HIGH-FREQUENCY OF THYMIC ECTOPY IN THYROIDS FROM AUTOIMMUNE-PRONE NONOBESE DIABETIC FEMALE MICE

BACKGROUND: The female nonobese diabetic (NOD) mouse, a well known exp erimental model to study autoimmune type 1 diabetes, also spontaneousl y develops thyroiditis. In this study, we report an abnormally high fr equency of thymic ectopy in thyroids from NOD mice. EXPERIMENTAL DESIG N: Thyroids and thymuses from NOD mice and from control mice of differ ent strains were processed for light and electron microscopy and for i mmunohistochemistry. RESULTS: Ectopic thymic tissue was observed in th e thyroids of 80% of female NOD mice, whereas it was not found in cont rol age-paired female mice from various other strains. The thymic tiss ue was present beneath the capsule as a large and unique fragment cons isting of both a cortical dark one and a medullary light region. Thymi c ectopies, as the thymus itself, contained thymocytes expressing both L3T4 and Lyt2 antigens, specific respectively for T helper and T supp ressor/cytotoxic cells. Cortical and medullary epithelial cells were a lso easily identified by electron microscopy and by immunohistochemica l staining using ER-TR4 and ER-TR5 monoclonal antibodies. CONCLUSIONS: Our observation could be an indication for a relation between abnorma l thymus development and autoimmune disorder such as thyroiditis.