Symbiotic bacteria direct expression of an intestinal bactericidal lectin

Ileal mucosal and fecal pancreatitis associated protein levels reflect severity of salmonella infection in rats

BACKGROUND

Microbial infections induce ileal pancreatitis-associated protein/regenerating gene III (PAP/RegIII) mRNA expression. Despite increasing interest, little is known about the PAP/RegIII protein. Therefore, ileal mucosal PAP/RegIII protein expression, localization, and fecal excretion were studied in rats upon Salmonella infection.

RESULTS

Salmonella infection increased ileal mucosal PAP/RegIII protein levels in enterocytes located at the crypt-villus junction. Increased colonization and translocation of Salmonella was associated with higher ileal mucosal PAP/RegIII levels and secretion of this protein in feces.

CONCLUSIONS

PAP/RegIII protein is increased in enterocytes of the ileal mucosa during Salmonella infection and is associated with infection severity. PAP/RegIII is excreted in feces and might be used as a new and non-invasive infection marker.

Polymorphisms in toll-like receptor 4 and toll-like receptor 9 influence viral load in a seroincident cohort of HIV-1-infected individuals

OBJECTIVES

Toll-like receptors (TLRs) are innate immune sensors that are integral to resisting chronic and opportunistic infections. Mounting evidence implicates TLR polymorphisms in susceptibilities to various infectious diseases, including HIV-1. We investigated the impact of TLR single nucleotide polymorphisms (SNPs) on clinical outcome in a seroincident cohort of HIV-1-infected volunteers.

DESIGN

We analyzed TLR SNPs in 201 antiretroviral treatment-naive HIV-1-infected volunteers from a longitudinal seroincident cohort with regular follow-up intervals (median follow-up 4.2 years, interquartile range 4.4). Participants were stratified into two groups according to either disease progression, defined as peripheral blood CD4(+) T-cell decline over time, or peak and setpoint viral load.

METHODS

Haplotype tagging SNPs from TLR2, TLR3, TLR4, and TLR9 were detected by mass array genotyping, and CD4(+) T-cell counts and viral load measurements were determined prior to antiretroviral therapy initiation. The association of TLR haplotypes with viral load and rapid progression was assessed by multivariate regression models using age and sex as covariates.

RESULTS

Two TLR4 SNPs in strong linkage disequilibrium [1063 A/G (D299G) and 1363 C/T (T399I)] were more frequent among individuals with high peak viral load compared with low/moderate peak viral load (odds ratio 6.65, 95% confidence interval 2.19-20.46, P < 0.001; adjusted P = 0.002 for 1063 A/G). In addition, a TLR9 SNP previously associated with slow progression was found less frequently among individuals with high viral setpoint compared with low/moderate setpoint (odds ratio 0.29, 95% confidence interval 0.13-0.65, P = 0.003, adjusted P = 0.04).

CONCLUSION

This study suggests a potentially new role for TLR4 polymorphisms in HIV-1 peak viral load and confirms a role for TLR9 polymorphisms in disease progression.

The recognition unit of FIBCD1 organizes into a noncovalently linked tetrameric structure and uses a hydrophobic funnel (S1) for acetyl group recognition

We have recently identified FIBCD1 (Fibrinogen C domain containing 1) as a type II transmembrane endocytic receptor located primarily in the intestinal brush border. The ectodomain of FIBCD1 comprises a coiled coil, a polycationic region, and a C-terminal FReD (fibrinogen-related domain) that assembles into disulfide-linked homotetramers. The FIBCD1-FReD binds Ca(2+) dependently to acetylated structures like chitin, N-acetylated carbohydrates, and amino acids. FReDs are present in diverse innate immune pattern recognition proteins including the ficolins and horseshoe crab TL5A. Here, we use chemical cross-linking, combined with analytical ultracentrifugation and electron microscopy of the negatively stained recombinant FIBCD1-FReD to show that it assembles into noncovalent tetramers in the absence of the coiled coil. We use surface plasmon resonance, carbohydrate binding, and pulldown assays combined with site-directed mutagenesis to define the binding site involved in the interaction of FIBCD1 with acetylated structures. We show that mutations of central residues (A432V and H415G) in the hydrophobic funnel (S1) abolish the binding of FIBCD1 to acetylated bovine serum albumin and chitin. The double mutations (D393N/D395A) at the putative calcium-binding site reduce the ability of FIBCD1 to bind ligands. We conclude that the FReDs of FIBCD1 forms noncovalent tetramers and that the acetyl-binding site of FReDs of FIBCD1 is homologous to that of tachylectin 5A and M-ficolin but not to the FReD of L-ficolin. We suggest that the spatial organization of the FIBCD1-FReDs determine the molecular pattern recognition specificity and subsequent biological functions.

Balancing inflammatory, lipid, and xenobiotic signaling pathways by VSL#3, a biotherapeutic agent, in the treatment of inflammatory bowel disease

BACKGROUND

The interleukin 10 knockout mouse (IL10-KO) is a model of human inflammatory bowel disease (IBD) used to study host microbial interactions and the action of potential therapeutics. Using Affymetrix data analysis, important signaling pathways and transcription factors relevant to gut inflammation and antiinflammatory probiotics were identified.

METHODS

Affymetrix microarray analysis on both wildtype (WT) and IL10-KO mice orally administered with and without the probiotic VSL#3 was performed and the results validated by real-time polymerase chain reaction (PCR), immunocytochemistry, proteomics, and histopathology. Changes in metabolically active bacteria were assessed with denaturing gradient gel electrophoresis (DGGE).

RESULTS

Inflammation in IL10-KO mice was characterized by differential regulation of inflammatory, nuclear receptor, lipid, and xenobiotic signaling pathways. Probiotic intervention resulted in downregulation of CXCL9 (fold change [FC] = -3.98, false discovery rate [FDR] = 0.019), CXCL10 (FC = -4.83, FDR = 0.0008), CCL5 (FC = -3.47, FDR = 0.017), T-cell activation (Itgal [FC = -4.72, FDR = 0.00009], Itgae [FC = -2.54 FDR = 0.0044]) and the autophagy gene IRGM (FC = -1.94, FDR = 0.01), a recently identified susceptibility gene in human IBD. Consistent with a marked reduction in integrins, probiotic treatment decreased the number of CCL5+ CD3+ double-positive T cells and upregulated galectin2, which triggers apoptosis of activated T cells. Importantly, genes associated with lipid and PPAR signaling (PPARalpha [FC = 2.36, FDR = 0.043], PPARGC1alpha [FC = 2.58, FDR = 0.016], Nr1d2 [FC = 3.11, FDR = 0.0067]) were also upregulated. Altered microbial diversity was noted in probiotic-treated mice.

CONCLUSIONS

Bioinformatics analysis revealed important immune response, phagocytic and inflammatory pathways dominated by elevation of T-helper cell 1 type (TH1) transcription factors in IL10-KO mice. Probiotic intervention resulted in a site-specific reduction of these pathways but importantly upregulated PPAR, xenobiotic, and lipid signaling genes, potential antagonists of NF-kappaB inflammatory pathways.

