IL-4 can signal through type I and type II receptor complexes, which share a common γ chain (γc). The type I receptor contains in addition to the γ chain an IL-4Rα subunit, whereas the type II receptor contains the IL-13Rα. The secreted extracellular domain of IL-4Rα, called sIL-4Rα, binds IL-4 and antagonizes its activity. It plays an important role in regulating the differentiation of naive CD4 T cells and class switching to IgG1 and IgE. Recombinant human sIL-4Rα is a 209 amino acid protein which corresponds to the entire extracellular domain of IL-4Rα.