A pneumococcal pilus influences virulence and host inflammatory responses

Streptococcus pneumoniae (pneumococcus) is a major cause of morbidity and mortality world-wide. The initial event in invasive pneumococcal disease is the attachment of encapsulated pneumococci to epithelial cells in the upper respiratory tract. This work provides evidence that initial bacterial adhesion and subsequent ability to cause invasive disease is enhanced by pili, long organelles able to extend beyond the polysaccharide capsule, previously unknown to exist in pneumococci. These adhesive pili-like appendages are encoded by the pneumococcal rlrA islet, present in some, but not all, clinical isolates. Introduction of the rlrA islet into an encapsulated rlrA-negative isolate allowed pilus expression, enhanced adherence to lung epithelial cells, and provided a competitive advantage upon mixed intranasal challenge of mice. Furthermore, a pilus-expressing rlrA islet-positive clinical isolate was more virulent than a nonpiliated deletion mutant, and it out-competed the mutant in murine models of colonization, pneumonia, and bacteremia. Additionally, piliated pneumococci evoked a higher TNF response during systemic infection, compared with nonpiliated derivatives, suggesting that pneumococcal pili not only contribute to adherence and virulence but also stimulate the host inflammatory response.

Cloning, expression, purification, and characterization of Streptococcus pneumoniae IgA1 protease

The IgA1 protease of Streptococcus pneumoniae is a Zn-metalloproteinase of 1964 amino acids that specifically cleaves the hinge region of IgA1, the predominant class of immunoglobulin present on mucosal membranes. This protease is associated to the bacterial cell surface via an N-terminal membrane anchor. Following proteolysis it is released in several forms of different molecular weight. Here, we describe the cloning, expression, and characterization of the enzymatic activity and immunogenicity of three fragments of IgA1 protease, including a large one lacking only the 103 N-terminal amino acids that constitute a typical prokaryotic signal sequence. Further, a proteolytically inactive mutant was generated by replacement of the glutamate residue with an alanine residue in the active site motif HExxH (1605-1609). This is the first report of recombinant active forms of S. pneumoniae IgA1 protease, which open the possibility of identifying specific inhibitors that could interfere with the mucosal colonization by pneumococcus. Moreover the inactive mutant could be considered as a candidate vaccine component.

The design of vaccines against Helicobacter pylori and their development

Helicobacter pylori is a gram negative, spiral, microaerophylic bacterium that infects the stomach of more than 50% of the human population worldwide. It is mostly acquired during childhood and, if not treated, persists chronically, causing chronic gastritis, peptic ulcer disease, and in some individuals, gastric adenocarcinoma and gastric B cell lymphoma. The current therapy, based on the use of a proton-pump inhibitor and antibiotics, is efficacious but faces problems such as patient compliance, antibiotic resistance, and possible recurrence of infection. The development of an efficacious vaccine against H. pylori would thus offer several advantages. Various approaches have been followed in the development of vaccines against H. pylori, most of which have been based on the use of selected antigens known to be involved in the pathogenesis of the infection, such as urease, the vacuolating cytotoxin (VacA), the cytotoxin-associated antigen (CagA), the neutrophil-activating protein (NAP), and others, and intended to confer protection prophylactically and/or therapeutically in animal models of infection. However, very little is known of the natural history of H. pylori infection and of the kinetics of the induced immune responses. Several lines of evidence suggest that H. pylori infection is accompanied by a pronounced Th1-type CD4(+) T cell response. It appears, however, that after immunization, the antigen-specific response is predominantly polarized toward a Th2-type response, with production of cytokines that can inhibit the activation of Th1 cells and of macrophages, and the production of proinflammatory cytokines. The exact effector mechanisms of protection induced after immunization are still poorly understood. The next couple of years will be crucial for the development of vaccines against H. pylori. Several trials are foreseen in humans, and expectations are that most of the questions being asked now on the host-microbe interactions will be answered.

Composition and gene expression of the cag pathogenicity island in Helicobacter pylori strains isolated from gastric carcinoma and gastritis patients in Costa Rica

The composition and in vitro expression of the cag pathogenicity island genes in a group of Helicobacter pylori strains obtained from patients suffering from chronic gastritis-associated dyspepsia (n = 26) or gastric carcinoma (n = 17) were analyzed. No significant difference in the distribution of the 10 studied regions was found between the cases and the controls. Nine strains did not harbor any of the selected regions: eight (30.8%) isolated from patients with gastritis only and one (5.9%) from a patient with gastric carcinoma. No association was found between the number of repeated sequences at the 3' end of the cagA gene or the presence of tyrosine phosphorylation motifs and the clinical origin of the strains. The virB10 homolog gene was the sole gene studied to be significantly expressed more often in cancer strains than in gastritis strains (P = 0.03).

Cellular responses induced after contact with Helicobacter pylori

Contact-dependent activation of the cag organelle, a type IV secretion system of Helicobacter pylori, promotes translocation of CagA into the host cell. CagA is an immunodominant antigen of H. pylori, encoded by cag. It is thought to be associated with severe clinical outcomes, but has an unclear role in pathogenesis. Now we know that CagA is injected into the host and is tyrosine-phosphorylated by a membrane-associated eukaryotic tyrosine kinase. After activation, CagA induces morphological changes in the host, as well as actin reorganization, variations in the cell cycle and autocrine effects. Subversion of cell control may ultimately lead to cellular damage and to increased risks for gastric cancer development. cag instability contributes to long-term persistence within the host by attenuating bacterial virulence. We still do not know if additional factors are co-translocated with CagA and we do not know their specific mechanisms of action, but there is a strong experimental evidence that indicates that cag is the major player in the host-pathogen relationship.

"Cervia Working Group Report": guidelines on the diagnosis and treatment of Helicobacter pylori infection

Different national attitudes exist between countries in Europe concerning eradication of Helicobacter pylori infection due to the wide differences in Helicobacter pylori prevalence, gastric cancer risk, bacterial resistance to antibiotics, health care systems and financial resources. The Cervia Working Group Report has been established in order to fill the gap in the absence of National Guidelines in Italy concerning the diagnosis and treatment of Helicobacter pylori infection. The recommendations made are, by and large, similar to the European Guidelines but differ slightly with regard to the "test-and-treat" approach to young dyspeptics without sinister symptoms. In the absence of a national validation of this strategy a case-by-case assessment of dyspepsia has been promoted, both at primary care and specialist level. Another area of partial disagreement concerns the eradication of Helicobacter pylori in patients undergoing long-term proton pump inhibitor treatment which has not been generally recommended as scientific evidence in support of this policy is at present rather weak.

