Innate immunity and mucosal bacterial interactions in the intestine

Immunomodulatory peptides: new therapeutic horizons for emerging and re-emerging infectious diseases

The emergence and re-emergence of multi-drug-resistant (MDR) infectious diseases have once again posed a significant global health challenge, largely attributed to the development of bacterial resistance to conventional anti-microbial treatments. To mitigate the risk of drug resistance globally, both antibiotics and immunotherapy are essential. Antimicrobial peptides (AMPs), also referred to as host defense peptides (HDPs), present a promising therapeutic alternative for treating drug-resistant infections due to their various mechanisms of action, which encompass antimicrobial and immunomodulatory effects. Many eukaryotic organisms produce HDPs as a defense mechanism, for example Purothionin from Triticum aestivum plant, Defensins, Cathelicidins, and Histatins from humans and many such peptides are currently the focus of research because of their antibacterial, antiviral and anti-fungicidal properties. This article offers a comprehensive review of the immunomodulatory activities of HDPs derived from eukaryotic organisms including humans, plants, birds, amphibians, reptiles, and marine species along with their mechanisms of action and therapeutic benefits.

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

Mucosal immunity to pathogenic intestinal bacteria

The intestinal mucosa is a particularly dynamic environment in which the host constantly interacts with trillions of commensal microorganisms, known as the microbiota, and periodically interacts with pathogens of diverse nature. In this Review, we discuss how mucosal immunity is controlled in response to enteric bacterial pathogens, with a focus on the species that cause morbidity and mortality in humans. We explain how the microbiota can shape the immune response to pathogenic bacteria, and we detail innate and adaptive immune mechanisms that drive protective immunity against these pathogens. The vast diversity of the microbiota, pathogens and immune responses encountered in the intestines precludes discussion of all of the relevant players in this Review. Instead, we aim to provide a representative overview of how the intestinal immune system responds to pathogenic bacteria.

Modeling inflammatory bowel disease: the zebrafish as a way forward

The zebrafish has proved to be an informative model of vertebrate development and, more recently, an emerging model of human disease. The realization of the full potential of the zebrafish as a disease model lies in two interdependent areas. The first is an appreciation that the often overlooked strength of this species lies in allowing the design of experiments that address the interplay of genetics and the environment in a manipulable manner. The second is in the application and further development of gene targeting approaches. These twin features will be addressed in this review in the context of modeling inflammatory bowel disease.

Recombinant Salmonella enterica serovar Typhimurium as a vaccine vector for HIV-1 Gag

The HIV/AIDS epidemic remains a global health problem, especially in Sub-Saharan Africa. An effective HIV-1 vaccine is therefore badly required to mitigate this ever-expanding problem. Since HIV-1 infects its host through the mucosal surface, a vaccine for the virus needs to trigger mucosal as well as systemic immune responses. Oral, attenuated recombinant Salmonella vaccines offer this potential of delivering HIV-1 antigens to both the mucosal and systemic compartments of the immune system. So far, a number of pre-clinical studies have been performed, in which HIV-1 Gag, a highly conserved viral antigen possessing both T- and B-cell epitopes, was successfully delivered by recombinant Salmonella vaccines and, in most cases, induced HIV-specific immune responses. In this review, the potential use of Salmonella enterica serovar Typhimurium as a live vaccine vector for HIV-1 Gag is explored.

PepT1 expressed in immune cells has an important role in promoting the immune response during experimentally induced colitis

