Enhanced iodine supplementation alters the immune process in a transgenic mouse model for autoimmune thyroiditis

Context: The impact of excessive iodine intake on the development of autoimmune thyroiditis (AIT) is still under debate. Transgenic, antibody devoid, TAZ10 mice spontaneously develop AIT due to autoreactive thyreoperoxidase-specific T cells. In this model, development of AIT is determined by a T cell infiltration of the thyroid gland leading to an elevation of serum TSH levels and a significant gain in weight. In the present study we investigated the impact of moderate and high iodine supplementation on the course of disease in these mice, which are immunologically prone to AIT. Methods: In addition to normal nutrition, mice were supplemented for 20 weeks with 2.5 µg vs. 5 µg iodine per ml drinking water which corresponds to a human daily iodine supplementation of 150 µg, 315 µg, and 615 µg iodine. AIT-defining parameters (gain in weight, elevation of serum TSH levels, and cellular infiltration of the thyroid) and immunological effects were analyzed. Results: No significant differences were displayed when comparing weight and serum TSH levels in the iodine supplemented versus control groups. Increased thyroid infiltrates with CD8+ T cells were detected by FACS and immunofluorescence staining in mice supplemented with elevated iodine amounts (315 µg respectively 615 µg iodine per day). Immunological monitoring revealed selective changes in immune cell frequencies (CD8+ and regulatory T cells, NK cells) and cytokine production (interferon-gamma, interleukin 1α and 17), however, without affecting the overall immune balance. Conclusion: Our results demonstrate that elevated iodine supplementation has no physical impact on the course of disease in transgenic, antibody devoid, TAZ10 mice, which are immunologically prone to AIT.