Skip to main content Accessibility help
×
Home

Information:

  • Access
  • Cited by 1

Actions:

      • Send article to Kindle

        To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

        Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

        Find out more about the Kindle Personal Document Service.

        Gastric lymphoma: association with Helicobacter pylori outer membrane protein Q (HopQ) and cytotoxic-pathogenicity activity island (CPAI) genes
        Available formats
        ×

        Send article to Dropbox

        To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

        Gastric lymphoma: association with Helicobacter pylori outer membrane protein Q (HopQ) and cytotoxic-pathogenicity activity island (CPAI) genes
        Available formats
        ×

        Send article to Google Drive

        To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

        Gastric lymphoma: association with Helicobacter pylori outer membrane protein Q (HopQ) and cytotoxic-pathogenicity activity island (CPAI) genes
        Available formats
        ×
Export citation

Summary

B-cell non-Hodgkin lymphoma (B-cell NHL) is the second commonest malignancy in the stomach. We determined the distribution of Helicobacter pylori outer membrane protein Q (HopQ) allelic type, cytotoxin-associated gene (cag)-pathogenicity activity island (cag-PAI) and vacuolation activating cytotoxin A (vacA) genes, respectively, in patients with B-cell NHL. We also compared them with their distribution in non-ulcer dyspepsia (NUD). H. pylori was cultured from gastric biopsy tissue obtained at endoscopy. Polymerase chain reaction was performed. Of 170 patients enrolled, 114 (63%) had NUD and 56 (37%) had B-cell NHL. HopQ type 1 was positive in 66 (58%) in NUD compared with 46 (82%) (P = 0·002) in B-cell NHL; HopQ type 2 was positive in 93 (82%) with NUD compared with 56 (100%) (P < 0·001) in B-cell NHL. Multiple HopQ types were present in 46 (40%) in NUD compared with 46 (82%) (P < 0·001) in B-cell NHL. CagA was positive in 48 (42%) in NUD vs. 50 (89%) (P < 0·001) in B-cell NHL; cagT was positive in 35 (31%) in NUD vs. 45 (80%) (P < 0·001) in B-cell NHL; left end of the cagA gene (LEC)1 was positive in 23 (20%) in NUD vs. 43 (77%) (P < 0·001) in B-cell NHL. VacAs1am1 positive in B-cell NHL in 48 (86%) (P < 0·001) vs. 50 (44%) in NUD, while s1am2 was positive in 20 (17%) in NUD vs. 46 (82%) (P < 0·001) in B-cell NHL. H. pylori strains with multiple HopQ allelic types, truncated cag-PAI evidenced by expression of cagA, cagT and cag LEC with virulent vacAs1 alleles are associated with B-cell NHL development.

INTRODUCTION

Helicobacter pylori (H. pylori) is a common pathogen associated with human gastric and extragastric diseases. The failure of the host immune response to clear this infection results in chronicity. H. pylori infection is associated with the gastro-duodenal diseases that include chronic gastritis, peptic ulcer, i.e. gastric and duodenal ulcer, gastric carcinoma (GC) and mucosa-associated lymphoid tissue lymphoma (MALToma) [1]. H. pylori infection elicits an acute-phase response that activates an immune host response causing an imbalance between cell proliferation and cell apoptosis [2]. The gastric colonization of H. pylori depends on several factors that include urease enzyme, cytotoxin-associated geneA (cagA), vacuolating cytotoxin A (vacA) and H. pylori outer membrane proteins [3]. The genetic diversity among H. pylori strains accounts for varying manifestations among persons colonized with H. pylori [4]. The virulence of H. pylori is determined by markers, e.g. the cytotoxin-associated gene pathogenicity island (cag-PAI), vacA alleles, outer immunoproteinA and membrane protein Q (HopQ) type [59].

The genetic diversity in H. pylori is associated with high mutation rate [10, 11]. Infection with multiple strains promotes recombination between them. Genes encoding H. pylori outer membrane proteins are significant among the imported DNA fragments [10]. H. pylori genome sequences possess a large family of Hop genes [12]. H. pylori strains expressing HopQ have facilitated attachment to gastric epithelial cells [13]. Previously, we studied 241 H. pylori strains that showed HopQ type 1 in 70 (29%), type 2 in 60 (25%), and types 1 and 2 in 111 (46%) strains, respectively [5].