Helicobacter pylori activates mitogen-activated protein kinase cascades and induces expression of the proto-oncogenes c-fos and c-jun

Helicobacter pylori is an etiological agent in the development of mucosa-associated lymphoid tissue lymphoma and gastric adenocarcinoma. Patients infected with H. pylori carry a 3-6-fold increased risk of developing cancer compared with uninfected individuals. H. pylori strains expressing the cytotoxin-associated antigen A (CagA) are more frequently associated with the development of neoplasia than cagA-negative strains. However, the molecular mechanism by which H. pylori causes neoplastic transformation remains unclear. Here we report that exposure of gastric epithelial cells to H. pylori induces activation of the transcription factor activator protein 1. Activation of the proto-oncogenes c-fos and c-jun is strongly induced. We show that H. pylori activates the ERK/MAP kinase cascade, resulting in Elk-1 phosphorylation and increased c-fos transcription. H. pylori strains that do not express CagA or that are mutated in cag genes encoded by the CagI pathogenicity island do not induce activator protein 1, MAP kinase activity, or c-fos or c-jun activation. Proto-oncogene activation may represent a crucial step in the pathomechanism of H. pylori induced neoplasia.

The alleles of the bft gene are distributed differently among enterotoxigenic Bacteroides fragilis strains from human sources and can be present in double copies

Enterotoxigenic Bacteroides fragilis (ETBF) strains are associated with diarrheal disease in children. These strains produce a zinc metalloprotease enterotoxin, or fragilysin, that can be detected by a cytotoxicity assay with HT-29 cells. Recently, three different isoforms or variants of the enterotoxin gene, designated bft-1, bft-2, and bft-3, have been identified and sequenced. We used restriction fragment length polymorphism analysis of the PCR-amplified enterotoxin gene to detect the isoforms bft-1 and bft-2 or bft-3 borne by ETBF. By sequencing the portion of the bft gene corresponding to the mature toxin in some strains and applying allele-specific PCR for strains categorized as bft-2 or bft-3, we found in our collection two strains harboring bft-3, a variant that had been described for isolates from East Asia. Analysis of 66 ETBF strains from different sources showed that bft-1 is the most frequent allele, being present in 65% of isolates; it is largely predominant in isolates from feces of adults, while bft-2 is present in isolates from feces of children. This association is statistically significant (P, 0.0064). Sixteen strains were examined by Southern hybridization using, as probes, the bft and second metalloprotease genes, both included in a pathogenicity islet. Five strains were found to harbor double copies of both genes, suggesting that the whole islet was duplicated. Four of these strains, harboring bft-1 (three strains) or bft-2 (one strain), were found to produce a large amount of biologically active toxin, as determined by a cytotoxicity assay with HT-29 cells. The strains harboring bft-3, either in a single copy or in double copies, produced the smallest amount of toxin in our collection.

Tyrosine phosphorylation of the Helicobacter pylori CagA antigen after cag-driven host cell translocation

Helicobacter pylori strains associated with severe tissue damage and inflammation possess a unique genetic locus, cag, containing 31 genes originating from a distant event of horizontal transfer and retained as a pathogenicity island. The cag system is an Helicobacter-specific type IV secretion engine involved in cellular responses like induction of pedestals, secretion of IL-8, and phosphorylation of proteic targets. It has previously been reported that cocultivation of epithelial cells with Helicobacter pylori triggers signal transduction and tyrosine phosphorylation of a 145-kDa putative host cell protein. Herein, we demonstrate that this protein is not derived from the host but rather is the bacterial immunodominant antigen CagA, a virulence factor commonly expressed in peptic ulcer disease and thought to be an orphan of a specific biological function. Thus, CagA is delivered into the epithelial cells by the cag type IV secretion system where it is phosphorylated on tyrosine residues by an as yet unidentified host cell kinase and wired to eukaryotic signal transduction pathways and cytoskeletal plasticity.

Seropositivity to Helicobacter pylori and CagA protein in schoolchildren of different ages living in urban and rural areas in southern Estonia

OBJECTIVE

To evaluate Helicobacter pylori and CagA seropositivity in a non-selected group of schoolchildren in southern Estonia, with reference to previous studies where high seroprevalence to H. pylori (87%) and anti-CagA positivity (63%) in an adult population from the same region were found.

STUDY POPULATION

A total of 421 schoolchildren selected haphazardly from a random population (n = 1018, ages 9, 12 or 15 years) and living in urban or rural areas.

METHODS

H. pylori status was determined by evaluation of IgG antibodies against cell surface proteins of H. pylori, strain CCUG 17874, using standard ELISA. Anti-CagA IgGs were determined by ELISA using a recombinant fragment of CagA (CCUG 17874) as solid-phase antigen. Absorbance values > 0.3 (405 nm) were taken as a CagA-positive result based on a study of 25 sera from H. pylori-negative children.

RESULTS

Of the 421 subjects, 235 (56%) were H. pylori-ELISA positive, and 109 out of the 235 (46%) were anti-CagA positive. Neither H. pylori nor CagA positivity were significantly different in girls and boys, or in children aged 9, 12 or 15 years. The H. pylori prevalence rate (118/181, 65%) as well as CagA positivity (64/181, 35%) in rural areas were higher compared with those in towns (117/240, 49% and 54/240, 22%, respectively; P = 0.001 and P = 0.005).

CONCLUSION

Of schoolchildren living in southern Estonia, 56% were seropositive to H. pylori. Half of them had anti-CagA antibodies. Schoolchildren living in rural areas were infected significantly more often with CagA-seropositive strains compared with those living in towns.

