Antibody-independent protective mucosal immunity to gastric helicobacter infection in mice

The role of type-specific antibodies in colonization and infection by Helicobacter pylori

PURPOSE OF REVIEW

Helicobacter pylori is a Gram-negative spiral bacterium that colonizes the stomach of humans, causing gastritis, peptic ulcer disease, or gastric cancer. H. pylori infection accounts for a high percentage of mortality and morbidity rates in developing as well as developed countries. H. pylori bacteria reside in the mucus layer covering the gastric epithelium, and therefore the type of protective measures that could confer resistance appear to be limited. Although H. pylori infection stimulates strong local and systemic specific IgA and IgG antibody production, the influence of antibodies on bacterial colonization and gastric inflammation is still controversial.

RECENT FINDINGS

Recent studies in experimental animal models have indicated a non-essential role of specific antibodies for host resistance against H. pylori infection. Recent data show that protection is mediated by T cells, CD4 T helper type 1 cells, in particular. Antibodies are not only dispensable for protection, but they impair both the elimination of bacteria and the development of gastritis. This effect appears to be IgA-dependent and is not a function of specific IgM or IgG antibodies.

SUMMARY

This review highlights the recent advances in our understanding of how antibodies may influence the development of gastric inflammation and bacterial colonization. Such information can significantly increase our basic knowledge of immune regulation and protection against H. pylori infection, but can also indicate new strategies for vaccine development.

IgA Antibodies Impair Resistance againstHelicobacter pyloriInfection: Studies on Immune Evasion in IL-10-Deficient Mice

We recently reported that Helicobacter pylori-specific Abs impair the development of gastritis and down-regulate resistance against H. pylori infection. In this study, we asked whether IgA Abs specifically can have an impact on H. pylori colonization and gastric inflammation. To obtain a sensitive model for the study of inflammation we crossed IgA- and IL-10-deficient mice. We found that IL-10(-/-)/IgA(-/-) mice were significantly less colonized than IL-10(-/-)/IgA(+/+) mice, which in turn were less colonized than wild-type (WT) mice. The IL-10(-/-)/IgA(-/-) mice exhibited a 1.2-log reduction in bacterial counts compared with that in IL-10(-/-)/IgA(+/+) mice, suggesting that IgA Abs rather promoted than prevented infection. The reduced colonization in IL-10(-/-)/IgA(-/-) mice was associated with the most severe gastritis observed, albeit all IL-10(-/-) mice demonstrated more severe gastric inflammation than wild-type mice. The gastritis score and the infiltration of CD4(+) T cells into the gastric mucosa were significantly higher in IL-10(-/-)/IgA(-/-) mice than in IL-10(-/-)/IgA(+/+) mice, arguing that IgA Abs counteracted inflammation. Moreover, following oral immunization, IL-10(-/-)/IgA(-/-) mice were significantly better protected against colonization than IL-10(-/-)/IgA(+/+) mice. However, the stronger protection was associated with more severe postimmunization gastritis and gastric infiltration of CD4(+) T cells. There was also a clear increase in complement receptor-expressing cells in IL-10(-/-)/IgA(-/-) mice, though C3b-fragment deposition in the gastric mucosa was comparable between the two. Finally, specific T cell responses to recall Ag demonstrated higher levels of IFN-gamma production in IL-10(-/-)/IgA(-/-) as compared with IL-10(-/-)/IgA(+/+) mice. Thus, it appears that IgA and IL-10 help H. pylori bacteria evade host resistance against infection.

Molecular analysis of Helicobacter pylori-associated gastric inflammation in naïve versus previously immunized mice

To identify mechanisms of immunity against Helicobacter pylori, we performed microarray analysis on gastric tissue from infected mice and mice vaccinated prior to challenge. RNA from gastric tissue was used to screen over 10,000 genes. MHC antigens and GTP binding proteins were upregulated in both groups. Infected mice were characterized by expression of innate host defense markers while immune mice expressed many IFN-gamma response genes and T cell markers. Results were confirmed for several genes by RT-PCR. CD4+ spleen cells from immune mice produced significantly more IFN-gamma than from infected mice. These results support a role for T cell regulated inflammation in H. pylori immunity.

Vaccine-induced protection against gastrointestinal bacterial infections in the absence of secretory antibodies

Secretory IgA (SIgA) is widely held to be responsible for the defense of the mucosae against pathogenics and other potentially harmful agents. In this study, polymeric Ig receptor (pIgR) knockout mice, which lack secretory antibodies (SAb), were used to investigate the role of vaccine-elicited SAb in protection against gastrointestinal bacterial infections. An essential role for specific SAb in protection against Vibrio cholerae was evident from experiments showing that vaccinated pIgR(-/-) mice, but not vaccinated C57BL/6 mice, were susceptible to cholera toxin challenge. Vaccination of C57BL/6 mice with Salmonella typhimurium elicited strong antigen-specific, mucosal responses, which blocked in vitro invasion of epithelia. However, vaccinated C57BL/6 and pIgR(-/-) mice were equally resistant to challenge infection with virulent S. typhimurium. Finally, we investigated the importance of SIgA in protection against recurrent infections with Citrobacter rodentium. Although higher numbers of bacteria were detected early after challenge infection in feces of vaccinated pIgR(-/-) mice compared with vaccinated C57BL/6 mice, both mouse strains showed complete clearance after 9 days. These results suggested that, in immune animals, SIgA is crucial for the protection of gastrointestinal surfaces against secreted bacterial toxins, may inhibit early colonization by C. rodentium, but is not essential for protection against re-infection with S. typhimurium or C. rodentium.

Intranasal CpG-oligodeoxynucleotide is a potent adjuvant of vaccine against Helicobacter pylori, and T helper 1 type response and interferon-gamma correlate with the protection

BACKGROUND

Although a series of vaccines against Helicobacter pylori have emerged in the past 10 years, the mechanism involved in their protective effect is yet to be elucidated, and more effective vaccine adjuvants remain to be developed. In this study, CpG-oligodeoxynucleotide (CpG-ODN) was investigated as a new candidate for a H. pylori vaccine adjuvant. Furthermore, the role of T helper 1 (Th1) type response and interferon (IFN)-gamma in the protective immunity was explored.

METHODS

C57BL/6 mice and IFN-gamma knockout mice were intranasally or orally immunized with H. pylori whole cell sonicate (WCS)/CpG-ODN and challenged with different doses [5 x 10(8) and 5 x 10(6) colony-forming units (CFU)] of H. pylori. The protective effect was assessed as the percentage of noninfected mice. The responsive antibodies and cytokines were analyzed using an enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

The prevention rates against H. pylori infection in mice intranasally immunized with WCS plus CpG-ODN were dramatically higher than those in sham-immunized mice (70% vs. 0%, challenged with 5 x 10(8) CFU H. pylori; 90% vs. 20%, challenged with 5 x 10(6) CFU H. pylori). Significantly higher levels of immunoglobulin G2a (IgG2a) and IFN-gamma were detected in the mice immunized with WCS/CpG than in sham-immunized controls. However, vaccination failed to effectively protect IFN-gamma knockout mice challenged with H. pylori.

