PERSISTENCE OF DONOR-DERIVED CELLS IN THYMUS GRAFTS LYMPH NODES AND SPLEENS OF RECIPIENT MICE

Abstract

Thymus was labelled in vivo by injecting newborn C3H/Bi mice with three or four doses of 2 [mu]q of [H3]thymidine. The labelled thymus was grafted into the kidney capsule of 22-25-day-old intact and thymectomized svngeneic recipients which were killed 18, 41 or 42 days later. The grafts and lymphoid tissue were sectioned and examined by autoradiography after exposure times of up to 26 weeks. Small and medium labelled lymphocytes were seen in the thymus-dependent areas of the lymph nodes and spleen of all recipients provided the sections were exposed for a sufficiently long period. More labelled cells were seen in recipients killed at 18 days than at 41 or 42 days after grafting. It was concluded that these cells were the direct descendants of those cells labelled in the graft. There was no evidence of re-utilization of the isotope label. Most of the cells originally labelled in the graft either lost their label by multiple divisions or were replaced by unlabelled cells; although the epithelial-reticular cells remained heavily labelled. The importance of this last finding is discussed.