Dietary Fiber Drives IL-1ß-Dependent Peritonitis Induced by Bacteroides fragilis via Activation of the NLRP3 Inflammasome.

Intestinal barrier is essential for dietary products and microbiota compartmentalization and therefore gut homeostasis. When this barrier is broken, cecal content overflows into the peritoneal cavity, leading to local and systemic robust inflammatory response, characterizing peritonitis and sepsis. It has been shown that IL-1ß contributes with inflammatory storm during peritonitis and sepsis and its inhibition has beneficial effects to the host. Therefore, we investigated the mechanisms underlying IL-1ß secretion using a widely adopted murine model of experimental peritonitis. The combined injection of sterile cecal content (SCC) and the gut commensal bacteria Bacteroides fragilis leads to IL-1ß-dependent peritonitis, which was mitigated in mice deficient in NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome components. Typically acting as a damage signal, SCC, but not B. fragilis, activates canonical pathway of NLRP3 promoting IL-1ß secretion in vitro and in vivo. Strikingly, absence of fiber in the SCC drastically reduces IL-1ß production, whereas high-fiber SCC conversely increases this response in an NLRP3-dependent manner. In addition, NLRP3 was also required for IL-1ß production induced by purified dietary fiber in primed macrophages. Extending to the in vivo context, IL-1ß-dependent peritonitis was worsened in mice injected with B. fragilis and high-fiber SCC, whereas zero-fiber SCC ameliorates the pathology. Corroborating with the proinflammatory role of dietary fiber, IL-1R-deficient mice were protected from peritonitis induced by B. fragilis and particulate bran. Overall, our study highlights a function, previously unknown, for dietary fibers in fueling peritonitis through NLRP3 activation and IL-1ß secretion outside the gut.

Association of Pre-diagnostic Antibody Responses to Escherichia coli and Bacteroides fragilis Toxin Proteins with Colorectal Cancer in a European Cohort.

Experimental evidence has implicated genotoxic Escherichia coli (E. coli) and enterotoxigenic Bacteroides fragilis (ETBF) in the development of colorectal cancer (CRC). However, evidence from epidemiological studies is sparse. We therefore assessed the association of serological markers of E. coli and ETBF exposure with odds of developing CRC in the European Prospective Investigation into Nutrition and Cancer (EPIC) study.Serum samples of incident CRC cases and matched controls (n = 442 pairs) were analyzed for immunoglobulin (Ig) A and G antibody responses to seven E. coli proteins and two isoforms of the ETBF toxin via multiplex serology. Multivariable-adjusted conditional logistic regression analyses were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association of sero-positivity to E. coli and ETBF with CRC.The IgA-positivity of any of the tested E. coli antigens was associated with higher odds of developing CRC (OR: 1.42; 95% CI: 1.05-1.91). Dual-positivity for both IgA and IgG to E. coli and ETBF was associated with >1.7-fold higher odds of developing CRC, with a significant association only for IgG (OR: 1.75; 95% CI: 1.04, 2.94). This association was more pronounced when restricted to the proximal colon cancers (OR: 2.62; 95% CI: 1.09, 6.29) compared to those of the distal colon (OR: 1.24; 95% CI: 0.51, 3.00) (pheterogeneity = 0.095). Sero-positivity to E. coli and ETBF was associated with CRC development, suggesting that co-infection of these bacterial species may contribute to colorectal carcinogenesis. These findings warrant further exploration in larger prospective studies and within different population groups.

α-Defensins Promote Bacteroides Colonization on Mucosal Reservoir to Prevent Antibiotic-Induced Dysbiosis.

