IFNγ-dependent silencing of TFF1 during Helicobacter pylori infection

Chronic Helicobacter pylori infection is the leading cause of intestinal-type adenocarcinoma, as prolonged Helicobacter colonization triggers chronic active gastritis, which may evolve into adenocarcinoma of the intestinal type. In this environment, cytokines play a significant role in determining the evolution of the infection. In combination with other factors (genetic, environmental and nutritional), the pro-inflammatory response may trigger pro-oncogenic mechanisms that lead to the silencing of tumour-suppressor genes, such as trefoil factor 1 (TFF1). The latter is known to play a protective role by maintaining the gastric mucosa integrity and retaining H. pylori in the mucus layer, preventing the progression of infection and, consequently, the development of gastric cancer (GC). Since TFF1 expression is reduced during chronic Helicobacter infection with a loss of gastric mucosa protection, we investigated the molecular pathways involved in this reduction. Specifically, we evaluated the effect of some pro-inflammatory cytokines on TFF1 regulation in GC and primary gastric cells by RT-qPCR and luciferase reporter assay analyses and the repressor role of the transcription factor C/EBPβ, overexpressed in gastric-intestinal cancer. Our results show that, among several cytokines, IFNγ stimulates C/EBPβ expression, which acts as a negative regulator of TFF1 by binding its promoter at three different sites.

Correlation of T cell response and bacterial clearance in human volunteers challenged with Helicobacter pylori revealed by randomised controlled vaccination with Ty21a-based Salmonella vaccines

BACKGROUND

Helicobacter pylori remains a global health hazard, and vaccination would be ideal for its control. Natural infection appears not to induce protective immunity. Thus, the feasibility of a vaccine for humans is doubtful.

METHODS

In two prospective, randomised, double-blind, controlled studies (Paul Ehrlich Institute application nos 0802/02 and 1097/01), live vaccines against H pylori were tested in human volunteers seronegative for, and without evidence of, active H pylori infection. Volunteers (n = 58) were immunised orally with Salmonella enterica serovar Typhi Ty21a expressing H pylori urease or HP0231, or solely with Ty21a, and then challenged with 2x10(5) cagPAI(-) H pylori. Adverse events, infection, humoral, cellular and mucosal immune response were monitored. Gastric biopsies were taken before and after vaccination, and postchallenge. Infection was terminated with antibiotics.

RESULTS

Vaccines were well tolerated. Challenge infection induced transient, mild to moderate dyspeptic symptoms, and histological and transcriptional changes in the mucosa known from chronic infection. Vaccines did not show satisfactory protection. However, 13 of 58 volunteers, 8 vaccinees and 5 controls, became breath test negative and either cleared H pylori (5/13) completely or reduced the H pylori burden (8/13). H pylori-specific T helper cells were detected in 9 of these 13 (69%), but only in 6 of 45 (13%) breath test-positive volunteers (p = 0.0002; Fisher exact test). T cells were either vaccine induced or pre-existing, depending on the volunteer.

CONCLUSION

Challenge infection offers a controlled model for vaccine testing. Importantly, it revealed evidence for T cell-mediated immunity against H pylori infection in humans.

Helicobacter pylori infection in anterior uveitis

BACKGROUND

Despite intensive research, the etiology of acute anterior uveitis (AAU) remains poorly defined. Infection with gram-negative bacteria such as Yersinia, Salmonella, Shigella, and Chlamydia have already been suggested as a possible trigger event for AAU. Helicobacter pylori is also a gram-negative bacterium, shares the lipopolysaccharides, but did not attract the attention of many ophthalmologists until recently. Having in mind the relatively high incidence of H. pylori infection in the population, we propose that H. pylori may also be a trigger factor for AAU.

PATIENTS AND METHODS

The presence of anti-H. pylori antibodies in matching serum and aqueous humor samples of 15 idiopathic AAU patients was determined using a commercial Western blot assay. Control serum and aqueous humor were obtained from five patients undergoing cataract surgery.

RESULTS

Six out of 15 AAU patients (40%) were serum-positive for H. pylori, and half of these (n = 3) also had anti-H. pylori antibodies in the aqueous humor. All five aqueous humor and sera controls tested negative for H. pylori infection.

CONCLUSION

These are the first results demonstrating anti-H. pylori antibodies in the aqueous humor of AAU patients. Further studies are needed to demonstrate whether this antibody is indeed locally produced. Our data may provide first evidence for a causative link between H. pylori infection and AAU.

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).

The integration site of the iga gene in commensal Neisseria sp

An IgA1 protease is produced by the human pathogens Neisseria gonorrhoeae and N. meningitidis but not by related non-pathogenic, commensal, Neisseria species. In this study, the chromosomal iga locus was characterized in the N. gonorrhoeae strain MS11 and compared to corresponding loci in N. meningitidis and commensal Neisseria species. In N. gonorrhoeae, the genes trpB and ksgA were found immediately downstream of iga. In addition to comL and comA, a homolog of the Escherichia coli YFII gene was identified upstream of iga. Each gene in the iga region (YFII and comL, comA and iga, and trpB and ksgA) is transcribed in the opposite direction to its neighbors. The comL/ comA and iga/ trpB pairs each have a transcriptional terminator in the correct position for joint use. These terminators contain the common gonococcal DNA uptake sequence (DUS). A highly conserved direct repeat of 25 bp located immediately adjacent to the iga gene in N. gonorrhoeae was also found in N. meningitidis. In Southern hybridization experiments, no homology to iga was detectable in the chromosomal DNAs of the commensal species N. mucosa, N. lactamica, N. flavescens, N. cinerea, N. subflava, N. flava, N. sicca or N. elongata. When N. gonorrhoeae comL and trpB were used as probes, signals were detected on the same restriction fragment in six of the eight species. This indicated that commensal Neisseria species share a possible integration site for the iga gene between comA and trpB. The region between comA and trpB was therefore amplified by PCR. The fragment obtained from N. lactamica showed a high degree of homology to gonococcal comA and trpB, respectively, but iga was replaced by a sequence of 13 bp that shows no homology to any known gonococcal sequence. Our data suggest that iga was acquired by a common ancestor of N. gonorrhoeae and N. meningitidis rather than being distributed by horizontal gene transfer. N. lactamica, which is more closely related to N. gonorrhoeae than other commensals, may have lost iga by deletion.

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.

