IL-15 Ra (Interleukin 15 Receptor alpha), also known as CD215, is a transmembrane glycoprotein that plays an important role in NK and CD8+ memory T cell homeostasis and activation. It transmits IL-15 induced signals and additionally interacts with a complex of IL-2 R beta and the common gamma chain (gammaC) which are also subunits of the IL-2 receptor complex. In transpresentation, IL-15/IL-15 Ra complexes are expressed on the surface of one cell and interact with complexes of IL-2 R beta/gammaC on adjacent cells. IL-15/IL-15 Ra complexes can transmit reverse signaling that promotes adhesion and activation of the IL-15/IL-15 Ra expressing cells. Shed soluble forms of IL-15 Ra retain the ability to bind tightly to IL-15 and can inhibit IL-15 bioactivity.