Figure 3. Secretion of proinflammatory cytokines during severe illness or stress inhibits the activity of hepatic deiodinase type 1- suppressing the peripheral conversion of T4 to T3. They also suppress intrathyroidal hormone synthesis, TRH release and TSH secretion from the pituitary. IL-6, interleukin-6; IL-1, interleukin-1; TNF-α, tumor necrosis factor alpha; INF-γ, interferon gamma; TGF-β, tumor growth factor beta; TG, thyroglobulin; NIS, sodium/iodide symporter; TSH, thyroid stimulating hormone; TRH, Thyrotropin-releasing hormone.