Intrathyroidal and circulating lymphocyte subsets in different stages of autoimmune postpartum thyroiditis

Postpartum thyroiditis (PPT) is a reversible form of lymphocytic thyroiditis which has been attributed to an aggravation of preexisting subclinical autoimmune thyroiditis. In this study no differences in circulating lymphocyte subsets were found between 9 thyrotoxic and 18 hypothyroid PPT patients and normal subjects. We obtained sufficient numbers of thyroid-infiltrating lymphocytes for surface marker characterization in 3 women in the thyrotoxic phase and in 10 women in the hypothyroid phase of PPT. Cells were identified by conventional T and B cell markers as well as by monoclonal antibodies (OKT) directed against different T cell subsets in a microscale immunofluorescence assay. In the hypothyroid patients a relative accumulation of B cells (31% vs. 17%; P less than 0.01 by the Wilcoxon signed rank test) was found within the thyroid when compared to peripheral blood. A relative decrease in intrathyroidal supressor-cytotoxic (OKT 8+) T cells (19% vs. 28%; P less than 0.01) resulted in an increased intrathyroidal helper to suppressor-cytotoxic (OKT 4+/OKT 8+) T cell ratio (3.0 vs. 2.0; P less than 0.01). Intrathyroidal lymphocyte subsets in the thyrotoxic patients were comparable to those in the hypothyroid patients. These findings, which are similar to those we previously obtained in patients with chronic Hashimoto's thyroiditis, may indicate that local synthesis of thyroid-directed autoantibodies is of primary importance in all stages of autoimmune thyroiditis.