- About this Journal ·
- Abstracting and Indexing ·
- Advance Access ·
- Aims and Scope ·
- Annual Issues ·
- Article Processing Charges ·
- Articles in Press ·
- Author Guidelines ·
- Bibliographic Information ·
- Citations to this Journal ·
- Contact Information ·
- Editorial Board ·
- Editorial Workflow ·
- Free eTOC Alerts ·
- Publication Ethics ·
- Reviewers Acknowledgment ·
- Submit a Manuscript ·
- Subscription Information ·
- Table of Contents
Gastroenterology Research and Practice
Volume 2013 (2013), Article ID 436727, 6 pages
The Clinical Correlations of Helicobacter pylori Virulence Factors and Chronic Spontaneous Urticaria
1Division of Hepato-Gastroenterology, Department of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, 123 Ta-Pei Road, Niao-Sung District, Kaohsiung 833, Taiwan
2Division of Gastroenterology, Department of Internal Medicine, Kaohsiung Veteran General Hospital and National Yang-Ming University, Kaohsiung 813, Taiwan
3Cancer Center, Division of Gastroenterology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 807, Taiwan
4Department of Pathology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung 833, Taiwan
5Department of Dermatology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung 833, Taiwan
6Department of Dermatology and Allergy, Christine Kuehne-Center for Allergy Research and Education (CK-CARE), Technical University of Munich, Biedersteiner Str. 29, 80802 Munich, Germany
Received 17 May 2013; Accepted 27 June 2013
Academic Editor: Chao-Hung Kuo
Copyright © 2013 Yi-Chun Chiu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background and Study Aims. The association between Helicobacter pylori (H. pylori) and chronic spontaneous urticaria (CSU) remains controversial. This study explored the role of H. pylori in CSU among different virulent genotypes patients. Patients and Methods. Patients infected by H. pylori were sorted into two groups as group A (with CSU) and group B (without CSU). The tissue materials were taken via endoscopy for polymerase chain reaction study to determine virulence factors. After H. pylori eradication therapy, the eradication rate and response of urticaria were evaluated by using C13-UBT and a three-point scale (complete remission, partial remission, or no improvement). Results. The results were comparable between patients of groups A and B in terms of H. pylori infection rates and eradication rate. Longitudinal follow-up of 23.5 months showed complete remission of urticaria in 63.6% but no improvement in 36.4% of the patients after H. pylori eradication. H. pylori infected patients with different virulence factors such as cytotoxin-associated gene A, vacuolating cytotoxin gene A signal region and middle region have similar remission rates for CSU. Conclusions. Current study suggests that H. pylori may play a role in the development and disease course of CSU but may be irrelevant to different virulent genotypes.
Chronic spontaneous urticaria (CSU), defined as spontaneous occurrence of wheal and/or angioedema lasting for a period of longer than 6 weeks, is a common and often frustrating problem, affecting up to 1 percent of the general population [1, 2]. The causes of CSU are numerous; however, in at least 80–90% of the patients, the etiology is undetermined [2, 3]. Recent data show that about 30% of the affected patients may have functional autoantibodies . On the other hand, Helicobacter pylori (H. pylori) infection is probably the most common chronic bacterial infection in humans, with the prevalence rate in general population estimated to be around 50% in developing countries . It has been generally accepted that H. pylori infection plays an etiologic role in the development of chronic active gastritis, peptic ulcer disease, gastric malignancy, and low-grade gastric mucosa-associated lymphoid tissue lymphoma [5–8]. H. pylori is genetically highly diverse, and several genotypes have been identified to associate with severe gastric mucosal inflammation . Cytotoxin-associated gene A (cagA) and vacuolating cytotoxin gene A (vacA), the two most important virulence factors of H. pylori , have been reported to enhance its pathogenicity  while cagA is related to peptic ulcer and gastric malignancy in certain populations [11, 12]; vacA can induce host cell vacuolation and eventually cell death . A high degree of sequence variability exists in the vacA gene, with its signal and middle region being classified into s1/s2 and m1/m2 subtypes, respectively . The s1 subtype and m1 subtype have been linked to more severe gastrointestinal manifestations .
A potential association between CSU and H. pylori infection of the upper gastrointestinal tract has been proposed, but the studies so far showed controversial results [15–18]. Moreover, little is known about the association between the genotypes of H. pylori and CSU . This study aimed to explore the potential role of H. pylori in the development and disease course of CSU among the different virulent genotypes of patients.
