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1.  Dissecting the Interplay Between Intestinal Microbiota and Host Immunity in Health and Disease: Lessons Learned from Germfree and Gnotobiotic Animal Models 
This review elaborates the development of germfree and gnotobiotic animal models and their application in the scientific field to unravel mechanisms underlying host–microbe interactions and distinct diseases. Strictly germfree animals are raised in isolators and not colonized by any organism at all. The germfree state is continuously maintained by birth, raising, housing and breeding under strict sterile conditions. However, isolator raised germfree mice are exposed to a stressful environment and exert an underdeveloped immune system. To circumvent these physiological disadvantages depletion of the bacterial microbiota in conventionally raised and housed mice by antibiotic treatment has become an alternative approach. While fungi and parasites are not affected by antibiosis, the bacterial microbiota in these “secondary abiotic mice” have been shown to be virtually eradicated. Recolonization of isolator raised germfree animals or secondary abiotic mice results in a gnotobiotic state. Both, germfree and gnotobiotic mice have been successfully used to investigate biological functions of the conventional microbiota in health and disease. Particularly for the development of novel clinical applications germfree mice are widely used tools, as summarized in this review further focusing on the modulation of bacterial microbiota in laboratory mice to better mimic conditions in the human host.
doi:10.1556/1886.2016.00036
PMCID: PMC5146645  PMID: 27980855
isolator-raised germfree animals; gnotobiotic animals; secondary abiotic mice; commensal gut microbiota; in vivo model; bacteria/pathogen-host interaction; inflammatory bowel diseases; gut–brain axis
2.  The Immunopathogenic Potential of Arcobacter butzleri – Lessons from a Meta-Analysis of Murine Infection Studies 
PLoS ONE  2016;11(7):e0159685.
Background
Only limited information is available about the immunopathogenic properties of Arcobacter infection in vivo. Therefore, we performed a meta-analysis of published data in murine infection models to compare the pathogenic potential of Arcobacter butzleri with Campylobacter jejuni and commensal Escherichia coli as pathogenic and harmless reference bacteria, respectively.
Methodology / Principal Findings
Gnotobiotic IL-10-/- mice generated by broad-spectrum antibiotic compounds were perorally infected with A. butzleri (strains CCUG 30485 or C1), C. jejuni (strain 81-176) or a commensal intestinal E. coli strain. Either strain stably colonized the murine intestines upon infection. At day 6 postinfection (p.i.), C. jejuni infected mice only displayed severe clinical sequelae such as wasting bloody diarrhea. Gross disease was accompanied by increased numbers of colonic apoptotic cells and distinct immune cell populations including macrophages and monocytes, T and B cells as well as regulatory T cells upon pathogenic infection. Whereas A. butzleri and E. coli infected mice were clinically unaffected, respective colonic immune cell numbers increased in the former, but not in the latter, and more distinctly upon A. butzleri strain CCUG 30485 as compared to C1 strain infection. Both, A. butzleri and C. jejuni induced increased secretion of pro-inflammatory cytokines such as IFN-γ, TNF, IL-6 and MCP-1 in large, but also small intestines. Remarkably, even though viable bacteria did not translocate from the intestines to extra-intestinal compartments, systemic immune responses were induced in C. jejuni, but also A. butzleri infected mice as indicated by increased respective pro-inflammatory cytokine concentrations in serum samples at day 6 p.i.
Conclusion / Significance
A. butzleri induce less distinct pro-inflammatory sequelae as compared to C. jejuni, but more pronounced local and systemic immune responses than commensal E. coli in a strain-dependent manner. Hence, data point towards that A. butzleri is more than a commensal in vertebrate hosts.
doi:10.1371/journal.pone.0159685
PMCID: PMC4954699  PMID: 27438014
3.  The IL-23/IL-22/IL-18 axis in murine Campylobacter jejuni infection 
Gut Pathogens  2016;8:21.
Background
Human Campylobacter jejuni infections are worldwide on the rise. Information about the distinct molecular mechanisms underlying campylobacteriosis, however, are scarce. In the present study we investigated whether cytokines including IL-23, IL-22 and IL-18 sharing pivotal functions in host immunity were involved in mediating immunopathological responses upon C. jejuni infection.
Results
To address this, conventionally colonized IL-23p19−/−, IL-22−/− and IL-18−/− mice were perorally infected with C. jejuni strain ATCC 43431. Respective gene-deficient, but not wildtype mice were susceptible to C. jejuni infection and could be readily colonized with highest pathogenic loads in the terminal ileum and colon at day 14 postinfection (p.i.). In IL-23p19−/−, IL-22−/− and IL-18−/− mice viable C. jejuni were detected in MLNs, but did not translocate to spleen, liver, kidney and blood in the majority of cases. Susceptible IL-22−/−, but neither IL-23p19−/−, nor IL-18−/− mice harbored higher intestinal commensal E. coli loads when compared to resistant wildtype mice. Alike C. jejuni, commensal E. coli did not translocate from the intestinal to extra-intestinal tissue sites. Despite C. jejuni infection, mice lacking IL-23p19, IL-22 or IL-18 exhibited less apoptotic cells, but higher numbers of proliferating cells in their colonic epithelium as compared to wildtype mice at day 14 p.i. Less pronounced apoptosis was parallelled by lower abundance of neutrophils within the colonic mucosa and lamina propria of infected IL-23p19−/− and IL-22−/− as compared to wildtype control mice, whereas less distinct colonic TNF secretion could be measured in IL-22−/− and IL-18−/− than in wildtype mice at day 14 p.i. Notably, in infected IL-22−/− mice, colonic IL-23p19 mRNA levels were lower, whereas the other way round, colonic IL-22 expression rates were lower in IL-23p19−/− mice as compared to wildtype controls. Moreover, IL-18 mRNA was less distinctly expressed in large intestines of naive and infected IL-22−/− mice, but not vice versa, given that IL-22 mRNA levels did not differ between in IL-18−/− and wildtype mice.
Conclusion
Cytokines belonging to the IL-23/IL-22/IL-18 axis mediate immunopathological responses upon murine C. jejuni infection in a differentially orchestrated manner. Future studies need to further unravel the underlying regulatory mechanisms orchestrating pathogenic-host interaction.
