IL-15 is a member of the four α-helix bundle cytokine family. It is produced by different cell types, including epithelial cells, monocytes, muscle and placenta cells. IL-15 is a potent lymphoid cell growth factor. It stimulates the proliferation of activated T cells and promotes the generation of cytotoxic T lymphocytes (CTLs). IL-15 also induces the generation, proliferation, and activation of NK cells as well as B cell growth and immunoglobulin production. In addition, IL-15 is important for the maintenance of CD8+ memory T cells. For binding and signaling IL-15 uses the unique IL-15 receptor α-chain, but shares the β- and γ-chain of the IL-2 receptor.