Helicobacter pylori in health and disease

Abstract

Helicobacter pylori is highly adapted for colonization of the human stomach and is present in about half of the human population. When present, H pylori is usually the numerically dominant gastric microorganism. H pylori typically does not cause any adverse effects, but it is associated with an increased risk of noncardia gastric adenocarcinoma, gastric lymphoma, and peptic ulcer. Disorders such as esophageal diseases and childhood-onset asthma were recently reported to occur more frequently in individuals who lack H pylori than in H pylori-positive persons. In this review, we discuss biologic factors that allow H pylori to colonize the human stomach, mechanisms by which H pylori increases the risk of peptic ulcer disease and noncardia gastric adenocarcinoma, and potential benefits that H pylori might confer to humans.

Figure 1

Major bacterial phyla in the stomach and at diverse anatomical sites ^{, , , ,} . Stomach 1 depicts a stomach in which H. pylori is detected by conventional methods and Stomach 2 depicts a stomach in which H. pylori is not detected.

Figure 2

Interactions of H. pylori with human gastric mucosa. Within the gastric mucosa, most H. pylori localize within the gastric mucus layer and do not directly adhere to gastric epithelial cells. VacA, secreted by non-adherent bacteria, can cause alterations in several cell types, including gastric epithelial cells and T cells . Binding of H. pylori to gastric epithelial cells is mediated by several bacterial adhesins, including BabA and SabA^, . Adherent H. pylori assemble a type IV secretion apparatus (comprised of proteins encoded by genes in the cag pathogenicity island), which translocates the CagA protein into gastric epithelial cells ^, . Within gastric epithelial cells, CagA is phosphorylated by host cell kinases; both phosphorylated and non-phosphorylated CagA can cause numerous cellular alterations. Strain-specific variations in the expression of these bacterial factors are an important determinant of interactions between H. pylori and the human host.