Electronic supplementary material
The online version of this article (doi:10.1186/s13099-016-0106-4) contains supplementary material, which is available to authorized users.
doi:10.1186/s13099-016-0106-4
PMCID: PMC4934010  PMID: 27385977
Campylobacter jejuni; In vivo infection; IL-23/IL-22/IL-18 axis; IL-17A;  IL-1β; Pro-inflammatory immune responses; Systemic immune responses; Translocation; Intestinal microbiota; Colonization resistance; Apoptosis
4.  Interleukin-18 Mediates Immune Responses to Campylobacter jejuni Infection in Gnotobiotic Mice 
PLoS ONE  2016;11(6):e0158020.
Background
Human Campylobacter jejuni infections are progressively rising worldwide. Information about the molecular mechanisms underlying campylobacteriosis, however, are limited. In the present study we investigated whether cytokines such as IL-23, IL-22 and IL-18, which share pivotal functions in host immunity, were involved in mediating intestinal and systemic immunopathological responses upon C. jejuni infection.
Methodology/Principal Findings
To assure stable infection, gnotobiotic (i.e. secondary abiotic) IL-23p19-/-, IL-22-/- and IL-18-/- mice were generated by broad-spectrum antibiotic treatment. Following peroral C. jejuni strain 81–176 infection, mice of all genotypes harbored comparably high pathogenic loads in their intestines. As compared to wildtype controls, however, IL-18-/- mice displayed less distinct C. jejuni induced sequelae as indicated by less pronounced large intestinal shrinkage and lower numbers of apoptotic cells in the colonic epithelial layer at day 8 postinfection (p.i.). Furthermore, lower colonic numbers of adaptive immune cells including regulatory T cells and B lymphocytes were accompanied by less distinct secretion of pro-inflammatory cytokines such as TNF and IFN-γ and lower IL-17A mRNA expression levels in colonic ex vivo biopsies of infected IL-18-/- as compared to wildtype mice. Upon C. jejuni infection, colonic IL-23p19 expression was up-regulated in IL-18-/- mice only, whereas IL-22 mRNA levels were lower in uninfected and infected IL-23p19-/- as well as infected IL-18-/- as compared to respective wildtype control mice. Remarkably, not only intestinal, but also systemic infection-induced immune responses were less pronounced in IL-18-/- mice as indicated by lower TNF, IFN-γ and IL-6 serum levels as compared to wildtype mice.
Conclusion/Significance
We here show for the first time that IL-18 is essentially involved in mediating C. jejuni infection in the gnotobiotic mouse model. Future studies need to further unravel the underlying regulatory mechanisms orchestrating pathogen-host interaction.
doi:10.1371/journal.pone.0158020
PMCID: PMC4913948  PMID: 27322540
5.  Colonic Expression of Genes Encoding Inflammatory Mediators and Gelatinases During Campylobacter Jejuni Infection of Conventional Infant Mice 
Within 1 week following peroral Campylobacter jejuni infection, infant mice develop acute enteritis resolving thereafter. We here assessed colonic expression profiles of mediators belonging to the IL-23/IL-22/IL-18 axis and of matrix-degrading gelatinases MMP-2 and MMP-9 at day 6 post C. jejuni strain 81-176 infection. Whereas the pathogen readily colonized the intestines of infant IL-18–/– mice only, colonic mucin-2 mRNA, a pivotal mucus constituent, was downregulated in IL-22–/– mice and accompanied by increased expression of pro-inflammatory cytokines including IFN-γ, TNF, IL-17A, and IL-1β. Furthermore, in both naive and infected IL-22–/– mice, colonic expression of IL-23p19 and IL-18 was lower as compared to wildtype mice, whereas, conversely, colonic IL-22 mRNA levels were lower in IL-18–/– and colonic IL-18 expression lower in IL-23p19–/– as compared to wildtype mice. Moreover, colonic expression of MMP-2 and MMP-9 and their endogenous inhibitor TIMP-1 were lower in IL-22–/– as compared to wildtype mice at day 6 postinfection. In conclusion, mediators belonging of the IL-23/IL-22/IL-18 axis as well as the gelatinases MMP-2 and MMP-9 are involved in mediating campylobacteriosis of infant mice in a differentially regulated fashion.
doi:10.1556/1886.2016.00009
PMCID: PMC4936336  PMID: 27429796
Campylobacter jejuni; infant mice infection model; IL-23/IL-22/IL-18 axis; Th17 cytokines; matrix metalloproteinases; gelatinases; pro-inflammatory immune responses; colonization resistance; intestinal microbiota; apoptosis
6.  The Role of IL-23, IL-22, and IL-18 in Campylobacter Jejuni Infection of Conventional Infant Mice 
We have recently shown that, within 1 week following peroral Campylobacter jejuni infection, conventional infant mice develop self-limiting enteritis. We here investigated the role of IL-23, IL-22, and IL-18 during C. jejuni strain 81-176 infection of infant mice. The pathogen efficiently colonized the intestines of IL-18–/– mice only, but did not translocate to extra-intestinal compartments. At day 13 postinfection (p.i.), IL-22–/– mice displayed lower colonic epithelial apoptotic cell numbers as compared to wildtype mice, whereas, conversely, colonic proliferating cells increased in infected IL-22–/– and IL-18–/– mice. At day 6 p.i., increases in neutrophils, T and B lymphocytes were less pronounced in gene-deficient mice, whereas regulatory T cell numbers were lower in IL-23p19–/– and IL-22–/– as compared to wildtype mice, which was accompanied by increased colonic IL-10 levels in the latter. Until then, colonic pro-inflammatory cytokines including TNF, IFN-γ, IL-6, and MCP-1 increased in IL-23p19–/– mice, whereas IL-18–/– mice exhibited decreased cytokine levels and lower colonic numbers of T and B cell as well as of neutrophils, macrophages, and monocytes as compared to wildtype controls. In conclusion, IL-23, IL-22, and IL-18 are differentially involved in mediating C. jejuni-induced immunopathology of conventional infant mice.
doi:10.1556/1886.2016.00008
PMCID: PMC4936335  PMID: 27429795
Campylobacter jejuni; in vivo infection model; conventional infant mice; IL-23/IL-22/IL-18 axis; Th17 cytokines; pro-inflammatory immune responses; translocation; colonization resistance; intestinal microbiota; apoptosis
7.  Depletion of Cultivatable Gut Microbiota by Broad-Spectrum Antibiotic Pretreatment Worsens Outcome After Murine Stroke 
Supplemental Digital Content is available in the text.
