Abstract
Age-dependent changes in follicle-associated epithelium (FAE), size and density of lymphoid follicles were investigated in the bursa of Fabricius of devolping chicks (0 week old to 24 week old). The effects of testosterone (TES) and cyclophosphamide (CY) on the structures of the bursa were also studied in chicks. The number of FAE determined by uptake of carbon particles increased until 6 week old. The value, however, declined gradually at following ages. On the other hand, the number of lymphoid follicles in the bursa estimated by size and density of lymphoid follicles was considered to change only a little before 22 week old. The results suggest that the number of FAE in the bursa determined by endocytic activity does not necessarily imply the number of lymphoid follicles in the bursa. The cells which uptake carbon particles at the bursal surface disappeared after administration of large amount of TES, although the lymphoid follicles remained even after the administration of TES. The result suggests that apparent decrease of the number of FAE after 6 week old may be caused by the fall in endocytic activity of FAE. Administration of CY caused a transient damage in FAE of the bursa. The result supports the view that FAE differs from other epithelial components of the bursa.
