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Fc Receptors (FcR)

Fc receptors play a major role in immune defenses against pathogens and in inflammatory processes.

Because of their ability to bind the Fc portion of antibodies, Fc receptors provide a link between humoral and cellular immune responses. There are Fc receptors for each Ig isotype.


FcRs fall into two general classes: those involved in effector functions and those that transport immunoglobulins across epithelial barriers.


Except for FcΕRII (CD23), which is C-type lectin-like, all other known Fc receptors are members of the immunoglobulin superfamily [1].


FcγRI and FcΕRI are high-affinity receptors with dissociation constants ranging from 10-8 to 10-10 M, whereas the other receptors, such as FcγRII and FcγRIII, are low-affinity receptors with dissociation constants ranging from 10-5 to 10-7.

FcγRIIB (CD32), the low-affinity receptor for the Fc fragment of IgG, is expressed on almost all hematopoietic cells, including B lymphocytes, NK KIR*cells,etc.

3D structures

The recent crystal structures of a human FcΕRIa [2], FcγRIIa [3], FcγRIIb [4] and FcγRIII [5] revealed a conserved immunoglobulin-like (Ig-like) structure, particularly the small hinge angle between the two Ig-like domains, that is unique to the Fc receptors.

[1] Daëron, M. (1997) Annu. Rev. Immunol. 15, 203-234.
[2] Garman, S. C. et al. (1998) Cell 95, 951-961.
[3] Maxwell, K. F. et al. (1999) Nat. Struct. Biol. 6, 437-442.
[4] Sondermann, P. et al. (1999) EMBO J. 18, 1095-1103.
[5] Zhang, Y. et al. (2000) Immunity 13, 387-395.