Campylobacter jejuni induces acute enterocolitis in gnotobiotic IL-10-/- mice via Toll-like-receptor-2 and -4 signaling

Toll-like receptor-4 differentially mediates intestinal and extra-intestinal immune responses upon multi-drug resistant Pseudomonas aeruginosa association of IL10-/- mice with chronic colitis

Background

Infections with multi-drug resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (PA) have become a serious threat particularly in hospitalized patients with immunopathological co-morbidities. The well-balanced interplay between immune cells, pattern recognition receptors such as Toll-like receptor (TLR)-4 sensing lipopolysaccharide from Gram-negative bacteria including PA, and evolving pathways is crucial to prevent the host from invading (opportunistic) pathogens. Information regarding the molecular mechanisms underlying the interactions between intestinal carriage of MDR PA and host immunity during chronic large intestinal inflammation is scarce, however.

Methods and results

We therefore perorally challenged conventionally colonized TLR4-deficient IL10^−/− mice and IL10^−/− counterparts displaying comparably severe chronic colitis with a clinical MDR PA strain. PA could more sufficiently establish in the intestinal tract of TLR4-deficient IL10^−/− mice until day 14 postinfection (p.i.), whereas within 48 h the majority of IL10^−/− mice had already expelled the opportunistic pathogen from their guts. Intestinal colonization properties of PA in TLR4-deficient IL10^−/− mice were associated with distinct genotype-dependent differences in gut microbiota compositions before challenge given that TLR4-deficient IL10^−/− mice harbored more fecal enterobacteria and enterococci, but lower Clostridium/Eubacterium burdens. At day 14 p.i., PA-induced increases in colonic immune cells such as macrophages, monocytes and T-lymphocytes could be observed in TLR4-deficient IL10^−/− mice, but not IL10^−/− counterparts, that were accompanied by a more distinct secretion of IFN-γ in the colon and TNF in the mesenteric lymph nodes (MLN) of the former as compared to the latter. Conversely, splenic TNF levels were lower in TLR4-deficient IL10^−/− mice as compared to IL10^−/− controls at day 14 p.i. Interestingly, more pronounced apoptotic responses could be assessed in colonic epithelia of PA-challenged IL10^−/− mice only. This was paralleled by enhanced pro-inflammatory cytokine secretion not only in the intestines, but also in extra-intestinal compartments of IL10^−/− mice as indicated by increased concentrations of nitric oxide in the colon, IFN-γ in the MLN and IL-12p70 in the spleen at day 14 p.i.

Conclusions

Under chronic intestinal inflammatory conditions including IL10^−/− colitis MDR PA-association results in well-orchestrated TLR4-dependent immune responses both in intestinal and extra-intestinal compartments. Further studies should unravel the underlying molecular mechanisms in more detail.

Electronic supplementary material

The online version of this article (10.1186/s13099-017-0211-z) contains supplementary material, which is available to authorized users.

Toll-Like Receptor-4 Dependent Inflammatory Responses Following Intestinal Colonization of Secondary Abiotic IL10-Deficient Mice with Multidrug-Resistant Pseudomonas Aeruginosa

The rising incidences of infections with multidrug-resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (PA) have gained increasing attention in medicine, but also in the general public and global health politics. The mechanisms underlying opportunistic pathogen–host interactions are unclear, however. To address this, we challenged secondary abiotic IL10^–/– mice deficient for Toll-like receptor-4 (TLR4^–/– × IL10^–/–), the main receptor of the Gram-negative cell wall constituent lipopolysaccharide, with a clinical MDR PA isolate. Despite higher intestinal colonization densities, apoptotic colonic epithelial cell numbers were lower in TLR4^–/– × IL10^–/– mice as compared to IL10^–/– controls at day 14 postinfection (p.i.), whereas proliferating/regenerating cells had increased in the latter only. Furthermore, PA-colonized TLR4^–/– × IL10^–/– mice displayed less distinct innate and adaptive immune cell responses in the colon as compared to IL10^–/– counterparts that were accompanied by lower nitric oxide concentrations in mesenteric lymph nodes in the former at day 14 p.i. Conversely, splenic NO levels were higher in both naive and PA-colonized TLR4-deficient IL10^–/– mice versus IL10^–/– controls. Remarkably, intestinal MDR PA was able to translocate to extra-intestinal including systemic compartments of TLR4^–/– × IL10^–/– mice only. Hence, MDR PA-induced intestinal and systemic immune responses observed in secondary abiotic IL10^–/– mice are TLR4-dependent.

Multidrug-Resistant Pseudomonas Aeruginosa Induce Systemic Pro-Inflammatory Immune Responses in Colonized Mice

The World Health Organization has rated multidrug-resistant (MDR) Pseudomonas aeruginosa as a critical threat to human health. In the present study, we performed a survey of intestinal colonization, and local and systemic immune responses following peroral association of secondary abiotic mice with either a clinical MDR P. aeruginosa or a commensal murine Escherichia coli isolate. Depletion of the intestinal microbiota following antibiotic treatment facilitated stable intestinal colonization of both P. aeruginosa and E. coli that were neither associated with relevant clinical nor histopathological sequelae. Either stable bacterial colonization, however, resulted in distinct innate and adaptive immune cell responses in the intestines, whereas a pronounced increase in macrophages and monocytes could be observed in the small as well as large intestines upon P. aeruginosa challenge only, which also applied to colonic T lymphocytes. In addition, TNF secretion was exclusively elevated in large intestines of P. aeruginosa-colonized mice. Strikingly, association of secondary abiotic mice with MDR P. aeruginosa, but not commensal E. coli, resulted in pronounced systemic pro-inflammatory responses, whereas anti-inflammatory responses were dampened. Hence, intestinal carriage of MDR P. aeruginosa as compared to a mere commensal Gram-negative strain in otherwise healthy individuals results in distinct local and systemic pro-inflammatory sequelae.