We and others have shown that the dipeptide cotransporter PepT1 is expressed in immune cells, including macrophages that are in close contact with the lamina propria of the small and large intestines. In the present study, we used PepT1-knockout (KO) mice to explore the role played by PepT1 in immune cells during dextran sodium sulfate (DSS)-induced colitis. DSS treatment caused less severe body weight loss, diminished rectal bleeding, and less diarrhea in PepT1-KO mice than in wild-type (WT) animals. A histological examination of colonic sections revealed that the colonic architecture was less disrupted and the extent of immune cell infiltration into the mucosa and submucosa following DSS treatment was reduced in PepT1-KO mice compared with WT animals. Consistent with these results, the DSS-induced colitis increase in colonic myeloperoxidase activity was significantly less in PepT1-KO mice than in WT littermates. The colonic levels of mRNAs encoding the inflammatory cytokines CXCL1, interleukin (IL)-6, monocyte chemotactic protein-1, IL-12, and interferon-γ were significantly lower in DSS-treated PepT1-KO mice than in DSS-treated WT animals. Colonic immune cells from WT had significantly higher level of proinflammatory cytokines then PepT1 KO. In addition, we observed that knocking down the PepT1 expression decreases chemotaxis of immune cells recruited during intestinal inflammation. Antibiotic treatment before DSS-induced colitis eliminated the differential expression of inflammatory cytokines between WT and PepT1-KO mice. In conclusion, PepT1 in immune cells regulates the secretion of proinflammatory cytokines triggered by bacteria and/or bacterial products, and thus has an important role in the induction of colitis. PepT1 may transport small bacterial products, such as muramyl dipeptide and the tripeptide L-Ala-gamma-D-Glu-meso-DAP, into macrophages. These materials may be sensed by members of the nucleotide-binding site-leucine-rich repeat family of intracellular receptors, ultimately resulting in altered homeostasis of the intestinal microbiota.

Modulation of intestinal barrier by intestinal microbiota: pathological and therapeutic implications

Mammals and their intestinal microbiota peacefully coexist in a mutualistic relationship. Commensal bacteria play an active role in shaping and modulating physiological processes in the host, which include, but are not restricted to, the immune system and the intestinal barrier. Both play a crucial role in containing intestinal bacteria and other potentially noxious luminal antigens within the lumen and mucosal compartment. Although mutualism defines the relationship between the host and the intestinal microbiota, disruptions in this equilibrium may promote disease. Thus, alterations in gut microbiota (dysbiosis) have been linked to the recent increased expression of obesity, allergy, autoimmunity, functional and inflammatory disorders such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). In this article, we review the evidence supporting a role of gut microbiota in regulating intestinal barrier function. We discuss the hypothesis that microbial factors can modulate the barrier in ways that can prevent or promote gastrointestinal disease. A better understanding of the role of the intestinal microbiota in maintaining a functional intestinal barrier may help develop targeted strategies to prevent and treat disease.

Probiotics for prevention of nosocomial infections: efficacy and adverse effects

PURPOSE OF REVIEW

In this era of increasing antimicrobial resistance, use of probiotics in infection prevention has brought new perspective. However, in 2008 the, until then considered, safe use of probiotics became an important topic after publication of a trial showing excess mortality in patients on probiotic prophylaxis. In this article, we review the concept of infection prevention by probiotics and the present knowledge of the efficacy of probiotics in prevention of infections among patients with abdominal diseases and in intensive care. Safety issues of probiotics will be discussed extensively.

RECENT FINDINGS

Over 30 clinical trials with probiotics to prevent infections have been published, some of which were prematurely stopped recently. Studies with critically ill patients and patients with abdominal diseases showed conflicting results regarding the effects of probiotics on infection rates, as did meta-analyses. These studies are difficult to compare because different probiotics were used which all have different efficacy and safety profiles.

SUMMARY

The efficacy of probiotics in infection prevention among critically ill patients is still not unequivocally determined. The safety profile differs per probiotic strain and should not be generalized towards other strains and patient populations. A well designed and well powered clinical trial with clear endpoints to demonstrate efficacy is warranted.

Enteric alpha defensins in norm and pathology

Microbes living in the mammalian gut exist in constant contact with immunity system that prevents infection and maintains homeostasis. Enteric alpha defensins play an important role in regulation of bacterial colonization of the gut, as well as in activation of pro- and anti-inflammatory responses of the adaptive immune system cells in lamina propria. This review summarizes currently available data on functions of mammalian enteric alpha defensins in the immune defense and changes in their secretion in intestinal inflammatory diseases and cancer.

Correlation between expression of human cathelicidin peptide LL-37 and colon inflammation in patients with ulcerative colitis

AIM: To investigate the expression of human cathelicidin LL-37 in the colon mucosa of patients suffering from ulcerative colitis and to assess its relationship with colon inflammation.

