CD32 is a surface receptor protein and part of a large population of B cell co-receptors, which act to modulate signaling. It has a low-affinity for IgG antibodies and down-regulates antibody production in the presence of IgG. This feedback loop acts to lower the production of IgG by B cells when there is a surplus in the body. Monoclonal antibodies can distinguish between CD32A and CD32B.