CONCLUSIONS

CpG-ODN given intranasally is a potent adjuvant for development of a H. pylori vaccine. Th1-type response and IFN-gamma are involved in the protection.

Impact of vector-priming on the immunogenicity of a live recombinant Salmonella enterica serovar typhi Ty21a vaccine expressing urease A and B from Helicobacter pylori in human volunteers

Orally administered recombinant Salmonella vaccines represent an attractive option for mass vaccination programmes against various infectious diseases. Therefore, it is crucial to gather knowledge about the possible impact of preexisiting immunity to carrier antigens on the immunogenicity of recombinant vaccines. Thirteen volunteers were preimmunized with Salmonella typhi Ty21a in order to evaluate the effects of prior immunization with the carrier strain. Then, they received three doses of 1-2 x 10(10) viable organisms of either the vaccine strain S. typhi Ty21a (pDB1) expressing subunits A and B of recombinant Helicobacter pylori urease (n = 9), or placebo strain S. typhi Ty21a (n = 4). Four volunteers were preimmunized and boosted with the vaccine strain S. typhi Ty21a (pDB1). No serious adverse effects were observed in any of the volunteers. Whereas none of the volunteers primed and boosted with the vaccine strain responded to the recombinant antigen, five of the nine volunteers preimmunized with the carrier strain showed cellular immune responses to H. pylori urease (56%). This supports the results of a previous study in non-preimmunized volunteers where 56% (five of nine) of the volunteers showed a cellular immune response to urease after immunisation with S. typhi Ty21a (pDB1).

Augmentation of Helicobacter pylori urease activity by its specific IgG antibody: implications for bacterial colonization enhancement

Gastric colonization of Helicobacter pylori (H. pylori) occurs in a very early age via infected mothers having H. pylori-specific IgG antibodies that would be transplacentally transferred to infants. In addition, H. pylori urease-specific IgG was associated with chronic gastric atrophy and post-immunization gastritis is usually correlated with a strong local IgG response. These findings indicate that H. pylori-specific IgG antibodies, in particular its urease-specific IgG, may induce unfavorable influence on host resistance against H. pylori. Here, we show that we have found a unique H. pylori urease-specific IgG monoclonal antibody (MAb), termed S3, recognizing the conformational structure of the small subunit Ure-A, which enhanced the urease enzymatic activity. Such enhancement of the H. pylori urease activity induced by 1 microg of S3 was almost completely cancelled by simultaneously added the same amount of L2 MAb, which has a strong and specific inhibitory activity against H. pylori urease and recognizes a liner epitope of 8-mer peptide (F8: SIKEDVQF) within its large subunit Ure-B (Infect. Immun. 69: 6597, 2001). Intravenous pre-administration of purified S3 into BALB/c mice showed significant augmentation for gastric colonization with the susceptible strain Sydney Strain-1 (SS-1). To our knowledge, this is the first demonstration that a H. pylori urease-specific IgG MAb induced an augmentation of their gastric colonization in vivo.

TGF-beta receptor signaling is critical for mucosal IgA responses

TGF-beta receptor (TbetaR) signaling is important for systemic IgA production; however, its contribution to IgA secretion at mucosal sites remained uncertain. This important question was addressed using mice lacking the TbetaR in B cells (TbetaRII-B). Although reduced, IgA-secreting cells and IgA were still present in the systemic and mucosal compartments. The adaptive immune response was investigated after oral or nasal immunization using adjuvants acting on different molecular targets, namely, the cholera toxin B subunit and the macrophage-activating lipopeptide-2. Efficient Ag-specific cellular and humoral responses were triggered both in controls and TbetaRII-B mice. However, a significant reduction in Ag-specific IgG2b and increased levels of IgG3 were observed in sera from TbetaRII-B mice. Furthermore, Ag-specific IgA-secreting cells, serum IgA, and secretory IgA were undetectable in TbetaRII-B mice. These results demonstrate the critical role played by TbetaR in Ag-driven stimulation of secretory IgA responses in vivo.

Vaccine-induced immunity against Helicobacter pylori infection is impaired in IL-18-deficient mice

Protective immunity against Helicobacter pylori infection in mice has been associated with a strong Th1 response, involving IL-12 as well as IFN-gamma, but recent studies have also demonstrated prominent eosinophilic infiltration, possibly linked to local Th2 activity in the gastric mucosa. In this study we investigated the role of IL-18, because this cytokine has been found to be a coregulator of Th1 development as well as involved in Th2-type responses with local eotaxin production that could influence gastric eosinophilia and resistance to infection. We found that IL-18(-/-) mice failed to develop protection after oral immunization with H. pylori lysate and cholera toxin adjuvant, indicating an important role of IL-18 in protection. Well-protected C57BL/6 wild-type (WT) mice demonstrated substantial influx of CD4(+) T cells and eosinophilic cells in the gastric mucosa, whereas IL-18(-/-) mice had less gastritis, few CD4(+) T cells, and significantly reduced numbers of eosinophilic cells. T cells in well-protected WT mice produced increased levels of IFN-gamma and IL-18 to recall Ag. By contrast, unprotected IL-18(-/-) mice exhibited significantly reduced gastric IFN-gamma and specific IgG2a Ab levels. Despite differences in gastric eosinophilic cell infiltration, protected WT and unprotected IL-18(-/-) mice had comparable levels of local eotaxin, suggesting that IL-18 influences protection via Th1 development and IFN-gamma production rather than through promoting local production of eotaxin and eosinophilic cell infiltration.

Helicobacter pylori with a truncated lipopolysaccharide O chain fails to induce gastritis in SCID mice injected with splenocytes from wild-type C57BL/6J mice

The goal of this study was to determine whether Helicobacter pylori lipopolysaccharide (LPS) O-chain polysaccharide contributes to gastritis in a mouse model. C57BL/6J or C57BL/6-Prkdc(scid) (severe combined immunodeficient [SCID]) mice were inoculated with H. pylori strain SS1 or SS1::0826kan, in which a beta-1,4-galactosyltransferase (HP0826), an LPS biosynthetic enzyme, had been disrupted. H. pylori strain SS1::0826kan expresses truncated LPS lacking O chain. Recipient SCID mice were given C57BL/6J splenocytes by intraperitoneal injection. Bacterial colonization, gastric lesions (gastritis, neutrophilic infiltration, and gastric epithelial metaplasia), cellular (delayed-type hypersensitivity) and humoral immune responses to H. pylori sonicate, and gastric gamma interferon (IFN-gamma) mRNA expression were quantified. Recipient SCID mice colonized by H. pylori strain SS1 developed extensive gastritis with loss of normal fundic gland morphology. In contrast, gastric mucosa of recipient SCID mice colonized by H. pylori strain SS1::0826kan was not statistically distinguishable from that of uninfected recipient mice. Delayed-type hypersensitivity and humoral immune responses were detected in infected mice inoculated with wild-type SS1, but not with SS1::0826kan. IFN-gamma transcription was lower in mice infected with SS1::0826kan than in mice infected with SS1. In this model of rapidly progressive gastritis due to H. pylori, the O chain contributed to the extent of gastritis and to the host immune response. These data support a role for H. pylori LPS O chain in direct induction of the host immune response leading to gastritis and gastric damage and are in contrast to protein antigens, such as urease and cag products which do not contribute to gastritis in mice.