Background and Purpose—
Antibiotics disturbing microbiota are often used in treatment of poststroke infections. A bidirectional brain–gut microbiota axis was recently suggested as a modulator of nervous system diseases. We hypothesized that gut microbiota may be an important player in the course of stroke.
Methods—
We investigated the outcome of focal cerebral ischemia in C57BL/6J mice after an 8-week decontamination with quintuple broad-spectrum antibiotic cocktail. These microbiota-depleted animals were subjected to 60 minutes middle cerebral artery occlusion or sham operation. Infarct volume was measured using magnetic resonance imaging, and mice were monitored clinically throughout the whole experiment. At the end point, tissues were preserved for further analysis, comprising histology and immunologic investigations using flow cytometry.
Results—
We found significantly decreased survival in the middle cerebral artery occlusion microbiota-depleted mice when the antibiotic cocktail was stopped 3 days before surgery (compared with middle cerebral artery occlusion specific pathogen-free and sham-operated microbiota-depleted mice). Moreover, all microbiota-depleted animals in which antibiotic treatment was terminated developed severe acute colitis. This phenotype was rescued by continuous antibiotic treatment or colonization with specific pathogen-free microbiota before surgery. Further, infarct volumes on day one did not differ between any of the experimental groups.
Conclusions—
Conventional microbiota ensures intestinal protection in the mouse model of experimental stroke and prevents development of acute and severe colitis in microbiota-depleted mice not given antibiotic protection after cerebral ischemia. Our experiments raise the clinically important question as to whether microbial colonization or specific microbiota are crucial for stroke outcome.
doi:10.1161/STROKEAHA.115.011800
PMCID: PMC4839545  PMID: 27056982
animal model; antibiotic; brain–gut microbiota axis; ischemic stroke; microbiota depletion
8.  Intestinal Expression of Genes Encoding Inflammatory Mediators and Gelatinases During Arcobacter Butzleri Infection of Gnotobiotic Il-10 Deficient Mice 
We have previously shown that Arcobacter butzleri induces intestinal, extra-intestinal, and systemic immune responses in perorally infected gnotobiotic IL-10–/– mice in a strain-dependent fashion. Here, we present a comprehensive survey of small and large intestinal expression profiles of inflammatory and regulatory mediators as well as of the matrix-degrading gelatinases MMP-2 and MMP-9 following murine A. butzleri infection. Gnotobiotic IL-10–/– mice were infected with A. butzleri strains CCUG 30485 or C1 of human and chicken origin, respectively. At day 6 following A. butzleri infection, mucin-2 mRNA, an integral part of the intestinal mucus layer, was downregulated in the colon, whereas TNF and IL-23p19 mRNA were upregulated in the ileum. Furthermore, IFN-γ, IL-17A, IL-1β, and IL-22 mRNA were upregulated in both colonic and ileal ex vivo biopsies at day 6 post strain CCUG 30485 infection. These changes were accompanied by downregulated colonic MMP-9 levels, whereas both MMP-2 and MMP-9 mRNA were upregulated in the ileum. In conclusion, these data indicate that A. butzleri infection induces changes in the expression of genes involved in pro-inflammatory and regulatory immune responses as well as in tissue degradation.
doi:10.1556/1886.2016.00005
PMCID: PMC4838986  PMID: 27141315
Arcobacter butzleri; Campylobacterales; IL-23/Th17 axis; IL-22/IL-18 axis; pro-inflammatory immune responses; intestinal tract; gnotobiotic IL-10–/– mouse infection model; gelatinases; host defence; mucosal immunology
9.  Toll-Like Receptor-4 Dependent Intestinal Gene Expression During Arcobacter Butzleri Infection of Gnotobiotic Il-10 Deficient Mice 
We have previously shown that Arcobacter butzleri infection induces Toll-like receptor (TLR) -4 dependent immune responses in perorally infected gnotobiotic IL-10–/– mice. Here, we analyzed TLR-4-dependent expression of genes encoding inflammatory mediators and matrix-degrading gelatinases MMP-2 and -9 in the small and large intestines of gnotobiotic TLR-4-deficient IL-10–/– mice that were perorally infected with A. butzleri strains CCUG 30485 or C1, of human and chicken origin, respectively. At day 6 following A. butzleri infection, colonic mucin-2 mRNA, as integral part of the intestinal mucus layer, was downregulated in the colon, but not ileum, of IL-10–/– but not TLR-4–/– IL-10–/– mice. CCUG 30485 strain-infected TLR-4-deficient IL-10–/– mice displayed less distinctly upregulated IFN-γ, IL-17A, and IL-1β mRNA levels in ileum and colon, which was also true for colonic IL-22. These changes were accompanied by upregulated colonic MMP-2 and ileal MMP-9 mRNA exclusively in IL-10–/– mice. In conclusion, TLR-4 is essentially involved in A. butzleri mediated modulation of gene expression in the intestines of gnotobiotic IL-10–/– mice.
doi:10.1556/1886.2016.00006
PMCID: PMC4838987  PMID: 27141316
Arcobacter butzleri; IL-23/Th17 axis; IL-22/IL-18 axis; TLR-4; lipooligosaccharide; lipopolysaccharide; pro-inflammatory immune responses; intestinal innate and adaptive immunity; gnotobiotic IL-10–/– mouse infection model; gelatinases
10.  Toll-Like Receptor-4 is Essential for Arcobacter Butzleri-Induced Colonic and Systemic Immune Responses in Gnotobiotic IL-10–/– Mice 
Arcobacter butzleri causes sporadic cases of gastroenteritis, but the underlying immunopathological mechanisms of infection are unknown. We have recently demonstrated that A. butzleri-infected gnotobiotic IL-10–/– mice were clinically unaffected but exhibited intestinal and systemic inflammatory immune responses. For the first time, we here investigated the role of Toll-like receptor (TLR)-4, the main receptor for lipopolysaccharide and lipooligosaccharide of Gram-negative bacteria, in murine arcobacteriosis. Gnotobiotic TLR-4/IL-10-double deficient (TLR-4–/– IL-10–/–) and IL-10–/– control mice generated by broad-spectrum antibiotics were perorally infected with A. butzleri. Until day 16 postinfection, mice of either genotype were stably colonized with the pathogen, but fecal bacterial loads were approximately 0.5–2.0 log lower in TLR-4–/– IL-10–/– as compared to IL-10–/– mice. A. butzleri-infected TLR-4–/– IL-10–/– mice displayed less pronounced colonic apoptosis accompanied by lower numbers of macrophages and monocytes, T lymphocytes, regulatory T-cells, and B lymphocytes within the colonic mucosa and lamina propria as compared to IL-10–/– mice. Furthermore, colonic concentrations of nitric oxide, TNF, IL-6, MCP-1, and, remarkably, IFN-γ and IL-12p70 serum levels were lower in A. butzleri-infected TLR-4–/– IL-10–/– versus IL-10–/– mice. In conclusion, TLR-4 is involved in mediating murine A. butzleri infection. Further studies are needed to investigate the molecular mechanisms underlying Arcobacter–host interactions in more detail.
