Fc receptors

Fc receptors – the constant region (Fc) of IgG on bacterial surfaces can bind to the Fc receptor on phagocytes. Such binding requires prior antigen-antibody interaction. The binding of IgG-coated bacteria to Fc receptors on phagocytes stimulates both metabolic activity in the phagocytes (respiratory burst) and phagocytic engulfment of the target. Fc receptors include the clusters of differentiation, CD16 (Fcγ RIII), CD32 (Fcγ RII-A, Fcγ RII-B2, Fcγ RII-B1), and CD64 (Fcγ RI), Fcε RI, and Fcα RI. All FcR are stimulatory except the inhibitory Fcγ RII-B1 and B2, which contain immunoreceptor tyrosine based inhibition motifs (ITIMs) in their cytoplasmic tail.  Immune Cytokines  Immunoglobulins  Interferons

FcR

relative binding

expressed on

activity

Fcγ RI (CD64)

IgG1 ~200

macrophages, neutrophils, eosinophils, dendritic cells

Uptake

Stimulation

Activation of respiratory burst

Induction of killing

Fcγ RII-A (CD32)

IgG1~4

macrophages, neutrophils, eosinophils, platelets, Langerhans cells

Uptake

Granule release from eosinophils

Fcγ RII-B2 (CD32)

IgG1~4

macrophages, neutrophils, eosinophils

Uptake

Inhibition of stimulation

Fcγ RII-B1 (CD32)

IgG1~4

B cells, mast cells

No uptake

Inhibition of stimulation

Fcγ RIII (CD16)

IgG1~1

NK cells, eosinophils, macrophages, neutrophils, mast cells, FDCs

Induction of killing by NK cells

Fcε RI

IgE~20,000

mast cells, eosinophils, basophils, FDCs

Secretion of granules

Eosinophilic attack of parasites such as Schistosoma mansoni

Fcα RI

IgA1, IgA2~20

macrophages, neutrophils, eosinophils

Uptake

Induction of killing

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