The crystal structure of the assembled IL2:IL2 receptor complex and experiments using isothermal titration calorimetry suggest that the complex of IL2 with IL2R alpha is likely to preferentially associate with IL2R bet (Rickert et al. 2004, Stauber et al. 2006). Binding of IL-2/IL-2R alpha to IL-2R beta significantly slows the dissociation of IL-2. However, the trimeric complex of IL-2:IL-2R alpha:IL-2R beta is incapable of signaling without participation of the gamma chain.