Fcγ receptors

		FcɣRI CD64	FcɣRlla CD32a	FcɣRllb CD32b	FcɣRllc CD32c	FcɣRllIa CD16a		FcɣRIlIb CD16b
Structure
Allotypes (*not in the ECD)			167H167R	232I*232T*	57Q57stop	176F176V		NA1NA2SH*
Affinity		High	Low	Low	Low	Low	Low	Low
Relative specificity		lgG1:+++lgG2:-lgG3:+++lgG4:+++	lgG1:+++lgG2:+lgG3:++lgG4:+ 167H has↑bindingto IgG1/2/3	lgG1:+lgG2:+/-lgG3:+lgG4:+	lgG1:+lgG2:+/-lgG3:+lgG4:+	lgG1:+++lgG2:+lgG3:++lgG4:+ 176v has ↑ binding to all lgG
Expression	B-cell	–	–	+	–	–	–	–
	T-cell	–	–	–	–	–	–	–
	NK cell	–	–	Genotype	Genotype	+	–	–
	DC	+	+	+	Genotype	+	–	–
	Macro	+	+	+	Genotype	+	–	–
	Mono	+	+	Subsets	Genotype	Subsets	–	–
	Neutro	Induced	+	Genotype	Genotype	–	–	+
	Eosino	Induced	+	–	–	–	–	induced
	Baso	–	+	+	–	+	+	–
	Mast	Induced	+	Subsets	Genotype	+	+	–
	Platelet	–	+	–	–	–	–	–
Function		Activation	Activation	Inhibition	Activation	Activation		Decoy

FcγRI
High affinity immunoglobulin gamma Fc receptor I, also known as FcgRI or CD64, is a type I integral membrane glycoprotein. CD64 is a member of the immunoglobulin superfamily and is expressed on monocytes, macrophages, dendritic cells and activated granulocytes. CD64 binds with high affinity to the Fc domain of IgG and it plays a role in antigen capture, phagocytosis of IgG/antigen complexes, and antibody-dependent cellular cytotoxicity (ADCC). CD64 is structurally composed of three extracellular immunoglobulin domains of the C2-type that interact with the IgG Fc domain, a transmembrane domain and a short cytoplasmic tail. CD64 is associated with a dimer of the common Fc receptor gamma-chain which contains the immunoreceptor tyrosine-based activation (ITAM) motif. The product provided only contains the extracellular portion of CD64.

Synonyms: CD64, CD64A, Fc gamma R1, Fc gamma RI, Fcg R1, Fcg RI, FCGR1, FCGR1A, FCGRI, FCGRIA, FCR1, FCRI, IGFR1, IGFRI

FcγRII
Low affinity immunoglobulin gamma Fc receptor II, also known as FcgRII or CD32, is actually a collection of three highly related isoforms: FcgRIIa (CD32a), FcgRIIb (CD32b) and FcgRIIc (CD32c). They all consist of two extracellular immunoglobulin domains, a transmembrane domain and a cytoplasmic tail with an intrinsic signaling motif. CD32a and CD32c contain an activatory motif (ITAM) and FcγRIIb contains an inhibitory motif (ITAM).

CD32a is the most widely expressed isoform and is found on monocytes, macrophages, dendritic cells, granulocytes and platelets. FcγRIIa binds monomeric IgG with low affinity but is very efficient at binding immune complexes and is involved in phagocytosis and clearing of immune complexes. CD32a has two allotypic variants differing at amino acid position 167, one containing histidine (H167) and the other arginine (R167). H131 exhibits a higher affinity to human IgG1 and IgG2 than the R167 does and is thought to be primarily responsible for the phagocytosis of IgG-opsonized bacteria.

Synonyms: CD32, CD32A, Fc gamma R2, Fc gamma R2a, Fc gamma RII, Fc gamma RIIa, Fcg R2, Fcg R2a, Fcg RII, Fcg RIIa, FCGR2, FCGR2A, FCGRII, FCGRIIA, FCR2, FCR2A, FCRII, FCRIIA

CD32b is highly expressed on B-cells, where is it the only surface expressed FcγR, and at much lower levels on monocytes, macrophages, dendritic cells. CD32b binds monomeric IgG with low affinity but is efficient at binding immune complexes and is a negative regulator of cell activation, proliferation, endocytosis, phagocytosis, and degranulation.

Synonyms: CD32, CD32B, CD32b/c, Fc gamma R2, Fc gamma R2b, Fc gamma RII, Fc gamma RIIb, Fcg R2, Fcg R2b, Fcg RII, Fcg RIIb, FCGR2, FCGR2B, Fcgr2b/c, FCGRII, FCGRIIB, FCR2, FCR2B, FCRII, FCRIIB

FcγRIII
Low affinity immunoglobulin gamma Fc receptor III, also known as FcgRIII or CD16, has two isoforms: FcgRIIIa (CD16a) and FcgRIIIb (CD16b).

CD16a is composed of two extracellular immunoglobulin domains, a transmembrane domain and a shot cytoplasmic tail. On basophils and mast cells it associates with a heterodimer of γ/ζ chains and an extra β chain, whereas on other cell types it associates with a dimer of the common Fc receptor γ-chain. FcgRIIIa binds monomeric IgG with low affinity but is efficient at binding immune complexes and functions in NK cell activation, phagocytosis and antibody-dependent cellular cytotoxicity (ADCC). CD16a has two allotypic variants differing at amino acid position 176, one containing phenylalanine (F176) and the other valine (V176). The V176 variant has a greater affinity for all the IgG subclasses and thus results in greater effector function.

Synonyms: CD16, CD16A, Fc gamma R3, Fc gamma R3a, Fc gamma RIII, Fc gamma RIIIa, Fcg R3, Fcg R3a, Fcg RIII, Fcg RIIIa, FCGR3, FCGR3A, FCGRIII, FCGRIIIA, FCR3, FCR3A, FCRIII, FCRIIIA

Unlike other Fc gamma receptors, FcgRIIIb (CD16b) is a GPI-anchored protein containing two extracellular immunoglobulin domains and no intracellular signaling motif. It acts primarily as a decoy receptor and is expressed only on neutrophils and eosinophils. CD16b has two allotypic variants, referred to as human neutrophil antigen 1 (NA1 or HNA1a) and 2 (NA2 or HNA1b). The allotypes have differing affinities to human IgG1 and IgG3 with the NA1 form capable of better ingestion of IgG1 or opsonized IgG3 particles than NA2.

Synonyms: CD16, CD16B, Fc gamma R3, Fc gamma R3b, Fc gamma RIII, Fc gamma RIIIb, Fcg R3, Fcg R3b, Fcg RIII, Fcg RIIIb, FCGR3, FCGR3B, FCGRIII, FCGRIIIB, FCR3, FCR3B, FCRIII, FCRIIIB