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,
Departments of
*
Pediatrics and
Microbiology and Immunology, and
The Sealy Center for Molecular Sciences, University of Texas Medical Branch, Galveston, TX 77555;
Department of Infectious Diseases and Microbiology, Imperial College School of Medicine, London, United Kingdom; and
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AstraZeneca R&D Boston, Waltham, MA 02451
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Several studies suggest that the manifestation of peptic gastroduodenal disease is partly attributed to the presence of a cluster of genes within a region referred to as the cag pathogenicity island (PAI)3 (2, 4, 5). The presence of the cag PAI is not only associated with the more severe disease manifestations of infection but also contributes to the modulation of local immune-inflammatory response (6, 7, 8). Although both cag PAI-positive and -negative strains can persistently infect subjects, 70–90% of infected subjects carry cag PAI-positive strains (3). The overwhelming predominance of the cag PAI-positive strains implies that these strains have a selective advantage in growth or in their ability to cope with the host immune response. Given the association between the cag PAI and disease, it is important to understand the interaction between these strains and the host response to facilitate the design of effective vaccines.
Studies have identified both H. pylori Ag-specific Abs and T cell clones in infected patients (9, 10). However, these responses cannot clear a natural infection and, in fact, both B cell (11) and T cell (12, 13) responses induced during natural infection have been implicated as a cause of epithelial cell damage and the pathogenesis of gastroduodenal disease. Most of the T cells associated with infection are of the Th1 type (10, 14, 15, 16, 17, 18). Thus the failure of the host response to clear infection may in part be due to the type of immune response that is induced. Furthermore, H. pylori may evade host responses through the inhibition of Ag-specific T cell proliferation. Early reports have suggested that T cells exposed to H. pylori are impaired in their ability to proliferate (9, 14, 19, 20). More recently, Koyama and colleagues (21) have reported that gastric T cells express Fas ligand (FasL) and undergo apoptosis in situ. Although the effect of H. pylori on epithelial cell health has been investigated widely (22), there are essentially no studies describing a mechanism by which T cell responses are impaired. Therefore, the current studies have investigated the mechanisms by which cag PAI-bearing strains of H. pylori limit host immunity through the induction of T cell death as a means of immune evasion.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Mouse-anti-human CD95 IgG (clone ZB4) and IgM (clone CH11) were purchased from Kamiya Biomedical (Thousand Oaks, CA). PE-conjugated anti-human CD95 Ab (clone DX2) and all isotype controls (mouse IgG, IgM, and rabbit Ig) were purchased from PharMingen (San Diego, CA). Rabbit anti-human FasL (Santa Cruz Biotechnology, Santa Cruz, CA) was used in the detection of FasL by flow cytometry, whereas mouse anti-human FasL Ab (clone 33), purchased from Transduction Laboratories (Lexington, KY), was used to detect FasL by Western blotting. Recombinant H. pylori urease was provided by Oravax (Cambridge, MA) (23). The caspase 8 inhibitor (Z-IETD) was purchased from Enzyme Systems Products (Torrance, CA). The protein synthesis inhibitor for eukaryotic cells, emetine, and the metalloproteinase inhibitor 1,10-phenanthroline (PHE) were purchased from Sigma (St. Louis, MO).
Bacteria and cell lines
Bacteria.
