Interleukin 15 is a cytokine with structural similarity to IL-2. Like IL-2, IL-15 binds to and signals the IL-2 / IL-15 β chain (CD122) and the common γ chain (γ-C, CD132). After virus infection, mononuclear phagocytes can secrete IL-15. This cytokine can induce cell proliferation of natural killer cells. IL-15 can also regulate the activation and proliferation of T cells and natural killer cells.