Spatial and temporal colonization dynamics of segmented filamentous bacteria is influenced by gender, age and experimental infection with Helicobacter hepaticus in Swiss Webster mice

Environmental Microbial Factors Determine the Pattern of Inflammatory Lesions in a Murine Model of Crohn's Disease-Like Inflammation

Crohn's disease (CD) patients can be grouped into patients suffering from ileitis, ileocolitis, jejunoileitis, and colitis. The pathophysiological mechanism underlying this regional inflammation is still unknown. Although most murine models of inflammatory bowel disease (IBD) develop inflammation in the colon, there is an unmet need for novel models that recapitulate the spontaneous and fluctuating nature of inflammation as seen in CD. Recently, mice with an intestinal epithelial cell-specific deletion for Caspase-8 (Casp8ΔIEC mice), which are characterized by cell death-driven ileitis and disrupted Paneth cell homeostasis, have been identified as a novel model of CD-like ileitis. Here we uncovered that genetic susceptibility alone is sufficient to drive ileitis in Casp8ΔIEC mice. In sharp contrast, environmental factors, such as a disease-relevant microbial flora, determine colonic inflammation. Accordingly, depending on the microbial environment, isogenic Casp8ΔIEC mice either exclusively developed ileitis or suffered from pathologies in several parts of the gastrointestinal tract. Colitis in these mice was characterized by massive epithelial cell death, leading to spread of commensal gut microbes to the extra-intestinal space and hence an aberrant activation of the systemic immunity. We further uncovered that Casp8ΔIEC mice show qualitative and quantitative changes in the intestinal microbiome associated with an altered mucosal and systemic immune response. In summary, we identified that inflammation in this murine model of CD-like inflammation is characterized by an immune reaction, presumably directed against a disease-relevant microbiota in a genetically susceptible host, with impaired mucosal barrier function and bacterial clearance at the epithelial interface.

[Age distribution characteristics of intestinal segmented filamentous bacteria and their relationship with intestinal mucosal immunity in children]

OBJECTIVE

To investigate the age distribution characteristics of intestinal segmented filamentous bacteria (SFB) in children and their relationship with intestinal mucosal immunity.

METHODS

The fresh feces of 177 children and the ileocecal fluid of 47 children during colonoscopy were collected. The SFB was determined by real-time PCR. The concentration of secretory immunoglobulin A (sIgA) was determined by enzyme-linked immunosorbent assay. The numbers of interleukin 17A (IL-17A) cells and intraepithelial lymphocytes in the terminal ileum mucosa and the expression of transcription factors associated with the differentiation of T helper (Th) cells, T-box transcription factor (T-bet), forkhead box P3 (FOXP3), and retinoid-related orphan receptor gamma t (ROR-γt), were determined by immunohistochemistry.

RESULTS

The positive rate of intestinal SFB in these children was 19.2% (34/177). Trend analysis showed that the positive rate of SFB was correlated with age: the rates for children aged 0-, 1-, 2-, 3-, 4-, 5-, 6-, and 7-15 years were 40%, 47%, 32%, 15%, 12%, 13%, 15% and 4% respectively (P<0.001). The concentration of sIgA in intestinal fluid was significantly higher in SFB-positive children (n=24) than in SFB-negative children (n=23) (P<0.01). The number of intraepithelial lymphocytes in the terminal ileum mucosa and the expression of T-bet, FOXP3, and ROR-γt were not significantly different between the SFB-positive group (n=12) and the SFB-negative group (n=11), but the number of IL-17A cells in the terminal ileum mucosa was significantly lower in the SFB-positive group than in the SFB-negative group (P<0.05).

CONCLUSIONS

Intestinal SFB colonization in children is age-related, and the colonization rate is relatively high in children under 3 years old. In SFB-positive children, the secretion of intestinal sIgA is increased, while the number of IL-17A cells in the terminal ileum is reduced.

Helicobacter pylori-infected C57BL/6 mice with different gastrointestinal microbiota have contrasting gastric pathology, microbial and host immune responses

C57BL/6 (B6) mice from Taconic Sciences (Tac) and the Jackson Laboratory (Jax) were infected with H. pylori PMSS1 (Hp) for 16 week; there was no significant difference in the gastric histologic activity index between Hp infected Tac and Jax B6. However, the degree of gastric mucous metaplasia and Th1-associated IgG2c levels in response to Hp infection were increased in Tac mice over Jax mice, whereas the colonization levels of gastric Hp were higher by 8-fold in Jax B6 compared with Tac B6. Additionally, mRNA expression of gastric Il-1β, Il-17A and RegIIIγ were significantly lower in the infected Tac compared to the infected Jax mice. There were significant differences in the microbial community structures in stomach, colon, and feces between Jax and Tac B6 females. Differences in gastric microbial communities between Jax and Tac B6 females are predicted to affect the metagenome. Moreover, Hp infection perturbed the microbial community structures in the stomach, colon and feces of Jax mice, but only altered the colonic microbial composition of Tac mice. Our data indicate that the GI microbiome of Tac B6 mice is compositionally distinct from Jax B6 mice, which likely resulted in different pathological, immunological, and microbial responses to Hp infection.

