Nuclear Medicine Technology and Other Health Applications Project Title: [ymphocytopoiesis and Transplantation Immunology 16. Technical Progress in FY 1973: (Cont'd.) RX-01-03-(d) Routes of migration of lymphocytes from the calf thymus were shown to be through the thymic lymphatics and veins. The daily output of lymphocytes from the thymus is 3-4 times greater than the number of small Lymphocytes in the blood, The question of magnitude of thymic cell migration to bovine Peyer's patches is unresolved. The animal studies were completed, but the autoradiographic data analysis is not. Most investigators studying thymic lymphocytopoiesis and migration either label suspensions of thymic cells or inject directly into the thymus, distorting its architecture. Since studies following intra-arterial perfusion of the thymus with tritiated thymidine showed a different distribution than the above techniques, distribution of thymic cells after intravenous injectidn of labeled thymic cell suspension was compared to that following intraarterial perfusion. Following i.v. injection a greatly increased trapping of thymic cells within the spleen was observed, suggesting that infusion of thymic cell suspensions may provide quantitatively erroneous results. Since transplanted allogeneic lymphocytes are believed responsible for the development of graft vs host disease after bone marrow transplantation, the capability of isogeneic and allogeneic lymphocytes to recirculate from blood to lymph was investigated using in vivo and in vitro thymidine and cytidine labeling followed by transfusion or cross circulation. Preliminary results show that isogeneic lymphocytes are capable of recirculating from blood to lymph whereas the allogeneic are not endowed with this capacity. This work was planned for completion in FY 1973 but due to Lack of personnel its completion is now planned for FY 1974, The turnover, in various lymphoid organs, of DNA labeled with tritiated thymidine was compared to that of DNA labeled with I-125deoxyuridine using mice 1-8 days after birth. Significant differences in the exponential declines of these two isotopes indicate that in addition to immigration, there is a significant cell death taking place in the thymus during this period of development. Similar analyses of peripheral lymph nodes suggest that cell death and reutilization of thymidine occurs in these organs. This is contrary to findings in lymph nodes of young adult mice and further studies are underway utilizing iso d lymph node perfusion to eliminate the effect of migration of labelcells into and out of the Lymph node. ke response of the lymphocytic system of the goats to ECIB was studied during and up to two months after ECIB by observing changes in the lymphocyte concentration and the "flash" labeling index of lymphocytes in blood, thoracic duct lymph, thymus, prescapular lymph node, spleen, (See Continuation Sheec) 1119230 RX-72 t