Two type 1 membrane proteins belonging to the hemopoietin receptor family have been cloned and shown to bind IL-13 with differing affinities. The lower affinity IL-13 binding protein, previously designated IL-13 R alpha, IL-13 R alpha ' or NR4, is now referred to as IL-13 R alpha 1. The high-affinity IL-13 binding protein, previously also designated IL-13 R or IL-13 R alpha ', is now referred to as IL-13 R alpha 2.

> 95% as determined by Tris-Bis PAGE; > 95% as determined by HPLC