Symbiotic bacteria direct expression of an intestinal bactericidal lectin

IL-22 in mucosal immunity

Recent studies in infectious disease and autoimmune disease models have revealed that interleukin (IL)-22 might have both proinflammatory and anti-inflammatory functions. There is, however, lack of evidence for IL-22 directly repressing immune responses of leukocytes. We propose that IL-22 promotes innate immunity of tissues, as well as repairing and healing mechanisms during inflammation. Consequently, the restoration of tissue homeostasis helps to attenuate the inflammatory responses involving various immune cells.

Role of glycan synthesis in colonization of the mammalian gut by the bacterial symbiont Bacteroides fragilis

Bacteroides species are the most abundant Gram-negative bacteria of the human colonic microbiota. These endogenous organisms are unique in that they synthesize an extensive number of phase-variable surface polysaccharides. Pathogenic bacteria phase vary expression of surface molecules for immune evasion, but the importance of the synthesis of multiple phase-variable polysaccharides to these commensal bacteria is unknown. We previously showed that a Bacteroides fragilis mutant unable to synthesize 4 of the 8 capsular polysaccharides and unable to glycosylate proteins properly is rapidly outcompeted by the wild-type strain for colonization of the gnotobiotic mouse intestine. In the present study, we constructed mutants defective only in capsule polysaccharide synthesis to define better the importance of these surface molecules to intestinal colonization. We discovered a key enzymatic activity required for synthesis of 7 of the 8 capsular polysaccharides. Deletion of its gene resulted in the first B. fragilis mutant able to synthesize only one phase-variable polysaccharide, and further mutation resulted in a stable acapsular mutant. We show that the acapsular mutant is rapidly outcompeted, but synthesis of a single polysaccharide is sufficient for the organism to colonize the gnotobiotic intestine competitively. These data demonstrate that initial colonization of the gnotobiotic mouse intestine by B. fragilis requires that the organism synthesize only a single polysaccharide and suggest that the synthesis of multiple phase-variable polysaccharides is important for the bacteria's long-term maintenance in the normally complex and competitive ecosystem.

Pancreatitis-associated protein 2 modulates inflammatory responses in macrophages

Pancreatitis-associated proteins (PAP) are stress-induced secretory proteins that are implicated in immunoregulation. Previous studies have demonstrated that PAP is up-regulated in acute pancreatitis and that gene knockdown of PAP correlated with worsening severity of pancreatitis, suggesting a protective effect for PAP. In the present study, we investigated the effect of PAP2 in the regulation of macrophage physiology. rPAP2 administration to clonal (NR8383) and primary macrophages were followed by an assessment of cell morphology, inflammatory cytokine expression, and studies of cell-signaling pathways. NR8383 macrophages which were cultured in the presence of PAP2 aggregated and exhibited increased expression of IL-1, IL-6, TNF-alpha, and IL-10; no significant change was observed in IL-12, IL-15, and IL-18 when compared with controls. Chemical inhibition of the NFkappaB pathway abolished cytokine production and PAP facilitated nuclear translocation of NF-kappaB and phosphorylation of IkappaB alpha inhibitory protein suggesting that PAP2 signaling involves this pathway. Cytokine responses were dose dependent. Interestingly, similar findings were observed with primary macrophages derived from lung, peritoneum, and blood but not spleen. Furthermore, PAP2 activity was inhibited by the presence of serum, inhibition which was overcome with increased PAP2. Our results demonstrate a new function for PAP2: it stimulates macrophage activity and likely modulates the inflammatory environment of pancreatitis.

Micro-eukaryotic diversity of the human distal gut microbiota: qualitative assessment using culture-dependent and -independent analysis of faeces

Molecular ecological surveys of the human gut microbiota to date have focused on the prokaryotic fraction of the community and have revealed a remarkable degree of bacterial diversity and functionality. However, there is a dearth of information on the eukaryotic composition of the microbiota, and no culture-independent sequence-based surveys of human faeces are available. Culture-independent analyses based on DNA extraction and polymerase chain reaction targeting both the total eukaryotic 18S rRNA genes and fungal internal transcribed regions (ITS), together with culture-dependent analyses of fungi, were performed on a group of healthy volunteers. Temporal analysis was also included wherever possible. Collectively, the data presented in this study indicate that eukaryotic diversity of the human gut is low, largely temporally stable and predominated by different subtypes of Blastocystis. Specific analyses of the fungal populations indicate that a disparity exists between the cultivable fraction, which is dominated by Candida sp, and culture-independent analysis, where sequences identical to members of the genera Gloeotinia/Paecilomyces and Galactomyces were most frequently retrieved from both fungal ITS profiles and subsequent clone libraries. Collectively, these results highlight the presence of unprecedented intestinal eukaryotic inhabitants whose functional roles are as yet unknown in healthy individuals. Furthermore, differences between results obtained from traditionally employed culture-based methods and those obtained from culture-independent techniques highlight similar anomalies to that encountered when first analysing the bacterial diversity of the human faecal microbiota using culture-independent surveys.

Mannose-specific interaction of Lactobacillus plantarum with porcine jejunal epithelium

Host-microorganism interactions in the intestinal tract are complex, and little is known about specific nonpathogenic microbial factors triggering host responses in the gut. In this study, mannose-specific interactions of Lactobacillus plantarum 299v with jejunal epithelium were investigated using an in situ pig Small Intestinal Segment Perfusion model. The effects of L. plantarum 299v wild-type strain were compared with those of two corresponding mutant strains either lacking the gene encoding for the mannose-specific adhesin (msa) or sortase (srtA; responsible for anchoring of cell surface proteins like Msa to the cell wall). A slight enrichment of the wild-type strain associated with the intestinal surface could be observed after 8 h of perfusion when a mixture of wild-type and msa-mutant strain had been applied. In contrast to the mutant strains, the L. plantarum wild-type strain tended to induce a decrease in jejunal net fluid absorption compared with control conditions. Furthermore, after 8 h of perfusion expression of the host gene encoding pancreatitis-associated protein, a protein with proposed bactericidal properties, was found to be upregulated by the wild-type strain only. These observations suggest a role of Msa in the induction of host responses in the pig intestine.

