Afferent migration of the Kurloff cells via lymphatics into the thymus of estradiol-treated guinea pigs.

Abstract

The spatial distribution and migration of Kurloff cells containing PAS-positive large inclusion bodies in the thymus of estradiol-treated guinea pigs were histochemically studied by a combination of light and electron microscopy. Male guinea pigs were examined at various intervals from 7 days to 3 months after a single subcutaneous injection of estradiol. Differentiation of lymphatics from blood capillaries was performed by a 5'-nucleotidase (5'-Nase) staining method and the occurrence of Kurloff cells within 5'-Nase-positive lymphatics was confirmed by ultrastructural histochemistry. Several Kurloff cells first appeared at 7 days within lymphatics in the thymic capsule or interlobular connective tissues. At 12-15 days after estradiol administration, a lymphatic accumulation, a so-called "lymphatic center", was seen in the thymic septa even though few Kurloff cells were present within the thymic parenchyma. The "lymphatic center" contained many Kurloff cells located in its periphery and in the surrounding marginal sinus which communicated with the thymic interlobular lymphatics. At 21 days after estradiol, Kurloff cells were preferentially accumulated along the corticomedullary junction extravascularly. Later the distribution was more diffuse. The conspicuous accumulation of Kurloff cells in the corticomedullary region could reflect an inability of Kurloff cells to use blood vessels as a route for migration. These findings strongly suggest the afferent migration of Kurloff cells into the thymus via lymphatics.