Arsenic induces tumor necrosis factor α release and tumor necrosis factor receptor 1 signaling in T helper cell apoptosis

Long-term exposure to arsenic induces arsenical cancers in human beings. Arsenic has been shown to induce apoptosis in a variety of cell systems. Previous studies revealed that patients with arsenic-induced Bowen's disease showed a defective cell-mediated immunity and decreased percentages of T cell and T helper cell subpopulations in peripheral mononuclear cells. The purpose of this study was to investigate the effects of arsenic on T cell survival and function in mononuclear cells. Arsenic concentrations higher than 1 muM induced tumor necrosis factor alpha release from mononuclear cells and caused a cytotoxic effect on T cells. When exposed to higher concentrations of arsenic, apoptosis was induced. CD4+ cells were the major apoptoic population in mononuclear cells. Tumor necrosis factor receptor 1 expression on CD4+ cells, but not Fas/FasL, was significantly enhanced by arsenic treatment compared to other mononuclear cells. Increased expressions of tumor necrosis factor receptor 1 related death domain proteins and activated caspases were observed. These findings indicate that tumor necrosis factor receptor 1 signaling is the major pathway in arsenic-induced T helper cell apoptosis.