Absence of Nucleotide-Oligomerization-Domain-2 Is Associated with Less Distinct Disease in Campylobacter jejuni Infected Secondary Abiotic IL-10 Deficient Mice

Human Campylobacter jejuni-infections are progressively increasing worldwide. Despite their high prevalence and socioeconomic impact the underlying mechanisms of pathogen-host-interactions are only incompletely understood. Given that the innate immune receptor nucleotide-oligomerization-domain-2 (Nod2) is involved in clearance of enteropathogens, we here evaluated its role in murine campylobacteriosis. To address this, we applied Nod2-deficient IL-10-/- (Nod2-/- IL-10-/-) mice and IL-10-/- counterparts both with a depleted intestinal microbiota to warrant pathogen-induced enterocolitis. At day 7 following peroral C. jejuni strain 81-176 infection, Nod2 mRNA was down-regulated in the colon of secondary abiotic IL-10-/- and wildtype mice. Nod2-deficiency did neither affect gastrointestinal colonization nor extra-intestinal and systemic translocation properties of C. jejuni. Colonic mucin-2 mRNA was, however, down-regulated upon C. jejuni-infection of both Nod2-/- IL-10-/- and IL-10-/- mice, whereas expression levels were lower in infected, but also naive Nod2-/- IL-10-/- mice as compared to respective IL-10-/- controls. Remarkably, C. jejuni-infected Nod2-/- IL-10-/- mice were less compromised than IL-10-/- counterparts and displayed less distinct apoptotic, but higher regenerative cell responses in colonic epithelia. Conversely, innate as well as adaptive immune cells such as macrophages and monocytes as well as T lymphocytes and regulatory T-cells, respectively, were even more abundant in large intestines of Nod2-/- IL-10-/- as compared to IL-10-/- mice at day 7 post-infection. Furthermore, IFN-γ concentrations were higher in ex vivo biopsies derived from intestinal compartments including colon and mesenteric lymph nodes as well as in systemic tissue sites such as the spleen of C. jejuni infected Nod2-/- IL-10-/- as compared to IL10-/- counterparts. Whereas, at day 7 postinfection anti-inflammatory IL-22 mRNA levels were up-regulated, IL-18 mRNA was down-regulated in large intestines of Nod2-/- IL-10-/- vs. IL-10-/- mice. In summary, C. jejuni-infection induced less clinical signs and apoptosis, but more distinct colonic pro- and (of note) anti-inflammatory immune as well as regenerative cell responses in Nod2 deficient IL-10-/- as compared to IL-10-/- control mice. We conclude that, even though colonic Nod2 mRNA was down-regulated upon pathogenic challenge, Nod2-signaling is essentially involved in the well-balanced innate and adaptive immune responses upon C. jejuni-infection of secondary abiotic IL-10-/- mice, but does neither impact pathogenic colonization nor translocation.

Small Intestinal Pro-Inflammatory Immune Responses Following Campylobacter Jejuni Infection of Secondary Abiotic IL-10-/- Mice Lacking Nucleotide-Oligomerization-Domain-2

Host immune responses are crucial for combating enteropathogenic infections including Campylobacter jejuni. Within 1 week following peroral C. jejuni infection, secondary abiotic IL-10^–/– mice develop severe immunopathological sequelae affecting the colon (ulcerative enterocolitis). In the present study, we addressed whether pathogen-induced pro-inflammatory immune responses could also be observed in the small intestines dependent on the innate receptor nucleotide-oligomerization-domain-protein 2 (Nod2). Within 7 days following peroral infection, C. jejuni stably colonized the gastrointestinal tract of both IL-10^–/– mice lacking Nod2 (Nod2^–/– IL-10^–/–) and IL-10^–/– controls displaying bloody diarrhea with similar frequencies. Numbers of apoptotic and regenerating epithelial cells increased in the small intestines of C. jejuni-infected mice of either genotype that were accompanied by elevated ileal T and B lymphocyte counts. Notably, ileal T cell numbers were higher in C. jejuni-infected Nod2^–/– IL-10^–/– as compared to IL-10^–/– counterparts. Furthermore, multifold increased concentrations of pro-inflammatory cytokines including IFN-γ, TNF, and MCP-1 could be measured in small intestinal ex vivo biopsies derived from C. jejuni-infected mice of either genotype. In conclusion, C. jejuni-induced pro-inflammatory immune responses affected the small intestines of both Nod2^–/– IL-10^–/– and IL-10^–/– mice, whereas ileal T lymphocyte numbers were even higher in the former.

Immune responses upon Campylobacter jejuni infection of secondary abiotic mice lacking nucleotide-oligomerization-domain-2

Background

Campylobacter jejuni infections are of rising importance worldwide. Given that innate immune receptors including nucleotide-oligomerization-domain-2 (Nod2) are essentially involved in combating enteropathogenic infections, we here surveyed the impact of Nod2 in murine campylobacteriosis.

Methods and results

In order to overcome physiological colonization resistance preventing from C. jejuni infection, we generated secondary abiotic Nod2^−/− and wildtype (WT) mice by broad-spectrum antibiotic treatment. Mice were then perorally infected with C. jejuni strain 81-176 on 2 consecutive days and could be stably colonized by the pathogen at high loads. Notably, Nod2 deficiency did not affect gastrointestinal colonization properties of C. jejuni. Despite high intestinal pathogenic burdens mice were virtually uncompromised and exhibited fecal blood in single cases only. At day 7 postinfection (p.i.) similar increases in numbers of colonic epithelial apoptotic cells could be observed in mice of either genotype, whereas C. jejuni infected Nod2^−/− mice displayed more distinct regenerative properties in the colon than WT controls. C. jejuni infection was accompanied by increases in distinct immune cell populations such as T lymphocytes and regulatory T cells in mice of either genotype. Increases in T lymphocytes, however, were less pronounced in large intestines of Nod2^−/− mice at day 7 p.i. when compared to WT mice, whereas colonic numbers of B lymphocytes were elevated in WT controls only upon C. jejuni infection. At day 7 p.i., colonic pro-inflammatory mediators including nitric oxide, TNF, IFN-γ and IL-22 increased more distinctly in Nod2^−/− as compared to WT mice, whereas C. jejuni induced IL-23p19 and IL-18 levels were lower in the large intestines of the former. Converse to the colon, however, ileal concentrations of nitric oxide, TNF, IFN-γ, IL-6 and IL-10 were lower in Nod2^−/− as compared to WT mice at day 7 p.i. Even though MUC2 was down-regulated in C. jejuni infected Nod2^−/− mice, this did not result in increased pathogenic translocation from the intestinal tract to extra-intestinal compartments.

