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Immunobiology of Helicobacter pylori infection
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Immunobiology of Heficobacter pylori infection John L Telford*t, Antonello Covacci* , Rino Rappuoli*§ and Paolo Ghiara# 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.
These two aspects of the pathology are to some extent functionally distinguishable, as discussed hereafter [3].
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*Department of Molecular Biology, Chiron Vaccines, Immunobiological Research Institute Siena, Via Fiorentina 1, 53100 Siena, Italy re-mail: [email protected] Se-mail: [email protected] §e-mail: [email protected] #Department of Immunology, Chiron Vaccines, Immunobiological Research Institute Siena, Via Fiorentina 1, 53100 Siena, Italy; e-mail: [email protected]
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Current Opinion in Immunology 1997, 9:498-503
http:llbiomednet.comlelecref10952791500900498 © Current Biology Ltd ISSN 0952-7915 Abbreviations
CT IFN IL Lex LeY LT MALT PAl
Th TNF VacA
cholera toxin interferon interleukin Lewis X Lewis Y heat-labile toxin mucosal associated lymphoid tissue
pathogenicity island T helper tumor necrosis factor vacuolating cytotoxin A
Introduction
Helicobacter pyloH infection is the second most common bacterial infection after the Streptococcus mutans infection which is responsible for dental caries. It afflicts about 50% of the population in developed countries and about 80% of the population in the developing world (reviewed in [1,2]). Overt disease, however, occurs in only 10-20% of infected individuals. T h e most common pathology associated with H. pyloH infection is chronic active gastritis and peptic ulceration, although long term chronic infection is a risk factor for gastric adenocarcinoma and lymphoma [2] (Figure 1). T h e histopathological hallmarks ofH. pylori induced disease are a massive inflammatory cell infiltration of the lamina propria and erosion of the gastric epithelium.
H. pylori induced diseases in humans. Infection with H. pylori (represented by the cartoon bacterium) leads to diseases listed in the boxes. A striking feature of H. pylori infection is that it may take years or decades to lead to a symptomatic disease, as shown by the timescale on the right hand side of the figure. This is therefore a superb example of optimized adaptation of a bacterium to its host.
Experiments in mouse models that mimic the human
H. pyloH induced disease [4--6] suggest that the severe aspects of this disease are associated with a subset of H. pyloH strains, Type I, containing 40 kilobase pairs (kbp) of alien DNA, called the cag pathogenicity island (PAl) [7"'1. These strains produce a potent toxin, vacuolating cytotoxin A (VacA), that is believed to be responsible for the tissue erosion [4,5,8,9], and factors, not yet identified, that induce the pro-inflammatory cytokine interleukin (IL)-8 that may be responsible for the observed inflammation. T h e cag PAI includes a gene (cagA) which codes for an immunodominant surface antigen of approximately 120kDa [10,11]. In man seropositivity for this antigen is strongly associated.with the more severe forms of H. pylori induced disease such as peptic ulcer and gastric cancer [12,13]. Strains of H. pyloH which lack expression of this protein (Type II) do not generally produce functional VacA toxin [14] and cause only mild gastritis in the mouse model of infection [6]. Here we summarize the recent advances in
Immunobiologyof Helicobacter
our understanding of the immunopathogenesis of H. pylori infection.
Type I strains harbour a pathogenicity island H. pylor~ Type I strains contain a PAl of approximately 40 kbp integrated in the bacterial genome, which is absent from the Type II strains [7"']. This island is flanked by short direct repeats and has a guanosine plus cytosine content of about 35% which is significantly different as compared with the 38-45% guanosine plus cytosine value typical of chromosomal sequences of H. pylorL This finding strongly suggests an 'alien' origin of the PAl which could likely have been acquired from the external environment by transfer from a donor organsim (horizontal transfer). PAls have been described in other pathogenic bacteria such as Salmonella, Yersinia and Escher~chia coli. In all cases, the PAls code for a cluster of genes associated with virulence that are believed to have been acquired by horizontal transmission and which confer a selective advantage to the bacteria. Of the nineteen open reading frames so far identified in the PAl, most code for proteins which are predicted to be membrane associated. One gene of the PAl, cagE, shows a striking similarity to virB4 of Agrobacterium tumefaciens and ptlC of Bordetella pertussis. These homologous genes code for proteins that are components of cellular engines responsible for the export of either tDNA (virB4) or pertussis toxin (ptlC) and are thought to have originated by adaptation of a conjugation system present in some self-transmissible plasmids. Hence it is likely that the H. p),/oTi PAl codes for a novel secretion system for the export of virulence factors [7"']. Interestingly, individual ablation of several of the genes in the PAl results in abrogation of the capacity of the bacterium to induce IL-8 expression in gastric epithelial cell lines [7"']. Expression of IL-8, which has also been demonstrated in vivo [15,16], is believed to play a major role in the inflammatory response to H. pylori by acting as a chemotactic and activating factor for neutrophils. It is thus likely that genes in the PAl code for a secretory system necessary for the export of a factor(s) that induces IL-8 expression. It is not clear at this stage whether the IL-8 inducing factor is also coded for by the PAl or whether PAl genes may control the secretion of proteins encoded elsewhere on the chromosome [7"']. One may also consider the possibility that the putative IL-8 inducing factor may induce the expression of other cytokines, or conversely that the PAl secretory functions may regulate the release of other virulence factors involved in maintaining inflammation. In support of this possibility, Basso et al. [17] have demonstrated increased mucosai expression of IL-6, IL-11~ and the IL-2 receptor in H. pylori infected individuals as compared with noninfected controls. Moreover, in patients infected by Type I strains
pylori
infectionTelfordet al.
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IL-113 expression was higher than in patients infected by Type II strains.
A strongly polarized Thl response is associated with disease severity Antigens released by H. pylori during infection have been reported to induce macrophages to synthesize in vitro pro-inflammatory cytokines [18] which may be responsible
in vivo for the recruitment of inflammatory cells into the lamina propria. Given that all H. pylori infected individuals mount a vigorous but ineffective systemic immune response regardless of the disease outcome, it is of enormous importance to understand the nature of the local immune response at the site of infection. Since the initial report identifying H. pylori specific T helper (Th) cells in the gastric mucosa of infected patients [19], several groups have investigated the nature of this response. Mohammadi et al. [20"], using the mouse model of H.felis infection, showed a predominantly T h l response in gastric T lymphocytes as evidenced by constitutive interferon (IFN)-y production. T h e authors hypothesized that the T h l type cytokines (IFN-y and tumor necrosis factor [TNF]-c~) could contribute to the inflammation induced by the Helicobacter infection. T h e y tested this hypothesis by treating mice before and after infection with neutralizing anti-IFN-y antibodies. This treatment dramatically reduced the level of inflammation induced by the infection but did not affect the level of colonization with the bacteria. Further evidence for a role for T h l driven inflammation in this model comes from the infection of inbred mouse strains. Inflammation scores in BALB/c mice infected with H. felis were considerably lower than those from infected C57BL/6 mice which correlates with the difference in the tendency of these mouse strains to mount strong T h l cell responses [21"]. Strong support for this model comes from a recent report describing CD4+ T cell clones from gastric biopsies of H. pylori infected patients with peptic ulcer disease [22"']. In this study, in vivo activated T cells were expanded by culture in medium containing IL-2, the cells were then tested for their capacity to proliferate in response to H. pylor~ antigens and for their T h phenotype. Over 80% of the clones tested showed a T h l phenotype, displaying high levels of production of I F N - y and T N F - ~ . T h e remaining clones were all of the nonpolarized Th0 phenotype and produced both T h l and Th2 type cytokines (IFN-y, IL-4, IL-5 and TNF-c0. All clones produced high levels of the inflammatory cytokine TNF-oc Production of predominantly T h l type cytokines was confirmed in vivo in both this [22"'] and another report [23]. Remarkably, 50% of the T h l clones isolated were specific for the CagA antigen indicating that, in addition to being a systemic immunodominant antigen, CagA also drives an antigen specific T h l response at the site of infection. In contrast, T lymphocytes from the gastric mucosa of H. pylori infected patients with mild gastritis
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Immunityto infection
had a much more balanced T h l / T h 0 ratio but again lacked any significant Th2 response (MM D'Elios, JL Telford, G Del Prete, unpublished data).
