Interleukin-5 receptor subunit alpha (IL5RA) is also known as IL-5 receptor subunit alpha, IL-5R subunit alpha and CD125,which is a single-pass type I membrane protein that belongs to the type I cytokine receptor family and type 5 subfamily.IL5R, a heterodimer of an alpha and a beta subunit, is expressed on eosinophils and basophils. IL5RA / CD125 is the receptor for interleukin-5 (IL5) and the alpha chain can bind to IL5. The WSXWS motif of IL5RA appears to be necessary for proper protein folding and thereby efficient intracellular transport and cell-surface receptor binding.The beta subunit of IL5R is common to the IL3, IL5 and GM-CSF receptors.