In addition to their established functions in host defense, accumulating evidence has suggested an emerging role for antimicrobial proteins (AMPs) in shaping commensal microbiota. However, the role of α-defensins, the most abundant AMPs of intestine, in regulating microbial ecology remains inconclusive. Here, we report that α-defensins promote commensal Bacteroides colonization by enhancing bacterial adhesion to the mucosal reservoir. Experiments utilizing mice deficient in matrix metalloproteinase 7 (MMP7), the α-defensin-activating enzyme, with rigorous littermate controls showed that α-defensin deficiency did not significantly influence steady-state intestinal microbiota. In contrast, α-defensins are essential for replenishment of commensal Bacteroides from the mucosal reservoir following antibiotics-induced dysbiosis, shown by markedly compromised recovery of Bacteroides in Mmp7-/- animals. Mechanistically, α-defensins promote Bacteroides colonization on epithelial surfaces in vivo and adhesion to epithelial cells in vitro. Moreover, α-defensins unexpectedly does not show any microbicidal activities against Bacteroides. Together, we propose that α-defensins promote commensal bacterial colonization and recovery to maintain microbial diversity upon environmental challenges.

Chlorogenic Acid Protects Against Indomethacin-Induced Inflammation and Mucosa Damage by Decreasing Bacteroides-Derived LPS.

Background: Chlorogenic acid (CGA), a natural bioactive polyphenol, exerts anti-inflammatory, antioxidant, and antibacterial effects that support the maintenance of intestinal health. However, the influence of CGA on gut microbiota and their metabolites, as well as its potential effects and mechanism of action in inflammatory bowel disease, remain to be elucidated. Methods: First, an oral gavage was used to administer CGA to indomethacin-treated mice. Then, fecal microbiota transplantation was performed to explore the role of intestinal microbiota in indomethacin-induced inflammation. Results: CGA treatment protected against body weight loss, damage to intestinal morphology and integrity, inflammation, and alteration of microbiota composition in indomethacin-treated mice. Interestingly, CGA failed to inhibit inflammation or protect intestine integrity in mice treated with antibiotics. Notably, mice who had been colonized with intestinal microbiota from CGA-treated or CGA-and-indomethacin-treated mice, through the fecal microbiota transplantation program, were protected from indomethacin-induced inflammation, growth of Bacteroides, and the accumulation of Bacteroides-derived LPS, in congruence with those who had been treated with CGA. Conclusion: The results suggest that CGA may protect intestine integrity and alleviate inflammatory responses, primarily by inhibiting the growth of Bacteroides and the accumulation of Bacteroides-derived LPS, in indomethacin-induced colitis. This newly identified mechanism broadens our knowledge of how CGA exerts protective effects on intestinal inflammation and provides strategies for the prevention of gastrointestinal mucosal damage in patients treated with indomethacin.

The uroS and yifB Genes Conserved among Tetrapyrrole Synthesizing-Deficient Bacteroidales Are Involved in Bacteroides fragilis Heme Assimilation and Survival in Experimental Intra-abdominal Infection and Intestinal Colonization.

The human intestinal anaerobic commensal and opportunistic pathogen Bacteroides fragilis does not synthesize the tetrapyrrole protoporphyrin IX in order to form heme that is required for growth stimulation and survival in vivo Consequently, B. fragilis acquires essential heme from host tissues during extraintestinal infection. The absence of several genes necessary for de novo heme biosynthesis is a common characteristic of many anaerobic bacteria; however, the uroS gene, encoding a uroporphyrinogen III synthase for an early step of heme biosynthesis, is conserved among the heme-requiring Bacteroidales that inhabit the mammalian gastrointestinal tract. In this study, we show that the ability of B. fragilis to utilize heme or protoporphyrin IX for growth was greatly reduced in a ΔuroS mutant. This growth defect appears to be linked to the suppression of reverse chelatase and ferrochelatase activities in the absence of uroS In addition, this ΔuroS suppressive effect was enhanced by the deletion of the yifB gene, which encodes an Mg2+-chelatase protein belonging to the ATPases associated with various cellular activities (AAA+) superfamily of proteins. Furthermore, the ΔuroS mutant and the ΔuroS ΔyifB double mutant had a severe survival defect compared to the parent strain in competitive infection assays using animal models of intra-abdominal infection and intestinal colonization. This shows that the presence of the uroS and yifB genes in B. fragilis seems to be linked to pathophysiological and nutritional competitive fitness for survival in host tissues. Genetic complementation studies and enzyme kinetics assays indicate that B. fragilis UroS is functionally different from canonical bacterial UroS proteins. Taken together, these findings show that heme assimilation and metabolism in the anaerobe B. fragilis have diverged from those of aerobic and facultative anaerobic pathogenic bacteria.