Induction of intestinal Th17 cells by segmented filamentous bacteria

The gastrointestinal tract of mammals is inhabited by hundreds of distinct species of commensal microorganisms that exist in a mutualistic relationship with the host. How commensal microbiota influence the host immune system is poorly understood. We show here that colonization of the small intestine of mice with a single commensal microbe, segmented filamentous bacterium (SFB), is sufficient to induce the appearance of CD4(+) T helper cells that produce IL-17 and IL-22 (Th17 cells) in the lamina propria. SFB adhere tightly to the surface of epithelial cells in the terminal ileum of mice with Th17 cells but are absent from mice that have few Th17 cells. Colonization with SFB was correlated with increased expression of genes associated with inflammation and antimicrobial defenses and resulted in enhanced resistance to the intestinal pathogen Citrobacter rodentium. Thus, manipulation of this commensal-regulated pathway may provide new opportunities for enhancing mucosal immunity and treating autoimmune disease.

Probiotic and gut lactobacilli and bifidobacteria: molecular approaches to study diversity and activity

Lactobacilli and bifidobacteria have traditionally been recognized as potential health-promoting microbes in the human gastrointestinal tract, which is clearly reflected by the pre- and probiotic supplements on the market. Bacterial genomics of lactobacilli and bifidobacteria is initiating the identification and validation of specific effector molecules that mediate host health effects. Combined with advanced postgenomic mammalian host response analyses, elucidations of the molecular interactions and mechanisms that underlie the host-health effects observed are beginning to be gathered. These developments should be seen in the complexity of the microbiota-host relationships in the intestine, which through the new metagenomic era has regained momentum and will undoubtedly progress to functional microbiomics and host response analyses within the next decade. Taken together, these developments are anticipated to dramatically alter the scope and impact of the probiotic field, offering tremendous new opportunities with accompanying challenges for research and industrial application.

Potential therapeutic efficacy of a bactericidal-immunomodulatory fusion peptide against methicillin-resistant Staphylococcus aureus skin infection

To enhance the potential therapeutic efficacy of an antimicrobial peptide human beta-defensin 3, two fusion peptides, a bactericidal-immunomodulatory fusion peptide human beta-defensin 3-mannose-binding lectin and a bactericidal-bactericidal fusion peptide human beta-defensin 3-lysozyme were synthesized and the bactericidal activities in vitro and in vivo against methicillin-resistant Staphylococcus aureus N315 were demonstrated in this study. Peptide human beta-defensin 3-lysozyme showed the best bactericidal activity in vitro, but human beta-defensin 3-mannose-binding lectin showed a significant improvement in angiogenesis and tissue reconstruction. Our results illustrated that outstanding bactericidal activity in vitro is not essential in the development of antimicrobial peptides. Fusion strategy and immunomodulatory factors should be utilized in novel antimicrobial peptide development.

Life in the inflamed intestine, Salmonella style

The lower gastrointestinal tract is densely populated with resident microbial communities (microbiota), which do not elicit overt host responses but rather provide benefit to the host, including niche protection from pathogens. However, introduction of bacteria into the underlying tissue evokes acute inflammation. Non-typhoidal Salmonella serotypes (NTS) elicit this stereotypic host response by actively penetrating the intestinal epithelium and surviving in tissue macrophages. Initial responses generated by bacterial host cell interaction are amplified in tissue through the interleukin (IL)-18/interferon-gamma and IL-23/IL-17 axes, resulting in the activation of mucosal barrier functions against NTS dissemination. However, the pathogen is adapted to survive antimicrobial defenses encountered in the lumen of the inflamed intestine. This strategy enables NTS to exploit inflammation to outcompete the intestinal microbiota, and promotes the Salmonella transmission by the fecal/oral route.

The vaginal bacterial communities of Japanese women resemble those of women in other racial groups

To determine whether different racial groups shared common types of vaginal microbiota, we characterized the composition and structure of vaginal bacterial communities in asymptomatic and apparently healthy Japanese women in Tokyo, Japan, and compared them with those of White and Black women from North America. The composition of vaginal communities was compared based on community profiles of terminal restriction fragments of 16S rRNA genes and phylogenetic analysis of cloned 16S rRNA gene sequences of the numerically dominant bacterial populations. The types of vaginal communities found in Japanese women were similar to those of Black and White women. As with White and Black women, most vaginal communities were dominated by lactobacilli, and only four species of Lactobacillus (Lactobacillus iners, Lactobacillus crispatus, Lactobacillus jensenii, and Lactobacillus gasseri) were commonly found. Communities dominated by multiple species of lactobacilli were common in Japanese and White women, but rare in Black women. The incidence, in Japanese women, of vaginal communities with several non-Lactobacillus species at moderately high frequencies was intermediate between Black women and White women. The limited number of community types found among women in different ethnic groups suggests that host genetic factors, including the innate and adaptive immune systems, may be more important in determining the species composition of vaginal bacterial communities than are cultural and behavioral differences.

Inflammatory bowel disease, gut bacteria and probiotic therapy

Crohn's disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel disease (IBD) and both diseases lead to high morbidity and health care costs. Complex interactions between the immune system, enteric commensal bacteria and host genotype are thought to underlie the development of IBD although the precise aetiology of this group of diseases is still unknown. The understanding of the composition and complexity of the normal gut microbiota has been greatly aided by the use of molecular methods and is likely to be further increased with the advent of metagenomics and metatranscriptomics approaches, which will allow an increasingly more holistic assessment of the microbiome with respect to both diversity and function of the commensal gut microbiota. Studies thus far have shown that the intestinal microbiota drives the development of the gut immune system and can induce immune homeostasis as well as contribute to the development of IBD. Probiotics which deliver some of the beneficial immunomodulatory effects of the commensal gut microbiota and induce immune homeostasis have been proposed as a suitable treatment for mild to moderate IBD. This review provides an overview over the current understanding of the commensal gut microbiota, its interactions with the mucosal immune system and its capacity to induce both gut homeostasis as well as dysregulation of the immune system. Bacterial-host events, including interactions with pattern recognition receptors (PRRs) expressed on epithelial cells and dendritic cells (DCs) and the resultant impact on immune responses at mucosal surfaces will be discussed.

T-bet-/- RAG2-/- ulcerative colitis: the role of T-bet as a peacekeeper of host-commensal relationships

Inflammatory bowel disease is a disease that reflects a disequilibrium in host-commensal homeostasis. T-bet-/-xRAG2-/- deficient mice develop a spontaneous juvenile ulcerative colitis resulting from a pro-inflammatory response to the commensal microbiota that is dendritic cell and TNF-alpha driven [schematized in Fig. 1]. The TRUC (T-bet-/- RAG2-/- ulcerative colitis) model is discussed in the broader context of the adaptive and innate immune mechanisms that regulate host-commensal relationships within the intestine.

