<p> 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 [<cite idref="PUB00006640"/>] and the corresponding ligands as hematopoietins. Further, hematopoietins have been subdivided into two major structural groups: large (long) and small (short) hematopoietins.</p> <p> 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:</p><p> <ul> <li>Granulocyte/macrophage colony stimulating factor receptor alpha (GMCSFRA)</li><li>Interleukin-3 receptor alpha chain (IL3RA)</li><li>Interleukin-5 receptor alpha chain (IL5RA)</li><li>Interleukin-13 receptor alpha-1 chain (IL13RA1)</li><li>Interleukin-13 receptor alpha-2 chain (IL13RA2)</li> </ul> </p> <p> 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 [<cite idref="PUB00006637"/>]. 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 [<cite idref="PUB00006657"/>]. </p> Short hematopoietin receptor, family 2, conserved site