Influence of thymectomy, transfer of thymus and bone marrow cells and treatment with thymosin on the depressed splenic release of lymphocytes into the blood after irradiation.

The content of lymphocytes in blood samples from the splenic vein and the splenic artery of guinea pigs was determined and the veno-arterial difference in number of cells was used as measure of the net release of cells from the spleen into the blood. The splenic release of lymphocytes was reduced after whole body irradiation with 300 rad. This reduction could partly be prevented by transfusion of bone marrow cells after irradiation, 106 cells being the most effective dose. In thymectomized, irradiated animals the restoration of the splenic release of lymphocytes after irradiation was impaired in comparison with sham-operated animals. In the thymectomized animals the transfusion of 106 thymus cells had a restitutive effect on the splenic release of lymphocytes, while transfusion of bone marrow cells or daily treatments with thymosin, alone or combined with transfusion of bone marrow cells, had no such restitutive effect. The results indicate that restoration of the splenic release of lymphocytes into the blood after irradiation is thymus dependent and probably caused by a traffic of lymphocytes from the thymus to the spleen.