Zerumbone Suppresses Enterotoxigenic Bacteroides fragilis Infection-Induced Colonic Inflammation through Inhibition of NF-κΒ.

Enterotoxigenic Bacteroides fragilis (ETBF) is human intestinal commensal bacterium and a potent initiator of colitis through secretion of the metalloprotease Bacteroides fragilis toxin (BFT). BFT induces cleavage of E-cadherin in colon cells, which subsequently leads to NF-κB activation. Zerumbone is a key component of the Zingiber zerumbet (L.) Smith plant and can exhibit anti-bacterial and anti-inflammatory effects. However, whether zerumbone has anti-inflammatory effects in ETBF-induced colitis remains unknown. The aim of this study was to determine the anti-inflammatory effect of orally administered zerumbone in a murine model of ETBF infection. Wild-type C57BL/6 mice were infected with ETBF and orally administered zerumbone (30 or 60 mg/kg) once a day for 7 days. Treatment of ETBF-infected mice with zerumbone prevented weight loss and splenomegaly and reduced colonic inflammation with decreased macrophage infiltration. Zerumbone treatment significantly decreased expression of IL-17A, TNF-α, KC, and inducible nitric oxide synthase (iNOS) in colonic tissues of ETBF-infected mice. In addition, serum levels of KC and nitrite was also diminished. Zerumbone-treated ETBF-infected mice also showed decreased NF-κB signaling in the colon. HT29/C1 colonic epithelial cells treated with zerumbone suppressed BFT-induced NF-κB signaling and IL-8 secretion. However, BFT-mediated E-cadherin cleavage was unaffected. Furthermore, zerumbone did not affect ETBF colonization in mice. In conclusion, zerumbone decreased ETBF-induced colitis through inhibition of NF-κB signaling.

Bacterial Immunogenicity Is Critical for the Induction of Regulatory B Cells in Suppressing Inflammatory Immune Responses.

B cells fulfill multifaceted functions that influence immune responses during health and disease. In autoimmune diseases, such as inflammatory bowel disease, multiple sclerosis and rheumatoid arthritis, depletion of functional B cells results in an aggravation of disease in humans and respective mouse models. This could be due to a lack of a pivotal B cell subpopulation: regulatory B cells (Bregs). Although Bregs represent only a small proportion of all immune cells, they exhibit critical properties in regulating immune responses, thus contributing to the maintenance of immune homeostasis in healthy individuals. In this study, we report that the induction of Bregs is differentially triggered by the immunogenicity of the host microbiota. In comparative experiments with low immunogenic Bacteroides vulgatus and strong immunogenic Escherichia coli, we found that the induction and longevity of Bregs depend on strong Toll-like receptor activation mediated by antigens of strong immunogenic commensals. The potent B cell stimulation via E. coli led to a pronounced expression of suppressive molecules on the B cell surface and an increased production of anti-inflammatory cytokines like interleukin-10. These bacteria-primed Bregs were capable of efficiently inhibiting the maturation and function of dendritic cells (DCs), preventing the proliferation and polarization of T helper (Th)1 and Th17 cells while simultaneously promoting Th2 cell differentiation in vitro. In addition, Bregs facilitated the development of regulatory T cells (Tregs) resulting in a possible feedback cooperation to establish immune homeostasis. Moreover, the colonization of germfree wild type mice with E. coli but not B. vulgatus significantly reduced intestinal inflammatory processes in dextran sulfate sodium (DSS)-induced colitis associated with an increase induction of immune suppressive Bregs. The quantity of Bregs directly correlated with the severity of inflammation. These findings may provide new insights and therapeutic approaches for B cell-controlled treatments of microbiota-driven autoimmune disease.

TLR2-stimulating contaminants in glycoconjugate fractions prepared from Bacteroides fragilis.

