| Fcy 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 50-70kD type I transmembrane activating receptor expressed by NK cells, T cells, monocytes, and macrophages.1 Fcy 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 Fcy RIIIa shares 63%, 61%, 65%, 59% and 58% aa identity with mouse Fcy RIV, rat Fcy RIIIa, feline CD16, bovine CD16 and porcine Fcy RIIIb paralogs, respectively. The Fcy 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 (T230A) creates high binding (176V) and low binding (176F) forms that may influence susceptibility to autoimmune diseases or response to therapeutic IgG antibodies.3, 4 Fcy RIIIa surface expression requires interaction of an accessory chain, either the common y-chain or CD3c.5, 6 Glycosylation patterns, electrophoretic mobility and binding affinity appear to differ between NK cell and monocyte Fcy RIIIa.7 The ECD of both Fcy 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 Fcy RIIIa release.11 Soluble Fcy RIII can be detected in normal plasma and is increased in rheumatoid arthritis and in coronary artery diseases.9, 10 Recombinant protein corresponding to Gly17-Gln208 from human Fc gamma RIIIA/CD16a, with a C-terminal 6-His tag, expressed in a mouse myeloma cell line, NS0. Molecular Weight: Calculated molecular mass of ~22.6kD. As a result of glycosylation, recombinant human Fcy RIIIa migrates as an approximately 40-50kD protein in SDS-PAGE under reducing conditions. Activity: Measured by its ability to bind human IgG with an estimated KD < 50nM. Storage and Stability: Lyophilized and reconstituted products are stable for 6 months after receipt at -20C. Reconstitute with sterile PBS. Aliquot to avoid repeated freezing and thawing. Store at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer. |
