3H-uridine incorporation as a T lymphocyte indicator in the rat

Tridimensional study of the deep cortex of the rat lymph node. IV. Differential labelling of the deep cortex units with 3H-uridine

Using tridimensional reconstruction, it was recently found that the deep cortex of rat lymph nodes comprises one to several basic "units." Each unit is a semi-rounded structure contiguous to the peripheral cortex and bulging into the medulla of a node. Other investigators reported that transfused lymphocytes, heavily labelled in vitro by 3H-uridine, became concentrated in an ill-defined region of nodes, referred to as the mid and deep cortex. This suggested to us that the in vivo labelling of nodes with 3H-uridine might allow to further characterize the units on a physiological basis. Therefore, rats were injected intravenously with a dose of 1--20 muCi of 3H-uridine/gm body weight and sacrificed 1 hour to 3 days later. The radioautographs of their nodes were exposed up to 535 days. The observations revealed that a large dose of 3H-uridine combined with a long exposure of the radioautographs yielded a differential labelling of the cell population of the units, characterized by a much more intense reaction than that of the surrounding structures. This demonstrated that the physiology of the lymphocyte population of the deep cortex units differs from the morphologically similar lymphocyte population of the extrafollicular zone of the peripheral cortex. The possible reason(s) for the differential labelling of the units is discussed.

The pattern of lymphocytes in the thymus and spleen after labeling with 3H-thymidine and 3H-deoxycytidine

Adult male untreated mice (NMRI) were investigated after radioactive labeling with 3H-thymidine and 3H-deoxycytidine to find out whether the lymphocytes in the cortex and medulla of the thymus as well as in the perifollicular and periarteriolar regions of the spleen show a labeling pattern which allows a classification into T- and B-lymphocytes. The percentages of radioactively labeled small lymphocytes and their mean grain counts were determined. The percentages of radioactively labeled small lymphocytes after 3H-TdR and 3H-CdR showed no significant differences in both splenic zones. The grain counts over the lymphocyte nuclei in the periarteriolar zone showed lower values after 3H-TdR than after 3H-CdR. The lymphocytes in the perifollicular zone were strongly labeled with 3H-TdR and weakly labeled with 3H-CdR. In the thymus medulla, lymphocytes were weakly labeled with 3H-thymidine and strongly labeled with 3H-CdR. In the cortex no significant differences were observed. 75 to 80% of the small lymphocytes in the peripheral blood were weakly and 20-25% strongly labeled after 3H-TdR. Therefore there are similarities in the radioactive labeling pattern of thymic medulla lymphocytes and that of small lymphocytes of the periarteriolar zone of the spleen by both DNA precursors. The small lymphocytes in the peripheral T-dependent tissue zones, for example in the spleen, as well as in the mixed lymphocyte population of the peripheral blood can be differentiated from the B-lymphocytes through the difference in the amount of incorporation of 3H-thymidine and 3H-deoxycytidine.

Labelling of lymphocytes with various radiosotopes for in vivo tracer studies; a review

Several methods are available for labelling lymphoid cells with radioactive markers e.g. 3H, 14C, 125I, 131I, 35S, 75Se, based on general metabolic processes, involving DNA, RNA and protein synthesis in these cells. Together with methods for labelling lymphoid cells with 51Cr and 99mTc, radioisotopes which are captured in cells but not incorporated in its metabolites, these will be reviewed in the present paper. Attention will be given to possible applications of the use of radiosotope labels.