H. pylori cagA+ strain ATCC 26695 and a
cagA-deficient isogenic knockout strain 8-1 were provided by
D. Berg (Washington University School of Medicine, St. Louis, MO)
(24). LC-11 (a cag-positive strain) was
obtained from a subject with duodenal ulceration as described
previously (25), whereas AH 244 (a naturally occurring
strain lacking cagA and cagE) was obtained from
R. Alms (AstraZeneca, Boston, MA). A nongastric pathogen,
Campylobacter jejuni, originally obtained from the American
Type Culture Collection (ATCC) (33291; Manassas, VA), was provided by
the Microbiology Laboratories in the Department of Pathology at the
University of Texas Medical Branch. Both species of bacteria were grown
on blood agar plates at 37°C as described previously
(25). Bacteria were harvested on day 3 into 10 ml of
sterile PBS (pH 7.4). After centrifugation at 2500 x g
for 15 min, bacteria were resuspended in PBS while the supernatants
were collected and diluted 1/4 with growth medium before being used to
stimulate T cells as described below. Bacterial density was determined
by measuring the absorbance (A530 nm) using a DU-65 spectrophotometer
(Beckman Coulter, Fullerton, CA) and comparing the value to a standard
curve generated by quantifying viable organisms from aliquots of
bacteria at varying concentrations that were also assessed for
absorbance. One A530 OD unit was equivalent to 2 x
108 bacteria/ml. The motility of the bacteria was
confirmed by phase-contrast microscopy before experimental use. To
solubilize H. pylori, 108 freshly
cultured H. pylori were washed with PBS three times and
homogenized with a PRO200 post-mounted homogenizer (PRO Scientific,
Monroe, CO) at high speed (18,000–24,000 rpm) for 10 min on ice. After
centrifugation at 12,000 x g at 4°C, the supernatant
was collected and stored at -20°C. The protein concentration was
determined by measuring the absorbance (A280) using a DU-65
spectrophotometer (Beckman Coulter). One microgram of soluble whole Ag
was equivalent to 
106 viable H.
pylori.
T cell lines. The leukemia T cell line Jurkat cell (E6.1) was purchased from ATCC, whereas the CD4+ leukemia T cell clone CEM-C7 was provided by E. B. Thompson at the University of Texas Medical Branch. Both lines were cultured in RPMI 1640 supplemented with 10 mM HEPES buffer, 10 mM glutamine, and 10% FBS at 37°C. The gastric T cell line, 279, was isolated as previously described from gastric biopsies with H. pylori infection (16).
The BR-6 T cell line has a frame-shift mutation in exon 3 of one allele of the Fas gene that encodes the proximal amino terminus of the extracellular domain (26). Although some protein is expressed on the cell surface, this mutation renders it poorly responsive to Fas-mediated killing. The 279 and BR-6 T cells were cultured in RPMI 1640 containing 15% FCS, 10 mM HEPES, and 100 U/ml penicillin plus streptomycin, 10 ng/ml IL-2 (ICN Pharmaceuticals, Irvine, CA), and 10% PHA-stimulated lymphocyte supernatant. Subsequently, cells were fed with 5 mg/ml PHA (Difco, Detroit, MI) and irradiated B cells (3000 rad) every 2 wk.
Stimulation of T cell lines
Approximately 1.0 x 104 T cells were added to each well of a 96-well flat-bottom plate (Falcon, through BD Biosciences, Franklin Lakes, NJ). Subsequently, the plates were incubated for 24 h with the bacteria that were diluted to various bacteria-cell ratios using RPMI 1640 prepared as described above or a medium control. Preliminary experiments suggested that a ratio of 300 bacteria to 1 T cell was optimal. In other experiments, T cells were stimulated for 24 h with the supernatant of H. pylori prepared as described above at a dilution of 1/4 in RPMI 1640 or varying protein concentrations (1 pg to 1 µg) of sonicates of the bacteria diluted again, in RPMI 1640. After stimulation, T cells were washed and assayed as described below.
Examination of Fas and FasL expression by flow cytometry
Fas. To measure the expression of Fas receptor, T cells were harvested, washed, and stained with an optimal amount of PE-conjugated mouse anti-human Fas Ab (1 µg DX2) or PE-conjugated mouse IgG1 as an isotype control. Subsequently, cells were washed with PBS and 0.1% BSA and fixed in 1% paraformaldehyde in PBS before specific fluorescence was measured using a FACScan (BD Biosciences, San Jose, CA).
