Studies on Lymphocytes. III. Effects of Extracorporeal Irradiation of the Circulating Blood upon the Lymphoreticular Organs in the Calf

1. Extracorporeal x-irradiation of the circulating blood of the calf severely depletes the population of small lymphocytes within the body.

2. The number of circulating blood lymphocytes drops to a low constant level after 12 hours of extracorporeal irradiation that is maintained up to 48 hours of extracorporeal irradiation. On the other hand the lymphoreticular tissues continue to lose lymphocytes between the twelfth and forty-eighth hour of extracorporeal irradiation. Therefore, the apparent steady-state lymphocyte level in the peripheral blood is maintained by a non-steady-state process in the lymphoreticular organs where the new production of lymphocytes is far insufficient to replace the cells leaving these tissues.

3. The cellular debris caused by extracorporeal irradiation of the circulating blood is found within the spleen, lung, liver, lymph nodes and elsewhere, in this order of relative concentration.

4. A unique pathologic phenomenon is produced within two days of extracorporeal irradiation of the circulating blood, e.g., a combination of intact or even actively proliferating germinal centers with a marked diminution in the concentration of small lymphocytes. This technic of depletion of small lymphocytes, leaving germinal centers intact, should permit studies for evaluation of the relative importance of germinal centers vs. small lymphocytes in primary and secondary immune responses.

5. The above findings are discussed in relation to lymphocyte production rate, stores, mobilization and recirculation.