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 fa mily which shares many biological activities with IL-2, probably due t o its interaction with the IL-2 receptor beta and gamma (IL-2R beta an d gamma(c)) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone di splays an affinity of binding for IL-15 equivalent to that of the hete rotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated t hrough reconstruction experiments in a murine myeloid cell line. IL-15 R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R al pha mRNA suggests that IL-15 may have biological activities distinct f rom IL-2.