Description
Interleukin-5 Receptor alpha (IL-5Ralpha, CD125) is a 60 kDa hematopoietin receptor that plays a dominant role in eosinophil biology. Mature human IL-5 Ralpha consists of a 322 aa extracellular domain (ECD) with a WSxWS motif and a four cysteine motif, a 20 aa transmembrane segment, and a 58 aa cytoplasmic domain. Within the ECD, human IL-5Ralpha shares 71% aa sequence identity with mouse and rat IL-5 Ralpha. Alternate splicing of human IL-5 Ralpha generates soluble secreted forms which function as IL-5 antagonists. The high affinity receptor for IL-5 is a complex that consists of the ligand binding IL-5 Ralpha and the transmembrane common beta chain (betac/CD131) which is shared with the receptor complexes for IL-3 and GMCSF. IL-5 Ralpha binds IL-5 at low affinity and then associates with preformed betac oligomers to form the signaling competent receptor complex. IL-5 stimulation of CD34+ hematopoietic progenitor cells induces the up-regulation of transmembrane IL-5Ralpha followed by eosinophilic differentiation and activation