Interleukin 2 (IL-2) is a pleiotropic cytokine produced primarily by mitogen- or antigen-activated T lymphocytes. IL-2 plays a key role in promoting the clonal expansion of antigen-specific T cells. In addition, IL-2 has also been shown to mediate multiple immune responses on a variety of cell types.

IL-2 stimulates the proliferation of thymocytes; stimulates the proliferation and differentiation of activated B cells; promotes the growth, differentiation and cytocidal activity of monocytes; induces the growth of and cytokine production and cytolytic activity by natural killer cells; enhances the production of lymphocyte-activated killer (LAK) cells; and induces the proliferation and differentiation of oligodendrocytes .