THE USE OF DEOXYCYTIDINE LABELED WITH TRITIUM IN THE 5-POSITION FOR AUTORADIOGRAPHIC STUDY OF LYMPHOCYTES IN VIVO

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The patterns of labeling of thymic lymphocytes and germinal-center cells of the rat with [5-³H] deoxycytidine (labeled in the 5-position) in vivo were studied by autoradiographic technique, and compared with the patterns of labeling with [G-³H] deoxycytidine (generally labeled).
With respect to the thymic lymphocytes, no significant difference was observed in labeling intensity between the two labeled markers. In the germinal-center cells, on the other hand, the labeling intensity with [5-³H]-deoxycytidine was found to be significantly weaker than [G-³H] deoxycytidine labeling. The results are discussed in relation to the ability of these cells to utilize deoxycytidine for the synthesis of DNA-thymine, and the pool size of thymidine within the tissue which suppresses such utilization of deoxycytidine by these cells. It was found that the thymus contained a large pool of thymidine, while in the lymph node the pool seemed much smaller in size.