containing 134 amino acids and having a molecular mass of 15,517 Daltons. Recombinant human IL-2 has a Ser substitute for Cysteine at position 126.