Interleukin 15 (IL15) binds Interleukin 15 receptor subunit alpha (IL15RA, IL15Rα). The high affinity Interleukin 15 receptor is a heterotrimer of IL15RA, Interleukin 2 receptor subunit beta (IL2RB, IL2Rβ, IL15RB) and Cytokine receptor common subunit gamma (IL2RG, IL2Rγ). IL15RA is structurally related to the alpha subunit of the Interleukin-2 receptor and determines high affinity binding for Interleukin 15 (IL15) (Giri et al. 1994, 1995, Anderson et al. 1995, Dubois et al. 2002). More in detail, IL15RA binds specifically to IL15 with high affinity (Kd=30-100 pM), whereas IL2RA specifically binds to IL2 with a comparatively lower affinity (Kd=10-30 nM) (Bernard et al. 2004).