CD3 activation induces concentrative nucleoside transport in human T lymphocytes

Nucleoside transport, assessed by measuring deoxythymidine influx, was investigated in normal and CD3-activated human peripheral blood mononuclear cells (PBMC) and in the CEM cell line. On both cell types, an equilibrative nitrobenzylmercaptopurine (NBMPR)-sensitive (es) transporter encoded by the hENT(1) gene was identified on resting cells, although the expression level was about 20-fold higher on CEM cells than on resting peripheral T lymphocytes. After stimulation with anti-CD3, a strong increase of nucleoside transport was observed in PBMC accompanied by a mild augmentation of NBMPR binding sites on the cell surface. Most of this improved transport capacity was NBMPR insensitive, dependent on Na(+) concentration in the medium, and displayed the features of a concentrative process. Similar results were obtained with CEM cells despite their high basal es level, indicating that the induction of a concentrative process for nucleoside salvage is a specific metabolic response associated with antigen-driven stimulation. In CEM cells, this induction did not affect the growth rate. The concentrative transporter involved does not correspond to any of those which have been cloned so far. Molecular characterization of this transporter should provide a new marker of antigen stimulation and will allow to define whether activation of the corresponding gene is under the control of TCR-CD3-induced second messengers.