Gastritis associated with infection by Helicobacter pylori: comparative pathology in humans and swine

Isolation and preliminary characterization of a novel Helicobacter species from swine

OBJECTIVE

To determine whether a Helicobacter sp similar to Helicobacter pylori in the stomachs of humans could be isolated from the stomachs of pigs.

ANIMALS

4 young conventionally reared and 21 gnotobiotic pigs.

PROCEDURE

Gastric mucosal homogenates (10% wt/vol) from 4 young conventionally reared pigs were cultured on Skirrow medium under microaerophilic conditions to assess the presence of Helicobacter spp. Colonies with morphologic features compatible with Helicobacter organisms were selected, tested for urease activity, and subpassaged on Skirrow medium. Isolates were examined via SDS-PAGE electrophoresis and reciprocal western blot analyses involving convalescent sera from monoinfected gnotobiotic pigs.

RESULTS

Urease- and catalase-positive, gram-negative, microaerophilic, small, curved rod bacteria were isolated from the gastric mucosa of young healthy pigs. The first isolate (2662) was structurally and immunologically closely related to H pylori isolated from humans. The second isolate (1268) displayed an SDS-PAGE profile dissimilar to that of H pylori and isolate 2662, yet it shared limited immunologic cross-reactivity with these microbes.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings of this study indicate that development of gastric mucosal ulcers and ulceration of the nonglandular pars esophagea in pigs may be associated with gastric colonization by swine-origin Helicobacter spp, which are similar to H pylori isolated from humans.

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.

Induction of chemokine and cytokine responses by Helicobacter pylori in human stomach explants

BACKGROUND

The cytokine response during the acute phase of Helicobacter pylori infection in humans has not been studied. The aim of this study was therefore to investigate the early cytokine responses against H. pylori using cultured human stomach explants as a model of acute infection.

METHODS

Gastric corpus tissue obtained from 13 adult uninfected and 3 H. pylori-infected patients undergoing gastric surgery due to obesity was used for preparation of mucosal explants. The cultured explants were exposed to different H. pylori strains or antigens, that is, lipopolysaccharides (LPS), urease and heat-shock protein (Hsp) B. The responses of the CXC chemokines interleukin (IL)-8, growth-related oncogene alpha (GROalpha) and interferon-inducible protein (IP) 10 as well as the CC chemokine regulated on activation normal T-cell expressed and secreted (RANTES) were determined by ELISA. In addition, IL-4, IL-6, IL-10, IL-12, interferon gamma (IFNgamma), tumour necrosis factor alpha (TNFalpha) and granulocyte-macropage-colony stimulating factor (GM-CSF) were studied.

RESULTS

In vitro H. pylori infection of the explants preferentially induced responses of the CXC chemokines GROalpha (P < 0.05) and IL-8 (P < 0.05), whereas the CC chemokine response (RANTES) was weak. In addition, the production of IL-6 was increased after H. pylori infection. Stimulation of the explants with different LPS preparations also induced strong GROalpha, IL-8 and IL-6 responses; the GROalpha responses being significantly higher after stimulation with rough than smooth H. pylori LPS (P < 0.05).

CONCLUSIONS

GROalpha, IL-8 and IL-6 are increased early during acute H. pylori infection and may influence the development of gastric disease.

Production of gastroesophageal erosions and ulcers (GEU) in gnotobiotic swine monoinfected with fermentative commensal bacteria and fed high-carbohydrate diet

Erosions and gastroesophageal ulcers (GEU) were produced in the pars esophagea of young gnotobiotic swine fed a carbohydrate-enriched liquid diet and monoinfected with two different fermentative commensal bacteria, Lactobacillus and Bacillus sp. In contrast, piglets, fed a similar diet and inoculated with Gastrospirillum sp. (Helicobacter heilmannii), a helicobacter species that colonizes the gastric mucosa, did not develop GEU. Experimental GEU likely develops secondary to epithelial damage mediated by microbial-origin acids whose production is potentiated by high dietary carbohydrate and parietal cell-origin hydrochloric acid.

