Ultracytochemistry of thymic epithelial cells in rats given organotin.

A combined light-and electron microscopic study of thymic changes in the adult rats after di-n-butyltin dichloride (DBTC) administration has been made. A rapid depletion of thymocytes in the cortex of thymus and subsequent rapid recovery of the number of thymocytes occurred. In this process, at 1-3 days after DBTC treatment the number of necrotic thymocytes was maximal. At 3-6 days, reticular epithelial cells were predominantly phagocytizing and acid phosphatase-positive in the cortex and cortico-medullary regions, where they appeared to develop from macrophage-like cells. During acute involution, it was likely that reticular epithelial cells were phagocytic and remove the necrotic thymocytes. The proportion of CD4+ CD8+ cells in the cortex of thymus was maximally reduced from day 3 onwards and reached the lowest level at 6 days after single oral dose of DBTC. On these days, the proportions of CD4- CD8- and single positive cell (CD4- CD8+ or CD4+ CD8-) subsets were relatively increased. These data suggest that DBTC preferentially causes an initial depletion of CD4+ CD8+ cells in thymus, and both macrophages and reticular epithelial cells of the cortex may be involved in the rapid removal of damaged thymocytes from thymus.