Regional variations in Paneth cell antimicrobial peptide expression along the mouse intestinal tract

BACKGROUND

Enteric antimicrobial peptides secreted from Paneth cells, including alpha-defensins (in mice named cryptdins), are key effector molecules of innate immunity in the small intestine. The importance of Paneth cells alpha-defensins emerged from studies of enteric bacterial infection in genetically modified mice, as well as from recent studies linking reduced levels of these alpha-defensins to Crohn's disease localized to the ileum. However, analysis of expression of Paneth cell alpha-defensins is incomplete. We therefore performed a comprehensive evaluation of the distribution of antimicrobial molecules along the mouse small intestinal tract to identify potential variations in regional expression.

RESULTS

In conventionally reared mice, the repertoire of Paneth cell antimicrobials differs between duodenum and ileum. In contrast to the uniform expression of most Paneth cell antimicrobials, both cryptdin 4 and cryptdin-related sequences (CRS) 4C peptides were expressed at progressively increasing amounts (101- and 104-fold, respectively) comparing duodenum and ileum. In tissues other than the small intestine, expression of CRS peptides was noted in thymus and caecum. Most Paneth cell products were also produced in the small intestine of germ-free mice at levels similar to those in controls, however CRS4C and RegIIIgamma had reduced levels in the former (3- and 8-fold, respectively). No significant changes in expression levels of Paneth cell antimicrobial peptides was observed after oral challenge with either Salmonella enterica serovar typhimurium or Listeria monocytogenes, supporting current notions on the constitutive nature of this defensive system.

CONCLUSION

The repertoire of antimicrobial peptides changes along the small intestinal tract, and a subset of these molecules are up-regulated upon colonization, but not in response to enteric bacterial pathogens. The changes detected upon colonization suggest that Paneth cell antimicrobial peptides may play an important role in commensal microbial homeostasis, in addition to their proposed role in protection against infection. In addition, the differential expression of CRS4C along the small intestine suggests mechanisms of regulation that are distinct from other Paneth cell derived antimicrobial peptides.

Metagenomic approaches for defining the pathogenesis of inflammatory bowel diseases

The human gastrointestinal tract is home to immense and complex populations of microorganisms. Using recent technical innovations, the diversity present in this human body habitat is now being analyzed in detail. This review focuses on the microbial ecology of the gut in inflammatory bowel diseases and on how recent studies provide an impetus for using carefully designed, comparative metagenomic approaches to delve into the structure and activities of the gut microbial community and its interrelationship with the immune system.

Odorranalectin is a small peptide lectin with potential for drug delivery and targeting

Background

Lectins are sugar-binding proteins that specifically recognize sugar complexes. Based on the specificity of protein–sugar interactions, different lectins could be used as carrier molecules to target drugs specifically to different cells which express different glycan arrays. In spite of lectin's interesting biological potential for drug targeting and delivery, a potential disadvantage of natural lectins may be large size molecules that results in immunogenicity and toxicity. Smaller peptides which can mimic the function of lectins are promising candidates for drug targeting.

Principal Findings

Small peptide with lectin-like behavior was screened from amphibian skin secretions and its structure and function were studied by NMR, NMR-titration, SPR and mutant analysis. A lectin-like peptide named odorranalectin was identified from skin secretions of Odorrana grahami. It was composed of 17 aa with a sequence of YASPKCFRYPNGVLACT. L-fucose could specifically inhibit the haemagglutination induced by odorranalectin. ¹²⁵I-odorranalectin was stable in mice plasma. In experimental mouse models, odorranalectin was proved to mainly conjugate to liver, spleen and lung after i.v. administration. Odorranalectin showed extremely low toxicity and immunogenicity in mice. The small size and single disulfide bridge of odorranalectin make it easy to manipulate for developing as a drug targeting system. The cyclic peptide of odorranalectin disclosed by solution NMR study adopts a β-turn conformation stabilized by one intramolecular disulfide bond between Cys6-Cys16 and three hydrogen bonds between Phe7-Ala15, Tyr9-Val13, Tyr9-Gly12. Residues K5, C6, F7, C16 and T17 consist of the binding site of L-fucose on odorranalectin determined by NMR titration and mutant analysis. The structure of odorranalectin in bound form is more stable than in free form.

Conclusion

These findings identify the smallest lectin so far, and show the application potential of odorranalectin for drug delivery and targeting. It also disclosed a new strategy of amphibian anti-infection.

Transcriptional responses to pathogens in Caenorhabditis elegans

Evolutionarily conserved signaling pathways, such as the p38 and ERK MAPK pathways, the TGF-beta pathway, and the insulin-signaling pathway are required for resistance to pathogens in Caenorhabditis elegans. Recent microarray expression profiling studies have identified both candidate immune effector genes which may recognize and eliminate microbial pathogens as well as uncharacterized gene classes that are broadly induced in response to pathogen. Comparative analysis of these microarray studies is suggestive of basal versus induced components of the ancient innate immune response in C. elegans. In particular, whereas the PMK-1 p38 MAPK pathway regulates genes that are induced by pathogen, the Forkhead family transcription factor DAF-16 confers pathogen resistance through the regulation of genes that are non-overlapping with pathogen-induced genes.

Transcriptional responses to pathogens in Caenorhabditis elegans

Evolutionarily conserved signaling pathways, such as the p38 and ERK MAPK pathways, the TGF-beta pathway, and the insulin-signaling pathway are required for resistance to pathogens in Caenorhabditis elegans. Recent microarray expression profiling studies have identified both candidate immune effector genes which may recognize and eliminate microbial pathogens as well as uncharacterized gene classes that are broadly induced in response to pathogen. Comparative analysis of these microarray studies is suggestive of basal versus induced components of the ancient innate immune response in C. elegans. In particular, whereas the PMK-1 p38 MAPK pathway regulates genes that are induced by pathogen, the Forkhead family transcription factor DAF-16 confers pathogen resistance through the regulation of genes that are non-overlapping with pathogen-induced genes.

