Recombinant Human IL-5 R alpha (CHO-expressed) Protein

Interleukin‑5 Receptor alpha (IL‑5 R alpha ), also known as CD125, is a 60 kDa hematopoietin receptor that plays a dominant role in eosinophil biology (1‑3). Mature human IL‑5 R alpha consists of a 322 amino acid (aa) extracellular domain (ECD) with a WSxWS motif and a four cysteine motif, a 20 aa transmembrane segment, and a 58 aa cytoplasmic domain (4, 5). Within the ECD, human IL-5 R alpha shares 71% aa sequence identity with mouse and rat IL‑5 R alpha. Alternate splicing of human IL‑5 R alpha generates soluble secreted forms which function as IL‑5 antagonists (5‑7). The high affinity receptor for IL‑5 is a complex that consists of the ligand binding IL‑5 R alpha and the transmembrane common beta chain ( beta c/CD131) which is shared with the receptor complexes for IL‑3 and GM‑CSF (4). IL‑5 R alpha binds IL‑5 at low affinity and then associates with preformed beta c oligomers to form the signaling‑competent receptor complex (8). IL‑5 stimulation of CD34⁺ hematopoietic progenitor cells induces the up‑regulation of transmembrane IL‑5 R alpha followed by eosinophilic differentiation and activation (9 ‑ 11). IL‑5 R alpha also promotes the differentiation of basophils and B cells (12, 13). Exposure of mature eosinophils to IL‑5 attenuates their IL‑5 responsiveness by inducing the down‑regulation of surface IL‑5 R alpha and increased production of soluble IL‑5 R alpha (14, 15). Elevated production of IL‑5 at sites of allergic inflammation induces eosinophilia and exacerbation of immune cell infiltration, tissue damage, and remodeling (2, 3).