The relationship of HLA-DR3 and outcome after antithyroid drugs to the IgG subclass distribution of thyroid autoantibodies in Graves' disease.

We have examined the IgG subclass distribution of thyroglobulin (Tg) and microsomal (M) autoantibodies in 31 patients with Graves' disease before and after treatment with carbimazole. IgG1 and IgG2 subclass antibodies were detected before treatment in nearly all patients, and in over a third there was an excess of activity in the IgG3 and IgG4 subclasses. There were significant differences between the IgG subclasses composing Tg and M antibodies (less IgG1 and IgG3 but more IgG2 in the latter). Patients who were HLA-DR3-positive had significantly lower levels of IgG4 in M antibodies than in those who were DR3-negative. A variety of changes were found after treatment, and these depended on whether the patient entered remission or relapse. In particular, IgG1 levels of M antibodies were consistently higher in the relapse group, whereas after 1 year in remission IgG4 levels fell, and IgG2 levels rose. These results show preferential production of certain IgG subclasses composing thyroid autoantibodies in Graves' disease which appears to be associated with HLA-DR3 status and the response to antithyroid drugs.