H. pylori infection predates the development of gastric lymphoma [6]. Previously, an association between H. pylori and gastric low-grade B-cell non-Hodgkin lymphoma (B-cell NHL) was described [14]. H. pylori was less common in high-grade gastric B-cell NHL in 38–51% with no specific mucosa-associated lymphoid tumor (MALT) features [6, 14]. H. pylori infection causes a chronic immuno-inflammatory reaction. This antigenic stimulation leads to lymphoid hyperplasia and acquisition of genetic instability, which follows activation of intracellular pathways [15]. The disease progresses with cellular proliferation, resistance to apoptosis and emergence of a malignant clone [15].

Ours is a low-risk region for GC with a high prevalence of H. pylori infection [16]. In a retrospective study that looked at the GC over a period of 10 years, 42 (11%) were cases of B-cell NHL [16]. In the current study, we determined the distribution of H. pylori and its virulence marker, i.e. cagA, cagAP, cagE, cagT, LEC, vacA alleles, and HopQ types 1 and 2 in B-cell NHL and compared their distribution with H. pylori strains associated with non-ulcer dyspepsia (NUD) and chronic gastritis.

MATERIAL AND METHODS

Patients

One hundred and seventy patients with upper gastrointestinal symptom that included abdominal pain were enrolled from the endoscopy unit extending from November 2012 to June 2016. Their mean age was 48 ± 13 years and range 21–83, male:female ratio was 1·4:1. Ours is a tertiary care center where the healthcare facilities are being availed by patients from all over the country. The hospital is located in a cosmopolitan city with an urban population of over 16 618 million in 2015. Population has varying ethnicity contributed by all the provinces of the country. Socio-economic status (SES) of majority of our patients varies from low to middle SES. One hundred and fourteen (67%) were diagnosed as NUD and in 56 (33%) B-cell NHLs. Other NHL subtypes, e.g. follicular, mantle, etc. were not found in this cohort of patients. Institutional ethics committee approved the study. Informed consent was obtained from all patients. The patients enrolled were not on any medications, such as antibiotics, H2-receptor antagonists, proton pump inhibitors, bismuth compounds in the last 3 months. A note was made of presenting symptoms and endoscopic findings (Table 1). Two gastric biopsies for histology were collected in formalin and four in normal saline two each for H. pylori culture and polymerase chain reaction (PCR). The PCR for HopQ alleles identified in H. pylori were single (i.e. type 1 or type 2) or multiple types (i.e. type 1 and type 2). CagA, cagA-promoter region (cagAP), cagE, cagT, left end of the cagA gene (LEC) and vacA alleles, i.e. s1a, s1b, m1, m2 and s2 were analyzed. Patients with H. pylori infection were treated with Bismuth-based quadruple therapy, while patients diagnosed with B-cell NHL were referred to oncologist for further management.

Table 1. Comparison of patients with non-ulcer dyspepsia and non-Hodgkin B cell lymphoma

H. pylori culture

Each specimen was homogenized in eppendorf tubes with electric homogenizer and inoculated onto Columbia blood agar (Oxoid) medium supplemented with Dents supplement (containing trimethoprim, vancomycin, amphotericin B and cefsulodin) and 7% defibrinated sheep blood and incubated at 37 °C under microaerophilic conditions using anaerobic jars and strips (Campygen strips, Oxoid, UK) for 5 days producing microaerophilic conditions essential for the growth. Plates were then examined for bacterial growth. The identity of H. pylori was confirmed by colony morphology, Gram stain and production of urease and catalase. H. pylori isolates were defined as Gram-negative spiral-shaped bacilli that were urease and catalase positive.

Histology

An expert pathologist, unaware of the clinical details, reviewed all the biopsies and reported the diagnosis. All cases were shown to be of B-cell phenotype by immunochemistry with a panel of antibodies that included CD20, CD19, CD79a, CD22 and CD3. Diagnosis of B-cell NHLs was based on a positive CD20, CD19, CD79a and CD22· [17]. The criteria used for the diagnosis of B-cell NHL included diffuse sheets of large, blastic lymphoid cells, two to four times larger than normal lymphocytes, often infiltrating and destroying the gastric glandular architecture. Criteria for diagnosis of low-grade lymphoma of MALT type were as defined consisting of a diffuse proliferation of cells with epithelium infiltration forming characteristic lymphoepithelial lesions [18]. High-grade tumors were diffuse infiltrates of large blast cells [19]. Following endoscopy patients underwent whole-body computerized tomographic scan to determine the extent of involvement. Patients were referred to oncology service for further management. There were 15 cases of low-grade and 41 of high-grade B-cell NHL. Paraffin-coated gastric tissues were stained with hematoxylin and eosin to study histopathology and H. pylori [20].