Molecular mimicry and autoimmunity An autoimmune response has long been postulated to play a role in H. pylori gastritis. Negrini et al. [24] originally demonstrated that 1-1. pylor~ infection results in the induction of antibodies which recognize antigens present on normal (uninfected) gastric mucosa. More recently, H. pyloH lipopolysaccharide has been shown to contain the Lewis X (Le x) and Lewis Y (LeY) blood group antigens [25]. Recent evidence indicates an intriguing correlation between the recognition of these antigens by the host immune system and H. pylori induced gastritis [26"',27"']. Furthermore chronic infection of mice with 1t. pyloH elicits antibodies against these structures [26"']. Interestingly, Le x and LeY expression is associated with the expression of CagA and may therefore also be associated with the more severe forms of disease [28"]. Le x and LeY antigens are expressed on the gastric H+K+-ATPase, a well-recognized target of gastric autoimmunity in pre-anaemic atrophic gastritis. T h e etiology of pernicious anaemia (sometimes a consequence of atrophic gastritis) is unknown, but the recent results described above prompt us to investigate whether H. pylori infection might be a factor involved. Hence, carbohydrate structures expressed in the lipopolysaccharide of tl. pylori, identical to structures expressed on the gastric epithelium, may induce a pathogenic autoimmune response to this structure. Readers are referred to a recent authoritative review on the subject of 11. pylori molecular mimicry by BJ Appelmelk et al. [29"'].
by Hussel et al. [37 °] has now demonstrated that tumour infiltrating T cells proliferate specifically in response to H. pyloH antigens and that it is these T cells which are required to maintain the proliferation of the B cell lymphoma.
Vaccines against H. pylori A major question that remains unanswered is whether the immune system can be manipulated by immunization to mount a response capable of protecting against H. pylori infection. Natural infection by the organism neither induces a response capable of resolving the disease nor capable of protecting against re-infection after antibiotic eradication [38]. Nevertheless, in mouse models of Helicobacter infection, oral immunization with either lysates or purified recombinant antigens of 1-1. pyloH induces protective immunity [6,39-43]. Moreover, immunization of mice chronically infected with H. felis has been demonstrated to induce an immune response capable of clearing the infection as well as protecting against subsequent challenge [44]. Therapeutic immunization has also been demonstrated in ferrets naturally infected by the H. pyloH related Helicobacter species, H. mustelae [45"']. T h e nature of the protective immune response has been difficult to characterize. It has been shown that protection after immunization with 11. pylori urease correlates with an increase in gastric, urease-specific IgA levels [46]. No difference has, however, been observed in either the susceptibility to infection or the degree of pathology in IgA-deficient patients infected with H. pyloH [47"°]. Moreover, a protective immune response has been induced in IgA-deficient mice by immunization with H. pylori antigens [48"'].
H. pylori and lymphoproliferative disorders In addition to the strong statistical association with gastric adenocarcinoma [30], H. pylori infection has been associated with a low-grade B cell gastric lymphoma of the mucosal associated lymphoid tissue (MALT) [31]. T h e human stomach does not normally contain organized lymphoid structures, however, infection with H. pyloH results in the infiltration of small lymphoid aggregates [32] indicating that antigens can in fact be taken up and presented to the immune system in this organ. In recent years, the causal role for H. pylori infection in B cell MALT iymphoma has been well documented. Of partigular importance is the fact that antibiotic eradication of 1t. pylori results in the complete regression of low grade MALT lymphomas [33]. Carlson et al. [34"] have now documented the progression from H. pylori gastritis to monoclonal B cell lymphoma in a case study. It was recognized fairly early on in the studies investigating the association between MALT lymphoma and H.pylori infection that H.pyloH did not have a direct effect on the proliferation of B cells and that, although usually monoclonal, the specificity of the B cells in the lymphoma was not for H. pylori products [35,36]. A recent report
A key to understanding the induction of a protective immune response against H. pyloH may be provided by studying the use of strong mucosal adjuvants in immunization. To date, all successful oral immunizations against H. pylori infection in mice have employed either cholera toxin (CT) or the related heat-labile toxin (LT) from enteropathogenic E. coli as adjuvants. These molecules are not only highly immunogenic but they also stimulate the immune response to the co-administered antigens. Reports from the group of J McGhee [49,50] have shown that C T and LT induce Th2 immune responses. C T induced a strongly polarized Th2 response [49] and LT induced a more balanced T h l / T h 2 response [50]. Given the almost complete lack of Th2 response in H. pyloH associated disease, it is tempting to speculate that protection against infection in mouse models may involve the capacity of C T or LT to induce this type of immune response.
Conclusions This past year has seen important progress in our understanding of the interaction between H. pylori and the host immune response (Figure 2). T h e discovery of
Immunobiology of Helicobacter pylori infection Telford eta/.
