Mouse FcgRIV is an activating receptor for mouse IgG2a and IgG2b antibodies. Structurally, it is an ortholog of the nonrodent CD16/FcgRIIIA and has been designated as CD16-2. Unlike human FcgRIIIA, mouse FcgRIV is also a low affinity receptor for mouse IgE such that the FcgRIV-bound monomeric IgG2a or IgG2b can be readily displaced by IgE immune complexes.
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|Synonym:||Fcrl3; CD16-2; FcgRIV; Fcgr3a; FcgammaRIV; FCGR4|
|Tag:||Gly-His6-GST (glutathione S-transferase)|
|Construction:||Mouse FcγRIV (G21-F198)-GGG-H6-GST|
|MW (calculated):||46962.8 daltons|
|MW (SDS-PAGE)||50 Kd|
|Abs 0.1% (= 1 mg/ml):||1.667|
While Human FcγRs share same name and CD as mouse FcγRs, they are however quite different in the binding specificities toward each IgG subclasses. Together, there are four mouse FcγRs: the FcγRI, FcγRIIB, FcγRIII, and FcγRIV, with FcγRIIB as the only inhibitory receptor and is the only one carries the intrinsic ITIM motif just like the human FcγRIIB. FcγRIV is unique in mouse and is not found in human.
Mouse FcγRI binds to IgG2a, IgG2b, and IgG3, but not IgG1, with high affinity toward IgG2a only. Mouse FcγRIIB differs from mouse FcγRIII in their associated ITIM vs. ITAM, bind with low affinities to IgG1, IgG2a and IgG2b. Mouse FcγRIV binds both IgG2a and IgG2b with high affinities. Interestingly, mouse FcγRIIB, FcγRIII, and FcγRIV, but not FcγRI, also binds to igE, though with low affinity. Hence, FcγRI is a “strict” IgG receptor. Compared with the human FcγR homologs, FcγRIIA, FcγRIIC and FcγRIIIB exist in human but not in mouse.
Overall, the FcγRs expression is less restricted in mouse than human, with the exception of FcγRI which is primarily expressed in mouse, but not human monocytes and DC. Human FcγRIIB, but not mouse, expression is restricted in B cells and basophile, human FcγRIIIA, but not mouse FcγRIII, is restricted in NK cells, monocytes/macrophages.
Amino Acid Sequence
1. Takizawa F, Adamczewski M, Kinet JP. (1992) Identification of the low affinity receptor for immunoglobulin E on mouse mast cells and macrophages as Fc gamma RII and Fc gamma RIII. Exp Med. 176:469-475.
2. Hirano M, Davis RS, Fine WD, Nakamura S, Shimizu K, Yagi H, Kato K, Stephan RP, Cooper MD. (2007) IgEb immune complexes activate macrophages through FcgammaRIV binding. Nat Immunol. 8:762-771
3. Mancardi DA, Iannascoli B, Hoos S, England P, Daëron M, Bruhns P. (2008) FcgammaRIV is a mouse IgE receptor that resembles macrophage FcepsilonRI in humans and promotes IgE-induced lung inflammation. J Clin Invest. 118:3738-3750.
4. Bruhns P, Iannascoli B, England P, Mancardi DA, Fernandez N, Jorieux S, Daëron M. (2009) Specificity and affinity of human Fcgamma receptors and their polymorphic variants for human IgG subclasses. Blood. 113:3716-3725.