Human lymphocyte binding and deiodination of thyroid hormones in relation to thyroid function

The human lymphocyte has been investigated regarding its function as a thyroid hormone target cell. Binding and deiodination of the thyroid hormones were determined after simultaneous incubation of 131I-labelled L-thyroxine (131I-T4) and 125I-labelled L-triiodothyronine (125I-T3) with lymphocytes from healthy subjects, from hyperthyroid and primary hypothyroid patients before and after treatment. The mean percentages of binding, 8.0 +/- 0.5 (mean +/- SEM) for 131I-T4, and 9.7 +/- 0.4 for 125I-T3 in the control group, were increased in the hyperthyroids to 10.1 +/- 0.4 and 12.7 +/- 0.6 respectively, and in the hypothyroids to 10.9 +/- 0.7 and 12.8 +/- 0.6. All elevated values returned to normal with successful treatment. The mean percentage of deiodination, 12.0 +/- 1.7 for 131I-T4, and 6.5 +/- 0.9 for 125I-T3 in the control group, showed a threefold increase in the hyperthyroid patients, to 35.9 +/- 3.2 and 20.2 +/- 1.9 respectively and remained unaltered in the hypothyroid patients. The values of successfully treated hyperthyroid patients were normal and those of the treated hypothyroid patients below normal.