a pathogenicity island in the bacterial genome of Type I strains goes a long way toward explaining the association of these strains with severe disease, and the functional characterization of this island's genes is giving new insights into the understanding of the interactions between H. pyloH and the host [ 5 1 " ] . It is likely that the polarized Thl responses and the inflammatory cytokines induced by H. pylori gene products play major roles in the gastric epithelial inflammation associated with 1-1. pyloH disease. Together with the epithelial erosion induced by the toxic products of the bacteria, these responses may well account for most
501
of the peptic ulceration and chronic active gastritis. Furthermore, antigen mimicry by H. pylori may result in the induction of autoimmune reactivity which may contribute to the severity of the disease. Genetic or environmentally influenced variability in the propensity to mount these type of inflammatory responses may, at least in part, help to explain the different outcomes of H. pyloH induced disease in different individuals. Further study of the immune response to H. pyloH infection will be required to understand better 11. pylori pathology and to design effective vaccines. Studies of infection and vaccination in genetically manipulated mice
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inflammation (gastritis) © 1997 Current Opinion in Immunology
H. pylori induced gastric damage and inflammation. (a) H. pylori infection leads to the presence of bacteria in the mucin of the gastric lumen. The lipopolysacchafide of H. py/ori (indicated by the v-like structures on the bacteria) contains the human blood group antigens Lex and Ley. (b) Thus, H. pylori has a capacity to exert antigen mimicry of these host structures which may lead to the production of autoantibodies against Lex and LeY on the gastric epithelium. This process may, in some circumstances, be important for the induction of disease. (c) Upon contact with the epithelium, Type l, PAl-containing, bacteria induce the epithelial cells, through signaling pathways, to (d) synthesize and release IL-8 which (e) is strongly chemoattractive for polymorphonuclear leukocytes (PMNs). Contact with the epithelium also leads (f) to the release by H. p¥1ori of virulence factors that play an important role in disease. The toxin VacA is a major virulence factor that is considered important for the capacity of H. pylori to directly induce epithelial gastric damage (vacuoles) that ultimately lead to peptic ulcer. A biologically active VacA toxin is expressed only by Type I bacteria. (g) H. py/ori antigens that cross the epithelial layer are able to activate macrophages (Md)) to release several pro-inflammatory cytokines, such as IL-8, IL-6, IL-1 and possibly IL-12. (h) This IL-12 microenvironment is important for polarizing the CD4 + T helper response into a prominent Thl phenotype. (|) H. pylori antigens may also drive an antigen specific Thl response at the site of infection and, interestingly, most of the Thl clones isolated from peptic ulcer patients have antigen specificity for the protein CagA, which is expressed only by Type I bacteria [22"]. (J) Thl cells release pro-inflammatorycytokines such as TNF-(x and IFN-~which contribute to the maintenance of gastritis. These effects explain why Type I strains of H. py/ori are the most pathogenic.
502
Immunity to infection
are a very promising approach to this end. The availability of strains of mice deficient in antibody responses, T h l responses or Th2 responses should provide valuable models in which to study the roles of these specific responses in pathology and immunization. Finally, promising safety studies on human adult volunteers with purified urease have been done [52°] and we await eagerly to see whether the experiences gained in vaccination in the mouse models can be transferred to man.
Acknowledgements We are grateful to Sandra Granai for her invaluable help during, the preparation of this review.
12.
Xiang Z, Bugnoli M, Rappuoli R, Covacci A, Ponzetto A, Crabtree JE: Helicobacter pylori; host responses in peptic ulceration. Lancet 1993, 341:900-901.
13.
Blaser MJ, Perez-Pemz GI, Kleanthous H, Cover TL, Peek RM, Chyou PH, Stemmermann GN, Nomura A: Infection with Helicobacter pylori strains possessing cagA is associated with an increased risk of developing edenocarcinoma of the stomach. Cancer Res 1995, 55:2111-2115.
14.
Xiang ZY, Censini S, Bayeli PF, Telford JL, Figura N, Rappuoli R, Covacci A: 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. Infect Immun 1995, 63:94-98.
15.
Crabtree JE, Peichl P, Wyatt JI, Stachl U, Lindley U: Gastric interleukin-8 and IgA IL-8 autoantibodies in Helicobacter pylori infection. Scand J Immuno/1993, 37:65-70.
16.
Crabtree JE: Gastric mucosal inflammatory responses to Helicobacter pylori. Ailment Pharmaco/ Ther 1996, 10:29-37.
17.
Basso D, Scrigner M, Toma A, Navaglia F, DiMario F, Rugge M, Plebani M: Helicobacter pylori infection enhances mucosal interleukin-1 beta, interleukin-6, and the soluble receptor of interleukin-2. Int J C/in Lab Res 1996, 26:207-210.
18.
Harris PR, Mobley HLT, Perez-Perez GI, Blaser MJ, Smith PD: Helicobacter pylori urease is a potent stimulus of mononuclear phagocyte activation and inflammatory cytokine production. Gastroenterology 1996, 111:419-425.
19.
Di Tommaso A, Xiang ZY, Bugnoli M, Pileri P, Figura N, Bayeli PF, Rappuoli R, Abrignani S, De Magistris MT: Helicobecter pylorispecific CD4(+) T-call clones from peripheral blood and gastric biopsies. Infect/mmun 1995, 63:1102-1106.
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4.
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5.
Ghiara P, Marchetti M, Blaser MJ, Tummuru MKR, Cover TL, Segal ED, Tompkins LS, Rappuoli R: Role of the Helicobacter pylori virulence factors vacuolating cytotoxin, CagA and urease in a mouse model of disease. Infect Immun 1995, 63:41544160.
6.
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7. o•
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Mohammadi M, Czinn S, Redline R, Nedrud J: Helicobacterspecific cell-mediated immune responses display a predominant Thl phenotype and promote a delayed-type hypersensitivity response in the stomachs of mice. J Immuno/ 1996, 156:4729-4738. See annotation [21"]. •
21. •
Mohammadi M, Redline R, Nedrud J, Czinn S: Role of the host in pathogenesis of Helicobacter-associated gastritis: H. fells infection of inbred and congenic mouse strains./nfect/mmun 1996, 64:238-245. This paper, along with [20"], introduces the concept of a role for a Thl type of immune response in the induction of disease in an animal model of Helicobacter infection. 22. •.
D'Elios MM, Manghetti M, DeCarli M, Costa F, Baldari CT, Burroni D, Telford JL, Romagnani S, Del Prete G: T helper 1 effector cells specific for Helicobacter pylori in the gastric antrum of patients with peptic ulcer disease. J Immuno/1997, 158:962-967. This paper shows for the first time in humans that H. pylori specific T cell clones with a predominant Thl phenotype can be more frequently isolated from patients with peptic ulcer disease than from patients with mild gastritis. 23.
KarttunenRA, Karttunen TJ, Yousfi MM, Elzimaity HMT, Graham DY, Elzaatari FAK: Expression of mRNA for interferon-gamma, interleukin-10, and interleukin-12 (p40) in normal gastric mucosa and in mucosa infected with Helicobacter pylori. Scand J Gastroenterol 1997, 32:22-27.
24.
Negrini R, Lisato L, Zanella I, Cavazzini L, Gullini S, Villanacci V, Poiesi C, Albertini A, Ghielmi S: Helicobacter pylori infection induces antibodies cross-reacting with human gastric mucosa. Gastroenterology 1991, 101:437-445.
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Aspinall GO, Monteiro MA, Pang H, Walsh EJ, Moran AP: O antigen and the lipopolysaccharide of Helicobacter pylori NCTC 11637. Carbohyd Lett 1994, 1:151-156.
26. •-
Appelmelk BJ, Simoons-Smit I, Negrini R, Moran AP, Aspinall GO, Forte JG, DeVries T, Quan H, Verboom T, Maaskant JJ et al.: Potential role of molecular mimicry between Helicobacter pylori lipopolysaccharide and host Lewis blood group antigens in autoimmunity. Infect Immun 1996, 64:2031-2040. This paper describes the role of antigen mimicry by the H. pylorilipopolysaccharide of Lex and LeY in the induction of autoimmunity. It also reports that chronic H. pylori infection in mice elicits serum antibodies against these antigens. 27. •e
Negrini R, Savio A, Poiesi C, Appelmelk B J, Buffoli F, Paterlini A, Cesari P, Graffeo M, Vaira D, Franzin G: Antigenic mimicry
Immunobiology of Helicobacter pylori infection Telford et aL
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between Helicobacter pylori and gastric mucosa in the pathogenesis of body atrophic gastritis. Gastroenterology 1996, 111:655-665. The association of the molecular mimicry between H. py/ori and antigens of the gastric epithelium with the occurrence of gastric atrophy is described. The presence of cross-reactive antibodies correlates with the degree of inflammation and with the severity of gastric atrophy. Gastric atrophy is a histopathological condition that is strongly associated with the subsequent malignant transformation that leads to gastric adenocarcinoma.