METHODS: Thirty-two patients with ulcerative colitis were included in the study. The severity of ulcerative colitis was assessed using the Ulcerative Colitis Disease Activity Index (UCDAI). The expression of LL-37 and cytokines (TNF-α, IL-1β and IL-4) in the colon mucosa was detected by real-time RT-PCR. Immunohistochemistry was used to investigate the location of the LL-37 peptide in the normal and inflamed colon mucosa. Colon epithelial cells were stimulated in vitro with cytokines to evaluate mechanisms that influence cathelicidin production.

RESULTS: The mRNA expression of LL-37 and cytokines in the colon mucosa was significantly elevated with the severity of disease activity in UC patients compared to controls (LL-37: 4.97 ± 6.95, 31.46 ± 10.74, 75.50 ± 13.19 vs 0.27 ± 0.45; TNF-α: 97.04 ± 23.74, 201.07 ± 33.46, 290.81 ± 30.45 vs 72.82 ± 18.85; IL-1β: 72.98 ± 38.03, 153.46 ± 22.68, 211.34 ± 25.12 vs 38.56 ± 10.38; IL-4: 26.04 ± 12.47, 46.38 ± 15.12, 46.94 ± 16.53 vs 19.34 ± 11.61, all P < 0.05). Significant correlations were found between the mRNA expression of LL-37 and cytokines (r = 0.965, 0.940, 0.628, all P < 0.01). Immunohistochemistry analysis showed that the LL-37 peptide was located in the colon epithelial surface in both normal controls and UC patients. In addition, the LL-37 peptide was detected easily in inflammatory cells infiltrating into the inflamed colon mucosa in UC patients. In vitro stimulation with cytokines did not up-regulate LL-37 expression in colon epithelial cells.

CONCLUSION: The up-regulation of LL-37 expression in inflamed colon mucosa of UC patients and high correlation between the expression of LL-37 and cytokines indicate a close relationship between LL-37 and immune inflammatory response in UC patients with ulcerative colitis; however, this process does not involve colonic epithelial cells.

Campylobacter capsule and lipooligosaccharide confer resistance to serum and cationic antimicrobials

The innate immune system plays a critical role in host defense against mucosal bacteria. Campylobacter jejuni is a major cause of human gastroenteritis that usually resolves spontaneously within several days, suggesting that innate mechanisms are important to control the infection. However, the specific means by which this occurs is not well understood. While diarrheal isolates of C. jejuni usually are susceptible to human serum, we found that a systemic strain of C. jejuni, isolated from the cerebrospinal fluid of an infant with meningitis, is relatively more resistant to human serum, the Bactericidal/Permeability-Increasing Protein (BPI), an endogenous cationic antimicrobial protein, and the cationic peptide antibiotic polymyxin B. To test the hypothesis that the surface properties of this strain contributed to its ability to withstand these innate host defenses, we constructed isogenic mutants in capsule (kpsM) and lipooligosaccharide (waaF) and complemented these mutants by insertion of the complementation construct in trans into hipO, a chromosomal locus. We found that capsule expression was essential for serum resistance, whereas lipooligosaccharide played no substantial role. In contrast, the lipooligosaccharide mutant showed increased sensitivity to polymyxin B, α-defensins, cathelicidins, and BPI. These findings suggest that the polysaccharides of C. jejuni strains contribute differently to resistance against host innate immunity; whereby capsule is more important for resisting human complement and lipooligosaccharide is more important for protection against killing mediated by cationic antimicrobial peptides and proteins.

New concepts of microbial translocation in the neonatal intestine: mechanisms and prevention

Bacterial translocation from the gastrointestinal tract is an important pathway initiating late-onset sepsis and necrotizing enterocolitis in very low-birth-weight infants. The emerging intestinal microbiota, nascent intestinal epithelia, naive immunity, and suboptimal nutrition (lack of breast milk) have roles in facilitating bacterial translocation. Feeding lactoferrin, probiotics, or prebiotics has presented exciting possibilities to prevent bacterial translocation in preterm infants, and clinical trials will identify the most safe and efficacious prevention and treatment strategies.