Tyrosine phosphorylation patterns and size modification of the Helicobacter pylori CagA protein after translocation into gastric epithelial cells

Helicobacter pylori is one of the most common bacterial pathogens that causes a variety of gastric diseases. During infection, the immuno-dominant H. pylori CagA protein is translocated and tyrosine-phosphorylated in gastric epithelial cells. We compared tyrosine phosphorylation patterns of five CagA variants by two-dimensional electrophoresis (2-DE) and immunoblotting studies. Tyrosine-phosphorylated CagA was detected as two distinct protein species in strains P12, P227, G27 and 26695 suggesting that two tyrosine residues of CagA can be phosphorylated both separately and simultaneously. Prediction programs revealed the presence of three putative tyrosine phosphorylation motifs in the sequences of CagA. Mutations in these motifs were identified suggesting that only two putative phosphorylation-relevant tyrosines are present in each CagA variant. CagA of strain J99 was found to be unique because essential codons were mutated in each of the three motifs and, consequently, revealed no tyrosine phosphorylation signals at all. These findings support the view that CagA from different H. pylori strains can be tyrosine-phosphorylated at one or two out of three predicted positions. Additionally, truncated CagA protein species of about 100-105 kDa (p100CagA) have been detected after infection with some of the H. pylori strains. The isoelectric point determined by both 2-DE and sequence analysis suggested that p100CagA represents the amino (N)-terminal part of the protein. Translocation, tyrosine phosphorylation and size modification of CagA might be involved in host signal transduction and development of gastric disease.

Identification of a tyrosine-phosphorylated 35 kDa carboxy-terminal fragment (p35CagA) of the Helicobacter pylori CagA protein in phagocytic cells: processing or breakage?

Helicobacter pylori is a very common bacterial pathogen that causes gastric disease by inducing the infiltration of immune cells as an initial event. Virulent H. pylori strains express a type IV secretion system composed of several virulence (Vir) proteins encoded by the cag pathogenicity island (cag PAI). During infection of phagocytic cells (U937, Josk-M and J774A.1) we have detected a de novo tyrosine-phosphorylated protein (p35p-Tyr) with sizes of 30 kDa, 38 kDa or 40 kDa, depending on the H. pylori strain. p35p-Tyr occurrence required functional virB4, virB7, virB10, virB11, virD4 and cagA (cytotoxin-associated gene A) genes encoded by the cag PAI suggesting that p35p-Tyr is a bacterial protein of variable size. We have biochemically purified p35p-Tyr from infected U937 cells. Tryptic peptides of p35p-Tyr determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) identified the carboxy (C)-terminal part of the H. pylori CagA protein. Subsequent analysis by two-dimensional electrophoresis (2-DE) and immunoblotting using anti-CagA antibodies revealed the presence of three stable CagA protein species in phagocytes: (i) 130-140 kDa full-length CagA (p135CagA), (ii) a 100-105 kDa fragment (p100CagA) and (iii) a 30-40 kDa fragment (p35CagA). Unlike p135CagA, p35CagA and p100CagA were also detected in much lower amounts in H. pylori without host cell contact. Therefore, breakage or processing leads to the production of p35CagA and p100CagA, a process that is enhanced after translocation into host cells. MALDI-MS data and the isoelectric point determined by both 2-DE and sequence analysis suggested that p35CagA represents the C-terminal part of CagA and p100CagA corresponds to the remaining amino (N)-terminal fragment. The possible function of CagA in host signal transduction and development of gastric disease is discussed.

Proteome analysis of the common human pathogen Helicobacter pylori

The common human pathogen Helicobacter pylori is the major cause of gastric and duodenal ulcers. Based on the complete genome sequences of two independent isolates more than 1800 protein species have been resolved by two-dimensional gel electrophoresis and more than 200 of them have been identified (http://www.mpiib-berlin.mpg.de/2D-PAGE). Using these data, a large range of research areas including strain fingerprinting, protein composition and subcellular localization, gene regulation, and pathogen-host interactions have been investigated. The results that have been obtained led to a more detailed understanding of the Helicobacter biology and pathology and open further interesting fields for future work.

Safety and immunogenicity of live recombinant Salmonella enterica serovar Typhi Ty21a expressing urease A and B from Helicobacter pylori in human volunteers

Helicobacter pylori urease was expressed in the common live typhoid vaccine Ty21a yielding Ty21a(pDB1). Nine volunteers received Ty21a(pDB1) and three control volunteers received Ty21a. No serious adverse effects were observed in any of the volunteers. Ten out of 12 volunteers developed humoral immune responses to the Salmonella carrier as detected by antigen-specific antibody-secreting cells but only two volunteers seroconverted. A total of five volunteers showed responses in one or two out of three assays for cellular responses to the carrier (proliferation, IFN-gamma-secretion, IFN-gamma-ELISPOT). Three of the volunteers that had received Ty21a(pDB1) showed a weak but significant T-cell response to Helicobacter urease, while no volunteer had detectable humoral responses to urease. Ty21a(pDB1) is a suitable prototype to optimize Salmonella-based vaccination for efficient cellular responses that could mediate protective immunity against Helicobacter.

Epithelial cells infected with Chlamydophila pneumoniae (Chlamydia pneumoniae) are resistant to apoptosis

The obligate intracellular pathogen Chlamydophila pneumoniae (Chlamydia pneumoniae) initiates infections in humans via the mucosal epithelia of the respiratory tract. Here, we report that epithelial cells infected with C. pneumoniae are resistant to apoptosis induced by treatment with drugs or by death receptor ligation. The induction of protection from apoptosis depended on the infection conditions since only cells containing large inclusions were protected. The underlying mechanism of infection-induced apoptosis resistance probably involves mitochondria, the major integrators of apoptotic signaling. In the infected cells, mitochondria did not respond to apoptotic stimuli by the release of apoptogenic factors required for the activation of caspases. Consequently, active caspase-3 was absent in infected cells. Our data suggest a direct modulation of apoptotic pathways in epithelial cells by C. pneumoniae.

Vaccination of mice with live recombinant Salmonella typhimurium aroA against H. pylori: parameters associated with prophylactic and therapeutic vaccine efficacy

Previously we described a recombinant attenuated Salmonella typhimurium aroA strain (SL3261[pYZ97]) with constitutive expression of plasmid encoded Helicobacter pylori urease subunits A and B (UreAB). Single dose oral vaccination effectively induced prophylactic immunity against bacterial challenge in BALB/c mice. Here we successfully extended this approach to several mouse strains with allelic differences in NRAMP-1 and H-2 genes. The respective host determinants are known to influence the immune response against S. typhimurium. A comparative analysis of the vaccine efficacy in C57BL/6 and BALB/c mice showed that the live vaccine confers long lasting immunity in both strains (>18 weeks). In C57BL/6 mice, protection was still observed 54 weeks while not all vaccinated BALB/c were immune when challenged after this time. BALB/c mice also needed higher doses of SL3261[pYZ97] for full protection. We also demonstrate a therapeutic potential of SL3261[pYZ97] in H. pylori infected BALB/c and C57BL/6 mice. Urease- and carrier-specific serum antibody responses as well as the level of colonization by the Salmonella were analyzed in both mouse strains after immunization with low (4 x 10(7)CFU) or high (1 x 10(9)CFU) vaccine doses. The results are discussed in the context of inoculum size and the mode of antigen supply required for effective vaccination with recombinant Salmonella.

