Abstract
The distribution of cells labeled with generally tritiated de-oxycytidine ([G-3H]CdR) was similar to that of cells labeled with 5-tritium labeled deoxycytidine ([5-3H]CdR) in the thymus and mesenteric lymph nodes. In the thymic cortex and germinal centers of mesenteric lymph nodes, however, radioautographic reactions showed more intense labeling with [G-3H]CdR than with [5-3H]CdR. In the thymic medulla and areas outside the germinal centers, no significant difference in labeling intensity was found between tissue sections labeled with [G-3H]CdR and with [5-3H]CdR. Labeling intensities with tritiated thymidine ([3H]TdR) in the thymic cortex and germinal centers of mesenteric lymph nodes were greatly enhanced by the administration of 5-fluorodeoxyuridine (5-FUdR), whereas those in the thymic medulla and areas outside the germinal centers were only slightly enhanced with 5-FUdR treatment. In the presence of 5-FUdR, the total thymic and mesenteric lymph node cell populations incorporated only little [G-3H]CdR. These results indicate that the lymphocytes which are labeled heavily with [G-3H]CdR in the thymic cortex and germinal centers have the strong metabolic ability to utilize CdR for DNA synthesis, whereas this ability is relatively weak in cells which are labeled strongly with [3H]TdR in the thymic medulla and areas outside the germinal centers.
