Interleukin 15 (IL-15) belongs to the 4-α-helix bundle family of glycoprotein cytokines that include IL-2, IL-3, IL-4 and IL-21. It exerts profounds effects on the proliferation, survival and differentiation of NK cells and T cells. IL-15 signaling is mainly mediated via a transmembrane heterotrimeric receptor complex that consists of a high affinity ligand binding subunit IL-15Rα and -β and -γ signal transducing subunits. The latter two it shares with IL-2. IL-15 can also signal via an intermediate affinity receptor...