'''Interleukin 15''' (IL-15) is a cytokine+ with structural similarity to IL-2+. Like IL-2+, IL-15 binds to and signals through a complex composed of IL-2/IL-15 receptor 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 cell+s; cells of the innate immune system+ whose principal role is to kill virally infected cells.