A number of receptors for lymphokines, hematopoietic growth factors and growth hormone-related molecules have been found to share a common binding domain. These receptors are designated as hematopoietin receptors []and the corresponding ligands as hematopoietins. Further, hematopoietins have been subdivided into two major structural groups: large (long) and small (short) hematopoietins.One subset of individual receptor chains that are part of receptor complexes for small hematopoietins contain common structural elements: an extracellular receptor domain that contains an immunoglobulin-like region at the N-terminal end; a transmembrane domain; and a short cytoplasmic domain. They define a structural subgroup containing the following chains:Granulocyte/macrophage colony stimulating factor receptor alpha (GMCSFRA)Interleukin-3 receptor alpha chain (IL3RA)Interleukin-5 receptor alpha chain (IL5RA)Interleukin-13 receptor alpha-1 chain (IL13RA1)Interleukin-13 receptor alpha-2 chain (IL13RA2)GMCSFRA, IL3RA or IL5RA chains of this subgroup bind to their cognate cytokines: GM-CSF, IL-3 and IL-5, with a common beta chain, KH97/AIC2B []. Either IL13RA1 chain or IL13RA2 chain form the IL13R complex together with IL4RA chain. IL-4 can compete with IL-13 to bind to either IL13R form [].