2. Patients and Methods
2.1. Study Design
From August 2008 to July 2009, 25 patients (age 27–68 years, mean = 45.5 years, female/male = 13/12) diagnosed as CSU with unremarkable findings in allergy diagnostics (basis examination) were recruited from the Dermatology Outpatient Department of Chang Gung Memorial Hospital-Kaohsiung, Taiwan . The duration of CSU ranged between 6 and 360 months with a median of 12 months. Only six of them (6/25, 24%) suffered from upper gastrointestinal symptom. All of them received a C13-urea breath test (C13-UBT). Infection of H. pylori was diagnosed by a positive C13-UBT test and sorted as group A (). Meanwhile, 24 patients (age 18–83 years, mean = 41.5 years, female/male = 13/11) with gastrointestinal symptoms but without urticaria/pruritus were enrolled from the Gastroenterology Department for C13-UBT examination, and the infected patients were categorized into group B. All the C13-UBT-positive patients underwent upper gastrointestinal endoscopy, using a GIF XQ 240 endoscope (Olympus Optical Company, Tokyo, Japan), and tissue biopsies were taken from the gastric antrum and body (). Criteria for exclusion included (a) ingestion of antibiotics, bismuth, or proton-pump inhibitors within the prior 4 weeks, (b) use of nonsteroidal anti-inflammatory drugs within the prior 4 weeks, (c) patients with previous gastric surgery, (d) the coexistence of serious concomitant illness (e.g., decompensated liver cirrhosis or uremia), (e) pregnant women, and (f) those who refused endoscopic examination and subsequent H. pylori eradication. H. pylori infection was defined as positive results by a positive C13-UBT test.
All the biopsied specimens were stored in 70% ethanol in Eppendorf tubes at −80°C until processed for polymerase chain reaction (PCR) examination, in which the tissue specimens were homogenized with a sterile micropestle, and the DNA was extracted and purified using a commercial kit following the tissue protocol of the manufacturer (QIAGEN QIAamp DNA mini kit, Hilden, Germany). To detect the virulence factors of H. pylori, PCR studies with three respective species-specific primer sets were designed to amplify highly conserved regions within the genes encoding cagA and vacA (s and m regions) .
2.2. Treatment Allocation
All the infected patients then received oral eradication therapy comprising esomeprazole (40 mg twice daily), clarithromycin (500 mg twice daily), and either amoxicillin (1 gm twice daily) or metronidazole (500 mg twice daily) for patients with penicillin allergy in the history . Esomeprazole and amoxicillin were taken one hour before breakfast and dinner, clarithromycin and metronidazole twice daily after breakfast and dinner. To assess eradication efficacy, a repeated C13-UBT was performed to each patient at six weeks after the end of anti-H. pylori therapy. The effectiveness of eradication therapy on CSU was assessed three months later after treatment, using a three-point rating scale, that is, complete remission, partial remission (50% or more), or no improvement. The differences in cagA, vacA s, and vacA m of H. pylori between patients of group A and group B as well as the differences in clinical course of CSU before and after eradication therapy relating to the various virulent factors were analyzed. The study was approved by the ethic committee of Chang Gung Memorial Hospital-Kaohsiung, Taiwan (no. 95-1314B), and signed informed consent was obtained from all the participants.
2.3. Statistical Analysis
Continuous variables, given as means and standard deviations (SD), were analyzed using the Mann-Whitney U test. Categorical variables, given in total and as percentages, were analyzed using the Chi-square test or Fisher exact test. Two-sided values of <0.05 were considered significant. All the statistics were performed using SPSS (WIN version 15.0).
Allocation diagrams of patients with chronic spontaneous urticaria are summarized in Figure 1. Demographic data of H. pylori-infected patients with or without chronic spontaneous urticaria (CSU) was summarized in Table 1. In group A, clinical follow-up of 11 successfully treated patients three months later revealed complete remission of urticaria in 54.5% (6/11), partial remission in 18.2% (2/11), and no improvement in 27.3% (3/11). In longitudinal follow-up studies for a duration of 12–29 months after H. pylori eradication (median = 23.5 months), complete remission was found in 63.6% (7/11) and no improvement in 36.4% (4/11) of the patients. One patient with partial remission turned into complete remission while another one showed deterioration of urticaria. All the three patients in group A who failed H. pylori eradication showed clinically persisting urticarial symptoms. The duration of urticaria was months in the treatment responders as compared to months in the nonresponders. However, there was no statistical difference observed in the clinical response rates of CSU between the treatment success and treatment failure patients (7/11, 63.6% versus 0/3, 0%, , Fisher’s exact test). None of the patients in group B developed urticarial lesions in an average follow-up of 14.1 months.
