Macrophages via Alterations in the Endocytic Pathway acidophilus-Induced Interferon Beta Signaling in Helicobacter pylori VacA Suppresses Lactobacillus 2013

Helicobacter pylori causes chronic gastritis and avoids elimination by the immune system of the infected host. The commensal bacterium Lactobacillus acidophilus has been suggested to exert beneficial effects as a supplement during H. pylori eradication therapy. In the present study, we applied whole-genome microarray analysis to compare the immune responses induced in murine bone marrow-derived macrophages (BMDMs) stimulated with L. acidophilus, H. pylori, or both bacteria in combination. While L. acidophilus induced a Th1-polarizing response characterized by high expression of interferon beta (IFN) and interleukin 12 (IL-12), H. pylori strongly induced the innate cytokines IL-1 and IL-1 . In BMDMs prestimulated with L. acidophilus, H. pylori blocked the expression of L. acidophilus-induced IFNand IL-12 and suppressed the expression of key regulators of the Rho, Rac, and Cdc42 GTPases. The inhibition of L. acidophilus-induced IFNwas independent of H. pylori viability and the virulence factor CagPAI; however, a vacuolating cytotoxin (vacA) mutant was unable to block IFN. Confocal microscopy demonstrated that the addition of H. pylori to L. acidophilus-stimulated BMDMs redirects intracellular processing, leading to an accumulation of L. acidophilus in the endosomal and lysosomal compartments. Thus, our findings indicate that H. pylori inhibits the development of a strong Th1-polarizing response in BMDMs stimulated with L. acidophilus by blocking the production of IFNin a VacA-dependent manner. We suggest that this abrogation is caused by a redirection of the endocytotic pathway in the processing of L. acidophilus. IMPORTANCE Approximately half of the world’s population is infected with Helicobacter pylori. The factors that allow this pathogen to persist in the stomach and cause chronic infections have not yet been fully elucidated. In particular, how H. pylori avoids killing by macrophages, one of the main types of immune cell underlying the epithelium, remains elusive. Here we have shown that the H. pylori virulence factor VacA plays a key role by blocking the activation of innate cytokines induced by the probiotic Lactobacillus acidophilus in macrophages and suppresses the expression of key regulators required for the organization and dynamics of the intracellular cytoskeleton. Our results identify potential targets for the treatment of H. pylori infection and vaccination, since specific inhibition of the toxin VacA possibly allows the activation of an efficient immune response and thereby eradication of H. pylori in the host. Received 20 December 2012 Accepted 3 May 2013 Published 11 June 2013 Citation Weiss G, Forster S, Irving A, Tate M, Ferrero RL, Hertzog P, Frøkiær H, Kaparakis-Liaskos M. 2013. Helicobacter pylori VacA suppresses Lactobacillus acidophilus-induced interferon beta signaling in macrophages via alterations in the endocytic pathway. mBio 4(3):e00609-12. doi:10.1128/mBio.00609-12. Invited Editor Indira Mysorekar, Washington University School of Medicine Editor Scott Hultgren, Washington University School of Medicine Copyright © 2013 Weiss et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Address correspondence to Gudrun Weiss, gudrun.weiss@imperial.ac. uk. The Gram-negative bacterium Helicobacter pylori colonizes the human stomach and has infected more than half of the world’s population (1, 2). Upon infection, H. pylori activates an inflammatory response which leads to the recruitment of macrophages, neutrophils, and lymphocytes to the gastric tissue (3). Macrophages can efficiently engulf H. pylori; however, this pathogenic bacterium has developed mechanisms to avoid killing upon phagocytosis and prevents the induction of an adaptive immune response (4–7). It is likely that the failure of macrophages to eliminate H. pylori contributes to bacterial persistence in the host and thereby to the development of chronic infection. Indeed, we have previously reported the requirement for macrophages in the development of H. pylori-induced gastritis in vivo (8). It is currently not fully understood how H. pylori avoids elimination by the immune system and is able to survive and persist in human macrophages. Several different mechanisms have been suggested based on the virulence factors expressed by H. pylori (9). H. pylori retards its own uptake by phagocytes, which has been suggested to be dependent on type IV secretion components encoded by the cytotoxin-associated gene pathogenicity island (CagPAI) (10, 11), one of the main pathogenic factors in H. pylori infection (12). Once it is intracellular, H. pylori actively delays RESEARCH ARTICLE May/June 2013 Volume 4 Issue 3 e00609-12 ® mbio.asm. org 1 m b.asm . rg on Jne 1, 2013 P ubished by m b.asm . rg D ow nladed fom