40.
Michetti P, Corthesy-Theulaz I, Davin C, Haas R, Vaney AC, Heitz M, Bille J, Kraehenbuhl JP, Saraga E, Blum AL: Immunization of BALB/c mice against Helicobacter fells infection with H. pylori urease. Gastroenterology 1994, 107:1002-1011.
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Corthesy-Theulaz I, Porta N, Glauser M, Saraga E, Vaney AC, Haas R, Kraehenbuhl JP, Blum AL, Michetti P: Oral immunization with Helicobacter pylori urease B subunit as a treatment against Helicobacter infection in mice. Gastroenterology 1995, 109:115-121.
Wirth HP, Yang MQ, Karita M, Blaser MJ: Expression of the human cell surface glycoconjugates Lewis X and Lewis Y by Helicobacter pylori isolates is related to cagA status. Infect Immun 1996, 64:4598-4605. This paper shows that the capacity to exert molecular mimicry of host Lex and LeY structures is correlated with the capacity of the strain to express the antigen CagA. Induction of autoreactive antibodies could contribute to worsen and amplify the gastric inflammation that occurs during infections with Type I strains of H. pylori. This study is therefore a further demonstration of the enhanced virulence potential conferred by the cag PAl of the type I strains. 29. Appelmelk BJ, Negrini R, Moran AP, Kuipers F_J:Molecular •• mimicry between Helicobacter pylori and the hosL Trends Microbiol 1997, 5:70-73. An excellent review on antigen mimicry by H. py/ori. 30.
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Parsonnet J, Hansen S, Rodriguez L, Gelb AB, Warnke RA, Jellurn E, Orentreich N, Vogelman HJ, Friedman GD: Helicobacter pylori infection and gastric lymphoma. New Engl J Med 1994, 330:1267-1271.
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33.
Wotherspoon AC, Doglioni C, Diss TC, Pan L, Moschini A, de Boni M, Isaacson PG: Regression of primary low-grade Bcell gastric lymphoma of mucosa-associated lymphoid tissue type after eradication of Helicobacter pylori. Lancet 1993, 342:575-577. 34. Carlson SJ, Yokoo H, Vanagunas A: Progression of gastritis to • monoclonal B-cell lymphoma with resolution and recurrence following eradication of Helicobacter pylori. JAMA 1996, 275:937-939. A very good paper showing the progression of gastritis into malignant low grade B cell lymhoma. The observations reported in this paper support the association between H. py/ori infection and the development of a gastric monoclonal B cell lymphoma. This lesion appears to develop in the setting of H. pylori gastritis and progresses through lymphoid hyperplasia which is followed by the lymphoma. The process is intially driven by H. py/ori antigens and thereafter becomes autonomous, as genetic damage accumulates as a consequence of chronic inflammation. 35.
Hussell T, Isaacson PG, Crabtree JE, Dogan A, Spencer A: Immunoglobulin specificity of low grade B cell gastric lymphoma of mucosa associated lymphoid tissue. Am J Patho/ 1993, 142:285~292.
36.
Greiner A, Marx A, Heesemann J, Leebmann J, Schumausser B, Mullerhermelink HK: Idiotype identity in a MALT-type lymphoma and B cells in Helicobacter pylori associated chronic gastritis. Lab Invest 1994, 70:572-578.
Hussell T, Isaacson PG, Crabtree JE, Spencer J: Helicobacter pylori-specific tumour-infiltrating T cells provide contact dependent help for the growth of malignant B cells in lowgrade gastric lymphoma of mucosa-associated lymphoid tissue. J Pathol 1996, 178:122-127. Demonstration of H. py/ori specific T cells in low-grade B cell lymphoma indicating a causal role for H. pylori in this disease. 38. Schutze K, Hentschel E, Dragosics B, Hirschl AM: Helicobacter pylori reinfection with identical organisms: transmission by the patients' spouses. Gut 1995, 36:831-833.
37. •
39.
Chen M, Lee A, Hazell S: Immunisation against gastric helicobacter infection in a mouse/Helicobacter fells model. Lancet 1992, 339:1120-1121.
45. •-
Cuenca R, Blanchard TG, Czinn S J, Nedrud JG, Monath TP, Lee CK, Redline RW: Therapeutic immunization against Helicobacter mustelae in naturally infected ferrets. Gastroenterology 1996, 110:1770-1775. This paper describes the eradication of a natural infection of H. mustelae in ferrets using a subunit vaccine composed of recombinant H. pylori urease plus cholera toxin. 46.
Lee CK, Weltzin R, Thomas WD, Kleanthous H, Ermak TH, Soman G, Hill JE, Ackerman SK, Monath TP: Oral immunization with recombinant Helicobacter pylori urease induces secretory IgA antibodies and protects mice from challenge with Helicobacter fells. J Infect Dis 1995, 172:161-1 72.
Bogstedt AK, Nava S, Wadstrom T, Hammarstrom L: Helicobacter pylori infections in IgA deficiency: lack of role for the secretory immune system. C/in Exp Immuno/1996, 105:202-204. This paper describes the lack of increase in incidence and severity of H. pylori infection in humans carrying IgA deficiency, which is one of the most common innate immunodeficiency conditions in man. 48. Nedrud T, Blanchard S, Czinn GR, Harriman GR: Orally •immunized IgA-deficient mice are protected against H. fells infection [abstract]. Gut 1996, 39(suppl 2):A45. So far only an abstract, but a paper to look for. It describes the lack of the role of the secretory IgA system in the protective effector mechanism elicited by mucosal vaccination against Heficobacter infection. 47. •.
49.
MarinaroM, Staats HF, Hiroi T, Jackson RJ, Coste M, Boyaka PN, Okahashi N, Yamamoto M, Kiyono H, Bluethmann H e t al.: Mucosal adjuvant effect of cholera toxin in mice results from induction of T helper 2 (Th2) cells and IL-4. J Immuno11995, 155:4621~4629.
50.
TakahashiI, Marinaro M, Kiyono H, Jackson RJ, Nakagawa I, Fujihashi K, Hamada S, Clements JD, Bost KL, McGhee JR: Mechanisms for mucosal immunogenicity and adjuvancy of Escherichia coil labile toxin. J Infect Dis 1996, 173:627-635.