Antimicrobial therapies for Helicobacter pylori infection in gnotobiotic piglets

Gnotobiotic piglets infected with Helicobacter pylori were treated with various antimicrobials as monotherapy and dual therapy, and the results were compared to those for piglets treated with a triple-therapy regimen (bismuth subsalicyclate at 5.7 mg/kg of body weight, metronidazole at 4.4 mg/kg, and amoxicillin at 6.8 mg/kg four times a day [QID]). Clearance of infection was assessed after 7 days of treatment, and eradication was assessed following 7 days of treatment and a 14-day posttreatment observation interval. Monotherapy with amoxicillin, clarithromycin, and ciprofloxacin cleared and eradicated the organism from porcine stomachs; monotherapy with metronidazole cleared the infection and eradicated it from some piglets. Metronidazole-resistant microbes were recovered from treated piglets which cleared but did not eradicate the infection. Monotherapy with bismuth subsalicylate, erythromycin, nitrofurantoin, and tetracycline in the dosage range of 5.0 to 7.1 mg/kg QID was less than 100% effective in clearance and eradication, in that these drugs cleared and/or eradicated the infection from some of the piglets but did not eradicate the infection from all of the piglets. Monotherapy with an H-2 receptor antagonist (ranitidine) or a proton pump inhibitor (omeprazole) was ineffective at either clearance or eradication. In vivo dose titrations with several effective monotherapies were performed to determine the lowest effective in vivo dose of drug. In piglets, eradication was associated with a statistically significant decline in serum H. pylori-specific immunoglobulin M (IgM) antibodies; the titers of both IgA and IgG also declined, but the values were not statistically significant. For many antimicrobials, piglets are more sensitive indicators of clearance and eradication than humans. These data establish the H. pylori-infected gnotobiotic piglet as a useful model for the identification of novel antimicrobials for the treatment of this disease and for drug assessment during preclinical evaluations.

Role of vacuolating cytotoxin in gastritis due to Helicobacter pylori in gnotobiotic piglets

To investigate the role of the Helicobacter pylori cytotoxin in the pathogenesis of gastritis, gnotobiotic piglets were colonized with either toxigenic H. pylori or a nontoxigenic isogenic mutant. Only piglets given the toxigenic strain developed toxin-neutralizing antibodies (indicating that toxin is expressed in vivo), but there was no difference in bacterial colonization, epithelial vacuolation, or gastritis between the two groups of piglets.

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

The presence and features of mucosa associated lymhoid tissue (MALT), analogous to Peyer's patches, in the cardia of the lesser curvature of the porcine stomach are described. The gastric mucosa associated lymphoid tissue (gastric-MALT) is histologically distinct from gastric inflammation associated with colonization by normal gastric microflora and experimental bacterial colonization with a human gastric bacterial pathogen, Helicobacter pylori. The gastric-MALT consists of well-demarcated encapsulated and organized lymphoid tissue, intimately associated with overlying gastric epithelium, centered below the muscularis mucosae and drained by efferent lymphatics. Gastric-MALT was identified in all piglets studied including microbially sterile uninfected gnotobiotes; these structures were enlarged with age and local (gastric) antigenic stimulation. Significant (P < 0.05) expansion of the gastric-MALT occurred in H. pylori-infected gnotobiotic piglets. These distinct morphologic features and location in the cardia suggest that lymphoid elements in the gastric-MALT are involved in gastric antigen processing and regional lymphoid maturation, differentiation and proliferation in the stomach.

Cell envelope characteristics of Helicobacter pylori: their role in adherence to mucosal surfaces and virulence

Helicobacter pylori colonises the gastric mucosa of humans and causes both antral gastritis and duodenal ulcer disease. Exactly how H. pylori causes disease is not known but several pathogenic determinants have been proposed for the organism. These include adhesins, cytotoxins and a range of different enzymes including urease, catalase and superoxide dismutase. Surface molecules of H. pylori such as flagella, lipopolysaccharide, the urease enzyme and outer membrane proteins are putative adhesin molecules. While phosphatidylethanolamine and the Lewis(b) blood group antigen have been proposed as receptor molecules for the organism the exact mechanism by which H. pylori adheres to the gastric mucosa has still to be identified. Characterisation of the adhesins of H. pylori could lead to the development of adhesin analogues for use in the inhibition of colonisation and improved therapy for ulcer disease. In vivo studies with isogenic mutants which are incapable of adhering to the gastric mucosa would greatly clarify the significance of adherence. Such mutants could possibly be useful as a vaccine against infection with wild-type organisms.

