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.
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