Activation of activator protein 1 and stress response kinases in epithelial cells colonized by Helicobacter pylori encoding the cag pathogenicity island

Helicobacter pylori interacts with the apical membrane of the gastric epithelium and induces a number of proinflammatory cytokines/chemokines. The subsequent infiltration of macrophages and granulocytes into the mucosa leads to gastric inflammation accompanied by epithelial degeneration. Gastric diseases, e.g. peptic ulcer or gastric adenocarcinoma, are more common among people infected with H. pylori strains producing VacA (vacuolating cytotoxin A) and possessing a cag (cytotoxin-associated antigen A) pathogenicity island. For the induction of the cytokine/chemokine genes in response to H. pylori, we studied the signaling leading to the nuclear activation of the early response transcription factor activator protein 1 (AP-1). We found that H. pylori strains carrying the pathogenicity island induce activation of AP-1 and nuclear factor kappaB. In contrast to the wild type or an isogenic strain without the vacA gene, isogenic H. pylori strains with mutations in certain cag genes revealed only weak AP-1 and nuclear factor kappaB activation. In respect to the molecular components that direct AP-1 activity, our results indicate a cascade of the cellular stress response kinases c-Jun N-terminal kinase, MAP kinase kinase 4, and p21-activated kinase, and small Rho-GTPases including Rac1 and Cdc42, which contributes to the activation of proinflammatory cytokines/chemokines induced by H. pylori encoding the cag pathogenicity island.

Seroprevalence of cytotoxin-associated gene A positive Helicobacter pylori strains in Changle, an area with very high prevalence of gastric cancer in south China

BACKGROUND

Helicobacter pylori, especially the CagA-positive strains, are closely associated with peptic ulcers and gastric cancers. We performed a large scale gastric cancer screening project and examined the prevalence of H. pylori and CagA-positive strains in Changle, China, an area with one of the World's highest gastric cancer mortality. We also compared the prevalence with that in Hong Kong which has one-tenth of the gastric cancer mortality of that in Changle.

METHODS

A total of 2424 subjects in Changle and 523 subjects in Hong Kong had endoscopic examination and venesection. Sera were tested for anti-H. pylori antibody and anti-CagA antibody and correlated with endoscopic findings.

RESULTS

In Changle, 80. 9% of the subjects were H. pylori carriers. Out of 551 carriers, 408 (74%) were positive for anti-CagA antibody. A total of 76% and 87% of the asymptomatic and gastric cancer patients were positive for anti-CagA antibody, respectively (P > 0.05). Compared to Hong Kong, there was a significantly (P < 0.0001) higher prevalence of CagA-positive strains in asymptomatic subjects in Changle (76%) than in Hong Kong (28%), but not in peptic ulcers or gastric cancers.

CONCLUSIONS

Subjects in Changle had a high prevalence of H. pylori infection and a high prevalence of the CagA-positive strains. The contrast in the prevalence of CagA-positive strains, in asymptomatic subjects in two areas with differing gastric cancer mortality, supports the pathogenic role of CagA-positive strains in gastric carcinogenesis.

Patients younger than 40 years with gastric carcinoma: Helicobacter pylori genotype and associated gastritis phenotype

BACKGROUND

In the general population, Helicobacter pylori (H. pylori), particularly the cagA positive strain, has been associated with intestinal-type gastric carcinoma. Gastric carcinomas are rarely observed in patients age < or = 40 years. Host-related factors have been thought to be more important than environmental agents in these early-onset cancers. The aim of this study was to ascertain the possible role of H. pylori infection and that of cagA positive strains in the development of gastric carcinoma in these young patients.

METHODS

In this case-control study, 105 gastric carcinoma patients (male-to-female ratio = 1.1; mean age, 34.4 years; range, 16-40 years) and an equal number of controls (matched for gender and age) were retrospectively selected from the same geographic area. The phenotypes of gastritis and H. pylori were histologically assessed, and the presence of the ureC gene, which is indicative of H. pylori infection, and the cagA genotype were determined by polymerase chain reaction. Gastric carcinoma risk was calculated by both univariate and multivariate statistical methods, taking into account the cancer phenotype, the gastritis phenotype detected in both patients and controls, and the H. pylori genotype.

RESULTS

For 74 diffuse and 31 intestinal gastric carcinomas, multivariate logistic regression analysis produced results consistent with those of univariate statistical tests, showing a significant association between gastric carcinoma and both H. pylori infection (odds ratio [OR] = 2.79; 95% confidence interval [CI] = 1.52-5.11) and cagA positive status (OR = 2.94; 95% CI = 1.56-5.52).

CONCLUSIONS

In young Italian patients with gastric carcinoma, the significant association with cagA positive H. pylori infection suggests that the bacterium has an etiologic role in both diffuse-type and intestinal-type gastric carcinoma.

Helicobacter pylori virulence and genetic geography

Isolated for the first time in 1982 from human gastric biopsy, Helicobacter pylori is responsible for gastritis, peptic ulcer, and gastric cancer. A pathogenicity island acquired by horizontal transfer, coding for a type IV secretion system, is a major determinant of virulence. The infection is now treated with antibiotics, and vaccines are in preparation. The geographic distribution suggests coevolution of man and Helicobacter pylori.

Immune response to a recombinant fragment of the CagA protein of Helicobacter pylori in blood donors and patients with gastric cancer: relation to ABO(H) blood group phenotype, stage of the disease and tumor morphology

IgG immune response to CagA was evaluated by enzyme-linked imunosorbent assay (ELISA) using a recombinant fragment of CagA as antigen in 171 patients with gastric cancer and 298 blood donors to determine whether it could be related to the ABO(H) blood group phenotype, stage of cancer or tumor morphology. The CagA-ELISA showed a good specificity (93.5%) and sensitivity (88.5%) as compared with immunoblotting for blot CagA-negative and -positive donors. The Helicobacter pylori seropositive blood group A donors revealed the lowest proportion (37.6%) of strong responders to CagA: A<O (51.2%)<B (56.9%)<AB (62.5%). The proportion of strong responders to CagA was significantly lower among the H. pylori-seropositive patients with non-cardial cancer (35.4%) than in donors (48.8%). A significant suppression of immune response to CagA was found in the patients with advanced cancer. The proportion of CagA strong responders was higher at the first stage of gastric cancer in only blood group O and A individuals as compared with related controls. The overall CagA seroprevalence was not influenced by tumor histology. Thus, the IgG immune response to CagA is dependent on the ABO(H) blood group phenotype of the host and the stage of cancer. The host-dependent differences in the immune response to CagA may be more pronounced than those related to the putative disease-specific features of the H. pylori infection.