FasL. Because FasL protein is easily digested by metalloproteinase (27), T cells were cultured in medium containing only 2% FCS. The metalloproteinase inhibitor PHE (2.5 mM) was added to the medium in the last 4 h of culture. After harvesting the cells by centrifugation, cells were washed using PBS with 0.1% BSA and 2.5 mM of PHE, stained with mouse anti-human FasL (C-20) or isotype control (mouse IgG), and restained with FITC-conjugated anti-mouse IgG (PharMingen) as the second Ab. After fixation with 1% paraformaldehyde in PBS, specific fluorescence was measured using a FACScan. To examine the effect of H. pylori on FasL expression, T cells were incubated with H. pylori or the supernatant of broth culture at various doses and time points before FasL was detected by flow cytometry. To examine the inhibition of FasL expression by a protein synthesis inhibitor, T cells were pretreated with 10 mM emetine for 45 min before incubation with H. pylori.
Detection of FasL mRNA expression by RT-PCR
Extraction of total RNA and reverse transcription. Total RNA of T cell lines were extracted using TRIzol reagent (Life Technologies, Houston, TX) according to the protocol provided by the manufacturer as described previously (25). The purity and the amount of the RNA were determined by measuring absorbance at 260 and 280 nm using a DU-65 spectrophotometer (Beckman Coulter). cDNA was synthesized using superscript II reverse transcriptase and oligo(dT)s primer (Life Technologies, Gaithersburg, MD) at 42°C according to the protocol of the manufacturer.
Amplification of FasL.
Primers for FasL were designed according to the human gene sequences
(28) to generate a product of 344 bases in length.
-actin primers were purchased from Clontech Laboratories (Palo Alto,
CA) and yielded a product of 838 bases in length. The sequences of FasL
primers were as follows: FasL: sense primer:
5'-CAGCTCTTCCACCTACAGAAGG-3'; anti-sense primer:
5'-GAGAGACCAGTTAAAACTCCTTAGA-3'. The thermal cycling was as
follows: denaturation at 96°C for 15 s; annealing at 55°C for
30 s, and extension at 72°C for 150 s. Forty cycles were
performed. Primers were used at the final concentration of 0.1 µm
each in a 50-µl volume and the concentration of
Mg2+ was 1.5 mM. The PCR products were separated
on a 1.2% agarose gradient by electrophoresis and stained with
ethidium bromide.
Detection of FasL protein by Western blotting
T cells stimulated with H. pylori, PMA (10 ng/ml; Sigma), and ionomycin (500 ng/ml; Calbiochem) for indicated times were washed in ice-cold PBS and lysed for 10 min in 50 mM Tris-HCl, pH 7.6, containing 1% Nonidet P-40, 300 mM NaCl, and protease inhibitors (3 µg/ml leupeptin, 3 µg/ml aprotinin, and 2 mM PMSF). After centrifugation at 14,000 x g at 4°C, cellular protein concentration was determined. Twenty micrograms was loaded into each lane and separated by electrophoresis on a polyacrylamide gel with a 5% stacking gel and a 12% separating gel. Following the electrophoresis, proteins were transferred to a nitrocellulose membrane (Schleicher & Schuell, Keene, NH). Subsequently, the membrane was blocked with 5% nonfat milk in TBS overnight before incubation with 0.2 µg/ml of mouse anti-human FasL mAb (Transduction Laboratories) for 1 h. After three washings with TBS containing 0.05% Tween 20, the membrane was incubated with peroxidase-conjugated donkey anti-mouse IgG Ab (1/10,000 dilution) for 2 h and quantified using an ECL kit according to the manufacturer’s instructions (Amersham, Little Chalfont, U. K.). The pictures of Western blotting were scanned using an Alphaimager system, and the density of each band was measured using AlphaEase software (Alpha Innotech, San Leandro, CA).
Detection of apoptosis
Flow cytometry. T cells with or without H. pylori treatment were washed three times with PBS and incubated with 7-aminoactinomycin D (7-AAD, Sigma) and PE-conjugated annexin V (BD Biosciences) for 15 min and were assayed by flow cytometry within 1 h. In this assay, healthy cells will not bind annexin V or take up 7-AAD, whereas during the onset of apoptosis, cells can bind annexin V because they transfer a large amount of phospholipid phosphatidylserine from the inner leaflet of the plasma membrane to the outer leaflet (29).
