Effect of irradiation on the release of lymphocytes from the thymus

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, 10(6) 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 10(6) 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.

A comparison of the acute effects of radiation therapy, including or excluding the thymus, on the lymphocyte subpopulations of cancer patients

Radiation therapy to either mediastinum or pelvis causes a rapid decrease in circulating lymphocytes of both B and T types and in addition an impairment in the function of the remaining lyphocytes, as measured by their ability to proliferate in response to mitogens. The acute depression is short-lived. Substantial recovery is apparent within 3 wk after cessation of therapy; however, most patients show a modest, chronic depression in both numbers and functional capacities of circulating lymphocytes. T cells are somewhat more sensitive than B cells, but both are affected. Irradiation of the thymus per se seems to have little influence on the acute changes which occur, as patients receiving pelvic and mediastinal (including thymic) radiotherapy show a similiar degree of lymphopenia and depression of lymphocyte responsiveness.