Th17 cytokines and host-pathogen interactions at the mucosa: dichotomies of help and harm

The mucosal surfaces are often the first site of interaction between pathogenic microorganisms and the host. Activation of the mucosal immune response has the important function of containing an infection and preventing dissemination of pathogens to systemic sites (barrier function). Numerous lines of evidence suggest that the barrier function is orchestrated by a subset of cytokines (interleukin (IL-)17 and IL-22), which belong to the Th17 family. IL-17 and IL-22 induce expression of antimicrobial peptides and neutrophil chemoattractants at mucosal sites, and thus play an important role in controlling mucosal infections. However, there is increasing evidence that mucosal pathogens achieve greater colonization during inflammation because they are resistant to a subset of these antimicrobial responses. In this review we compare the antimicrobial responses elicited by Th17 cytokines during mucosal infections with four different pathogens: Klebsiella pneumoniae, Citrobacter rodentium, Candida albicans and Salmonella typhimurium. We will then discuss which responses may constitute the mucosal barrier, thus providing a benefit to the host, and which ones may promote the colonization of pathogens, thereby providing a benefit to the microbes.

Immune responses to the microbiota at the intestinal mucosal surface

The mammalian intestinal mucosal surface is continuously exposed to a complex and dynamic community of microorganisms. These microbes establish symbiotic relationships with their hosts, making important contributions to metabolism and digestive efficiency. The intestinal epithelial surface is the primary interface between the vast microbiota and internal host tissues. Given the enormous numbers of enteric bacteria and the persistent threat of opportunistic invasion, it is crucial that mammalian hosts monitor and regulate microbial interactions with intestinal epithelial surfaces. Here we discuss recent insights into how the innate and adaptive arms of the immune system collaborate to maintain homeostasis at the luminal surface of the intestinal host-microbial interface. These findings are also yielding a better understanding of how symbiotic host-microbial relationships can break down in inflammatory bowel disease.

The role of innate signaling in the homeostasis of tolerance and immunity in the intestine

In the intestine innate recognition of microbes is achieved through pattern recognition receptor (PRR) families expressed in immune cells and different cell lineages of the intestinal epithelium. Toll-like receptor (TLR) and nucleotide-binding and oligomerization domain-like receptor (NLR) families are emerging as key mediators of immunity through their role as maturation factors of immune cells and triggers for the production of cytokines and chemokines and antimicrobial factors. At the mucosal surface chronic activation of the immune system is avoided through the epithelial production of a glycocalyx, steady-state production of antimicrobial factors as well as the selective expression and localization of PRRs. Additionally, the polarization of epithelial TLR signaling and suppression of NF-kappaB activation by luminal commensals appears to contribute to the homeostasis of tolerance and immunity. Several studies have demonstrated that TLR signaling in epithelial cells contributes to a range of homeostatic mechanisms including proliferation, wound healing, epithelial integrity, and regulation of mucosal immune functions. The intestinal epithelium appears to have uniquely evolved to maintain mucosal tolerance and immunity, and future efforts to further understand the molecular mechanisms of intestinal homeostasis may have a major impact on human health.

Characterization of FIBCD1 as an acetyl group-binding receptor that binds chitin

Chitin is a highly acetylated compound and the second most abundant biopolymer in the world next to cellulose. Vertebrates are exposed to chitin both through food ingestion and when infected with parasites, and fungi and chitin modulate the immune response in different directions. We have identified a novel homotetrameric 55-kDa type II transmembrane protein encoded by the FIBCD1 gene and highly expressed in the gastrointestinal tract. The ectodomain of FIBCD1 is characterized by a coiled-coil region, a polycationic region and C-terminal fibrinogen-related domain that by disulfide linkage assembles the protein into tetramers. Functional analysis showed a high-affinity and calcium-dependent binding of acetylated components to the fibrinogen domain, and a function in endocytosis was demonstrated. Screening for ligands revealed that the FIBCD1 is a high-affinity receptor for chitin and chitin fragments. FIBCD1 may play an important role in controlling the exposure of intestine to chitin and chitin fragments, which is of great relevance for the immune defense against parasites and fungi and for immune response modulation.

Gut commensal bacteria direct a protective immune response against Toxoplasma gondii

Toxoplasma gondii is a universally distributed pathogen that infects over one billion people worldwide. Host resistance to this protozoan parasite depends on a Th1 immune response with potent production of the cytokines interleukin-12 and interferon gamma. Although Toll-like receptor 11 (TLR11) plays a major role in controlling Th1 immunity to this pathogen in mice, this innate immune receptor is nonfunctional in humans, and the mechanisms of TLR11-independent sensing of T. gondii remain elusive. Here, we show that oral infection by T. gondii triggers a TLR11-independent but MyD88-dependent Th1 response that is impaired in TLR2xTLR4 double knockout and TLR9 single knockout mice. These mucosal innate and adaptive immune responses to T. gondii rely on the indirect stimulation of dendritic cells by normal gut microflora. Thus, our results reveal that gut commensal bacteria can serve as molecular adjuvants during parasitic infection, providing indirect immunostimulation that protects against T. gondii in the absence of TLR11.

Alpha-defensins in enteric innate immunity: functional Paneth cell alpha-defensins in mouse colonic lumen

Paneth cells are a secretory epithelial lineage that release dense core granules rich in host defense peptides and proteins from the base of small intestinal crypts. Enteric alpha-defensins, termed cryptdins (Crps) in mice, are highly abundant in Paneth cell secretions and inherently resistant to proteolysis. Accordingly, we tested the hypothesis that enteric alpha-defensins of Paneth cell origin persist in a functional state in the mouse large bowel lumen. To test this idea, putative Crps purified from mouse distal colonic lumen were characterized biochemically and assayed in vitro for bactericidal peptide activities. The peptides comigrated with cryptdin control peptides in acid-urea-PAGE and SDS-PAGE, providing identification as putative Crps. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry experiments showed that the molecular masses of the putative alpha-defensins matched those of the six most abundant known Crps, as well as N-terminally truncated forms of each, and that the peptides contain six Cys residues, consistent with identities as alpha-defensins. N-terminal sequencing definitively revealed peptides with N termini corresponding to full-length, (des-Leu)-truncated, and (des-Leu-Arg)-truncated N termini of Crps 1-4 and 6. Crps from mouse large bowel lumen were bactericidal in the low micromolar range. Thus, Paneth cell alpha-defensins secreted into the small intestinal lumen persist as intact and functional forms throughout the intestinal tract, suggesting that the peptides may mediate enteric innate immunity in the colonic lumen, far from their upstream point of secretion in small intestinal crypts.

