Fc γ RIIB, also known as CD32b, is a low affinity inhibitory receptor for the Fc part of the IgG molecule. It is a single-channel type I membrane protein with two IgG-like C2 (immunoglobulin-like) domains. Fc γ RIIB is expressed on B cells, macrophages, neutrophils, mast cells and bone marrow dendritic cells, and participates in B cell phagocytosis of immune complexes and regulation of antibody production. In some cases, it can promote cell apoptosis. CD32b may also be a target for monoclonal antibodies in the treatment of malignant tumors.