doi:10.1556/1886.2015.00043
PMCID: PMC4681360  PMID: 26716021
Arcobacter butzleri; Toll-like receptor-4; lipopolysaccharide; lipooligosaccharide; gnotobiotic IL-10–/–; mice; pro-inflammatory immune responses; systemic immune responses; colon; apoptosis; innate and adaptive immunity
11.  Toll-Like Receptor-4 Dependent Small Intestinal Immune Responses Following Murine Arcobacter Butzleri Infection 
Sporadic cases of gastroenteritis have been attributed to Arcobacter butzleri infection, but information about the underlying immunopathological mechanisms is scarce. We have recently shown that experimental A. butzleri infection induces intestinal, extraintestinal and systemic immune responses in gnotobiotic IL-10–/– mice. The aim of the present study was to investigate the immunopathological role of Toll-like Receptor-4, the receptor for lipopolysaccharide and lipooligosaccharide of Gram-negative bacteria, during murine A. butzleri infection. To address this, gnotobiotic IL-10–/– mice lacking TLR-4 were generated by broad-spectrum antibiotic treatment and perorally infected with two different A. butzleri strains isolated from a patient (CCUG 30485) or fresh chicken meat (C1), respectively. Bacteria of either strain stably colonized the ilea of mice irrespective of their genotype at days 6 and 16 postinfection. As compared to IL-10–/– control animals, TLR-4–/– IL-10–/– mice were protected from A. butzleri-induced ileal apoptosis, from ileal influx of adaptive immune cells including T lymphocytes, regulatory T-cells and B lymphocytes, and from increased ileal IFN-γ secretion. Given that TLR-4-signaling is essential for A. butzleri-induced intestinal inflammation, we conclude that bacterial lipooligosaccharide or lipopolysaccharide compounds aggravate intestinal inflammation and may thus represent major virulence factors of Arcobacter. Future studies need to further unravel the molecular mechanisms of TLR-4-mediated A. butzleri-host interactions.
doi:10.1556/1886.2015.00042
PMCID: PMC4681361  PMID: 26716022
Arcobacter butzleri; Toll-like Receptor-4; lipopolysaccharide; lipooligosaccharide; pro-inflammatory immune responses; small intestine; spleen; apoptosis; innate immunity; host-pathogen interactions
12.  The Role of Gelatinases in Campylobacter Jejuni Infection of Gnotobiotic Mice 
Matrix metalloproteinases (MMP)-2 and -9 (also referred to gelatinases-A and -B, respectively) are upregulated in the inflamed gut of mice and men. We recently demonstrated that synthetic gelatinase blockage reduced large intestinal pro-inflammatory immune responses and apoptosis following murine Campylobacter (C.) jejuni infection. In order to address which gelatinase mediates C. jejuni-induced immune responses, gnotobiotic MMP-2–/–, MMP-9–/–, and wildtype (WT) mice were generated by broadspectrum antibiotic treatment and perorally infected with C. jejuni strain 81-176. The pathogen stably colonized the murine intestinal tract irrespective of the genotype but did not translocate to extra-intestinal compartments. At days 8 and 14 postinfection (p.i.), less pronounced colonic histopathological changes were observed in infected MMP-2–/– mice, less distinct epithelial apoptosis, but more epithelial proliferation in both MMP-2–/– and MMP-9–/– mice, as compared to WT controls. Reduced immune responses in gelatinase-deficient mice were characterized by lower numbers of effector as well as innate and adaptive immune cells within the colonic mucosa and lamina propria. The expression of IL-22, IL-18, IL-17A, and IL-1β mRNA was higher in the colon of MMP-2–/– as compared to WT mice. In conclusion, both MMP-2 and MMP-9 are differentially involved in mediating C. jejuni-induced intestinal immunopathology.
doi:10.1556/1886.2015.00033
PMCID: PMC4681353  PMID: 26716014
Campylobacter jejuni; in vivo infection model; gnotobiotic mice; matrix metalloproteinases; gelatinases; pro-inflammatory immune responses; translocation; IL-22; IL-18; apoptosis
13.  Survey of small intestinal and systemic immune responses following murine Arcobacter butzleri infection 
Gut Pathogens  2015;7:28.
Background
Arcobacter (A.) butzleri has been described as causative agent for sporadic cases of human gastroenteritis with abdominal pain and acute or prolonged watery diarrhea. In vitro studies revealed distinct adhesive, invasive and cytotoxic properties of A. butzleri. Information about the underlying immunopathological mechanisms of infection in vivo, however, are scarce. The aim of this study was to investigate the immunopathological properties of two different A.butzleri strains in a well-established murine infection model.
Results
Gnotobiotic IL-10−/− mice, in which the intestinal microbiota was depleted by broad-spectrum antibiotic treatment, were perorally infected with two different A. butzleri strains isolated from a diseased patient (CCUG 30485) or fresh chicken meat (C1), respectively. Eventhough bacteria of either strain could stably colonize the intestinal tract at day 6 and day 16 postinfection (p.i.), mice did not exert infection induced symptoms such as diarrhea or wasting. In small intestines of infected mice, however, increased numbers of apoptotic cells could be detected at day 16, but not day 6 following infection with either strain. A strain-dependent influx of distinct immune cell populations such as T and B cells as well as of regulatory T cells could be observed upon A. butzleri infection which was accompanied by increased small intestinal concentrations of pro-inflammatory cytokines such as TNF, IFN-γ, MCP-1 and IL-6. Remarkably, inflammatory responses following A. butzleri infection were not restricted to the intestinal tract, given that the CCUG 30485 strain induced systemic immune responses as indicated by increased IFN-γ concentrations in spleens at day 6, but not day 16 following infection.
