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Infection and Immunity, May 2004, p. 2889-2898, Vol. 72, No. 5
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.5.2889-2898.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Helicobacter pylori Induces Apoptosis of Macrophages in Association with Alterations in the Mitochondrial Pathway

Rena J. Menaker,1,2 Peter J. M. Ceponis,1,3 and Nicola L. Jones1,2,4*

Research Institute, Hospital for Sick Children,1 Department of Physiology,2 Department of Laboratory Medicine and Pathobiology,3 Department of Paediatrics, University of Toronto, Toronto, Canada4

Received 21 July 2003/ Returned for modification 15 September 2003/ Accepted 19 January 2004

Helicobacter pylori is a gastric bacterial pathogen that evades host immune responses in vivo and is associated with the development of gastritis, peptic ulcer disease, and gastric cancers. Induction of macrophage apoptosis is a method employed by multiple pathogens to escape host immune responses. Therefore, we hypothesized that H. pylori induces apoptosis of infected macrophages. RAW 264.7 cells were infected with H. pylori strain 60190, and apoptosis was assessed. Transmission electron microscopy and fluorescence microscopy showed that infected macrophages displayed morphological features characteristic of apoptosis. Quantification by acridine orange-ethidium bromide fluorescent-dye staining showed that apoptosis was dose and time dependent, and apoptosis was further confirmed by increased binding of annexin V-fluorescein isothiocyanate (FITC) to externalized phosphatidylserine of infected but not of control macrophages. Macrophages infected with isogenic mutants of H. pylori strain 60190 deficient in either cagA or vacA induced significantly less apoptosis than the parental strain, as assessed by increased binding of annexin V-FITC. Western blot analysis of whole-cell protein lysates revealed that infection with strain 60190 induced a time-dependent increase in cleavage of procaspase 8 and disappearance of full-length Bid compared with uninfected cells. Furthermore, pharmacological inhibition of caspase 8 caused a decrease in levels of apoptosis. Finally, infection caused a time-dependent increase in mitochondrial-membrane permeability and release of cytochrome c into the cytosol. These results suggest that H. pylori induces apoptosis of macrophages in association with alterations in the mitochondrial pathway. Elimination of this key immunomodulatory cell may represent a mechanism employed by the bacterium to evade host immune responses.

* Corresponding author. Mailing address: Rm. 8409, Hospital for Sick Children, 555 University Ave., Toronto, ON, Canada M5G 1X8. Phone: (416) 813-7734. Fax: (416) 813-6531. E-mail: nicola.jones{at}sickkids.ca.

Editor: B. B. Finlay

Infection and Immunity, May 2004, p. 2889-2898, Vol. 72, No. 5
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.5.2889-2898.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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