EFFECT OF THYROID-HORMONES AND OTHER IODINATED COMPOUNDS ON THE TRANSITION OF MONOCYTES INTO VEILED DENDRITIC CELLS - ROLE OF GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR, TUMOR-NECROSIS-FACTOR-ALPHA AND INTERLEUKIN-6/

Stimulation of human peripheral blood monocytes with the thyroid hormo nes tri-iodothyronine (T-3) and thyroxine (T-4) enhanced their ability to mature into cytologically and functionally characteristic veiled/d endritic cells. Veiled/dendritic cell transition induced by T-3 and T- 4 was dependent on the production of granulocyte-macrophage colony-sti mulating factor (GM-CSF), tumour necrosis factor-alpha (TNF alpha) and interleukin-6 (IL-6) in the culture, since the addition of antibodies specific for GM-CSF, TNF alpha, and IL-6 to the culture system had bl ocking effects. The addition of antibodies to macrophage colony-stimul ating factor and IL-1 had no effects. Contaminating T cells and B cell s did not contribute to the transition of monocytes to veiled/dendriti c cells, and it is therefore likely that the GM-CSF, TNF alpha and IL- 6 produced in the culture system were derived from the monocytes thems elves. Stimulation of the blood monocytes with an optimal concentratio n of metrizamide (14.5%), reverse T-3 (rT(3); 2 x 10(-10) M) Or highly iodinated thyroglobulin (Tg; 2 x 10(-11) M) also resulted in an incre ased transition of monocytes to veiled/dendritic cells, but to a lesse rextent in comparison with the thyroid hormones (T-3, 31 +/- 6% and T- 4, 25 +/- 5% vs rT(3), 22 +/- 8% and Tg with an iodination grade of 0. 37%: 20 +/- 4% veiled/dendritic cells). Administration of anti-GM-CSF, anti-TNF alpha and anti-IL-6 to the culture system also had blocking effects on the transition from monocytes to veiled/dendritic cells ind uced by theiodinated compounds. The mechanisms by which such iodinated compounds act on the monocyte to veiled/dendritic cell transition can only be speculated on (interference H2O2-generating system?).