Conclusion
Upon peroral infection A. butzleri stably colonized the intestinal tract of gnotobiotic IL-10−/− mice. The dynamics of distinct local and systemic inflammatory responses could be observed in a strain-dependent fashion pointing towards an immunopathogenic potential of A. butzleri in vivo. These results indicate that gnotobiotic IL-10−/− mice are well suited to further investigate the molecular mechanisms underlying arcobacteriosis in vivo.
doi:10.1186/s13099-015-0075-z
PMCID: PMC4610047  PMID: 26483849
Arcobacter butzleri; Strain differences; Pro-inflammatory immune responses; Extra-intestinal sequelae; Systemic immune responses; Small intestine; Spleen; Apoptosis; Regenerating cells; Innate and adaptive immunity
14.  Arcobacter butzleri Induce Colonic, Extra-Intestinal and Systemic Inflammatory Responses in Gnotobiotic IL-10 Deficient Mice in a Strain-Dependent Manner 
PLoS ONE  2015;10(9):e0139402.
Background
The immunopathological impact of human Arcobacter (A.) infections is under current debate. Episodes of gastroenteritis with abdominal pain and acute or prolonged watery diarrhea were reported for A. butzleri infected patients. Whereas adhesive, invasive and cytotoxic capacities have been described for A. butzleri in vitro, only limited information is available about the immunopathogenic potential and mechanisms of infection in vivo.
Methodology/Principal Findings
Gnotobiotic IL-10-/- mice were generated by broad-spectrum antibiotic treatment and perorally infected with the A. butzleri strains CCUG 30485 and C1 shown to be invasive in cell culture assays. Bacterial colonization capacities, clinical conditions, intestinal, extra-intestinal and systemic immune responses were monitored at day six and 16 postinfection (p.i.). Despite stable intestinal A. butzleri colonization at high loads, gnotobiotic IL-10-/- mice were virtually unaffected and did not display any overt symptoms at either time point. Notably, A. butzleri infection induced apoptosis of colonic epithelial cells which was paralleled by increased abundance of proliferating cells. Furthermore A. butzleri infection caused a significant increase of distinct immune cell populations such as T and B cells, regulatory T cells, macrophages and monocytes in the colon which was accompanied by elevated colonic TNF, IFN-γ, nitric oxide (NO), IL-6, IL-12p70 and MCP-1 concentrations. Strikingly, A. butzleri induced extra-intestinal and systemic immune responses as indicated by higher NO concentrations in kidney and increased TNF, IFN-γ, IL-12p70 and IL-6 levels in serum samples of infected as compared to naive mice. Overall, inflammatory responses could be observed earlier in the course of infection by the CCUG 30485 as compared to the C1 strain.
Conclusion/Significance
Peroral A. butzleri infection induced not only intestinal but also extra-intestinal and systemic immune responses in gnotobiotic IL-10-/- mice in a strain-dependent manner. These findings point towards an immunopathogenic potential of A. butzleri in vertebrate hosts.
doi:10.1371/journal.pone.0139402
PMCID: PMC4584000  PMID: 26406497
15.  Matrix Metalloproteinase-2 Mediates Intestinal Immunopathogenesis in Campylobacter Jejuni-Infected Infant Mice 
Increased levels of the matrix metalloproteinases (MMPs)-2 and -9 (also referred to gelatinase-A and -B, respectively) can be detected in the inflamed gut. We have recently shown that synthetic gelatinase blockage reduces colonic apoptosis and pro-inflammatory immune responses following murine Campylobacter (C.) jejuni infection. In order to dissect whether MMP-2 and/or MMP-9 is involved in mediating C. jejuni-induced immune responses, infant MMP-2–/–, MMP-9–/–, and wildtype (WT) mice were perorally infected with the C. jejuni strain B2 immediately after weaning. Whereas, at day 2 postinfection (p.i.), fecal C. jejuni B2 loads were comparable in mice of either genotype, mice expelled the pathogen from the intestinal tract until day 4 p.i. Six days p.i., colonic MMP-2 but not MMP-9 mRNA was upregulated in WT mice. Remarkably, infected MMP-2–/– mice exhibited less frequent abundance of blood in feces, less distinct colonic histopathology and apoptosis, lower numbers of effector as well as innate and adaptive immune cells within the colonic mucosa, and higher colonic IL-22 mRNA levels as compared to infected WT mice. In conclusion, these results point towards an important role of MMP-2 in mediating C. jejuni-induced intestinal immunopathogenesis.
doi:10.1556/1886.2015.00020
PMCID: PMC4598886  PMID: 26495129
Campylobacter jejuni; infant mice; matrix metalloproteinase-2; gelatinases; pro-inflammatory immune responses; intestinal microbiota; IL-22; IL23; IL-18; apoptosis
16.  Anti-Inflammatory Properties of NAP in Acute Toxoplasma Gondii-Induced Ileitis in Mice 
The octapeptide NAP has been shown to exert neuroprotective properties. Here, we investigated potential anti-inflammatory effects of NAP in an acute ileitis model. To address this, C57BL/6j mice were perorally infected with Toxoplasma gondii (day 0). Within 1 week postinfection (p.i.), placebo (PLC)-treated mice developed acute ileitis due to Th1-type immune responses. Mice that were subjected to intraperitoneal NAP treatment from day 1 until day 6 p.i., however, developed less distinct macroscopic and microscopic disease as indicated by less body weight loss, less distinct histopathological ileal changes, and lower ileal apoptotic, but higher proliferating cell numbers, less abundance of neutrophils, macrophages, monocytes, and T lymphocytes, but higher numbers of regulatory T cells in the ileal mucosa and lamina propria, and lower concentrations of pro-inflammatory mediators in the ilea as compared to PLC controls at day 7 p.i. Remarkably, NAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments including liver and spleen. Strikingly, lower MCP-1, TNF, and IL-12p70 serum concentrations in NAP as compared to PLC-treated mice at day 7 p.i. indicate a pronounced systemic anti-inflammatory effect of NAP in acute ileitis. These findings provide first evidence for NAP as a potential novel treatment option in intestinal inflammation.
doi:10.1556/1886.2015.00025
PMCID: PMC4598889  PMID: 26495132
NAP; ADNP; Toxoplasma gondii; acute ileitis; Th1-type immunopathology; anti-inflammatory effects; immunomodulatory properties; gut–brain axis
17.  The Goblet Cell Protein Clca1 (Alias mClca3 or Gob-5) Is Not Required for Intestinal Mucus Synthesis, Structure and Barrier Function in Naive or DSS-Challenged Mice 
PLoS ONE  2015;10(7):e0131991.
