Homing Receptor Expression in Grafts of Purified Thymic Epithelium

Abstract

Grafts of purified thymic epithelium have been used to study the role of the thymic microenvironment in T cell differentiation^1–6. The ability of such grafts to immunologically reconstitute either nude mice or thymectomized, irradiated and hematopoietically reconstituted hosts has demonstrated that they are only partially able to reconstitute the host animal, as neither lymphocyte phenotype frequencies nor functional responsiveness of the graft derived peripheral (splenic) T cell population reaches normal (intact) levels^2,3,6. More recently it has been suggested that the expression of lymphocyte homing receptors may be important in the selection of thymocytes destined to emigrate from the thymus, as well as their localization in the periphery^7–9. In the studies reported here, we have examined homing receptor expression in grafts of purified thymic epithelium and in the peripheral lymphoid organs of grafted nude mice. Results showed that, although incomplete, T cell reconstitution did take place in these animals. The presence of MEL-14 positive cells in the graft suggests that the presence or absence of homing receptor expression in these grafts was not solely responsible for the incomplete T cell emigration and peripheralization seen in these animals.