Conclusion

In secondary abiotic mice, Nod2 signaling is involved in the orchestrated host immune responses upon C. jejuni infection, but does not control pathogen loads in the gastrointestinal tract.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0182-0) contains supplementary material, which is available to authorized users.

The Probiotic Compound VSL#3 Modulates Mucosal, Peripheral, and Systemic Immunity Following Murine Broad-Spectrum Antibiotic Treatment

There is compelling evidence linking the commensal intestinal microbiota with host health and, in turn, antibiotic induced perturbations of microbiota composition with distinct pathologies. Despite the attractiveness of probiotic therapy as a tool to beneficially alter the intestinal microbiota, its immunological effects are still incompletely understood. The aim of the present study was to assess the efficacy of the probiotic formulation VSL#3 consisting of eight distinct bacterial species (including Streptococcus thermophilus, Bifidobacterium breve, B. longum, B. infantis, Lactobacillus acidophilus, L. plantarum, L. paracasei, and L. delbrueckii subsp. Bulgaricus) in reversing immunological effects of microbiota depletion as compared to reassociation with a complex murine microbiota. To address this, conventional mice were subjected to broad-spectrum antibiotic therapy for 8 weeks and perorally reassociated with either VSL#3 bacteria or a complex murine microbiota. VSL#3 recolonization resulted in restored CD4+ and CD8+ cell numbers in the small and large intestinal lamina propria as well as in B220+ cell numbers in the former, whereas probiotic intervention was not sufficient to reverse the antibiotic induced changes of respective cell populations in the spleen. However, VSL#3 application was as efficient as complex microbiota reassociation to attenuate the frequencies of regulatory T cells, activated dendritic cells and memory/effector T cells in the small intestine, colon, mesenteric lymph nodes, and spleen. Whereas broad-spectrum antibiotic treatment resulted in decreased production of cytokines such as IFN-γ, IL-17, IL-22, and IL-10 by CD4+ cells in respective immunological compartments, VSL#3 recolonization was sufficient to completely recover the expression of the anti-inflammatory cytokine IL-10 without affecting pro-inflammatory mediators. In summary, the probiotic compound VSL#3 has an extensive impact on mucosal, peripheral, and systemic innate as well as adaptive immunity, exerting beneficial anti-inflammatory effects in intestinal as well as systemic compartments. Hence, VSL#3 might be considered a therapeutic immunomodulatory tool following antibiotic therapy.

Amelioration of intestinal and systemic sequelae of murine Campylobacter jejuni infection by probiotic VSL#3 treatment

Background

The incidence of human Campylobacter jejuni infections is progressively increasing worldwide. Probiotic compounds might open up valuable tools to decrease pathogen burden and subsequent pro-inflammatory immune responses, but in vivo data are scarce.

Methods and results

Secondary abiotic mice generated by broad-spectrum antibiotic treatment were perorally challenged with the commercial probiotic compound VSL#3 consisting of Streptococcus thermophilus, Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus delbrueckii ssp. bulgaricus) either 5 days before (i.e. prophylactic regimen) or after (i.e. therapeutic regimen) peroral C. jejuni strain 81–176 infection, and analyzed 3 weeks following the initial bacterial re-association. Upon challenge, mice were colonized with the probiotic bacteria and/or C. jejuni at comparable intestinal loads, but co-colonization did not result in reduction of the pathogen burden. Remarkably, prophylactic as well as therapeutic VSL#3 treatment of C. jejuni infected mice ameliorated intestinal apoptosis and pro-inflammatory immune responses as indicated by lower numbers of innate and adaptive immune cell populations in the murine colon upon probiotic prophylaxis or treatment and reduced colonic concentrations of pro-inflammatory mediators including IL-6 and MCP-1. Importantly, concentrations of anti-inflammatory mediators such as IL-10 were significantly elevated in the colon of probiotics treated mice as compared to untreated controls. Strikingly, prophylactic VSL#3 treatment attenuated C. jejuni induced systemic pro-inflammatory responses as indicated by less TNF and IL-12p70 secretion in the spleen of VSL#3 pre-treated as compared to non-treated mice.

Conclusion

Administration of probiotic formulations such as VSL#3 might open up valuable strategies for prophylaxis and/or treatment of C. jejuni induced intestinal and systemic sequelae in vivo by the suppression of pro-inflammatory and induction of anti-inflammatory responses.

Mechanisms of inflammation-driven bacterial dysbiosis in the gut

The gut microbiota has diverse and essential roles in host metabolism, development of the immune system and as resistance to pathogen colonization. Perturbations of the gut microbiota, termed gut dysbiosis, are commonly observed in diseases involving inflammation in the gut, including inflammatory bowel disease, infection, colorectal cancer and food allergies. Importantly, the inflamed microenvironment in the gut is particularly conducive to blooms of Enterobacteriaceae, which acquire fitness benefits while other families of symbiotic bacteria succumb to environmental changes inflicted by inflammation. Here we summarize studies that examined factors in the inflamed gut that contribute to blooms of Enterobacterieaceae, and highlight potential approaches to restrict Enterobacterial blooms in treating diseases that are otherwise complicated by overgrowth of virulent Enterobacterial species in the gut.

