Interleukin 2 (IL-2) belongs to the interleukin family, a type of cytokine signaling molecule in the immune system, and it is a protein that regulates the activities of the white blood cells responsible for immunity. Interleukin 2, a soluble hormone-like mediator of the immune system, was the first interleukin molecule to be identified and characterized. IL-2 is normally produced by T cells during an immune response and is necessary for the development of T cell immunologic memory, which depends upon the expansion of the number and function of antigen-selected T cell clones.