Cationic amino acid transport in human T lymphocytes is markedly increased in the CD45RA, CD8+ population after activation.
Membrane transport of cationic amino acids is essential for cells which are actively metabolizing L-arginine or L-lysine. In human cells most of this transport occurs through y+, a transport system which is only now being characterized at the molecular level. We have previously shown that phytohaemagglutinin (PHA) stimulation of peripheral blood E rosette positive (T) lymphocytes specifically activated lysine transport through system y+, whereas Staphlyococcus aureus Cowan A (SAC) stimulation of the E rosette negative fraction did not. We have now analysed this effect in PHA-activated CD4, CD8, CD45RO and CD45RA T-cell subsets. Both PHA-activated CD4+ and CD8+ T cells have increased lysine transport through y+, and in seven out of eight experiments, more activity was seen in the CD8+ fraction. In contrast, marked differences in y+ activity were seen between the PHA-activated CD45RO and CD45RA subsets. Thus in six experiments y+ activity was markedly increased in the CD45RA (naive T cell) population but not in the CD45RO (memory) cells. In one further experiment the activated CD45RO, CD4- population (enriched for CD45RA+, CD8+) was studied and y+ activity was shown to be maximal in this cell subset. Transport of arginine is essential for nitric oxide synthesis. Our findings therefore suggest that activated CD45RA, CD8+ T cells are capable of nitric oxide production.
Department of Clinical Sciences, London School of Hygiene and Tropical Medicine, U.K.
D H
DH
Crawford
S
S
Chen
C A
CA
Boyd
D000328:Adult; D000596:Amino Acids / Q000097:blood*; D001120:Arginine / Q000097:blood; D001692:Biological Transport; D016827:CD8 Antigens / Q000032:analysis*; D002478:Cells, Cultured; D006801:Humans; D017493:Leukocyte Common Antigens / Q000032:analysis*; D008213:Lymphocyte Activation / Q000502:physiology*; D008239:Lysine / Q000097:blood; D010835:Phytohemagglutinins / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000378:metabolism*
D000596:Amino Acids; D016827:CD8 Antigens; D010835:Phytohemagglutinins; D001120:Arginine; D017493:Leukocyte Common Antigens; D008239:Lysine