A Human High Affinity Interleukin-5 Receptor (IL5R) is Composed of an IL5-specific Alpha Chain and a Beta Chain Shared with the Receptor for GM-CSF

cDNA clones encoding two receptor proteins involved in the binding of human interleukin 5 (hIL5) have been isolated. A first class codes for an IL5-specific chain (hIL5R alpha). The major transcript of this receptor gene, as analyzed in both HL-60 eosinophilic cells and eosinophilic myelocytes grown from cord blood, encodes a secreted form of this receptor. This soluble hIL5R alpha has antagonistic properties. A second component of the hIL5R is found to be identical to the beta chain of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) high affinity receptor. The finding that IL5 and GM-CSF share a receptor subunit provides a molecular basis for the observation that these cytokines can partially interfere with each other's binding and have highly overlapping biological activities on eosinophils.