Phosphorylation of tyrosine 972 of the Helicobacter pylori CagA protein is essential for induction of a scattering phenotype in gastric epithelial cells

Helicobacter pylori colonizes the human stomach and is the causative agent of a variety of gastric diseases. After bacterial attachment, the H. pylori CagA protein is translocated into gastric epithelial cells and tyrosine phosphorylated. This process is associated with characteristic cytoskeletal rearrangements, resulting in a scatter factor-like ('hummingbird') phenotype. In this study, using a cagA mutant complemented with wild-type cagA and transiently expressing CagA in AGS cells, we have demonstrated that translocated CagA is necessary for rearrangements of the actin cytoskeleton to occur. Anti-phosphotyrosine immunoblotting studies and treatment of infected cells with phosphotyrosine kinase inhibitors suggested that not only translocation but also phosphorylation of CagA is important in this process. Transient expression of CagA-green fluorescent protein (GFP) fusion proteins and two-dimensional gel electrophoresis of CagA protein species demonstrated tyrosine phosphorylation in the C-terminus. Site-directed mutagenesis of CagA revealed that tyrosine residue 972 is essential for induction of the cellular phenotype. We have also demonstrated that translocation and phosphorylation of CagA is necessary but not sufficient for induction of the hummingbird phenotype in AGS cells, indicating the involvement of as yet unidentified bacterial factor(s).

Pathogenic Neisseria trigger expression of their carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1; previously CD66a) receptor on primary endothelial cells by activating the immediate early response transcription factor, nuclear factor-kappaB

Neisseria gonorrhoeae express opacity-associated (Opa) protein adhesins that mediate binding to various members of the carcinoembryonic antigen-related cellular adhesion molecule (CEACAM; previously CD66) receptor family. Although human umbilical vein endothelial cells express little CEACAM receptor in vitro, we found neisserial infection to induce expression of CEACAM1, CEACAM1-3L, and CECAM1-4L splice variants. This mediates an increased Opa(52)-dependent binding of gonococci by these cells. The induced receptor expression did not require bacterial Opa expression, but it was more rapid with adherent bacteria. Because the time course of induction was similar to that seen for induced proinflammatory cytokines, we tested whether CEACAM1 expression could be controlled by a similar mechanism. Gonococcal infection activated a nuclear factor-kappaB (NF-kappaB) heterodimer consisting of p50 and p65, and inhibitors that prevent the nuclear translocation of activated NF-kappaB complex inhibited CEACAM1 transcript expression. Each of these effects could be mimicked by using culture filtrates or purified lipopolysaccharide instead of intact bacteria. Together, our results support a model whereby the outer membrane "blebs" that are actively released by gonococci trigger a Toll-like receptor-4-dependent activation of NF-kappaB, which up-regulates the expression of CEACAM1 to allow Opa(52)-mediated neisserial binding. The regulation of CEACAM1 expression by NF-kappaB also implies a broader role for this receptor in the general inflammatory response to infection.

Low iron availability modulates the course of Chlamydia pneumoniae infection

Chlamydiae are obligate intracellular bacteria residing exclusively in host cell vesicles termed inclusions. We have investigated the effects of deferoxamine mesylate (DAM)-induced iron deficiency on the growth of Chlamydia pneumoniae and Chlamydia trachomatis serovar L2. In epithelial cells subjected to iron starvation and infected with either C. pneumoniae or C. trachomatis L2, small inclusions were formed, and the infectivity of chlamydial progeny was impaired. Moreover, for C. trachomatis L2, we observed a delay in homotypic fusion of inclusions. The inhibitory effects of DAM were reversed by adding exogenous iron-saturated transferrin, which restored the production of infectious chlamydiae. Electron microscopy examination of iron-deprived specimens revealed that the small inclusions contained reduced numbers of C. pneumoniae that were mostly reticulate bodies. We have previously reported specific accumulation of transferrin receptors (TfRs) around C. pneumoniae inclusions within cells grown under normal conditions. Using confocal and electron microscopy, we show here a remarkable increase in the amount of TfRs surrounding the inclusions in iron-starved cultures. It has been shown that iron is an essential factor in the growth and survival of C. trachomatis. Here, we postulate that, for C. pneumoniae also, iron is an indispensable element and that Chlamydia may use iron transport pathways of the host by attracting TfR to the phagosome.

Pathogenicity island-dependent activation of Rho GTPases Rac1 and Cdc42 in Helicobacter pylori infection

Helicobacter pylori has been identified as the major aetiological agent in the development of chronic gastritis and duodenal ulcer, and it plays a role in the development of gastric carcinoma. Attachment of H. pylori to gastric epithelial cells leads to nuclear and cytoskeletal responses in host cells. Here, we show that Rho GTPases Rac1 and Cdc42 were activated during infection of gastric epithelial cells with either the wild-type H. pylori or the mutant strain cagA. In contrast, no activation of Rho GTPases was observed when H. pylori mutant strains (virB7 and PAI) were used that lack functional type IV secretion apparatus. We demonstrated that H. pylori-induced activation of Rac1 and Cdc42 led to the activation of p21-activated kinase 1 (PAK1) mediating nuclear responses, whereas the mutant strain PAI had no effect on PAK1 activity. Activation of Rac1, Cdc42 and PAK1 represented a very early event in colonization of gastric epithelial cells by H. pylori. Rac1 and Cdc42 were recruited to the sites of bacterial attachment and are therefore probably involved in the regulation of local and overall cytoskeleton rearrangement in host cells. Finally, actin rearrangement and epithelial cell motility in H. pylori infection depended on the presence of a functional type IV secretion system encoded by the cag pathogenicity island (PAI).