Manifestations of the local gastric immune response in gnotobiotic piglets infected with Helicobacter pylori

Helicobacter pylori, a human gastric bacterial pathogen, was inoculated into gnotobiotic piglets and manifestations of the resultant gastric inflammation was analyzed by in situ immunochemistry and flow cytometric analysis of isolated lamina propria leukocytes (LPL) and peripheral blood leukocytes (PBL) recovered from infected and control piglets. Gastric mucosa tissue sections from uninfected control piglets were essentially negative for cluster differentiation- (CD-) positive leukocytes. Failure to isolate significant numbers of LPL from the gastric lamina propria confirmed this observation. A local and systemic immune response occurs in piglets after infection with H. pylori. This is manifest by the appearance of cells associated with a local immune response in gastric mucosa. In gastric tissue sections from H. pylori-infected piglets, CD4-positive leukocytes were sparse and closely associated with developing lymphoid follicles whereas the CD8-positive cellular phenotype was abundant. The latter formed a continuous band in the lamina propria just above the muscularis mucosa. Perivascular accumulations of lymphocytes in the outer muscular tunic(s) were strongly positive for expression of CD8 antigen. Class II-positive cells were prominent in CD8 lymphocytic infiltrates, developing follicles and vascular endothelia but were uniformly absent from gastric epithelia even in sites overlying areas of immunocyte proliferation and infiltration. Leukocytes possessing the monocyte and granulocyte markers were rare. Plasma cells containing IgA were common in the periphery of developing lymphoid follicles or distributed as discrete foci around individual gastric pits. Fewer numbers of IgG- and IgM-positive plasma cells were identified. When the LPL flow cytometry data were compared with the flow cytometry data obtained from PBL in these same H. pylori-infected piglets, leukocytes bearing the CD8 marker predominated in LPL whereas leukocytes bearing the CD4-reactive and MHC class II markers predominated in PBL. Finally, local ELISA antibody responses were measured in mucosal explant culture supernatants and compared with in vivo antibody levels in sera, bile, and gastric juice. Antibody activity, specific for H. pylori, was detected in supermatants and serum in all three isotypes in actively infected piglets whereas gastric juice lacked antibodies. Gastric explants prepared from piglets in which infection had been successfully eradicated failed to produce local antibody into supermatant fluids. These data support the concept that the gastric inflammation observed is mediated by local immunological events.

The role of gastric mast cells, enterochromaffin-like cells and parietal cells in the regulation of acid secretion

The idea presented here is that, in gastric mucosa, two independent regulatory systems use the same transmitter: histamine molecules. The IgE/mast cell system is dispersed throughout the body, while the other regulates the gastric acid secretion. IgE molecules in gastric mucosa are attached to the mast cells. Mast cells release histamine molecules after the antigen has been recognized by IgE. These molecules normally act on vascular H1 receptors to promote extravasation and chemotaxy. Gastrin molecules are released from antral G cells to stimulate gastric acid secretion. Their influence on parietal cells is indirectly augmented by gastrin governed release of histamine molecules from enterochromaffin-like cells. These histamine molecules normally act on H2 receptors of parietal cells to promote gastric acid secretion. Chronic infection of gastric mucosa (i.e. with Helicobacter pylori), autoimmune disorders or repetitive mucosal exposure to the same antigen, can develop chronic inflammation of gastric mucosa. Gastric acid secretion is diminished with secondary hypergastrinemia and increased release of histamine from enterochromaffin-like cells in an attempt to stimulate the few remaining parietal cells. Hypothetically, increased concentrations of released histamine in gastric mucosa might activate the vascular H1 receptors with extravasation and aggravated inflammation. This can further decrease the number of active parietal cells, reduce gastric acid secretion and potentiate hypergastrinemia. In this hypothetical setting, H1 blockers might reduce the damage by abolishing the vascular reactions. The prolonged antigen load on gastric mucosa can promote production of specific IgE antibodies. Further exposures to the same antigen degranulate sensitized mucosal mast cells. Liberated histamine can produce extravasation through the vascular H1 receptor and, hypothetically, local hyperacidity through the parietal cell H2 receptors. The result would be hyperacidity and hypogastrinemia with possible ulcer disease. Some individuals are more predisposed to IgE production or have increased numbers of mast cells that might explain why only some people develop ulcer disease after H. pylori infection.

Occurrence of gastric ulcers in gnotobiotic piglets colonized by Helicobacter pylori

Archival gastric tissues from 10 of 39 gnotobiotic piglets colonized with Helicobacter pylori 26695 contained stromal leukocytic inflammation along with ulcers and erosions. In contrast, gastric tissues from 54 archival control piglets were devoid of both inflammation and ulcers. These data confirm the hypothesis that H. pylori infection alone is ulcerogenic.