Increase in antimicrosomal antibody-related IgG1 and IgG4, and titers of antithyroid peroxidase antibodies, but not antibody dependent cell-mediated cytotoxicity in post-partum thyroiditis with transient hyperthyroidism

To evaluate possible immunological mechanisms involved in the development of postpartum thyroiditis with transient hyperthyroidism followed by transient hypothyroidism (PPT), antithyroid peroxidase antibodies (anti-TPO), antimicrosomal antibody (AMA) related immunoglobin G subclass and antibody-dependent cell-mediated cytotoxicity (ADCC) were studied in 43 post-partum (PP) women who were euthyroid at delivery and completed a subsequent 1 year follow up. Among the 25 mothers who developed PPT, 14 had positive AMA (PPT:AMA+) and 11 negative AMA (PPT:AMA-) at delivery. Among the 18 mothers who remained euthyroid (E) up to one year post-partum and were used as controls, 8 were AMA positive (E:AMA+) and 10 AMA negative (E:AMA-) at delivery. AMA measured by a hemagglutination method correlated well with anti-TPO antibodies measured by RIA in the PP mothers studied. When AMA-related IgG subclass activity was analysed comparing PPT women with appropriate euthyroid controls at the different time intervals studied, it was seen that PPT:AMA+ when compared to E:AMA+ women have significantly increased activity of AMA related IgG1 at all PP time intervals studied (p less than 0.001), but IgG4 was only increased at 5-7 months PP (p less than 0.05). PPT:AMA-when compared to E:AMA- have significantly increased IgG4 at 2-4 (p less than 0.001), 5-7 and 10-12 (p less than 0.05) months PP, but IgG1 is only increased at 5-7 months PP (p less than 0.05).