Bacteroides fragilis is a member of the normal intestinal flora and is involved in host immunostimulation via TLR2. On the bacterial cell surface, glycoconjugates, such as LPS and capsular polysaccharide A (PSA), have been reported to participate in host immunostimulation via TLR2. Previously, we identified a TLR2-stimulating lipoprotein in B. fragilis cells. In this study, we demonstrated that TLR2-stimulating principal molecules in glycoconjugate fractions prepared from B. fragilis are contaminating proteinous molecules, which may also be lipoproteins. The glycoconjugate fractions were prepared by phenol-hot water extraction of B. fragilis wild type and PSA-deficient strains, followed by hydrophobic interaction chromatography. TLR2-stimilating activities of the fractions were not affected by PSA deficiency. By in-gel TLR2-stimulation assay, molecules in high-molecular-mass area, where capsular polysaccharides were migrated, were found not to stimulate TLR2, but those in the range of 15-40 kDa were active. Further, proteinase K could digest the latter molecules and the TLR2-stimulating activities were migrated to the area of below 15 kDa. These results support that proteinous molecules, which are estimated to be lipoproteins, are responsible for almost all TLR2-stimulating activity in the glycoconjugate fractions prepared from B. fragilis.

Monoclonal antibodies specific for Bacteroides fragilis enterotoxins BFT1 and BFT2 and their use in immunoassays.

We have developed 22 mouse IgG1 monoclonal antibodies (mAbs) against Bacteroides fragilis zinc metalloprotease toxins 1 and 2 (BFT1 and BFT2). Mice were immunized with recombinant BFT1 or BFT2 proteins with metalloprotease activity. Eight of the mAbs bind specifically to BFT1. One mAb, 2H6, binds specifically to BFT2. The remaining 13 mAbs bind to both BFT1 and BFT2. The eight BFT1-specific mAbs recognize at least five different epitopes on the toxin. Four of the BFT1-specific mAbs neutralized rBFT1 metalloprotease activity. Only one of these four mAbs, 1D9, neutralizes the cytotoxic effect of BFT1. Here, we describe the development of enzyme-linked immunosorbent assays (ELISAs) to detect BFT1 or BFT2 toxin in an isotype-specific manner. The sandwich ELISAs have a detection limit of 20 to 40 ng/ml when purified recombinant BFT protein is diluted into PBS. The sandwich ELISA can be used to distinguish and quantify levels of rBFT1 and rBFT2 in stool. This ELISA can be an important tool to investigate the association between BFT expression by enterotoxigenic B. fragilis and diseases such as diarrhea, inflammatory bowel disease and colorectal cancer.

The myeloid immune signature of enterotoxigenic Bacteroides fragilis-induced murine colon tumorigenesis.

Enterotoxigenic Bacteroides fragilis (ETBF), a human commensal and candidate pathogen in colorectal cancer (CRC), is a potent initiator of interleukin-17 (IL-17)-dependent colon tumorigenesis in MinApc+/- mice. We examined the role of IL-17 and ETBF on the differentiation of myeloid cells into myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages, which are known to promote tumorigenesis. The myeloid compartment associated with ETBF-induced colon tumorigenesis in Min mice was defined using flow cytometry and gene expression profiling. Cell-sorted immature myeloid cells were functionally assayed for inhibition of T-cell proliferation and inducible nitric oxide synthase expression to delineate MDSC populations. A comparison of ETBF infection with that of other oncogenic bacteria (Fusobacterium nucleatum or pks+Escherichia coli) revealed a specific, ETBF-associated colonic immune infiltrate. ETBF-triggered colon tumorigenesis is associated with an IL-17-driven myeloid signature characterized by subversion of steady-state myelopoiesis in favor of the generation of protumoral monocytic-MDSCs (MO-MDSCs). Combined action of the B. fragilis enterotoxin BFT and IL-17 on colonic epithelial cells promoted the differentiation of MO-MDSCs, which selectively upregulated Arg1 and Nos2, produced NO, and suppressed T-cell proliferation. Evidence of a pathogenic inflammatory signature in humans colonized with ETBF may allow for the identification of populations at risk for developing colon cancer.

Symbiotic gut commensal bacteria act as host cathepsin S activity regulators.

