Increased numbers of CD5+ B cells in the thymus of estradiol benzoate-treated rats.

In the present work we combine both flow cytometry and in situ immunohistochemical techniques to study the changes affecting a minor B cell population described within the normal rat thymus, after treatment with estradiol benzoate (EB). Our results, in agreement with previous data, show that the vast majority of these intrathymic B cells are CD5+. The existence of CD5+ B cells was confirmed flow cytometrically in both cervical lymph nodes and spleen of control, adult Wistar rats. Moreover, after EB administration intrathymic B cells increased significantly especially in those rats receiving 500 micrograms of EB, constituting cell masses around the blood vessels of cortico-medullary area and in the thymic medulla. We discuss the significance of this increased number of intrathymic CD5+ B cells, which is probably due to a selective cell migration from the periphery into the thymus, from the view of the effects of estradiol on the thymic vascular permeability.