Transcriptomics of enterotoxigenic Escherichia coli infection. Individual variation in intestinal gene expression correlates with intestinal function

Acute secretory diarrhea is a major cause of morbidity and mortality in young animals and humans. Deaths result from excessive fluid and electrolyte losses. The disease is caused by non-invasive bacteria such as Vibrio cholerae and Escherichia coli which produce enterotoxins, however, much less is known about the role of individual host responses. Here we report the response of intact porcine small intestinal mucosa to infection with enterotoxigenic E. coli (ETEC). Jejunal segments in four piglets were infused with or without ETEC, and perfused for 8h, and net absorption measured. Microarray analysis at 8h post-infection showed significant differential regulation of on average fifteen transcripts in mucosa, with considerable individual variation. Differential net absorption varied between animals, and correlated negatively with the number of up regulated genes, and with one individual gene (THO complex 4). This shows that quantitative differences in gene regulation can be functionally linked to the physiological response in these four animals.

Protein constituents of the eggshell: eggshell-specific matrix proteins

In this article, we review the results of recent proteomic and genomic analyses of eggshell matrix proteins and draw attention to the impact of these data on current understanding of eggshell formation and function. Eggshell-specific matrix proteins from avian (ovocleidins and ovocalyxins) and non-avian (paleovaterin) shells are discussed. Two possible roles for eggshell-specific matrix proteins have been proposed; both reflect the protective function of the eggshell in avian reproduction: regulation of eggshell mineralization and antimicrobial defense. An emerging concept is the dual role (mineralization/antimicrobial protection) that certain eggshell matrix proteins can play.

Low counts of Faecalibacterium prausnitzii in colitis microbiota

BACKGROUND

The intestinal microbiota is suspected to play a role in colitis and particularly in inflammatory bowel disease (IBD) pathogenesis. The aim was to compare the fecal microbiota composition of patients with colitis to that of healthy subjects (HS).

METHODS

fecal samples from 22 active Crohn's disease (A-CD) patients, 10 CD patients in remission (R-CD), 13 active ulcerative colitis (A-UC) patients, 4 UC patients in remission (R-UC), 8 infectious colitis (IC) patients, and 27 HS were analyzed by quantitative real-time polymerase chain reaction (PCR) targeting the 16S rRNA gene. Bacterial counts were transformed to logarithms (Log(10) CFU) for statistical analysis.

RESULTS

Bacteria of the phylum Firmicutes (Clostridium leptum and Clostridium coccoides groups) were less represented in A-IBD patients (9.7; P = 0.004) and IC (9.4; P = 0.02), compared to HS (10.8). Faecalibacterium prausnitzii species (a major representative of the C. leptum group) had lower counts in A-IBD and IC patients compared to HS (8.8 and 8.3 versus 10.4; P = 0.0004 and P = 0.003). The Firmicutes/Bacteroidetes ratio was lower in A-IBD (1.3; P = 0.0001) and IC patients (0.4; P = 0.002). Compared to HS, Bifidobacteria were less represented in A-IBD and IC (7.9 and 7.7 versus 9.2; P = 0.001 and P = 0.01).

CONCLUSIONS

The fecal microbiota of patients with IBD differs from that of HS. The phylum Firmicutes and particularly the species F. prausnitzii, are underrepresented in A-IBD patients as well as in IC patients. These bacteria could be crucial to gut homeostasis since lower counts of F. prausnitzii are consistently associated with a reduced protection of the gut mucosa.

Crosstalk between components of the innate immune system: promoting anti-microbial defenses and avoiding immunopathologies

Because it reaches full functional efficacy rapidly upon encounter with a pathogen, the innate immune system is considered as the first line of defense against infections. The sensing of microbes or of transformed or infected cells, through innate immune recognition receptors (referred to as activating I2R2), initiates pro-inflammatory responses and innate immune effector functions. Other I2R2 with inhibitory properties bind self-ligands constitutively expressed in host. However, this dichotomy in the recognition of foreign or induced self versus constitutive self by I2R2 is not always respected in certain non-infectious conditions reminiscent of immunopathologies. In this review, we discuss that immune mechanisms have evolved to avoid inappropriate inflammatory disorders in individuals. Molecular crossregulation exists between components of I2R2 signaling pathways, and intricate interactions between cells from both innate and adaptive immune systems set the bases of controlled immune responses. We also pinpoint that, like T or B cells, some cells of the innate immune system must go through education processes to prevent autoreactivity. In addition, we illustrate how gene expression profiling of immune cell types is a useful tool to find functional homologies between cell subsets of different species and to speculate about unidentified functions of these cells in the responses to pathogen infections.

Differential enzymatic activity of common haplotypic versions of the human acidic Mammalian chitinase protein

Mouse models have shown the importance of acidic mammalian chitinase activity in settings of chitin exposure and allergic inflammation. However, little is known regarding genetic regulation of AMCase enzymatic activity in human allergic diseases. Resequencing the AMCase gene exons we identified 8 non-synonymous single nucleotide polymorphisms including three novel variants (A290G, G296A, G339T) near the gene area coding for the enzyme active site, all in linkage disequilibrium. AMCase protein isoforms, encoded by two gene-wide haplotypes, and differentiated by these three single nucleotide polymorphisms, were recombinantly expressed and purified. Biochemical analysis revealed the isoform encoded by the variant haplotype displayed a distinct pH profile exhibiting greater retention of chitinase activity at acidic and basic pH values. Determination of absolute kinetic activity found the variant isoform encoded by the variant haplotype was 4-, 2.5-, and 10-fold more active than the wild type AMCase isoform at pH 2.2, 4.6, and 7.0, respectively. Modeling of the AMCase isoforms revealed positional changes in amino acids critical for both pH specificity and substrate binding. Genetic association analyses of AMCase haplotypes for asthma revealed significant protective associations between the variant haplotype in several asthma cohorts. The structural, kinetic, and genetic data regarding the AMCase isoforms are consistent with the Th2-priming effects of environmental chitin and a role for AMCase in negatively regulating this stimulus.

Prolonged impact of antibiotics on intestinal microbial ecology and susceptibility to enteric Salmonella infection

The impact of antibiotics on the host's protective microbiota and the resulting increased susceptibility to mucosal infection are poorly understood. In this study, antibiotic regimens commonly applied to murine enteritis models are used to examine the impact of antibiotics on the intestinal microbiota, the time course of recovery of the biota, and the resulting susceptibility to enteric Salmonella infection. Molecular analysis of the microbiota showed that antibiotic treatment has an impact on the colonization of the murine gut that is site and antibiotic dependent. While combinations of antibiotics were able to eliminate culturable bacteria, none of the antibiotic treatments were effective at sterilizing the intestinal tract. Recovery of total bacterial numbers occurs within 1 week after antibiotic withdrawal, but alterations in specific bacterial groups persist for several weeks. Increased Salmonella translocation associated with antibiotic pretreatment corrects rapidly in association with the recovery of the most dominant bacterial group, which parallels the recovery of total bacterial numbers. However, susceptibility to intestinal colonization and mucosal inflammation persists when mice are infected several weeks after withdrawal of antibiotics, correlating with subtle alterations in the intestinal microbiome involving alterations of specific bacterial groups. These results show that the colonizing microbiotas are integral to mucosal host protection, that specific features of the microbiome impact different aspects of enteric Salmonella pathogenesis, and that antibiotics can have prolonged deleterious effects on intestinal colonization resistance.