Tyrosine phosphorylation patterns and size modification of the Helicobacter pylori CagA protein after translocation into gastric epithelial cells

Helicobacter pylori is one of the most common bacterial pathogens that causes a variety of gastric diseases. During infection, the immuno-dominant H. pylori CagA protein is translocated and tyrosine-phosphorylated in gastric epithelial cells. We compared tyrosine phosphorylation patterns of five CagA variants by two-dimensional electrophoresis (2-DE) and immunoblotting studies. Tyrosine-phosphorylated CagA was detected as two distinct protein species in strains P12, P227, G27 and 26695 suggesting that two tyrosine residues of CagA can be phosphorylated both separately and simultaneously. Prediction programs revealed the presence of three putative tyrosine phosphorylation motifs in the sequences of CagA. Mutations in these motifs were identified suggesting that only two putative phosphorylation-relevant tyrosines are present in each CagA variant. CagA of strain J99 was found to be unique because essential codons were mutated in each of the three motifs and, consequently, revealed no tyrosine phosphorylation signals at all. These findings support the view that CagA from different H. pylori strains can be tyrosine-phosphorylated at one or two out of three predicted positions. Additionally, truncated CagA protein species of about 100-105 kDa (p100CagA) have been detected after infection with some of the H. pylori strains. The isoelectric point determined by both 2-DE and sequence analysis suggested that p100CagA represents the amino (N)-terminal part of the protein. Translocation, tyrosine phosphorylation and size modification of CagA might be involved in host signal transduction and development of gastric disease.

Proteome analysis of the common human pathogen Helicobacter pylori

The common human pathogen Helicobacter pylori is the major cause of gastric and duodenal ulcers. Based on the complete genome sequences of two independent isolates more than 1800 protein species have been resolved by two-dimensional gel electrophoresis and more than 200 of them have been identified (http://www.mpiib-berlin.mpg.de/2D-PAGE). Using these data, a large range of research areas including strain fingerprinting, protein composition and subcellular localization, gene regulation, and pathogen-host interactions have been investigated. The results that have been obtained led to a more detailed understanding of the Helicobacter biology and pathology and open further interesting fields for future work.

Identification of a tyrosine-phosphorylated 35 kDa carboxy-terminal fragment (p35CagA) of the Helicobacter pylori CagA protein in phagocytic cells: processing or breakage?

Helicobacter pylori is a very common bacterial pathogen that causes gastric disease by inducing the infiltration of immune cells as an initial event. Virulent H. pylori strains express a type IV secretion system composed of several virulence (Vir) proteins encoded by the cag pathogenicity island (cag PAI). During infection of phagocytic cells (U937, Josk-M and J774A.1) we have detected a de novo tyrosine-phosphorylated protein (p35p-Tyr) with sizes of 30 kDa, 38 kDa or 40 kDa, depending on the H. pylori strain. p35p-Tyr occurrence required functional virB4, virB7, virB10, virB11, virD4 and cagA (cytotoxin-associated gene A) genes encoded by the cag PAI suggesting that p35p-Tyr is a bacterial protein of variable size. We have biochemically purified p35p-Tyr from infected U937 cells. Tryptic peptides of p35p-Tyr determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) identified the carboxy (C)-terminal part of the H. pylori CagA protein. Subsequent analysis by two-dimensional electrophoresis (2-DE) and immunoblotting using anti-CagA antibodies revealed the presence of three stable CagA protein species in phagocytes: (i) 130-140 kDa full-length CagA (p135CagA), (ii) a 100-105 kDa fragment (p100CagA) and (iii) a 30-40 kDa fragment (p35CagA). Unlike p135CagA, p35CagA and p100CagA were also detected in much lower amounts in H. pylori without host cell contact. Therefore, breakage or processing leads to the production of p35CagA and p100CagA, a process that is enhanced after translocation into host cells. MALDI-MS data and the isoelectric point determined by both 2-DE and sequence analysis suggested that p35CagA represents the C-terminal part of CagA and p100CagA corresponds to the remaining amino (N)-terminal fragment. The possible function of CagA in host signal transduction and development of gastric disease is discussed.

Helicobacter pylori resists phagocytosis by macrophages: quantitative assessment by confocal microscopy and fluorescence-activated cell sorting

Helicobacter pylori infection of the stomach epithelium is characterized by an infiltration of polymorphonuclear and mononuclear cells. These immune cells contribute to mucosal damage which may eventually lead to gastritis, peptic ulcer, gastric cancer, and/or MALT-associated gastric lymphoma. Here we show that H. pylori inhibits its own uptake, as well as in trans the phagocytosis of Neisseria gonorrhoeae, by human and murine macrophages. This antiphagocytic activity is dependent on the presence of the cag pathogenicity island in the H. pylori genome. We demonstrate that H. pylori also expresses its antiphagocytic activity towards the myelomonocytic cell line JOSKM, thus providing a potent model for the study of the interaction between H. pylori and phagocytes. Our data were obtained using laser confocal microscopy and flow cytometry after quenching the fluorescence of labeled extracellular bacteria. The antiphagocytic activity of H. pylori may explain the persistence of H. pylori and its pathological consequences. The use of cell lines and flow cytometry will hopefully facilitate progress in our understanding of the immune escape of these persistent bacteria.

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-induced prostaglandin E(2) synthesis involves activation of cytosolic phospholipase A(2) in epithelial cells

Helicobacter pylori initiates an inflammatory response and gastric diseases, which are more common in patients infected with H. pylori strains carrying the pathogenicity island, by colonizing the gastric epithelium. In the present study we investigated the mechanism of prostaglandin E(2) (PGE(2)) synthesis in response to H. pylori infection. We demonstrate that H. pylori induces the synthesis of PGE(2) via release of arachidonic acid predominately from phosphatidylinositol. In contrast to H. pylori wild type, an isogenic H. pylori strain with a mutation in the pathogenicity island exerts only weak arachidonic acid and PGE(2) synthesis. The H. pylori-induced arachidonic acid release was abolished by phospholipase A(2) (PLA(2)) inhibitors and by pertussis toxin (affects the activity of G alpha(i)/G alpha(o)). The role of phospholipase C, diacylglycerol lipase, or phospholipase D was excluded by using specific inhibitors. An inhibitor of the stress-activated p38 kinase (SB202190), but neither inhibitors of protein kinase C nor an inhibitor of the extracellular-regulated kinase pathway (PD98059), decreased the H. pylori-induced arachidonic acid release. H. pylori-induced phosphorylation of p38 kinase and cytosolic PLA(2) was blocked by SB202190. These results indicate that H. pylori induces the release of PGE(2) from epithelial cells by cytosolic PLA(2) activation via G alpha(i)/G alpha(o) proteins and the p38 kinase pathway.

PrimeArray: genome-scale primer design for DNA-microarray construction

PrimeArray is a Windows program that computes oligonuceotide primer pairs for genome-scale gene amplification by the Polymerase Chain Reaction (PCR). The program supports the automated extraction of coding sequences (CDS) from various input-file formats and allows highly automated primer pair-optimization.