Maturation of paneth cells induces the refractory state of newborn mice to Shigella infection

The intestinal tract of adult mice is naturally resistant to infection by Shigella, the causative agent of bacillary dysentery in humans. Conversely, newborn mice are highly susceptible to intragastric Shigella infection and develop inflammatory lesions of the jejunal mucosa, very similar to those observed in the colon of dysenteric patients. However, the susceptibility period is short and one week after birth, animals have acquired a status of resistance characteristic of adult animals. To identify the developmental changes controlling the switch from disease susceptibility to resistance, we performed global gene expression analysis on noninfected and infected intestinal tissues taken from 4-day- and 7-day-old animals. Transcriptomic analysis of 4-day-old mice infected with the invasive Shigella strain showed a profile reflecting a strong inflammatory response with no evidence for retro-control, suggesting that the invasive process had occurred, whereas inflammation had been controlled after infection with the noninvasive strain. Differences in gene expression profiles between noninfected 4-day- and 7-day-old mice corresponded mainly to genes encoding anti-microbial peptides and proteases, suggesting that these molecules could be candidates for host antimicrobial resistance in the course of shigellosis. Indeed, expression of genes specific of Paneth cells was higher in 7-day- than in 4-day-old mice, and histological analysis indicated that Paneth cells were present only at day 7. Finally, using Sox9(flox/flox)-vil-cre mice, we showed that depletion of Paneth cells restored the susceptibility to Shigella of 7-day-old mice, clearly indicating that Paneth cells development is crucial for the clearance of intestinal infection.

Inflammatory bowel disease, past, present and future: lessons from animal models

Accumulating data from animal models indicate that Inflammatory bowel disease (IBD) is mediated by a much more complicated mechanism than previously predicted. For example, the role of an individual molecule in the pathogenesis of IBD distinctly differs depending on several factors, including the fundamental mechanism of induction of the disease, the target cell type, the phase of disease, and the environment. Therefore, it has been difficult in the past to fully explain the complicated mechanism. Novel concepts have recently been proposed to further explain the complicated mechanism of IBD. In this review, we introduce past, current, and possible future concepts for IBD models regarding T helper (Th) 1, Th2, and Th17, antigen sampling and presentation, regulatory cell networks, NOD2, Toll-like receptors, bacteria/epithelia interaction, stem cells, autophagy, microRNAs, and glycoimmunology, and we also discuss the relevance of these new concepts, developed at the bench (in animal models), to the bedside.

Evolution, development, mechanism and function of IgA in the gut

Since its discovery as the most abundant Ig produced at mucosal surfaces, IgA has been the subject of continuous studies. The concepts emerged were that the precursors for IgA plasma cells are efficiently generated in follicular organized structures in the gut with the help of CD4 T cells and that secretory IgA provides protection against mucosal pathogens. Novel conceptual advances have been made in the past few years in describing new sites, mechanisms and functions of mucosal IgA synthesis.

New horizons for the infectious diseases specialist: how gut microflora promote health and disease

The human intestine provides an expansive interface for interactions with the microflora. Increasing data support the hypothesis that host-microflora relationships are markedly dynamic, contributing to host health and disease pathogenesis. Despite outnumbering human cells 10-fold, the microflora most often assist the host through symbiotic relationships. The microflora are involved in maximizing host utilization of nutrients, induction of host immune responses, and promotion of intestinal cell and mucosal development. However, evolving data suggest that disturbances in this symbiotic relationship can lead the microflora to be pathogenic in diverse conditions such as inflammatory bowel disease, irritable bowel disease, obesity, graft-versus-host disease, HIV immunopathogenesis, and possibly cancer. Defining those microflora attributes that result in health and those that trigger disease is key to harnessing the microflora to promote human health.

Early molecular and functional changes in colonic epithelium that precede increased gut permeability during colitis development in mdr1a(-/-) mice

BACKGROUND

The early molecular changes preceding the onset of mucosal inflammation in colitis and their temporal relationship with gut permeability remain poorly defined. This study investigated functional and transcriptomic changes in mdr1a(-/-) mice lacking the intestinal transporter P-glycoprotein, which develop colitis spontaneously when exposed to normal enteric flora.

METHODS

Mdr1a(-/-) mice were housed in specific pathogen-free conditions to slow colitis development and compared to congenic controls. Mucosal permeability and cytokine secretion were analyzed in ex vivo colon. Gene expression in colonic mucosal and epithelial preparations was analyzed by microarray and qPCR. Colonocyte responsiveness to bacterial antigens was measured in short-term culture.

RESULTS

Colon from 4-5-week-old, disease-free mdr1a(-/-) mice was histologically normal with no evidence of increased permeability compared to controls. However, these tissues display a distinctive pattern of gene expression involving significant changes in a small number of genes. The majority of upregulated genes were associated with bacterial recognition and the ubiquitin-proteasome system and were gamma-interferon (IFN-gamma) responsive. Expression of the antiinflammatory factor pancreatitis-associated protein (PAP) and the related gene RegIIIgamma were markedly reduced. Colonocytes from 4-5-week mdr1a(-/-) exhibit similar transcriptomic changes, accompanied by higher basal chemokine secretion and increased responsiveness to LPS. Significant increases in colonic permeability were associated with older (12-16-week) mdr1a(-/-) mice displaying molecular and functional evidence of active inflammation.

CONCLUSIONS

These studies show that early epithelial changes associated with altered responsiveness to bacteria precede increased permeability and mucosal inflammation in this model of colitis, highlighting the importance of P-glycoprotein in regulating interactions with the commensal microflora.

Loss of epithelial RelA results in deregulated intestinal proliferative/apoptotic homeostasis and susceptibility to inflammation

NF-kappaB plays a central, proinflammatory role in chronic intestinal inflammation, yet recent work suggests a predominantly protective function for this transcription factor group in some cell types of the intestine. We herein describe the conditional deletion of the NF-kappaB RelA gene in murine intestinal epithelia and determine its function in homeostatic control of enterocyte proliferation/apoptosis and susceptibility to colonic inflammation. Mice lacking RelA in ileal and colonic enterocytes were born in expected Mendelian ratios, and RelA-null epithelia differentiated normally. Spontaneous intestinal disease and death occurred with low penetrance in neonates lacking epithelial RelA. IkappaBalpha and IkappaBbeta were significantly diminished in RelA-null epithelia, and endotoxin challenge revealed elevated p50 and c-Rel DNA binding activity as compared with controls. Deletion of RelA resulted in diminished expression of antimicrobial (defensin-related cryptdin 4, defensin-related cryptdin 5, RegIIIgamma) and antiapoptotic, prorestitution genes (Bcl-x(L), RegIV, IL-11, IL-18), and basal rates of epithelial apoptosis and proliferation were elevated. Mice lacking colonic RelA were sensitive to dextran sodium sulfate-induced colitis. Although experimental colitis enhanced proliferation in cells lacking RelA, sustained epithelial cell apoptosis precluded mucosal healing and decreased animal survival. We conclude that activation of RelA is required for homeostatic regulation of cell death and division in intestinal epithelia, as well as for protection from development of severe, acute inflammation of the intestine.

