Testosterone binding sites in the rat thymus during late embryonal and postnatal period.

Using immunoperoxidase staining with anti-testosterone Ab, has been shown that the cells binding testosterone were present in the rat thymus and that these cells are localized in the outer thymic cortex as well as in cortico-medullary region and medulla. Immunoperoxidase staining with that Ab at electron microscopy level showed that thymocytes as well as thymic epithelial cells bind this hormone. Combined immunoperoxidase staining with anti-testosterone Ab and immunofluorescence method with mAbs specific for thymocytes or thymic epithelial cells, revealed that thymocytes binding this hormone are localized mainly in the outer cortex, while thymic epithelial cells binding testosterone were found in cortico-medullary region and medulla. These testosterone binding cells were found, for the first time, in the thymus of 18-day-old fetus. It has also been shown that their density increased markedly by the day 3 of postnatal life and continued to increase up to the adult stage of organ development. These results indicate that testosterone can influence upon function of specific thymic epithelial cells, localized in the corticomedullary region and medulla. Thus, the results also suggest that this hormone can modulate T cell proliferation and/or differentiation, not only directly acting on the T cells localized in the outer thymic cortex, but also indirectly modulating function of the thymic epithelial cells that bind this hormone.