Fc gamma RII/CD32 and Fc gamma RIII/CD16 proteins are low/intermediate affinity receptors for polyvalent immune-complexed IgG. Fc gamma RII is expressed on cells of both myeloid and lymphoid lineages as well as on cells of non-hematopoietic origin. Fc gamma RIIA associates with FcR gamma and delivers an activating signal through its cytoplasmic ITAM motif. In contrast, Fc gamma RIIB delivers an inhibitory signal through its ITIM motif. Fc gamma RIIC represents an unequal cross-over event between the IIA and IIB genes. Fc gamma RIII is expressed on NK cells, T cells, monocytes, and macrophages. It is involved in phagocytosis, secretion of enzymes and inflammatory mediators, antibody-dependent cytotoxicity, and clearance of immune complexes.