Pathogenicity island mediates Helicobacter pylori interaction with the host

In Helicobacter pylori, a pathogenicity island (PAI) of approximately 40 kb, named cag, is present in a subset of strains. The strains containing the PAI are more virulent than those that do not contain it, and are associated with peptic ulcer and gastric cancer. A putative secretory mechanism is encoded by this PAI. This secretory system is thought to be involved in the induction of the proiflammatory lymphokine IL-8 and tyrosine phosphorylation of proteins in the gastric cells. We are currently investigating the potential toxic factors exported by this region.

cagA positive and negative Helicobacter pylori strains are simultaneously present in the stomach of most patients with non-ulcer dyspepsia: relevance to histological damage

BACKGROUND/AIMS

Infection with Helicobacter pylori strains harbouring the cagA gene (cagA+) is associated with an increased risk of developing peptic ulcer and gastric cancer. The aim of this study was to assess whether H pylori isolates with different cagA status were present in patients with non-ulcer dyspepsia, and whether a variable cagA status is relevant to histological gastric mucosal damage and glandular cell proliferation.

METHODS

Well separated H pylori colonies (between 2 and 25) from primary plates, per gastric area, for each of 19 patients with non-ulcer dyspepsia were examined for cagA by hybridisation. Western blotting was used to examine both representative colonies for CagA expression and the patients' sera for antibody response to CagA. Glandular gastric cell proliferation was assessed immunohistochemically.

RESULTS

Of the 747 colonies examined, 45.3% were cagA+. All colonies from four patients were cagA+, and all colonies from two patients were cagA-. In 13 patients (68%) both cagA+ and cagA- colonies were found. CagA expression of isolates corresponded to their cagA status. H pylori strains with different CagA molecular masses were present in three patients. Results based on all 19 patients studied showed that the prevalence of cagA+ colonies in areas with mucosal atrophy associated or not with intestinal metaplasia (67.9%) was significantly higher than in normal mucosa (44.7%) and mucosa from patients with chronic gastritis (44.0%) (p < 0.001). High levels of cell proliferation were associated with histological atrophy with or without intestinal metaplasia, but not with the possession of cagA by organisms colonising the same mucosal sites.

CONCLUSIONS

Most patients with nonulcer dyspepsia are infected by both cagA+ and cagA- H pylori colonies. The cagA status of infecting organisms may play a role in the development of atrophy and intestinal metaplasia.

Proteins encoded by the cag pathogenicity island of Helicobacter pylori are required for NF-kappaB activation

Helicobacter pylori is the etiological agent in the development of chronic gastritis, duodenal ulceration, and gastric adenocarcinoma. The difference in virulence between individual strains is reflected in their ability to induce interleukin-8 (IL-8) secretion from gastric epithelial cells. It has been shown that virulence is associated with the presence of a bacterial gene cluster (a pathogenicity island). We have recently demonstrated that H. pylori-mediated IL-8 secretion requires activation of the transcription factor NF-kappaB. Here, we show that NF-kappaB induction requires six membrane proteins encoded within the pathogenicity island.

Hemolytic properties and riboflavin synthesis of Helicobacter pylori: cloning and functional characterization of the ribA gene encoding GTP-cyclohydrolase II that confers hemolytic activity to Escherichia coli

Various strains of Helicobacter pylori were able to lyse erythrocytes from sheep, horse, and human when grown on blood agar. The hemolysis did not depend on the production of the vacuolating cytotoxin VacA as demonstrated by the hemolytic behavior of an isogenic vacA-negative mutant strain. The hemolytic activity could be detected in cell-free supernatants and was not regulated by iron. To isolate genes coding for proteins involved in the destruction of erythrocytes, a plasmid-based DNA library was screened for expression of lytic activity on blood agar. This approach revealed that the H. pylori ribA gene confers hemolytic properties to Escherichia coli. The ribA gene encodes the enzyme GTP-cyclohydrolase II [EC 3.5.4.25] that catalyzes the initial step in the synthesis of riboflavin. The predicted amino acid sequence of the H. pylori RibA protein showed a high degree of similarity to equivalent enzymes from microorganisms and from plants. The single gene on a plasmid restored riboflavin synthesis in a ribA mutant of E. coli and induced hemolytic activity. Furthermore, ribA overexpression was associated with the production of a fluorescent yellow molecule that was not identical with riboflavin. Hemolysis was also seen for the ribA gene from E. coli, indicating that this feature was not specific for the H. pylori gene. The presence of ribA in various H. pylori strains was confirmed by Southern blot hybridization and by polymerase chain reaction with specific primers. This analysis revealed that microdiversity exists within the DNA region upstream from ribA, which was further confirmed by nucleotide sequence analysis.

A recombinant fragment of Helicobacter pylori CagA affects proliferation of human cells

The outcome of H. pylori infectins depends on proliferation of various host cells, including lymphocytes, monocytes and epithelial cells. In this study we showed that a recombinant fusion protein carrying an immunodominant region of H. pylori CagA antigen affected the proliferation of human cells. The rCagA inhibited PHA-driven T cell proliferation but enhanced the growth of epithelial HeLa cells, especially in the presence of granulocyte macrophage colony stimulating factor (GM-CSF). When THP-1 monocytes and Kato-3 epithelial cells from metastasis of gastric carcinoma were stimulated with GM-CSF, they were also susceptible to the inhibitory effect of rCagA. These results confirmed our earlier suggestion on the inhibition of T cell function by H. pylori CagA protein. However, antiproliferative activity of CagA antigen appears to be not restricted to T lymphocytes but modulatory effect of this protein seems to depend on the cell type.

Helicobacter pylori: molecular evolution of a bacterial quasi-species

Helicobacter pylori persists chronically within individuals and as they spread the mutating bacteria migrate with them. The continuous selection and microevolution generates a population of closely related but different bacteria that behave like a quasi-species. Within this heterogeneity, H. pylori strains fall into distinct types, into the virulent (type I) and less virulent (type II) strains, based on the presence of a pathogenicity island (cag) that encodes a specialized secretion machinery. We propose that during chronic infection a dynamic equilibrium between bacteria expressing a disparate degree of virulence is established, and that diverse forms prevail at different times.

Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging

The bacterium Helicobacter pylori is the causative agent for peptic ulcer disease. Bacterial adherence to the human gastric epithelial lining is mediated by the fucosylated Lewis b (Leb) histo-blood group antigen. The Leb-binding adhesin, BabA, was purified by receptor activity-directed affinity tagging. The bacterial Leb-binding phenotype was associated with the presence of the cag pathogenicity island among clinical isolates of H. pylori. A vaccine strategy based on the BabA adhesin might serve as a means to target the virulent type I strains of H. pylori.

CagA protein seropositivity in a random sample of adult population and gastric cancer patients in Estonia

OBJECTIVE

The prevalence of antibodies to CagA protein, associated with the risk of developing gastric cancer (GC), was studied in an Estonian adult population with a high prevalence of Helicobacter pylori (HP) infection and in a group of GC patients.

DESIGN

In a representative sample of a random adult population from the South Estonian town of Karksi-Nuia, containing 199 subjects (86 M, 113 F, mean age 42.4) and in 45 (22 M, 23 F, mean age 64.5) consecutive patients with gastric adenocarcinoma, recruited during the periods 1986-87 and 1995-96 in the Hospital of Oncology, University of Tartu, anti-CagA IgG antibodies were determined by enzyme-linked immunosorbent assay (ELISA) using a recombinant fragment of CagA protein. The occurrence of anti-CagA IgG in ELISA was compared with immunoblot results for 141 subjects.

RESULTS

Seropositivity to acid glycine extracted cell surface proteins of HP was 85% in the population and 91% in GC patients (p = 0.39). Anti-CagA IgG antibodies were present in 63% of the population and in 87% of GC patients (p = 0.004). The highest prevalence of anti-CagA IgG in the population sample occurred in the age group 20-29 (76%). A comparison of anti-CagA positivity evaluated by using ELISA and immunoblot showed an agreement of results in 80% of cases.

CONCLUSION

HP seropositivity was similarly high in the Estonian random adult population sample and in GC patients, however, the prevalence of anti-CagA IgG was significantly higher in GC patients. Moreover, persons aged 20-29 years in the population possess the highest prevalence of anti-CagA IgG and should be given further attention with respect to the development of GC later in life.

Protection against Helicobacter pylori infection in mice by intragastric vaccination with H. pylori antigens is achieved using a non-toxic mutant of E. coli heat-labile enterotoxin (LT) as adjuvant

We have previously shown that infection of mice with H. pylori can be prevented by oral immunization with H. pylori antigens given together with E. coli heat-labile enterotoxin (LT) as adjuvant. Since LT cannot be used in humans because of its unacceptable toxicity, we investigated whether protection of mice could be achieved by co-administration of antigens with non-toxic LT mutants. Here we show that CD1/SPF mice are protected against infection after oral vaccination with either purified H. pylori antigens (native and recombinant VacA, urease and CagA), or whole-cell vaccine formulations, given together with the non-toxic mutant LTK63 as a mucosal adjuvant. Furthermore we show that such protection is antigen-specific since immunization with recombinant or native VacA plus LTK63 conferred protection against infection by an H. pylori Type I strain, which expresses VacA, but not against challenge with a Type II strain which is not able to express this antigen. These results show that: (1) protection against H. pylori can be achieved in the mouse model of infection using subunit recombinant constructs plus non-toxic mucosal adjuvants; and (2) this mouse model is an useful tool in testing H. pylori vaccine formulations for eventual use in humans.

A secreted/shed product of Helicobacter pylori activates transcription factor nuclear factor-kappa B

Helicobacter pylori is an etiologic agent in the development of chronic gastritis, duodenal ulceration, and gastric adenocarcinoma. Exposure of gastric epithelial cells to H. pylori induces secretion of the cytokine IL-8, which plays a pivotal role in the immunopathogenesis of H. pylori infections. Isolated Helicobacter strains differ in their virulence and in their ability to induce cytokine production. High degrees of virulence correlate with enhanced IL-8 production. However, the molecular mechanism of this variance in Helicobacter pathogenicity remains poorly understood. Here we show that H. pylori-mediated IL-8 secretion requires activation of the transcription factor nuclear factor-kappaB (NF-kappaB) in a gastric epithelial cell line. Several H. pylori strains which fail to induce IL-8 secretion do not activate NF-kappaB, while all IL-8-inducing strains activate the transcription factor. Moreover, the antioxidant curcumin, which inhibits NF-kappaB activation, also completely suppresses IL-8 induction by H. pylori. NF-kappaB activation is not mediated by LPSs, since purified H. pylori LPS had no effect on gastric epithelial cells. In contrast, both IL-8 secretion and NF-kappaB activation require a secreted H. pylori product, which is not secreted by strains mutated in picB/cagE, a recently identified putative transport protein.

A secreted/shed product of Helicobacter pylori activates transcription factor nuclear factor-kappa B

Helicobacter pylori is an etiologic agent in the development of chronic gastritis, duodenal ulceration, and gastric adenocarcinoma. Exposure of gastric epithelial cells to H. pylori induces secretion of the cytokine IL-8, which plays a pivotal role in the immunopathogenesis of H. pylori infections. Isolated Helicobacter strains differ in their virulence and in their ability to induce cytokine production. High degrees of virulence correlate with enhanced IL-8 production. However, the molecular mechanism of this variance in Helicobacter pathogenicity remains poorly understood. Here we show that H. pylori-mediated IL-8 secretion requires activation of the transcription factor nuclear factor-kappaB (NF-kappaB) in a gastric epithelial cell line. Several H. pylori strains which fail to induce IL-8 secretion do not activate NF-kappaB, while all IL-8-inducing strains activate the transcription factor. Moreover, the antioxidant curcumin, which inhibits NF-kappaB activation, also completely suppresses IL-8 induction by H. pylori. NF-kappaB activation is not mediated by LPSs, since purified H. pylori LPS had no effect on gastric epithelial cells. In contrast, both IL-8 secretion and NF-kappaB activation require a secreted H. pylori product, which is not secreted by strains mutated in picB/cagE, a recently identified putative transport protein.

