Thymus reticulum of autoimmune mice. 3. Ultrastructural study of NOD (non-obese diabetic) mouse thymus.

The non-obese diabetic (NOD) mouse develops spontaneous insulin-dependent diabetes mellitus. Converging lines of evidence indicate that the disease is of autoimmune origin and is primarily mediated by T cells. It thus appeared interesting to study the morphology of the thymic microenvironment in order to determine whether the architecture and/or the cellular components of the organ are altered. In the NOD mouse, significant aspects of involution were observed as early as the first month of life, forming a heterogeneous pattern with non-involuted areas. With time, these involuted aspects increased in surface and severity. In non-involuted zones vacuolization of epithelial cells was noted, as well as infiltration by plasma cells and the presence of numerous macrophages with high phagocytic activity. Involuted areas, forming a cellular layer as if cells had lost their limiting membranes, were crossed by a great number of cystic cavities bordered by epithelial cells and cells containing granulations. Their lumens contained lymphocytes and a few macrophages. These observations, which are reminiscent of similar reports made in other autoimmune mouse strains, may be related to the functional thymic abnormality thought to participate in the pathogenesis of autoimmune disease.