Interleukin-15 (IL-15) is a pleiotropic cytokine that plays a pivotal role in both innate and adaptive immunity and has structural similarity to IL-2 that is secreted by mononuclear phagocytes following infection by viruses. Stimulation by IL-15 requires interaction of Il gamma, but not IL-2R alpha. This cytokine is the proliferation of T-lymphocytes and induces the generation of cytotoxic T activated killer (LAK) cells.