M. T. Szabo

An inhibitory factor of DNA synthesis derived from the medium of short-time incubated human lymphocytes

Abstract The medium of human tonsillar lymphocytes incubated for 4 h without any in vitro activation was found to contain a non-dialyzable, soluble inhibitor of DNA synthesis. The spontaneous- as well as the PHA-stimulated DNA synthesis of lymphocytes were both affected by the inhibitor, which was not cytotoxic for its target cells. The factor was isolated by ammonium sulphate precipitation and was purified on a DEAE-cellulose column. It is assumed that the factor is continuously produced by lymphocytes in vivo and plays a role in the homeostatic regulation of lymphocytes.

A lymphokine-like factor isolated by deoxycholate from the membrane of human lymphocytes

1. Membranous protein fractions containing carbohydrates were solubilized from human tonsillar lymphocytes in the presence or basence of deoxycholate. The optimal conditions for the detergent treatment, high solubilized protein yield without cell disruption, temperature and time of the treatment and concentration of the detergent were elucidated. 2. The protein fractions inhibited both the mitogen-activated and the nonactivated DNA synthesis in human lymphocyte targets in vitro but did not affect the uptake of [3H]thymidine. The fractions had a slight effect on the amino acid incorporation into proteins and failed to influence the uptake of amino acids. 3. It is assumed that the investigated membranous proteins are lymphokine-like materials produced continuously by lymphocytes in vivo and are incorporated into the membrane of the cells.

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.