Human polymeric IgA is superior to IgG and single-chain Fv of the same monoclonal specificity to inhibit urease activity associated with Helicobacter pylori

Helicobacter-induced gastritis is considered nowadays an epidemic, the prevalence of which is one of the highest world-wide (70%), with as much as 40% of the population in industrialized countries. Helicobacter pylori (H. pylori) antigens (Ag) capable to elicit a protective immune response in animal models have been identified, but these antigens have not been shown to be strongly immunogenic when administered to humans. Due to their stability in the gastric environment and avidity, passive administration of secretory immunoglobulin A (SIgA) antibodies (Ab) targeting protective Ag might be particularly relevant as a substitute or complement to current therapies. To this aim, we have designed expression vectors to convert a scFv polypeptide specific for H. pylori urease subunit A into human IgG, polymeric IgA (IgAp/d) and SIgA. Purified proteins show proper binding characteristics toward both the native and denatured forms of H. pylori urease. The direct comparison between different isotype and molecular forms, but of unique specificity, demonstrates that SIgA and IgAp/d are more efficient in blocking free and H. pylori-associated urease than IgG and scFv. We conclude that the expression system reported herein will represent a valuable tool to produce human SIgA Ab of multiple specificities against H. pylori antigens involved in colonization and persistence.

Helicobacter pylori-specific antibodies impair the development of gastritis, facilitate bacterial colonization, and counteract resistance against infection

In recent years, Abs have been considered a correlate rather than an effector of resistance against Helicobacter pylori infection. However, it is still poorly understood to what extent Ab production correlates with gastric immunopathology. Here we report that Abs not only are dispensable for protection, but they are detrimental to elimination of the bacteria and appear to impair gastric inflammatory responses. We found that the initial colonization with H. pylori bacteria was normal in the B cell-deficient (microMT) mice, whereas at later times (>8 wk) most of the bacteria were cleared, concomitant with the development of severe gastritis. In contrast, wild-type (WT) mice exhibited extensive bacterial colonization and only mild gastric inflammation, even at 16 wk after inoculation. Oral immunizations with H. pylori lysate and cholera toxin adjuvant stimulated comparable levels of protection in microMT and WT mice. The level of protection in both strains correlated well with the severity of the postimmunization gastritis. Thus, T cells were responsible for the gastritis, whereas Abs, including potentially host cell cross-reactive Abs, were not involved in causing the gastritis. The T cells in micro MT and WT mice produced high and comparable levels of IFN-gamma to recall Ag at 2 and after 8 wk, whereas IL-4 was detected after 8 wk only, indicating that Th1 activity dominated the early phase of protection, whereas later a mixed Th1 and Th2 activity was seen.

Clearance of Helicobacter pylori infection through immunization: the site of T cell activation contributes to vaccine efficacy

Helicobacter pylori vaccine development has progressed rapidly in animal models. Both H. pylori-associated pathogenesis and protective immunity are CD4+ T cell dependent, with no discernable phenotypic difference to distinguish pathogenic T cells from protective T cells. Functionally however, protective T cells promote enhanced inflammation upon H. pylori challenge. Additionally, only mouse models such as phagocyte oxidase- or IL-10-deficient mice that respond to H. pylori infection with intense gastritis are capable of demonstrating spontaneous eradication of the bacteria. These data, combined with recent descriptions of down-regulatory T cells in infected humans and mice, support an emerging model of H. pylori pathogenesis in which H. pylori induces inflammation that is limited by regulatory T cells in the stomach. Immunization therefore may succeed by activating T cells in peripheral lymph nodes that are capable of promoting qualitatively or quantitatively different inflammation when recruited to the stomach. Evidence in support of this model will be discussed.

Host anti-microbial response to Helicobacter pylori infection

beta-Defensin peptides are known to be potent anti-bacterials with a wide spectrum of activity. They, therefore, represent an important aspect of innate immunity. In the present study, we have extended our understanding of the regulation of the beta-defensins in response to Helicobacter pylori (H. pylori) infection. We found elevated levels of hBD2 and hBD3 transcripts within gastric cells following infection. This was reflected by increased secretion of the corresponding peptide. The relative bactericidal potency of the beta-defensins was also assessed. Our findings show that hBD3 was the most potent peptide tested followed by hBD2 and hBD1. Relatively modest synergy between hBD1 and hBD2 was also noted. More importantly, we observed endogenous production of putative anti-microbial factors by infected gastric epithelial cells. Our study highlights the active participation of the epithelium in protection against potential pathogens.

Protective immunity against Helicobacter is characterized by a unique transcriptional signature

Immunization with a whole-cell sonicate vaccine of Helicobacter felis in conjunction with cholera toxin as a mucosal adjuvant induces long-term protective immunity in a majority of laboratory mice. We have combined gene expression profiling and immunohistochemical analysis on a set of immunized animals to better understand the mechanism of protection. The stomachs of protected animals exhibited a strikingly different transcriptional profile compared with those of nonprotected or control mice, indicating that vaccination targets the appropriate site and leaves a molecular signature. Among the genes whose up-regulation is significantly correlated with protection are a number of adipocyte-specific factors. These include the fat-cell-specific cytokines adipsin, resistin, and adiponectin and the adipocyte surface marker CD36. Interestingly, potentially protective T and B lymphocytes can be found embedded in the adipose tissue surrounding protected stomachs but never in control or unprotected stomachs. Adipsin-specific immunohistochemical staining of protected stomach sections further revealed molecular cross-talk between adjacent lymphoid and adipose cell populations. We propose a mechanism of protection that involves the effector responses of either or both lymphocyte subclasses as well as the previously unappreciated paracrine functions of adipose tissue surrounding the resident lymphocytes.

