Porcine gastric mucosa associated lymphoid tissue (MALT): stimulation by colonization with the gastric bacterial pathogen, Helicobacter pylori

A comprehensive evaluation of an animal model for Helicobacter pylori-associated stomach cancer: Fact and controversy

Even though Helicobacter pylori infection was the most causative factor of gastric cancer, numerous in vivo studies failed to induce gastric cancer using H. pylori infection only. The utilization of established animal studies in cancer research is crucial as they aim to investigate the coincidental association between suspected oncogenes and pathogenesis as well as generate models for the development and testing of potential treatments. The methods to establish gastric cancer using infected animal models remain limited, diverse in methods, and showed different results. This study investigates the differences in animal models, which highlight different pathological results in gaster by literature research. Electronic databases searched were performed in PubMed, Science Direct, and Cochrane, without a period filter. A total of 135 articles were used in this study after a full-text assessment was conducted. The most frequent animal models used for gastric cancer were Mice, while Mongolian gerbils and Transgenic mice were the most susceptible model for gastric cancer associated with H. pylori infection. Additionally, transgenic mice showed that the susceptibility to gastric cancer progression was due to genetic and epigenetic factors. These studies showed that in Mongolian gerbil models, H. pylori could function as a single agent to trigger stomach cancer. However, most gastric cancer susceptibilities were not solely relying on H. pylori infection, and numerous factors are involved in cancer progression. Further study using Mongolian gerbils and Transgenic mice is crucial to conduct and establish the best models for gastric cancer associated H. pylori.

Endoscopic and histologic analysis of gastric mucosa-associated lymphoid tissue in children with Helicobacter pylori infection

OBJECTIVES

Nodular gastritis (NG) associated with Helicobacter pylori infection can occur commonly in childhood and is regarded to be benign without clinical significance. This study includes endoscopic and histologic analysis of gastric mucosa-associated lymphoid tissue (MALT) to clarify the significance of NG on endoscopy in H pylori-infected children.

METHODS

Of the 758 children who underwent endoscopy, 80 were identified as having H pylori infection. These patients were divided into 3 groups based on endoscopic severity of gastric nodularity. Histopathologic grading of MALT and immunohistochemistry of CD3, CD20, cytokeratin, and Ki-67 were evaluated.

RESULTS

On endoscopy, severe NG was observed in the antrum of 38 of the 80 subjects, mild NG in 27, and an absence of NG in 15. Density of H pylori and lymphocyte infiltration differed among the 3 groups (P=0.022 and P=0.025, respectively). Histological grading for gastric lymphoid infiltrates was compatible with grade 1 in 47 (58.8%), grade 2 in 21 (26.3%), grade 3 in 7 (8.8%), and grade 4-5 in 4 (5.1%) in the antrum. Degree of NG, density of H pylori, neutrophil activity, and gastritis score in the antrum varied with MALT grades (P=0.003, P=0.042, P=0.028, and P=0.006, respectively).

CONCLUSIONS

Our study suggests NG may present as a significant gastric manifestation of childhood H pylori infection that indicates gastric MALT. Thorough histologic investigation may be useful in the evaluation of gastric MALT in children infected with H pylori that manifests as severe NG in the antrum.

Distribution, organization and innervation of gastric MALT in conventional piglet

Mucosa-associated lymphoid tissue (MALT) is the initial inductive site for mucosal immunity. It is present in the different layers of the mucosal wall and consists of organized lymphoid tissue which may occur as isolated or aggregated lymphoid follicles (LFs) and interfollicular areas. It is present in many organs, including the pig stomach. Gastric MALT has been intensely studied in experimentally infected pigs but few data are available in healthy, non-gnotobiotic or germ-free animals. In the present study we described the gastric MALT in conventional piglets in the cardiac mucosa of the gastric diverticulum, in the pyloric mucosa, and in the sites of transition from cardiac to oxyntic and from cardiac to pyloric mucosa by means of histological and immunohistochemical stains. The majority of LFs were located in the cardiac mucosa and in the transition from the cardiac to the oxyntic mucosa. Here the LFs were mainly located in the submucosa and reached the mucosa; we called these submucosal lymphoid follicles (SLFs). In the pyloric mucosa and in the transition sites from the cardiac to the pyloric mucosa, LFs were located in the mucosa; we called these mucosal lymphoid follicles (MLFs). In SLFs, a compartmental organization of T and B lymphocytes was present; by contrast, in the MLFs, the T and B cells were intermingled, suggesting the possibility of different roles for the two types of follicles. In the epithelium overlying the lymphoid tissue, numerous T lymphocytes and some cells immunoreactive to cytokeratin-18 were observed. Following the application of the fluorescent tracer DiI into the SLFs of the diverticulum, enteric neurones located in the submucosal plexus were labelled, confirming the interplay between the immune and the enteric nervous system.