Determination of virulence factors via PCR study showed the size of the amplified products as follows: cagA (324 bp), vacA s1 (259 bp), vacA s2 (286 bp), vacA m1 (290 bp), and vacA m2 (352 bp) (Figure 2). The cagA genotype was detected in 11/14 (78.6%) in group A and 13/14 (92.9%) in group B (). The ratio of s1 to s2 alleles in vacA was 11 (78.6%) to 3 (21.4%) in group A and 13 (92.9%) to 1 (7.1%) in group B (78.6% versus 92.9%, ). The ratio of m1 to m2 alleles was 6 (42.9%) to 8 (51.7%) in group A and 2 (14.3%) to 12 (85.7%) in group B (42.9% versus 14.3%, ). The expression of cagA, vacA (s1/s2), and vacA (m1/m2) did not differ between patients in group A and group B (, 0.596, and 0.209, resp.) (Table 2). In analysis of the association between virulence genotypes and therapeutic response of urticaria (group A), the cagA genotype was detected in 5 (71.4%) of 7 CSU patients with remissions (complete and partial) and 6 (85.7%) of 7 patients without improvement (). The s1/s2 ratio of vacA genotype was 5 (71.4%) to 2 (28.6%) in remission patients and 6 (85.7%) to 1 (14.3%) in nonremission patients (). The ratio of m1 to m2 alleles in vacA was 3 (42.9%) to 4 (57.1%) with remission of CSU posttreatment and 3 (42.9%) to 4 (57.1%) with persisting CSU (). As summarized in Table 2, there was no significant difference observed between CSU patients in remission and nonremission status after successful H. pylori eradication treatment for the expression of virulence factors such as cagA, vacA (s1/s2), vacA (m1/m2), vacA s1m1, or (cagA + vacA) s1m1.
A potential association between CSU and H. pylori infection of the upper gastrointestinal tract has been proposed, but the studies so far showed controversial results not to mention the relevance to the genotypes of H. pylori [15–18]. In current study, the prevalence rate of H. pylori infection of 56% in our CSU patients which is rational as reported in other studies varied from 47% to 80% [20–23]. All of these studies, including ours, also observed that the prevalence of H. pylori infection between patients with and without CSU is similar. Moreover, follow-up of the 14 infected patients with gastric complaints but without skin problems (group B) for an average of 14.1 months did not find a later development of CSU. However, clinical regression of CSU was observed after a successful eradication of H. pylori, among 17.6% to 88% of these patients [20–23]. 58.3% of our CSU patients had a long-term complete remission of their CSU after an effective eradication therapy. Given that a relatively low reported spontaneous remission rate of 6% in the natural course of CSU persisting for more than 6 months , current study demonstrated an apparent benefit from H. pylori eradication therapy for CSU patients and suggested that a possible etiopathogenetic role of H. pylori may exist.
H. pylori species is genetically highly diverse . Differences in the genotypes of bacterial virulence factors can induce variable degrees of gastric inflammation and elicit different clinical manifestations in gastrointestinal tract. The strains have been categorized into type I with expression and type II without expression of the virulence factors . Type I H. pylori can cause mucosal damage by stimulating gastric epithelial cytokine responses and produce a variety of other factors that determine the local inflammatory response . Among the well-characterized virulence factors of type I strains, cagA, vacA-s, and vacA-m have been reported to enhance pathogenicity of H. pylori . CagA-positive strains induce a higher production of proinflammatory cytokines in the gastric mucosa and are linked with an increased risk of peptic ulcer disease, gastric atrophy, and gastric cancer in certain populations [27, 28]. VacA, which is produced by 50–60% of H. pylori strains, causes fusion of the endocellular lysosomes leading to a consequent reswelling of the gastric epithelium cells . H. pylori bacteria carrying vacA-s1 and vacA-m1 subtypes have also been related to more severe clinical manifestations [9, 27].
