Critical role for IL-15 in innate immunity.

Although some functional activities of interleukin (IL)-15 on NK and T cells overlap with those of IL-2, recent findings obtained from gene-targeted mice deficient in components of IL-2/IL-15 system demonstrate distinct roles of IL-15 for the activation of innate immune system. IL-15 is a pivotal cytokine for the development and survival of NK cells, NKT cells, TCRydelta+ intestinal intraepithelial lymphocytes (ilEL), and for the functional maturation of dendritic cells and macrophages. IL-15 is also important for memory T cell maintenance in vivo. In this review, I summarize recent progress of studies in the IL-15/IL-15R system.