Enhanced mucosal and systemic immune responses to Helicobacter pylori antigens through mucosal priming followed by systemic boosting immunizations

It is estimated that Helicobacter pylori infects the stomachs of over 50% of the world's population and if not treated may cause chronic gastritis, peptic ulcer disease, gastric adenocarcinoma and gastric B-cell lymphoma. The aim of this study was to enhance the mucosal and systemic immune responses against the H. pylori antigens cytotoxin-associated gene A (CagA) and neutrophil-activating protein (NAP), through combinations of mucosal and systemic immunizations in female BALB/c mice. We found that oral or intranasal (i.n.) followed by i.m. immunizations induced significantly higher serum titres against NAP and CagA compared to i.n. alone, oral alone, i.m. alone, i.m. followed by i.n. or i.m. followed by oral immunizations. However, only oral followed by i.m. immunizations induced anti-NAP antibody-secreting cells in the stomach. Moreover, mucosal immunizations alone or in combination with i.m., but not i.m. immunizations alone, induced mucosal immunoglobulin A (IgA) responses in faeces. Any single route or combination of immunization routes with NAP and CagA preferentially induced antigen-specific splenic interleukin-4-secreting cells and far fewer interferon-gamma-secreting cells in the spleen. Moreover, i.n. immunizations alone or in combination with i.m. immunizations induced predominantly serum IgG1 and far less serum IgG2a. Importantly, we found that while both i.n. and i.m. recall immunizations induced similar levels of serum antibody responses, mucosal IgA responses in faeces were only achieved through i.n. recall immunization. Collectively, our data show that mucosal followed by systemic immunization significantly enhanced local and systemic immune responses and that i.n. recall immunization is required to induce both mucosal and systemic memory type responses.

A coordinated cytotoxic effect of IFN-gamma and cross-reactive antibodies in the pathogenesis of Helicobacter pylori gastritis

BACKGROUND

Helicobacter pylori (H. pylori) infection is associated with chronic infiltration into the stomach by T cells and plasma cells producing IFN-gamma and antibodies of various specificities, respectively. It is unknown whether these lymphocyte-products may play coordinated roles in the gastric pathology of this infection.

AIMS

To know how IFN-gamma may relate to anti-H. pylori antibodies in their roles in pathogenesis, we determined the isotype subclass of those antibodies as well as their cross-reactivity and cytotoxicity to gastric epithelium.

METHODS AND RESULTS

We infected BALB/c mice with H. pylori (SS1, Sydney Strain 1) and generated monoclonal antibodies, which were comprised of 240 independent clones secreting immunoglobulin and included 80 clones reactive to SS1. Ninety percent of the SS1-reactive clones had IgG2a isotype. Two clones, 2B10 and 1A9, were cross reactive to cell surface antigens in H. pylori and to antigens of 28 KDa and 42 KDa, respectively, which were present on the cell surface of and shared by both mouse and human gastric epithelial cells. The antigens recognized by these monoclonal antibodies localized a distinctive area in the gastric glands. In the presence of complement, 2B10 showed cytotoxicity to gastric epithelial cells. The effect was dose dependant and augmented by IFN-gamma. Finally, administration of 2B10 to mice with SS1 infection aggravated gastritis by increasing cellular infiltration.

CONCLUSION

IFN-gamma by gastric T cells may participate in pathogenesis of the H. pylori infected stomach by directing an isotype-switch of anti-H. pylori antibodies to complement-binding subclass and by augmenting cytotoxic activity of a certain autoantibody. This may explain a host-dependent diversity in gastric pathology of the patients with H. pylori infection.

Vaccine-induced protection against Helicobacter pylori in mice lacking both antibodies and interleukin-4

To test the hypothesis that a Th2 response to Helicobacter pylori is necessary for protection and to address the possibility that humoral and Th2 cellular responses may compensate for each other, we generated mice deficient in both interleukin-4 (IL-4) and antibodies. The immunized double-knockout mice were protected from H. pylori challenge, as were the parental strains and wild-type C57BL/6 mice. Neutralization of IL-4 in B-cell-deficient mice did not prevent protection. Immunized IL-5-deficient mice were also protected. Thus, IL-4 and IL-5 are not essential for protection.

Passive immunity in Helicobacter-challenged neonatal mice conferred by immunized dams lasts until weaning

The objective of this study was to examine the effect of breast-feeding by immunized dams on Helicobacter colonization in newborns. Urease-based immunization regimens failed to protect nursing pups against H. felis, whereas H. felis lysate-cholera toxin resulted in protection. This observation correlated with a high recognition of cell surface-expressed bacterial antigens by milk antibodies. Protection lasted until weaning, indicating that infection is maintained at undetectable levels by passive immunity but then resumes when breast-feeding stops.

Protective efficacy of anti-Helicobacter pylori immunity following systemic immunization of neonatal mice

Helicobacter pylori infection of the gastric mucosa is a significant cause of morbidity and mortality because of its etiologic role in symptomatic gastritis, peptic ulcer disease, and gastric adenocarcinoma. Infection occurs in young children; therefore, a prophylactic vaccine would have to be administered within the first year of life, a period thought to be immunologically privileged. We investigated vaccine formulations administered by different routes to confer protective anti-H. pylori immunity in neonatal mice. Neonatal mice immunized with a single dose of vaccine in complete Freund's adjuvant (CFA) generated antigen-specific gamma interferon-, interleukin-2 (IL-2)-, IL-4-, and IL-5-secreting T cells in numbers similar to those in immunized adult mice, while vaccine administered to neonates in incomplete Freund's adjuvant (IFA) induced such cells in reduced numbers compared to those in adult mice. Both IFA and CFA, however, provided partial protection from a challenge with infectious H. pylori when the vaccine was administered subcutaneously. Neonatal immunized mice also had reduced bacterial loads when immunized intraperitoneally with CFA. In all cases, protection was equivalent to that achieved when adult counterparts were immunized. These studies suggest that an efficacious vaccine might be successfully administered to very young children to prevent perinatal infection of H. pylori.

Role of the polymeric Ig receptor in mucosal B cell homeostasis

Secretory IgA (SIgA) is the most characteristic component of the mucosal immune system and has long been considered the major protective factor that prevents pathogens from invading hosts through the mucosae. Recent studies, however, have suggested that complete immunity against a range of mucosal bacterial and viral pathogens can be achieved in the absence of IgA. Therefore, to further dissect the role of SIgA, we generated mice deficient in the polymeric Ig receptor (pIgR(-/-) mice). As a result of an inability to transport dimeric IgA to the secretions, pIgR(-/-) mice are deficient in SIgA and accumulate circulating dimeric IgA, with serum levels 100-fold greater than those observed in normal mice. Examination of lamina propria mononuclear cells showed that pIgR(-/-) mice had approximately 3 times as many IgA-secreting cells as C57BL/6 mice. Further analysis showed that these cells displayed the differentiated IgA(+) B220(-) phenotype and accounted for a 2-fold increase in the number of lamina propria blast cells in the pIgR(-/-) mice. Subsequent experiments showed that OVA-specific CD4(+) T cell expansion following OVA feeding was not elevated in pIgR(-/-) mice. Furthermore, no differences in CD8(+) T cell tolerance or induction of influenza virus-specific CD8(+) T cells were detected in pIgR(-/-) mice compared with controls. Therefore, while SIgA is clearly involved in maintaining some parameters of mucosal homeostasis in the intestine, the mechanisms associated with its barrier function and the clinical consequences of its deficiency are yet to be identified.

