Interleukin 15 (IL-15) is a cytokine with structural similarity to IL-2. Like IL-2, IL-15 binds to and signals through the IL-2/IL-15 beta chain (CD122) and the common gamma chain (gamma-C, CD132). IL-15 is secreted by mononuclear phagocytes (and some other cells) following infection by virus(es). This cytokine induces cell proliferation of natural killer cells, cells of the innate immune system whose principal role is to kill virally infected cells. Alternative Names: IL-15 protein, IL-15 protein, IL 15 protein, IL-15, IL 15, IL15, Interleukin 15 protein, MGC9721 protein, IL-15 protein, IL-T protein