Host pathogen interactions in Helicobacter pylori related gastric cancer

Helicobacter pylori (H. pylori), discovered in 1982, is a microaerophilic, spiral-shaped gram-negative bacterium that is able to colonize the human stomach. Nearly half of the world's population is infected by this pathogen. Its ability to induce gastritis, peptic ulcers, gastric cancer and mucosa-associated lymphoid tissue lymphoma has been confirmed. The susceptibility of an individual to these clinical outcomes is multifactorial and depends on H. pylori virulence, environmental factors, the genetic susceptibility of the host and the reactivity of the host immune system. Despite the host immune response, H. pylori infection can be difficult to eradicate. H. pylori is categorized as a group?Ⅰ?carcinogen since this bacterium is responsible for the highest rate of cancerrelated deaths worldwide. Early detection of cancer can be lifesaving. The 5-year survival rate for gastric cancer patients diagnosed in the early stages is nearly 90%. Gastric cancer is asymptomatic in the early stages but always progresses over time and begins to cause symptoms when untreated. In 97% of stomach cancer cases, cancer cells metastasize to other organs. H. pylori infection is responsible for nearly 60% of the intestinaltype gastric cancer cases but also influences the development of diffuse gastric cancer. The host genetic susceptibility depends on polymorphisms of genes involved in H. pylori-related inflammation and the cytokine response of gastric epithelial and immune cells. H. pylori strains differ in their ability to induce a deleterious inflammatory response. H. pylori-driven cytokines accelerate the inflammatory response and promote malignancy. Chronic H. pylori infection induces genetic instability in gastric epithelial cells and affects the DNA damage repair systems. Therefore, H. pylori infection should always be considered a pro-cancerous factor.

Molecular mimicry in Helicobacter pylori infections

Gram-negative bacteria Helicobacter pylori(H. pylori) colonize gastric mucosa in humans and increase the risk of serious diseases such as gastric and duodenal ulcers, stomach cancers and mucosa associated lymphoid tissue lymphoma. The role of H. pylori infection in the pathogenesis of several extragastric diseases has been suggested including immune thrombocytopenic purpura, iron deficiency anemia, vitamin D deficiency, cardiovascular diseases,diabetes mellitus and dermatological disorders. Also neurological diseases and even lung cancer have attracted researchers concern. The relation between H. pylori infection and a growth retardation in children has also been suggested. Many mechanisms of molecular mimicry between H. pylori and the host have been proposed as a pathogen strategy to manipulate the immune system of the host in order to remain unrecognized and avoid eradication. A lot of effort has been put into the demonstration of homologous sequences between H. pylori and host compounds. However, knowledge about how often autoantibodies or autoreactive T lymphocytes induced during H. pylori infections cause pathological disorders is insufficient. This review provides data on H. pylori antigenic mimicry and possible deleterious effects due to the induction of immune response to the components common to these bacteria and the host.