Hürthle cells predict hypothyroidism in interferon-γ transgenic mice of different genetic backgrounds

Hürthle cells have long been described in Hashimoto thyroiditis but remain of undetermined significance. We have previously shown that Hürthle cells and hypothyroidism develop in C57BL/6J mice expressing interferon-γ (IFNγ) in the thyroid. To assess the influence of genetic backgrounds on Hürthle cell development, we crossed C57BL/6J IFNγ transgenic mice to 14 strains and analyzed thyroid histopathology and function in a cohort of 389 mice (225 transgenic and 164 wild type) using a multiple linear regression model that also included strain, sex, genotype, and major histocompatibility complex haplotype. We then queried the Johns Hopkins surgical pathology electronic archive for "Hashimoto" and/or "thyroiditis" keywords, reviewed the reports, and reexamined the Hashimoto slides. Hürthle cells were markedly affected by the genetic background: they were prominent and associated with hypothyroidism in the C57BL/6J, C57BL/6ByJ, C57BL/10J, C57BLKS/J, C57L/J, C58/J, and BPN/3J IFNγ transgenic strains, whereas they are mild or absent in the BPH/2J, BPL/1J, LP/J, CBA/J, Balb/cJ, DBA/1J, and NOD/ShiLtJ strains. Hürthle cells were the strongest predictor of hypothyroidism after adjusting for all the other covariates in the regression model. Interestingly, transgenic mice of the BPL/1J, DBA/1J, and NOD/ShiLtJ strains developed a marked accumulation of intrathyroidal brown adipocytes that was significantly associated with improved thyroid function. Hürthle cells were mentioned in 23% of the Hashimoto reports but increased to 79% upon our slide review. This study reports a novel association of Hürhtle cells and brown adipocytes on thyroid function that should prompt a reconsideration of their significance and role in pathogenesis of autoimmune thyroiditis.