Extraction of genomic DNA

DNA was extracted from gastric biopsy tissue as previously described [21].

PCR

Amplification of 16S rRNA, cagA, cagAP, cagE, cag LEC and cagT and vacA alleles by PCR was performed by the method previously used before [22] (Table 2).

Table 2. Primers used in PCR experiments

HopQ genotyping

The HopQ type 1 and type 2 were determined by PCR methods described previously [23] (Table 2).

Sequencing of PCR product and BLAST Query

Sequence analysis was carried out by Macrogen (Seoul, South Korea). HopQ type 1 and type 2 sequences were published in our previous study and deposited in GenBank with accession numbers (KJ946296-KJ946308) and (KJ946309-KJ946314), respectively [5].

Sample size

The study determined the distribution of HopQ types in patients with B-cell NHL. From previous studies, H. pylori was present in 46% B-cell NHL [24] HopQ type 1 in GC in 53% and type 2 isolates in NUD in 41% [5]. Gastric ulcers were associated with H. pylori infection with multiple HopQ alleles in 46% compared with 23% with HopQ type 1. Therefore, the frequency of 46% with 95% level of confidence and (0·074) 7% bound on the error of estimation, a sample size of 175 patients was required. A total of 134 patients were required to establish their association with gastritis with 80% power. A sample size of 175 patients was required to cover both the study objectives.

Statistical analysis

Pearson χ 2, Fisher exact or likelihood ratio test were used where appropriate. A P value of <0·05 was significant. Data were analyzed using the SPSS version 19.0.

RESULTS

Patients with NUD were significantly younger than with B-cell NHL (Table 1). Abdominal pain was also significantly common in patients with NUD (Table 1). Endoscopically, there was gastritis in 114 (100%) NUD patients, while in B-cell NHL, there was a mass lesion 51 (91%) (P < 0·001). On histology, H. pylori was positive in 70 (61%) with NUD compared with 19 (34%) (P = 0·001) with B-cell NHL (Table 1). Lymphoid aggregates were common in B-cell NHL 56 (100%) compared with 40 (35%) (P < 0·001) in NUD (Table 1). Majority of B-cell NHL were diffuse large B cell that were high grade 41 (73%) with 30 out of 41 having >90% proliferative index (Table 3).

Table 3. Distribution of non-Hodgkin B-cell lymphoma

n (%), number and percentage.

HopQ allelic type

HopQ type 1 was positive in 66 (58%) in NUD compared with 46 (82%) (P = 0·002) in B-cell NHL; while HopQ type 2 was positive in 93 (82%) with NUD compared with 56 (100%) (P < 0·001) in B-cell NHL (Table 1). Single HopQ allele was present in 69 (60%) with NUD compared with 10 (18%) in B-cell NHL, while multiple HopQ was present in 46 (40%) in NUD compared to 46 (82%) (P < 0·001) in B-cell NHL (Table 1).

Cag-PAI gene

CagA was positive in 48 (42%) in NUD compared with 50 (89%) (P < 0·001) in B-cell NHL; cagT was positive in 35 (31%) in NUD compared with 45 (80%) (P < 0·001) in B-cell NHL; cag LEC1 was positive in 23 (20%) in NUD compared with 43 (77%) (P < 0·001) in B-cell NHL; while cag LEC2 was positive in 7 (6%) in NUD compared with 27 (48%) (P < 0·001) in B-cell NHL (Table 4).

Table 4. Comparison of Helicobacter pylori virulence groups marker in different

n (%), number and percentage.