The secreted, goblet cell-derived protein Clca1 (chloride channel regulator, calcium-activated-1) has been linked to diseases with mucus overproduction, including asthma and cystic fibrosis. In the intestine Clca1 is found in the mucus with an abundance and expression pattern similar to Muc2, the major structural mucus component. We hypothesized that Clca1 is required for the synthesis, structure or barrier function of intestinal mucus and therefore compared wild type and Clca1-deficient mice under naive and at various time points of DSS (dextran sodium sulfate)-challenged conditions. The mucus phenotype in Clca1-deficient compared to wild type mice was systematically characterized by assessment of the mucus protein composition using proteomics, immunofluorescence and expression analysis of selected mucin genes on mRNA level. Mucus barrier integrity was assessed in-vivo by analysis of bacterial penetration into the mucus and translocation into sentinel organs combined analysis of the fecal microbiota and ex-vivo by assessment of mucus penetrability using beads. All of these assays revealed no relevant differences between wild type and Clca1-deficient mice under steady state or DSS-challenged conditions in mouse colon. Clca1 is not required for mucus synthesis, structure and barrier function in the murine colon.
doi:10.1371/journal.pone.0131991
PMCID: PMC4498832  PMID: 26162072
18.  Saponins increase susceptibility of vancomycin-resistant enterococci to antibiotic compounds 
The resistance of commensal bacteria to first and second line antibiotics has reached an alarming level in many parts of the world and endangers the effective treatment of infectious diseases. In this study, the influence of the plant-derived natural saponins glycyrrhizic acid, β-aescin, α-hederin, hederacoside C, and primulic acid 1 on the susceptibility of vancomycin-resistant enterococci (VRE) against antibiotics of clinical relevance was investigated in 20 clinical isolates. Furthermore, the antibacterial properties of saponins under study against VRE were determined in vitro. Results reveal that the susceptibility of VRE against gentamicin, teicoplanin, and daptomycin was enhanced in the presence of the saponin glycyrrhizic acid. Most importantly, glycyrrhizic acid (1 mg/ml) diminished the minimal inhibitory concentration (MIC) of gentamicin in gentamicin low-level intrinsic resistant VRE from 2 – >8 mg/l to ≤ 0.125–1 mg/l. The adding of β-aescin, α-hederin, hederacoside C, and primulic acid 1 to the antibiotics under study showed, compared to glycyrrhizic acid, less influence on the antibiotic potency. Only glycyrrhizic acid (1 mg/ml) and α‑hederin (0.2 mg/ml) showed weak antibacterial properties against the clinical isolates. Our study points towards a therapeutic potential of saponins in the coapplication with antibiotics for bacterial infections.
doi:10.1556/EUJMI-D-14-00029
PMCID: PMC4271817  PMID: 25544893
combination effect; daptomycin; gentamicin; glycyrrhizic acid; saponins; teicoplanin; vancomycin-resistant enterococci
19.  Composition of Intestinal Microbiota in Immune-Deficient Mice Kept in Three Different Housing Conditions 
PLoS ONE  2014;9(11):e113406.
Background
Abundance of commensals constituting the intestinal microbiota (IM) affects the immune system and predisposes to a variety of diseases, including intestinal infections, cancer, inflammatory and metabolic disorders. Housing conditions determine the IM and can hence influence the immune system. We analyzed how both variables affect the IM of four immune-compromized mouse lines kept under different housing conditions.
Methodology/Principal Findings
We investigated the IM composition in mice by quantitative 16S rRNA RT-PCR analysis of the main fecal bacterial groups (Enterobacteriaceae, enterococci, lactobacilli, bifidobacteria, Bacteroides/Prevotella (BP) spp., Clostridium leptum and coccoides groups). Mice were homozygous (HO) or heterozygous (HE) for a targeted inactivating mutation of either the IFN-γ Receptor (R), IFN-γ, Rag1 or IL-4 genes. Overall, differences in IM composition were subtle. However, in the SPF-barrier, total eubacterial loads were higher in Rag1 HE versus Rag1 HO mice as well as in IFN-γR HE versus IFN-γR HO and WT animals. Although absent in WT mice, bifidobacterial loads were higher in HO and HE IFN-γ and Rag1 as well as IL-4 HO mice. Furthermore, BP was slightly lower in HO and HE IFN-γR and IFN-γ mice as well as in IL-4 HO mice as compared to WT controls. Interestingly, IM compositions were comparable in WT mice when kept in individual ventilated cages (IVC) or open cages (OC). IFN-γ HO and HE mice, however, had higher enterobacteria and BP loads, but lacked bifidobacteria when kept in OC versus IVC, as was the case in HO and HE Rag1 mice. In addition, Rag1 HO mice harbored higher clostridial loads when housed in OC as compared to IVC. Unexpectedly, lactobacilli levels were higher in IFN-γR mice when kept in OC versus IVC.
Conclusion/Significance
Housing-dependent and immune-deficiency mediated changes in intestinal microbiota composition were rather subtle but may nevertheless impact immunopathology in experimental models.
doi:10.1371/journal.pone.0113406
PMCID: PMC4234647  PMID: 25401702
20.  Pituitary Adenylate Cyclase-Activating Polypeptide Ameliorates Experimental Acute Ileitis and Extra-Intestinal Sequelae 
PLoS ONE  2014;9(9):e108389.
Background
The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) plays pivotal roles in immunity and inflammation. So far, potential immune-modulatory properties of PACAP have not been investigated in experimental ileitis.
