CD32

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. Cellular responses regulated by CD32 include phagocytosis, cytokine stimulation, and endocytic transport. Dysregulated CD32 is associated with different forms of autoimmunity, including systemic lupus erythematosus. 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.

== Structure and signaling == CD32 is a type I transmembrane protein with a helical transmembrane region. Whereas the extracellular region consists of three immunoglobulin domains (roughly 100 a.a. in length), the cytosolic region varies by subtype. CD32A and CD32C possess an immunoreceptor tyrosine-based activation motif (ITAM), while CD32B has an immunoreceptor tyrosine-based inhibitory motif (ITIM). Both motif types rely upon interactions with SH2 domain-containing proteins to transduce signals upon binding to an IgG immune complex. When an ITIM is phosphorylated, it activates effector proteins that dephosphorylate the downstream targets of the ITAM signal cascade, such as MAP kinases.