Microbiota Composition and Immune Responses During Campylobacter Jejuni Infection in Conventionally Colonized IL-10-/- Mice Lacking Nucleotide Oligomerization Domain 2

Host immune responses are pivotal for combating enteropathogenic infections. We here assessed the impact of the innate receptor nucleotide oligomerization domain protein 2 (NOD2) in murine Campylobacter jejuni-infection. Conventionally colonized IL-10^–/– mice lacking NOD2 and IL-10^–/– controls were perorally challenged with C. jejuni strain 81-176 and displayed comparable pathogenic colonization of intestines until day 14 postinfection (p.i.). Whereas overall intestinal microbiota compositions were comparable in naive mice, NOD2^–/– IL-10^–/– mice exhibited less fecal bifidobacteria and lactobacilli than IL-10^–/– counterparts after infection. Interestingly, NOD2^–/– IL-10^–/– mice were clinically more compromised during the early phase of infection, whereas, conversely, IL-10^–/– animals exhibited more frequently bloody feces lateron. While colonic apoptotic cell and T lymphocyte numbers were comparable in either C. jejuni-infected mice, B lymphocytes were lower in the colon of infected NOD2^–/– IL-10^–/– mice versus controls. At day 14 p.i., colonic TNF and IL-23p19 mRNA levels were upregulated in NOD2^–/– IL-10^–/– mice only. Translocation rates of intestinal commensals to mesenteric lymphnodes and extra-intestinal compartments including liver and kidney were comparable, whereas viable bacteria were more frequently detected in spleens derived from IL-10^–/– as compared to NOD2^–/– IL-10^–/– mice. In conclusion, NOD2 is involved during C. jejuni infection in conventionally colonized IL-10^–/– mice in a time-dependent manner.

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.

The Immunopathogenic Potential of Arcobacter butzleri - Lessons from a Meta-Analysis of Murine Infection Studies

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.

Interleukin-18 Mediates Immune Responses to Campylobacter jejuni Infection in Gnotobiotic Mice

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.

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.

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.

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.

Probiotics: a proactive approach to health. A symposium report

This report summarises talks given at the 8th International Yakult Symposium, held on 23-24 April 2015 in Berlin. Two presentations explored different aspects of probiotic intervention: the small intestine as a probiotic target and inclusion of probiotics into integrative approaches to gastroenterology. Probiotic recommendations in gastroenterology guidelines and current data on probiotic efficacy in paediatric patients were reviewed. Updates were given on probiotic and gut microbiota research in obesity and obesity-related diseases, the gut-brain axis and development of psychobiotics, and the protective effects of equol-producing strains for prostate cancer. Recent studies were presented on probiotic benefit for antibiotic-associated diarrhoea and people with HIV, as well as protection against the adverse effects of a short-term high-fat diet. Aspects of probiotic mechanisms of activity were discussed, including immunomodulatory mechanisms and metabolite effects, the anti-inflammatory properties of Faecalibacterium prausnitzii, the relationship between periodontitis, microbial production of butyrate in the oral cavity and ageing, and the pathogenic mechanisms of Campylobacter. Finally, an insight was given on a recent expert meeting, which re-examined the probiotic definition, advised on the appropriate use and scope of the term and outlined different probiotic categories and the prevalence of different mechanisms of activity.

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.

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.

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.

Survey of small intestinal and systemic immune responses following murine Arcobacter butzleri infection

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.

Arcobacter butzleri Induce Colonic, Extra-Intestinal and Systemic Inflammatory Responses in Gnotobiotic IL-10 Deficient Mice in a Strain-Dependent Manner

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.

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.

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.

The Intestinal Microbiota Influences Campylobacter jejuni Colonization and Extraintestinal Dissemination in Mice

Campylobacter jejuni is a leading cause of human foodborne gastroenteritis worldwide. The interactions between this pathogen and the intestinal microbiome within a host are of interest as endogenous intestinal microbiota mediates a form of resistance to the pathogen. This resistance, termed colonization resistance, is the ability of commensal microbiota to prevent colonization by exogenous pathogens or opportunistic commensals. Although mice normally demonstrate colonization resistance to C. jejuni, we found that mice treated with ampicillin are colonized by C. jejuni, with recovery of Campylobacter from the colon, mesenteric lymph nodes, and spleen. Furthermore, there was a significant reduction in recovery of C. jejuni from ampicillin-treated mice inoculated with a C. jejuni virulence mutant (ΔflgL strain) compared to recovery of mice inoculated with the C. jejuni wild-type strain or the C. jejuni complemented isolate (ΔflgL/flgL). Comparative analysis of the microbiota from nontreated and ampicillin-treated CBA/J mice led to the identification of a lactic acid-fermenting isolate of Enterococcus faecalis that prevented C. jejuni growth in vitro and limited C. jejuni colonization of mice. Next-generation sequencing of DNA from fecal pellets that were collected from ampicillin-treated CBA/J mice revealed a significant decrease in diversity of operational taxonomic units (OTUs) compared to that in control (nontreated) mice. Taken together, we have demonstrated that treatment of mice with ampicillin alters the intestinal microbiota and permits C. jejuni colonization. These findings provide valuable insights for researchers using mice to investigate C. jejuni colonization factors, virulence determinants, or the mechanistic basis of probiotics.

Insights into Campylobacter jejuni colonization of the mammalian intestinal tract using a novel mouse model of infection

A lack of relevant disease models for Campylobacter jejuni has long been an obstacle to research into this common enteric pathogen. We recently published that mice deficient in Single IgG Interleukin-1 related receptor (SIGIRR), a repressor of MyD88-dependent innate immune signaling, were highly susceptible to enteric infection by murine bacterial pathogens. Subsequently, we successfully employed these mice as an animal model for the human pathogen C. jejuni and gained substantial new insights into infection by this pathogen. The infected mice developed significant intestinal inflammation, primarily via TLR4 stimulation. Furthermore, the resulting gastroenteritis was dependent on C. jejuni pathogenesis as bacterial strains suffering mutations in key virulence factors were attenuated in causing disease. The ability to infect SIGIRR-deficient mice with C. jejuni sheds new light onto how these bacteria colonize the mucus layer of the intestinal tract, invade epithelial cells, and raises new prospects for studying the virulence strategies and pathogenesis of C. jejuni.