51. °,
Covacci A, Falkow S, Berg DE, Rappuoli R: Did the inheritance of a pathogenicity island modify the virulence of Helicobacter pylon~t Trends Microbiol 1997, 5:205-208. This review describes the current knowledge on the molecular basis of evolution of virulence in H. pylori Type I virulent strains through the inheritance of DNA insertions that contain genes associated with disease. 52. •
Kreiss C, Buclin T, Cosma M, Corthesy-Theulaz I, Michetti P: Safety of oral immunisation with recombinant urease in patients with Helicobacter pylori infection. Lancet 1996, 347:1630-1631. The first official report of a subunit vaccine Phase I trial performed last year with purified recombinant enzymatically inactive urease. 12 nonsymptomatic H. pylori infected volunteers were randomized to receive, orally, either 6Omg of urease or a placebo once weekly for 4 weeks. Urease was well tolerated and no major adverse reactions occurred. Mean gastritis score assessed on bioptic specimens was not altered by treatment and only minor erosions were observed in three volunteers receiveing urease and in one receiving the placebo. As expected, however, as no mucosal adjuvant was used in this trial, all volunteers remained infected.
Immunobiology of Heficobacter pylori infection John L Telford*t, Antonello Covacci* , Rino Rappuoli*§ and Paolo Ghiara# 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.
These two aspects of the pathology are to some extent functionally distinguishable, as discussed hereafter [3].
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*Department of Molecular Biology, Chiron Vaccines, Immunobiological Research Institute Siena, Via Fiorentina 1, 53100 Siena, Italy re-mail: [email protected] Se-mail: [email protected] §e-mail: [email protected] #Department of Immunology, Chiron Vaccines, Immunobiological Research Institute Siena, Via Fiorentina 1, 53100 Siena, Italy; e-mail: [email protected]
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Current Opinion in Immunology 1997, 9:498-503
http:llbiomednet.comlelecref10952791500900498 © Current Biology Ltd ISSN 0952-7915 Abbreviations
CT IFN IL Lex LeY LT MALT PAl
Th TNF VacA
cholera toxin interferon interleukin Lewis X Lewis Y heat-labile toxin mucosal associated lymphoid tissue
pathogenicity island T helper tumor necrosis factor vacuolating cytotoxin A
Introduction
Helicobacter pyloH infection is the second most common bacterial infection after the Streptococcus mutans infection which is responsible for dental caries. It afflicts about 50% of the population in developed countries and about 80% of the population in the developing world (reviewed in [1,2]). Overt disease, however, occurs in only 10-20% of infected individuals. T h e most common pathology associated with H. pyloH infection is chronic active gastritis and peptic ulceration, although long term chronic infection is a risk factor for gastric adenocarcinoma and lymphoma [2] (Figure 1). T h e histopathological hallmarks ofH. pylori induced disease are a massive inflammatory cell infiltration of the lamina propria and erosion of the gastric epithelium.
H. pylori induced diseases in humans. Infection with H. pylori (represented by the cartoon bacterium) leads to diseases listed in the boxes. A striking feature of H. pylori infection is that it may take years or decades to lead to a symptomatic disease, as shown by the timescale on the right hand side of the figure. This is therefore a superb example of optimized adaptation of a bacterium to its host.
Experiments in mouse models that mimic the human
H. pyloH induced disease [4--6] suggest that the severe aspects of this disease are associated with a subset of H. pyloH strains, Type I, containing 40 kilobase pairs (kbp) of alien DNA, called the cag pathogenicity island (PAl) [7"'1. These strains produce a potent toxin, vacuolating cytotoxin A (VacA), that is believed to be responsible for the tissue erosion [4,5,8,9], and factors, not yet identified, that induce the pro-inflammatory cytokine interleukin (IL)-8 that may be responsible for the observed inflammation. T h e cag PAI includes a gene (cagA) which codes for an immunodominant surface antigen of approximately 120kDa [10,11]. In man seropositivity for this antigen is strongly associated.with the more severe forms of H. pylori induced disease such as peptic ulcer and gastric cancer [12,13]. Strains of H. pyloH which lack expression of this protein (Type II) do not generally produce functional VacA toxin [14] and cause only mild gastritis in the mouse model of infection [6]. Here we summarize the recent advances in
Immunobiologyof Helicobacter
our understanding of the immunopathogenesis of H. pylori infection.
Type I strains harbour a pathogenicity island H. pylor~ Type I strains contain a PAl of approximately 40 kbp integrated in the bacterial genome, which is absent from the Type II strains [7"']. This island is flanked by short direct repeats and has a guanosine plus cytosine content of about 35% which is significantly different as compared with the 38-45% guanosine plus cytosine value typical of chromosomal sequences of H. pylorL This finding strongly suggests an 'alien' origin of the PAl which could likely have been acquired from the external environment by transfer from a donor organsim (horizontal transfer). PAls have been described in other pathogenic bacteria such as Salmonella, Yersinia and Escher~chia coli. In all cases, the PAls code for a cluster of genes associated with virulence that are believed to have been acquired by horizontal transmission and which confer a selective advantage to the bacteria. Of the nineteen open reading frames so far identified in the PAl, most code for proteins which are predicted to be membrane associated. One gene of the PAl, cagE, shows a striking similarity to virB4 of Agrobacterium tumefaciens and ptlC of Bordetella pertussis. These homologous genes code for proteins that are components of cellular engines responsible for the export of either tDNA (virB4) or pertussis toxin (ptlC) and are thought to have originated by adaptation of a conjugation system present in some self-transmissible plasmids. Hence it is likely that the H. p),/oTi PAl codes for a novel secretion system for the export of virulence factors [7"']. Interestingly, individual ablation of several of the genes in the PAl results in abrogation of the capacity of the bacterium to induce IL-8 expression in gastric epithelial cell lines [7"']. Expression of IL-8, which has also been demonstrated in vivo [15,16], is believed to play a major role in the inflammatory response to H. pylori by acting as a chemotactic and activating factor for neutrophils. It is thus likely that genes in the PAl code for a secretory system necessary for the export of a factor(s) that induces IL-8 expression. It is not clear at this stage whether the IL-8 inducing factor is also coded for by the PAl or whether PAl genes may control the secretion of proteins encoded elsewhere on the chromosome [7"']. One may also consider the possibility that the putative IL-8 inducing factor may induce the expression of other cytokines, or conversely that the PAl secretory functions may regulate the release of other virulence factors involved in maintaining inflammation. In support of this possibility, Basso et al. [17] have demonstrated increased mucosai expression of IL-6, IL-11~ and the IL-2 receptor in H. pylori infected individuals as compared with noninfected controls. Moreover, in patients infected by Type I strains
pylori
infectionTelfordet al.
499
IL-113 expression was higher than in patients infected by Type II strains.
