Cytolytic T lymphocytes with natural killer activity in thyroid infiltrate of patients with Hashimoto's thyroiditis: analysis at clonal level.

T Lymphocytes from thyroid infiltrates and peripheral blood (PB) of 3 patients with Hashimoto's thyroiditis (HT) were cloned using a microculture system previously shown to allow the clonal expansion of virtually all PB T lymphocytes from normal individuals. The phenotypic and functional features of a total number of 153 clones from thyroid infiltrates and 206 clones from PB were examined and compared with those of 272 clones derived from normal PB and spleens. The majority of clones derived from thyroid infiltrates of patients with HT had the cytotoxic/suppressor (T8+) phenotype, whereas the majority of clones from PB expressed the helper/inducer (T4+) phenotype. In addition, a consistent proportion (25%) of clones derived from PB of one patient had a phenotype (T3+T4-T8-) that was only occasionally found on clones obtained from PB or spleens of normal subjects. Most clones derived from both PB and thyroid infiltrates of the patients with HT had cytolytic activity, assessed by a lectin-dependent cytolytic assay against the murine P815 tumor cell line. The high frequency of cytotoxic T cells in thyroid infiltrates was related to the increased proportion of T8+ cells, whereas enhanced percentages of cytotoxic cell precursors with T4+ and T3+T4-T8- phenotypes primarily accounted for the high frequency of cytolytic T cells in the PB of the same patients. Many cytolytic T cell clones derived from thyroid infiltrates also had natural killer activity against human K562 and MOLT-4 target cells. These data provide the first functional analysis of T lymphocytes infiltrating the thyroid gland in patients with HT and suggest that the high proportions of cytolytic T cell precursors found in both thyroid infiltrates and PB of these patients may be of importance in determining the tissue damage in thyroid autoimmune disease.