Gene structure of the Helicobacter pylori cytotoxin and evidence of its key role in gastric disease.

Abstract

The gram negative, microaerophilic bacterium Helicobacter I~Iori colonizes the human gastric mucosa and establishes a chronic infection that is tightly associated with atrophic gastritis, peptic ulcer, and gastric carcinoma. Cloning of the H. pylori cytotoxin gene shows that the protein is synthesized as a 140-kD precursor that is processed to a 94-kD fully active toxin. Oral administration to mice of the purified 94-kD protein caused ulceration and gastric lesions that bear some similarities to the pathology observed in humans. The cloning of the cytotoxin gene and the development of a mouse model of human gastric disease will provide the basis for the understanding of H. ~lori pathogenesis and the development of therapeutics and vaccines. The recently discovered, gram negative, microaerophilic bacterium Helicobacter pylori colonizes the human gastric mucosa and establishes a chronic infection that is tightly associated with atrophic gastritis, peptic ulcer, and gastric carcinoma (1-5). H. pylori infection is a worldwide problem, since in developing countries it affects over 80% of the population older than 20. Also in developed countries the infection is present in 20% of the population by the age of 30 rising to over 50% by the age of 60. Clinical isolates of H. pylori can be classified into two groups based on the presence or absence of the vacuolating cytotoxin (6, 7) whose expression is linked to a surface exposed immunodominant antigen (CagA) (8, 9). Since high titers of serum antibodies to the CagA protein are detected in all patients with duodenal ulcer (8) and most of those with gastric carcinoma (10, 11), it has been proposed that disease development requires infection with cytotoxin-producing strains.The cytotoxin causes massive vacuolation in several mammalian cell lines (6), and similar vacuoles have also been observed in the gastric epithelia of patients with active chronic gastritis associated with H. pylori infection (12), indicating that the cytotoxin can contribute significantly to the pathogenesis of gastritis. Cell vacuolation in vitro can be blocked and reversed by inhibitors of V-type ATPases and potentiated by inhibitors of the Na+-K + ATPase (13,14), suggesting that the mechanism of action of the toxin is due to aberrant cation transport within the target cells. The purified toxin has been described as a protein of ~87 kD that is found in the bacterial culture supernatants, and the sequence of the NH2-terminal 23 amino acids has been determined (7).Despite the epidemiological correlation between infection with cytotoxic strains and disease (8) and the in vitro evidence for the presence of a cytotoxin, the in vivo roles of infection and cytotoxin have not been established due to the lack of a suitable animal model. H. ~lori does not colonize the gastric mucosa of mice or other small laboratory animals.To overcome this limitation, we administered H. pylori extracts and purified cytotoxin orally to mice. Using this model, extracts from cytotoxic H. Ioylori strains and purified cytotoxin ind...

Impaired T-cell regulation of B-cell growth in Helicobacter pylori–related gastric low-grade MALT lymphoma

“…The reason gastric T cells of MALT lymphoma, while delivering full help to B cells, are apparently deficient in 2 mechanisms involved in the concomitant control of B-cell growth remains unclear. It has been shown that VacA toxin released by H. pylori strains harboring a pathogenicity island 32 inhibits antigen processing in APCs but not the exocytosis of perforin-containing granules of natural killer cells. 33 It is possible that, in some H. pylori-infected individuals, other bacterial components affect the development or expression of regulatory cytotoxic mechanisms on B-cell proliferation by gastric T cells, allowing exhaustive and unbalanced B-cell help and lymphomagenesis.…”

Use of a Novel Enzyme Immunoassay Based on Detection of Circulating Antigen in Serum for Diagnosis ofHelicobacter pyloriInfection

“…In the present study, we were able to detect a specific 58-kDa antigen in H. pylori lysate and in serum samples from H. pylori-infected individuals. The molecular mass of the serum antigen is analogous to the 58-kDa fragment of the 87-kDa cytotoxin domain of the VacA protein (8,23,27), the subunit cellular antigen (59 kDa) of the native H. pylori catalase (26), and the H. pylori catalase gene product (20). However, further investigation of the structure of the target H. pylori serum antigen will be performed.…”

Helicobacter pylori: recent advances in the study of its pathogenicity and prevention

“…The mature monomer could be cleaved proteolytically into two fragments: an N-terminal 34 kDa fragment and a C-terminal 58 kDa fragment that remain associated after cleavage. 71 The ability to induce vacuoles is localized mostly but not entirely in the first fragment, whereas the second fragment is mostly involved in cell targeting.…”

“…102 I strains promote gastric damage similar to that observed in humans. 71,104 To date, studies have shown that CagA is one of the proteins produced by the pathogenicity island (cag PAI). Recent studies using isogenic mutants strains lacking the cagA gene have shown that IL-8 induction may not be directly due to CagA protein but to the products of cag PAI genes.…”