Interleukin 15 (Il15) is a cytokine important for the development, maturation, and function of many cells of the immune system including NK, NKT, gammadeltaT, and CD8(+) T cells. Its expression affects homeostasis and function of B cells through NK cell-derived IFNG. Il-15 binds a trimeric Il-15 receptor (Il-15R) complex formed by a specific receptor chain (Il-15Rα) combined with theβandγchains of the IL-2R, acting as signal transducing components. The transgenic mice overexpressing Il15 exhibit an increase in the number of memory CD8+ T cells in a naive state and enhanced protection against bacterial infections. Mice lacking Il15 exhibit impaired protection against a strain of attenuated Mycobacterium.