Therapeutic intragastric vaccination against Helicobacter pylori in mice eradicates an otherwise chronic infection and confers protection against reinfection

Chronic infection of the gastroduodenal mucosae by the gram-negative spiral bacterium Helicobacter pylori is responsible for chronic active gastritis, peptic ulcers, and gastric cancers such as adenocarcinoma and low-grade gastric B-cell lymphoma. The success of eradication by antibiotic therapy is being rapidly hampered by the increasing occurrence of antibiotic-resistant strains. An attractive alternative approach to combat this infection is represented by the therapeutic use of vaccines. In the present work, we have exploited the mouse model of persistent infection by mouse-adapted H. pylori strains that we have developed to assess the feasibility of the therapeutic use of vaccines against infection. We report that an otherwise chronic H. pylori infection in mice can be successfully eradicated by intragastric vaccination with H. pylori antigens such as recombinant VacA and CagA, which were administered together with a genetically detoxified mutant of the heat-labile enterotoxin of Escherichia coli (referred to as LTK63), in which the serine in position 63 was replaced by a lysine. Moreover, we show that therapeutic vaccination confers efficacious protection against reinfection. These results represent strong evidence of the feasibility of therapeutic use of VacA- or CagA-based vaccine formulations against H. pylori infection in an animal model and give substantial preclinical support to the application of this kind of approach in human clinical trials.

Immunobiology of Helicobacter pylori infection

Helicobacter pylori is a 'slow' bacterial pathogen. While infection is usually acquired early in life, only decades later does severe pathology appear. During this long period of incubation, the host mounts a vigorous immune response against H. pylori which fails to resolve the infection and may in fact contribute to the severity of the disease. In the past year, evidence has accumulated indicating a role for a polarized T helper 1 cell response in the gastric pathology induced by H. pylori. Furthermore, a pathogenicity island in type I H. pylori strains has been shown to be responsible for H. pylori induced inflammation. Recent advances in animal models have provided the rationale for entering into human clinical trials of an H. pylori vaccine

Induction of host signal transduction pathways by Helicobacter pylori

Adherence of Helicobacter pylori to cultured gastric epithelial cells is associated with several cellular events, including the tyrosine phosphorylation of a 145-kDa host protein; the reorganization of the host cell actin and associated cellular proteins, like vasodilator-stimulated phosphoprotein, adjacent to the attached bacterial cell; and the subsequent release of the cytokine, interleukin 8 (IL-8). H. pylori isolated from patients with ulcer disease and gastric cancer contain a DNA insertion, the cag pathogenicity island (PAI), that is not present in bacteria isolated from individuals with asymptomatic infection. Mutations in a number of PAI genes abolish tyrosine phosphorylation and IL-8 synthesis but not the cytoskeletal rearrangements. Kinase inhibition studies suggest there are two distinct pathways operative in stimulating IL-8 release from host cells and one of these H. pylori pathways is independent of the tyrosine phosphorylation step.

Did the inheritance of a pathogenicity island modify the virulence of Helicobacter pylori?

Strains of Helicobacter pylori from patients with peptic ulcer disease and gastric cancer contain a 40-kb fragment of DNA that is not present in isolates from carriers with asymptomatic infections. The discovery of the cag pathogenicity island suggests that virulence has evolved by quantum leaps through the inheritance of one or more DNA insertions.

cag, a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors

cagA, a gene that codes for an immunodominant antigen, is present only in Helicobacter pylori strains that are associated with severe forms of gastroduodenal disease (type I strains). We found that the genetic locus that contains cagA (cag) is part of a 40-kb DNA insertion that likely was acquired horizontally and integrated into the chromosomal glutamate racemase gene. This pathogenicity island is flanked by direct repeats of 31 bp. In some strains, cag is split into a right segment (cagI) and a left segment (cagII) by a novel insertion sequence (IS605). In a minority of H. pylori strains, cagI and cagII are separated by an intervening chromosomal sequence. Nucleotide sequencing of the 23,508 base pairs that form the cagI region and the extreme 3' end of the cagII region reveals the presence of 19 ORFs that code for proteins predicted to be mostly membrane associated with one gene (cagE), which is similar to the toxin-secretion gene of Bordetella pertussis, ptlC, and the transport systems required for plasmid transfer, including the virB4 gene of Agrobacterium tumefaciens. Transposon inactivation of several of the cagI genes abolishes induction of IL-8 expression in gastric epithelial cell lines. Thus, we believe the cag region may encode a novel H. pylori secretion system for the export of virulence determinants.

Antibodies to CagA protein are associated with gastric atrophy in Helicobacter pylori infection

Strains of Helicobacter pylori which express the product of the cytotoxin associated gene A(CagA) are associated with duodenal ulceration. Also there is evidence that the presence of serum IgG antibodies to CagA is associated with an increased risk of gastric cancer of the intestinal type. Gastric atrophy is a precursor of intestinal-type gastric cancer so we have investigated whether antibodies to CagA are associated with gastric atrophy. In H. pylori infected patients, IgG antibodies to CagA were present in 24/38 (63%) of non-ulcer patients with atrophy compared with 13/40 (33%) of patient-controls with neither atrophy nor ulcer (P < 0.02). CagA antibodies were also more prevalent in patients with duodenal ulcers; 15/20 (75%) or gastric ulcers 5/5 (100%) than in the patient-controls (P < 0.005 and < 0.02 respectively). These results show that circulating IgG antibodies to CagA are associated with gastric atrophy, as well as peptic ulcer disease. Atrophy is a precursor of gastric cancer so support the hypothesis that certain strains of H. pylori are more likely to cause gastric cancer.

Detection of a vacuolating cytotoxin in stools from children with diarrhea

A cytotoxin inducing vacuolation in HEp-2 cells was detected in 19 (3.1%) of 618 stool specimens from children with diarrhea but in none of 135 from control children. Common enteric pathogens were found in only two (10.5%) of the 19 cytotoxin-positive stool specimens. The vacuoles induced by stool filtrates resembled those induced by the vacuolating toxin (VacA) of Helicobacter pylori. The vacuolating toxin was heat-labile and protease-sensitive, and it had an apparent molecular weight of > 100,000 but was not neutralized by an antiserum to H. pylori VacA. Although proper prospective case-control studies are needed to definitely assess the etiologic association between the new vacuolating cytotoxin and diarrhea, the present study suggests that microorganisms of the gastrointestinal tract produce a Helicobacter-like vacuolating toxin and may be responsible for cases of childhood diarrhea whose etiology is currently considered unknown.

