Persistent increase in myofibroblasts in Helicobacter heilmannii-infected mice but not in Helicobacter pylori-infected Mongolian gerbils: colocalization of COX-2 and bFGF immunoreactivity

Gastric lesions and immune responses caused by long-term infection with Helicobacter heilmannii in C57BL/6 mice

Helicobacter heilmannii is a gastric micro-organism that can induce gastritis and B-cell MALT (mucosa-associated lymphoid tissue) lymphoma in mice, in a host-dependent manner. The present study was designed to examine gastric lesions and immune responses caused by intragastric H. heilmannii infection of an inbred mouse strain, C57BL/6. Long-term infection led to the formation of gastric nodules and increased mucosal thickness of the stomach, due to gastric epithelial proliferation. Infection also induced the formation of lymphoid follicles in the corpus mucosa and submucosa. The follicular cells were mainly CD45R+ cells that did not produce immunoglobulin. However, scattered in the lamina propria and corpus submucosa, numerous IgA+ cells were found in infected mice, but not in control mice. RT-PCR results showed that H. heilmannii infection led to increased mRNA expression for IFN-gamma (a Th1 cytokine) and IL-10 (a Th2 cytokine) in the mouse stomach, suggesting that both Th1 and Th2 responses are associated with H. heilmannii infection. The mRNA of other cytokines and chemokines (IL-1beta, IL-12p40, TNF-alpha, MCP-1, KC and MIP-2) was also increased by infection.

Increased apoptosis and angiogenesis in gastric low-grade mucosa-associated lymphoid tissue-type lymphoma by Helicobacter heilmannii infection in C57/BL6 mice

Helicobacter heilmannii has been reported to cause gastric low-grade mucosa-associated lymphoid tissue-type (MALT) lymphoma, but its precise pathophysiological mechanism remains to be clarified. We recently established a model of gastric B-cell MALT lymphoma in C57BL/6 mice by means of peroral infection of H. heilmannii primarily obtained from cynomolgus monkeys. Using this model, macroscopic, immunohistochemical, and electron microscopic observations of MALT lymphomas were carried out in order to examine the development of apoptosis and angiogenesis. Enhancement of the microvascular network and an increase in vascular endothelial growth factor-A were detected in the central region of the MALT lymphoma tissue in the infected mouse stomach, while vascular endothelial growth factor-C was detected at the margins of the MALT lymphomas. In addition, many H. heilmannii-invaded parietal cells showed caspase-3 immunoreactivity in the fundic mucosal tissue surrounding the MALT lymphoma. In conclusion, in H. heilmannii-induced MALT lymphoma, enhanced immunoreactivity of vascular endothelial growth factor-A and factor-C was observed in areas encircled by increased parietal cell apoptosis, which indicates the pathophysiological relevance of both angiogenesis and apoptosis in MALT lymphoma formation.

"Candidatus Helicobacter heilmannii" from a cynomolgus monkey induces gastric mucosa-associated lymphoid tissue lymphomas in C57BL/6 mice

Both Helicobacter pylori and "Candidatus Helicobacter heilmannii" infections are associated with peptic ulcers, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue (MALT) lymphomas. However, good animal models of H. pylori clinical diseases are rare. In this study, we aimed to establish an animal model of "Candidatus Helicobacter heilmannii" gastric MALT lymphoma. We used a urease-positive gastric mucosal and mucus homogenate from a cynomolgus monkey maintained in C57BL/6 mouse stomachs. The bacterium in the homogenate was identified as "Candidatus Helicobacter heilmannii" based on a DNA sequence analysis of the 16S rRNA and urease genes. Mucosal and mucus homogenates were used to inoculate C57BL/6 mice, which were then examined for 24 months. We observed a gradual increase in the surface area of protrusive lesions in almost all infected C57BL/6 mouse fundic stomachs 6 months after infection. Light microscopic observations revealed an accumulation of B lymphocytes along with destruction of glandular elements and the presence of lymphoepithelial lesions consistent with low-grade MALT lymphomas. Electron microscopic observation revealed numerous "Candidatus Helicobacter heilmannii" bacilli in the fundic glandular lumen, the intracellular canaliculi, and the cytoplasm of intact cells, as well as damaged parietal cells. In conclusion, "Candidatus Helicobacter heilmannii" induced gastric MALT lymphomas in almost 100% of infected C57BL/6 mice after a 6-month period associated with the destruction of parietal cells.

Cloning of Mongolian gerbil cDNAs encoding inflammatory proteins, and their expression in glandular stomach during H. pylori infection

Mongolian gerbils are considered to be a good animal model for understanding the development of Helicobacter pylori-associated diseases. However, limitations regarding the genetic information available for this animal species hamper the elucidation of underlying mechanisms. Thus, we have focused on identifying the nucleotide sequences of cDNAs encoding Mongolian gerbil inflammatory proteins, such as interleukin-1 (IL-1beta), tumor necrosis factor alpha (TNF-alpha), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). Furthermore, we examined the mRNA expression of these genes in the glandular stomach by RT-PCR at 1-8 weeks after H. pylori infection. The deduced amino acid homologies to mouse, rat and human proteins were 86.2%, 83.6% and 67.8% for IL-1beta, 87.2%, 85.1% and 78.4% for TNF-alpha , 91.9%, 90.2% and 84.8% for COX-2 and 90.8%, 89.1% and 80.1% for iNOS, respectively. The average stomach weight of Mongolian gerbils inoculated with H. pylori was increased in a time-dependent manner at 1, 2, 4 and 8 weeks after inoculation. In the pyloric region, mRNA expression levels of IL-1beta, TNF-alpha and iNOS were increased in H. pylori-infected animals at the 2 weeks time point, while in the fundic region, expression levels of IL-1beta, TNF-alpha and iNOS were elevated at 4 and 8 weeks. The COX-2 expression level in the fundic region was clearly elevated in infected animals compared with control animals at 4 and 8 weeks, but in the pyloric region, expression levels were similar in both infected and control animals. Thus, our results indicate that oxidative stress occurs from an early stage of H. pylori infection in the glandular stomach of Mongolian gerbils.