Cathepsin S (CTSS) is a lysosomal protease whose activity regulation is important for MHC-II signaling and subsequent activation of CD4+ T cell mediated immune responses. Dysregulation of its enzymatic activity or enhanced secretion into extracellular environments is associated with the induction or progression of several autoimmune diseases. Here we demonstrate that commensal intestinal bacteria influence secretion rates and intracellular activity of host CTSS and that symbiotic bacteria, i.e. Bacteroides vulgatus mpk, may actively regulate this process and help to maintain physiological levels of CTSS activities in order to prevent from induction of pathological inflammation. The symbiont-controlled regulation of CTSS activity is mediated by anticipating reactive oxygen species induction in dendritic cells which, in turn, maintains cystatin C (CysC) monomer binding to CTSS. CysC monomers are potent endogenous CTSS inhibitors. This Bacteroides vulgatus caused and CysC dependent CTSS activity regulation is involved in the generation of tolerant intestinal dendritic cells contributing to prevention of T-cell mediated induction of colonic inflammation. Taken together, we demonstrate that symbionts of the intestinal microbiota regulate host CTSS activity and secretion and might therefore be an attractive approach to deal with CTSS associated autoimmune diseases.

[DYNAMICS OF INDICES OF A LOCAL IMMUNITY IN AN ACUTE APPENDICITIS].

Abstract The results of investigation on dynamics of a local immunity indices in an acute appendicitis, depending on the pathological process stage as well as on bacteriological investigation of parietal microflora of processus vermicularis, were adduced. The sIgA and lisocymal dynamics have witnessed that while a destructive process progressing their concentration was enhanced, and in a gangrenous acute appendicitis they practically disappeared. Due to affection of a barrier function of the processus vermicularis wall a favorable conditions were created for the microorganisms intramural translocation as well as to abdominal cavity.

Helminth infection promotes colonization resistance via type 2 immunity.

Increasing incidence of inflammatory bowel diseases, such as Crohn's disease, in developed nations is associated with changes to the microbial environment, such as decreased prevalence of helminth colonization and alterations to the gut microbiota. We find that helminth infection protects mice deficient in the Crohn's disease susceptibility gene Nod2 from intestinal abnormalities by inhibiting colonization by an inflammatory Bacteroides species. Resistance to Bacteroides colonization was dependent on type 2 immunity, which promoted the establishment of a protective microbiota enriched in Clostridiales. Additionally, we show that individuals from helminth-endemic regions harbor a similar protective microbiota and that deworming treatment reduced levels of Clostridiales and increased Bacteroidales. These results support a model of the hygiene hypothesis in which certain individuals are genetically susceptible to the consequences of a changing microbial environment.

Latent Infections as a Risk Factor for Posttrabeculectomy Bleb Failure.

PURPOSE: To investigate latent conjunctival Chlamydia trachomatis (CT) and Bacteroides fragilis (BF) infections as potential risk factors for posttrabeculectomy bleb failure. PATIENTS AND METHODS: This retrospective observational study included 50 primary open-angle glaucoma eyes of 50 patients who were submitted to trabeculectomy without cytostatics from September 2010 to June 2011 and were followed up for at least a year. Preoperatively, conjunctival scrapings were taken and their specimens subjected to polymerase chain reaction, direct fluorescent assay and cell culture testing for CT, and culture for BF on blood agar medium. Serum CT-specific IgG and IgA and tear interleukin (IL)-1ß and IL-8 concentrations were measured with enzyme-linked immunosorbent assay. We defined bleb failure as intraocular pressure >21 mm Hg with antiglaucoma medications, resulting from reduced bleb filtration capacity due to bleb fibrosis, fistula obstruction, flattened bleb, or encapsulated bleb, and no earlier than 2 weeks after surgery. At the time of the reintervention, a scleroconjunctival biopsy was obtained for histopathology (including direct fluorescent assay testing for CT). Eyes were divided into a failure group and a nonfailure group, depending on whether they developed bleb failure (required reintervention) or not within a follow-up year. RESULTS: In the failure group (n=18), the frequencies of detection of CT and BF in conjunctival specimens were 27.8% and 66.7%, respectively, versus 0% and 9.4% in the nonfailure group (n=32). CT and BF were detected in 11.1% and 11.1%, respectively, of scleroconjunctival biopsies. IgG and IgA seropositivity to CT was found in 66.7% and 33.3%, respectively, of the failure group patients, versus 9.4% and 0% of the nonfailure group patients. Tear IL-1ß and IL-8 levels were markedly elevated in the failure group (468.83±80.43 and 107.89±15.11 pg/mL, respectively) versus the nonfailure group (22.34±5.43 and 9.34±2.83 pg/mL, respectively). CONCLUSION: Being a contributor to low-grade conjunctival inflammation, latent conjunctival CT, and BF infections in primary open-angle glaucoma patients represent risk factors for posttrabeculectomy bleb failure.