Roles of galectins in infection

Galectins, which were first characterized in the mid-1970s, were assigned a role in the recognition of endogenous ('self') carbohydrate ligands in embryogenesis, development and immune regulation. Recently, however, galectins have been shown to bind glycans on the surface of potentially pathogenic microorganisms, and function as recognition and effector factors in innate immunity. Some parasites subvert the recognition roles of the vector or host galectins to ensure successful attachment or invasion. This Review discusses the role of galectins in microbial infection, with particular emphasis on adaptations of pathogens to evasion or subversion of host galectin-mediated immune responses.

Regulatory lymphocytes and intestinal inflammation

The immune system is pivotal in mediating the interactions between host and microbiota that shape the intestinal environment. Intestinal homeostasis arises from a highly dynamic balance between host protective immunity and regulatory mechanisms. This regulation is achieved by a number of cell populations acting through a set of shared regulatory pathways. In this review, we summarize the main lymphocyte subsets controlling immune responsiveness in the gut and their mechanisms of control, which involve maintenance of intestinal barrier function and suppression of chronic inflammation. CD4(+)Foxp3(+) T cells play a nonredundant role in the maintenance of intestinal homeostasis through IL-10- and TGF-beta-dependent mechanisms. Their activity is complemented by other T and B lymphocytes. Because breakdown in immune regulatory networks in the intestine leads to chronic inflammatory diseases of the gut, such as inflammatory bowel disease and celiac disease, regulatory lymphocytes are an attractive target for therapies of intestinal inflammation.

Proteolytic activation of human pancreatitis-associated protein is required for peptidoglycan binding and bacterial aggregation

PAP (pancreatitis-associated protein) is a 16 kDa lectin-like protein, which becomes robustly up-regulated in the pancreatic juice during acute pancreatitis. Trypsin cleaves the N-terminus of PAP, which in turn forms insoluble fibrils. PAP and its paralogue, the pancreatic stone protein, induce bacterial aggregation and, more recently, PAP was shown to bind to the peptidoglycan of Gram-positive bacteria and exert a direct bactericidal effect. However, the role of N-terminal processing in the antibacterial function of PAP has remained unclear. In the present study, we demonstrate that N-terminal cleavage of PAP by trypsin at the Arg37-Ile38 peptide bond or by elastase at the Ser35-Ala36 peptide bond is a prerequisite for binding to the peptidoglycan of the Gram-positive bacterium Bacillus subtilis. The tryptic site in PAP was also efficiently cleaved by nprE (extracellular neutral metalloprotease) secreted from B. subtilis. Trypsin-mediated processing of PAP resulted in the formation of the characteristic insoluble PAP species, whereas elastase-processed PAP remained soluble. N-terminally processed PAP induced rapid aggregation of B. subtilis without significant bacterial killing. The bacteria-aggregating activities of trypsin-processed and elastase-processed PAP were comparable. In contrast with previous reports, the Gram-negative Escherichia coli bacterium was not aggregated. We conclude that N-terminal processing is necessary for the peptidoglycan binding and bacteria-aggregating activity of PAP and that trypsin-processed and elastase-processed forms are functionally equivalent. The observations also extend the complement of proteases capable of PAP processing, which now includes trypsins, pancreatic elastases and bacterial zinc metalloproteases of the thermolysin type.

The gut microbiota shapes intestinal immune responses during health and disease

Immunological dysregulation is the cause of many non-infectious human diseases such as autoimmunity, allergy and cancer. The gastrointestinal tract is the primary site of interaction between the host immune system and microorganisms, both symbiotic and pathogenic. In this Review we discuss findings indicating that developmental aspects of the adaptive immune system are influenced by bacterial colonization of the gut. We also highlight the molecular pathways that mediate host-symbiont interactions that regulate proper immune function. Finally, we present recent evidence to support that disturbances in the bacterial microbiota result in dysregulation of adaptive immune cells, and this may underlie disorders such as inflammatory bowel disease. This raises the possibility that the mammalian immune system, which seems to be designed to control microorganisms, is in fact controlled by microorganisms.

Do symbiotic bacteria subvert host immunity?

The mammalian intestine is home to dense and complex indigenous bacterial communities. Most of these bacteria establish beneficial symbiotic relationships with their hosts, making important contributions to host metabolism and digestive efficiency. The vast numbers of intestinal bacteria and their proximity to host tissues raise the question of how symbiotic host-bacterial relationships are established without eliciting potentially harmful immune responses. In light of the varied ways in which pathogenic bacteria manipulate host immunity, this Opinion article explores the role of immune suppression, subversion and evasion in the establishment of symbiotic host-bacterial associations.

Clostridium difficile associated infection, diarrhea and colitis

A new, hypervirulent strain of Clostridium difficile, called NAP1/BI/027, has been implicated in C. difficile outbreaks associated with increased morbidity and mortality since the early 2000s. The epidemic strain is resistant to fluoroquinolones in vitro, which was infrequent prior to 2001. The name of this strain reflects its characteristics, demonstrated by different typing methods: pulsed-field gel electrophoresis (NAP1), restriction endonuclease analysis (BI) and polymerase chain reaction (027). In 2004 and 2005, the US Centers for Disease Control and Prevention (CDC) emphasized that the risk of C. difficile-associated diarrhea (CDAD) is increased, not only by the usual factors, including antibiotic exposure, but also gastrointestinal surgery/manipulation, prolonged length of stay in a healthcare setting, serious underlying illness, immune-compromising conditions, and aging. Patients on proton pump inhibitors (PPIs) have an elevated risk, as do peripartum women and heart transplant recipients. Before 2002, toxic megacolon in C. difficile-associated colitis (CDAC), was rare, but its incidence has increased dramatically. Up to two-thirds of hospitalized patients may be infected with C. difficile. Asymptomatic carriers admitted to healthcare facilities can transmit the organism to other susceptible patients, thereby becoming vectors. Fulminant colitis is reported more frequently during outbreaks of C. difficile infection in patients with inflammatory bowel disease (IBD). C. difficile infection with IBD carries a higher mortality than without underlying IBD. This article reviews the latest information on C. difficile infection, including presentation, vulnerable hosts and choice of antibiotics, alternative therapies, and probiotics and immunotherapy. We review contact precautions for patients with known or suspected C. difficile-associated disease. Healthcare institutions require accurate and rapid diagnosis for early detection of possible outbreaks, to initiate specific therapy and implement effective control measures. A comprehensive C. difficile infection control management rapid response team (RRT) is recommended for each health care facility. A communication network between RRTs is recommended, in coordination with each country’s department of health. Our aim is to convey a comprehensive source of information and to guide healthcare professionals in the difficult decisions that they face when caring for these oftentimes very ill patients.