DNA circle formation in Neisseria gonorrhoeae: a possible intermediate in diverse genomic recombination processes

An important attribute that contributes to the virulence of Neisseria gonorrhoeae is its phenotypic variability, which is based on recombination within complex gene families in the genome. In this study we report on the in vivo amplification of large segments of the genome and the existence of circular DNA intermediates in the cell, which might help to explain the evolution of these gene families and provide possible clues as to how genetic variability is maintained. Using an inserted chromosomal marker (cat) in the N. gonorrhoeae MS11 genome that confers low-level resistance to chloramphenicol (Cm), we isolated variants that express resistance to high levels of Cm. Genetic analysis revealed that virtually all variants harboured single or multiple tandem amplifications of the respective genome segments carrying the cat insert. This process occurred independently of both the location of the cat insertion site and of the presence of a functional recA gene. Analysis of the genetically well characterised pilC region revealed a head-to-tail orientation of the amplified segments, with the junctions being located within direct repeats. Identical junctions were detected in extra-chromosomal circular DNA molecules isolated from non-selected wild-type and recA strains, suggesting that both types of structure arise by related processes. The existence of DNA circles was shown by their banding behaviour in caesium chloride/ethidium bromide density centrifugation and their resistance to digestion by exonuclease. The possible roles of such circles in processes such as pilin gene recombination, chromosomal gene amplification and genetic transformation are discussed.

Immunity against Helicobacter pylori: significance of interleukin-4 receptor alpha chain status and gender of infected mice

Vaccination of interleukin-4 (IL-4) receptor alpha (IL-4Ralpha) chain-deficient BALB/c mice with Helicobacter pylori urease and cholera toxin or with urease-expressing, live attenuated Salmonella enterica serovar Typhimurium cells revealed that protection against H. pylori infection is independent of IL-4- or IL-13-mediated signals. A comparison of male and female mice suggests a sexual dimorphism in the extent of bacterial colonization that is particularly evident in the absence of the IL-4Ralpha chain.

Neisseria gonorrhoeae porin modifies the oxidative burst of human professional phagocytes

A hallmark of infection with the gram-negative bacterium Neisseria gonorrhoeae is the local infiltration and subsequent activation of polymorphonuclear neutrophils. Several gonococcal outer membrane proteins are involved in the interaction with and the activation of these phagocytes, including gonococcal porin, the most abundant protein in the outer membrane. Previous work suggests that this porin plays a role in various cellular processes, including inhibiting neutrophils activation and phagosome maturation in professional phagocytes. Here we investigated the ability of porin to modify the oxidative metabolism of human peripheral blood neutrophils and monocytes in response to particulate stimuli (including live gonococci) and soluble agents. The activation of the oxidative metabolism was determined by chemiluminescence amplified with either luminol or lucigenin. We found that treatment of the phagocytes with porin inhibits the release of reactive oxygen species measured as luminol-enhanced chemiluminescence in response to zymosan, latex particles, and gonococci. The engulfment of these particles was not, however, affected by porin treatment. Similar effects of porin on the chemiluminescence response were observed in cytochalasin B-treated neutrophils exposed to the soluble chemotactic peptide N-formylmethionyl-leucyl-phenylalanine. This indicates that porin selectively inhibits granule fusion with those cellular membranes that are in direct contact with porin, namely, the phagosomal and plasma membranes. This porin-induced downregulation of oxidative metabolism may be a potent mechanism by which gonococci modulate oxygen-dependent reactions by activated phagocytes at inflammation sites.

Improvement of the T7 expression system by the use of T7 lysozyme

One of the most efficient systems for the high-level expression of cloned genes in Escherichia coli makes use of a phage T7 late promoter whose activity depends on a regulated transcription unit supplying the specific T7 RNA polymerase. Various T7 RNA polymerase/T7 promoter-based vector host systems with differential control on expression of the T7 RNA polymerase are in use. Most of them show high levels of expression in non-induced cells, low factor of induction or impaired growth of host cells. We describe a novel and efficient control system in which basal level expression of T7 RNA polymerase is suppressed by the use of the genes for the Lac repressor and T7 lysozyme, integrated on the expression vector. T7 lysozyme expression is probably down-regulated in the induced expression system by antisense RNA. This overcomes the inhibitory effect of T7 lysozyme on T7 RNA polymerase as shown by SDS PAGE and flow cytometry analysis of expressed GFP. The main features of the expression vector compared with other systems are low background, high factor of induction and unaffected growth of non-induced cells.

Targeting of the pro-apoptotic VDAC-like porin (PorB) of Neisseria gonorrhoeae to mitochondria of infected cells

Infection of cell cultures with Neisseria gonorrhoeae results in apoptosis that is mediated by the PorB porin. During the infection process porin translocates from the outer bacterial membrane into host cell membranes where its channel activity is regulated by nucleotide binding and voltage-dependent gating, features that are shared by the mitochondrial voltage-dependent anion channel (VDAC). Here we show that porin is selectively and efficiently transported to mitochondria of infected cells. Prevention of porin translocation also blocked the induction of apoptosis. Mitochondria of cells treated with porin both in vitro and in vivo were depleted of cytochrome c and underwent permeability transition. Overexpression of Bcl-2 blocked porin-induced apoptosis. The release of cytochrome c occurred independently of active caspases but was completely prevented by Bcl-2. Our data suggest that the Neisseria porin can, like its eukaryotic homologue, function at the mitochondrial checkpoint to mediate apoptosis.

Helicobacter pylori induces but survives the extracellular release of oxygen radicals from professional phagocytes using its catalase activity

Helicobacter pylori can colonize the gastric epithelium of humans, leading to the induction of an intense inflammatory response with the infiltration of mainly polymorphonuclear leucocytes (PMNs) and monocytes. These professional phagocytes appear to be a primary cause of the damage to surface epithelial layers, and probably contribute to the pathogenesis associated with persistent H. pylori infections. We have shown previously that H. pylori adheres to professional phagocytes, but is not engulfed efficiently, suggesting an antiphagocytic escape mechanism that is dependent on the pathogen's type IV secretion system. Here, we show that H. pylori induces the generation and extracellular release of oxygen metabolites as a consequence of its attachment to phagocytic cells, but is capable of surviving this response. The catalase activity of H. pylori is apparently essential for survival at the phagocytes' cell surface. Opsonization of H. pylori leads to an increased burst, and the inhibition of bacterial protein synthesis to a decreased one. Ca2+ concentration, cytoskeleton rearrangement and protein kinase C (PKC) are involved in the H. pylori-induced oxidative burst in both monocytes and PMNs. This survival phenomenon has important implications for both the persistence of this important pathogen and the host tissue damage that accompanies persistent H. pylori infection.