A Metalloproteinase Mirolysin of Tannerella forsythia Inhibits All Pathways of the Complement System.

Recent reports focusing on virulence factors of periodontal pathogens implicated proteinases as major determinants of remarkable pathogenicity of these species, with special emphasis on their capacity to modulate complement activity. In particular, bacteria-mediated cleavage of C5 and subsequent release of C5a seems to be an important phenomenon in the manipulation of the local inflammatory response in periodontitis. In this study, we present mirolysin, a novel metalloproteinase secreted by Tannerella forsythia, a well-recognized pathogen strongly associated with periodontitis. Mirolysin exhibited a strong effect on all complement pathways. It inhibited the classical and lectin complement pathways due to efficient degradation of mannose-binding lectin, ficolin-2, ficolin-3, and C4, whereas inhibition of the alternative pathway was caused by degradation of C5. This specificity toward complement largely resembled the activity of a previously characterized metalloproteinase of T. forsythia, karilysin. Interestingly, mirolysin released the biologically active C5a peptide in human plasma and induced migration of neutrophils. Importantly, we demonstrated that combination of mirolysin with karilysin, as well as a cysteine proteinase of another periodontal pathogen, Prevotella intermedia, resulted in a strong synergistic effect on complement. Furthermore, mutant strains of T. forsythia, devoid of either mirolysin or karilysin, showed diminished survival in human serum, providing further evidence for the synergistic inactivation of complement by these metalloproteinases. Taken together, our findings on interactions of mirolysin with complement significantly add to the understanding of immune evasion strategies of T. forsythia and expand the knowledge on molecular mechanisms driving pathogenic events in the infected periodontium.

Inflammatory response to Porphyromonas gingivalis partially requires interferon regulatory factor (IRF) 3.

Innate immune activation with expression of pro-inflammatory molecules such as TNF-α is a hallmark of the chronic inflammation associated with periodontal disease (PD). Porphyromonas gingivalis, a bacterium associated with PD, engages TLRs and activates MyD88-dependent and TIR-domain-containing adapter-inducing IFN-ß (TRIF)-dependent signaling pathways. IFN regulatory factor (IRF) 3 is activated in a TRIF-dependent manner and participates in production of cytokines such as TNF-α; however, little is known regarding IRF3 and the host response to PD pathogens. We speculated that IRF3 participates in the host inflammatory response to P. gingivalis. Our results show that bone marrow macrophages (MØ) from WT mice respond to P. gingivalis with activation and nuclear translocation of IRF3. Compared with WT, MØ from IRF3(-/-), TRIF(-/-), and TLR4(-/-) mice responded with reduced levels of TNF-α on P. gingivalis challenge. In addition, full expression of IL-6 and RANTES by MØ to P. gingivalis was dependent on IRF3. Lastly, employing MØ from IRF3(-/-) and IRF7(-/-) mice we observed a significant role for IRF3 and a modest role for IRF7 in the P. gingivalis-elicited TNF-α response. These studies identify a role for IRF3 in the inflammatory response by MØ to the periodontal pathogen P. gingivalis.

IgA production in the large intestine is modulated by a different mechanism than in the small intestine: Bacteroides acidifaciens promotes IgA production in the large intestine by inducing germinal center formation and increasing the number of IgA+ B cells.