Tissue-specific emergence of regulatory and intraepithelial T cells from a clonal T cell precursor

Peripheral Foxp3⁺ regulatory T cells (pT_regs) maintain immune homeostasis by controlling potentially harmful effector T cell responses toward dietary and microbial antigens. Although the identity of the T cell receptor (TCR) can impose commitment and functional specialization of T cells, less is known about how TCR identity governs pT_reg development from conventional CD4⁺ T cells. To investigate the extent to which TCR identity dictates pT_reg fate, we used somatic cell nuclear transfer to generate a transnuclear (TN) mouse carrying a monoclonal TCR from a pT_reg (pT_reg TN mice). We found that the pT_reg TCR did not inevitably predispose T cells to become pT_reg but instead allowed for differentiation of noninflammatory CD4⁺CD8αα⁺ intraepithelial lymphocytes (CD4_IELs) in the small intestine. Only when we limited the number of T cell precursors that carried the TN pT_reg TCR did we observe substantial pT_reg development in the mesenteric lymph nodes and small intestine lamina propria of mixed bone marrow chimeras. Small clonal sizes and therefore decreased intraclonal competition were required for pT_reg development. Despite bearing the same TCR, small intestine CD4_IEL developed independently of precursor frequency. Both pT_reg and CD4_IEL development strictly depended on the resident microbiota. A single clonal CD4⁺ T cell precursor can thus give rise to two functionally distinct and anatomically segregated T cell subsets in a microbiota-dependent manner. Therefore, plasticity of the CD4 T cell compartment depends not only on the microbiota but also on specialized environmental cues provided by different tissues.

Development and clinical application of a nested-PCR assay for Helicobacter hepaticus detection

AIM: To develop a nested-PCR assay for the detection of Helicobacter hepaticus (H. hepaticus) with a high sensitivity and specificity and to analyze its clinical application.

METHODS: The nested primers were designed based on the sequences of 16S rRNA gene of nine subtypes of H. hepaticus. After optimizing reaction condition, the sensitivity and specificity of the assay were examined using simulated feces and bile samples, related bacteria, mouse infection model and clinical inpatients samples.

RESULTS: The detection limit for H. hepaticus strain in simulated feces and bile samples was 10² CFU/mL. No specific PCR product was detected with DNA from Helicobacter pylori, Helicobacter bilis, Campylobacter jejuni, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa and Staphylococcus aureus. H. hepaticus was successfully detected in the liver, caecum and feces of experimentally infected mice. Moreover, H. hepaticus was successfully detected in the gallbladder bile, gallbladder mucosa and fecal samples from two of ten patients with cholelithiasis. PCR methods, medical intervention, sample type and management may all influence the detection.

CONCLUSION: Due to the high sensitivity and specificity of the PCR assay, it may be used to detect H. hepaticus infection. H. hepaticus may be associated with the pathogenesis of human cholelithiasis. PCR methods, medical intervention, sample type and management may all influence the detection of clinical samples.

The Other Helicobacters

In the past year, a substantial number of (putative) novel Helicobacter species have been described, including Helicobacter himalayensis colonizing the Himalayan marmot and Helicobacter apodemus, colonizing the Korean striped field mouse. In addition, a putative novel gastric Helicobacter species was identified in wild gorillas and chimpanzees, for which the name "Candidatus H. homininae" was proposed. A high incidence of gastric non-H. pylori Helicobacter infection was described in China and multiple case reports have described the involvement of enterohepatic Helicobacter species, especially Helicobacter cinaedi, in a wide range of diseases. Several studies in rodent models further elucidated the mechanisms underlying the development of gastric mucosa-associated lymphoid tissue lymphoma during infection with gastric non-H. pylori Helicobacters. The effects of infection with gastric Helicobacters on the development of neuroinflammation were investigated and several enterohepatic Helicobacter species were shown to affect the composition of the gut microbiota, to influence vaccine efficiency as well as the progression of cancer in distant sites of the body.