CHANGES IN THE BLOOD THYMUS BARRIER OF ADULT RATS AFTER ESTRADIOL TREATMENT

The accessibility of the thymus parenchyma for relatively large Mw (+/ - 150 Kd) proteins has been studied by the intravenous injection of mo noclonal antibodies (mAbs) specific either for all T cells (His-17) or MHC class II molecules (His-19) in control and estradiol benzoate (EB )-treated adult Wistar rats. In controls, the transcapsular route rath er than cortical capillaries seems to be involved in the entry of mole cules into the thymus. By contrast, a specific staining for either T c ells (His 17) or MHC class II molecules (His-19 positive cells) disapp ears almost completely from the thymic cortex of EB-treated rats excep t in the immediate subcapsular epithelial cell layer. In these rats, T cells and epithelial cells intimately associated to blood vessels fro m both inner cortex and cortico-medullary border showed additional sta ining with the respective mAbs confirmed by electron microscopy. The d isappearance of the transcapsular route together with the increased va scular permeability of cortical blood vessels would be related to the reinforcement of the subcapsular epithelial cell layer and to direct e ffects of EB on vascular endothelia, respectively. These results are d iscussed in relationship to the cell migration into and out of adult t hymus, as suggested by the changes in intrathymic T cell subsets evalu ated by flow cytometry.