Interleukin 2 (IL2) is a secreted cytokine that is important for the proliferation of T and B lymphocytes. The receptor of this cytokine 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.