Inhibition of apoptosis in human neutrophils by Helicobacter pylori water-soluble surface proteins

Background: Helicobacter pylori infection in humans causes persistent neutrophil infiltration into the gastric mucosa. It is believed that a prolongation of neutrophil life-span could contribute to the pathogenesis of H. pylori infection. We therefore examined whether the water-soluble surface proteins of H. pylori can influence the apoptosis of neutrophils. Methods: After neutrophils were incubated with H. pylori water extract (HPWE), neutrophil apoptosis was evaluated by TUNEL, assay, Hoechst 33342 staining, electron microscopy and ELISA for cytosolic oligonucleosome-bound DNA for up to 48 h. To investigate the regulatory mechanisms of neutrophil apoptosis associated with HPWE, mRNA expression and protein production of Fas, Fas ligand (FasL) and tumor necrosis factor receptor 1 (TNF-R1) were analyzed by RT-PCR, ribonuclease protection assay, Northern blot and Western blotting. Cell surface expression of these death factors was also measured by flow cytometry. Results: HPWE inhibited neutrophil apoptosis and cytotoxicity for up to 48 h. The mRNA and protein expression of Fast and the cell surface expression of Fas, Fast and TNF-R1 in HPWE-treated neutrophils were suppressed compared with the controls. Conclusion: The water-soluble surface proteins of H. pylori could suppress neutrophil apoptosis. This may be caused by the suppression of Fast expression in neutrophils and Fas, Fast and TNF-R1 expression on the surface of neutrophils.