JAM assay. A cytotoxicity assay (JAM assay) was used to evaluate the killing of T cells by H. pylori (30). Briefly, T cells (target cells = T) were labeled with 10 µCi/ml of [3H]thymidine (ICN Pharmaceuticals) for 12 h and seeded into 96-well plates at a concentration of 2 x 104 cells per well. H. pylori or its supernatant (effector = E) were cocultured with T cells at various E:T ratios for various times. To harvest the JAM test, cells and their media were aspirated onto fiberglass membranes using a cell harvester (Skatron, Sterling, VA). The degraded DNA was washed through the membrane and the undegraded, high m.w. DNA was left on the membrane. After drying the filters, liquid scintillation fluid was added and the samples were counted in a liquid scintillation counter (Beckman Coulter). The percent specific killing relative to medium-stimulated controls was calculated as (S - E)/S x 100, where the cpm in T cells exposed to control medium was defined as S and that of treated cells was defined as E.
To study the mechanism of H. pylori-mediated killing upon T cells, blocking anti-Fas Ab ZB4 or isotype control (mouse IgG) (500 ng/ml), caspase 8 inhibitor (100 µM Z-IETD), emetine (10 mM), or PHE (2.5 mM) were preincubated with 3H-labeled T cells for 1 h (ZB4, PHE, and caspase 8 inhibitor) or 45 min (emetine). After washing (ZB4 and emetine) or not (caspase 8 inhibitor and PHE), effector cells were added to the system and the specific killing was evaluated.
Statistical analyses
Results are expressed as the mean ± SEM. Specific killings were compared using a two-tailed Student’s t test and considered significant if p values were <0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To determine whether H. pylori can induce apoptosis of
T cells in vitro, two T cell lines, Jurkat (Fig. 1
) and CEM-C7 (data not shown) cells were incubated with viable
cagA+ H. pylori strain 26695 or
their bacterial supernatant, then double-stained with 7-AAD and annexin
V. As shown in Fig. 1A, H. pylori or bacterial
supernatants disrupted T cell membranes, permitting the binding of
annexin-V in Jurkat T cells. Cells binding annexin V also began to
stain with 7-AAD, indicating cell death. To confirm that this process
of cell death was due to apoptosis, the JAM assay was performed to
detect DNA fragmentation in T cells stimulated with medium, H.
pylori, or a related bacterium, C. jejuni. These data
showed that the Jurkat, CEM-C7, and the gastric T cell line, 279, were
more sensitive to killing by H. pylori than by C.
jejuni, (p < 0.05, Fig. 1B)
suggesting that this response was relatively specific to H.
pylori. Moreover, as little as 2 pg protein from H.
pylori bacterial sonicates/ml were capable of inducing T cell
apoptosis (data not shown), confirming that live bacteria were not
needed. Although previous studies have shown that H. pylori
urease is capable of inducing apoptosis in gastric epithelial cells
(23), 10–100 µg/ml of urease had no effect on T cell
death (data not shown).
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C). Other cag PAI-bearing strains of H.
pylori, including LC11, induced T cell death whereas
non-cag PAI-bearing such as AH244 did not (our unpublished
observation). Apoptosis of T cells induced by H. pylori is Fas-dependent
To determine whether Fas/FasL interactions were involved in
H. pylori-mediated killing of T cells, Fas expression of T
cells was examined. As shown in Fig. 2, the three T cell lines tested expressed high levels of Fas protein
constitutively. IgG anti-Fas mAb ZB4 blocked the interaction
between FasL and Fas and inhibited the killing of all three T cell
lines stimulated with H. pylori compared with the isotype
control (p < 0.05). In addition, H.
pylori-mediated killing was assessed in a T cell line, BR-6. This
cell line has a frame-shift mutation in open reading frame 3 of one
allele of the Fas gene that encodes the proximal amino
terminus of the extracellular domain (26). Although some
protein is expressed on the cell surface, this mutation renders it
poorly responsive to Fas-mediated killing. As shown in Fig. 3A, BR-6 expressed immunoreactive Fas protein. However, it was
resistant to anti-Fas IgM (CH11)-mediated apoptosis as well as
H. pylori-induced apoptosis (Fig. 3B). This
resistance to the induction of apoptosis occurred despite the fact that
FasL was present after stimulation (data not shown).