The biological functions of T helper 17 cell effector cytokines in inflammation

T helper 17 (Th17) cells belong to a recently identified T helper subset, in addition to the traditional Th1 and Th2 subsets. These cells are characterized as preferential producers of interleukin-17A (IL-17A), IL-17F, IL-21, and IL-22. Th17 cells and their effector cytokines mediate host defensive mechanisms to various infections, especially extracellular bacteria infections, and are involved in the pathogenesis of many autoimmune diseases. The receptors for IL-17 and IL-22 are broadly expressed on various epithelial tissues. The effector cytokines of Th17 cells, therefore, mediate the crucial crosstalk between immune system and tissues, and play indispensable roles in tissue immunity.

Bugs inside Bugs: what the fruit fly can teach us about immune and microbial balance in the gut

In their coexistence with microbes, animals must fortify themselves against the onslaught of pathogens while maintaining a healthful consortium of resident commensals. In a recent paper in Science, Ryu and colleagues report that in fruit flies the Caudal transcription factor regulates appropriate immune responses to commensal bacteria, and that when these immune responses are perturbed, the gut microbial consortium shifts to one that is harmful to its host.

Impaired luminal processing of human defensin-5 in Crohn's disease: persistence in a complex with chymotrypsinogen and trypsin

Human defensin (HD)-5 is an antimicrobial peptide expressed in small intestinal Paneth cells, and alterations in HD-5 expression may be important in Crohn's disease (CD) pathogenesis. Levels of HD-5 in Paneth cells and ileostomy fluid from control and CD patients were studied by quantitative immunodot analysis, immunohistochemistry, acid urea-polyacrylamide gel electrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis Western blotting, reverse phase-high performance liquid chromatography, N-terminal amino acid sequencing, and ES-QToF mass spectrometry. In both control and CD patients, HD-5 in Paneth cell extracts was present almost exclusively in the precursor form. HD-5 levels in ileostomy fluid were lower in CD patients (n = 51) than in controls (n = 20): median (range), 7.9 (5.5 to 35.0) microg/ml versus 10.5 (6.0 to 30.4) microg/ml; P = 0.05; this difference was most marked in CD patients with homozygous/compound heterozygous mutations in NOD2 (P = 0.03). In control ileostomy fluid, HD-5 was present in the mature form only. In contrast, CD patient ileostomy fluid contained both precursor and mature forms of HD-5, with the majority present in a complex with trypsin, chymotrypsinogen/chymotrypsin, and alpha1-anti-trypsin. Pro-HD-5 was not associated with trypsin or chymotrypsinogen in Paneth cell extracts. In conclusion, pro-HD-5 in the intestinal lumen is processed by trypsin in a complex in which chymotrypsinogen is also cleaved for activation. The persistence of this complex in CD may be attributable to increased luminal levels of proteinase inhibitors such as alpha1-anti-trypsin.

Interleukin-22 mediates early host defense against attaching and effacing bacterial pathogens

Infections by attaching and effacing (A/E) bacterial pathogens, such as Escherichia coli O157:H7, pose a serious threat to public health. Using a mouse A/E pathogen, Citrobacter rodentium, we show that interleukin-22 (IL-22) has a crucial role in the early phase of host defense against C. rodentium. Infection of IL-22 knockout mice results in increased intestinal epithelial damage, systemic bacterial burden and mortality. We also find that IL-23 is required for the early induction of IL-22 during C. rodentium infection, and adaptive immunity is not essential for the protective role of IL-22 in this model. Instead, IL-22 is required for the direct induction of the Reg family of antimicrobial proteins, including RegIIIbeta and RegIIIgamma, in colonic epithelial cells. Exogenous mouse or human RegIIIgamma substantially improves survival of IL-22 knockout mice after C. rodentium infection. Together, our data identify a new innate immune function for IL-22 in regulating early defense mechanisms against A/E bacterial pathogens.

Therapeutic impact of toll-like receptors on inflammatory bowel diseases: a multiple-edged sword

Recent studies have begun to define the mechanisms through which Toll-like receptors (TLRs) regulate intestinal homeostasis in health and disease. Current therapies for inflammatory bowel diseases (IBDs) mostly aim at interrupting the inflammatory cascade through agents that regulate TH1 or TH2 cytokine responses. As recognition grows for TLR dysfunction to play a role in IBD pathogenesis, TLRs could provide another valid interventional target for novel therapy development. However, seemingly contradictory results from studying different murine models of colitis have so far confounded whether therapeutically useful modulation of TLRs is best accomplished by activating, inhibiting, or rather a combination of both at different stages of mucosal disease. This review evaluates potential strategies as well as their rationale and future prospects.

The role of microbiota in infectious disease

The intestine harbors an ecosystem composed of the intestinal mucosa and the commensal microbiota. The microbiota fosters development, aids digestion and protects host cells from pathogens - a function referred to as colonization resistance. Little is known about the molecular basis of colonization resistance and how it can be overcome by enteropathogenic bacteria. Recently, studies on inflammatory bowel diseases and on animal models for enteric infection have provided new insights into colonization resistance. Gut inflammation changes microbiota composition, disrupts colonization resistance and enhances pathogen growth. Thus, some pathogens can benefit from inflammatory defenses. This new paradigm will enable the study of host factors enhancing or inhibiting bacterial growth in health and disease.

Immune responses to commensal and environmental microbes

The mammalian immune system discriminates among microbes, inactivating pathogens while tolerating colonization by commensal organisms. Calibrating immune responses to microbes on this basis, however, is complex, as microbial virulence is often context dependent, being influenced by the host's immune status and the microbial milieu. Many microbial pathogens infecting immunocompromised hosts, for example, are innocuous in immune-competent individuals, and other microbes cause disease only when the commensal flora is compromised by antibiotic therapy. Recent studies have begun to reveal how the immune system tips the balance in favor of some microbes, allowing commensals to persist on mucosal surfaces while eliminating disease-causing pathogens.

