Tumor Necrosis Factor Alpha and Interleukin 1β Up-Regulate Gastric Mucosal Fas Antigen Expression inHelicobacter pyloriInfection

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Abstract
Fas-mediated gastric mucosal apoptosis is gaining attention as a cause of tissue damage due toHelicobacter pyloriinfection. We explored the effects ofH. pyloridirectly, and the effects of the inflammatory environment established subsequent toH. pyloriinfection, on Fas-mediated apoptosis in a nontransformed gastric mucosal cell line (RGM-1). Exposure toH. pylori-activated peripheral blood mononuclear cells (PBMCs), but notH. pyloriitself, induced Fas antigen (Fas Ag) expression, indicating a Fas-regulatory role for inflammatory cytokines in this system. Of various inflammatory cytokines tested, only interleukin 1β and tumor necrosis factor alpha induced Fas Ag expression, and removal of either of these from the conditioned medium abrogated the response. When exposed to Fas ligand, RGM-1 cells treated with PBMC-conditioned medium underwent massive and rapid cell death, interestingly, with a minimal effect on total cell numbers early on. Cell cycle analysis revealed a substantial increase in S phase cells among cells exposed to Fas ligand, suggesting an increase in their proliferative response. Taken together, these data indicate that the immune environment secondary toH. pyloriinfection plays a critical role in priming gastric mucosal cells to undergo apoptosis or to proliferate based upon their Fas Ag status.