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). Although caspase 8 is also involved in signaling through the TNF
receptor, the absence of detectable TNF production by the H.
pylori-stimulated T cells (our unpublished observations) suggested
that the predominant signaling pathway was through Fas.
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Because FasL expression is increased in gastric mononuclear cells
in association with H. pylori infection (33),
the direct effect of H. pylori on FasL expression was
examined. T cells were stimulated with H. pylori 26695 and
8-1 or their supernatant, and FasL expression was detected by flow
cytometry. It was found that resting T cells lacked detectable surface
FasL expression. However, both viable H. pylori strain 26695
and its supernatant enhanced FasL expression by Jurkat T cells (Fig. 5A) and CEM-C7 cells (data not shown) as determined by flow
cytometry. In contrast, the isogenic mutant, 8-1, had virtually no
effect on FasL expression. These findings were confirmed by Western
blotting (Fig. 5B). As little as 2 pg protein from H.
pylori bacterial sonicates/ml were capable of inducing Fas L (data
not shown) again confirming that live bacteria were not needed.
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C, FasL mRNA was undetectable in resting CEM-C7 and Jurkat
T cells. However, after incubation with H. pylori 26695,
FasL expression was increased in both cell lines. Requirement of de novo protein synthesis in T cell apoptosis induced by H. pylori
Because FasL was undetectable on the Jurkat or CEM-C7 T cells
before stimulation with H. pylori, the dependence of the
cell death on new protein synthesis was determined. As shown in Fig. 6, FasL expression by Jurkat T cells increased after 5–7 h (Fig. 6, A and B) of incubation with H. pylori,
concomitant with the induction of apoptosis by H. pylori
(Fig. 6C). Similar kinetics for FasL induction and T cell
killing were observed in CEM-C7 cells (data not shown). Moreover, the
protein synthesis inhibitor, emetine, inhibited FasL expression by T
cells as well as the induction of apoptosis (Fig. 7). These results suggested that H. pylori-induced killing of
T cells required de novo FasL protein synthesis.
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), thereby further implicating the role of FasL in mediating the
induction of apoptosis.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The Fas/FasL interaction has been described as being responsible for depleting immature, autoimmune T cells in the thymus and mature T cells in the periphery (34, 35). Thus, the ZB4 Ab that binds to Fas and prevents its activation by FasL (36) was used to show that T cell death is dependent on signaling through the Fas receptor. This notion was consistent with the lack of apoptosis in the mutant Fas T cell line, BR-6. Moreover, inhibition of caspase 8 did block the activation of downstream caspases and the ensuing degradation of DNA while inhibition of the metalloproteinase that cleaves FasL increased apoptosis. The finding that H. pylori killing required de novo synthesized protein including FasL and that the killing did not occur immediately after the coculture of the bacterium with T cells helped to exclude the possibility that H. pylori could directly interact with Fas that was constitutively expressed on T cells. These observations, along with the absence of detectable TNF production by the H. pylori-stimulated T cells (our unpublished observations) provided substantial evidence for the role of Fas signaling in mediating the T cell death after exposure to H. pylori.
Several studies have shown that apoptosis is increased in gastric
epithelium in situ in response to natural infection with H.
pylori (37, 38). Epithelial cells undergo apoptosis
in response to bacteria alone although this response is augmented by
inflammatory cytokines such as IFN-
and TNF-
(12, 33, 39). Th1 cytokines such as IFN- can also cause an increase in
the expression of class II MHC molecules, which serve as receptors for
H. pylori and signal apoptosis (12).
The mechanism of apoptosis in gastric epithelial cells differs from that in T cells based on several observations. First of all, stimulation with viable strains of H. pylori with or without the cag PAI induce apoptosis in epithelial cells (S. Crowe, manuscript in preparation), whereas T cell death was only observed using the cag PAI-bearing strains of the bacteria. In most epithelial cell lines tested to date, the killing is dependent on the bacteria binding to class II MHC (12). In contrast, the T cells used in this study did not express class II MHC. Moreover, urease is sufficient to induce apoptosis in gastric epithelial cell lines (23) but does not induce cell death in T cells. H. pylori has been shown to increase the expression of Fas on gastric epithelial cells (40, 41, 42), which is fully capable of triggering cell death by adjacent T cells expressing FasL (13). However, unlike T cell responses, induction of FasL in epithelial cells is modest and most of the epithelial cell death cannot be inhibited by blocking the Fas receptor (33). Thus, H. pylori can induce cell death in cells of different lineage using a variety of mechanisms. However, in T cells, the response appears to be highly dependent on the induction of FasL by the cag PAI-bearing strains of H. pylori.