VacA alleles

VacAs1am1 was positive in B-cell NHL in 48 (86%) (P < 0·001) compared with 50 (44%) in NUD, while s1bm1 was positive in 31 (55%) (P < 0·001) in B-cell NHL compared with 19 (17%) in NUD; s1am2 was positive in 20 (17%) in NUD compared with 46 (82%) (P < 0·001) in B-cell NHL; while s1bm2 was positive in 2 (2%) in NUD and in 33 (59%) (P < 0·001) in B-cell NHL (Table 4).

DISCUSSION

PCR for the H. pylori 16S rRNA PCR did not demonstrate any difference in the association of H. pylori with NUD and B-cell NHL (Table 3). This is particularly likely if H. pylori tested on the biopsy obtained from the B-cell NHL involved area, which may be necrotic and has low H. pylori load. PCR for H. pylori is known to have a higher yield [25]. Chronic active gastritis was predominant in both groups (Table 1). Infiltration of the gastric mucosa with neutrophils and lymphocytes leads to increased apoptosis and clearance of epithelial cell. H. pylori-induced macrophages and dendritic cells (DCs) that are known to secrete tumor necrosis factor-α that further promote inflammation [26]. After activation via Toll-like receptors, DCs are known to activate T cells to Th1 or Th2 response by expression of interleukin (IL)-12 or IL-10, respectively [27]. Dendritic cells exposed to H. pylori for 48 h exhibited a markedly attenuated ability to induce interferon-γ production that contributed to the persistence of the infection [28].

HopQ has a role in the pathogenesis of gastric B-cell NHL as it promotes attachment of the H. pylori to the epithelial cells. H. pylori binds to host cell receptors via adhesion molecule of the carcinoembryonic antigen (CEACAM) located on the gastric epithelial cell membrane to translocate cagA into host cells [29]. Multiple types of HopQ types were associated with B-cell NHL compared with the NUD (Table 1). In patients with B-cell NHL, both HopQ type 1 and HopQ type 2 were present and a multiplicity of the HopQ types was demonstrated in 82% of B-cell NHL (Table 1). In an animal study, naïve B cell exposed to H. pylori demonstrated a biphasic response in which low multiplicity of infection (MOI) (1–10) induced cellular proliferation and markedly inhibited apoptosis [30, 31]. Low levels of H. pylori infection that occur in vivo are associated with B-cell survival and proliferation, consistent with their potential to evolve into MALToma. The difference in the clinical outcome was not only due to the longer duration of the H. pylori infection in the B-cell NHL but was also contributed to by the virulence of the infecting H. pylori strains.

The limitation of this study is that we did not do immunohistochemical (IHC) staining to detect the genetic aberrations such as t(11;18)(q21;q21) and t(1;14)(p22;q32) that are associated with H. pylori-independent B-cell NHL [32]. For patients without t(11;18)(q21;q21) or t(1;14)(p22;q32), nuclear translocation of BCL10 and nuclear factor-κB (NF-κB) detected by IHC is predictive of H. pylori-independent state [33]. CagA expression in tumor cells, particularly with nuclear expression is a useful biomarker in lymphoma cells, and is associated with the direct lymphomagenic effect of H. pylori on B cells. The titers of anti-H. pylori and anti-cagA antibodies were not checked. These titers have been reported to be significantly higher in H. pylori-dependent cases than in H. pylori-independent cases of t(11;18)(q21;q21)-negative gastric MALT lymphoma [34, 35]. In the presence of cagA, B-cell lymphocytes evade apoptosis through the inhibition of p53 accumulation [36, 37]. An important limitation of this study is that lymphoma patients are older than non-lymphoma patients, raising the possibility that lymphoma is a consequence of duration of infection, age, or some other factor, apart from H. pylori pathogenicity factors. The high mutation rates of H. pylori and chronic infection in the lymphoma patients may involve strains lacking the pathogenic markers. The cross-sectional nature of this study cannot account for the duration of infection with more or less pathogenic strains. However, these limitations do not invalidate the study.