Methodology/Principal Findings
Mice were perorally infected with Toxoplasma (T.) gondii to induce acute ileitis (day 0) and treated daily with synthetic PACAP38 from day 1 to 6 post infection (p.i.; prophylaxis) or from day 4 to 6 p.i. (therapy). Whereas placebo-treated control mice suffered from acute ileitis at day 7 p.i. and succumbed to infection, intestinal immunopathology was ameliorated following PACAP prophylaxis. PACAP-treated mice exhibited increased abundance of small intestinal FOXP3+ cells, but lower numbers of ileal T lymphocytes, neutrophils, monocytes and macrophages, which was accompanied by less ileal expression of pro-inflammatory cytokines such as IL-23p19, IL-22, IFN-γ, and MCP-1. Furthermore, PACAP-treated mice displayed higher anti-inflammatory IL-4 concentrations in mesenteric lymph nodes and liver and higher systemic anti-inflammatory IL-10 levels in spleen and serum as compared to control animals at day 7 p.i. Remarkably, PACAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments as indicated by reduced pro-inflammatory mediator levels in spleen (TNF-α, nitric oxide) and liver (TNF-α, IFN-γ, MCP-1, IL-6) and less severe histopathological sequelae in lungs and kidneys following prophylactic PACAP treatment. Strikingly, PACAP prolonged survival of T. gondii infected mice in a time-of-treatment dependent manner.
Conclusion/Significance
Synthetic PACAP ameliorates acute small intestinal inflammation and extra-intestinal sequelae by down-regulating Th1-type immunopathology, reducing oxidative stress and up-regulating anti-inflammatory cytokine responses. These findings provide novel potential treatment options of inflammatory bowel diseases.
doi:10.1371/journal.pone.0108389
PMCID: PMC4169633  PMID: 25238233
21.  Nucleotide-Oligomerization-Domain-2 Affects Commensal Gut Microbiota Composition and Intracerebral Immunopathology in Acute Toxoplasma gondii Induced Murine Ileitis 
PLoS ONE  2014;9(8):e105120.
Background
Within one week following peroral high dose infection with Toxoplasma (T.) gondii, susceptible mice develop non-selflimiting acute ileitis due to an underlying Th1-type immunopathology. The role of the innate immune receptor nucleotide-oligomerization-domain-2 (NOD2) in mediating potential extra-intestinal inflammatory sequelae including the brain, however, has not been investigated so far.
Methodology/Principal Findings
Following peroral infection with 100 cysts of T. gondii strain ME49, NOD2-/- mice displayed more severe ileitis and higher small intestinal parasitic loads as compared to wildtype (WT) mice. However, systemic (i.e. splenic) levels of pro-inflammatory cytokines such as TNF-α and IFN-γ were lower in NOD2-/- mice versus WT controls at day 7 p.i. Given that the immunopathological outcome might be influenced by the intestinal microbiota composition, which is shaped by NOD2, we performed a quantitative survey of main intestinal bacterial groups by 16S rRNA analysis. Interestingly, Bifidobacteria were virtually absent in NOD2-/- but not WT mice, whereas differences in remaining bacterial species were rather subtle. Interestingly, more distinct intestinal inflammation was accompanied by higher bacterial translocation rates to extra-intestinal tissue sites such as liver, spleen, and kidneys in T. gondii infected NOD2-/- mice. Strikingly, intracerebral inflammatory foci could be observed as early as seven days following T. gondii infection irrespective of the genotype of animals, whereas NOD2-/- mice exhibited higher intracerebral parasitic loads, higher F4/80 positive macrophage and microglia numbers as well as higher IFN-γ mRNA expression levels as compared to WT control animals.
Conclusion/Significance
NOD2 signaling is involved in protection of mice from T. gondii induced acute ileitis. The parasite-induced Th1-type immunopathology at intestinal as well as extra-intestinal sites including the brain is modulated in a NOD2-dependent manner.
doi:10.1371/journal.pone.0105120
PMCID: PMC4139296  PMID: 25141224
22.  Helicobacter pylori Induced Gastric Immunopathology Is Associated with Distinct Microbiota Changes in the Large Intestines of Long-Term Infected Mongolian Gerbils 
PLoS ONE  2014;9(6):e100362.
Background
Gastrointestinal (GI) inflammation in mice and men are frequently accompanied by distinct changes of the GI microbiota composition at sites of inflammation. Helicobacter (H.) pylori infection results in gastric immunopathology accompanied by colonization of stomachs with bacterial species, which are usually restricted to the lower intestine. Potential microbiota shifts distal to the inflammatory process following long-term H. pylori infection, however, have not been studied so far.
Methodology/Principal Findings
For the first time, we investigated microbiota changes along the entire GI tract of Mongolian gerbils after 14 months of infection with H. pylori B8 wildtype (WT) or its isogenic ΔcagY mutant (MUT) strain which is defective in the type IV secretion system and thus unable to modulate specific host pathways. Comprehensive cultural analyses revealed that severe gastric diseases such as atrophic pangastritis and precancerous transformations were accompanied by elevated luminal loads of E. coli and enterococci in the caecum and together with Bacteroides/Prevotella spp. in the colon of H. pylori WT, but not MUT infected gerbils as compared to naïve animals. Strikingly, molecular analyses revealed that Akkermansia, an uncultivable species involved in mucus degradation, was exclusively abundant in large intestines of H. pylori WT, but not MUT infected nor naïve gerbils.
Conclusion/Significance
Taken together, long-term infection of Mongolian gerbils with a H. pylori WT strain displaying an intact type IV secretion system leads to distinct shifts of the microbiota composition in the distal uninflamed, but not proximal inflamed GI tract. Hence, H. pylori induced immunopathogenesis of the stomach, including hypochlorhydria and hypergastrinemia, might trigger large intestinal microbiota changes whereas the exact underlying mechanisms need to be further unraveled.
doi:10.1371/journal.pone.0100362
PMCID: PMC4062524  PMID: 24941045
23.  The impact of Toll-like-receptor-9 on intestinal microbiota composition and extra-intestinal sequelae in experimental Toxoplasma gondii induced ileitis 
Gut Pathogens  2014;6:19.
Background
Following peroral Toxoplasma (T.) gondii infection, susceptible mice develop acute ileitis due to a microbiota-dependent Th1 type immunopathology. Toll-like-receptor (TLR)-9 is known to recognize bacterial DNA and mediates intestinal inflammation, but its impact on intestinal microbiota composition and extra-intestinal sequelae following T. gondii infection has not yet been elucidated.
