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.