Bench-to-bedside review: Immunoglobulin therapy for sepsis - biological plausibility from a critical care perspective

Table 1 Salient characteristics of Fcγ Receptors [38, 40–43]

	Fcγ receptors
Characteristics	FcγRIA	FcγRIIA	FcγRIIC	FcγRIIIA	FcγRIIIB	FcγRIIB
Function	Activatory	Activatory	Activatory	Activatory	Activatory	Inhibitory
Affi nity to IgG	High	Low	Low	Low	Low	Low
IgG subtype affinity	IgG1 >>> IgG3 = IgG4 = IgG2	IgG1 = IgG3 >> IgG2 > IgG4	IgG1 > IgG3 > IgG4 >> IgG2	IgG1 >> IgG3 = IgG2 > IgG4	IgG1 = IgG3 >> IgG2 = IgG4	IgG1 > IgG3 > IgG4 >> IgG2
Cell type receptor	Monocytes, macrophages, neutrophils, eosinophils, dendritic cells	Monocytes, macrophages, neutrophils, dendritic cells, platelets	Natural killer cells	Monocytes, macrophages natural killer cells, dendritic cells	Neutrophils, eosinophils, basophils	Monocytes, macrophage mast cells, B cells, plasma cells, neutrophils, basophils, dedritic cells
Binding	IgG	Only to IgG immune complexes
Signal transfer	ITAM	ITAM	ITAM	ITAM	ITAM	ITIM
Other characteristics		1. Immune response to streptococcal infection			1.Glycosylphosphatidyl-inositol-linked receptor that has no cytoplasmic domain	1. Regulates B-cell activation and plasma cell survival
		2. Low affi nity to IgG2 isoform - FcγRIIA-R131 homozygous state predisposes to infection				2. Basal level inhibition to dendritic cell maturation
						3. Polymorphisms important in malaria

FcγR, Fcγ receptor; Ig, immunoglobulin; ITAM, immunoreceptor tyrosine-based activating motif; ITIM, immunoreceptor tyrosine-based inhibitory motif; IVIg, polyvalent intravenous immunoglobulin.

ISSN: 1364-8535