There is proposal of potential association between CSU and H. pylori infection of the upper gastrointestinal tract [15–18], but only one study reported the clinical relevance between virulence factors of H. pylori and CSU . Fukuda and his colleagues found a high incidence of cagA expression in CSU patients (100%, 13/13) and similarly in control group (100%, 26/26) . This was the same to current study. Longitudinal follow-up (range 12–29 months, median 23.5 months) showed complete remission of urticaria in 63.6% (7/11) and no improvement in 36.4% (4/11) of our patients after H. pylori eradication. In addition, we had shown that the expression of other virulence factors did not differ between patients with and without CSU. H. pylori infected patients with different virulence factors such as cytotoxin-associated gene A, vacuolating cytotoxin gene A signal region and middle region had similar remission rates for CSU. Moreover, among CSU patients, the genotypes of H. pylori virulence factors did not correlate with the onset age, gender difference, or the response to bacterial eradication therapy.
H. pylori colonizes the gastric mucosa in approximately half of the world’s population, but only a minority (10–20%) of the infected individuals develop clinical manifestations, most commonly with gastrointestinal disorders [7, 27]. There were debates on the clinical association of H. pylori with certain dermatological disorders which includes issues such as CSU, rosacea, psoriasis, or immune thrombocytopenic purpura [25, 29]. Like peptic ulcer disease, rosacea may be triggered by the more virulent type I strain of H. pylori . It is also believed that many environmental, bacterial, and host-related factors can influence the course of infection. The cagA protein of the more virulent strain stimulates the gastric epithelium to secret greater amounts of inflammatory cytokines such as IL-8, IL-1, TNF-α, interferon-γ, leukotrienes, and platelet-activating factors . On the other hand, it is suggested that H. pylori infection may facilitate penetration of allergens with induction of an IgE response to certain common alimentary antigens thereby enhancing the development of food allergy . Infection with H. pylori has been shown to increase antigen absorption across the cultured digestive epithelium in vitro and across the gastric mucosa of mice in vivo [32, 33]. Nevertheless, it is still unclear whether the immunologic reactions induced by H. pylori can directly elicitate the mast cell degranulation leading to urticarial formation.
Current study encounters some limitations. First, the sample size is relatively small so bias may still exist. Second, there is no matched control group for this study which should be untreated from H. pylori infections. The bottom line is that it is practically unethical not to treat a diagnosed infection. Third, there are other virulence factors of H. pylori which were not studied, such as iceA, babA, flaA/flaB (the genes for flagellins), and ureA/ureB (urease-encoding genes). As we know, iceA is induced by contact with epithelium; babA is associated with binding to blood-group antigens [34, 35]. However, unlike cagA, vacA-s1, and -m1, iceA1 and babA2 which are associated with a more severe gastrointestinal manifestation [35, 36], flaA/flab and ureA/ureB genotypes are of less clinical significance .
Current study suggests that H. pylori may play a role in the development and disease course of CSU. Different virulent genotypes of H. pylori may be irrelevant to the remission of CSU after eradication. However, it remains to be determined whether a quantitative effect of the examined virulence factors may exist or other virulent and nonvirulent genes of H. pylori may play a role in the pathogenesis of CSU. A better understanding of the bacterial virulence factors and the corresponding host immune response is still needed to further clarify the pathogenic role of H. pylori in certain groups of patients with CSU.
Conflict of Interests
The authors declare that they have no conflict of interests.
This work was supported by Grants from National Science Council, Taiwan (NSC 96-2314-B-182A-063). The authors thank Jyh-Chwan Wang for the laboratory work and Yun-Lan Ku for diagramming the figures.
- J. Ring, Allergy in Practice, Springer, Berlin, Germany, 2005.
- T. Zuberbier, R. Asero, C. Bindslev-Jensen et al., “EAACI/GA2LEN/EDF/WAO guideline: definition, classification and diagnosis of urticaria,” Allergy, vol. 64, no. 10, pp. 1417–1426, 2009.
- K. M. Nichols and F. E. Cook-Bolden, “Allergic skin disease: major highlights and recent advances,” Medical Clinics of North America, vol. 93, no. 6, pp. 1211–1224, 2009.
- H. Philpott, F. Kette, P. Hissaria, D. Gillis, and W. Smith, “Chronic urticaria: the autoimmune paradigm,” Internal Medicine Journal, vol. 38, no. 11, pp. 852–857, 2008.
- S. J. Konturek, P. C. Konturek, J. W. Konturek et al., “Helicobacter pylori and its involvement in gastritis and peptic ulcer formation,” Journal of Physiology and Pharmacology, vol. 57, supplement 3, pp. 29–50, 2006.
