Virulence factors of Helicobacter pylori responsible for gastric diseases in Mongolian gerbil

Abstract

Helicobacter pylori infection induces various gastroduodenal diseases. We examined the role of two genes, vacA and cagE, in the gastric pathogenesis induced by H. pylori using a long-term (62 wk) animal model. Reportedly, both genes are associated with the virulence of H. pylori: vacA encodes vacuolating cytotoxin, and cagE, with other genes in the cag pathogenicity islands, encodes a type IV secretion system. Mongolian gerbils were challenged in this study by a wild-type TN2 strain and its isogenic mutants of cagE or vacA. The wild-type and vacA mutants induced severe gastritis, whereas cagE mutants induced far milder changes. Gastric ulcer was induced at the highest rate (22/23) by the wild-type TN2, followed by the vacA mutant (19/28). No ulcer was found in the gerbils infected with the cagE mutant (0/27) or in controls (0/27). Intestinal metaplasia was also found in the gerbils infected with the wild-type (14/23) or vacA mutant (15/28). Gastric cancer developed in one gerbil with wild-type infection and in one with vacA mutant infection. In conclusion, the knocking out of the cagE gene deprived wild-type H. pylori of the pathogenicity for gastritis and gastric ulcer, suggesting that the secretion system encoded by cag pathogenicity island genes plays an essential role.

Figure 1

Changes in body weight of Mongolian gerbils inoculated orally with H. pylori TN2 (○) and its isogenic vacA (▴) or cagE (□) mutants and intact control gerbils (♦). The data and error bars represent means and the standard error of body weights.

Figure 3

Ulcers, extending to the muscular layer, developed in the region of the fundus–pylorus border of animals infected with TN2 (A) or TN2ΔvacA (C). No gastric ulcers are seen in animals infected with TN2ΔcagE (B) or uninfected animals (D). H&E stain; original magnifications 10×.

Figure 2

Histopathological findings in the gastric mucosa of gerbils 62 wk after H. pylori inoculation. Gastritis (A–D, pyloric region; and E–H, fundic region): severe gastritis characterized by dense neutrophil and mononuclear cell infiltrations and epithelial hyperplasia can be seen in the animals infected with TN2 (A and E) and TN2ΔvacA (C and G). The gastritis extends throughout the pyloric region (A and C) and into a part of the fundic region (E and G). Mucosal thickness increases remarkably as compared with uninfected animals (D and H). Only mononuclear cell infiltration and lymphoid follicle formation are noted in the pyloric region of animals infected with TN2ΔcagE, and neutrophil infiltration and epithelial alterations are not evident (B). There was no inflammation in the fundic regions of animals infected with TN2ΔcagE (F). H&E stain; original magnifications 35×.

Figure 4

Other histopathological findings. Adenocarcinoma (A): an adenocarcinoma observed in animals infected with TN2. Neoplastic glands consisted of well-differentiated intestinal-type epithelium (inset) and penetrated into the muscle layer. Intestinal metaplasia (B): intestinal metaplasia observed in animals infected with TN2. Metaplastic epithelium containing AB-PAS–positive goblet cells frequently formed near the ulcer. Carcinoids (C): carcinoids detected in the animal infected with TN2ΔvacA. A and C, H&E stain; original magnifications 15 (A) and 80× (C). A, inset, and B, AB-PAS: original magnifications 80 (A, inset) and 30× (B).