Novel insights in preventing Gram-negative bacterial infection in cirrhotic patients: review on the effects of GM-CSF in maintaining homeostasis of the immune system

Cirrhotic patients with dysfunctional and/or low numbers of leukocytes are often infected with bacteria, especially Gram-negative bacteria, which is characterized by producing lipopolysaccharide (LPS). Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that influences the production, maturation, function, and survival of various immune cells. In this paper, we reviewed not only Toll-like receptors 4 (TLR4) signaling pathway and its immunological effect, but also the specific stimulating function and autocrine performance of GM-CSF on hematopoietic cells, as well as the recent discovery of innate response activator-B cells in protection against microbial sepsis and the direct LPS-TLR4 signaling on hematopoiesis. Thus we concluded that GM-CSF might play important roles in preventing Gram-negative bacterial infections in cirrhotic patients through maintaining immune system functions and homeostasis.

Selective gelatinase inhibition reduces apoptosis and pro-inflammatory immune cell responses in Campylobacter jejuni-infected gnotobiotic IL-10 deficient mice

Increased levels of the matrix metalloproteinases-2 and -9 (also referred to gelatinase-A and -B, respectively) can be detected in intestinal inflammation. We have recently shown that selective gelatinase blockage by the synthetic compound RO28-2653 ameliorates acute murine ileitis and colitis. We here investigated whether RO28-2653 exerts anti-inflammatory effects in acute Campylobacter jejuni-induced enterocolitis of gnotobiotic IL-10(-/-) mice generated following antibiotic treatment. Mice were perorally infected with C. jejuni (day 0) and either treated with RO28-2653 (75 mg/kg body weight/day) or placebo from day 1 until day 6 post infection (p.i.) by gavage. Irrespective of the treatment, infected mice displayed comparable pathogen loads within the gastrointestinal tract. Following RO28-2653 administration, however, infected mice exhibited less severe symptoms such as bloody diarrhea as compared to placebo controls. Furthermore, less distinct apoptosis but higher numbers of proliferating cells could be detected in the colon of RO28-2653-treated as compared to placebo-treated mice at day 7 p.i. Remarkably, gelatinase blockage resulted in lower numbers of T- and B-lymphocytes as well as macrophages and monocytes in the colonic mucosa of C. jejuni-infected gnotobiotic IL-10(-/-) mice. Taken together, synthetic gelatinase inhibition exerts anti-inflammatory effects in experimental campylobacteriosis.

Pituitary adenylate cyclase-activating polypeptide ameliorates experimental acute ileitis and extra-intestinal sequelae

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.

Nucleotide-oligomerization-domain-2 affects commensal gut microbiota composition and intracerebral immunopathology in acute Toxoplasma gondii induced murine ileitis

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.

A novel mouse model of Campylobacter jejuni gastroenteritis reveals key pro-inflammatory and tissue protective roles for Toll-like receptor signaling during infection

Campylobacter jejuni is a major source of foodborne illness in the developed world, and a common cause of clinical gastroenteritis. Exactly how C. jejuni colonizes its host's intestines and causes disease is poorly understood. Although it causes severe diarrhea and gastroenteritis in humans, C. jejuni typically dwells as a commensal microbe within the intestines of most animals, including birds, where its colonization is asymptomatic. Pretreatment of C57BL/6 mice with the antibiotic vancomycin facilitated intestinal C. jejuni colonization, albeit with minimal pathology. In contrast, vancomycin pretreatment of mice deficient in SIGIRR (Sigirr^−/−), a negative regulator of MyD88-dependent signaling led to heavy and widespread C. jejuni colonization, accompanied by severe gastroenteritis involving strongly elevated transcription of Th1/Th17 cytokines. C. jejuni heavily colonized the cecal and colonic crypts of Sigirr^−/− mice, adhering to, as well as invading intestinal epithelial cells. This infectivity was dependent on established C. jejuni pathogenicity factors, capsular polysaccharides (kpsM) and motility/flagella (flaA). We also explored the basis for the inflammatory response elicited by C. jejuni in Sigirr^−/− mice, focusing on the roles played by Toll-like receptors (TLR) 2 and 4, as these innate receptors were strongly stimulated by C. jejuni. Despite heavy colonization, Tlr4^−/−/Sigirr^−/− mice were largely unresponsive to infection by C. jejuni, whereas Tlr2^−/−/Sigirr^−/− mice developed exaggerated inflammation and pathology. This indicates that TLR4 signaling underlies the majority of the enteritis seen in this model, whereas TLR2 signaling had a protective role, acting to promote mucosal integrity. Furthermore, we found that loss of the C. jejuni capsule led to increased TLR4 activation and exaggerated inflammation and gastroenteritis. Together, these results validate the use of Sigirr^−/− mice as an exciting and relevant animal model for studying the pathogenesis and innate immune responses to C. jejuni.

Research into the key virulence strategies of the bacterial pathogen Campylobacter jejuni, as well as the host immune responses that develop against this microbe have, in many ways, been limited by the lack of relevant animal models. Here we describe the use of Sigirr deficient (^−/−) mice as a model for C. jejuni pathogenesis. Not only do Sigirr^−/− mice develop significant intestinal inflammation in response to colonization by C. jejuni, but the ability of this pathogen to trigger gastroenteritis was dependent on key virulence factors. We also found that the induction of the inflammatory and Th1/Th17 immune responses to infection in these mice depended on specific Toll-like receptors, principally TLR4, which we identified as the main driver of inflammation. In contrast, TLR2 signaling was found to protect mucosal integrity, with Tlr2^−/−/Sigirr^−/− mice suffering exaggerated mucosal damage and inflammation. Notably, we found that C. jejuni's capsule helped conceal it from the host's immune system as its loss led to significantly increased activation of host TLRs and exaggerated gastroenteritis. Our research shows that the increased sensitivity of Sigirr^−/− mice can be used to generate a unique and exciting model that facilitates the study of C. jejuni pathogenesis as well as host immunity to this enteric pathogen.