Although the current studies focused on in vitro experiments, the results are supported by the observation that T cells undergo apoptosis during infection as evidenced by TUNEL staining of biopsy specimens (21). Furthermore, mononuclear cells including lymphocytes in the human gastric lamina propria can express Fas and FasL during infection (13, 21). Clearly, human, gastric T cells expressing FasL can induce apoptosis in gastric epithelial cells expressing Fas (13) and likely can extend this killing to adjacent T cells that also express the Fas receptor. The consequences of this may include a relatively rapid turnover of T cells that are responding to the infection.
Although most of the bacteria reside in the lumen during natural infection, immunoreactive H. pylori Ags have been detected in the lamina propria (43) and, therefore, could contribute to the expansion of Ag-specific T cells. Indeed, investigators have successfully grown T cell clones that can recognize some H. pylori Ags (10, 15, 44, 45, 46). However, the generation of Ag-specific clones requires polyclonal expansion using high doses of IL-2 (50 U/ml) or potent polyclonal activators (10, 15, 44, 45). The fact that H. pylori induced apoptosis in T cells is consistent with other reports demonstrating that proliferation of mononuclear cells from infected subjects is modest and always lower than that observed using responder cells from uninfected subjects (47, 48). Moreover, H. pylori Ags inhibit T cell growth in vitro (19, 20, 31). As little as 2 pg protein from bacterial sonicates/T cell were capable of inducing T cell apoptosis. Thus, Ag-specific T cell responses may exist in a limited fashion although small concentrations of H. pylori products reach the lamina propria and could impair T cell reactivity.
Interestingly, we found that the induction of FasL and specific killing
by cag PAI-deficient H. pylori were much lower
than those of the cag PAI-positive strain, implicating a
role for cag PAI-associated proteins in this process. The
role of cag PAI proteins is of particular interest because
most humans are infected with strains bearing the cag PAI,
and infection with these strains has been associated with more severe
diseases such as gastroduodenal ulcers or gastric cancer in certain
geographic regions (1, 2). Recent studies demonstrate that
the type IV secretion engine encoded by genes within the cag
PAI delivers the CagA protein from the bacteria into the host cell
(49), leading to the phosphorylation of host and microbial
proteins within the host cells (50). These phosphoproteins
may activate transcription factors, including NF-
B, and
subsequently, enhance the expression of proinflammatory genes
(51, 52, 53). Binding sites for NF-B have been identified
in the promoter region of FasL gene (54) implying that
H. pylori may boost FasL expression as a consequence of
NF-B activation. Experiments are in progress to evaluate the
regulation of gene transcription in T cells activated by H.
pylori.
Because sonicates or supernatants from the bacteria are sufficient to kill the T cells, live bacteria are not required and some effector molecule is sufficient. Although the cag PAI appears essential for the induction of apoptosis in T cells, it is unclear which gene product is responsible for the response. A recent report suggests that the cagA gene is directly responsible for the inhibition of T cell responses to PHA (20). The transport of the CagA protein into the host cell may play a role in regulating FasL expression and the induction of apoptosis described herein; however, other proteins may be imported via this pathway and contribute to the induction of cell death. For example, the product of the recently described oip gene that regulates inflammation (55) may also play a role in a cag-dependent pathway. The role of CagA and other proteins in regulating the T cell response to H. pylori is currently under investigation.
