RAC2,also named as GX,belongs to the small GTPase superfamily and Rho family. RAC2 is a plasma membrane-associated small GTPase which cycles between an active GTP-bound and inactive GDP-bound state. In active state binds to a variety of effector proteins to regulate cellular responses,such as secretory processes,phagocytose of apoptotic cells and epithelial cell polarization. RAC2 augments the production of reactive oxygen species (ROS) by NADPH oxidase. Defects in RAC2 are the cause of neutrophil immunodeficiency syndrome.