H. pylori cagA was significantly associated with B-cell NHL (Table 4). This is consistent with a previously reported cagA 78–100% association with B-cell NHL [31]. CagPAI genes, i.e. cagA promoter and cagE genes, were not significantly associated with either of the two conditions (Table 4). This variability may be attributed to DNA motifs that exhibited sequence heterogeneity in the cagA gene [38]. The cagPAI in B-cell NHL appears to be partially truncated as cagA promoter was 20 (36%) and cagE 17 (30%), respectively, compared with cagT and cagA LEC (Table 4). In an earlier local study, the presence of the cagA did not signify an intact cagPAI [39]. Most of the H. pylori strains studied had partial cagPAI with missing cagE and cagAPs [39]. CagA-positive H. pylori strains are potent in induction of host inflammatory responses, including activation of neutrophils, which releases highly genotoxic oxygen reactive species that induces barrier dysfunction and apoptosis in the gastric epithelium. CagA activation of the NF-κB affects cell proliferation through c-Fos and c-Jun and impaired immune response by inducing apoptosis of T cells [40]. In our study, cagT and LEC genes were significantly associated with B-cell NHL (Table 4). CagE is required for the induction of IL-8 by host cells [41] and is a component of the H. pylori Type 4 Secretion System (T4SS) [42]. It was also equally common in the H. pylori strains associated with NUD and B-cell NHL (Table 4). The cagT gene encoded an extracellular lipoprotein of the T4SS complex that stabilizes the other proteins [42]. H. pylori also induces IL-8 via T4SS constituent cagL interaction with the host receptor integrin b1 and the subsequent activation of the mitogen-activated protein kinases and NF-kB pathway [43].

VacA s1 alleles were significantly associated with B-cell NHL compared with NUD (Table 4). Both vacAs1/m1 and s1/m2 are virulent form common in gastric diseases [44]. VacAs1/m2 has been variably reported about its association with MALToma [14, 45]. The underlying mechanisms involve v acA blocking antigen presentation to T cells [46], T-lymphocyte activation [47] and maturation of macrophage phagosomes [48], thus suppressing T-cell responses to H. pylori and contributing to the immunosuppression and chronicity of H. pylori infection [49]. Immune cells that recognize and attack H. pylori accumulate near the site of infection but are ineffective in eliminating the bacterium.

In conclusion, H. pylori infection with multiple HopQ types, truncated cagPAI with increased expression of cagT, LEC and vacAs1 alleles are associated with B-cell NHL in our patients. IHC will be useful in these cases to look for the genetic aberrations associated with H. pylori-independent B-cell NHL.

ACKNOWLEDGEMENTS

Supported by Higher Education Commission of Pakistan grant (No.20-2290/NRPU/R&D/HEC/12) to JY.

AUTHOR CONTRIBUTIONS

Study concept and design – J.Y., Z.A.; acquisition of data – J.Y., Z.u.A., K.M.; analysis and interpretation of data – J.Y., Z.A., K.T., S.A., Z.u.A.; drafting of the manuscript – J.Y., Z.A., S.A., R.K.; critical revision of the manuscript for important intellectual content – J.Y., Z.A., S.A., Z.u.A., R.K., K.M.; statistical analysis – J.Y., S.A., Z.A.; obtained funding – J.Y.; administrative, technical or material support – K.T., J.Y., K.M.; study supervision – R.K., J.Y., K.T.

DECLARATION OF INTEREST

None.

