IgG Fc receptor (Fc γ R) is a member of the Ig superfamily, which plays a role in activating or inhibiting immune response. Human Fc γ Rs is identified as three types: RI (CD64), RII (CD32) and RIII (CD16). CD16 is a low-affinity Fc receptor, which has been identified as Fc receptor Fc γ RIII (a (CD16a) and Fc γ RIIIb (CD16b). These receptors bind to the Fc portion of the IgG antibody and are encoded by two different highly homologous genes in a cell type-specific manner. In human, CD16a is a 50-70 kDa type I transmembrane activated receptor expressed by NK cells, T cells, monocytes and macrophages. It exists on the surface of natural killer cells, neutrophils, polymorphonuclear leukocytes, monocytes and macrophages, and participates in phagocytosis, secretion of enzymes and inflammatory mediators, antibody-dependent cytotoxicity and clearance of immune complexes. Abnormal expression or mutation of CD16a is associated with recurrent viral infection, systemic lupus erythematosus and neutropenia in newborns with alloimmunity. In humans, single amino acid mutations (176V) and (176F) may affect susceptibility to autoimmune diseases or response to therapeutic IgG antibodies.
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