Chicken lung lectin is a functional C-type lectin and inhibits haemagglutination by influenza A virus

Many proteins of the calcium-dependent (C-type) lectin family have been shown to play an important role in innate immunity. They can bind to a broad range of carbohydrates, which enables them to interact with ligands present on the surface of micro-organisms. We previously reported the finding of a new putative chicken lectin, which was predominantly localized to the respiratory tract, and thus termed chicken lung lectin (cLL). In order to investigate the biochemical and biophysical properties of cLL, the recombinant protein was expressed, affinity purified and characterized. Recombinant cLL was expressed as four differently sized peptides, which is most likely due to post-translational modification. Crosslinking of the protein led to the formation of two high-molecular weight products, indicating that cLL forms trimeric and possibly even multimeric subunits. cLL was shown to have lectin activity, preferentially binding to alpha-mannose in a calcium-dependent manner. Furthermore, cLL was shown to inhibit the haemagglutination-activity of human isolates of influenza A virus, subtype H3N2 and H1N1. These result show that cLL is a true C-type lectin with a very distinct sugar specificity, and that this chicken lectin could play an important role in innate immunity.

IgA response to symbiotic bacteria as a mediator of gut homeostasis

Colonization of germ-free mice with a normal gut microbiota elicits bacteria-specific IgA antibody responses. The effects of these responses on microbial and host biology remain poorly defined. Therefore, we developed a gnotobiotic mouse model where the microbiota is reduced to one bacterial species, and the antibody repertoire to a single, monoclonal IgA against the bacterium's capsular polysaccharide. Bacteroides thetaiotaomicron was introduced into germ-free wild-type, immunodeficient Rag1(-/-), or Rag1(-/-) mice harboring IgA-producing hybridoma cells. Without IgA, B. thetaiotaomicron elicits a more robust innate immune response and reacts to this response by inducing genes that metabolize host oxidative products. IgA reduces intestinal proinflammatory signaling and bacterial epitope expression, thereby balancing suppression of the oxidative burst with the antibody's negative impact on bacterial fitness. These results underscore the adaptive immune system's critical role in establishing a sustainable host-microbial relationship. Immunoselection of bacterial epitope expression may contribute to the remarkable strain-level diversity in this ecosystem.

Innate immune recognition at the epithelial barrier drives adaptive immunity: APCs take the back seat

Innate immune recognition of microbe-associated molecular patterns by multiple families of pattern-recognition molecules such as Toll-like receptors and Nod-like receptors instructs the innate and adaptive immune system to protect the host from pathogens while also acting to establish a beneficial mutualism with commensal organisms. Although this task has been thought to be performed mainly by specialized antigen-presenting cells such as dendritic cells, recent observations point to the idea that innate immune recognition by stromal cells has important implications for the regulation of mucosal homeostasis as well as for the initiation of innate and adaptive immunity.

Bacteroides: the good, the bad, and the nitty-gritty

SUMMARY

Bacteroides species are significant clinical pathogens and are found in most anaerobic infections, with an associated mortality of more than 19%. The bacteria maintain a complex and generally beneficial relationship with the host when retained in the gut, but when they escape this environment they can cause significant pathology, including bacteremia and abscess formation in multiple body sites. Genomic and proteomic analyses have vastly added to our understanding of the manner in which Bacteroides species adapt to, and thrive in, the human gut. A few examples are (i) complex systems to sense and adapt to nutrient availability, (ii) multiple pump systems to expel toxic substances, and (iii) the ability to influence the host immune system so that it controls other (competing) pathogens. B. fragilis, which accounts for only 0.5% of the human colonic flora, is the most commonly isolated anaerobic pathogen due, in part, to its potent virulence factors. Species of the genus Bacteroides have the most antibiotic resistance mechanisms and the highest resistance rates of all anaerobic pathogens. Clinically, Bacteroides species have exhibited increasing resistance to many antibiotics, including cefoxitin, clindamycin, metronidazole, carbapenems, and fluoroquinolones (e.g., gatifloxacin, levofloxacin, and moxifloxacin).

An ecological and evolutionary perspective on human-microbe mutualism and disease

The microbial communities of humans are characteristic and complex mixtures of microorganisms that have co-evolved with their human hosts. The species that make up these communities vary between hosts as a result of restricted migration of microorganisms between hosts and strong ecological interactions within hosts, as well as host variability in terms of diet, genotype and colonization history. The shared evolutionary fate of humans and their symbiotic bacteria has selected for mutualistic interactions that are essential for human health, and ecological or genetic changes that uncouple this shared fate can result in disease. In this way, looking to ecological and evolutionary principles might provide new strategies for restoring and maintaining human health.

Salmonella enterica serovar typhimurium exploits inflammation to compete with the intestinal microbiota

Most mucosal surfaces of the mammalian body are colonized by microbial communities ("microbiota"). A high density of commensal microbiota inhabits the intestine and shields from infection ("colonization resistance"). The virulence strategies allowing enteropathogenic bacteria to successfully compete with the microbiota and overcome colonization resistance are poorly understood. Here, we investigated manipulation of the intestinal microbiota by the enteropathogenic bacterium Salmonella enterica subspecies 1 serovar Typhimurium (S. Tm) in a mouse colitis model: we found that inflammatory host responses induced by S. Tm changed microbiota composition and suppressed its growth. In contrast to wild-type S. Tm, an avirulent invGsseD mutant failing to trigger colitis was outcompeted by the microbiota. This competitive defect was reverted if inflammation was provided concomitantly by mixed infection with wild-type S. Tm or in mice (IL10(-/-), VILLIN-HA(CL4-CD8)) with inflammatory bowel disease. Thus, inflammation is necessary and sufficient for overcoming colonization resistance. This reveals a new concept in infectious disease: in contrast to current thinking, inflammation is not always detrimental for the pathogen. Triggering the host's immune defence can shift the balance between the protective microbiota and the pathogen in favour of the pathogen.

Varied role of the gut epithelium in mucosal homeostasis

PURPOSE OF REVIEW

The epithelium makes numerous important contributions to intestinal function. It acts as a physical barrier to prevent pathogenic infection, but allows nutrient uptake and the bidirectional passage of ions and water to lubricate the intestinal lumen while restricting fluid loss. The epithelium mediates communication between the immune system and the commensal flora, and plays a major role in antigen sampling and development of tolerance. After mucosal injury, the epithelium must reestablish its barrier and transport functions for homeostasis to be restored. Here, we will discuss recent advances in our understanding of the roles of the epithelium in intestinal homeostasis.

