CDw119 is a 90-100 kD type I transmembrane protein, also known as IFN-gamma R alpha chain or IFN-gammaRI. The IFN-gamma receptor is a complex of a high affinity IFN-gamma-binding chain (aka, IFN-gamma R alpha chain) and a second accessory protein required for signal transduction known as IFN-gamma R beta chain. The IFN-gamma R alpha chain is a member of the class II cytokine receptor family. Binding of IFN-gamma induces receptor dimerization and internalization. Signal transduction involves Jak1 and Jak2 protein kinases and involves STAT1 activation. The IFN-gamma receptor is expressed at moderate levels on virtually every cell with the exception of erythrocytes.