High frequency of thymic ectopy in thyroids from autoimmune prone nonobese diabetic female mice.

BACKGROUND

The female nonobese diabetic (NOD) mouse, a well known experimental model to study autoimmune type 1 diabetes, also spontaneously develops thyroiditis. In this study, we report an abnormally high frequency of thymic ectopy in thyroids from NOD mice.

EXPERIMENTAL DESIGN

Thyroids and thymuses from NOD mice and from control mice of different strains were processed for light and electron microscopy and for immunohistochemistry.

RESULTS

Ectopic thymic tissue was observed in the thyroids of 80% of female NOD mice, whereas it was not found in control age-paired female mice from various other strains. The thymic tissue was present beneath the capsule as a large and unique fragment consisting of both a cortical dark one and a medullary light region. Thymic ectopies, as the thymus itself, contained thymocytes expressing both L3T4 and Lyt2 antigens, specific respectively for T helper and T suppressor/cytotoxic cells. Cortical and medullary epithelial cells were also easily identified by electron microscopy and by immunohistochemical staining using ER-TR4 and ER-TR5 monoclonal antibodies.

CONCLUSIONS

Our observation could be an indication for a relation between abnormal thymus development and autoimmune disorder such as thyroiditis.