Inhibition of early events in the human T-lymphocyte response to mitogens and alloantigens by hydrogen peroxide.

Hydrogen peroxide (100 to 200 microM) inhibited the response of human peripheral-blood mononuclear cells (PBMCs) in phytohemagglutinin, concanavalin A, and mixed lymphocyte culture assays by more than 90% without affecting cell viability. The response of PBMCs to pokeweed mitogen was stimulated twofold by 50 microM H2O2, but 200 microM H2O2 inhibited the pokeweed mitogen response by more than 95%. A 50 microM concentration of H2O2 completely blocked the generation of cytotoxic T cells in the mixed lymphocyte culture but did not inhibit the production of interleukin 2. Concentrations of 100 microM to 200 microM H2O2 inhibited interleukin 2 production by 45% to 57%. The H2O2 appeared to block early events in T-cell activation, since 200 microM H2O2 was not inhibitory when added one hour after stimulating the cells with phytohemagglutinin. Treatment of PBMCs with 200 microM H2O2 did not decrease the total cellular thiol pool, suggesting that H2O2-mediated inhibition of the proliferative response was not due to thiol oxidation. However, pretreatment of PBMCs with the lipid antioxidants butylated hydroxyanisole, butylated hydroxytoluene, and n-propyl gallate blocked more than 75% of the inhibitory effect of H2O2, suggesting that H2O2 inhibits T-cell activation by inducing lipid peroxidation.