Comparative analysis of Salmonella enterica serovar Enteritidis mutants with a vaccine potential

If any new live Salmonella vaccine is introduced in the future, it is quite probable that detailed characterisation of its attenuation will be required. In this study we therefore compared 34 isogenic mutants of S. Enteritidis in aroA, aroD, galE, ssrA, sseA, phoP, rpoS, ompR, htrA, clpP, lon, rfaL, rfaG, rfaC, hfq, sodCI, hilA, sipA, avrA, sopB, sopA, sopE, sifA, shdA, fliC, fur, relA, spoT, rel-spoT, misL, rmbA, STM4258, STM4259 and spvBC genes for their resistance to stresses likely to be expected in the host and for their virulence and immunogenicity in Balb/C mice. We found that the cold and bile resistances essentially did not correlate with the resistances to other stress factors. Resistance to acid pH, heat, polymyxin and serum correlated with each other and also with the attenuation. When the residual virulence and immunogenicity were both considered, mutants in htrA, ompR, aroA, aroD and lon performed the best in mice. Furthermore, when a detailed comparison of polymyxin and serum sensitive mutants was performed, the serum sensitive mutants were more immunogenic.

Innate immune signaling by Toll-like receptor-4 (TLR4) shapes the inflammatory microenvironment in colitis-associated tumors

BACKGROUND

Patients with ulcerative colitis are at increased risk for developing colorectal cancer. We have shown that Toll-like receptor-4 (TLR4) is overexpressed in human colitis-associated cancer (CAC) and that mice deficient in TLR4 are markedly protected against colitis-associated neoplasia. We wished to elucidate the specific contributions of TLR4 signaling by myeloid cells and colonic epithelial cells (CEC) in colitis-associated tumorigenesis.

METHODS

TLR4-deficient mice or wildtype littermates (WT) were transplanted with bone marrow (BM) cells: TLR4(-/-) BM-->WT mice (TLR4-expressing CEC) and WT BM-->TLR4(-/-) mice (TLR4-expressing myeloid cells). Colitis-associated neoplasia was induced by azoxymethane (AOM 7.3 mg/kg) injection and 2 cycles of dextran sodium sulfate (DSS) treatment.

RESULTS

The number and size of dysplastic lesions were greater in TLR4(-/-) BM-->WT mice than in WT BM-->TLR4(-/-) mice (P < 0.005). Histologically, TLR4(-/-) BM-->WT mice had greater numbers of mucosal neutrophils and macrophages compared to WT BM-->TLR4(-/-) mice. The chemokines KC and CCL2, important in recruitment of neutrophils and macrophages, respectively, were induced in mice expressing TLR4 in CEC rather than the myeloid compartment. The lamina propria infiltrate of mice expressing TLR4 in CEC was characterized by macrophages expressing Cox-2. Moreover, mice expressing TLR4 in CEC rather than the myeloid compartment had increased production of amphiregulin and EGFR activation.

CONCLUSIONS

These findings indicate that TLR4 signaling on CEC is necessary for recruitment and activation of Cox-2-expressing macrophages and increasing the number and size of dysplastic lesions. Our results implicate innate immune signaling on CEC as a key regulator of a tumor-promoting microenvironment.

Immune response and gene polymorphism profiles in Crohn's disease and ulcerative colitis

BACKGROUND

Polymorphisms in genes linked to the innate and adaptive immune response may be involved in inflammatory bowel disease pathogenesis. Our aim was to investigate associations among IL1B-511, IL1B-31, IL1RN, TNFA-307, TLR-2, TLR-4, IL2-330, NOD2 G908R, NOD2 L1007fsinsC polymorphisms and both Crohn's disease (CD) and ulcerative colitis (UC) in a Brazilian population.

METHODS

We studied 43 patients with CD, 42 with UC, and 541 blood donors. Polymorphisms were evaluated by PCR, PCR-CTPP, or PCR-RFLP. Data were analyzed in multivariate models adjusting for confounding factors.

RESULTS

IL1RN VNTR (P = 0.00, odds ratio [OR] = 2.43, 95% confidence interval [CI] = 1.50-3.90), as well as TNFA-307 polymorphic allele (P = 0.05, OR = 1.70, 95% CI = 1.00-2.94) were associated with UC. Both NOD2 mutations (G908R, P = 0.02, OR = 6.83, 95% CI = 1.62-25.45, and L1007fsinsC, P = 0.00, OR = 20.00, 95% CI = 3.21-124.69) were associated with CD.

