Identification and cloning of a novel IL‐15 binding protein that is structurally related to the alpha chain of the IL‐2 receptor.

Interleukin‐15 (IL‐15) is a novel cytokine of the four‐helix bundle family which shares many biological activities with IL‐2, probably due to its interaction with the IL‐2 receptor beta and gamma (IL‐2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL‐15R alpha chain. IL‐15R alpha alone displays an affinity of binding for IL‐15 equivalent to that of the heterotrimeric IL‐2R for IL‐2. A biologically functional heteromeric IL‐15 receptor complex capable of mediating IL‐15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL‐15R alpha is structurally similar to IL‐2R alpha; together they define a new cytokine receptor family. The distribution of IL‐15 and IL‐15R alpha mRNA suggests that IL‐15 may have biological activities distinct from IL‐2.