Vaccine-induced reduction of Helicobacter pylori colonization in mice is interleukin-12 dependent but gamma interferon and inducible nitric oxide synthase independent

Previous studies with mice have shown that major histocompatibility complex class II (MHC-II) is required for protection from Helicobacter pylori, while MHC-I and antibodies are not. Thus, CD4(+) T cells are presumed to play an essential role in protective immunity via secretion of cytokines. To determine which cytokines are associated with a reduction of bacterial load in immunized mice, gastric cytokine expression was examined by semiquantitative reverse transcription-PCR in protected (defined as > or =2-log-unit decrease in bacterial load) and unprotected mice 4 weeks after challenge. Elevated levels of mRNA for interleukin-12p40 (IL-12p40), gamma interferon (IFN-gamma), tumor necrosis factor alpha, and inducible nitric oxide synthase (iNOS) were associated with protection in immunized-challenged (I/C) mice, but Th2 cytokine (IL-4, IL-5, IL-10, and IL-13) and chemokine (KC, MIP-2, and MCP-1) expression was not associated with protection. Despite the association of IFN-gamma and iNOS message with protection, I/C mice genetically lacking either of these products were able to reduce the bacterial load as well as the wild-type I/C controls. The I/C mice lacking IL-12p40 were not protected compared to unimmunized-challenged mice. All I/C groups developed gastritis. We conclude that neither IFN-gamma nor iNOS is essential for vaccine-induced protection from H. pylori infection. The p40 subunit of IL-12, which is a component of both IL-12 and IL-23, is necessary for protection in immunized mice. These findings suggest a novel IFN-gamma-independent function of IL-12p40 in effective mucosal immunization against H. pylori.

Colonization of C57BL/6J and BALB/c wild-type and knockout mice with Helicobacter pylori: effect of vaccination and implications for innate and acquired immunity

The gram-negative bacterial pathogen Helicobacter pylori is a major cause of peptic ulcer disease and a risk factor for gastric cancer in humans. Adapted H. pylori strains, such as strain SS1, are able to infect mice and are a useful model for gastric colonization and vaccination studies. In this study we used a streptomycin-resistant derivative of H. pylori SS1 to analyze the colonization behavior and the success of vaccination in wild-type (wt) and various knockout mice of the BALB/c and C57BL/6J genetic backgrounds. We here report that BALB/c interleukin-4 knockout (IL-4(-/-)) mice are weakly overcolonized compared to the wt strain but that the IL-12(-/-) knockout results in a strong overcolonization (500%). Unexpectedly, in the C57BL/6J background the same knockouts behaved in diametrically opposed manners. The IL-4(-/-) mutation caused a 50% reduction and the IL-12(-/-) knockout caused a 95% reduction compared to the wt colonization rate. For C57BL/6J mice we further analyzed the IL-18(-/-) and Toll-like receptor 2 knockout mutations, which showed reductions to 66 and 57%, respectively, whereas mice with the IL-10(-/-) phenotype were hardly infected at all (5%). In contrast, the tumor necrosis factor receptor knockout (p55(-/-) and p55/75(-/-)) mice showed an overcolonization compared to the C57BL/6J wt strain. With exception of the low-level infected C57BL/6J IL-10(-/-) and IL-12(-/-) knockout mice, all knockout mutants were accessible to a prophylactic vaccination and their vaccination behavior was comparable to that of the wt strains.

Protection against Helicobacter pylori infection following immunization is IL-12-dependent and mediated by Th1 cells

The regulatory roles of Th1 and Th2 cells in immune protection against Helicobacter infection are not clearly understood. In this study, we report that a primary H. pylori infection can be established in the absence of IL-12 or IFN-gamma. However, IFN-gamma, but not IL-12, was involved in the development of gastritis because IFN-gamma(-/-) (GKO) mice exhibited significantly less inflammation as compared with IL-12(-/-) or wild-type (WT) mice. Both IL-12(-/-) and GKO mice failed to develop protection following oral immunization with H. pylori lysate and cholera toxin adjuvant. By contrast, Th2-deficient, IL-4(-/-), and WT mice were equally well protected. Mucosal immunization in the presence of coadministered rIL-12 in WT mice increased Ag-specific IFN-gamma-producing T cells by 5-fold and gave an additional 4-fold reduction in colonizing bacteria, confirming a key role of Th1 cells in protection. Importantly, only protected IL-4(-/-) and WT mice demonstrated substantial influx of CD4(+) T cells in the gastric mucosa. The extent of inflammation in challenged IL-12(-/-) and GKO mice was much reduced compared with that in WT mice, indicating that IFN-gamma/Th1 cells also play a major role in postimmunization gastritis. Of note, postimmunization gastritis in IL-4(-/-) mice was significantly milder than WT mice, despite a similar level of protection, indicating that immune protection is not directly linked to the degree of gastric inflammation. Only protected mice had T cells that produced high levels of IFN-gamma to recall Ag, whereas both protected and unprotected mice produced high levels of IL-13. We conclude that IL-12 and Th1 responses are crucial for H. pylori-specific protective immunity.

Multiparameter selection of Helicobacter pylori antigens identifies two novel antigens with high protective efficacy

A multiparameter selection of Helicobacter pylori antigens for vaccine development identified 15 candidates, 6 of which are known protective antigens. Two novel antigens with low homology to other organisms (HP0231 and HP0410) were overexpressed and purified with high yields. Both confer protective immunity in the mouse Helicobacter infection model.

A comparison of murine and human immunoproteomes of Helicobacter pylori validates the preclinical murine infection model for antigen screening

Preclinical mouse infection models are widely used for Helicobacter vaccine development, but how well such models mimic important aspects of human infections is unknown. A comparison of Helicobacter pylori immunoproteomes of infected mice with previously reported patient data reveals a high agreement in the antigens recognized, suggesting that H. pylori in vivo protein composition and recognition by the host immune system are comparable in mice and humans. Murine Helicobacter models may thus be valid to screen antigens for human vaccination.

Clearance of Helicobacter pylori Infection and Resolution of Postimmunization Gastritis in a Kinetic Study of Prophylactically Immunized Mice

Patients infected with Helicobacter pylori mount an immune response which fails to clear the infection and may contribute to disease. Mice can be protected by immunization. To further characterize the H. pylori-mouse model, stomachs of unimmunized or intranasally immunized C57BL/6 mice were quantitatively cultured 3 days and 1, 2, 4, 8, 16, 32, and 52 weeks after challenge with H. pylori. At 3 days and 1 week after challenge, colonization was the same in the immunized and unimmunized mice. By 2 weeks after challenge, the immunized mice had a >2-log decrease in bacterial load, and at all later time points, they either were culture negative or had at least a 2-log decrease in bacterial load. Gastritis in the immunized mice peaked at 1 to 2 weeks after challenge and was characterized by a mixed inflammatory infiltrate and epithelial proliferation centered at the transition between corpus and antrum. By 52 weeks postchallenge, the gastric histology in the immunized mice was not different from that in control unchallenged mice. The unimmunized group began to show a reduction in bacterial load as early as 16 weeks after challenge, and by 52 weeks seven of eight unimmunized mice had developed gastritis and reduced bacterial loads. These results indicate that prophylactic immunization does not prevent colonization by H. pylori but enables mice to clear the infection or significantly reduce the number of colonizing bacteria. The reduction in bacterial load is associated with gastric inflammation that subsides over time.