A strongly polarized Thl response is associated with disease severity Antigens released by H. pylori during infection have been reported to induce macrophages to synthesize in vitro pro-inflammatory cytokines [18] which may be responsible
in vivo for the recruitment of inflammatory cells into the lamina propria. Given that all H. pylori infected individuals mount a vigorous but ineffective systemic immune response regardless of the disease outcome, it is of enormous importance to understand the nature of the local immune response at the site of infection. Since the initial report identifying H. pylori specific T helper (Th) cells in the gastric mucosa of infected patients [19], several groups have investigated the nature of this response. Mohammadi et al. [20"], using the mouse model of H.felis infection, showed a predominantly T h l response in gastric T lymphocytes as evidenced by constitutive interferon (IFN)-y production. T h e authors hypothesized that the T h l type cytokines (IFN-y and tumor necrosis factor [TNF]-c~) could contribute to the inflammation induced by the Helicobacter infection. T h e y tested this hypothesis by treating mice before and after infection with neutralizing anti-IFN-y antibodies. This treatment dramatically reduced the level of inflammation induced by the infection but did not affect the level of colonization with the bacteria. Further evidence for a role for T h l driven inflammation in this model comes from the infection of inbred mouse strains. Inflammation scores in BALB/c mice infected with H. felis were considerably lower than those from infected C57BL/6 mice which correlates with the difference in the tendency of these mouse strains to mount strong T h l cell responses [21"]. Strong support for this model comes from a recent report describing CD4+ T cell clones from gastric biopsies of H. pylori infected patients with peptic ulcer disease [22"']. In this study, in vivo activated T cells were expanded by culture in medium containing IL-2, the cells were then tested for their capacity to proliferate in response to H. pylor~ antigens and for their T h phenotype. Over 80% of the clones tested showed a T h l phenotype, displaying high levels of production of I F N - y and T N F - ~ . T h e remaining clones were all of the nonpolarized Th0 phenotype and produced both T h l and Th2 type cytokines (IFN-y, IL-4, IL-5 and TNF-c0. All clones produced high levels of the inflammatory cytokine TNF-oc Production of predominantly T h l type cytokines was confirmed in vivo in both this [22"'] and another report [23]. Remarkably, 50% of the T h l clones isolated were specific for the CagA antigen indicating that, in addition to being a systemic immunodominant antigen, CagA also drives an antigen specific T h l response at the site of infection. In contrast, T lymphocytes from the gastric mucosa of H. pylori infected patients with mild gastritis
500
Immunityto infection
had a much more balanced T h l / T h 0 ratio but again lacked any significant Th2 response (MM D'Elios, JL Telford, G Del Prete, unpublished data).
Molecular mimicry and autoimmunity An autoimmune response has long been postulated to play a role in H. pylori gastritis. Negrini et al. [24] originally demonstrated that 1-1. pylor~ infection results in the induction of antibodies which recognize antigens present on normal (uninfected) gastric mucosa. More recently, H. pyloH lipopolysaccharide has been shown to contain the Lewis X (Le x) and Lewis Y (LeY) blood group antigens [25]. Recent evidence indicates an intriguing correlation between the recognition of these antigens by the host immune system and H. pylori induced gastritis [26"',27"']. Furthermore chronic infection of mice with 1t. pyloH elicits antibodies against these structures [26"']. Interestingly, Le x and LeY expression is associated with the expression of CagA and may therefore also be associated with the more severe forms of disease [28"]. Le x and LeY antigens are expressed on the gastric H+K+-ATPase, a well-recognized target of gastric autoimmunity in pre-anaemic atrophic gastritis. T h e etiology of pernicious anaemia (sometimes a consequence of atrophic gastritis) is unknown, but the recent results described above prompt us to investigate whether H. pylori infection might be a factor involved. Hence, carbohydrate structures expressed in the lipopolysaccharide of tl. pylori, identical to structures expressed on the gastric epithelium, may induce a pathogenic autoimmune response to this structure. Readers are referred to a recent authoritative review on the subject of 11. pylori molecular mimicry by BJ Appelmelk et al. [29"'].
by Hussel et al. [37 °] has now demonstrated that tumour infiltrating T cells proliferate specifically in response to H. pyloH antigens and that it is these T cells which are required to maintain the proliferation of the B cell lymphoma.
Vaccines against H. pylori A major question that remains unanswered is whether the immune system can be manipulated by immunization to mount a response capable of protecting against H. pylori infection. Natural infection by the organism neither induces a response capable of resolving the disease nor capable of protecting against re-infection after antibiotic eradication [38]. Nevertheless, in mouse models of Helicobacter infection, oral immunization with either lysates or purified recombinant antigens of 1-1. pyloH induces protective immunity [6,39-43]. Moreover, immunization of mice chronically infected with H. felis has been demonstrated to induce an immune response capable of clearing the infection as well as protecting against subsequent challenge [44]. Therapeutic immunization has also been demonstrated in ferrets naturally infected by the H. pyloH related Helicobacter species, H. mustelae [45"']. T h e nature of the protective immune response has been difficult to characterize. It has been shown that protection after immunization with 11. pylori urease correlates with an increase in gastric, urease-specific IgA levels [46]. No difference has, however, been observed in either the susceptibility to infection or the degree of pathology in IgA-deficient patients infected with H. pyloH [47"°]. Moreover, a protective immune response has been induced in IgA-deficient mice by immunization with H. pylori antigens [48"'].
H. pylori and lymphoproliferative disorders In addition to the strong statistical association with gastric adenocarcinoma [30], H. pylori infection has been associated with a low-grade B cell gastric lymphoma of the mucosal associated lymphoid tissue (MALT) [31]. T h e human stomach does not normally contain organized lymphoid structures, however, infection with H. pyloH results in the infiltration of small lymphoid aggregates [32] indicating that antigens can in fact be taken up and presented to the immune system in this organ. In recent years, the causal role for H. pylori infection in B cell MALT iymphoma has been well documented. Of partigular importance is the fact that antibiotic eradication of 1t. pylori results in the complete regression of low grade MALT lymphomas [33]. Carlson et al. [34"] have now documented the progression from H. pylori gastritis to monoclonal B cell lymphoma in a case study. It was recognized fairly early on in the studies investigating the association between MALT lymphoma and H.pylori infection that H.pyloH did not have a direct effect on the proliferation of B cells and that, although usually monoclonal, the specificity of the B cells in the lymphoma was not for H. pylori products [35,36]. A recent report
A key to understanding the induction of a protective immune response against H. pyloH may be provided by studying the use of strong mucosal adjuvants in immunization. To date, all successful oral immunizations against H. pylori infection in mice have employed either cholera toxin (CT) or the related heat-labile toxin (LT) from enteropathogenic E. coli as adjuvants. These molecules are not only highly immunogenic but they also stimulate the immune response to the co-administered antigens. Reports from the group of J McGhee [49,50] have shown that C T and LT induce Th2 immune responses. C T induced a strongly polarized Th2 response [49] and LT induced a more balanced T h l / T h 2 response [50]. Given the almost complete lack of Th2 response in H. pyloH associated disease, it is tempting to speculate that protection against infection in mouse models may involve the capacity of C T or LT to induce this type of immune response.
