Interferon-gamma suppresses thyrotropin receptor promoter activity by reducing thyroid transcription factor-1 (TTF-1) binding to its recognition site

Expression of TPO and ThOXs in human thyrocytes is downregulated by IL-1alpha/IFN-gamma, an effect partially mediated by nitric oxide

Morphological and functional alterations in Hashimoto's thyroiditis (HT) are predominantly mediated by Th1 cytokines through apoptotic cell death. This ultimate step could be preceded by functional injuries in thyroid hormone synthesis. The action of two Th1 cytokines (IL-1alpha/IFN-gamma) on thyroperoxidase (TPO) and thyroid oxidase (ThOXs) expression was tested in human thyrocytes isolated from normal tissues, Graves' disease (GD) tissues, and autonomous toxic nodules. There was no evidence of cell death. Nitric oxide (NO) release was induced by cytokines but was absent when NG-nitro-L-arginine methyl ester (L-NAME) was coincubated. When thyrotropin (TSH)-incubated normal and GD thyrocytes were treated with IL-1alpha/IFN-gamma, TPO and ThOXs protein and mRNA expression dropped, a decrease partially prevented by L-NAME, suggesting that NO acts as a mediator of Th1 effects. In thyrocytes from autonomous toxic nodules, the high level of TPO and ThOXs protein expression was not influenced by TSH or by cytokines, a finding partially reproduced when normal thyrocytes were treated with increasing concentrations of TSH. In conclusion, incubation of normal or GD thyrocytes with Th1 cytokines induces a significant reduction in TSH-increased expression of both TPO and ThOXs, an effect partially mediated by NO. The thyroid cell function can therefore be severely affected in HT, even when cells remain viable. In autonomous toxic nodules, cells become partially insensitive to exogenous Th1 cytokines.

Lower concentration of serum soluble CD8 in severe Hashimoto's disease

To investigate the roles of soluble CD4 (sCD4) and CD8 (sCD8) in the severity of autoimmune thyroid diseases, we examined serum concentrations of sCD4 and sCD8 in various degrees of severity of Hashimoto's disease (HD) and Graves' disease (GD) by enzyme immunoassay. The serum concentration of sCD8 was lower in euthyroid patients with HD undergoing treatment for hypothyroidism (severe HD) than in untreated, euthyroid patients with HD (mild HD), but the sCD4 concentration did not differ between patients with severe and mild HD. The serum sCD8 concentration was negatively correlated with the proportion of CD25(+) cells in CD8(+) cells in patients with severe HD. Serum sCD4 and sCD8 concentrations did not differ between euthyroid patients with GD in remission and those with intractable GD. These results indicate that serum sCD8 is involved in the severity of HD, possibly by down-regulating the function of cytotoxic T cells.

Complex roles of Stat1 in regulating gene expression

Stat1 is a fascinating and complex protein with multiple, yet contrasting transcriptional functions. Upon activation, it drives the expression of many genes but also suppresses the transcription of others. These opposing characteristics also apply to its role in facilitating crosstalk between signal transduction pathways, as it participates in both synergistic activation and inhibition of gene expression. Stat1 is a functional transcription factor even in the absence of inducer-mediated activation, participating in the constitutive expression of some genes. This review summarizes the well studied involvement of Stat1 in IFN-dependent and growth factor-dependent signaling and then describes the roles of Stat1 in positive, negative and constitutive regulation of gene expression as well as its participation in crosstalk between signal transduction pathways. Oncogene (2000).

Hypothyroidism in transgenic mice expressing IFN-gamma in the thyroid

IFN-gamma has been implicated with contradictory results in the pathogenetic process of autoimmune (Hashimoto's) thyroiditis, the most common cause of hypothyroidism in adults. To test whether the local production of IFN-gamma can lead to thyroid dysfunction, we have generated transgenic mice that express constitutively IFN-gamma in the thyroid follicular cells. This expression resulted in severe hypothyroidism, with growth retardation and disruption of the thyroid architecture. The hypothyroidism derived from a profound inhibition of the expression of the sodium iodide symporter gene. Taken together, these results indicate a direct role of IFN-gamma in the thyroid dysfunction that occurs in autoimmune thyroiditis.