Experimental Infection of Pigs with ‘Candidatus Helicobacter suis’

'Candidatus Helicobacter suis' is a spiral-shaped bacterium that colonizes the stomach of more than 60% of slaughter pigs. The role of 'Candidatus Helicobacter suis' in gastric disease of pigs is still unclear. Experimental studies in pigs are lacking because this bacterium is unculturable until now. An inoculation protocol using 'Candidatus Helicobacter suis' infected mouse stomach homogenate was used to reproduce the infection in pigs. Control animals were inoculated using negative mouse stomach homogenate. Pigs were inoculated three times with one-week intervals and euthanized 6 weeks post inoculation. Tissue samples were taken from different mucosal stomach regions to detect 'Candidatus Helicobacter suis' by PCR and urease test. Mucosal inflammation was evaluated on formalin-fixed tissue samples. Lesions in the pars oesophagea were scored macroscopically. Infection was successful in all challenged animals, with the antrum and the fundus being predominantly positive. Infection was associated with infiltration of lymphocytes and plasma cells in the antral mucosa, evolving to follicular gastritis. No apparent inflammation of the fundic stomach region was detected in the infected animals. A clear link between 'Candidatus Helicobacter suis' and pars oesophageal lesions could not be found.

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori.

The postnatal development of the mucosal immune system and mucosal tolerance in domestic animals

The mucosal immune system is exposed to a range of antigens associated with pathogens, to which it must mount active immune responses. However, it is also exposed to a large number of harmless antigens associated with food and with commensal microbial flora, to which expression of active, inflammatory immune responses to these antigens is undesirable. The mucosal immune system must contain machinery capable of evaluating the antigens to which it is exposed and mounting appropriate effector or regulatory responses. Since the immune system is likely to have evolved initially in mucosal tissues, the requirement to prevent damaging allergic responses must be at least as old as the adaptive immune system, and studies of the mechanisms should include a range of non-mammalian species. Despite the importance for rational design of vaccines and for control of allergic reactions, the mechanisms involved are still largely unclear. It is not clear that the classical experimental protocol of "oral tolerance" is, in fact, measuring a biologically important phenomenon, nor is it clear whether tolerance is regulated in the evolutionarily recent organised lymphoid tissue (the lymph nodes) or the more ancient, diffuse architecture in the intestine. The capacity of the immune system to discriminate between "dangerous" and "harmless" antigens appears to develop with age and exposure to microbial flora. Thus, the ability of an individual or a group of animals to correctly regulate mucosal immune responses will depend on age, genetics and on their microbial environment and history. Attempts to manipulate the mucosal immune system towards active immune responses by oral vaccines, or towards oral tolerance, are likely to be confounded by environmentally-induced variability between individuals and between groups of animals.

MALT structure and function in farm animals

Mucosa-associated lymphoid tissue (MALT) is defined as an organized lymphoid tissue in the mucosa that samples antigens. The morphological characteristics that distinguish MALT from lymphoid infiltrates are discussed. MALT has been extensively investigated in laboratory animals, while knowledge in cattle, sheep, goats, pigs and horses that are summarized under the term farm animals in this review is fragmentary. Literature data about the distribution, morphology, function and involvement in infectious diseases of MALT in farm animals are described. The understanding of specific features of MALT in other species than laboratory animals is important for comparative research, in order to understand pathological and immunological processes in the respective species and as a potential route of vaccination of mucosal surfaces.

Experimental induction of bacterial gastritis and gastric ulcer disease in gnotobiotic swine inoculated with porcine Helicobacter-like species

OBJECTIVE

To determine whether 2 isolates of recently isolated swine-origin Helicobacter pylori-like bacteria are pathogenic in pigs and compare the signs of gastric disease induced by these isolates with those detected in H pylori- and Helicobacter heilmannii-infected pigs.

ANIMALS

36 neonatal gnotobiotic pigs.

PROCEDURE

Groups of separately housed pigs were inoculated orally with swine-origin Helicobacter-like isolates 2662 or 1268, H pylori (human gastric pathogen), or a gastric homogenate from gnotobiotic swine containing H heilmannii. Noninoculated pigs were used as control animals. Clinical signs and development of homologous and heterologous antibodies against Helicobacter organisms were assessed. After euthanasia, gastric tissues were examined grossly and microscopically; Helicobacter organisms were detected by use of Warthin-Starry and immunohistochemical stains.

