Table 3.

Unique features of IgG subclass Fc and hinge.

IgG subclass	FcγR specificity	Light‐chain attachment	Hinge characteristics	Fc stability	Comment
IgG1	All FcγR	Upper hinge	Light‐chain attachment	Stable	Fc is >100× times more stable than IgG4 and IgG2.
			Stable core hinge
IgG2	FcγRIIa His131	CH1 of Fab and/or upper hinge	Stable core hinge with additional inter H‐chain disulfide bonds in the upper hinge.	Unstable CH3:CH3	Alternative light‐chain attachment creates distinct conformers. Unlike IgG4, the CH3:CH3 instability does not lead to half‐molecule exchange as a result of stable core and upper hinge disulfides.
IgG4	FcγRI, FcγRIIb, FcγRIIc	CH1 of Fab	Labile core hinge	Unstable CH3:CH3	Combined instability of core hinge and CH3:CH3 permits half‐IgG molecule exchange

Ig, immunoglobulin.