Prevalence of CagA-bearing Helicobacter pylori strains detected by the anti-CagA assay in patients with peptic ulcer disease and in controls

OBJECTIVE

Cytotoxin-associated gene (CagA)-bearing Helicobacter pylori strains have been associated with significant gastroduodenal pathologies. We have performed a study to evaluate the prevalence of CagA-bearing strains in a group of H. pylori-positive peptic ulcer disease and non-ulcer dyspepsia (NUD) patients, and healthy asymptomatic controls.

METHOD

Two hundred ninety-seven peptic ulcer disease, 45 NUD subjects, and 200 asymptomatic controls were studied. The newly developed anti-CagA antibody assay was used for the purpose of this study. The assay was performed by a conventional three-step enzyme-linked immunosorbent assay (ELISA) to detect the concentration of anti-CagA antibody present in the tested sera against the recombinant CagA 17/12 fusion protein. The final results were expressed with reference to a standard curve constructed from pooled CagA+ sera. Anti-CagA antibody assay reproducibility was assessed by intraplate and interplate variations.

RESULTS

The mean intraplate and interplate variations were 8.0% and 11.2%, respectively. Anti-CagA antibody was present in 165/197 (84%) duodenal ulcer disease, 80/100 (80%) gastric ulcer disease, 25/45 (55.6%) NUD subjects, and 29/100 (29%) asymptomatic controls. The ulcer disease subjects were significantly more likely than the NUD subjects and the asymptomatic controls to have a positive anti-CagA antibody assay ( p < 0.005 and p < 0.001, respectively). Moreover, the NUD subjects were more likely to be anti-CagA+ antibody than the asymptomatic controls (p < 0.005).

CONCLUSIONS

This newly developed anti-CagA antibody assay was highly reproducible. Anti-CagA antibody positivity was present in a significantly higher percentage of peptic ulcer disease subjects than in non-ulcer and asymptomatic healthy controls. Thus, anti-CagA antibody can be used as a clinical marker for peptic ulceration.

Induction of interleukin-8 secretion from gastric epithelial cells by a cagA negative isogenic mutant of Helicobacter pylori

The ability of Helicobacter pylori strains to induce interleukin-8 (IL-8) gene expression and protein secretion from gastric epithelial cell lines in vitro is variable. This cellular response is associated with bacterial expression of the CagA protein present in type I H pylori strains. To determine the role of CagA in this host cell response, an isogenic cagA negative mutant, N6.XA3, was constructed. The cagA negative isogenic mutant and the wild-type parental cagA positive strain, N6, were cocultured with AGS, ST-42 and KATO-3 gastric epithelial cell lines and secreted interleukin-8 assayed by enzyme linked immunosorbent assay. In all three cell lines there was no significant difference in the IL-8 secretion induced by the cagA negative isogenic mutant, N6.XA3, and the wild-type parent strain, N6. These studies show that CagA is not the inducer of IL-8 secretion from gastric epithelial cells. As all wild-type CagA positive strains studied to date induce IL-8, the bacterial factor(s) inducing this inflammatory response is closely associated with the expression of CagA.

Analysis of expression of CagA and VacA virulence factors in 43 strains of Helicobacter pylori reveals that clinical isolates can be divided into two major types and that CagA is not necessary for expression of the vacuolating cytotoxin

Colonization of the mucosa of the stomach and the duodenum by Helicobacter pylori is the major cause of acute and chronic gastroduodenal pathologies in humans. Duodenal ulcer formation strongly correlates with the expression of an antigen (CagA) that is usually coeexpressed with the vacuolating cytotoxin (VacA), a protein that causes ulceration in the stomach of mice. However, the relationship between these two virulence factors is unknown. To define whether CagA and VacA are coexpressed in all clinical isolates and their relationships, we collected 43 clinical isolates of H. pylori and studied their genetic and phenotypic properties. Based on this analysis, most of the strains could be classified into two major types. Type I bacteria had the gene coding for CagA and expressed the CagA protein and the vacuolating cytotoxin. Type II bacteria did not have the gene coding for CagA and did not express either the CagA protein or the vacuolating cytotoxin. Type I and type II bacteria represented 56 and 16%, respectively, of the 43 clinical isolates, while the remaining 28% had an intermediate phenotype, expressing CagA independently of VacA or vice versa. This finding shows that although it is present in most cytotoxic strains, CagA is not necessary for the expression of the vacuolating cytotoxin.

Helicobacter pylori induced interleukin-8 expression in gastric epithelial cells is associated with CagA positive phenotype

AIMS

To use a range of natural phenotypically variant strains of Helicobacter pylori with disparate CagA and VacA (vacuolating cytotoxin) expression to determine which bacterial factors are more closely associated with epithelial interleukin-8 (IL-8) induction.

METHODS

Gastric epithelial cells (AGS and KATO-3) were co-cultured with five H pylori strains which were variously shown to express the cagA gene/CagA protein, VacA and/or to exhibit biological cytotoxicity. Secreted IL-8 was assayed by enzyme leaked immunosorbent assay (ELISA) and IL-8 messenger RNA (mRNA) was assayed using a reverse transcription polymerase chain reaction based technique (RT-PCR).

RESULTS

Strains expressing CagA, including a variant strain (D931) which is non-cytotoxic and does not express the VacA protein, were found to upregulate epithelial IL-8 secretion and gene expression. In contrast, strains with no CagA expression, even in the presence of VacA and/or biological cytotoxicity, (G104, BA142), failed to induce IL-8 protein or mRNA above control values.

CONCLUSIONS

These results strongly support a role for H pylori CagA or coexpressed factors other than the cytotoxin in upregulation of gastric epithelial IL-8. Increased epithelial IL-8 secretion and concomitant neutrophil chemotaxis and activation in addition to direct cytotoxicity may be an important factor in tissue damage and ulceration.