Campylobacter jejuni is not merely a commensal in commercial broiler chickens and affects bird welfare

Campylobacter jejuni is the leading cause of bacterial food-borne infection; chicken meat is its main source. C. jejuni is considered commensal in chickens based on experimental models unrepresentative of commercial production. Here we show that the paradigm of Campylobacter commensalism in the chicken is flawed. Through experimental infection of four commercial breeds of broiler chickens, we show that breed has a significant effect on C. jejuni infection and the immune response of the animals, although these factors have limited impact on the number of bacteria in chicken ceca. All breeds mounted an innate immune response. In some breeds, this response declined when interleukin-10 was expressed, consistent with regulation of the intestinal inflammatory response, and these birds remained healthy. In another breed, there was a prolonged inflammatory response, evidence of damage to gut mucosa, and diarrhea. We show that bird type has a major impact on infection biology of C. jejuni. In some breeds, infection leads to disease, and the bacterium cannot be considered a harmless commensal. These findings have implications for the welfare of chickens in commercial production where C. jejuni infection is a persistent problem. Importance: Campylobacter jejuni is the most common cause of food-borne bacterial diarrheal disease in the developed world. Chicken is the most common source of infection. C. jejuni infection of chickens had previously not been considered to cause disease, and it was thought that C. jejuni was part of the normal microbiota of birds. In this work, we show that modern rapidly growing chicken breeds used in intensive production systems have a strong inflammatory response to C. jejuni infection that can lead to diarrhea, which, in turn, leads to damage to the feet and legs on the birds due to standing on wet litter. The response and level of disease varied between breeds and is related to regulation of the inflammatory immune response. These findings challenge the paradigm that C. jejuni is a harmless commensal of chickens and that C. jejuni infection may have substantial impact on animal health and welfare in intensive poultry production:

The role of serine protease HtrA in acute ulcerative enterocolitis and extra-intestinal immune responses during Campylobacter jejuni infection of gnotobiotic IL-10 deficient mice

Campylobacter jejuni infections have a high prevalence worldwide and represent a significant socioeconomic burden. C. jejuni can cross the intestinal epithelial barrier as visualized in biopsies derived from human patients and animal models, however, the underlying molecular mechanisms and associated immunopathology are still not well understood. We have recently shown that the secreted serine protease HtrA (high temperature requirement A) plays a key role in C. jejuni cellular invasion and transmigration across polarized epithelial cells in vitro. In the present in vivo study we investigated the role of HtrA during C. jejuni infection of mice. We used the gnotobiotic IL-10^−/− mouse model to study campylobacteriosis following peroral infection with the C. jejuni wild-type (WT) strain NCTC11168 and the isogenic, non-polar NCTC11168ΔhtrA deletion mutant. Six days post infection (p.i.) with either strain mice harbored comparable intestinal C. jejuni loads, whereas ulcerative enterocolitis was less pronounced in mice infected with the ΔhtrA mutant strain. Moreover, ΔhtrA mutant infected mice displayed lower apoptotic cell numbers in the large intestinal mucosa, less colonic accumulation of neutrophils, macrophages and monocytes, lower large intestinal nitric oxide, IFN-γ, and IL-6 as well as lower TNF-α and IL-6 serum concentrations as compared to WT strain infected mice at day 6 p.i. Notably, immunopathological responses were not restricted to the intestinal tract given that liver and kidneys exhibited mild histopathological changes 6 days p.i. with either C. jejuni strain. We also found that hepatic and renal nitric oxide levels or renal TNF-α concentrations were lower in the ΔhtrA mutant as compared to WT strain infected mice. In conclusion, we show here that the C. jejuni HtrA protein plays a pivotal role in inducing host cell apoptosis and immunopathology during murine campylobacteriosis in the gut in vivo.

The impact of Toll-like-receptor-9 on intestinal microbiota composition and extra-intestinal sequelae in experimental Toxoplasma gondii induced ileitis

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.

The impact of serine protease HtrA in apoptosis, intestinal immune responses and extra-intestinal histopathology during Campylobacter jejuni infection of infant mice

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.

Nucleotide-binding oligomerization domain-containing protein 2 controls host response to Campylobacter jejuni in Il10-/- mice

Innate signaling-induced antimicrobial response represents a key protective host feature against infectious microorganisms such as Campylobacter species. In this study, we investigated the role of nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in Campylobacter jejuni-induced intestinal inflammation. Specific-pathogen-free Il10(-/-), Nod2(-/-), and Il10(-/-); Nod2(-/-) mice were infected with C. jejuni (10(9) colony-forming units/mouse) 24 hours after a 7-day course of antibiotic treatment. Three weeks later, host responses were determined. The nitric oxide (NO) donor sodium nitroprusside was injected intraperitoneally (2 mg/kg daily) to supplement NO. Although healthy in specific-pathogen-free conditions, Il10(-/-); Nod2(-/-) mice developed severe intestinal inflammation following C. jejuni infection, compared with Nod2(-/-) and Il10(-/-) mice. The onset of colitis was associated with elevated neutrophil accumulation, crypt abscesses, and expression of the endogenous proinflammatory mediators Il-1β, Tnfα, and Cxcl1. Fluorescence in situ hybridization and culture assay showed enhanced C. jejuni invasion into the colon and mesenteric lymph nodes in Il10(-/-); Nod2(-/-) mice, compared with Il10(-/-) mice. C. jejuni-induced bactericidal NO production was reduced in peritoneal macrophages from Il10(-/-); Nod2(-/-) mice, compared with Il10(-/-) mice. Importantly, sodium nitroprusside attenuated C. jejuni-induced colitis in Il10(-/-); Nod2(-/-) mice. Our findings suggest that NOD2 signaling is critical to control campylobacteriosis in Il10(-/-) mice, a process involving NOD2-mediated bactericidal responses.

