Role of virulence factors, cell components and adhesion in Helicobacter pylori-mediated iNOS induction in murine macrophages

Abstract

To investigate the mechanisms involved in Helicobacter pylori-mediated inducible nitric oxide synthase (iNOS) upregulation in mononuclear cells we cocultivated human THP-1 acute monocytic leukemia cells and murine J774A.1 professional macrophages with different H. pylori wild-type strains and mutants. We have shown that H. pylori-mediated iNOS induction in J774A.1 is independent of established virulence factors but dependent on direct interaction between bacteria and cells. In J774A.1, iNOS was equally upregulated by the wild-type strains J99, 26695, P12, and P1 as well as by mutants lacking the cag pathogenicity island, vacA, katA, alpAB genes and the hp0043 gene taking part in lipopolysaccharide biosynthesis when direct cell contact was allowed but not when bacteria and cells were separated by protein-permeable filter membranes. In contrast, iNOS was not induced in THP-1. This indicates that H. pylori-mediated iNOS induction in J774A.1 is independent of important virulence factors whereas cell contact is crucial which suggests a role of adhesion or phagocytosis.

Reduced activation of inflammatory responses in host cells by mouse-adapted Helicobacter pylori isolates

“…The current work extends this suggestion to other pro‐inflammatory processes associated with Helicobacter infection, such as those mediated by macrophages. These processes appear to be independ‐ent of the presence of a functional Cag PAI in H. pylori strains (Assmann et al , 2001; Maeda et al , 2001).…”

The Immune Battle against Helicobacter pylori Infection: NO Offense

“…Although live H. pylori or its lipopolysaccharide (LPS) fails to induce NO production by human macrophages [24, 25], several groups have demonstrated NOS2 mRNA induction in human gastric epithelial cell lines after H. pylori infection [26-28]. However, in several of these studies, either: (i) the level of NOS2 induction is very low [26, 29]; (ii) the production of RNI does not reflect NOS2-dependent high-output NO generation – e.g., ~ 6 μM NO 2 − produced by AGS cells infected for 24 h with H. pylori [27]; or (iii) NO production is not shown in these papers [26, 28].…”

“…The novelty of the H. pylori –innate immune system response crosstalk resides mainly in the fact that H. pylori LPS is not effective in inducing macrophage NO generation [25, 32, 33], in contrast to the endotoxin of other Gram-negative bacteria [32, 34]. When live H. pylori is in direct contact with murine macrophages, a strong NOS2 induction and a high level of NO production are observed in the cells [32, 35].…”

“…When live H. pylori is in direct contact with murine macrophages, a strong NOS2 induction and a high level of NO production are observed in the cells [32, 35]. In this context, different mutant strains of H. pylori lacking CagA, the type IV secretion system, VacA, catalase, the outer membrane proteins AlpAB, or urease induce the same level of NO production than the parental strain [25, 36, 37], suggesting that more than one bacterial product can stimulate NOS2 expression after phagocytosis; however, when H. pylori and macrophages are physically separated by a filter, a urease mutant fails to activate NOS2 [36], demonstrating that urease released by H. pylori is a potent inducer of NO production (Figure 1). …”

Role of serum factors in epithelial cell responses to Helicobacter pylori infection in vitro

“…Numerous in vitro studies have investigated both the adherence of H. pylori to gastric epithelial cells, 12,14–17 and the ability of H. pylori to induce IL‐8 production following adherence of this gastric pathogen 18–23 . Recent reports have suggested that FCS can modify the cytoskeletal changes induced by H. pylori within epithelial cells and may modulate the adherence of H. pylori to epithelial cells 12 .…”