Intranasal immunization with recombinant antigens associated with new cationic particles induces strong mucosal as well as systemic antibody and CTL responses

New cationic nanoparticles (SMBV) were evaluated for use as a nasal vaccine delivery system for two recombinant proteins: HBsAg and beta-galactosidase. Each protein was formulated with SMBV and intranasally administrated to non-anesthetized mice. In each model, the formulated protein induced high levels of specific serum IgG antibodies and cytotoxic T lymphocyte (CTL) responses. Moreover, specific IgA antibodies were found in nasal as well as in vaginal washes of intranasally immunized mice with the protein associated with SMBV. In contrast, no IgG or IgA antibodies and no CTL were detected in mice immunized with free protein. The detection of a CTL response and an increase in both IgG1 and IgG2a antibodies in serum suggest that SMBV amplifies both Th1 and Th2 responses without modifying the Th1/Th2 profile of the immune response induced by the natural protein. These data demonstrate the high potential of SMBV for use as a nasal delivery system for sub-unit vaccines.

Immunoglobulin A-deficient mice exhibit altered T helper 1-type immune responses but retain mucosal immunity to influenza virus

We have previously demonstrated that immunoglobulin A (IgA)(-/-) knockout (KO) mice exhibit levels of susceptibility to influenza virus infection that are similar to those of their normal IgA(+/+) littermates. To understand the mechanism of this apparent mucosal immunity without IgA, immunoglobulin isotype and T helper 1 (Th1)-type [interferon-gamma (IFN-gamma)] and Th2-type [interleukin (IL)-4, IL-5)] cytokine responses to influenza vaccine were evaluated. Intranasal immunization with influenza virus subunit vaccine plus cholera toxin/cholera toxin B subunit (CT/CTB) induced significant influenza virus-specific immunoglobulin G (IgG) antibody in the serum and nasal passages of both IgA(-/-) and IgA(+/+) mice, while IgA antibodies were induced only in IgA(+/+) mice. IgA KO mice exhibited an IgG1 subclass haemagglutinin (HA)-specific response but no detectable IgG2a and IgG2b responses. In contrast, IgA(+/+) mice exhibited significant IgG1 as well as IgG2a responses. This indicates a predominant Th2-type response in IgA KO mice compared to normal mice. Following stimulation with influenza virus in vitro, splenic lymphocytes from immunized IgA(-/-) mice produced significantly lower levels of IFN-gamma than IgA(+/+) mice (P < 0.001), but elaborated similar levels of IL-4 and IL-5. This was true at both protein and mRNA levels. Immunized mice were challenged intranasally with a small inoculum of influenza virus to allow deposition of virus in the nasal mucosal passages. Compared to non-immunized mice, immunized IgA(-/-) and IgA(+/+) mice exhibited significant, but similar levels of reduction in virus titres in the nose and lung. These results demonstrate that in addition to IgA deficiency, IgA gene deletion also resulted in down-regulated Th1-type immune responses and confirm our previous data that IgA antibody is not indispensable for the prevention of influenza virus infection.

Role of immunoglobulin A in protection against reovirus entry into Murine Peyer's patches

Reovirus type 1 Lang (T1L) infects the mouse intestinal mucosa by adhering specifically to epithelial M cells and exploiting M-cell transport to enter the Peyer's patches. Oral inoculation of adult mice has been shown to elicit cellular and humoral immune responses that clear the infection within 10 days. This study was designed to determine whether adult mice that have cleared a primary infection are protected against viral entry upon oral rechallenge and, if so, whether antireovirus secretory immunoglobulin A (S-IgA) is a necessary component of protection. Adult BALB/c mice that were orally inoculated on day 0 with reovirus T1L produced antiviral S-IgA in feces and IgG in serum directed primarily against the reovirus sigma1 attachment protein. Eight hours after oral reovirus challenge on day 21, the Peyer's patches of previously exposed mice contained no detectable virus whereas Peyer's patches of naive controls contained up to 2,300 PFU of reovirus/mg of tissue. Orally inoculated IgA knockout (IgA(-/-)) mice cleared the initial infection as effectively as wild-type mice and produced higher levels of reovirus-specific serum IgG and secretory IgM than C57BL/6 wild-type mice. When IgA(-/-) mice were rechallenged on day 21, however, their Peyer's patches became infected. These results indicate that intestinal S-IgA is an essential component of immune protection against reovirus entry into Peyer's patch mucosa.

Helicobacter pylori infection as a model for gastrointestinal immunity and chronic inflammatory diseases

Approximately 50% of humanity is infected with Helicobacter pylori. It is a life-long infection that elicits a marked host inflammatory response; however, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection contributes to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. While bacterial factors are important triggers of inflammation, many subjects infected with strains bearing putative virulence factors remain free from disease. Recent genetic studies have implicated the host's immune and inflammatory responses, suggesting that disease results from an interaction between bacterial and environmental factors in genetically susceptible hosts. Other digestive diseases, including celiac disease and inflammatory bowel disease, mimic this paradigm, where it appears that luminal triggers only manifest disease in subjects with the right combination of host and environmental factors. Since infection with H. pylori is relatively common, it is possible to study the impact of a specific etiologic agent on the pathogenesis of disease in humans. This approach has illuminated the complexity of the pathogenic mechanisms, but the advances achieved to date may provide some hints regarding the pathogenesis of chronic inflammatory diseases elsewhere in the digestive tract.

Vaccination against Helicobacter pylori--an old companion of man

Helicobacter pylori infection induces an important systemic and mucosal antibody response and a predominant Th1 cellular response. These immune responses, although powerful, fail to eliminate the infection. Studies in animals have shown that prophylactic and therapeutic immunisations are efficacious, although complete protective immunity has usually not been achieved. Initial human trials with recombinant urease showed that a mucosal immune response can be obtained following immunisations, with a decrease in bacterial density, but successful immunisation is still awaited. Progress is being made in several areas of vaccine design. A human vaccine against H. pylori would be favourable in terms of health benefits and costs in developed and developing countries.

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.

