Cyclosporin A inhibits the proliferative response and the generation of helper, suppressor and cytotoxic T-cell functions in the autologous mixed lymphocyte reaction

Chemical oxidation or reduction of lymphocyte cell surface thiol or disulfide groups, respectively, has been shown to alter 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 A-induced proliferation which suggested that thiols 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 copper:phenanthroline complex (CuP), an impermeant oxidant of thiol groups, reduced the Con A-induced response >79%; however, the presence of 2-ME in culture completely reversed the inhibitory effect of CuP pretreatment. Oxidation of T cells by high oxygen tension (17% O₂) also ablated the Con A response but did not alter the response to Con A + 2-ME. Protection from oxidative inhibition also was afforded T cells by sequential reduction and blockage of cell surface thiol groups. Finally, a model which correlates the chemical study of cell surface residues with T-lymphocyte responsiveness is presented.