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.

Helicobacter pylori inhibits phagocytosis by professional phagocytes involving type IV secretion components

Gastric infections by Helicobacter pylori are characteristically associated with an intense inflammation and infiltration of mainly polymorphonuclear lymphocytes (PMNs) and monocytes. The inflammatory response by infiltrated immune cells appears to be a primary cause of the damage to surface epithelial layers and may eventually result in gastritis, peptic ulcer, gastric cancer and/or MALT-associated gastric lymphoma. Our analysis of the interaction between H. pylori and PMNs and monocytes revealed that H. pylori inhibits its own uptake by these professional phagocytes. To some degree, this effect resembles antiphagocytosis by Yersinia enterocolitica. Increasing numbers of bacteria associated per cell are more efficient at blocking their own engulfment. In H. pylori, bacterial protein synthesis is necessary to block phagocytic uptake, as shown by the time and concentration dependence of the bacteriostatic protein synthesis inhibitor chloramphenicol. Furthermore, H. pylori appears broadly to inhibit the phagocytic function of monocytes and PMNs, as infection with H. pylori abrogates the phagocytes' ability to engulf latex beads or adherent Neisseria gonorrhoeae cells. This antiphagocytic phenotype depends on distinct virulence (vir) genes, such as virB7 and virB11, encoding core components of a putative type IV secretion apparatus. Our data indicate that H. pylori exhibits an antiphagocytic activity that may play an essential role in the immune escape of this persistent pathogen.

Acid sphingomyelinase is involved in CEACAM receptor-mediated phagocytosis of Neisseria gonorrhoeae

The interaction with human phagocytes is a hallmark of symptomatic Neisseria gonorrhoeae infections. Gonococcal outer membrane proteins of the Opa family induce the opsonin-independent uptake of the bacteria that relies on CEACAM receptors and an active signaling machinery of the phagocyte. Here, we show that CEACAM receptor-mediated phagocytosis of Opa(52)-expressing N. gonorrhoeae into human cells results in a rapid activation of the acid sphingomyelinase. Inhibition of this enzyme by imipramine or SR33557 abolishes opsonin-independent internalization without affecting bacterial adherence. Reconstitution of ceramide, the product of acid sphingomyelinase activity, in imipramine- or SR33557-treated cells restores internalization of the bacteria. Furthermore, we demonstrate that CEACAM receptor-initiated stimulation of other signalling molecules, in particular Src-like tyrosine kinases and Jun N-terminal kinases, requires acid sphingomyelinase. These studies provide evidence for a crucial role of the acid sphingomyelinase for CEACAM receptor-initiated signalling events and internalization of Opa(52)-expressing N. gonorrhoeae into human neutrophils.

Autodisplay: functional display of active beta-lactamase on the surface of Escherichia coli by the AIDA-I autotransporter

Members of the protein family of immunoglobulin A1 protease-like autotransporters comprise multidomain precursors consisting of a C-terminal autotransporter domain that promotes the translocation of N-terminally attached passenger domains across the cell envelopes of gram-negative bacteria. Several autotransporter domains have recently been shown to efficiently promote the export of heterologous passenger domains, opening up an effective tool for surface display of heterologous proteins. Here we report on the autotransporter domain of the Escherichia coli adhesin involved in diffuse adherence (AIDA-I), which was genetically fused to the C terminus of the periplasmic enzyme beta-lactamase, leading to efficient expression of the fusion protein in E. coli. The beta-lactamase moiety of the fusion protein was presented on the bacterial surface in a stable manner, and the surface-located beta-lactamase was shown to be enzymatically active. Enzymatic activity was completely removed by protease treatment, indicating that surface display of beta-lactamase was almost quantitative. The periplasmic domain of the outer membrane protein OmpA was not affected by externally added proteases, demonstrating that the outer membranes of E. coli cells expressing the beta-lactamase AIDA-I fusion protein remained physiologically intact.

Host cell invasion by pathogenic Neisseriae

As outlined in this review, various experimental techniques have been employed in an attempt to understand neisserial pathogenesis. In vitro genetic analysis has been used to study the genetic basis for the structural variability of cell surface components. Transformed or primary epithelial cell cultures have provided the simplest model to analyze bacterial adherence and invasion, while the infection of polarized epithelial monolayers, fallopian tube and nasopharyngeal organ cultures, and ureteral tissue have each been used to more closely represent the events which occur in vivo. Finally, the in vivo infection of human volunteers with N. gonorrhoeae has provided a powerful means to confirm and expand the results obtained in vitro. By these various approaches, a number of neisserial adhesins (i.e. pilli, Opa, Opc and P36) and additional putative virulence determinants which affect bacterial adherence and invasion into host cells (i.e. LOS, capsule, PorB) have been identified. Clearly, neisserial surface variation serves as an adaptive mechanism which can modulate tissue tropism, immune evasion and survival in the changing host environment. Important progress has been made in recent years with respect to the host cellular receptors and subsequent signal transduction processes which are involved in neisserial adherence, invasion and transcytosis. This has led to the identification of (i) CD46 as a receptor for pilus which allows adherence to epithelial and endothelial cells, (ii) HSPGs, in cooperation with vitronectin and fibronectin, as receptors for a particular subset of Opa proteins and Opc, which may both mediate invasion into most epithelial and endothelial cells, and (iii) CD66 as the receptors for most Opa variants, potentially being involved in cellular interactions including adherence, invasion and transcytosis with epithelial, endothelial and phagocytic cells. As most of these data have been obtained using transformed cell lines growing in vitro, attempts must be made to translate these basic observations into a more natural situation. It can be expected that the successful ongoing integration of laboratory findings from the various infection models with human volunteer studies will further increase our understanding of the biology of neisserial infection. Perhaps the most difficult but also most rewarding challenge for the future will be to use volunteer studies to identify and understand the role of host factors which are important for the infectious process. Hopefully, insights gained from each of these studies will reveal new and useful strategies for the preventive and/or therapeutic intervention into infection and disease by these fascinating microbes.

