IL-15 is a pleiotropic cytokine that functions in NK cell development, lymphocyte homeostasis, and peripheral immune functions.

Multiple cell types elaborate IL-15, including activated (eg, virus- or bacteria-infected) monocytes/macrophages, dendritic cells, and epithelium, as well as constitutive production by BM stromal cells. IL-15 has a critical role in the development of the NK lineage, as well as in its survival, expansion, and function. Other innate lymphocytes (NK-T, CD8αα i-IEL, TCRγδ DETCs) and memory-phenotype CD8⁺ T cells depend upon IL-15 for survival or expansion. IL-15 also plays multiple roles in peripheral innate and adaptive immune cell function.