Inhibition of125I Organification and Thyroid Hormone Release by Interleukin-1, Tumor Necrosis Factor-α, and Interferon-γin Human Thyrocytes in Suspension Culture*

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Abstract
To elucidate the mechanism of decreased 131I uptake by the thyroid gland in patients with subacute thyroiditis and painless thyroiditis, human thyroid follicles were cultured with interleukin-1 (IL-1), tumor necrosis factor -α (TNFα), and/or interferon -γ (IFNγ), and the effects of these cytokines on thyroid function were studied in vitro. When human thyrocytes were cultured in RPMI-1640 medium containing 0.5% fetal calf serum and TSH for 5–8 days, the cells incorporated 125I, synthesized de novo [125I]iodotyrosines and [125I]iodothyronines, and secreted [125I]T4 and [125I]T3 into the medium. IL-lα and IL-β inhibited 125I incorporation and [125I]iodothyronine release in a concentration-dependent manner. The minimal inhibitory effect was detected at 10 pg/ml. Electron microscopic examination revealed a marked decrease in lysosome formation in IL-1-treated thyrocytes. TNFα and IFNγ also inhibited thyroid function in a concentration-dependent manner. Furthermore, when thyrocytes were cultured with IL-1, TNFα and IFNγ, these cytokines more than additively inhibited thyroid function. Although the main mechanism of 131I uptake suppression in the thyroid gland in subacute thyroiditis is due to cellular damage and suppression of TSH release, our present findings suggest that IL-1, TNFα, and IFNγ produced in the inflammatory process within the thyroid gland further inhibit iodine incorporation and at least partly account for the decreased 131I uptake by the thyroid gland in destruction-induced hyperthyroidism.