RESULTS

Both porcine Helicobacter-like isolates colonized the stomachs of swine. Isolate 2662 was highly pathogenic; in 13 isolate 2662-inoculated pigs, gastroesophageal ulcerations developed in 9 and ulceration of the gastric glandular mucosa was detected in 5. Histologically, inflammatory gastritis consisting of multifocal to diffuse lymphocytic and plasmacytic cellular infiltrates and lymphoid follicle formation in the gastric lamina propria accompanied bacterial colonization of the gastric compartment. In contrast, H heilmannii was minimally pathogenic in that only modest inflammatory cell infiltrates were seen. Gastroesophageal or mucosal ulcers were not evident in pigs inoculated with H heilmannii.

CONCLUSIONS AND CLINICAL RELEVANCE

These data indicate that swine-origin H pylori-like bacteria can be pathogenic in pigs and suggest that porcine gastric disease may be mediated, in part, by colonization of the stomach by swine-origin H pylori-like bacteria.

Helicobacter pylori-specific immunoglobulin synthesis in gnotobiotic piglets: evidence for the induction of mucosal immunity in the stomach

Short term tissue biopsy cultures and paired, sera, bile and gastric and intestinal contents from Helicobacter pylori-infected gnotobiotic piglets were tested for the synthesis of H. pylori-specific immunoglobulin (Ig) isotype production by antigen-specific ELISA from post-infection days (PIDs) 2-28. Serum antibody levels in all three Ig isotypes were elevated from baseline values by PID 14, serum IgM levels reached peak levels on PID 14 and by PID 28 bile was strongly positive for IgA and IgG.Intestinal, but not gastric contents from infected piglets, contained IgA-specific antibody from PID 14 onward. Gastric mucosal epithelia adjacent to areas of inflammation in infected but not uninfected control piglets produced readily detectable amounts of porcine secretory component (SC); IgA-positive plasma cells were identified in gastric submucosa and lamina propria in these areas. Culture fluid supernatants, collected from explanted gastric cardia and antra and intestinal ilea of H. pylori-infected piglets had trace amounts of IgA as early as PID 2 in some animals, and strong IgA reactivity in all by PID 28. Supernatants also contained H. pylori-specific IgG by PID 14. A strong gastric lymph node IgA response contrasted with moderate IgA production in mesenteric lymph nodes and spleen. Mucosal biopsy production of H. pylori-specific IgG was more evenly distributed throughout the lymphoid system. These data support the contention that the Ig response to H. pylori is initiated within the gastric compartment and matures over time to a generalized IgA-dominated mucosal and IgG-dominated nonmucosal humoral immune response.

Helicobacter pylori-induced gastritis in experimentally infected conventional piglets

A conventional nonmutant animal that could be experimentally infected with Helicobacter pylori isolates would be a useful animal model for human H. pylori-associated gastritis. Gnotobiotic and barrier-born pigs are susceptible to H. pylori infection, but attempts to infect conventional pigs with this bacterium have been unsuccessful. In the present study, a litter of eight 20-day-old crossbreed piglets were purchased from a commercial farm. Six of them were orally challenged two to five times at different ages, between 29 and 49 days, with doses of H. pylori inoculum containing approximately 10(9) bacterial cells. Two animals served as controls. The inoculation program began 2 days postweaning when the piglets were 29 days of age. Prior to every inoculation, the piglets were fasted and pretreated with cimetidine, and prior to the first and second inoculation each piglet also was pretreated with dexamethasone. The challenged piglets were euthanasized between 36 and 76 days of age. H. pylori colonized all six inoculated piglets. The pathology of the experimentally induced gastritis was examined macroscopically and by light and electron microscopy. H. pylori induced a severe lymphocytic gastritis in the conventional piglets and reproduced the large majority of the pathologic features of the human disease. Therefore, the conventional piglet represents a promising new model for study of the various pathogenic mechanisms involved in the development of lesions of the human H. pylori-associated gastritis.

Mucosa-associated lymphoid tissues as sites for uptake, carriage and excretion of tubercle bacilli and other pathogenic mycobacteria

Pathogenic mycobacteria, including those that cause tuberculosis and paratuberculosis, cross mucosal barriers by endocytosis within mucosal lymphoepithelial sites. These entry sites commonly include oropharyngeal and nasopharyngeal tonsils and Peyer's patches. Bacilli discharged at the basolateral surfaces of engulfing epithelial M cells are taken up by professional antigen-presenting cells associated with T lymphocytes of the parafollicular area. Dendritic cells and macrophages in these sites allow mycobacterial replication, due to the permissive immunological environment in lymphoepithelial tissues. Abrogation of local delayed-type hypersensitivity reactions generally ensures continuing integrity and function of these tissues. Phagocytes containing intracellular mycobacteria disseminate infection to other parts of the body and also probably migrate back onto the mucosal surface to shed bacilli.