Analysis of expression of CagA and VacA virulence factors in 43 strains of Helicobacter pylori reveals that clinical isolates can be divided into two major types and that CagA is not necessary for expression of the vacuolating cytotoxin

Colonization of the mucosa of the stomach and the duodenum by Helicobacter pylori is the major cause of acute and chronic gastroduodenal pathologies in humans. Duodenal ulcer formation strongly correlates with the expression of an antigen (CagA) that is usually coeexpressed with the vacuolating cytotoxin (VacA), a protein that causes ulceration in the stomach of mice. However, the relationship between these two virulence factors is unknown. To define whether CagA and VacA are coexpressed in all clinical isolates and their relationships, we collected 43 clinical isolates of H. pylori and studied their genetic and phenotypic properties. Based on this analysis, most of the strains could be classified into two major types. Type I bacteria had the gene coding for CagA and expressed the CagA protein and the vacuolating cytotoxin. Type II bacteria did not have the gene coding for CagA and did not express either the CagA protein or the vacuolating cytotoxin. Type I and type II bacteria represented 56 and 16%, respectively, of the 43 clinical isolates, while the remaining 28% had an intermediate phenotype, expressing CagA independently of VacA or vice versa. This finding shows that although it is present in most cytotoxic strains, CagA is not necessary for the expression of the vacuolating cytotoxin.

Pathogenesis of Helicobacter pylori and perspectives of vaccine development against an emerging pathogen

Infection of the stomach and the duodenum by Helicobacter pylori is the major cause of acute and chronic gastroduodenal pathologies in humans and increases the risk of gastric cancer. The recognition of the infectious nature of the illness is having a major impact in the management of the disease that is shifting from the treatment of symptoms by anti-H2 blockers to the eradication of the bacterial infection by antibiotic regimen. Experience with other bacterial diseases, suggests that antibiotic treatment will select resistant strains that in the long term will make the antibiotics infective. Vaccination that classically is the most effective way to prevent and control infectious diseases in large population, could be used to prevent infection and possibly also to treat the disease. Here we summarize the studies on the identification and characterization of the virulence factors that are important for the pathogenesis of the bacterium and that may be candidate components for a vaccine. Animal models of the infection are also described.

Unravelling the pathogenic role of Helicobacter pylori in peptic ulcer: potential new therapies and vaccines

The recognition that peptic ulcer is an infectious disease caused by the bacterium Helicobacter pylori has revolutionized the approach to diagnosis and therapy of this condition. Treatment of the symptoms of peptic ulcer with drugs that block acid secretion is already being replaced by antibiotic eradication of the causative agent. Studies of the molecular events that lead to H. pylori pathogenesis have shown that clinical isolates can be divided into two groups, only one of which produces a cytotoxin and is associated with severe disease. The cloning of the genes coding for molecules specific for disease-associated strains of H. pylori, and the development of animal models that mimic the human pathology, will provide the basis for better strategies to treat and prevent peptic-ulcer disease.

Active-site mutations of the diphtheria toxin catalytic domain: role of histidine-21 in nicotinamide adenine dinucleotide binding and ADP-ribosylation of elongation factor 2

Diphtheria toxin (DT) has been studied as a model for understanding active-site structure and function in the ADP-ribosyltransferases. Earlier evidence suggested that histidine-21 of DT is important for the ADP-ribosylation of eukaryotic elongation factor 2 (EF-2). We have generated substitutions of this residue by cassette mutagenesis of a synthetic gene encoding the catalytic A fragment (DTA) of DT, and have characterized purified mutant forms of this domain. Changing histidine-21 to alanine, aspartic acid, leucine, glutamine, or arginine diminished ADP-ribosylation activity by 70-fold or greater. In contrast, asparagine proved to be a functionally conservative substitution, which reduced ADP-ribosylation activity by < 3-fold. The asparagine mutant was approximately 50-fold-attenuated in NAD glycohydrolase activity, however. Dissociation constants (Kd) for NAD binding, determined by quenching of the intrinsic protein fluorescence, were 15 microM for wild-type DTA, 160 microM for the asparagine mutant, and greater than 500 microM NAD for the alanine, leucine, glutamine, and arginine mutants. These and previous results support a model of the ADP-ribosylation of EF-2 in which histidine-21 serves primarily a hydrogen-bonding function. We propose that the pi-imidazole nitrogen of His-21 hydrogen-bonds to the nicotinamide carboxamide, orienting the N-glycosidic bond of NAD for attack by the incoming nucleophile in a direct displacement mechanism, and then stabilizing the transition-state intermediate of this reaction.

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

The 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. 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. pylori pathogenesis and the development of therapeutics and vaccines.

Detection in an enzyme immunoassay of an immune response to a recombinant fragment of the 128 kilodalton protein (CagA) of Helicobacter pylori

The possibility of using a recombinant fragment of the CagA (128 kDa protein) for the diagnosis of Helicobacter pylori infection was evaluated. Following cloning of the gene coding for the CagA, a recombinant fragment of it was expressed in Escherichia coli, purified and used in Western blot and an EIA to screen sera from 82 patients with gastroduodenal disease who underwent endoscopic examination. In Western blot, good correlation was found between the serological data obtained with the recombinant antigen and those obtained using non-purified extracts of Helicobacter pylori. The EIA using the antigen showed a sensitivity of 96.2% and a specificity of 96.6% compared with Western blot. These data indicate that the recombinant protein is a reliable antigen for detection of infections with Helicobacter pylori strains that are associated with disease. The EIA assay described may be used in follow-up of the progression of the illness and the results of therapy.

The Hsp60 protein of Helicobacter pylori: structure and immune response in patients with gastroduodenal diseases

Helicobacter pylori is a human pathogen that has been associated with gastritis, peptic ulcer and gastric carcinoma. The role of the direct action of H. pylori virulence factors and of the induction of autoreactive immunity in the development of chronic gastritis has not been clarified yet. Here we report the cloning and molecular characterization of a gene of H. pylori coding for a protein of 58 kDa, recognized by sera of patients affected by H. pylori-induced gastroduodenal diseases. This antigen is present in all the H. pylori strains tested and it belongs to the Hsp60 family of heat-shock proteins, with high homology with other bacterial and eukaryotic proteins of the same family. This class of homologous proteins has been implicated in the induction of autoimmune disorders in different systems. The presence in infected patients of anti-H. pylori Hsp60 antibodies, potentially cross-reactivity between human Hsp60 and a rabbit antiserum against H. pylori Hsp60 suggest that a role of this protein in gastroduodenal diseases is possible.

Molecular characterization of the 128-kDa immunodominant antigen of Helicobacter pylori associated with cytotoxicity and duodenal ulcer

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 diseases and 100% of patients with duodenal ulcer (P < 0.0005), suggesting that only bacteria harboring this protein are associated with disease.