Conclusions This past year has seen important progress in our understanding of the interaction between H. pylori and the host immune response (Figure 2). T h e discovery of
Immunobiology of Helicobacter pylori infection Telford eta/.
a pathogenicity island in the bacterial genome of Type I strains goes a long way toward explaining the association of these strains with severe disease, and the functional characterization of this island's genes is giving new insights into the understanding of the interactions between H. pyloH and the host [ 5 1 " ] . It is likely that the polarized Thl responses and the inflammatory cytokines induced by H. pylori gene products play major roles in the gastric epithelial inflammation associated with 1-1. pyloH disease. Together with the epithelial erosion induced by the toxic products of the bacteria, these responses may well account for most
501
of the peptic ulceration and chronic active gastritis. Furthermore, antigen mimicry by H. pylori may result in the induction of autoimmune reactivity which may contribute to the severity of the disease. Genetic or environmentally influenced variability in the propensity to mount these type of inflammatory responses may, at least in part, help to explain the different outcomes of H. pyloH induced disease in different individuals. Further study of the immune response to H. pyloH infection will be required to understand better 11. pylori pathology and to design effective vaccines. Studies of infection and vaccination in genetically manipulated mice
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inflammation (gastritis) © 1997 Current Opinion in Immunology
H. pylori induced gastric damage and inflammation. (a) H. pylori infection leads to the presence of bacteria in the mucin of the gastric lumen. The lipopolysacchafide of H. py/ori (indicated by the v-like structures on the bacteria) contains the human blood group antigens Lex and Ley. (b) Thus, H. pylori has a capacity to exert antigen mimicry of these host structures which may lead to the production of autoantibodies against Lex and LeY on the gastric epithelium. This process may, in some circumstances, be important for the induction of disease. (c) Upon contact with the epithelium, Type l, PAl-containing, bacteria induce the epithelial cells, through signaling pathways, to (d) synthesize and release IL-8 which (e) is strongly chemoattractive for polymorphonuclear leukocytes (PMNs). Contact with the epithelium also leads (f) to the release by H. p¥1ori of virulence factors that play an important role in disease. The toxin VacA is a major virulence factor that is considered important for the capacity of H. pylori to directly induce epithelial gastric damage (vacuoles) that ultimately lead to peptic ulcer. A biologically active VacA toxin is expressed only by Type I bacteria. (g) H. py/ori antigens that cross the epithelial layer are able to activate macrophages (Md)) to release several pro-inflammatory cytokines, such as IL-8, IL-6, IL-1 and possibly IL-12. (h) This IL-12 microenvironment is important for polarizing the CD4 + T helper response into a prominent Thl phenotype. (|) H. pylori antigens may also drive an antigen specific Thl response at the site of infection and, interestingly, most of the Thl clones isolated from peptic ulcer patients have antigen specificity for the protein CagA, which is expressed only by Type I bacteria [22"]. (J) Thl cells release pro-inflammatorycytokines such as TNF-(x and IFN-~which contribute to the maintenance of gastritis. These effects explain why Type I strains of H. py/ori are the most pathogenic.
502
Immunity to infection
are a very promising approach to this end. The availability of strains of mice deficient in antibody responses, T h l responses or Th2 responses should provide valuable models in which to study the roles of these specific responses in pathology and immunization. Finally, promising safety studies on human adult volunteers with purified urease have been done [52°] and we await eagerly to see whether the experiences gained in vaccination in the mouse models can be transferred to man.
Acknowledgements We are grateful to Sandra Granai for her invaluable help during, the preparation of this review.
12.
Xiang Z, Bugnoli M, Rappuoli R, Covacci A, Ponzetto A, Crabtree JE: Helicobacter pylori; host responses in peptic ulceration. Lancet 1993, 341:900-901.
13.
Blaser MJ, Perez-Pemz GI, Kleanthous H, Cover TL, Peek RM, Chyou PH, Stemmermann GN, Nomura A: Infection with Helicobacter pylori strains possessing cagA is associated with an increased risk of developing edenocarcinoma of the stomach. Cancer Res 1995, 55:2111-2115.
14.
Xiang ZY, Censini S, Bayeli PF, Telford JL, Figura N, Rappuoli R, Covacci A: 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. Infect Immun 1995, 63:94-98.
15.
Crabtree JE, Peichl P, Wyatt JI, Stachl U, Lindley U: Gastric interleukin-8 and IgA IL-8 autoantibodies in Helicobacter pylori infection. Scand J Immuno/1993, 37:65-70.
16.
Crabtree JE: Gastric mucosal inflammatory responses to Helicobacter pylori. Ailment Pharmaco/ Ther 1996, 10:29-37.
17.
Basso D, Scrigner M, Toma A, Navaglia F, DiMario F, Rugge M, Plebani M: Helicobacter pylori infection enhances mucosal interleukin-1 beta, interleukin-6, and the soluble receptor of interleukin-2. Int J C/in Lab Res 1996, 26:207-210.
18.
Harris PR, Mobley HLT, Perez-Perez GI, Blaser MJ, Smith PD: Helicobacter pylori urease is a potent stimulus of mononuclear phagocyte activation and inflammatory cytokine production. Gastroenterology 1996, 111:419-425.
19.
Di Tommaso A, Xiang ZY, Bugnoli M, Pileri P, Figura N, Bayeli PF, Rappuoli R, Abrignani S, De Magistris MT: Helicobecter pylorispecific CD4(+) T-call clones from peripheral blood and gastric biopsies. Infect/mmun 1995, 63:1102-1106.
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21. •
Mohammadi M, Redline R, Nedrud J, Czinn S: Role of the host in pathogenesis of Helicobacter-associated gastritis: H. fells infection of inbred and congenic mouse strains./nfect/mmun 1996, 64:238-245. This paper, along with [20"], introduces the concept of a role for a Thl type of immune response in the induction of disease in an animal model of Helicobacter infection. 22. •.
D'Elios MM, Manghetti M, DeCarli M, Costa F, Baldari CT, Burroni D, Telford JL, Romagnani S, Del Prete G: T helper 1 effector cells specific for Helicobacter pylori in the gastric antrum of patients with peptic ulcer disease. J Immuno/1997, 158:962-967. This paper shows for the first time in humans that H. pylori specific T cell clones with a predominant Thl phenotype can be more frequently isolated from patients with peptic ulcer disease than from patients with mild gastritis. 23.
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Aspinall GO, Monteiro MA, Pang H, Walsh EJ, Moran AP: O antigen and the lipopolysaccharide of Helicobacter pylori NCTC 11637. Carbohyd Lett 1994, 1:151-156.
26. •-
Appelmelk BJ, Simoons-Smit I, Negrini R, Moran AP, Aspinall GO, Forte JG, DeVries T, Quan H, Verboom T, Maaskant JJ et al.: Potential role of molecular mimicry between Helicobacter pylori lipopolysaccharide and host Lewis blood group antigens in autoimmunity. Infect Immun 1996, 64:2031-2040. This paper describes the role of antigen mimicry by the H. pylorilipopolysaccharide of Lex and LeY in the induction of autoimmunity. It also reports that chronic H. pylori infection in mice elicits serum antibodies against these antigens. 27. •e
Negrini R, Savio A, Poiesi C, Appelmelk B J, Buffoli F, Paterlini A, Cesari P, Graffeo M, Vaira D, Franzin G: Antigenic mimicry
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Michetti P, Corthesy-Theulaz I, Davin C, Haas R, Vaney AC, Heitz M, Bille J, Kraehenbuhl JP, Saraga E, Blum AL: Immunization of BALB/c mice against Helicobacter fells infection with H. pylori urease. Gastroenterology 1994, 107:1002-1011.
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Radcliff F), Chen MH, Lee A: Protective immunization against Helicobacter stimulates long term immunity. Vaccine 1996, 14:780-784.
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Corthesy-Theulaz I, Porta N, Glauser M, Saraga E, Vaney AC, Haas R, Kraehenbuhl JP, Blum AL, Michetti P: Oral immunization with Helicobacter pylori urease B subunit as a treatment against Helicobacter infection in mice. Gastroenterology 1995, 109:115-121.
