Improvement of human lymphocyte proliferation and alteration of IL-2 secretion kinetics by alpha-thioglycerol.

Abstract

Using a novel flow cytometric assay (BrdU/Hoechst flow cytometry) for the visualization and quantitation of cell activation and cell progression through multiple cell cycles we show that (1) resting mononuclear cells from human venous blood respond to polyclonal activation in a highly asynchronous fashion, as some of these cells enter their first cell cycle as early as 30 and as late as 80 hrs after exposure to the mitogen; (2) reducing agents improve the mitogenic response of polyclonally activated human lymphocytes by increasing the recruitment of non-cycling G0/G1 cells; (3) of 8 reducing agents tested, alpha-thioglycerol proved most effective with respect to enhancing recruitment into the cell cycle; (4) the effective agents needs to be present permanently for maximum response; (5) the growth-promoting effect of alpha-thioglycerol is mediated, but not solely caused by increased IL2 production. The latter conclusion was arrived at by using the IL2-dependent CTLL cell line in conjunction with the BrdU/Hoechst flow technique as a sensitive bioassay system for the growth promoting activity of the cell cycle progression factor IL2; (6) exogenously added IL-2, however, did not improve cell activation towards proliferation. These data indicate that increased IL-2 levels are probably due to increased cell activation rates but are not the primary cause of improvement of human lymphocyte proliferation.