Gastric cancer arises through steps related to the presence of a chronic Helicobacter pylori infection, which leads to the precursor lesion, atrophic gastritis. The progression of gastric mucosal atrophy varies within and between different populations; and the differences relate to differences in H. pylori virulence, host genetic factors, and/or environmental factors. The important H. pylori virulence factors and host genetic factors are related to an increased inflammatory response and include the presence of the cag pathogenicity island, polymorphisms of host inflammationrelated cytokines (5, 6), drug metabolism-related enzymes (19,22), and growth factors (5,6,12,19,22,30).The vacuolating cytotoxin (VacA) was one of the first putative virulence factors discovered in H. pylori (4). Virtually all H. pylori strains possess a vacA gene; however, the in vitro vacuolating activities for cell lines vary considerably among strains; and the differences in the vacuolating activities are related to differences in the vacA structures at the signal (s) region (s1 and s2) and the middle (m) region (m1 and m2) (1). The s region encodes part of the signal peptide and the N terminus of the mature protein, whereas the m region encodes part of the 55,000-Da (55K) C-terminal subunit. The amount of toxin produced also varies according to the vacA m-region genotypes: vacA s1-m1 strains induce greater vacuolating activity than vacA s1-m2 strains (1, 11).Recently, a third polymorphic determinant of vacuolating activity was described as being located between the s and m regions and was termed the intermediate (i) region (16). Two i-region subtypes were described: the i1 and i2 subtypes. Among Western strains, vacA s1-m2 strains were noted to vary in their i-region genotypes; vacA s1-m1 and s2-m2 strains were exclusively i1 and i2, respectively. The vacA s1-i1-m2 strains induced vacuolation in rabbit kidney RK13 cells, whereas s1-i2-m2 strains did not. Clinically, the prevalence of the vacA i1 genotype in patients with gastric cancer was 80%, which was significantly higher than that in patients in an Iranian population with nonulcer dyspepsia (37%) (16). Subsequent studies showed that infection with vacA i1 strains was associated with gastric cancer in patients in Iranian and Italian populations and gastric ulcer in patients in Iraqi and Italian populations (2,8,16). This allowed the conclusion that the vacA i-region genotype might be a better predictor of the carcinogenic potential of H. pylori than the previously used vacA s-and mregion genotypes. However, our recent study shows that determination of the vacA genotypes for the combination of three regions (the s, m, and i regions) did not provide any advantage as a disease determinant marker over determination of s-and

The gastric mucosal immune response is thought to be comprised predominantly of the Th1 type; however, there are limited data regarding the role of IL-18 in Helicobacter pylori-induced inflammation. We investigated IL-18 levels in gastric mucosal biopsy specimens as well as in isolated gastric epithelial cells and lamina propria mononuclear cells. We also investigated IL-18 levels in gastric epithelial cells and the monocyte cell line THP-1 cocultured with H. pylori. In both systems, IL-18 levels were markedly enhanced in H. pylori-infected epithelial cells and monocytes. IL-18 levels in H. pylori-infected gastric mucosa were well correlated with the severity of gastric inflammation, confirming that H. pylori-induced IL-18 plays an important role in gastric injury. Virulence factors of H. pylori; the cag pathogenicity island and OipA affected IL-18 induction in different manners. Up-regulation of IL-18 mRNA/protein in epithelial cells was dependent on both virulence factors. Interestingly, up-regulation of IL-18 mRNA in monocytes was independent of both factors, whereas IL-18 protein was OipA dependent – cag pathogenicity island independent, indicating that OipA regulates IL-18 induction in monocytes at the posttranscriptional level. IL-18 levels in the gastric biopsy specimens showed similar patterns to those in lamina propria mononuclear cells with respect to virulence factors, suggesting that submucosal monocytes/macrophages are the main source of IL-18 induced by H. pylori infection. H. pylori appeared to regulate the ERK/JNK→AP-1 pathway in both cell types. In addition, OipA and its related p38 pathway may be closely involved in IL-18 induction in H. pylori-infected gastric mucosa and may contribute to gastric injury.

No abstract