Cytokine signalling by gp130 regulates gastric mucosal healing after ulceration and, indirectly, antral tumour progression

The cytokines IL-6 and IL-11, which signal via the receptor gp130, have been implicated in various gut pathologies, including inflammation and wound healing. We used mouse cytokine signalling mutants to evaluate the role of gp130 pathways in gastric ulceration and healing and the effect of spatially remote fundic ulceration on antral tumour progression, since compromised wound healing may impact tumourigenesis. Glacial acetic acid applied to the serosal surface of stomachs from wild-type, gp130(757FF), IL-6(-/-) and IL-11 receptor (R)alpha(-/-) mice was used to induce discrete haemostasis/necrosis and resultant mucosal ulceration. Wound pathology and mRNA expression of key cytokine target genes were examined 2 and 14 weeks after ulcer induction. The outcome of fundic ulceration on antral tumour development in gp130(757FF) mice was also examined. Chemical haemostasis in gp130(7575FF) mice produces more severe gastric ulcers than in wild-type mice. Lack of IL-6 produces more severe ulceration, while loss of IL-11Ralpha less severe ulcers, suggesting a role for IL-11 in ulcer induction. Increased expression of ulcer-associated IL-11 and its established mitogenic target genes RegI, IIIbeta and IIIgamma paralleled severe ulceration in gp130(757FF) mice. In this model, coincident with fundic ulceration, antral tumour development was inhibited and correlated with decreased RegI, IIIbeta and IIIgamma and reduced MMP9 and 13 expression. IL-11-driven transcription via gp130 contributes to the gastric mucosal response to ulceration. Fundic mucosal ulceration modulates antral growth factor and metalloproteinase gene expression, thereby contributing to restricted tumour growth.

Multidrug resistance gene deficient (mdr1a-/-) mice have an altered caecal microbiota that precedes the onset of intestinal inflammation

AIM

To compare caecal microbiota from mdr1a(-/-) and wild type (FVB) mice to identify differences in the bacterial community that could influence the intestinal inflammation.

METHODS AND RESULTS

Caecal microbiota of mdr1a(-/-) and FVB mice were evaluated at 12 and 25 weeks of age using denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR. DGGE fingerprints of FVB and mdr1a(-/-) mice (with no intestinal inflammation) at 12 weeks revealed differences in the presence of DNA fragments identified as Bacteroides fragilis, B. thetaiotaomicron, B. vulgatus and an uncultured alphaproteobacterium. Escherichia coli and Acinetobacter sp. were only identified in DGGE profiles of mdr1a(-/-) mice at 25 weeks (with severe intestinal inflammation), which also had a lower number of total bacteria in the caecum compared with FVB mice at same age.

CONCLUSIONS

Differences found in the caecal microbiota of FVB and mdr1a(-/-) mice (12 weeks) suggest that the lack of Abcb1 transporters in intestinal cells due to the disruption of the mdr1a gene might lead to changes in the caecal microbiota. The altered microbiota along with the genetic defect could contribute to the development of intestinal inflammation in mdr1a(-/-) mice.

SIGNIFICANCE AND IMPACT OF THE STUDY

Differences in caecal microbiota of mdr1a(-/-) and FVB mice (12 weeks) suggest genotype specific colonization. The results provide evidence that Abcb1 transporters may regulate host interactions with commensal bacteria. Future work is needed to identify the mechanisms involved in this possible cross-talk between the host intestinal cells and microbiota.

Reciprocal interactions between commensal bacteria and gamma delta intraepithelial lymphocytes during mucosal injury

The intestinal mucosal surface is in direct contact with a vast beneficial microbiota. The symbiotic nature of this relationship is threatened when the surface epithelium is injured, yet little is known about how mucosal surfaces maintain homeostasis with commensal microbes following damage. Gammadelta intraepithelial lymphocytes (gammadelta IEL) reside at the gut epithelial surface, where they stimulate mucosal healing following acute injury. A genome-wide analysis of the gammadelta IEL response to dextran sulfate sodium-induced colonic damage revealed induction of a complex transcriptional program, including coordinate regulation of cytoprotective, immunomodulatory, and antibacterial factors. Studies in germfree mice demonstrated that commensal microbiota regulate key components of this transcriptional program, thus revealing a dialogue between commensal bacteria and gammadelta IEL in injured epithelia. Analysis of TCRdelta-deficient mice indicated that gammadelta T cells are essential for controlling mucosal penetration of commensal bacteria immediately following dextran sulfate sodium-induced damage, suggesting that a key function of gammadelta IEL is to maintain host-microbial homeostasis following acute mucosal injury. Taken together, these findings disclose a reciprocal relationship between gammadelta T cells and intestinal microbiota that promotes beneficial host-microbial relationships in the intestine.

Regulation of C-type lectin antimicrobial activity by a flexible N-terminal prosegment

Members of the RegIII family of intestinal C-type lectins are directly antibacterial proteins that play a vital role in maintaining host-bacterial homeostasis in the mammalian gut, yet little is known about the mechanisms that regulate their biological activity. Here we show that the antibacterial activities of mouse RegIIIgamma and its human ortholog, HIP/PAP, are tightly controlled by an inhibitory N-terminal prosegment that is removed by trypsin in vivo. NMR spectroscopy revealed a high degree of conformational flexibility in the HIP/PAP inhibitory prosegment, and mutation of either acidic prosegment residues or basic core protein residues disrupted prosegment inhibitory activity. NMR analyses of pro-HIP/PAP variants revealed distinctive colinear backbone amide chemical shift changes that correlated with antibacterial activity, suggesting that prosegment-HIP/PAP interactions are linked to a two-state conformational switch between biologically active and inactive protein states. These findings reveal a novel regulatory mechanism governing C-type lectin biological function and yield new insight into the control of intestinal innate immunity.

Recognition between symbiotic Vibrio fischeri and the haemocytes of Euprymna scolopes

The light organ crypts of the squid Euprymna scolopes permit colonization exclusively by the luminous bacterium Vibrio fischeri. Because the crypt interior remains in contact with seawater, the squid must not only foster the specific symbiosis, but also continue to exclude other bacteria. Investigation of the role of the innate immune system in these processes revealed that macrophage-like haemocytes isolated from E. scolopes recognized and phagocytosed V. fischeri less than other closely related bacterial species common to the host's environment. Interestingly, phagocytes isolated from hosts that had been cured of their symbionts bound five times more V. fischeri cells than those from uncured hosts. No such change in the ability to bind other species of bacteria was observed, suggesting that the host adapts specifically to V. fischeri. Deletion of the gene encoding OmpU, the major outer membrane protein of V. fischeri, increased binding by haemocytes from uncured animals to the level observed for haemocytes from cured animals. Co-incubation with wild-type V. fischeri reduced this binding, suggesting that they produce a factor that complements the mutant's defect. Analyses of the phagocytosis of bound cells by fluorescence-activated cell sorting indicated that once binding to haemocytes had occurred, V. fischeri cells are phagocytosed as effectively as other bacteria. Thus, discrimination by this component of the squid immune system occurs at the level of haemocyte binding, and this response: (i) is modified by previous exposure to the symbiont and (ii) relies on outer membrane and/or secreted components of the symbionts. These data suggest that regulation of host haemocyte binding by the symbiont may be one of many factors that contribute to specificity in this association.

