Preferential Labeling of Rat Lymphocytes With a Rapid Rate of Turnover by Tritiated Deoxycytidine

Abstract

Lymphocytes in thymic cortex and germinal centers of lymphoid tissues are labeled intensely with generally labeled tritiated deoxycytidine [G-3H]dCyd whereas they are weakly labeled with methyl tritiated deoxythymidine [methyl-3H]dThd of the same specific activity, not only by single injection but also by an intensive injection schedule. [G-3H]dCyd can be used to label short-lived lymphocytes strongly, although not specifically. The distribution patterns of labeled lymphocytes were different depending on the injection schedules of [G-3H]dCyd.[G-3H]dCyd can be used as a precursor molecule for cytosine and also thymine found in DNA. The ratios of radioactive thymine to cytosine measured biochemically on DNA extracted from radioactive lymphocytes labeled by the various schedules indicate strongly that short-and long-lived lymphocyte populations have different abilities to utilize pyrimidine nucleosides for DNA synthesis.

Incorporation of Pyrimidine Nucleosides in Lymphoid Tissues of the Mouse Using 5-Fluorodeoxyuridine and [5-3H]Deoxycytidine

“…•~ 600 city for converting CdR to dTMP and for utilizing the dTMP for DNA synthesis was higher in the thymus than in the MLN or the spleen (2,12). .. Effect of 5-FUdR on incorporation of labeled DNA precursors.…”

“…When rats were given nonradioactive CdR together with [3H]TdR, the weak labeling of cells in the thymic cortex and germinal centers decreased even further, whereas there was only slight reduction in the labeling intensity of cells in the thymic medulla and outside the germinal centers (1). Furthermore, it has been shown that the ratio of radioactivity of thymine to that of cytosine in newly synthesized DNA is different among lymphoid tissues; this value in the thymus being higher than that in mesenteric lymph nodes (2,11,12). Thus, it is probable that the differences in labeling intensity between lymphocyte populations may be related to their different capacity for converting CdR to thymidine monophosphate (dTMP) and then utilizing the dTMP for DNA synthesis (1,2,12,17,18,22).…”

“…Furthermore, it has been shown that the ratio of radioactivity of thymine to that of cytosine in newly synthesized DNA is different among lymphoid tissues; this value in the thymus being higher than that in mesenteric lymph nodes (2,11,12). Thus, it is probable that the differences in labeling intensity between lymphocyte populations may be related to their different capacity for converting CdR to thymidine monophosphate (dTMP) and then utilizing the dTMP for DNA synthesis (1,2,12,17,18,22). Such a hypothesis has not been adequately tested ; much less have the reasons been explored which might account for the differences in the incorporation of radioactive DNA precursors by different lymphoid cell populations.…”

“…In the thymic cortex and germinal centers of mesenteric lymph nodes, however, radioautographic reactions showed more intense labeling with [G-3H] Although mitotic analyses consistently reveal high rates of cell division in the thymic cortex and germinal centers of rats and mice (1,4,5,9,10), the cells in these areas are characterized by weak labeling with tritiated thymidine ([3H]TdR), whereas lymphocytes outside these anatomical regions of the same organs are labeled intensely with the same nucleoside (1, 6-10, 12, 18, 25). Recently, tritiated deoxycytidine ([3H]CdR) or radioiodine-labeled 5-iodo-2'-deoxyuridine has been used as a substitute for [3H]TdR to study lymphocyte production (1,2,12,14,(16)(17)(18)(19)(20)(21)23). Radioautographs revealed that lymphocytes in the thymic cortex and germinal centers were much more heavily labeled with generally tritiated deoxycytidine ([G-3H]CdR) than with [3H]TdR, whereas outside the germinal centers labeling was far more intense * present address:…”

“…Recently, tritiated deoxycytidine ([3H]CdR) or radioiodine-labeled 5-iodo-2'-deoxyuridine has been used as a substitute for [3H]TdR to study lymphocyte production (1,2,12,14,(16)(17)(18)(19)(20)(21)23). Radioautographs revealed that lymphocytes in the thymic cortex and germinal centers were much more heavily labeled with generally tritiated deoxycytidine ([G-3H]CdR) than with [3H]TdR, whereas outside the germinal centers labeling was far more intense with [3H]TdR than with [G-3H]CdR (1,12,18).…”