Thyrotropin Alters T Cell Development in the Thymus in Subclinical Hypothyroidism Mouse Model

Subclinical hypothyroidism (SCH) is highly prevalent in the general population and is associated with potential deleterious effects. Although developing T cells express thyroid-stimulating hormone receptor (TSH-R), the changes of T cell development in thymus in SCH have not been fully clarified. SCH mouse model, which is characterized by elevated serum TSH but similar thyroid hormone levels, was used to study the role of TSH in T cell development. Thymus weight of SCH mice increased 18% compared with controls. Importantly, the frequencies of CD4⁺ and CD8⁺ single-positive (SP) thymocytes increased 38% and 44%, respectively. We demonstrated that TSH protected thymocytes from apoptosis as evidenced by a significant decrease of Annexin V-positive thymocytes in SCH mice. Further analysis showed that extracellular-regulated kinases (ERK) 1/2 in thymus were activated in SCH mice. With analysis of T cell receptor excision circles (TREC), we found that TSH increased recent thymic emigrants (RTE) in spleen tissue in SCH mice. Thus, these results suggest that TSH promoted T cell development and enhanced the thymic recent output in SCH mice, possibly by suppression of apoptosis of thymocytes, indicating that modification of the ERK signalling pathways.