To reflect human autoimmune thyroiditis, thyroid peroxidase (not thyroglobulin) antibodies should be measured in female (not sex‐independent) NOD. H2 h4 mice

Summary NOD. H2 h4 mice are the most commonly used model for human autoimmune thyroiditis. Because thyroid autoimmunity develops slowly (over months), NOD. H2 h4 mice are usually exposed to excess dietary iodide to accelerate and amplify the process. However, unlike the female bias in human thyroid autoimmunity, autoantibodies to thyroglobulin (TgAb) are reported to be similar in male and female NOD. H2 h4 . We sought evidence for sexual dimorphism in other parameters in this strain maintained on regular or iodized water. Without iodide, TgAb levels are higher in males than in females, the reverse of human disease. In humans, autoantibodies to thyroid peroxidase (TPOAb) are a better marker of disease than TgAb. In NOD. H2 h4 mice TPOAb develop more slowly than TgAb, being detectable at 6 months of age versus 4 months for the latter. Remarkably, unlike TgAb, TPOAb levels are higher in female than male NOD. H2 h4 mice on both regular and iodized water. As previously observed, serum T4 levels are similar in both sexes. However, thyroid‐stimulating hormone (TSH) levels are significantly higher in males than females with or without iodide exposure. TSH levels correlate with TgAb levels in male NOD. H2 h4 mice, suggesting a possible role for TSH in TgAb development. However, there is no correlation between TSH and TPOAb levels, the latter more important than TgAb in human disease. In conclusion, if the goal of an animal model is to closely reflect human disease, TPOAb rather than TgAb should be measured in older female NOD. H2 h4 mice, an approach requiring patience and the use of mouse TPO protein.