RECENT FINDINGS

Mechanisms responsible for epithelial communication with enteric flora and pathogens include the regulation and function of Toll-like receptors and nucleotide-binding oligomerization domain-2, and maintenance and repair of epithelial barrier properties, including the role of growth factors and bacterial peptides in epithelial repair.

SUMMARY

Recent advances in our understanding of mechanisms by which the gut epithelium modulates, and is modified by, enteric flora and the mucosal immune system illuminate the importance of the epithelium in gut physiology. The work discussed may also identify novel targets that can potentially be modulated therapeutically, either with existing medications or newer agents in development.

Host transmission of Salmonella enterica serovar Typhimurium is controlled by virulence factors and indigenous intestinal microbiota

Transmission is an essential stage of a pathogen's life cycle and remains poorly understood. We describe here a model in which persistently infected 129X1/SvJ mice provide a natural model of Salmonella enterica serovar Typhimurium transmission. In this model only a subset of the infected mice, termed supershedders, shed high levels (>10(8) CFU/g) of Salmonella serovar Typhimurium in their feces and, as a result, rapidly transmit infection. While most Salmonella serovar Typhimurium-infected mice show signs of intestinal inflammation, only supershedder mice develop colitis. Development of the supershedder phenotype depends on the virulence determinants Salmonella pathogenicity islands 1 and 2, and it is characterized by mucosal invasion and, importantly, high luminal abundance of Salmonella serovar Typhimurium within the colon. Immunosuppression of infected mice does not induce the supershedder phenotype, demonstrating that the immune response is not the main determinant of Salmonella serovar Typhimurium levels within the colon. In contrast, treatment of mice with antibiotics that alter the health-associated indigenous intestinal microbiota rapidly induces the supershedder phenotype in infected mice and predisposes uninfected mice to the supershedder phenotype for several days. These results demonstrate that the intestinal microbiota plays a critical role in controlling Salmonella serovar Typhimurium infection, disease, and transmissibility. This novel model should facilitate the study of host, pathogen, and intestinal microbiota factors that contribute to infectious disease transmission.

The human microbiome project

A strategy to understand the microbial components of the human genetic and metabolic landscape and how they contribute to normal physiology and predisposition to disease.

Defensins and Paneth cells in inflammatory bowel disease

Defensins are antimicrobial peptides produced by professional phagocytes, Paneth cells, and intestinal epithelial cells. In addition to their potent antimicrobial activity, defensins can also modulate the function and movement of neutrophils, monocytes, T-lymphocytes, dendritic cells, and epithelial cells. Paneth cells are equipped with multiple defensins and antimicrobial proteins and usually reside in the small intestine. This review highlights the diverse functions of defensins and changes in defensin expression and Paneth cell proliferation in Crohn's disease, ulcerative colitis, and animal models of inflammatory bowel disease. Current data favor the hypothesis that defensins and Paneth cells may play important roles in the maintenance of intestinal immune homeostasis through 2 distinct mechanisms. The first mechanism is to act as effector molecules and cells against pathogenic microbes, while the second is to regulate host immune cell functions.

Salmonella induces prominent gene expression in the rat colon

Background

Salmonella enteritidis is suggested to translocate in the small intestine. In vivo it induces gene expression changes in the ileal mucosa and Peyer's patches. Stimulation of Salmonella translocation by dietary prebiotics fermented in colon suggests involvement of the colon as well. However, effects of Salmonella on colonic gene expression in vivo are largely unknown. We aimed to characterize time dependent Salmonella-induced changes of colonic mucosal gene expression in rats using whole genome microarrays. For this, rats were orally infected with Salmonella enteritidis to mimic a foodborne infection and colonic gene expression was determined at days 1, 3 and 6 post-infection (n = 8 rats per time-point). As fructo-oligosaccharides (FOS) affect colonic physiology, we analyzed colonic mucosal gene expression of FOS-fed versus cellulose-fed rats infected with Salmonella in a separate experiment. Colonic mucosal samples were isolated at day 2 post-infection.

Results

Salmonella affected transport (e.g. Chloride channel calcium activated 6, H⁺/K⁺ transporting Atp-ase), antimicrobial defense (e.g. Lipopolysaccharide binding protein, Defensin 5 and phospholipase A2), inflammation (e.g. calprotectin), oxidative stress related genes (e.g. Dual oxidase 2 and Glutathione peroxidase 2) and Proteolysis (e.g. Ubiquitin D and Proteosome subunit beta type 9). Furthermore, Salmonella translocation increased serum IFNγ and many interferon-related genes in colonic mucosa. The gene most strongly induced by Salmonella infection was Pancreatitis Associated Protein (Pap), showing >100-fold induction at day 6 after oral infection. Results were confirmed by Q-PCR in individual rats. Stimulation of Salmonella translocation by dietary FOS was accompanied by enhancement of the Salmonella-induced mucosal processes, not by induction of other processes.

Conclusion

We conclude that the colon is a target tissue for Salmonella, considering the abundant changes in mucosal gene expression.

The identification and sequence analysis of a new Reg3gamma and Reg2 in the Syrian golden hamster

The regenerating (Reg) genes are associated with tissue repair and have been directly implicated in pancreatic beta-cell regeneration. A hamster Reg3, Islet neogenesis associated protein (INGAP), has been shown to possess anti-diabetic properties in rodent models. Although several Reg3 proteins have been identified in other species, INGAP is the only Reg3 found in hamsters. To identify new Reg3 genes in the hamster pancreas we employed homology reverse transcription polymerase chain reaction (RT-PCR) using degenerate Reg3 primers, followed by rapid amplification of cDNA ends (RACE). We report here the discovery of a new hamster Reg3 gene of 765 nucleotides (nt) that encodes a 174-amino acid (aa) protein. This protein sequence was identified as a novel hamster Reg3gamma with 78% and 75% identity to the rat Reg3gamma and mouse Reg3gamma protein, respectively. We also fully sequenced the previously reported partial sequence of the hamster Reg1 gene coding region using RACE to yield a 756-nt transcript that encodes a deduced 173 aa protein. This protein was identified as hamster Reg2, rather than Reg1 as was initially reported, with an 81% identity to mouse Reg2. The spatial gene expression patterns of the hamster Reg genes, analyzed by RT-PCR, were similarly distributed with low level expression being found globally throughout the body. Mice and hamsters are the only species known to carry either of the functional INGAP or Reg2 genes. It remains to be determined whether these genes bestow mice and hamsters with special regenerative abilities in the pancreas.

