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Abstract

In this study, we provide the first report on the production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by human thyroid epithelial cells. Primary cultures of highly purified thyrocytes and thyroid-derived fibroblasts (n=3) and three thyroid anaplastic and one largely papillary carcinoma cell lines were exposed to different potent GM-CSF stimulators, employing interleukin 1α (Il-1α) and tumour necrosis factor-α (TNF-α). Cytokine mRNA levels were monitored by semiquantitative reverse transcriptase-PCR including an internal heterologous competitor fragment after 3, 6 and 18 h of culture. Culture supernatants were assayed for GM-CSF using a highly sensitive ELISA (detection limit ≤ 0·5 pg/ml) after 24 h.

Basal GM-CSF mRNA expression was higher in fibroblasts and SW 1736 cells compared with thyrocytes, C 634, 8505 C and HTh 74 cells. GM-CSF was spontaneously secreted by fibroblasts (means ± s.e.m.; 43 ± 15 pg/ml), SW 1736 (59 ± 4 pg/ml), HTh 74 (34 ± 4 pg/ml) and C 643 cells (12 ± 1 pg/ml) but not by thyrocytes and 8505 C cells. Treatment with Il-1α (10 U/ml) resulted in a marked increase of GM-CSF mRNA within 3 h and an increase or induction of protein expression in thyrocyte (2350 ± 214 pg/ml), fibroblast (5242 ± 1400 pg/ml), SW 1736 (20016 ± 280 pg/ml) and C 643 cultures (1285 ± 79 pg/ml). Stimulation with TNF-α (10 U/ml) yielded divergent results. No significant increase of GM-CSF mRNA or protein expression was found in thyrocytes although TNF-α receptor expression in these cells is well documented. Stimulation with TNF-α resulted in an increased GM-CSF production in fibroblasts (361 ± 14 pg/ml), HTh 74 (148 ± 51 pg/ml) and SW 1736 cultures (235 ± 43 pg/ml). TSH (10 mU/ml) did not stimulate GM-CSF secretion in thyrocytes and HTh 74 cells, both expressing the TSH receptor. Phorbol 12-myristate 13-acetate (10 ng/ml) enhanced GM-CSF mRNA and protein levels in all cell types investigated.

Our data suggest that both thyrocytes and fibroblasts synthesize GM-CSF in response to Il-1α, but only fibroblasts respond to TNF-α with a significant increase in GM-CSF. Anaplastic thyroid carcinomas are potential GM-CSF producers.

Journal of Endocrinology (1996) 151, 277–285

Abstract

Stimulation of human peripheral blood monocytes with the thyroid hormones tri-iodothyronine (T₃) and thyroxine (T₄) enhanced their ability to mature into cytologically and functionally characteristic veiled/dendritic cells. Veiled/dendritic cell transition induced by T₃ and T₄ was dependent on the production of granulocyte-macrophage colony-stimulating factor (GM-CSF), tumour necrosis factor-α (TNFα) and interleukin-6 (IL-6) in the culture, since the addition of antibodies specific for GM-CSF, TNFα and IL-6 to the culture system had blocking effects. The addition of antibodies to macrophage colony-stimulating factor and IL-1 had no effects. Contaminating T cells and B cells did not contribute to the transition of monocytes to veiled/dendritic cells, and it is therefore likely that the GM-CSF, TNFα and IL-6 produced in the culture system were derived from the monocytes themselves.

Stimulation of the blood monocytes with an optimal concentration of metrizamide (14·5%), reverse T₃ (rT₃; 2 × 10⁻¹⁰ m) or highly iodinated thyroglobulin (Tg; 2 × 10⁻¹¹ m) also resulted in an increased transition of monocytes to veiled/dendritic cells, but to a lesser extent in comparison with the thyroid hormones (T₃, 31 ±6% and T₄, 25 ±5% vs rT₃, 22 ± 8% and Tg with an iodination grade of 0·37%: 20 ± 4% veiled/dendritic cells). Administration of anti-GM-CSF, anti-TNFα and anti-IL-6 to the culture system also had blocking effects on the transition from monocytes to veiled/dendritic cells induced by the iodinated 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?).

Journal of Endocrinology (1994) 140, 503–512