T-cell-mediated mucosal immunity in the absence of antibody: lessons from Helicobacter pylori infection

Approximately 50% of humanity is infected with Helicobacter pylori. This lifelong infection elicits a marked host response, including a robust gastric IgA response. However, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection can contribute to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. These immune responses are attributed to a subset of helper T cells, so-called Th1 cells, that enhance cell-mediated immunity and induce damage to the gastric epithelium. Thus, it is desirable to have effective vaccines that could prevent and cure infection and that may modify the host response in a manner that prevents immune-mediated disease. Using animal models as a tool to understand the immunobiology of Helicobacter infections, several investigators have shown that effective vaccines can be developed. Thus, prophylactic and even therapeutic vaccines have been described in various animal models. The basis for the effectiveness of these vaccines appears related to their ability to alter the gastric immune response, from a homogeneous Th1 response to a mixed Th1 and Th2 response. Interestingly, immunity can occur in the absence of B cells, suggesting that novel IgA-independent mechanisms exist that confer protection against a luminal infection. Thus, H. pylori infection provides a model with which new mechanisms of immunological protection can be identified and applied to other mucosal infections.

The role of T cell subsets and cytokines in the pathogenesis of Helicobacter pylori gastritis in mice

Gastritis due to Helicobacter pylori in mice and humans is considered a Th1-mediated disease, but the specific cell subsets and cytokines involved are still not well understood. The goal of this study was to investigate the immunopathogenesis of H. pylori-induced gastritis and delayed-type hypersensitivity (DTH) in mice. C57BL/6-Prkdc(scid) mice were infected with H. pylori and reconstituted with CD4+, CD4-depleted, CD4+CD45RB(high), or CD4+CD45RB(low) splenocytes from wild-type C57BL/6 mice or with splenocytes from C57BL/6(IFN-gamma-/-) or C57BL/6(IL-10-/-) mice. Four or eight weeks after transfer, DTH to H. pylori Ags was determined by footpad injection; gastritis and bacterial colonization were quantified; and IFN-gamma secretion by splenocytes in response to H. pylori Ag was determined. Gastritis and DTH were present in recipients of unfractionated splenocytes, CD4+ splenocytes, and CD4+CD45RB(high) splenocytes, but absent in the other groups. IFN-gamma secretion in response to H. pylori Ags was correlated with gastritis, although splenocytes from all groups of mice secreted some IFN-gamma. Gastritis was most severe in recipients of splenocytes from IL-10-deficient mice, and least severe in those given IFN-gamma-deficient splenocytes. Bacterial colonization in all groups was inversely correlated with gastritis. These data indicate that 1) CD4+ T cells are both necessary and sufficient for gastritis and DTH due to H. pylori in mice; 2) high expression of CD45RB is a marker for gastritis-inducing CD4+ cells; and 3) IFN-gamma contributes to gastritis and IL-10 suppresses it, but IFN-gamma secretion alone is not sufficient to induce gastritis. The results support the assertion that H. pylori is mediated by a Th1-biased cellular immune response.

Vaccination against Helicobacter pylori in non-human primate models and humans

Several vaccination studies have been performed in monkeys and humans testing the feasibility of prophylactic and therapeutic immunizations against Helicobacter pylori. The monkey studies showed that immune responses were induced by oral vaccination with the mucosal adjuvant LT (Escherichia coli heat-labile enterotoxin), parenteral administration with a cationic lipid adjuvant, and by mucosal priming followed by parenteral boosts. Both prophylactic and therapeutic activities were demonstrated in monkeys, providing a strong impetus for human vaccine trials. Preliminary studies in humans were undertaken in order to identify a tolerable dose of LT adjuvant or to test the effectiveness of mutant atoxic LT adjuvants. The results from these preliminary studies suggest that native LT causes diarrhoea at doses required for adjuvanticity while a mutant LT does not. In one study in which infected human subjects were vaccinated with orally administered urease antigen with native LT, there was a modest reduction in the level of H. pylori gastric colonization. A second clinical study employing H. pylori whole cell antigen and a mutant LT in infected subjects showed immune responses and although the subjects remained infected, the study was not designed to measure reduction in H. pylori colonization. Recombinant Salmonella expressing urease and other H. pylori antigens have been effective in mice (see accompanying Frontlines Topic Review by John O. Nedrud [1]), but monkey studies are not possible because of host range restriction. Human trials of parenteral immunization, mucosal immunization with mutant LT and live Salmonella vectors are needed to fully assess the ability of vaccines to prevent or treat H. pylori infections.

Helicobacter pylori infection: mechanism of colonization and functional dyspepsia Reduced colonization of gastric mucosa by Helicobacter pylori in mice deficient in interleukin-10

BACKGROUND AND AIMS

Interleukin-10 (IL-10) is a potent anti-inflammatory and immunoregulatory cytokine. Mice deficient in IL-10 production (IL-10-/-mice) develop a spontaneous chronic enterocolitis, suggesting that IL-10 is an important regulator of the mucosal immune response in vivo. The objective of this study was to determine the role of endogenous IL-10 in the host defense against gastric colonization by Helicobacter pylori by using IL-10-deficient mice.

METHODS

The IL-10-/-mice were inoculated intragastrically with a mouse-adapted H. pylori isolate (Sydney Strain 1). Gastric colonization by H. pylori (biopsy urease test and bacterial colony counts), serum levels of H. pylori-specific immunoglobulin (Ig) M, A, G, isotypes of IgG, and the gastric mucosal inflammatory scores were determined 6 weeks after inoculation. Results were compared with those obtained from H. pylori-infected control mice (IL-10+/-mice).

RESULTS

The colonization of gastric mucosa by H. pylori was reduced approximately 100-fold (P < 0.0001) in IL-10-/-mice (log10 4.87 +/- 0.26CFU/g tissue) as compared to IL-10+/-mice (log10 6.64 +/- 0.22 CFU/g tissue). Furthermore, IL-10-/-mice infected with H. pylori had significantly higher H. pylori-specific IgA and IgG antibodies in serum (P < or = 0.01), and developed much more severe chronic active gastritis than infected IL-10+/-mice. The median scores of the infiltration of gastric mucosa by mononuclear cells and neutrophils were up to threefold higher in IL-10-/-mice than they were in IL-10+/-mice.

CONCLUSION

Our studies suggest that endogenous IL-10 is an inhibitor of the protective immune response to H. pylori infection. Interleukin-10 participates in the downregulation of H. pylori-induced gastric inflammatory responses, which apparently confers a survival advantage to the organism promoting more effective colonization of gastric mucosa.

Progress in vaccination against Helicobacter pylori

This review discusses recent progress in the development of a vaccine against Helicobacter pylori. This progress includes demonstration that: effective immunisation is independent of antibodies but dependent upon CD4+ T helper cells, although their role remains unknown; the immunisation regime can be improved to increase efficacy; successful immunisation against H. pylori is possible using a live vector; a strain of H. pylori suitable for experimental infection of humans has been developed. Important issues that remain to be addressed include incomplete protection, non-availability of suitable mucosal adjuvants and post-immunisation gastritis. Significantly, commercial development of products for clinical trial is underway.

