Thymic reticulum of autoimmune mice. I. Ultrastructural studies of the diabetic (db/db) mouse thymus.

The thymus of the db/db mouse, an autoimmune strain with insulin-dependent diabetes mellitus and manifesting hyperglycemia, polyuria, glycosuria and obesity, was observed by electron microscopy. Its comparison with normal thymuses and thymuses from non-diabetic obese mice has revealed two major differences: first, the presence of crystal-like structures in some of the numerous clear vacuoles in cells, and second, a modification of the cells forming the border of cystic cavities. These cells contain two types of granules which are quite plentiful. One variety is clear and big, and a second type is small and dense, with an aspect similar to that of secretion granules. It is hypothesized that the crystalloid formations found in epithelial cells, and the presence of small, dense granulations in cells bordering the cystic cavities, are a consequence of the abnormal storage of the thymic hormone, thymulin, which results from a secretory function defect. These observations suggest a possible role for the thymic reticulum in thymic function deficiencies.