Wirth HP, Yang MQ, Karita M, Blaser MJ: Expression of the human cell surface glycoconjugates Lewis X and Lewis Y by Helicobacter pylori isolates is related to cagA status. Infect Immun 1996, 64:4598-4605. This paper shows that the capacity to exert molecular mimicry of host Lex and LeY structures is correlated with the capacity of the strain to express the antigen CagA. Induction of autoreactive antibodies could contribute to worsen and amplify the gastric inflammation that occurs during infections with Type I strains of H. pylori. This study is therefore a further demonstration of the enhanced virulence potential conferred by the cag PAl of the type I strains. 29. Appelmelk BJ, Negrini R, Moran AP, Kuipers F_J:Molecular •• mimicry between Helicobacter pylori and the hosL Trends Microbiol 1997, 5:70-73. An excellent review on antigen mimicry by H. py/ori. 30.
Parsonnet J, Friedman GD, Vandersteen DP, Chang Y, Vogelman JH, Orentreich N, Sibley RK: Helicobacter pylori infection and the risk of gastric carcinoma. N Engl J Med 1991, 325:1127-1231.
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Parsonnet J, Hansen S, Rodriguez L, Gelb AB, Warnke RA, Jellurn E, Orentreich N, Vogelman HJ, Friedman GD: Helicobacter pylori infection and gastric lymphoma. New Engl J Med 1994, 330:1267-1271.
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Wyatt JI, Rathbone BJ: Immune response of the gastric mucosa to Campylobacter pylori. Scand J Gastroenterol Suppl 1968, 142:44-49.
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Wotherspoon AC, Doglioni C, Diss TC, Pan L, Moschini A, de Boni M, Isaacson PG: Regression of primary low-grade Bcell gastric lymphoma of mucosa-associated lymphoid tissue type after eradication of Helicobacter pylori. Lancet 1993, 342:575-577. 34. Carlson SJ, Yokoo H, Vanagunas A: Progression of gastritis to • monoclonal B-cell lymphoma with resolution and recurrence following eradication of Helicobacter pylori. JAMA 1996, 275:937-939. A very good paper showing the progression of gastritis into malignant low grade B cell lymhoma. The observations reported in this paper support the association between H. py/ori infection and the development of a gastric monoclonal B cell lymphoma. This lesion appears to develop in the setting of H. pylori gastritis and progresses through lymphoid hyperplasia which is followed by the lymphoma. The process is intially driven by H. py/ori antigens and thereafter becomes autonomous, as genetic damage accumulates as a consequence of chronic inflammation. 35.
Hussell T, Isaacson PG, Crabtree JE, Dogan A, Spencer A: Immunoglobulin specificity of low grade B cell gastric lymphoma of mucosa associated lymphoid tissue. Am J Patho/ 1993, 142:285~292.
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Greiner A, Marx A, Heesemann J, Leebmann J, Schumausser B, Mullerhermelink HK: Idiotype identity in a MALT-type lymphoma and B cells in Helicobacter pylori associated chronic gastritis. Lab Invest 1994, 70:572-578.
Hussell T, Isaacson PG, Crabtree JE, Spencer J: Helicobacter pylori-specific tumour-infiltrating T cells provide contact dependent help for the growth of malignant B cells in lowgrade gastric lymphoma of mucosa-associated lymphoid tissue. J Pathol 1996, 178:122-127. Demonstration of H. py/ori specific T cells in low-grade B cell lymphoma indicating a causal role for H. pylori in this disease. 38. Schutze K, Hentschel E, Dragosics B, Hirschl AM: Helicobacter pylori reinfection with identical organisms: transmission by the patients' spouses. Gut 1995, 36:831-833.
37. •
39.
Chen M, Lee A, Hazell S: Immunisation against gastric helicobacter infection in a mouse/Helicobacter fells model. Lancet 1992, 339:1120-1121.
45. •-
Cuenca R, Blanchard TG, Czinn S J, Nedrud JG, Monath TP, Lee CK, Redline RW: Therapeutic immunization against Helicobacter mustelae in naturally infected ferrets. Gastroenterology 1996, 110:1770-1775. This paper describes the eradication of a natural infection of H. mustelae in ferrets using a subunit vaccine composed of recombinant H. pylori urease plus cholera toxin. 46.
Lee CK, Weltzin R, Thomas WD, Kleanthous H, Ermak TH, Soman G, Hill JE, Ackerman SK, Monath TP: Oral immunization with recombinant Helicobacter pylori urease induces secretory IgA antibodies and protects mice from challenge with Helicobacter fells. J Infect Dis 1995, 172:161-1 72.
Bogstedt AK, Nava S, Wadstrom T, Hammarstrom L: Helicobacter pylori infections in IgA deficiency: lack of role for the secretory immune system. C/in Exp Immuno/1996, 105:202-204. This paper describes the lack of increase in incidence and severity of H. pylori infection in humans carrying IgA deficiency, which is one of the most common innate immunodeficiency conditions in man. 48. Nedrud T, Blanchard S, Czinn GR, Harriman GR: Orally •immunized IgA-deficient mice are protected against H. fells infection [abstract]. Gut 1996, 39(suppl 2):A45. So far only an abstract, but a paper to look for. It describes the lack of the role of the secretory IgA system in the protective effector mechanism elicited by mucosal vaccination against Heficobacter infection. 47. •.
49.
MarinaroM, Staats HF, Hiroi T, Jackson RJ, Coste M, Boyaka PN, Okahashi N, Yamamoto M, Kiyono H, Bluethmann H e t al.: Mucosal adjuvant effect of cholera toxin in mice results from induction of T helper 2 (Th2) cells and IL-4. J Immuno11995, 155:4621~4629.
50.
TakahashiI, Marinaro M, Kiyono H, Jackson RJ, Nakagawa I, Fujihashi K, Hamada S, Clements JD, Bost KL, McGhee JR: Mechanisms for mucosal immunogenicity and adjuvancy of Escherichia coil labile toxin. J Infect Dis 1996, 173:627-635.
51. °,
Covacci A, Falkow S, Berg DE, Rappuoli R: Did the inheritance of a pathogenicity island modify the virulence of Helicobacter pylon~t Trends Microbiol 1997, 5:205-208. This review describes the current knowledge on the molecular basis of evolution of virulence in H. pylori Type I virulent strains through the inheritance of DNA insertions that contain genes associated with disease. 52. •
Kreiss C, Buclin T, Cosma M, Corthesy-Theulaz I, Michetti P: Safety of oral immunisation with recombinant urease in patients with Helicobacter pylori infection. Lancet 1996, 347:1630-1631. The first official report of a subunit vaccine Phase I trial performed last year with purified recombinant enzymatically inactive urease. 12 nonsymptomatic H. pylori infected volunteers were randomized to receive, orally, either 6Omg of urease or a placebo once weekly for 4 weeks. Urease was well tolerated and no major adverse reactions occurred. Mean gastritis score assessed on bioptic specimens was not altered by treatment and only minor erosions were observed in three volunteers receiveing urease and in one receiving the placebo. As expected, however, as no mucosal adjuvant was used in this trial, all volunteers remained infected.