Fine structure of chicken thymic epithelial vesicles.

This paper describes the fine structure of epithelial vesicles as observed in the thymus of the chicken. Three types of vesicles are found. The largest is made up of a stratified columnar epithelium containing lymphoid cells. The lumen contains a fairly light material and cell debris. The lumen-bordering cells are columnar and their microvilli are sometimes developed to such an extent as to appear as a brush border. The wall of the vesicles contains lymphocytes and granular cells with dense granules 100-500 nm in diameter. Smaller vesicles are found which contain no lymphoid cells. They are made of a simple or stratified epithelium containing typical mucous cells, and columnar cells similar to the bordering cells of the large vesicles. The third type is an intracytoplasmic vesicle in epithelial reticular cells, which differs from usual vacuoles by the presence of microvilli and its often unusually large size. The morphology of the first 2 types of vesicles indicates a secretory capability, the function of which is unknown. Data from the literature suggest that the third type produces the factor(s) conferring cellular immunological competence.