CONCLUSIONS

Our analyses showed positive associations between proinflammatory polymorphisms at IL1RN and TNFA-307 loci and UC, as well as polymorphisms in the NOD2 gene and CD. These results highlight the importance of different genetic profiles associated with CD and UC.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

Structural basis of pattern recognition by innate immune molecules

The importance of the innate immune system as a first line defence against pathogenic challenge has long been recognised. Over the last decade the identity of many of the key molecules mediating innate host defence have been clarified and a model of self/ nonself discrimination by families of pattern recognition receptors (PRRs) has emerged. Although a large amount of information is now available concerning the action of these innate immune molecules at the level of the cell and organism, little is known about the molecular interface between pathogens and innate immune recognition molecules. In this chapter the molecular basis for innate immune discrimination of a wide variety of pathogen derived molecules is discussed in the context of the emerging literature.

Board-invited review: porcine mucosal immunity of the gastrointestinal tract

The gastrointestinal tract (GIT) constitutes one of the largest immunological organs of the body. The GIT must permit absorption of nutrients while also maintaining the ability to respond appropriately to a diverse milieu of dietary and microbial antigenic components. Because of the diverse population of antigenic components within the GIT, a sophisticated mucosal immune system has evolved that relies on collaboration between the innate and adaptive arms of immunity. The collaborative, mucosal immune effort offers protection from harmful pathogens while also being tolerant of dietary antigens and normal microbial flora. Knowledge with respect to porcine mucosal immunity is important as we strive to understand the interrelationships among GIT physiology, immunology, and the resident microbiota. The aim of this review is to provide a descriptive overview of GIT immunity and components of the mucosal immune system and to highlight differences that exist between the porcine species and other mammals.

Development of inflammatory bowel disease in Long-Evans Cinnamon rats based on CD4+CD25+Foxp3+ regulatory T cell dysfunction

A mutant strain with defective thymic selection of the Long-Evans Cinnamon (LEC) rat was found to spontaneously develop inflammatory bowel disease (IBD)-like colitis. The secretion of Th1-type cytokines including IFN-gamma and IL-2 from T cells of mesenteric lymph node cells (MLNs) and lamina propria mononuclear cells, but not spleen cells, in LEC rats was significantly increased more than that of the control Long-Evans Agouti rats through up-regulated expression of T-bet and phosphorylation of STAT-1 leading to NF-kappaB activation. In addition, the number of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells of the thymus, MLNs, and lamina propria mononuclear cells from LEC rats was significantly reduced, comparing with that of the control rats. Moreover, bone marrow cell transfer from LEC rats into irradiated control rats revealed significantly reduced CD25(+)Foxp3(+) Treg cells in thymus, spleen, and MLNs compared with those from control rats. Indeed, adoptive transfer with T cells of MLNs, not spleen cells, from LEC rats into SCID mice resulted in the development of inflammatory lesions resembling the IBD-like lesions observed in LEC rats. These results indicate that the dysfunction of the regulatory system controlled by Treg cells may play a crucial role in the development of IBD-like lesions through up-regulated T-bet, STAT-1, and NF-kappaB activation of peripheral T cells in LEC rats.

Necrotizing enterocolitis: recent scientific advances in pathophysiology and prevention

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality among infants in the neonatal intensive care unit. Here we review the epidemiology and pathophysiology of NEC, with an emphasis on the latest research findings and potential areas for future research. NEC continues to be one of the most devastating and unpredictable diseases affecting premature infants. Despite decades of research, the pathogenesis of this disease remains unclear, and prevention and treatment strategies are limited. Hopefully, future studies aimed at understanding premature intestinal defenses, commensal or probiotic bacterial influences, and possible genetic predisposition will lead to the improvement of prevention and treatment strategies.

