BACKGROUND/AIMS: Helicobacter pylori (H. pylori) infection in human causes persistent neutrophil infiltration into gastric mucosa. The mechanisms of perpetuation of mucosal inflammation have not been clearly defined. It was believed that a prolongation of neutrophil life-span could contribute to the pathogenesis of H. pylori infection. Therefore, we examined whether the water-soluble surface proteins of H. pylori can influence the apoptosis of neutrophils. METHODS: After neutrophils were stimulated with H. pylori water extract (HPWE), neutrophil apoptosis was evaluated by fluorescent microscopy with Hoechst 33342 staining, electron microscopy, TUNEL assay, and cytosolic oligonucleosome-bound DNA enzyme linked immunosorbent assay for up to 48 hours. Cytotoxicity was determined by trypan blue exclusion test and LDH assay. To elucidate regulatory mechanisms of neutrophil apoptosis by HPWE, the expression of Fas, Fas ligand (FasL) and tumor necrosis factor receptor 1 (TNF-R1) mRNA and proteins was analyzed by reverse transcription-polymerase chain reaction, ribonuclease protection assay, Northern blotting and Western blotting. Cell surface expression of these death factors was also measured by flow cytometry. RESULTS: Stimulation with HPWE inhibited neutrophil apoptosis and cytotoxicity for up to 48 hours. Expression of FasL mRNA and proteins, and cell surface expression of Fas, FasL and TNF-R1 in stimulated neutrophils were suppressed as compared with controls. CONCLUSIONS: H. pylori water-soluble surface proteins inhibit neutrophil apoptosis in vitro. This may be caused by suppression of Fas, FasL and TNF-R1 expression on the neutrophil surface.