Human Fc gamma RIIIA/CD16a Antibody

Fc gamma RIIIa is a low/intermediate affinity receptor for polyvalent immune-complexed IgG. It is involved in phagocytosis, secretion of enzymes and inflammatory mediators, antibody-dependent cytotoxicity and clearance of immune complexes (1, 2). In humans, it is a 50-70 kDa type I transmembrane activating receptor expressed by NK cells, T cells, monocytes, and macrophages (1). Fc gamma RIIIb is highly related, sharing 97% amino acid (aa) identity within the extracellular domain (ECD), but is a GPI-linked receptor expressed on human neutrophils and eosinophils (1, 2). The ECD of Fc gamma RIIIa shares 63%, 61%, 65%, 59% and 58% aa identity with mouse Fc gamma RIV, rat Fc gamma RIIIa, feline CD16, bovine CD16 and porcine Fc gamma RIIIb paralogs, respectively. The Fc gamma RIIIa cDNA encodes 254 aa including a 16 aa signal sequence, 191 aa ECD with two C2-type Ig-like domains and five potential N-glycosylation sites, a 22 aa transmembrane (TM) sequence and a 25 aa cytoplasmic domain. In humans, a single nucleotide polymorphism creates high binding (176V) and low binding (176F) forms that, when homozygous, may influence susceptibility to autoimmune diseases or response to therapeutic IgG antibodies (3, 4). Catalog # 4325-FC is expressed as the 176V isoform of Fc gamma RIIIa. Fc gamma RIIIa surface expression requires interaction of an accessory chain, either the common gamma-chain or CD3 zeta (5, 6). Glycosylation patterns, electrophoretic mobility and binding affinity appear to differ between NK cell and monocyte Fc gamma RIIIa (7). The ECD of both Fc gamma RIIIa and b can be proteolytically cleaved and retain binding activity in soluble form (8-11). In monocytes and macrophages, activation and phagocytosis can trigger Fc gamma RIIIa release (11). Soluble Fc gamma RIII can be detected in normal plasma and is increased in rheumatoid arthritis and in coronary artery diseases (9, 10).