Apoptosis of Human Gastric Epithelial Cells via Caspase-3 Activation in Response to Helicobacter pylori Infection: Possible Involvement of Neutrophils through Tumor Necrosis Factor A and Soluble Fas Ligands

Abstract

Infection with Helicobacter pylori activates a proinflammatory gene program in human gastric epithelial cells and neutrophils and is associated with significant epithelial cell damage, including an increased level of apoptosis. We evaluated whether immune mediators produced by neutrophils could modulate gastric epithelial cell apoptosis in response to H. pylori infection. After gastric epithelial cells were infected with H. pylori in the presence of immune mediators, including tumor necrosis factor alpha (TNF-alpha) and Fas ligand (FasL), apoptosis and caspase-3 activity were assessed. The neutrophils were obtained from healthy volunteers, and Western blot for FasL and quantitative reverse transcription polymerase chain reaction for TNF-alpha transcripts were performed. Fas expression in gastric epithelial cells was explored by flow cytometric analysis. Activation of caspase-3 was first apparent 12 h after bacterial infection, and the phenotypic expression of apoptosis was first apparent 18 h after bacterial infection. The extent of apoptosis was similar in cases of cagA+ cytotoxin+, cagA+ cytotoxin-, cagA- cytotoxin- H. pylori-infected gastric epithelial cells. Approximately 20% of the Hs746T cells expressed Fas within 24 h of H. pylori infection. The soluble FasL was upregulated in neutrophils after treatment with H. pylori-soluble proteins for 24 and 48 h. The addition of TNF-alpha and the soluble form of FasL, produced by neutrophils, significantly increased H. pylori-infected cell apoptosis and caspase-3 activation. However, the combination of these two immune mediators showed only an additive increase. These results suggest that H. pylori-induced gastric epithelial cell apoptosis and caspase-3 activation can be modulated by the immune response of neutrophils.