Interleukin 15 (IL-15) is a pro-inflammatory protein that plays a role in the activation of neutrophils, dendritic cells, and macrophages and is essential for the development and survival of NK cells and CD8+ T cells.IL-15 activates the Jak/Stat pathway through heterotrimeric receptor signaling. Although IL-15 mRNA is expressed in many cell types, this secreted protein is rarely detected in biological samples. Recent studies have shown that IL-15 is retained intracellularly and can only be secreted extracellularly if it forms a complex with its sole receptor, IL-15Rα. The soluble IL-15/IL-15R complex is produced by mouse dendritic cells, fibroblasts, and macrophages, and its binding activity is 10-100-fold greater than that of IL-15 alone.