The Paneth cell alpha-defensin deficiency of ileal Crohn's disease is linked to Wnt/Tcf-4

Ileal Crohn's disease (CD), a chronic mucosal inflammation, is characterized by two pertinent features: a specific decrease of Paneth cell-produced antimicrobial alpha-defensins and the presence of mucosal-adherent bacteria. A mutation in NOD2, the muramyl dipeptide recognition receptor, is found in some patients, which leads to an even more pronounced alpha-defensin decrease. However, the underlying mechanism remains unclear for the majority of patients. In this study, we report a reduced expression in ileal CD of the Wnt-signaling pathway transcription factor Tcf-4, a known regulator of Paneth cell differentiation and alpha-defensin expression. Within specimens, the levels of Tcf-4 mRNA showed a high degree of correlation with both HD5 and HD6 mRNA. The levels of Tcf-4 mRNA were decreased in patients with ileal disease irrespective of degree of inflammation, but were not decreased in colonic CD or ulcerative colitis. As a functional indicator of Tcf-4 protein, quantitative binding analysis with nuclear extracts from small intestine biopsies to a Tcf-4 high-affinity binding site in the HD-5 and HD-6 promoters showed significantly reduced activity in ileal CD. Furthermore, a causal link was shown in a murine Tcf-4 knockout model, where the comparably reduced expression of Tcf-4 in heterozygous (+/-) mice was sufficient to cause a significant decrease of both Paneth cell alpha-defensin levels and bacterial killing activity. Finally, the association between Paneth cell alpha-defensins and Tcf-4 was found to be independent of the NOD2 genotype. This new link established between a human inflammatory bowel disease and the Wnt pathway/Tcf-4 provides a novel mechanism for pathogenesis in patients with ileal CD.

Bacteria- and host-derived mechanisms to control intestinal epithelial cell homeostasis: implications for chronic inflammation

The genetic predisposition to deregulated mucosal immune responses and the concurrent prevalence of certain environmental triggers in developed countries are strong etiologic factors for the development of inflammatory bowel diseases in human subjects, including Crohn's disease and ulcerative colitis. Numerous clinical and experimental studies have shown that the intestinal microbes are critical for the initiation and progression of chronic intestinal inflammation. Activation of pattern recognition receptor signaling via members of the Toll-like receptor (TLR) and the nucleotide-binding oligomerization domain (NOD)-like families initiates inflammatory defense mechanisms that are required to alert and protect the host. Key inflammatory mechanisms such as nuclear transcription factor kappaB (NF-kappaB) activation and endoplasmic reticulum stress responses are controlled by a complex network of pathways that includes intrinsic feedback effectors and is targeted by immunosuppressive cytokines such as interleukin 10 (IL-10) and transforming growth factor (TGF)-beta. In the absence or after functional loss of these antiinflammatory feedback signals, physiological defense mechanisms may turn into pathological responses. The data discussed in the present review suggest that disturbances in the homeostasis between bacteria- and host-derived signals at the epithelial cell level lead to a break in the intestinal barrier function and to the development of mucosal immune disorders in genetically susceptible hosts.

Immunologic and molecular mechanisms in inflammatory bowel disease

Molecular and immunologic mechanisms underlying inflammation in inflammatory bowel disease (IBD) are largely unknown. Recent studies have helped better characterize genetic and environmental factors associated with colitis. Discoveries of genetic variants have confirmed that IBD is a bacteria and cytokine-driven pathologic immune response. Data have demonstrated that certain T cell subsets are important in executing the inflammatory cascade. Insufficient regulatory cell activity or modulatory cytokine production results in unrestrained inflammation. Biologic agents that block inflammatory cytokines (anti-TNFalpha antibodies) have been used successfully to treat IBD. Recent advances have also identified mucosal regulatory pathways.

Experimental acute pancreatitis in PAP/HIP knock-out mice

BACKGROUND AND AIMS

PAP/HIP was first reported as an additional pancreatic secretory protein expressed during the acute phase of pancreatitis. It was shown in vitro to be anti-apoptotic and anti-inflammatory. This study aims to look at whether PAP/HIP plays the same role in vivo.

METHODS

A model of caerulein-induced pancreatitis was used to compare the outcome of pancreatitis in PAP/HIP(-/-) and wild-type mice.

RESULTS

PAP/HIP(-/-) mice showed the normal phenotype at birth and normal postnatal development. Caerulein-induced pancreatic necrosis was, however, less severe in PAP/HIP(-/-) mice than in wild-type mice, as judged by lower amylasemia and lipasemia levels and smaller areas of necrosis. On the contrary, pancreas from PAP/HIP(-/-) mice was more sensitive to apoptosis, in agreement with the anti-apoptotic effect of PAP/HIP in vitro. Surprisingly, pancreatic inflammation was more extensive in PAP/HIP(-/-) mice, as judged from histological parameters, increased myeloperoxidase activity and increased pro-inflammatory cytokine expression. This result, in apparent contradiction with the limited necrosis observed in these mice, is, however, in agreement with the anti-inflammatory function previously reported in vitro for PAP/HIP. This is supported by the observation that activation of the STAT3/SOCS3 pathway was strongly decreased in the pancreas of PAP/HIP(-/-) mice and by the reversion of the apoptotic and inflammatory phenotypes upon administration of recombinant PAP/HIP to PAP/HIP(-/-) mice.

CONCLUSION

The anti-apoptotic and anti-inflammatory functions described in vitro for PAP/HIP have physiological relevance in the pancreas in vivo during caerulein-induced pancreatitis.

