Helicobacter pylori has been associated with gastritis, peptic ulcer, and gastric adenocarcinoma. We report the nucleotide sequence and expression of an immunodominant antigen of H. pylori and the immune response to the antigen during disease. The antigen, named CagA (cytotoxin-associated gene A), is a hydrophilic, surface-exposed protein of 128 kDa produced by most clinical isolates. The size of the cagA gene and its protein varies in different strains by a mechanism that involves duplication of regions within the gene. Clinical isolates that do not produce the antigen do not have the gene and are unable to produce an active vacuolating cytotoxin. An ELISA to detect the immune response against a recombinant fragment of this protein detects 75.3% of patients with gastroduodenal diseass and 100% of patients with duodenal ulcer (P < 0.0005), suggesting that only bacteria harboring this protein are associated with disease.

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...

Immunization with chemically detoxified pertussis toxin can prevent severe whooping cough with an efficacy similar to that of the cellular pertussis vaccine, which normally gives unwanted side effects. To avoid the reversion to toxicity and the loss of immunogenicity that may follow chemical treatment of pertussis toxin, inactive toxins were constructed by genetic manipulation. A number of genetically engineered alleles of the pertussis toxin genes, constructed by replacing either one or two key amino acids within the enzymatically active S1 subunit, were introduced into the chromosome of strains of Bordetella pertussis, B. parapertussis, and B. bronchiseptica. These strains produce mutant pertussis toxin molecules that are nontoxic and immunogenic and that protect mice from the intracerebral challenge with virulent Bordetella pertussis. Such molecules are ideal for the development of new and safer vaccines against whooping cough.

Pathogenic strains of Helicobacter pylon cause progressive vacuolatlon and death of epithelial cells. To identify the nature of vacuoles, the distribution of markers of various membrane traffic compartments was studied. Vacuoles derive from the endocytic pathway since they include the fluid-phase marker Lucifer yellow. Early endosome markers such as rab5, trerrin, and trnsferrin receptor, as well as the lysosomal hydrolase cathepsin D, are excluded from these structures. In contrast, the vacuolar membrane is specifically stained by ity-purified antibodies against rab7, a small GTPase, localized to late endosomal compartments. The labeling of rab7 on vacuolar membranes increases as vacuolation progresses, without a concomitant increase of cellular rab7. Cell vacuolation is inhibited by the microtubule-depolymerizing agents nocodazole and colchicine. Taken together, these findins indicate that the vacuoles specifically originate from late endosomal compartments.Strong evidence indicates that toxigenic strains of Helicobacter pylori play a major role in the development of type B gastritis, peptic ulcers, and gastric adenocarcinoma (1-3). Biopsies of H. pylori-colonized stomach epithelium show cellular swelling, expansion of endosomal compartments, and extensive vacuolation (4). A vacuolar degeneration of epithelial cells, followed by cell death, is induced in vitro by H. pylori bacterial extracts (5-7). The luminal pH of these vacuoles is acidic, as deduced from the uptake of neutral red, a membrane-permeant amine that becomes protonated in the vacuolar lumen, and from the potentiating effect of ammonia (8). Two virulence factors, produced by pathogenic strains of H. pylori are thought to be mainly responsible for this cell degeneration and death: a urease and a cytotoxin (3,4,7,8). The urease hydrolyzes urea and the ammonia produced permeates membranes, as neutral red does, and accumulates as ammonium ions inside intracellular acidic compartments, thus causing their osmotic swelling (9-11). However important, this process alone cannot account for the manyfold increase in vacuole volume, because, without membrane addition, it would lead to vacuole rupture.Recently a cytotoxin has been isolated from culture supernatants of a virulent strain of H. pylori (12) and shown to cause vacuolation in vitro (12) and in vivo (13). The genes encoding this protein (vacA; H. pylori vacuolating toxin A), and a bacterial antigen (cagA) characteristic of H. pylori pathogenic strains, have been recently cloned and sequenced, and they share no similarity with any other known protein (13,14). Thus, the molecular mechanism of action of vacA and the sequence of events leading to vacuolar cell degeneration and death remain largely obscure.The inhibition of vacuole formation by bafilomycins, specific inhibitors of the vacuolar-type ATPase proton pump (V-ATPase) (15), indicates that vacuoles originate from intracellular compartments endowed with a V-ATPase, such as endosomes, lysosomes, or the trans-Golgi network (TGN) (16)(17)(18)....

Bafilomycin A1, a specific inhibitor of the vacuolar-type H(+)-ATPase, responsible for acidification of intracellular compartments, prevents the vacuolization of Hela cells induced by H. pylori, with an inhibitory concentration giving 50% of maximal (ID50) of 4 nM. Bafilomycin A1 is also very efficient in restoring vacuolated cells to a normal appearance. The vacuolating activity of Helicobacter pylori is not inhibited by a series of specific inhibitors of vacuolar H(+)-ATPases. These findings indicate that a transmembrane pH gradient is needed for the formation and growth of vacuoles caused by the bacterium and that this pH gradient is due to the activity of a vacuolar ATPase proton pump of HeLa cells.