The distribution of microsomal and thyroglobulin antibody activity among the IgG subclasses

The IgG subclass distribution of autoantibodies to thyroglobulin (TgAb) and thyroid microsomes (MicAb) in 13 Hashimoto's sera has been investigated using an ELISA technique based on monoclonal anti-subclass antibodies. Considerable subclass restriction was observed with TgAb predominantly but not exclusively associated with IgG4 (mean %TgAb activity associated with IgG4 = 60%) and MicAb predominantly associated with IgG 1 (mean = 49%) and IgG4 (mean = 38%). The tendency for TgAb to be associated with IgG4 accorded with the weak complement fixing properties of this antibody whereas the association of MicAb with IgG1 was consistent with its complement fixing and cytotoxic properties.