It has been demonstrated that intestinal commensal bacteria induce immunoglobulin (Ig) A production by promoting the development of gut-associated lymphoid tissues in the small intestine. However, the precise mechanism whereby these bacteria modulate IgA production in the large intestine, which harbors the majority of intestinal commensals, is poorly understood. In addition, it is not known which commensal bacteria induce IgA production in the small intestine and which induce production in the large intestine. To address these issues, we generated gnotobiotic mice mono-associated with different murine commensal bacteria by inoculating germ-free (GF) mice with Lactobacillus johnsonii or Bacteroides acidifaciens. In GF mice, IgA production was barely detectable in the small intestine and was not detected in the large intestine. Interestingly, total IgA secretion in the large intestinal mucosa of B. acidifaciens mono-associated (BA) mice was significantly greater than that of GF and L. johnsonii mono-associated (LJ) mice. However, there was no difference in total IgA production in the small intestine of GF, LJ and BA mice. In addition, in the large intestine of BA mice, the expression of IgA(+) cells and germinal center formation were more remarkable than in GF and LJ mice. Furthermore, B. acidifaciens-specific IgA was detected in the large intestine of BA mice. These results suggest that the production of IgA in the large intestine may be modulated by a different mechanism than that in the small intestine, and that B. acidifaciens is one of the predominant bacteria responsible for promoting IgA production in the large intestine.

A role for TLR1, TLR2 and NOD2 in cytokine induction by Bacteroides fragilis.

Bacteroides fragilis, an intestinal flora commensal microorganism, is frequently isolated from abscesses and soft tissue infections. This study aimed to identify pattern recognition receptors (PRRs) involved in B. fragilis recognition and to characterize the induced cytokine profile. Human PBMCs were stimulated with heat-killed B. fragilis and cytokine levels were determined by ELISA. Roles of individual PRRs were assessed using specific blockers of receptor signaling pathways and PBMCs carrying single nucleotide polymorphisms of PRR genes. Cell lines expressing human TLR2 or TLR4 were employed to assess TLR-specificity of B. fragilis. TLR1, TLR2 and NOD2 were the main PRRs responsible for recognition of B. fragilis, while TLR4, TLR6, NOD1 and Dectin-1 were not involved. B. fragilis induced strong IL-6 and IL-8, moderate IL-1ß and TNF-α, and poor IL-10, IL-17, IL-23 and IFN-γ production. This study identifies the receptor pathways of the innate immune response to B. fragilis, and thus provides new insights in the host defense against B. fragilis.

The yin yang of bacterial polysaccharides: lessons learned from B. fragilis PSA.

Over the past several years, there have been remarkable advances in our understanding of how commensal organisms shape host immunity. Although the full cast of immunogenic bacteria and their immunomodulatory molecules remains to be elucidated, lessons learned from the interactions between bacterial zwitterionic polysaccharides (ZPSs) and the host immune system represent an integral step toward better understanding how the intestinal microbiota effect immunologic changes. Somewhat paradoxically, ZPSs, which are found in numerous commensal organisms, are able to elicit both proinflammatory and immunoregulatory responses; both these outcomes involve fine-tuning the balance between T-helper 17 cells and interleukin-10-producing regulatory T cells. In this review, we discuss the immunomodulatory effects of the archetypal ZPS, Bacteroides fragilis PSA. In addition, we highlight some of the opportunities and challenges in applying these lessons in clinical settings.

Bacteroides fragilis-stimulated interleukin-10 contains expanding disease.

Commensal symbionts may become pathogens upon escaping their habitat. In the gut, Bacteroides fragilis protects against colitis through induction of interleukin 10 (IL-10) by CD4(+) T cells. When intestinal integrity is disrupted, B. fragilis and colonic contents escape into the peritoneum, causing abscesses and bacteremia. Whether the virulence mechanisms employed by B. fragilis during infections differ from those employed for symbiosis during commensalism is unknown. We demonstrate T cell-independent IL-10 production in response to B. fragilis during its pathogenic interactions with the host, and demonstrate the ability of the whole organism to activate Toll-like receptor 2-mediated MyD88 signaling in macrophages. Upon challenge with B. fragilis, mortality rates and serum proinflammatory cytokine levels were higher among IL-10(-/-) mice than among wild-type mice. Deaths were due to exuberant proinflammatory responses, not increased bacterial burden. During infection or commensalism, induction of IL-10 by B. fragilis is critical to this microbe's interactions with the immune system.