The human intestinal microbiome: a new frontier of human biology

To analyze the vast number and variety of microorganisms inhabiting the human intestine, emerging metagenomic technologies are extremely powerful. The intestinal microbes are taxonomically complex and constitute an ecologically dynamic community (microbiota) that has long been believed to possess a strong impact on human physiology. Furthermore, they are heavily involved in the maturation and proliferation of human intestinal cells, helping to maintain their homeostasis and can be causative of various diseases, such as inflammatory bowel disease and obesity. A simplified animal model system has provided the mechanistic basis for the molecular interactions that occur at the interface between such microbes and host intestinal epithelia. Through metagenomic analysis, it is now possible to comprehensively explore the genetic nature of the intestinal microbiome, the mutually interacting system comprising the host cells and the residing microbial community. The human microbiome project was recently launched as an international collaborative research effort to further promote this newly developing field and to pave the way to a new frontier of human biology, which will provide new strategies for the maintenance of human health.

Microbes in gastrointestinal health and disease

Most, if not all, animals coexist with a complement of prokaryotic symbionts that confer a variety of physiologic benefits. In humans, the interaction between animal and bacterial cells is especially important in the gastrointestinal tract. Technical and conceptual advances have enabled rapid progress in characterizing the taxonomic composition, metabolic capacity, and immunomodulatory activity of the human gut microbiota, allowing us to establish its role in human health and disease. The human host coevolved with a normal microbiota over millennia and developed, deployed, and optimized complex immune mechanisms that monitor and control this microbial ecosystem. These cellular mechanisms have homeostatic roles beyond the traditional concept of defense against potential pathogens, suggesting these pathways contribute directly to the well-being of the gut. During their coevolution, the bacterial microbiota has established multiple mechanisms to influence the eukaryotic host, generally in a beneficial fashion, and maintain their stable niche. The prokaryotic genomes of the human microbiota encode a spectrum of metabolic capabilities beyond that of the host genome, making the microbiota an integral component of human physiology. Gaining a fuller understanding of both partners in the normal gut-microbiota interaction may shed light on how the relationship can go awry and contribute to a spectrum of immune, inflammatory, and metabolic disorders and may reveal mechanisms by which this relationship could be manipulated toward therapeutic ends.

RORgammat and commensal microflora are required for the differentiation of mucosal interleukin 22-producing NKp46+ cells

The mucosal immune system of the intestine is separated from a vast array of microbes by a single layer of epithelial cells. Cues from the commensal microflora are needed to maintain epithelial homeostasis, but the molecular and cellular identities of these cues are unclear. Here we provide evidence that signals from the commensal microflora contribute to the differentiation of a lymphocyte population coexpressing stimulatory natural killer cell receptors and the transcription factor RORgammat that produced interleukin 22 (IL-22). The emergence of these IL-22-producing RORgammathiNKp46+NK1.1(int) cells depended on RORgammat expression, which indicated that these cells may have been derived from lymphoid tissue-inducer cells. IL-22 released by these cells promoted the production of antimicrobial molecules important in the maintenance of mucosal homeostasis.

Paneth cells directly sense gut commensals and maintain homeostasis at the intestinal host-microbial interface

The intestinal epithelium is in direct contact with a vast microbiota, yet little is known about how epithelial cells defend the host against the heavy bacterial load. To address this question we studied Paneth cells, a key small intestinal epithelial lineage. We found that Paneth cells directly sense enteric bacteria through cell-autonomous MyD88-dependent toll-like receptor (TLR) activation, triggering expression of multiple antimicrobial factors. Paneth cells were essential for controlling intestinal barrier penetration by commensal and pathogenic bacteria. Furthermore, Paneth cell-intrinsic MyD88 signaling limited bacterial penetration of host tissues, revealing a role for epithelial MyD88 in maintaining intestinal homeostasis. Our findings establish that gut epithelia actively sense enteric bacteria and play an essential role in maintaining host-microbial homeostasis at the mucosal interface.

Bacterial-mucosal interactions in inflammatory bowel disease: an alliance gone bad

The complex interaction of genetic, microbial, and environmental factors may result in continuous activation of the mucosal immune system leading to inflammatory bowel disease (IBD). Most present treatments for IBD involve altering or suppressing the aberrant immune response; however, the role of the intestinal microbiota in the pathophysiology of IBD is becoming more evident. The epithelial layer is essential for the proper functioning of the gastrointestinal tract, and its increased permeability to the luminal antigens may lead to the inflammatory processes and mucosal damage observed in IBD. Factors affecting the efficacy of the epithelial barrier include presence of pathogenic bacteria (e.g., Helicobacter spp.), presence of probiotic bacteria, availability of selected nutrients, and others. Defective function of the mucosal barrier might facilitate the contact of bacterial antigens and adjuvants with innate and adaptive immune cells to generate prolonged inflammatory responses. This review will briefly describe the complex structure of the epithelial barrier in the context of bacterial-mucosal interactions observed in human IBD and mouse models of colitis.

Symbiotic commensal bacteria direct maturation of the host immune system

PURPOSE OF REVIEW

Although commensal bacteria are known to play an important role in the proper maturation of the immune system of their mammalian hosts, the molecular mechanisms underlying this immunomodulation are poorly characterized. The present review summarizes recent findings in the field and describes new knowledge on the interplay of the innate and adaptive arms of the immune response induced by symbiotic bacterial carbohydrate antigens.

RECENT FINDINGS

Commensal bacteria in the intestine not only interact directly with dendritic cells but also engage in cross-talk with epithelial cells. These interactions lead to the induction of tolerogenic antigen-presenting cells in the lamina propria and ultimately to the regulation of functional maturation of effector T cells. Upon recognition of capsular polysaccharide antigens of commensal bacteria by dendritic cells (through toll-like receptor 2), innate immune responses facilitate and act in conjunction with adaptive responses to promote optimal Th1 polarization. In contrast, adaptive immunoglobulin A responses to symbiotic bacteria regulate the magnitude of oxidative innate immune responses in the mucosa as well as bacterial epitope expression in the lumen.

SUMMARY

Accumulating evidence is elucidating surface carbohydrate structures of symbiotic bacteria that drive the modulation of the intestinal immune system, resulting in mature, balanced immune responses and oral tolerance.

