Recombinant human CD125 (IL5RA: Interleukin 5 Receptor Subunit Alpha) encompassing amino acids 21-342. The protein is fused at the C-terminus with the Fc fragment of a human IgG1 followed by an Avi-Tag™. The recombinant protein was enzymatically biotinylated using the Avi-Tag™ and affinity purified.