The dietary histone deacetylase inhibitor sulforaphane induces human beta-defensin-2 in intestinal epithelial cells

Antimicrobial peptides like human beta-defensin-2 (HBD-2) play an important role in the innate immune system protecting the intestinal mucosa against bacterial invasion. The dietary histone deacetylase (HDAC) inhibitors sulforaphane (SFN) and butyrate have received a great deal of attention because of their ability to simultaneously modulate multiple cellular targets involved in cellular protection. In this study the influence of SFN and butyrate on HBD-2 expression as well as the molecular pathways involved in SFN-mediated induction of HBD-2 were scrutinized. Treatment of Caco-2, HT-29 and SW480 cells with SFN led to a time- and dose-dependent upregulation of HBD-2 mRNA expression as determined by semi-quantitative reverse transcription-polymerase chain reaction. Moreover, HBD-2 protein production increased in response to SFN, measured by enzyme-linked immunosorbent assay. Induction of HBD-2 was also observed in response to butyrate. Immunofluorescence analysis revealed that the protein was localized in the cytosol. Coincubation of SFN with a vitamin D receptor (VDR), or an extracellular-regulated kinase 1/2 or a nuclear factor-kappaB inhibitor all reduced HBD-2 mRNA upregulation. In contrast, transfection of cells with a dominant-negative peroxisome proliferator-activated receptor gamma (PPARgamma) mutant vector to inhibit PPARgamma wild-type action and inhibition of p38 mitogen-activated protein kinase (MAPK) signalling did not affect SFN-mediated upregulation of HBD-2 mRNA. Moreover, SFN induced the expression of VDR, PPARgamma and phosphorylated ERK1/2 but did not affect p38 MAPK activation. The data clearly demonstrate for the first time that the dietary HDAC inhibitor SFN is able to induce antimicrobial peptides in colonocytes. In this process HBD-2 expression is regulated via VDR, mitogen-activated protein kinase kinase/extracellular-regulated kinase and nuclear factor-kappaB signalling.

Flagellin-dependent and -independent inflammatory responses following infection by enteropathogenic Escherichia coli and Citrobacter rodentium

Enteropathogenic Escherichia coli (EPEC) and the murine pathogen Citrobacter rodentium belong to the attaching and effacing (A/E) family of bacterial pathogens. These noninvasive bacteria infect intestinal enterocytes using a type 3 secretion system (T3SS), leading to diarrheal disease and intestinal inflammation. While flagellin, the secreted product of the EPEC fliC gene, causes the release of interleukin 8 (IL-8) from epithelial cells, it is unclear whether A/E bacteria also trigger epithelial inflammatory responses that are FliC independent. The aims of this study were to characterize the FliC dependence or independence of epithelial inflammatory responses to direct infection by EPEC or C. rodentium. Following infection of Caco-2 intestinal epithelial cells by wild-type and DeltafliC EPEC, a rapid activation of several proinflammatory genes, including those encoding IL-8, monocyte chemoattractant protein 1, macrophage inflammatory protein 3alpha (MIP3alpha), and beta-defensin 2, occurred in a FliC-dependent manner. These responses were accompanied by mitogen-activated protein kinase activation, as well as the Toll-like receptor 5 (TLR5)-dependent activation of NF-kappaB. At later infection time points, a subset of these proinflammatory genes (IL-8 and MIP3alpha) was also induced in cells infected with DeltafliC EPEC. The nonmotile A/E pathogen C. rodentium also triggered similar innate responses through a TLR5-independent but partially NF-kappaB-dependent mechanism. Moreover, the EPEC FliC-independent responses were increased in the absence of the locus of enterocyte effacement-encoded T3SS, suggesting that translocated bacterial effectors suppress rather than cause the FliC-independent inflammatory response. Thus, we demonstrate that infection of intestinal epithelial cells by A/E pathogens can trigger an array of proinflammatory responses from epithelial cells through both FliC-dependent and -independent pathways, expanding our understanding of the innate epithelial response to infection by these pathogens.

Activated macrophages inhibit enterocyte gap junctions via the release of nitric oxide

