Synthesis and release of deoxycytidine by human B and T lymphoblasts.

Deoxycytidine kinase activity is abundant in human T and B lymphocytes. However, the role of the enzyme in endogenous deoxynucleoside metabolism has not been established. The present experiments show that dividing human B lymphoblasts, but not T lymphoblasts, release substantial amounts of deoxycytidine (dCyd) into the medium, and have an active dCyd-dCMP (deoxycytidine-deoxycytidine 5'-phosphate) substrate cycle. Exogenous dCyd has been shown to protect human lymphocytes from the toxic effects of deoxyadenosine, deoxyguanosine and related compounds. Thus, the differential rates of dCyd release by T and B lymphocytes may affect the sensitivities of the two cell types to the growth inhibitory effects of exogenous deoxynucleosides.