Carcinoembryonic antigen family receptor specificity of Neisseria meningitidis Opa variants influences adherence to and invasion of proinflammatory cytokine-activated endothelial cells

The carcinoembryonic antigen (CEA) family member CEACAM1 (previously called biliary glycoprotein or CD66a) was previously shown to function as a receptor that can mediate the binding of Opa protein-expressing Neisseria meningitidis to both neutrophils and epithelial cells. Since neutrophils and polarized epithelia have both been shown to coexpress multiple CEACAM receptors, we have now extended this work to characterize the binding specificity of meningococcal Opa proteins with other CEA family members. To do so, we used recombinant Escherichia coli expressing nine different Opa variants from three meningococcal strains and stably transfected cell lines expressing single members of the CEACAM family. These infection studies demonstrated that seven of the nine Opa variants bound to at least one CEACAM receptor and that binding to each of these receptors is sufficient to trigger the Opa-dependent bacterial uptake by these cell lines. The other two Opa variants do not appear to bind to either CEACAM receptors or heparan sulfate proteoglycan receptors, which are bound by some gonococcal Opa variants, thus implying a novel class of Opa proteins. We have also extended previous studies by demonstrating induction of CEACAM1 expression after stimulation of human umbilical vein endothelial cells with the proinflammatory cytokine tumor necrosis factor alpha, which is present in high concentrations during meningococcal disease. This induced expression of CEACAM1 leads to an increased Opa-dependent bacterial binding and invasion into the primary endothelia, implying that these interactions may play an important role in the pathogenesis of invasive meningococcal disease.

Comparative proteome analysis of Helicobacter pylori

Helicobacter pylori, the causative agent of gastritis, ulcer and stomach carcinoma, infects approximately half of the worlds population. After sequencing the complete genome of two strains, 26695 and J99, we have approached the demanding task of investigating the functional part of the genetic information containing macromolecules, the proteome. The proteins of three strains of H. pylori, 26695 and J99, and a prominent strain used in animal models SS1, were separated by a high-resolution two-dimensional electrophoresis technique with a resolution power of 5000 protein spots. Up to 1800 protein species were separated from H. pylori which had been cultivated for 5 days on agar plates. Using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) peptide mass fingerprinting we have identified 152 proteins, including nine known virulence factors and 28 antigens. The three strains investigated had only a few protein spots in common. We observe that proteins with an amino acid exchange resulting in a net change of only one charge are shifted in the two-dimensional electrophoresis (2-DE) pattern. The expression of 27 predicted conserved hypothetical open reading frames (ORFs) and six unknown ORFs were confirmed. The growth conditions of the bacteria were shown to have an effect on the presence of certain proteins. A preliminary immunoblotting study using human sera revealed that this approach is ideal for identifying proteins of diagnostic or therapeutic value. H. pylori 2-DE patterns with their identified protein species were added to the dynamic 2D-PAGE database (http://www.mpiib-berlin.mpg.de/2D-PAGE/). This basic knowledge of the proteome in the public domain will be an effective instrument for the identification of new virulence or pathogenic factors, and antigens of potentially diagnostic or curative value against H. pylori.

IgA1 protease from Neisseria gonorrhoeae inhibits TNFalpha-mediated apoptosis of human monocytic cells

The modulation of programmed cell death is a common theme in the patho-physiology of inflammation and infectious disease. The synthesis and secretion of an IgA1 protease is strictly associated with virulence of the Neisseria species. Here, we report on the inhibition of tumor necrosis factor alpha (TNFalpha)-mediated apoptosis of the human myelo-monocytic cell line U937 by highly purified IgA1 protease. Apoptosis was verified by the cell surface exposure of phosphatidyl serine and by terminal transferase mediated end-labeling of fragmented DNA. Interestingly, IgA1 protease specifically cleaved the TNF receptor II (TNF-RII) on the surface of intact cells whereas TNF-RI was not affected by the enzyme. Therefore, inhibition of TNFalpha-mediated apoptosis might be correlated to specific cleavage of the TNF-RII by neisserial IgA1 protease.

Recombinant live Salmonella spp. for human vaccination against heterologous pathogens

Live attenuated Salmonella spp. are promising candidates as oral vaccine delivery systems for heterologous antigens. Clinical trials have demonstrated that this approach is feasible for human vaccinations but further optimisation is necessary to obtain a better efficacy. Here, we discuss how existing clinical and pre-clinical data can be used to guide such optimisation efforts.

Translocation of the Helicobacter pylori CagA protein in gastric epithelial cells by a type IV secretion apparatus

Helicobacter pylori is one of the most common bacterial pathogens, infecting about 50% of the world population. The presence of a pathogenicity island (PAI) in H. pylori has been associated with gastric disease. We present evidence that the H. pylori protein encoded by the cytotoxin-associated gene A (cagA) is translocated and phosphorylated in infected epithelial cells. Two-dimensional gel electrophoresis (2-DE) of proteins isolated from infected AGS cells revealed H. pylori strain-specific and time-dependent tyrosine phosphorylation and dephosphorylation of several 125-135 kDa and 75-80 kDa proteins. Immunoblotting studies, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), cell fractionation and confocal microscopy demonstrated that one of the 125-135 kDa proteins represents the H. pylori CagA protein, which is translocated into the host cell membrane and the cytoplasm. Translocation of CagA was dependent on functional cagA gene and virulence (vir) genes of a type IV secretion apparatus composed of virB4, virB7, virB10, virB11 and virD4 encoded in the cag PAI of H. pylori. Our findings support the view that H. pylori actively translocates virulence determinants, including CagA, which could be involved in the development of a variety of gastric disease.

Helicobacter pylori activates the histidine decarboxylase promoter through a mitogen-activated protein kinase pathway independent of pathogenicity island-encoded virulence factors

Helicobacter pylori infection of the gastric mucosa is accompanied by an activated histamine metabolism. Histamine plays a central role in the regulation of gastric acid secretion and is involved in the pathogenesis of gastroduodenal ulcerations. Histidine decarboxylase (HDC) is the rate-limiting enzyme for histamine production, and its activity is regulated through transcriptional mechanisms. The present study investigated the effect of H. pylori infection on the transcriptional activity of the human HDC (hHDC) promoter in a gastric epithelial cell line (AGS) and analyzed the underlying molecular mechanisms. Our studies demonstrate that H. pylori infection potently transactivated the hHDC promoter. The H. pylori-responsive element of the hHDC gene was mapped to the sequence +1 to +27 base pairs, which shows no homology to known cis-acting elements and also functions as a gastrin-responsive element. H. pylori regulates the activity of this element via a Raf-1/MEK/ERK pathway, which was activated in a Ras-independent manner. Furthermore, we found that H. pylori-induced transactivation of the hHDC promoter was independent of the cag pathogenicity island and the vacuolating cytotoxin A gene and therefore may be exerted through (a) new virulence factor(s). A better understanding of H. pylori-directed hHDC transcription can provide novel insights into the molecular mechanisms of H. pylori-dependent gene regulation in gastric epithelial cells and may lead to new therapeutic approaches.