Impact of Campylobacter jejuni cj0268c knockout mutation on intestinal colonization, translocation, and induction of immunopathology in gnotobiotic IL-10 deficient mice

Background

Although Campylobacter jejuni infections have a high prevalence worldwide and represent a significant socioeconomic burden, the underlying molecular mechanisms of induced intestinal immunopathology are still not well understood. We have recently generated a C. jejuni mutant strain NCTC11168::cj0268c, which has been shown to be involved in cellular adhesion and invasion. The immunopathological impact of this gene, however, has not been investigated in vivo so far.

Methodology/Principal Findings

Gnotobiotic IL-10 deficient mice were generated by quintuple antibiotic treatment and perorally infected with C. jejuni mutant strain NCTC11168::cj0268c, its complemented version (NCTC11168::cj0268c-comp-cj0268c), or the parental strain NCTC11168. Kinetic analyses of fecal pathogen loads until day 6 post infection (p.i.) revealed that knockout of cj0268c did not compromise intestinal C. jejuni colonization capacities. Whereas animals irrespective of the analysed C. jejuni strain developed similar clinical symptoms of campylobacteriosis (i.e. enteritis), mice infected with the NCTC11168::cj0268c mutant strain displayed significant longer small as well as large intestinal lengths indicative for less distinct C. jejuni induced pathology when compared to infected control groups at day 6 p.i. This was further supported by significantly lower apoptotic and T cell numbers in the colonic mucosa and lamina propria, which were paralleled by lower intestinal IFN-γ and IL-6 concentrations at day 6 following knockout mutant NCTC11168::cj0268c as compared to parental strain infection. Remarkably, less intestinal immunopathology was accompanied by lower IFN-γ secretion in ex vivo biopsies taken from mesenteric lymphnodes of NCTC11168::cj0268c infected mice versus controls.

Conclusion/Significance

We here for the first time show that the cj0268c gene is involved in mediating C. jejuni induced immunopathogenesis in vivo. Future studies will provide further deep insights into the immunological and molecular interplays between C. jejuni and innate immunity in human campylobacteriosis.

Comparative variation within the genome of Campylobacter jejuni NCTC 11168 in human and murine hosts

Campylobacteriosis incited by C. jejuni is a significant enteric disease of human beings. A person working with two reference strains of C. jejuni National Collection of Type Cultures (NCTC) 11168 developed symptoms of severe enteritis including bloody diarrhea. The worker was determined to be infected by C. jejuni. In excess of 50 isolates were recovered from the worker's stool. All of the recovered isolates and the two reference strains were indistinguishable from each other based on comparative genomic fingerprint subtyping. Whole genome sequence analysis indicated that the worker was infected with a C. jejuni NCTC 11168 obtained from the American Type Culture Collection; this strain (NCTC 11168-GSv) is the genome sequence reference. After passage through the human host, major genetic changes including indel mutations within twelve contingency loci conferring phase variations were detected in the genome of C. jejuni. Specific and robust single nucleotide polymorphism (SNP) changes in the human host were also observed in two loci (Cj0144c, Cj1564). In mice inoculated with an isolate of C. jejuni NCTC 11168-GSv from the infected person, the isolate underwent further genetic variation. At nine loci, mutations specific to inoculated mice including five SNP changes were observed. The two predominant SNPs observed in the human host reverted in mice. Genetic variations occurring in the genome of C. jejuni in mice corresponded to increased densities of C. jejuni cells associated with cecal mucosa. In conclusion, C. jejuni NCTC 11168-GSv was found to be highly virulent in a human being inciting severe enteritis. Host-specific mutations in the person with enteritis occurred/were selected for in the genome of C. jejuni, and many were not maintained in mice. Information obtained in the current study provides new information on host-specific genetic adaptation by C. jejuni.

Modification of intestinal microbiota and its consequences for innate immune response in the pathogenesis of campylobacteriosis

Campylobacter jejuni is the leading cause of bacterial food-borne gastroenteritis in the world, and thus one of the most important public health concerns. The initial stage in its pathogenesis after ingestion is to overcome colonization resistance that is maintained by the human intestinal microbiota. But how it overcomes colonization resistance is unknown. Recently developed humanized gnotobiotic mouse models have provided deeper insights into this initial stage and host's immune response. These studies have found that a fat-rich diet modifies the composition of the conventional intestinal microbiota by increasing the Firmicutes and Proteobacteria loads while reducing the Actinobacteria and Bacteroidetes loads creating an imbalance that exposes the intestinal epithelial cells to adherence. Upon adherence, deoxycholic acid stimulates C. jejuni to synthesize Campylobacter invasion antigens, which invade the epithelial cells. In response, NF- κ B triggers the maturation of dendritic cells. Chemokines produced by the activated dendritic cells initiate the clearance of C. jejuni cells by inducing the actions of neutrophils, B-lymphocytes, and various subsets of T-cells. This immune response causes inflammation. This review focuses on the progress that has been made on understanding the relationship between intestinal microbiota shift, establishment of C. jejuni infection, and consequent immune response.

