Rat IL2, also known as T-cell growth factor, is a secreted immunoregulatory cytokine produced by T-cells due to antigenic or mitogenic stimulation. IL2 binds to the IL2 receptor, which is found in T and B cells and natural killer cells, and is composed of three distinct components: the cytokine specific _-chain, and the _– and _c-subunits. Its receptor complex IL2 induces the proliferation of T cells, generation of cytotoxic T lymphocytes (CTLs), proliferation and synthesis of immunoglobulin by B cells, and the survival of natural killer cells. Its heterotrimeric receptor complex is also shared by Interleukin 4 (IL4) and Interleukin 7 (IL7) by its gamma chain, and receptor signalling is essential for its expression and differentiation of regulatory T cells in the immune response.