Cellular [3H]uridine uptake and incorporation into RNA were compared in human tonsil lymphocyte subpopulations obtained by separation on nylon-wool column. While the nonadherent subpopulation, Fraction I, contained 74.5 ± 8% E-rosette forming T-lymphocytes, the adherent fraction, Fraction II, contained 6.5 ± 3.5% of the same cells. The B-cell-enriched Fraction II of lymphocytes, freshly prepared from tonsils, was 2.5-3 times as active as Fraction I with respect to both uptake and incorporation of [3H]uridine. However, in phytohaemagglutinin-stimulated cultures the T-cell-enriched Fraction I proved to be more active with regard to 3H-uridine incorporation. The size of the four ribonucleoside triphosphate pools determined by the RNA-polymerase test was practically the same in both lymphocyte subpopulations. The radioactivity of the acid soluble cell fraction after [3H]uridine labeling consisted of about 60% [3H]UTP in both B- and T-cell-rich lymphocyte fractions, as determined by chromatography on PEI cellulose. On the basis of these results it seems unlikely that [3H] uridine labeling is a specific marker of either of the lymphocyte subpopulations.
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