Cytokine-mediated regulation of antimicrobial proteins

Antimicrobial proteins constitute a phylogenetically ancient form of innate immunity that provides host defence at skin and mucosal surfaces. Although some components of this system are constitutively expressed, new evidence reviewed in this Progress article shows that the production of certain antimicrobial proteins by epithelial cells can also be regulated by cytokines of the innate and adaptive immune systems. In particular, the effector cytokines interleukin-17 and interleukin-22, which are produced by the T-helper-17-cell subset, are emerging as crucial regulators of antimicrobial-peptide production in the gut and the lungs. This suggests that this T-cell lineage and its cytokines have important roles in skin and mucosal immunity.

Application of ecological network theory to the human microbiome

In healthy humans, many microbial consortia constitute rich ecosystems with dozens to hundreds of species, finely tuned to functions relevant to human health. Medical interventions, lifestyle changes, and the normal rhythms of life sometimes upset the balance in microbial ecosystems, facilitating pathogen invasions or causing other clinically relevant problems. Some diseases, such as bacterial vaginosis, have exactly this sort of community etiology. Mathematical network theory is ideal for studying the ecological networks of interacting species that comprise the human microbiome. Theoretical networks require little consortia specific data to provide insight into both normal and disturbed microbial community functions, but it is easy to incorporate additional empirical data as it becomes available. We argue that understanding some diseases, such as bacterial vaginosis, requires a shift of focus from individual bacteria to (mathematical) networks of interacting populations, and that known emergent properties of these networks will provide insights that would be otherwise elusive.

Interactions of the intestinal epithelium with the pathogen and the indigenous microbiota: a three-way crosstalk

The mucosal surfaces of the gastrointestinal tract harbor a vast number of commensal microbiota that have coevolved with the host, and in addition display one of the most complex relationships with the host. This relationship affects several important aspects of the biology of the host including the synthesis of nutrients, protection against infection, and the development of the immune system. On the other hand, despite the existence of several lines of mucosal defense mechanisms, pathogenic organisms such as Shigella and Salmonella have evolved sophisticated virulence strategies for breaching these barriers. The constant challenge from these pathogens and the attempts by the host to counter them set up a dynamic equilibrium of cellular and molecular crosstalk. Even slight perturbations in this equilibrium may be detrimental to the host leading to severe bacterial infection or even autoimmune diseases like inflammatory bowel disease. Several experimental model systems, including germ-free mice and antibiotic-treated mice, have been used by various researchers to study this complex relationship. Although it is only the beginning, it promises to be an exciting era in the study of these host-microbe relationships.

Identification of the weevil immune genes and their expression in the bacteriome tissue

BACKGROUND

Persistent infections with mutualistic intracellular bacteria (endosymbionts) are well represented in insects and are considered to be a driving force in evolution. However, while pathogenic relationships have been well studied over the last decades very little is known about the recognition of the endosymbionts by the host immune system and the mechanism that limits their infection to the bacteria-bearing host tissue (the bacteriome).

RESULTS

To study bacteriome immune specificity, we first identified immune-relevant genes of the weevil Sitophilus zeamais by using suppressive subtractive hybridization (SSH) and then analyzed their full-length coding sequences obtained by RACE-PCR experiments. We then measured immune gene expression in the bacteriome, and in the aposymbiotic larvae following S. zeamais primary endosymbiont (SZPE) injection into the hemolymph, in order to consider the questions of bacteriome immune specificity and the insect humoral response to symbionts. We show that larval challenge with the endosymbiont results in a significant induction of antibacterial peptide genes, providing evidence that, outside the bacteriome, SZPE are recognized as microbial intruders by the host. In the bacteriome, gene expression analysis shows the overexpression of one antibacterial peptide from the coleoptericin family and, intriguingly, homologs to genes described as immune modulators (that is, PGRP-LB, Tollip) were also shown to be highly expressed in the bacteriome.

CONCLUSION

The current data provide the first description of immune gene expression in the insect bacteriome. Compared with the insect humoral response to SZPE, the bacteriome expresses few genes among those investigated in this work. This local immune gene expression may help to maintain the endosymbiont in the bacteriome and prevent its invasion into insect tissues. Further investigations of the coleoptericin, the PGRP and the Tollip genes should elucidate the role of the host immune system in the maintenance and regulation of endosymbiosis.

Vancomycin-resistant enterococci exploit antibiotic-induced innate immune deficits

Infection with antibiotic-resistant bacteria, such as vancomycin-resistant Enterococcus (VRE), is a dangerous and costly complication of broad-spectrum antibiotic therapy. How antibiotic-mediated elimination of commensal bacteria promotes infection by antibiotic-resistant bacteria is a fertile area for speculation with few defined mechanisms. Here we demonstrate that antibiotic treatment of mice notably downregulates intestinal expression of RegIIIgamma (also known as Reg3g), a secreted C-type lectin that kills Gram-positive bacteria, including VRE. Downregulation of RegIIIgamma markedly decreases in vivo killing of VRE in the intestine of antibiotic-treated mice. Stimulation of intestinal Toll-like receptor 4 by oral administration of lipopolysaccharide re-induces RegIIIgamma, thereby boosting innate immune resistance of antibiotic-treated mice against VRE. Compromised mucosal innate immune defence, as induced by broad-spectrum antibiotic therapy, can be corrected by selectively stimulating mucosal epithelial Toll-like receptors, providing a potential therapeutic approach to reduce colonization and infection by antibiotic-resistant microbes.

Interaction of Muc2 and Apc on Wnt signaling and in intestinal tumorigenesis: potential role of chronic inflammation

Somatic mutations of the adenomatous polyposis coli (APC) gene are initiating events in the majority of sporadic colon cancers. A common characteristic of such tumors is reduction in the number of goblet cells that produce the mucin MUC2, the principal component of intestinal mucus. Consistent with these observations, we showed that Muc2 deficiency results in the spontaneous development of tumors along the entire gastrointestinal tract, independently of deregulated Wnt signaling. To dissect the complex interaction between Muc2 and Apc in intestinal tumorigenesis and to elucidate the mechanisms of tumor formation in Muc2(-/-) mice, we crossed the Muc2(-/-) mouse with two mouse models, Apc(1638N/+) and Apc(Min/+), each of which carries an inactivated Apc allele. The introduction of mutant Muc2 into Apc(1638N/+) and Apc(Min/+) mice greatly increased transformation induced by the Apc mutation and significantly shifted tumor development toward the colon as a function of Muc2 gene dosage. Furthermore, we showed that in compound double mutant mice, deregulation of Wnt signaling was the dominant mechanism of tumor formation. The increased tumor burden in the distal colon of Muc2/Apc double mutant mice was similar to the phenotype observed in Apc(Min/+) mice that are challenged to mount an inflammatory response, and consistent with this, gene expression profiles of epithelial cells from flat mucosa of Muc2-deficient mice suggested that Muc2 deficiency was associated with low levels of subclinical chronic inflammation. We hypothesize that Muc2(-/-) tumors develop through an inflammation-related pathway that is distinct from and can complement mechanisms of tumorigenesis in Apc(+/-) mice.