Enterocytes exist in close association with tissue macrophages, whose activation during inflammatory processes leads to the release of nitric oxide (NO). Repair from mucosal injury requires the migration of enterocytes into the mucosal defect, a process that requires connexin43 (Cx43)-mediated gap junction communication between adjacent enterocytes. Enterocyte migration is inhibited during inflammatory conditions including necrotizing enterocolitis, in part, through impaired gap junction communication. We now hypothesize that activated macrophages inhibit gap junctions of adjacent enterocytes and seek to determine whether NO release from macrophages was involved. Using a coculture system of enterocytes and macrophages, we now demonstrate that "activation" of macrophages with lipopolysaccharide and interferon reduces the phosphorylation of Cx43 in adjacent enterocytes, an event known to inhibit gap junction communication. The effects of macrophages on enterocyte gap junctions could be reversed by treatment of macrophages with the inducible nitric oxide synthase (iNOS) inhibitor l-Lysine omega-acetamidine hydrochloride (l-NIL) and by incubation with macrophages from iNOS(-/-) mice, implicating NO in the process. Activated macrophages also caused a NO-dependent redistribution of connexin43 in adjacent enterocytes from the cell surface to an intracellular location, further suggesting NO release may inhibit gap junction function. Treatment of enterocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) markedly inhibited gap junction communication as determined using single cell microinjection of the gap junction tracer Lucifer yellow. Strikingly, activated macrophages inhibited enterocyte migration into a scraped wound, which was reversed by l-NIL pretreatment. These results implicate enterocyte gap junctions as a target of the NO-mediated effects of macrophages during intestinal inflammation, particularly where enterocyte migration is impaired.

The effects of NOD2/CARD15 mutations on the function of the intestinal barrier

NOD2 variants have been identified to be a susceptibility factor for Crohn's disease. The NOD2 protein is an intracellular sensor of the bacterial wall product muramyl dipeptide (MDP) and activates the transcription factor NF-kappaB upon MDP-binding. NOD2 variants are associated with reduced NF-kappaB activation and reduced production of epithelial derived antibacterial peptides such as defensins. A reduced expression of defensins is described and found in patients with Crohn's disease and ulcerative colitis especially when NOD2 variants are present. Furthermore recent evidence from mouse models suggests that the ability of intestinal epithelial cells to activate NF-kappaB upon bacterial stimulation protects from mucosal inflammation. Taken together these data indicate that NOD2 mediated NF-kappaB activation, subsequent induction of anti-microbial peptides such as defensins and induction of cytokine expression are essential for the function of the intestinal barrier and for the prevention of bacterial translocation. The data indicate why a defect in the induction of this acute defense response is associated with chronic inflammation. Invading bacteria that cannot be readily detected and eliminated may start a backup mechanism of inflammation finally resulting in chronic inflammatory reaction followed by further impairment of the mucosal barrier.

Probiotics for preventing and treating nosocomial infections: review of current evidence and recommendations

OBJECTIVE

To review the available clinical data supporting the use of probiotics in preventing and treating serious nosocomial infections.

DATA SOURCE

A Medline database from 1996 to July 2006 and references from identified articles were used to perform a literature search relating to the clinical applications of probiotics in preventing and treating Clostridium difficile-associated diarrhea (CDD) and prevention of hospital-associated pneumonia (HAP).

CONCLUSION

Nosocomial infections like HAP and CDD contribute significantly to health-care costs in the United States. These clinical problems are associated with prolonged hospital stays and increased mortality in critically ill patients. The emergence of multidrug-resistant pathogens in cases of HAP and the recent description of an epidemic, toxin gene-variant strain of C difficile, combined with the anticipated lack of new antimicrobial agents in the near future emphasize the need for new, innovative strategies to prevent and treat these diseases. Probiotics normally function as colonizers and contribute to the overall health of their hosts by multiple mechanisms including immune and antibacterial effects. There is no current clinical evidence to support the use of probiotics to restore the normal human flora in critically ill patients and reduce HAP rates. Probiotics can prevent episodes of antibiotic-associated diarrhea, but their utility in treating and preventing CDD requires demonstration of benefit in multicenter clinical trials, preferably sponsored by the National Institutes of Health.

Genetic variants in the NOD2/CARD15 gene are associated with early mortality in sepsis patients

OBJECTIVE

Genetic variants in the NOD2/CARD15 gene resulting in a diminished capacity to activate NF-kappaB in response to bacterial cell wall products have been associated with Crohn's disease (CD). Recently, we found an association between the variant Leu1007fsinsC of the NOD2/CARD15 gene (SNP13) and a significantly increased rate of transplant related mortality (TRM) due to intestinal and pulmonary complications in stem cell transplantation (SCT). To assess a possible contribution of variants in the NOD2/CARD15 gene to sepsis related mortality (SRM) we investigated 132 prospectively characterised, consecutive patients with sepsis.

