Figure 1 - In vitro and in vivo behaviors of the IgG subclasses IgG1, IgG2, IgG3 and IgG4.

Whereas IgG1 and IgG3 remain monomeric in vivo, IgG2 forms covalent dimers between identical or different IgG2 molecules with intermolecule disulfide bonds for which the exact structures have not been determined. In vivo, IgG4 is thought to be in equilibrium between the bivalent, monospecific form with normal interchain disulfide bonds (left), the half-molecule with an intra-chain disulfide bond (middle) and a mixed bivalent, bispecific form (right).