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