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Nucleoside transport and proliferative rate in human thymocytes and
lymphocytes
CL Smith, LM Pilarski, ML Egerton and JS Wiley
Department of Haematology, Austin Hospital, Heidelberg, Victoria,
Australia.
The thymus is a site of active T-lymphoid cell proliferation and DNA
synthesis. In this study, the capacity of human thymocytes for nucleoside
transport was assessed both by cytosine arabinoside influx and by
equilibrium binding of nitrobenzylmercaptopurine riboside (NBMPR), a
specific ligand for the equilibrative nucleoside transporter of leukocytes.
The proportion of freshly isolated thymocytes synthesizing DNA was 8.6% +/-
2.1% (n = 12) by 3H-thymidine labeling index and 7.8% +/- 2.9% (n = 4)
S-phase cells by flow cytometric analysis of DNA content. In comparison,
both methods gave proliferation S-phase values less than 1% for peripheral
blood lymphocytes (PBLs). Thymocytes expressed a high density of specific
NBMPR binding sites (26,068 +/- 8,776 sites per cell, n = 12) as compared
with PBLs (1,123 +/- 553 sites per cell, n = 8). The initial influx of
cytosine arabinoside into thymocytes was 14-fold greater than into PBLs,
and in both cell types the influx of nucleoside was totally inhibited by
0.5 mumol/L NBMPR, which is known to inhibit the major equilibrative
nucleoside transporter in white blood cells. Depletion of mature CD3+ cells
from the thymocyte preparation by anti-CD3 antibody left a residual
population with both increased labeling index and up to twofold greater
density of NBMPR binding sites. When PBLs were cultured for 48 hours with
the T-cell mitogen phytohemagglutinin, a 40-fold increase in labeling index
was observed, together with a 30-fold increase in the density of specific
NBMPR binding sites. Thus, fresh thymocytes from human thymus are actively
proliferating and express high densities of a functional nucleoside
transporter. The more immature cells in the thymocyte population which are
proliferating more actively have a greater density of nucleoside
transporters than the whole population. In contrast, mitotically inactive
PBLs-have few nucleoside transporters, but after mitogenic stimulation PBLs
express large numbers of this transmembrane molecule.
Volume 74,
Issue 6,
pp. 2038-2042,
11/01/1989
Copyright © 1989 by The American Society of Hematology
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