CD32 (cluster of differentiation 32), also known as FcγRII or FCGR2, is a surface receptor glycoprotein belonging to the Ig gene superfamily. CD32 can be found on the surface of a variety of immune cells. CD32 has a low-affinity for the Fc region of IgG antibodies in monomeric form, but high affinity for IgG immune complexes. CD32 has two major functions: cellular response regulation, and the uptake of immune complexes. In humans, there are three major CD32 subtypes: CD32A, CD32B, and CD32C. While CD32A and CD32C are involved in activating cellular responses, CD32B is inhibitory. however, the high degree of homology between the extracellular domains of CD32A and CD32C make differentiation difficult.
Functions and locations
CD32A
CD32A is an activating subtype of CD32 that can be found on a variety of immune cells - notably, CD32A is found on platelets, neutrophils, macrophages, and dendritic cells (DCs). On platelets, it is known to aid in the internalization of IgG-opsonized Escherichia coli, and it is more generally implicated in mediating bacterial-activated platelet responses. Thus, CD32B plays an important role in both antibody and memory immune responses.