In summary, this report describes the ability of H. pylori to induce death in T cells through Fas/FasL interactions. The fact that the induction of apoptosis was restricted to H. pylori bearing the cag PAI and not observed with cag PAI-deficient strains or C. jejuni suggests that it is a specific mechanism of immune evasion. Because cag PAI strains predominate in humans, it is possible that this ability to induce apoptosis in T cells confers a selective advantage that complements other mechanisms favoring the persistent growth and survival of these strains.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Peter B. Ernst, Children’s Hospital Room 2.300, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0366. E-mail address: pernst{at}utmb.edu
3 Abbreviations used in this paper: PAI, pathogenicity island; FasL, Fas ligand; PHE, 1,10-phenanthroline; 7-AAD, 7-aminoactinomycin D.
Received for publication January 9, 2001. Accepted for publication May 7, 2001.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and interleukin 1 up-regulate gastric mucosal Fas antigen expression in Helicobacter pylori infection. Infect. Immun. 68:1189.B activation. Infect. Immun. 66:2346.B in gastric epithelial cells. Gastroenterology 113:1099.[Medline]
B in gastric epithelial cells. J. Immunol. 160:2401.B sites in mouse CD95 ligand (Fas ligand) promoter: functional analysis in T cell hybridomas. J. Immunol. 161:3469.This article has been cited by other articles:
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  E. J. Beswick, I. V. Pinchuk, S. Das, D. W. Powell, and V. E. Reyes Expression of the Programmed Death Ligand 1, B7-H1, on Gastric Epithelial Cells after Helicobacter pylori Exposure Promotes Development of CD4+ CD25+ FoxP3+ Regulatory T Cells Infect. Immun., September 1, 2007; 75(9): 4334 - 4341. [Abstract] [Full Text] [PDF]
|
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 |
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 |
|
 H. M. S. Algood and T. L. Cover Helicobacter pylori Persistence: an Overview of Interactions between H. pylori and Host Immune Defenses Clin. Microbiol. Rev., October 1, 2006; 19(4): 597 - 613. [Abstract] [Full Text] [PDF]
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J. G. Kusters, A. H. M. van Vliet, and E. J. Kuipers Pathogenesis of Helicobacter pylori Infection Clin. Microbiol. Rev., July 1, 2006; 19(3): 449 - 490. [Abstract] [Full Text] [PDF]
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 |
|
 F. I. Bussiere, R. Chaturvedi, M. Asim, K. L. Hoek, Y. Cheng, J. Gainor, A. Scholz, W. N. Khan, and K. T. Wilson Low Multiplicity of Infection of Helicobacter pylori Suppresses Apoptosis of B Lymphocytes. Cancer Res., July 1, 2006; 66(13): 6834 - 6842. [Abstract] [Full Text] [PDF]
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|
 |
|
 J. Y. Kao, S. Rathinavelu, K. A. Eaton, L. Bai, Y. Zavros, M. Takami, A. Pierzchala, and J. L. Merchant Helicobacter pylori-secreted factors inhibit dendritic cell IL-12 secretion: a mechanism of ineffective host defense Am J Physiol Gastrointest Liver Physiol, July 1, 2006; 291(1): G73 - G81. [Abstract] [Full Text] [PDF]
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 |
|
 E. Yamasaki, A. Wada, A. Kumatori, I. Nakagawa, J. Funao, M. Nakayama, J. Hisatsune, M. Kimura, J. Moss, and T. Hirayama Helicobacter pylori Vacuolating Cytotoxin Induces Activation of the Proapoptotic Proteins Bax and Bak, Leading to Cytochrome c Release and Cell Death, Independent of Vacuolation J. Biol. Chem., April 21, 2006; 281(16): 11250 - 11259. [Abstract] [Full Text] [PDF]
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R. Chaturvedi, Y. Cheng, M. Asim, F. I. Bussiere, H. Xu, A. P. Gobert, A. Hacker, R. A. Casero Jr., and K. T. Wilson Induction of Polyamine Oxidase 1 by Helicobacter pylori Causes Macrophage Apoptosis by Hydrogen Peroxide Release and Mitochondrial Membrane Depolarization J. Biol. Chem., September 17, 2004; 279(38): 40161 - 40173. [Abstract] [Full Text] [PDF]