REFERENCES

1. Wroblewski, LE, Peek, RM, Wilson, KT. Helicobacter pylori and gastric cancer: factors that modulate disease risk. Clinical Microbiology Reviews 2007; 23: 713739.
2. Nurgalieva, ZZ, et al. B-cell and T-cell immune responses to experimental Helicobacter pylori infection in humans. Infection Immunity 2005; 73: 29993006.
3. Kao, CY, Sheu, BS, Wu, JJ. Helicobacter pylori infection: an overview of bacterial virulence factors and pathogenesis. Biomedical Journal 2016; 39: 1423.
4. Hopkins, RJ, Girardi, LS, Turney, EA. Relationship between Helicobacter pylori eradication and reduced duodenal and gastric ulcer recurrence: a review. Gastroenterology 1996; 110: 12441252.
5. Yakoob, J, et al. Helicobacter pylori outer membrane protein Q allele distribution is associated with distinct pathologies in Pakistan. Infection Genetics and Evolution 2016; 37: 5762.
6. Wotherspoon, AC. Helicobacter pylori infection and gastric lymphoma. British Medical Bulletin 1998; 54: 7985.
7. Falush, D, et al. Traces of human migrations in Helicobacter pylori populations. Science 2003; 299: 15821585.
8. Kersulyte, D, et al. Differences in genotypes of Helicobacter pylori from different human populations. Journal of Bacteriology 2000; 182: 32103218.
9. Achtman, M, et al. Recombination and clonal groupings within Helicobacter pylori from different geographical regions. Molecular Microbiology 1999; 32: 459470.
10. Morelli, G, et al. Microevolution of Helicobacter pylori during prolonged infection of single hosts and within families. PLoS Genetics 2010; 6: e1001036.
11. Kennemann, L, et al. Helicobacter pylori genome evolution during human infection. Proceeding of National Academy of Sciences USA 2011; 108: 50335038.
12. Ilver, D, et al. Helicobacter pylori adhesin binding fucosylated-histo blood group antigens revealed by retagging. Science 1998; 279: 373377.
13. Loh, JY, et al. Helicobacter pylori HopQ outer membrane protein attenuates bacterial adherence to gastric epithelial cells. FEMS Microbiology Letter 2008; 289: 5358..
14. Lehours, P, et al. Identification of a genetic marker of Helicobacter pylori strains involved in gastric extranodal marginal zone B-cell lymphoma of the MALT-type. Gut 2004; 53: 931937.
15. Pereira, MI, Medeiros, JA. Role of Helicobacter pylori in gastric mucosa-associated lymphoid tissue lymphomas. World Journal of Gastroenterology 2014; 20: 684698.
16. Yakoob, J, et al. Distribution of gastric carcinoma in an area with a high prevalence of Helicobacter pylori . Turk Journal of Gastroenterology 2017; 28: 98103.
17. Nakamura, S, Müller-Hermelink, HK. Tumors of the stomach. In: Bosman, FT, Carneiro, F, Hruban, RH, Theise, ND, eds. WHO Classification of Tumors of the Digestive System, 4th edn. Lyon, France: IARC (International Agency for Research on Cancer), 2010, pp. 4580.
18. Isaacson, PG. Recent developments in our understanding of gastric lymphomas. American Journal Surgical Pathology 1996; 20(Suppl. 1): S1S7.
19. de Jong, D, et al. Histological grading in gastric lymphoma: pretreatment criteria and clinical relevance. Gastroenterology 1997; 112: 14661474.
20. Price, AB. The Sydney system: histological division. Journal of Gastroenterology Hepatology 1991; 6: 209222.
21. Van Zwet, AA, et al. Sensitivity of culture compared with that of polymerase chain reaction for detection of Helicobacter pylori from antral biopsy samples. Journal of Clinical Microbiology 1993; 31: 19181920.
22. Yakoob, J, et al. Distribution of Helicobacter pylori virulence markers in patients with gastroduodenal diseases in Pakistan. BMC Gastroenterology 2009; 9: 87.
23. Cao, P, Cover, TL. Two different families of HopQ alleles in Helicobacter pylori . Journal of Clinical Microbiology 2005; 40: 45044511.
24. Ferreri, AJ, Montalbán, C. Primary diffuse large B-cell lymphoma of the stomach. Critical Review Oncology Hematology 2007; 63: 6571.
25. Yakoob, J, et al. Polymerase chain reaction in the detection of Helicobacter pylori infection. Journal of College of Physicians Surgeons Pakistan 2004; 14: 153156.
26. Fan, X, et al. The effect of class II major histocompatibility complex expression on adherence of Helicobacter pylori and induction of apoptosis in gastric epithelial cells: a mechanism for T helper cell type 1-mediated damage. Journal of Experimental Medicine 1998; 187: 16591669.
27. Bland, DA, et al. H. pylori receptor MHC-class II contributes to the dynamic gastric epithelial apoptotic response. World Journal of Gastroenterology 2006; 12: 53065310.
