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