Plasma lipoproteins and transferrin regulate the proliferation of a continuous T lymphocyte cell line

Lipoproteins of hydrated densities less than 1.063 g/ml, very low density (VLDL) and low density (LDL) lipoproteins, could both enhance and suppress the proliferation of T lymphocyte cell lines. Enhancement and suppression were dependent on lipoprotein and transferrin concentrations. Enhancement occurred at low lipoprotein and high transferrin; suppression, at high lipoprotein and low transferrin. Lipoprotein suppression required a constituent of cell-conditioned medium as evidenced by the fact that lipoproteins did not suppress the replicative response of the IL-2-dependent murine cell line CTLL-2 to purified IL-2 but could suppress the response to cell-conditioned medium IL-2. For lipoprotein suppression and its relief by transferrin, both growth-regulating factors were required early in the cell cycle, suggesting that events important to progression through G1 are influenced. The data establish that the interplay between plasma lipoproteins, transferrin, and an unknown constituent of cell-conditioned medium can regulate the proliferation of T lymphocytes.