Kinetics of thymidine entry into tonsillar lymphocytes and its alteration in the presence of a lymphokine.

Thymidine uptake into the acid soluble cell fraction of human tonsillar lymphocytes was studied in vitro. Uptake was linear for 15-20 minutes at low concentrations (less than 1.2 microM) of thymidine. The plot of uptake versus time could be extrapolated to the origin. Value for KM (0.5-0.6 microM) and values for Vmax were determined. In the presence of a lymphokine which inhibited thymidine incorporation into DNA the uptake of thymidine into the acid soluble cell fraction was also inhibited. The decreased uptake could be characterized by an increase in the apparent KM, without the alteration of Vmax. Lymphokines which inhibit thymidine incorporation may influence and regulate in vivo the entry of the exogenous thymidine into the cells.