Role of sugars in surface microbe?host interactions and immune reaction modulation

Sugars in the form of monosaccharides, oligosaccharides, polysaccharides and glycoconjugates (glycoproteins, glycolipids) are vital components of infecting microbes and host cells, and are involved in cell signalling associated with modulation of inflammation in all integumental structures. Indeed, sugars are the molecules most commonly involved in cell recognition and communication. In skin, they are essential to epidermal development and homeostasis. They play important roles in microbial adherence, colonization and biofilm formation, and in virulence. Two groups of pathogen recognition receptors, C-type lectins (CTL) and their receptors (CTLR), and the Toll-like receptors enable the host to recognize pathogen-associated molecular patterns (PAMPs), which are mainly glycolipids. The CTLs can recognize a wide variety of bacteria, fungi and parasites and are important in phagocytosis and endocytosis. TLRs are expressed on the surfaces of a variety of cells, including keratinocytes, dendritic cells, monocytes and macrophages; they play a major role in innate immunity. Interaction of TLRs with PAMPs initiates a cascade of events leading to production of reactive oxygen intermediates, cytokines and chemokines, and promotes inflammation. Exogenous sugars can block carbohydrate receptors and competitively displace bacteria from attachment to cells, including keratinocytes. Thus sugars may provide valuable adjunctive anti-inflammatory and/or antimicrobial treatment. A promising approach is the use of a panel of carbohydrate derivatives with anti-adhesive efficacy against bacteria frequently involved in diseases affecting skin and other epithelia. More complete characterization of sugar receptors and their ligands will provide further keys to use of carbohydrates in immunomodulation and infection control in skin.

MyD88-mediated signals induce the bactericidal lectin RegIII gamma and protect mice against intestinal Listeria monocytogenes infection

Listeria monocytogenes is a food-borne bacterial pathogen that causes systemic infection by traversing the intestinal mucosa. Although MyD88-mediated signals are essential for defense against systemic L. monocytogenes infection, the role of Toll-like receptor and MyD88 signaling in intestinal immunity against this pathogen has not been defined. We show that clearance of L. monocytogenes from the lumen of the distal small intestine is impaired in MyD88^−/− mice. The distal ileum of wild-type (wt) mice expresses high levels of RegIIIγ, which is a bactericidal lectin that is secreted into the bowel lumen, whereas RegIIIγ expression in MyD88^−/− mice is nearly undetectable. In vivo depletion of RegIIIγ from the small intestine of wt mice diminishes killing of luminal L. monocytogenes, whereas reconstitution of MyD88-deficient mice with recombinant RegIIIγ enhances intestinal bacterial clearance. Experiments with bone marrow chimeric mice reveal that MyD88-mediated signals in nonhematopoietic cells induce RegIIIγ expression in the small intestine, thereby enhancing bacterial killing. Our findings support a model of MyD88-mediated epithelial conditioning that protects the intestinal mucosa against bacterial invasion by inducing RegIIIγ.

Helicobacter and gastrin stimulate Reg1 expression in gastric epithelial cells through distinct promoter elements

The gastric pathogen Helicobacter pylori accelerates the progression to gastric cancer but the precise mechanisms that mediate carcinogenesis remain unidentified. We now describe how Helicobacter and gastrin stimulate the expression of a putative growth factor, Reg1, in primary gastric epithelial cells. RT-PCR and Western immunoblotting of human gastric corpus and antrum showed significantly increased Reg1alpha in H. pylori-infected patients. Similarly, Reg1 was increased in the stomachs of H. felis-infected INS-GAS mice. To study transcriptional regulation of the Reg1 gene, we transfected primary mouse gastric glands with -2111 bp and -104 bp Reg1 promoter-luciferase reporter constructs. Expression of both constructs was detected in pepsinogen- and VMAT-2-expressing cells, which corresponds to the normal pattern of expression of human and mouse endogenous Reg1. The expression of both constructs was increased in response to gastrin and H. pylori, and there were potentiating interactions between them; in contrast, only the -2111 bp construct responded to H. felis. Mutation of a C-rich putative regulatory element within the -104 bp sequence abolished the response to gastrin but not to H. pylori whereas mutation of the proximal -98 to -93 region of the promoter reduced the response to H. pylori but not to gastrin. Stimulation of Reg1 by H. pylori required the virulence factor CagA. These data indicate that expression of the putative growth factor Reg1 is controlled through separate promoter elements by gastrin and Helicobacter.

Defensins and other antimicrobial peptides in inflammatory bowel disease

PURPOSE OF REVIEW

Recently published studies presenting novel and relevant information on defensins and other antimicrobial peptides in Crohn's disease and ulcerative colitis are reviewed.

RECENT FINDINGS

Different clinical localizations of Crohn's disease are associated with different deficiencies in epithelial and leukocyte antimicrobial peptide expression. As compared with ulcerative colitis, Crohn's disease of the colon is characterized by an impaired induction of beta defensins, and antimicrobial antiproteases elafin and SLPI, as well as the cathelicidin LL37. The attenuated induction of beta defensins is linked to fewer gene copy numbers in this locus, which is associated with colonic but not ileal Crohn's disease. In contrast, ileal Crohn's disease patients are characterized by a reduced antibacterial activity and a specific reduction of ileal Paneth cell defensins. This decrease is independent of the grade of histological inflammation and cannot be found in inflammation controls. Thus, some of these defects can be explained either by direct or indirect genetic mechanisms and appear to be primary.

SUMMARY

Unlike ulcerative colitis, ileal and colonic Crohn's disease are characterized by localized deficiencies of antibacterial peptides. Understanding the precise molecular mechanisms of the defective antibacterial barrier function might provide new therapeutic directions.

In vivo imaging and genetic analysis link bacterial motility and symbiosis in the zebrafish gut

Complex microbial communities reside within the intestines of humans and other vertebrates. Remarkably little is known about how these microbial consortia are established in various locations within the gut, how members of these consortia behave within their dynamic ecosystems, or what microbial factors mediate mutually beneficial host-microbial interactions. Using a gnotobiotic zebrafish-Pseudomonas aeruginosa model, we show that the transparency of this vertebrate species, coupled with methods for raising these animals under germ-free conditions can be used to monitor microbial movement and localization within the intestine in vivo and in real time. Germ-free zebrafish colonized with isogenic P. aeruginosa strains containing deletions of genes related to motility and pathogenesis revealed that loss of flagellar function results in attenuation of evolutionarily conserved host innate immune responses but not conserved nutrient responses. These results demonstrate the utility of gnotobiotic zebrafish in defining the behavior and localization of bacteria within the living vertebrate gut, identifying bacterial genes that affect these processes, and assessing the impact of these genes on host-microbial interactions.