MODULATION OF T-CELL FUNCTION .2. CHEMICAL BASIS FOR THE INVOLVEMENT OF CELL-SURFACE THIOL-REACTIVE SITES IN CONTROL OF T-CELL PROLIFERATION

Chemical oxidation or reduction of lymphocyte cell surface thiol or disulfide groups, respectively, alters the proliferative activity of murine T cells. S-2-(3-aminopropylamino)ethylphosphothioic acid, a compound containing no free thiol group until it is intracellularly dephosphorylated, did not enhance Con[concanavalin] A-induced proliferation which suggested that thios did not mediate proliferative enhancement via an intracellular mechanism. Glutathione, an impermeant thiol, enhanced T-cell proliferation 68% as effectively as 2-mercaptoethanol (2-ME), which suggested that the thiol-sensitive site was at the cell surface. A battery of structural analogs to 2-ME was employed to elucidate the chemical requirements for the biological activity of the thiols. The necessity for a hydrogen-binding moiety on the thiol reagent was determined by the use of non-hydrogen-binding analogs and by competitive inhibition of the thiol-enhancing activity of 2-ME by non-thiol-containing hydrogen-binding analogs. Pretreatment of cells with the Cu:phenanthroline complex (CuP), an impermeant oxidant of thiol groups, reduced the Con A-induced response > 79%; the presence of 2-ME in culture completely reversed the inhibitory effect of CuP pretreatment. Oxidation of T cells by high O2 tension (17% O2) also ablated the Con A response but did not alter the response to Con A and 2-ME. Protection from oxidative inhibition also was afforded T cells by sequential reduction and blockage of cell surface thiol groups. A model which correlates the chemical study of cell surface residues with T-lymphocyte responsiveness is presented.