In Vivo Elimination of Allogeneic Lymphocytes in Normal and T‐Cell‐Deficient Rats

The distribution of allogeneic and syngencic thoracic duct lymphocytes was studied over 24 h in normal and T‐cell‐dcficient animals (thymectomized, irradiated rats.‘B rats’, or congenitally athymic nude rats). Initial migration from blood was no less for allogeneic than for syngencic cells. After 24 h, however, a marked deficit of radioactively labelled allogeneic cells as compared with syngeneic cells was found in the lymphoid tissue, whereas the allogeneic isotope was recovered in a relatively greater amount in liver, kidneys, and cell‐free plasma and lymph. Most of the allogeneic cells are evidently destroyed within the first 24 h and their isotope released into body fluids. Our studies also revealed this process to be even more evident in T‐cell‐depleled environments. Autoradiographic studies of recipient nude rat spleens showed that allogeneic cells were not found in the great number seen in syngeneic transfers, but a high grain density in the periarteriolat lymphocyte sheath area could be observed. Granula seemed to be predominantly located over large non‐lymphoid cells. The elimination of allogeneic lymphocytes is therefore governed by mechanisms independent of an intact thymus and may be due to a cell population or factor more active in nude animals than in their non‐nude littermates.