CD16a FCγRIIIA (Fc fragment of IgG low affinity IIIa receptor), FCGRIIIA
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
NK Cell
Macrophage
Mast Cell
Neutrophil
Monocyte
T Cell
Myeloid Cell
Thymocyte
50 / 50
60 / 60

Expression
CD16a is expressed on the transmembrane form in humans on NK cells, macrophages, activated monocytes, mast cells and γ/δ T cells.  In the mouse, no GPI-anchored form of CD16a has been identified and the transmembrane form is expressed on macrophages, NK cells, neutrophils, myeloid precursors and on the majority of early CD4-CD8-TCR- fetal thymocytes.

Structure
MOLECULAR FAMILY NAME: Belongs to the immunoglobulin supergene family.

CD16a is single-pass type-1 glycoprotein.  It contains an extracellular domain which contains 2 Ig-like C2-type domains, a transmembrane and a cytoplasmic domain.
 
MOLECULAR MASS
Cell Type Unreduced Reduced
50 kDa-60 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION: No information.



Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD16a

The transmembrane form is non-covalently associated with the FceRI g chain or the TCR z chain.  CD16a on mast cells is also associated with the b chain of the FceRI.         



Function
CD16a is a low affinity receptor for aggregated IgG2 and IgG3.  The transmembrane form binds IgG complexed to antigens and mediates phagocytosis and antibody-dependent cellular cytotoxicity (ADCC).  Triggering in NK cells leads to ADDC and lymphokine production, indicating a role in defense against viral infection and neoplasms.   On NK cells, signal transduction by CD16a is mediated through the g chain and crosslinking of CD16a with immune complexes or CD16a-specific mAbs induces calcium mobilization and hydrolysis of membrane phosphoinositides.  In contrast, the GPI-anchored form (CD16b) on neutrophils binds to ligands but is unable to induce any signal or functional effect.  CD16a associates with FcεRγ-chain on human phagocytes and mast cells and the TCR-ζ-chain in NK cells.  Targeted disruption of the mouse FcRg chain common to CD16a and FceRI results in immunocompromised mice.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD16a IN INTACT ANIMAL

CD16a is a phenotypic marker in leukemia and HIV-1 and is used to purify bone marrow and germinal center subsets.  CD16a alleles (and CD32) can be used as risk markers for systemic lupus erythematosus (SLE).  CD16a-dependent but antibody-independent lysis of tumor cells and virus infected cell has been demonstrated.


Comments
CD16a (FcgRIIIa) has a structural similarity to CD64 (FcgRI), CD32 (FcgRII) and CD64 (FcgRIa).  The sequence LFAVDTGL is completely conserved in the transmembrane regions of CD16a and FcgRIa  from human, mouse and rat.  A family of CD16a isoforms have been described in the rat. 

MOLECULAR INTERACTIONS-
PROTEIN AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD16a: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD16a: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 2214P08637
MouseS29360P08508M14215
RatP27645M64368-M64370
Antibodies
3G8   View Reactivity
G7   View Reactivity
NKP15   View Reactivity

Revised June 25, 2008


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