The fibronectin-binding motif within FlpA facilitates Campylobacter jejuni adherence to host cell and activation of host cell signaling

Campylobacter jejuni is a gram-negative, curved and rod-shaped bacterium that causes human gastroenteritis. Acute disease is associated with C. jejuni invasion of the intestinal epithelium. Epithelial cells infected with C. jejuni strains containing mutations in the FlpA and CadF fibronectin (Fn)-binding proteins exhibit reduced invasion of host cells and a C. jejuni CadF FlpA double mutant is impaired in the activation of epidermal growth factor receptor (EGFR) and Rho GTPase Rac1. Although these observations establish a role for Fn-binding proteins during C. jejuni invasion, their mechanistic contributions to invasion-associated signaling are unclear. We examined FlpA, a C. jejuni Fn-binding protein composed of three FNIII-like repeats D1, D2 and D3, to identify the interactions required for cellular adherence on pathogen-induced host cell signaling. We report that FlpA binds the Fn gelatin-binding domain via a motif within the D2 repeat. Epithelial cells infected with a flpA mutant exhibited decreased Rac1 activation and reduced membrane ruffling that coincided with impaired delivery of the secreted Cia proteins and reduced cell association. Phosphorylation of the Erk1/2 kinase, a downstream effector of EGFR signaling, was specifically associated with FlpA-mediated activation of β₁-integrin and EGFR signaling. In vivo experiments revealed that FlpA is necessary for C. jejuni disease based on bacterial dissemination to the spleen of IL-10^−/− germ-free mice. Thus, a novel Fn-binding motif within FlpA potentiates activation of Erk1/2 signaling via β₁-integrin during C. jejuni infection.

Campylobacter jejuni colonization is associated with a dysbiosis in the cecal microbiota of mice in the absence of prominent inflammation

Background

Campylobacter jejuni causes enterocolitis in humans, but does not incite disease in asymptomatic carrier animals. To survive in the intestine, C. jejuni must successfully compete with the microbiota and overcome the host immune defense. Campylobacter jejuni colonization success varies considerably amongst individual mice, and we examined the degree to which the intestinal microbiota was affected in mice (i.e. a model carrier animal) colonized by C. jejuni at high relative to low densities.

Methods

Mice were inoculated with C. jejuni or buffer, and pathogen shedding and intestinal colonization were measured. Histopathologic scoring and quantification of mRNA expression for α-defensins, toll-like receptors, and cytokine genes were conducted. Mucosa-associated bacterial communities were characterized by two approaches: multiplexed barcoded pyrosequencing and terminal restriction fragment length polymorphism analysis.

Results

Two C. jejuni treatments were established based on the degree of cecal and colonic colonization; C. jejuni Group A animals were colonized at high cell densities, and C. jejuni Group B animals were colonized at lower cell densities. Histological examination of cecal and colonic tissues indicated that C. jejuni did not incite visible pathologic changes. Although there was no significant difference among treatments in expression of mRNA for α-defensins, toll-like receptors, or cytokine genes, a trend for increased expression of toll-like receptors and cytokine genes was observed for C. jejuni Group A. The results of the two methods to characterize bacterial communities indicated that the composition of the cecal microbiota of C. jejuni Group A mice differed significantly from C. jejuni Group B and Control mice. This difference was due to a reduction in load, diversity and richness of bacteria associated with the cecal mucosa of C. jejuni Group A mice.

Conclusions

High density colonization by C. jejuni is associated with a dysbiosis in the cecal microbiota independent of prominent inflammation.

Can microbiota transplantation abrogate murine colonization resistance against Campylobacter jejuni?

Enterocolitis caused by Campylobacter jejuni represents an important socioeconomic burden worldwide. The host-specific intestinal microbiota is essential for maintaining colonization resistance (CR) against C. jejuni in conventional mice. Notably, CR is abrogated by shifts of the intestinal microbiota towards overgrowth with commensal E. coli during acute ileitis. Thus, we investigated whether oral transplantation (TX) of ileal microbiota derived from C. jejuni susceptible mice with acute ileitis overcomes CR of healthy conventional animals. Four days following ileitis microbiota TX or ileitis induction and right before C. jejuni infection, mice displayed comparable loads of main intestinal bacterial groups as shown by culture. Eight days following ileitis induction, but not ileal microbiota TX, however, C. jejuni could readily colonize the gastrointestinal tract of conventional mice and also translocate to extra-intestinal tissue sites such as mesenteric lymph nodes, spleen, liver, and blood within 4 days following oral infection. Of note, C. jejuni did not further deteriorate histopathology following ileitis induction. Lack of C. jejuni colonization in TX mice was accompanied by a decrease of commensal E. coli loads in the feces 4 days following C. jejuni infection. In summary, oral ileal microbiota TX from susceptible donors is not sufficient to abrogate murine CR against C. jejuni.

Campylobacter jejuni induces extra-intestinal immune responses via Toll-like-receptor-4 signaling in conventional IL-10 deficient mice with chronic colitis

Campylobacter jejuni is one of the predominant causes for foodborne bacterial infections worldwide. We investigated whether signaling of C. jejuni-lipoproteins and -lipooligosaccharide via Toll-like-receptor (TLR) -2 and -4, respectively, is inducing intestinal and extra-intestinal immune responses following infection of conventional IL-10(-/-) mice with chronic colitis. At day 3 following oral infection, IL-10(-/-) mice lacking TLR-2 or TLR-4 harbored comparable C. jejuni strain ATCC 43431 loads in their colon. Interestingly, infected TLR-4(-/-) IL-10(-/-) mice displayed less compromized epithelial barrier function as indicated by lower translocation rates of live gut commensals into mesenteric lymphnodes (MLNs), and exhibited less distinct B lymphocyte responses in their colonic mucosa as compared to naїve IL-10(-/-) controls. Furthermore, in extra-intestinal compartments such as MLNs and spleens, abundance of myeloid cells was less distinct whereas relative percentages of activated T helper cells and cytotoxic T cells were higher in spleens and dendritic cells more abundant in MLNs of infected IL-10(-/-) animals lacking TLR-4 as compared to IL-10(-/-) controls. Taken together, in conventionally colonized IL-10(-/-) mice, TLR-4, but not TLR-2, is involved in mediating extra-intestinal pro-inflammatory immune responses following C. jejuni infection. Thus, conventional IL-10(-/-) mice are well suited to further dissect mechanisms underlying Campylobacter infections in vivo.