Peripheral K Lymphocytes in Autoimmune Thyroid Disease: Decrease in Graves' Disease and Increase in Hashimoto's Disease*

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Abstract
Peripheral blood levels of K lymphocytes were measured in patients with autoimmune thyroid diseases using a plaque-forming cell technique. In thyrotoxic patients with Graves' disease, the percentage (mean ± SD, 2.6 ± 1.5% n = 16; P < 0.001) and absolute count (48 ± 23/mm3; P < 0.01) of K lymphocytes were significantly lower than those in normal controls (4.7 ± 1.4% and 79 ± 30/mm3; n = 24). These measurements of K cells were normal in euthyroid patients with Graves' disease on antithyroid drug therapy or in remission. In euthyroid or hypothyroid patients with Hashimoto's disease, the mean values for the percentage (6.0 ± 2.9% n = 16) and absolute count (120 ± 95/mm3) of K lymphocytes were higher than those in normal controls, but the differences were not statistically significant. However, the mean percentage of large plaque-forming K lymphocytes, which might have more active antibody-dependent cell-mediated cytotoxicity, was significantly higher in Hashimoto's disease (1.07 ± 0.79% n = 13) than in normal controls (0.47 ± 0.40% n = 24; P < 0.05) and cases of thyrotoxic Graves' disease (0.15 ± 0.34% n = 13; P < 0.001). In thyrotoxic patients with Hashimoto's disease (destruction-induced thyrotoxicosis), the K lymphocyte count (124 ± 55/mm3; n = 14; P < 0.01) was significantly higher than that in normal controls. The percentage and absolute count of K lymphocytes were inversely correlated with the serum level of T4, free T4 index, T3, and free T3 index in autoimmune thyroid disease when thyrotoxic patients with Hashimoto's disease were excluded. There was no correlation between K lymphocytes and other variables, such as goiter size, titers of antithyroid antibodies, and proptosis, in patients with untreated Graves' disease or in the whole group of cases of autoimmune thyroid disease. These data suggest that the higher number of K cells and increased antibody-dependent cell-mediated cytotoxicity lead to reduced thyroid function in autoimmune thyroid disease.