Functional IL-2 receptors can exist in two affinity states on cell surfaces, the high affinity complex consisting of heterotrimers of the alpha, beta, and gamma chains and the intermediate affinity complex comprising heterodimers of the beta and gamma chains. Individual beta chains and alpha chains exhibit low affinity IL-2 binding, and the gamma chain alone does not bind IL-2. In addition to their involvement in IL-2 mediated signal transduction, both the beta chain and gamma chain have been shown to be required for IL-15 mediated signaling. IL-2 R beta is a member of the cytokine receptor superfamily.