Methods and results
Seven days following peroral infection (p.i.) with 100 cysts of T. gondii ME49 strain, TLR-9-/- and wildtype (WT) mice suffered from comparable ileitis, whereas ileal parasitic loads as well as IFN-γ and nitric oxide levels were higher in TLR-9-/- compared to WT mice. Locally, TLR-9-/- mice exhibited increased ileal CD3+, but not FOXP3+ cell numbers at day 7 p.i.; in mesenteric lymph nodes IFN-γ-producing CD4+ cell numbers and TNF-α and IFN-γ concentrations were also increased in TLR-9-/- compared to WT mice. T. gondii DNA levels, however, did not differ in mice of either genotype. Differences in intestinal microbiota were rather subtle except for bifidobacteria that were virtually absent in both, naïve and T. gondii infected TLR-9-/-, but not WT mice. Extra-intestinally, TLR-9-/- mice displayed less distinct systemic immune responses as indicated by lower serum IL-6, and splenic TNF-α and IFN-γ levels as compared to WT mice despite higher translocation rates of intestinal bacteria to extra-intestinal compartments such as liver, spleen, kidney, and cardiac blood. Most importantly, brains were also affected in this inflammatory scenario as early as day 7 p.i. Remarkably, TLR-9-/- mice exhibited more pronounced inflammatory infiltrates with higher numbers of F4/80+ macrophages and microglia in the cortex and meninges as compared to WT mice, whereas T. gondii DNA levels did not differ.
Conclusion
We here show that TLR-9 is not required for the development of T. gondii induced ileitis but mediates distinct inflammatory changes in intestinal and extra-intestinal compartments including the brain.
doi:10.1186/1757-4749-6-19
PMCID: PMC4057803  PMID: 24932221
Toxoplasma gondii; Acute ileitis; TLR-9; Th1-type immunopathology; Extra-intestinal immune responses; Intracerebral inflammation; Pro-inflammatory cytokines; Intestinal microbiota composition; Bacterial translocation; Systemic inflammatory response; Bifidobacteria; FOXP3; Regulatory T cells; Gut-brain-axis
24.  The impact of serine protease HtrA in apoptosis, intestinal immune responses and extra-intestinal histopathology during Campylobacter jejuni infection of infant mice 
Gut Pathogens  2014;6:16.
Background
Campylobacter jejuni has emerged as a leading cause of bacterial enterocolitis. The serine protease HtrA has been shown to be a pivotal, novel C. jejuni virulence factor involved in cell invasion and transmigration across polarised epithelial cells in vitro. However, the functional relevance of the htrA gene for the interaction of C. jejuni with the host immune system in the infant mouse infection model has not been investigated so far.
Results
Here we studied the role of C. jejuni htrA during infection of 3-weeks-old infant mice. Immediately after weaning, conventional wild-type mice were perorally infected with the NCTC11168∆htrA mutant (∆htrA) or the parental wild-type strain. Approximately one third of infected infant mice suffered from bloody diarrhea until day 7 post infection (p.i.), whereas colonic histopathological changes were rather moderate but comparable between the two strains. Interestingly, parental, but not ∆htrA mutant infected mice, displayed a multifold increase of apoptotic cells in the colonic mucosa at day 7 p.i., which was paralleled by higher colonic levels of pro-inflammatory cytokines such as TNF-α and IFN-γ and the matrix-degrading enzyme matrixmetalloproteinase-2 (MMP-2). Furthermore, higher numbers of proliferating cells could be observed in the colon of ∆htrA infected mice as compared to the parental wild-type strain. Remarkably, as early as 7 days p.i. infant mice also exhibited inflammatory changes in extra-intestinal compartments such as liver, kidneys and lungs, which were less distinct in kidneys and lungs following ∆htrA versus parental strain infection. However, live C. jejuni bacteria could not be found in these organs, suggesting the induction of systemic effects during intestinal infection.
Conclusion
Upon C. jejuni ∆htrA strain infection of infant mice, intestinal and extra-intestinal pro-inflammatory immune responses were ameliorated in the infant mouse model system. Future studies will shed further light onto the molecular mechanisms of host-pathogen interactions.
doi:10.1186/1757-4749-6-16
PMCID: PMC4040118  PMID: 24883112
Cell invasion; Conventional infant mice; Ulcerative enterocolitis; Innate immunity; Host-pathogen-interaction; Apoptosis; Extra-intestinal immune responses; Hepatic; Renal; Pulmonal histopathology
25.  Small intestinal permeability in older adults 
Physiological Reports  2014;2(4):e00281.
Abstract
It is not yet clear whether intestinal mucosal permeability changes with advancing age in humans. This question is of high importance for drug and nutrition approaches for older adults. Our main objective was to answer the question if small intestinal barrier integrity deteriorates with healthy aging. We conducted a cross‐sectional study including the pooled data of 215 nonsmoking healthy adults (93 female/122 male), 84 of whom were aged between 60 and 82 years. After a 12‐h fast, all participants ingested 10 g of lactulose and 5 g of mannitol. Urine was collected for 5 h afterwards and analyzed for test sugars. The permeability index (PI = lactulose/mannitol) was used to assess small intestinal permeability. Low‐grade inflammation defined by high‐sensitivity C‐reactive protein ≥1 mL/L and kidney function (estimated glomerular filtration rate) were determined in the older age group. The PI was similar in older compared to younger adults (P =0.887). However, the urinary recovery of lactulose and mannitol was lower in the older adults and this change was neither associated with urinary volume nor glomerular filtration rate. The PI was not significantly correlated with low‐grade inflammation or presence of noninsulin‐dependent type 2 diabetes. However, it significantly deteriorated in the copresence of both conditions compared to low‐grade inflammation alone (P =0.043) or type 2 diabetes alone (P =0.015). Small intestinal mucosal barrier does not deteriorate with age per se. But low‐grade inflammation coupled with minor disease challenges, such as type 2 diabetes, can compromise the small intestinal barrier.
Until now, it has not been clear if the small intestinal mucosal barrier deteriorates with age per se. We investigated the pooled data of 215 nonsmoking healthy adults, 84 of whom were aged between 60 and 82 years and found similar intestinal permeability results in all age classes. However, in participants with low‐grade inflammation coupled with type 2 diabetes the small intestinal integrity was compromised.
doi:10.14814/phy2.281
PMCID: PMC4001874  PMID: 24771689
Aging; cardiovascular risk; gut leakiness; small intestine; sugar test

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