28. Hafsi, N, et al. Human dendritic cells respond to Helicobacter pylori, promoting NK cell andTh1-effector responses in vitro. Journal of Immunology 2004; 173: 12491257.
29. Javaheri, A, et al. Helicobacter pylori adhesin HopQ engages in a virulence enhancing interaction with human CEACAMs. Nature Microbiology 2016; 2: 161891.
30. Bussiere, FI, et al. Low multiplicity of infection of Helicobacter pylori suppresses apoptosis of B lymphocytes. Cancer Research 2006; 66: 68346842.
31. Delchier, JC, et al. Helicobacter pylori and gastric lymphoma: high seroprevalence of CagA in diffuse large B-cell lymphoma but not in low-grade lymphoma of mucosa- associated lymphoid tissue type. American Journal of Gastroenterology 2001; 96: 23242328.
32. Liu, H, et al. T(11;18) is a marker for all stage gastric MALT lymphomas that will not respond to H. pylori eradication. Gastroenterology 2002; 122: 12861294.
33. Yeh, KH, et al. Nuclear expression of BCL10 or nuclear factor kappa B helps predict Helicobacter pylori-independent status of low-grade gastric mucosa-associated lymphoid tissue lymphomas with or without t (11; 18)(q21;q21). Blood 2005; 106: 10371041.
34. Peng, H, et al. High frequency of CagA+ Helicobacter pylori infection in high-grade gastric MALT B-cell lymphomas. Journal of Pathology 1998; 185: 409412.
35. Eck, M, et al. MALT-type lymphoma of the stomach is associated with Helicobacter pylori strains expressing the CagA protein. Gastroenterology 1997; 112: 14821486.
36. Sumida, T, et al. Antibodies to Helicobacter pylori and CagA protein are associated with the response to antibacterial therapy in patients with H. pylori-positive API2-MALT1- negative gastric MALT lymphoma. Cancer Science 2009; 100: 10751081.
37. Umehara, S, et al. Effects of Helicobacter pylori CagA protein on the growth and survival of B lymphocytes, the origin of MALT lymphoma. Oncogene 2003; 22: 83378342.
38. Loh, JT, et al. Analysis of cagA in Helicobacter pylori strains from Colombian populations with contrasting gastric cancer risk reveal a biomarker for disease severity. Cancer Epidemiology Biomarkers Prevention 2011; 20: 22372249.
39. Yakoob, J, et al. Low prevalence of the intact cag pathogenicity island in clinical isolates of Helicobacter pylori in Karachi, Pakistan. British Journal of Biomedical Science 2009; 66: 137142.
40. Meyer-ter-Vehn, T, et al. Helicobacter pylori activates mitogen-activated protein kinase cascades and induces expression of the proto-oncogenes c-fos and c-jun. Journal of Biological Chemistry 2000; 275: 1606416072.
41. Owen, RJ, et al. Investigation of the biological relevance of Helicobacter pylori cagE locus diversity, presence of CagA tyrosine phosphorylation motifs and vacuolating cytotoxin genotype on IL-8 induction in gastric epithelial cells. FEMS Immunology Medical Microbiology 2003; 36: 135140.
42. Fronzes, R, Christie, PJ, Waksman, G. The structural biology of type IV secretion systems. Nature Reviews Microbiology 2009; 7: 703714.
43. Gorrell, RJ, et al. A novel NOD1- and CagA-independent pathway of interleukin-8 induction mediated by the Helicobacter pylori type IV secretion system. Cell Microbiology 2013; 15: 554570.
44. Fischer, W, et al. Systematic mutagenesis of the Helicobacter pylori cag-pathogenicity island: essential genes for CagA translocation in host cells and induction of interleukin-8. Molecular Microbiology 2001; 42: 13371348.
45. Koehler, CI, et al. Helicobacter pylori genotyping in gastric adenocarcinoma and MALT lymphoma by multiplex PCR analyses of paraffin wax embedded tissues. Molecular Pathology 2003; 56: 3642.
46. Torres, VJ, et al. Helicobacter pylori vacuolating cytotoxin inhibits activation-induced proliferation of human T and B lymphocyte subsets. Journal of Immunology 2007; 179: 54335440.
47. Boncristiano, M, et al. The Helicobacter pylori vacuolating toxin inhibits T cell activation by two independent mechanisms. Journal of Experimental Medicine 2003; 198: 18871897.
48. Sundrud, MS, et al. Inhibition of primary human T cell proliferation by Helicobacter pylori vacuolating toxin (VacA) is independent of VacA effects on IL-2 secretion. Proceedings of National Academy of Sciences USA 2004; 101: 77277732.
49. Salama, NR, et al. Vacuolating cytotoxin of Helicobacter pylori plays a role during colonization in a mouse model of infection. Infection and Immunity 2001; 69: 730736.