AbstractDuring inflammatory processes infiltrating cells produce large amounts of reactive oxygen intermediates (ROI). Increasing evidence suggests that ROI besides being cytotoxic may act as important mediators influencing various cellular and immunological processes. In this study, we have investigated the effects of hydrogen peroxide on several aspects of lymphocyte activation. In ESb‐L T lymphoma cells, micromolar concentrations of hydrogen peroxide rapidly induced activation of the transcription factor NF‐χB, whereas DNA‐binding activity of the transcription factor AP‐1 was virtually not affected. In addition, hydrogen peroxide induced early gene expression of interleukin‐2 (IL‐2) and the IL‐2 receptor α chain. The stimulation of IL‐2 expression was found to be conferred by a χB‐likecis‐regulatory region within the IL‐2 gene promoter. In contrast to these activating effects, addition of hydrogen peroxide was largely inhibitory on cell proliferation which is consistent with a general requirement of thiol compounds for lymphocyte proliferation. However, hydrogen peroxide significantly increased T cell proliferation when applied for a short period under reducing conditions. These data indicate that ROI may act as an important competence signal in T lymphocytes inducing early gene expression as we
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