Table 3.

Key functional characteristics of human IgG subclasses

Subclass	IgG1	IgG2	IgG3	IgG4
Serum half-life (days)	21	20	7	21
FcRna binding	++	++	+	++
FcγRIb binding	++++	−	++++	+++
FcγRIIAc binding	+++	+	++	+
FcγRIIBd binding	++	+	++	+
FcγRIICe binding	++	+	++	+
FcγRIIIAf binding	+++	+/−	+++	+
FcγRIIIBg binding	++	−	++	−
C1qh binding	++	+	+++	−

^aaFcRn is the neonatal FcR expressed on monocytes, macrophages, DCs, hepatocytes, epithelial cells, endothelium of small blood vessesl, intestinal endothelium and placenta.

^bFcγRI (CD64) is the high affinity receptor for IgG expressed on monocytes, macrophages, neutrophils, eosinophils, DCs, mast cells, platelets, microglia.

^cFcγIIA (CD32A) is the low/medium affinity receptor for IgG expressed on monocytes, macrophages, neutrophils, eosinophils, NK cells, platelets, microglial cells, Langerhans cells.

^dFcγRIIB (CD32B1) is the low affinity inhibitory receptor for IgG expressed on B cells and mast cells.

^eFcγRIIC (CD32B2) is the low affinity receptor for IgG expressed on macrophages, neutrophils, eosinophils.

^fFcγRIIIA is the low/medium affinity receptor for IgG expressed on NK cells, monocytes, macrophages, subset of T cells(?).

^gFcγRIIIB is the low affinity receptor for IgG expressed on eosinophils, neutrophils, monocytes, macrophages, mast cells, follicular DCs.

^hC1q is the first component of complement.