Helicobacter pylori is a gram-negative microaerophilic spiral bacterium that predominantly inhabits the antral region of the human stomach. While H. pylori can also be found in the body or fundus of the stomach or in gastric metaplasia of the duodenum, it seems well adapted only to gastric tissues. It is not found, for instance, in normal small or large intestine or esophagus. In vitro, it grows quite slowly and only under conditions of reduced (but not absent) oxygen. In the absence of relatively complex antimicrobial treatment protocols, this bacterium can apparently establish a life-long infection. The organism resides within the mucus layer of both surface and glandular epithelium. This ecologic niche serves to protect the organism from both the harsh environmental conditions of the stomach as well as from host-effector mechanisms. However, despite the fact that host responses are ineffective in clearing the organism, H. pylori induces a state of active/chronic gastric inflammation (involving both neutrophils and lymphocytes) in all infected individuals. While there is no overt disease in most infected people, a subset of infected individuals may develop peptic ulcers, gastric adenocarcinoma, or gastric mu-cosa-associated lymphoid tissue (MALT) lymphoma. The outcome of infection is determined by a complex interplay between bacterial virulence factors and the host response. Individuals with high gastric-acid output who are infected with virulent H. pylori strains may be predisposed towards antral-predominant infections and gastritis leading to peptic-ulcer disease. Individuals with lower gastric acid output are prone to infection of both the antrum and body of the stomach, pangastritis, atrophy of glandular and parietal cells in the body/fundus of the stomach, and gastric adenocarcinoma.
From immunologic points of view, animal models for H. pylori infection are useful in helping to understand disease processes and in vaccine development. In this unit the protocols for growing Helicobacter organisms on plates (see Basic Protocol 1; see Support Protocol 4 for solid medium preparation) or in liquid cultures (see Basic Protocol 2) are presented first, followed by protocols for infecting mice with Helicobacter felis and H. pylori (see Basic Protocol 3) and for infecting ferrets with H. mustelae (Basic Protocol 5). Also, a procedure is described for adapting an H. pylori isolate (e.g., from a clinical source) to growth in mice (see Basic Protocol 4). Support Protocols 1 and 3 describe methods for quantifying numbers of Helicobacter organisms, and Support Protocol 2 describes how to create a growth curve for Helicobacter cultures. One important technique in investigating Helicobacter infection is assaying the disease processes that occur in the stomach. It is important to have properly prepared tissue sections for this purpose, which is the subject of Support Protocol 5. It is also important to confirm that organisms recovered from tissue samples are, in fact, Helicobacter species. Support Protocol 6 describes morphological and biochemical tests that can be used for this purpose. Helicobacter bacteria produce large amounts of the enzyme urease, and this has been the basis for both human and animal diagnostic tests. Support Protocol 7 describes how to perform a rapid urease test on animal-tissue biopsies. Assays of Helicobacter-specific immune responses require appropriate antigens, and Support Protocols 8 and 9 describe how to prepare both Helicobacter lysates and outer-membrane proteins for use in these assays. Finally, H. pylori and the other organisms described in this unit are gastric pathogens. It may be useful to measure antibody responses in gastric secretions, the collection of which is described in Support Protocols 10 and 11.
Animal Models for Infectious Diseases
Contributed by John G. Nedrud and Thomas G. Blanchard
Current Protocols in Immunology (2000) 19.8.1-19.8.26 Copyright © 2000 by John Wiley & Sons, Inc.
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