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J. Zabaleta, D. J. McGee, A. H. Zea, C. P. Hernandez, P. C. Rodriguez, R. A. Sierra, P. Correa, and A. C. Ochoa Helicobacter pylori Arginase Inhibits T Cell Proliferation and Reduces the Expression of the TCR {zeta}-Chain (CD3{zeta}) J. Immunol., July 1, 2004; 173(1): 586 - 593. [Abstract] [Full Text] [PDF]
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R. J. Menaker, P. J. M. Ceponis, and N. L. Jones Helicobacter pylori Induces Apoptosis of Macrophages in Association with Alterations in the Mitochondrial Pathway Infect. Immun., May 1, 2004; 72(5): 2889 - 2898. [Abstract] [Full Text] [PDF]
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S. Wen, C. P. Felley, H. Bouzourene, M. Reimers, P. Michetti, and Q. Pan-Hammarstrom Inflammatory Gene Profiles in Gastric Mucosa during Helicobacter pylori Infection in Humans J. Immunol., February 15, 2004; 172(4): 2595 - 2606. [Abstract] [Full Text] [PDF]
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S. Kim, W. J. McAuliffe, L. S. Zaritskaya, P. A. Moore, L. Zhang, and B. Nardelli Selective Induction of Tumor Necrosis Receptor Factor 6/Decoy Receptor 3 Release by Bacterial Antigens in Human Monocytes and Myeloid Dendritic Cells Infect. Immun., January 1, 2004; 72(1): 89 - 93. [Abstract] [Full Text] [PDF]
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D. J. Mitchell, H. Q. Huynh, P. J. M. Ceponis, N. L. Jones, and P. M. Sherman Helicobacter pylori Disrupts STAT1-Mediated Gamma Interferon-Induced Signal Transduction in Epithelial Cells Infect. Immun., January 1, 2004; 72(1): 537 - 545. [Abstract] [Full Text] [PDF]
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F. Meyer, K. S. Ramanujam, A. P. Gobert, S. P. James, and K. T. Wilson Cutting Edge: Cyclooxygenase-2 Activation Suppresses Th1 Polarization in Response to Helicobacter pylori J. Immunol., October 15, 2003; 171(8): 3913 - 3917. [Abstract] [Full Text] [PDF]
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A. Lundgren, E. Suri-Payer, K. Enarsson, A.-M. Svennerholm, and B. S. Lundin Helicobacterpylori-Specific CD4+ CD25high Regulatory T Cells Suppress Memory T-Cell Responses to H. pylori in Infected Individuals Infect. Immun., April 1, 2003; 71(4): 1755 - 1762. [Abstract] [Full Text]
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A. A. Akhiani, J. Pappo, Z. Kabok, K. Schon, W. Gao, L. E. Franzen, and N. Lycke Protection Against Helicobacter pylori Infection Following Immunization Is IL-12-Dependent and Mediated by Th1 Cells J. Immunol., December 15, 2002; 169(12): 6977 - 6984. [Abstract] [Full Text] [PDF]
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 S. Suerbaum and P. Michetti Helicobacter pylori Infection N. Engl. J. Med., October 10, 2002; 347(15): 1175 - 1186. [Full Text] [PDF]
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 H Eguchi and S F Moss Helicobacter pylori Mol. Pathol., October 1, 2002; 55(5): 284 - 285. [Full Text] [PDF]
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N. L. Jones, A. S. Day, H. Jennings, P. T. Shannon, E. Galindo-Mata, and P. M. Sherman Enhanced Disease Severity in Helicobacter pylori-Infected Mice Deficient in Fas Signaling Infect. Immun., May 1, 2002; 70(5): 2591 - 2597. [Abstract] [Full Text] [PDF]
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R. Rad, M. Gerhard, R. Lang, M. Schoniger, T. Rosch, W. Schepp, I. Becker, H. Wagner, and C. Prinz The Helicobacter pylori Blood Group Antigen-Binding Adhesin Facilitates Bacterial Colonization and Augments a Nonspecific Immune Response J. Immunol., March 15, 2002; 168(6): 3033 - 3041. [Abstract] [Full Text] [PDF]
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