Adoptive transfer of CD4+ T cells specific for subunit A of Helicobacter pylori urease reduces H. pylori stomach colonization in mice in the absence of interleukin-4 (IL-4)/IL-13 receptor signaling

Protection in the murine model of Helicobacter pylori infection may be mediated by CD4+ T cells, but the mechanism remains unclear. To better understand how protection occurs in this model, we generated and characterized H. pylori urease-specific CD4+ T cells from BALB/c mice immunized with Salmonella enterica serovar Typhimurium expressing H. pylori urease (subunits A and B). The CD4+ T cells were found to be specific for subunit A (UreA). Upon antigen-specific stimulation, expression of interleukin 4 (IL-4), IL-10, gamma interferon (IFN-gamma), and tumor necrosis factor alpha was induced. Immunocytochemical analysis showed that the majority of cells produced IFN-gamma and IL-10. Adoptive transfer of the UreA-specific CD4+ T cells into naive syngeneic recipients led to a threefold reduction in the number of bacteria in the recipient group when compared to that in the nonrecipient group. Stomach colonization was also reduced significantly after transfer of these cells into patently infected mice. Adoptive transfer of UreA-specific CD4+ T cells into IL-4 receptor alpha chain-deficient BALB/c mice indicated that IL-4 and IL-13 were not critical in the control of bacterial load. In addition, synthetic peptides were used to identify three functional T-cell epitopes present in subunit A which were recognized by the UreA-specific T cells. Analysis of H. pylori-specific cellular immune responses in recipient challenged and nonrecipient infected mice indicated a strong local restriction of the response in infected animals. The implications of these findings for the mechanism of protection and the development of peptide-based vaccination are discussed.

Helicobacter pylori vaccines and mechanisms of effective immunity: is mucus the key?

In this theoretical article, the hypothesis is proposed that immunization against gastric helicobacter infection is mediated by CD4+ T-cell induced changes in mucus production. Vaccine development for the gastric pathogen Helicobacter pylori has encountered several problems. Resolving these problems is impeded by our lack of understanding of the mechanisms by which the immune response influences bacterial colonization. Protective immunity requires CD4+ T cells, but the majority of helicobacters are located in the mucus of the gastric lumen, away from the epithelial surface. Evidence suggests that this mechanism functions independently of antibodies, so how this is achieved is unknown. Clues to this mechanism may be provided by immune clearance of nematode infection. Similar to H. pylori, expulsion of the intestinal nematode, Nippostrongylus brasiliensis, in rodents is mediated by CD4+ T-cell changes in the numbers of goblet cells and the type of mucins secreted into the gut. Immune-mediated changes in secretion of gastric mucins could similarly be responsible for the reductions in helicobacter colonization seen in immunized animals. Helicobacter pylori are highly motile bacteria that have evolved to inhabit their specialized niche. Alterations in their mucus environment could influence their motility, such that the bacteria cannot remain efficiently within the mucus and are flushed away.

IgA immunodeficiency leads to inadequate Th cell priming and increased susceptibility to influenza virus infection

IgA is considered to be the principal Ab involved in defense against pathogens in the mucosal compartment. Using mice with a targeted disruption in IgA gene expression (IgA(-/-) mice), we have examined the precise role of IgA in protective anti-influenza responses after intranasal vaccination. IgA(-/-) mice immunized intranasally with soluble hemagglutinin (hemagglutinin subtype 1) and neuraminidase (neuraminidase subtype 1) vaccine in the absence of adjuvant were found to be more susceptible to influenza virus infection than IgA(+/+) mice (13 vs 75% survival after virus challenge). Inclusion of IL-12 during immunization restored the protective efficacy of the vaccine to that seen in IgA(+/+) animals. IgA(-/-) mice had no detectable IgA expression, but displayed enhanced serum and pulmonary IgM and IgG Ab levels after IL-12 treatment. Assessment of T cell function revealed markedly depressed splenic lymphoproliferative responses to PHA in IgA(-/-) animals compared with IgA(+/+) mice. Furthermore, IgA(-/-) animals displayed impaired T cell priming to the H1N1 subunit vaccine, with concomitant reduction in recall memory responses due to a defect in APC function. Collectively, these results provide evidence that a major role of IgA is to facilitate presentation of Ag to mucosal T cells. IL-12 treatment can overcome IgA deficiency by providing adequate T cell priming during vaccination.

How CD4(+) T cells may eliminate extracellular gastric Helicobacter?

Helicobacter pylori is recognised as a causal agent in the pathogenesis of gastritis, gastric and duodenal ulcer disease as well as gastric cancers. Eradication of the bacteria with antibiotics is currently used to treat symptomatic, infected individuals. Theoretically the infection could also be controlled by vaccination. Several immunisation protocols were developed in small animal models and primates in order to validate this approach. Recently making use of mice with defined genetic defects, H. pylori-specific CD4(+) T cells were found to be crucial for protective vaccination. This was unexpected and poses the question of how activation of CD4(+) T cells leads to the elimination of bacteria that reside primarily in the mucin layer behind a barrier of epithelial cells. CD4(+) T cells fulfil their effector function by secreting lymphokines and by engaging specific surface ligands on interacting cells. Here we propose that phagocytes and epithelial cells stimulated either by direct interaction with CD4(+) T cells or by soluble mediators such as cytokines or neuropeptides are the ultimate effector populations in protective immunity induced by vaccination.

Immunology of Helicobacter pylori and prospects for vaccine

Since the initial discovery of H. pylori by Marshall and Warren 17 years ago, much progress has been made in treating this infection. However, as we enter the millennium, H. pylori infection continues to be one of the most common infections of mankind. In addition, eradication of H. pylori still requires multiple antimicrobial agents. A better understanding of the host immune response to H. pylori infection should allow investigators to develop immunotherapies to prevent the acquisition of infection and eradicate existing chronic H. pylori infection.

Review article: Helicobacter pylori vaccines-the current status

In this review, we take a look at the current status in the development of a vaccine against the human pathogenic bacterium, Helicobacter pylori, a major aetiological factor in peptic ulcer disease and gastric adenocarcinoma. Various animal models are now in use from mice infected with H. pylori, through gnotobiotic pigs and primates to ferrets naturally infected with their own Helicobacter, H. mustelae. A significant problem remains the requirement for a suitable mucosal adjuvant. Detoxification or the use of low doses of adjuvants already available may provide a solution and new immune stimulating compounds have been tested with some success. New approaches include the delivery of Helicobacter antigens by DNA immunization, microparticles or live vectors such as attenuated salmonella and the examination of alternative routes of vaccine administration. The phenomenon of post-immunization gastritis and improvements in vaccine efficacy are also discussed. A major area of interest is the mechanism by which immunization actually influences Helicobacter colonization. This remains a mystery: antibodies appear to be unimportant whereas CD4+ T-cells essential. Finally, a viewpoint is given on whom should be immunized when a final vaccine becomes available.