- P. C. Konturek, S. J. Konturek, and T. Brzozowski, “Gastric cancer and Helicobacter pylori infection,” Journal of Physiology and Pharmacology, vol. 57, supplement 3, pp. 51–65, 2006.
- S.-K. Chuah, F.-W. Tsay, P.-I. Hsu, and D.-C. Wu, “A new look at anti-Helicobacter pylori therapy,” World Journal of Gastroenterology, vol. 17, no. 35, pp. 3971–3975, 2011.
- S.-K. Chuah, P.-I. Hsu, K.-C. Chang et al., “Randomized comparison of two non-bismuth-containing second-line rescue therapies for Helicobacter pylori,” Helicobacter, vol. 17, no. 3, pp. 216–223, 2012.
- B. J. Marshall, “Helicobacter pylori,” American Journal of Gastroenterology, vol. 89, supplement 8, pp. S116–S128, 1994.
- J. C. Atherton, P. Cao, R. M. Peek Jr., M. K. R. Tummuru, M. J. Blaser, and T. L. Cover, “Mosaicism in vacuolating cytotoxin alleles of Helicobacter pylori. Association of specific vacA types with cytotoxin production and peptic ulceration,” Journal of Biological Chemistry, vol. 270, no. 30, pp. 17771–17777, 1995.
- C. Figueiredo, L.-J. van Doorn, C. Nogueira et al., “Helicobacter pylori genotypes are associated with clinical outcome in portuguese patients and show a high prevalence of infections with multiple strains,” Scandinavian Journal of Gastroenterology, vol. 36, no. 2, pp. 128–135, 2001.
- M. Kidd, A. J. Lastovica, J. C. Atherton, and J. A. Louw, “Conservation of the cag pathogenicity island is associated with vacA alleles and gastroduodenal disease in South African Helicobacter pylori isolates,” Gut, vol. 49, no. 1, pp. 11–17, 2001.
- Y.-H. Chang, L. Wang, M.-S. Lee, C.-W. Cheng, C.-Y. Wu, and M.-Y. Shiau, “Genotypic characterization of Helicobacter pylori cagA and vacA from biopsy specimens of patients with gastroduodenal diseases,” Mount Sinai Journal of Medicine, vol. 73, no. 3, pp. 622–626, 2006.
- D. Basso, F. Navaglia, L. Brigato et al., “Analysis of Helicobacter pylori vacA and cagA genotypes and serum antibody profile in benign and malignant gastroduodenal diseases,” Gut, vol. 43, no. 2, pp. 182–186, 1998.
- S. Fukuda, T. Shimoyama, N. Umegaki, T. Mikami, H. Nakano, and A. Munakata, “Effect of Helicobacter pylori eradication in the treatment of Japanese patients with chronic idiopathic urticaria,” Journal of Gastroenterology, vol. 39, no. 9, pp. 827–830, 2004.
- D. G. Federman, R. S. Kirsner, J. P. Moriarty, and J. Concato, “The effect of antibiotic therapy for patients infected with Helicobacter pylori who have chronic urticaria,” Journal of the American Academy of Dermatology, vol. 49, no. 5, pp. 861–864, 2003.
- A. Moreira, J. Rodrigues, L. Delgado, J. Fonseca, and M. Vaz, “Is Helicobacter pylori infection associated with chronic idiopathic urticaria?” Allergologia et Immunopathologia, vol. 31, no. 4, pp. 209–214, 2003.
- P. Gaig, P. García-Ortega, E. Enrique, M. Papo, J. C. Quer, and C. Richard, “Efficacy of the eradication of Helicobacter pylori infection in patients with chronic urticaria. A placebo-controlled double blind study,” Allergologia et Immunopathologia, vol. 30, no. 5, pp. 255–258, 2002.
- S. Datta, S. Chattopadhyay, G. B. Nair et al., “Virulence genes and neutral DNA markers of Helicobacter pylori isolates from different ethnic communities of West Bengal, India,” Journal of Clinical Microbiology, vol. 41, no. 8, pp. 3737–3743, 2003.
- B. Tebbe, C. C. Geilen, J.-D. Schulzke, C. Bojarski, M. Radenhausen, and C. E. Orfanos, “Helicobacter pylori infection and chronic urticaria,” Journal of the American Academy of Dermatology, vol. 34, no. 4, pp. 685–686, 1996.