Human T-cell response to meningococcal immunoglobulin A1 protease associated alpha-proteins

A unique feature of the immunoglobulin A1 (IgA1) protease from pathogenic Neisseriae, i.e. N. meningitidis and N. gonorrhoeae, is its co-secretion with an amphipathic a-protein. Polymerase chain reaction (PCR) analysis of the respective iga(alpha). gene region in 48 meningococcal strains revealed that this protein domain is conserved throughout all isolates in four different principal variants. Despite strain-dependent size and sequence variations, sequence analysis showed common structural characteristics. More than 80% of the amino acid sequence of all a-proteins is dependent on the five amino acids Q, E, A, K and R, resulting in a pI> 10. The sequences are highly conserved at the N-terminus and the C-terminus and contain long amphipathic alpha-helical stretches. These stretches have a strong probability of forming coiled coil conformations and comprise short repetitive sequence modules with pronounced similarities to T-cell epitopes. We therefore analyzed the T-cell response of 20 volunteer blood donors to four peptides, representing such predicted epitopes, and a recombinant meningococcal alpha-protein. Sixteen donors reacted against at least one peptide after culture of peripheral blood mononuclear cells in interleukin (IL)-2-rich medium, while two individuals showed a positive reaction only against an IgA1 protease-derived control peptide. From one donor, we established and maintained T-cell clones specific for purified alpha-protein. Characterization of the T-cell clones revealed a CD3- and a CD4-positive phenotype and the secretion of IL-2 and interferon-gamma (IFN-gamma),

Syndecan-1 and syndecan-4 can mediate the invasion of OpaHSPG-expressing Neisseria gonorrhoeae into epithelial cells

Neisseria gonorrhoeae (Ngo) expressing the outer membrane protein OpaHSPG can adhere to and invade epithelial cells via binding to heparan sulphate proteoglycan (HSPG) receptors. In this study, we have investigated the role of syndecan-1 and syndecan-4, two members of the HSPG family, in the uptake of Ngo by epithelial cells. When overexpressed in HeLa cells, both syndecans co-localize with adherent Ngo on the host cell surface. This overexpression of syndecan-1 and syndecan-4 leads to a three- and sevenfold increase in Ngo invasion respectively. In contrast, transfection with the syndecan-1 and syndecan-4 mutant constructs lacking the intracellular domain results in an abrogation of the invasion process, characteristic of a dominant-negative mode of action. A concomitant loss of the capacity to mediate Ngo uptake was also observed with syndecan-4 mutant constructs carrying lesions in the dimerization motif necessary for the binding of protein kinase C (PKC) and phosphatidylinositol 4,5-bisphosphate (PIP2), and mutants that are deficient in a C-terminal EFYA amino acid motif responsible for binding to syntenin or CASK. We conclude that syndecan-1 and syndecan-4 can both mediate Ngo uptake into epithelial cells, and that their intracellular domains play a crucial role in this process, perhaps by mediating signal transduction or anchorage to the cytoskeleton.

Characterization of the essential transport function of the AIDA-I autotransporter and evidence supporting structural predictions

The current model for autodisplay suggests a mechanism that allows a passenger protein to be translocated across the outer membrane by coordinate action of a C-terminal beta-barrel and its preceding linking region. The passenger protein, linker, and beta-barrel are together termed the autotransporter, while the linker and beta-barrel are here referred to as the translocation unit (TU). We characterized the minimal TU necessary for autodisplay with the adhesin-involved-in-diffuse-adherence (AIDA-I) autotransporter. The assumed beta-barrel structure at the C terminus of the AIDA-I autotransporter was studied by constructing a set of seven AIDA-I-cholera toxin B subunit fusion proteins containing various portions of AIDA-I. Surface exposure of the cholera toxin B moiety was assessed by dot blot experiments and trypsin accessibility of the chimeric proteins expressed in Escherichia coli JK321 or UT5600. Export of cholera toxin B strictly depended on a complete predicted beta-barrel region. The absolute necessity for export of a linking region and its influence on expression as an integral part of the TU was also demonstrated. The different electrophoretic mobilities of native and denatured chimeras indicated that the proposed beta-barrel resides within the C-terminal 312 amino acids of AIDA-I. Together these data provide evidence for the predicted beta-barrel structure and support our formerly proposed model of membrane topology of the AIDA-I autotransporter.

Characterization and intracellular trafficking pattern of vacuoles containing Chlamydia pneumoniae in human epithelial cells

Chlamydiae are obligate intracellular pathogens that reside within a membrane-bound vacuole throughout their developmental cycle. In this study, the intraphagosomal pH of Chlamydia pneumoniae (Cpn) was qualitatively assessed, and the intracellular fate of the pathogen-containing vacuole and its interaction with endocytic organelles in human epithelial cells were analysed using conventional immunofluorescence and confocal microscopy. The pH-sensitive probes acridine orange (AO), LysoTracker (LyT) and DAMP did not accumulate in the bacterial inclusion. In addition, exposure of cells to bafilomycin A1(BafA1), a potent acidification inhibitor, did not inhibit or delay chlamydial growth. The chlamydial compartment was not accessible to the fluid-phase tracer Texas Red (TR)-dextran and did not exhibit any level of staining for the late endosomal marker cation-independent mannose-6-phosphate receptor (Ci-M6PR) or for the lysosomal-associated membrane proteins (LAMP-1 and -2) and CD63. In addition, transferrin receptor (TfR)-enriched vesicles were observed close to Cpn vacuoles, potentially indicating a specific translocation of these organelles through the cytoplasm to the vicinity of the vacuole. We conclude that Cpn, like other chlamydial spp., circumvents the host endocytic pathway and inhabits a non-acidic vacuole, which is dissociated from late endosomes and lysosomes, but selectively accumulates early endosomes.

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

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

Tyrosine phosphatase SHP-1 is involved in CD66-mediated phagocytosis of Opa52-expressing Neisseria gonorrhoeae

Opa proteins of Neisseria gonorrhoeae bind to CD66 receptors on human phagocytes, thereby inducing efficient uptake of the bacteria in the absence of opsonins. The interaction of Opa proteins and CD66 receptors leads to activation of Src family tyrosine kinases, a process that is of critical importance for the efficient, CD66-mediated internalization. Here we show that during Opa-mediated stimulation of CD66 the activity of the host cell tyrosine phosphatase SHP-1 is strongly downregulated, concomitant with increases in the tyrosine phosphorylation of several cellular proteins. Since the SHP-1 tyrosine phosphorylation level itself is influenced by Opa-induced events, this phosphatase comprises an important regulatory checkpoint of the pathogen-triggered signaling cascade in human phagocytes.