- C. di Campli, A. Gasbarrini, E. Nucera et al., “Beneficial effects of Helicobacter pylori eradication on idiopathic chronic urticaria,” Digestive Diseases and Sciences, vol. 43, no. 6, pp. 1226–1229, 1998.
- E. Daudén, I. Jiménez-Alonso, and A. García-Díez, “Helicobacter pylori and idiopathic chronic urticaria,” International Journal of Dermatology, vol. 39, no. 6, pp. 446–452, 2000.
- B. Wedi, U. Raap, D. Wieczorek, and A. Kapp, “Urticaria and infections,” Allergy Asthma Clin Immunol, vol. 5, p. 10, 2009.
- B. Schnyder, A. Helbling, and W. J. Pichler, “Chronic idiopathic urticaria: natural course and association with Helicobacter pylori infection,” International Archives of Allergy and Immunology, vol. 119, no. 1, pp. 60–63, 1999.
- Y. Tüzün, S. Keskin, and E. Kote, “The role of Helicobacter pylori infection in skin diseases: facts and controversies,” Clinics in Dermatology, vol. 28, no. 5, pp. 478–482, 2010.
- A. Shiotani, K. Okada, K. Yanaoka et al., “Beneficial effect of Helicobacter pylori eradication in dermatologic diseases,” Helicobacter, vol. 6, no. 1, pp. 60–65, 2001.
- K. Dzierzanowska-Fangrat and D. Dzierzanowska, “Helicobacter pylori: microbiology and interactions with gastrointestinal microflora,” Journal of Physiology and Pharmacology, vol. 57, no. 3, pp. 5–14, 2006.
- J. Q. Huang, G. F. Zheng, K. Sumanac, E. J. Irvine, and R. H. Hunt, “Meta-analysis of the relationship between cagA seropositivity and gastric cancer,” Gastroenterology, vol. 125, no. 6, pp. 1636–1644, 2003.
- A. C. Hernando-Harder, N. Booken, S. Goerdt, M. V. Singer, and H. Harder, “Helicobacter pylori infection and dermatologic diseases,” European Journal of Dermatology, vol. 19, no. 5, pp. 431–444, 2009.
- G. Argenziano, G. Donnarumma, M. R. Iovene, P. Arnese, M. A. Baldassarre, and A. Baroni, “Incidence of anti-Helicobacter pylori and anti-CagA antibodies in rosacea patients,” International Journal of Dermatology, vol. 42, no. 8, pp. 601–604, 2003.
- N. Figura, A. Perrone, C. Gennari et al., “Food allergy and Helicobacter pylori infection,” Italian Journal of Gastroenterology and Hepatology, vol. 31, no. 3, pp. 186–191, 1999.
- T. Matysiak-Budnik, K. Hashimoto, M. Heyman, A. de Mascarel, J.-F. Desjeux, and F. Mégraud, “Antral gastric permeability to antigens in mice is altered by infection with Helicobacter felis,” European Journal of Gastroenterology and Hepatology, vol. 11, no. 12, pp. 1371–1377, 1999.
- T. Matysiak-Budnik, K. Terpend, S. Alain et al., “Helicobacter pylori alters exogenous antigen absorption and processing in a digestive tract epithelial cell line model,” Infection and Immunity, vol. 66, no. 12, pp. 5785–5791, 1998.
- D. Ilver, A. Arnqvist, J. Ögren et al., “Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging,” Science, vol. 279, no. 5349, pp. 373–377, 1998.
- S. Suerbaum, C. Josenhans, and A. Labigne, “Cloning and genetic characterization of the Helicobacter pylori and Helicobacter mustelae flaB flagellin genes and construction of H. pylori flaA- and flaB-negative mutants by electroporation-mediated allelic exchange,” Journal of Bacteriology, vol. 175, no. 11, pp. 3278–3288, 1993.
- Y. Yamaoka, T. Kodama, O. Gutierrez, J. G. Kim, K. Kashima, and D. Y. Graham, “Relationship between Helicobacter pylori iceA, cagA, and vacA status and clinical outcome: studies in four different countries,” Journal of Clinical Microbiology, vol. 37, no. 7, pp. 2274–2279, 1999.
- M. Gerhard, N. Lehn, N. Neumayer et al., “Clinical relevance of the Helicobacter pylori gene for blood-group antigen-binding adhesin,” Proceedings of the National Academy of Sciences of the United States of America, vol. 96, no. 22, pp. 12778–12783, 1999.