DESIGN AND PATIENTS

The three most common NOD2/CARD15 variants (Arg702Trp, Gly908Arg, and Leu1007fsinsC) were determined in 132 prospectively characterised patients with sepsis attended to three intensive care units at the University of Regensburg by Taqman PCR. NOD2/CARD15 genotype and major patients' characteristics were correlated with SRM.

RESULTS

Patient groups with and without NOD2/CARD15 variants did not differ in their clinical characteristics such as median age, gender, reason for admission or APACHE score; however, SRM (day 30) was increased in patients with NOD2/CARD15 coding variants (42 vs. 31%) and was highest (57%) in 8 patients carrying the Leu1007fsinsC variant (p < 0.05). Multivariate analysis demonstrated the Leu1007fsinsC genetic variant as an independent risk factor for SRM.

CONCLUSION

Our findings indicate a major role of NOD2/CARD15 coding variants for SRM. This may be indicative for a role of impaired barrier function and bacterial translocation in the pathophysiology of early sepsis related death.

Fibrogenesis in Crohn's disease

INTRODUCTION

Over one-third of patients with Crohn's disease (CD) will develop an intestinal stricture and the great majority of these will require at least one surgical procedure. While the pathogenesis of inflammation in CD has been extensively investigated, knowledge of stricture pathogenesis remains limited. The aim of this review is to discuss the current understanding of fibrogenesis in CD and to outline potential directions in research and therapeutics.

METHODS

The electronic literature (January 1966 to May 2006) on CD-associated fibrosis was reviewed. Further references were obtained by cross-referencing from key articles.

RESULTS

CD-associated fibrosis results from chronic transmural inflammation and a complex interplay among intestinal mesenchymal cells, cytokines, and local inflammatory cells. The fibroblast is the key cell type mediating stricture formation. The cytoarchitecure of the bowel wall is altered with disruption of the muscularis mucosa, thickening of the muscularis propria, and deposition of collagen throughout. The cytokine TGF-beta appears critical in this process, acting to increase growth factor and extracellular matrix (ECM) production and dysregulate ECM turnover. Potential therapeutic interventions are likely to concentrate on modulating down-stream targets of TGF-beta.

CONCLUSIONS

Greater understanding of the biology of fibrostenosis is likely to yield significant advances in our ability to care for patients with stricturing CD. Potential dividends of this approach include identification of novel therapeutic targets and biomarkers useful for prognostication and therapeutic monitoring.

Role of intestinal subepithelial myofibroblasts in inflammation and regenerative response in the gut

Inflammatory bowel disease (IBD) is characterized by an ongoing mucosal inflammation caused by a dysfunctional host immune response to commensal microbiota and dietary factors. In the pathophysiology of IBD, mesenchymal cells such as intestinal subepithelial myofibroblasts (ISEMF) affect the recruitment, retention and activation of immune cells. Mesenchymal cells also promote resolution of inflammatory activity accompanied with balanced repair processes. The transient appearance of mesenchymal cells is a feature of normal wound healing, but the persistence of these cells is associated with tissue fibrosis. Recent studies suggest that mesenchymal cells derived from bone marrow (BM) stem cells play a crucial role in intestinal repair and fibrosis. This article focuses on recent knowledge about ISEMF in the field of immune response inflammation and repair. Two major topics were documented: interaction between interleukin (IL)-17-secreting CD4+ cells (Th-17 cells) and about role of BM-derived stem cells in mucosal regenerative response via differentiation to ISEMF. Recent therapeutic strategies targeting BM stem cells for IBD patients were also documented.

Protection of the neonate by the innate immune system of developing gut and of human milk

The neonatal adaptive immune system, relatively naïve to foreign antigens, requires synergy with the innate immune system to protect the intestine. Goblet cells provide mucins, Paneth cells produce antimicrobial peptides, and dendritic cells (DCs) present luminal antigens. Intracellular signaling by Toll-like receptors (TLRs) elicits chemokines and cytokines that modulate inflammation. Enteric neurons and lymphocytes provide paracrine and endocrine signaling. However, full protection requires human milk. Breast-feeding reduces enteric infection and may reduce chronic disease in later life. Although human milk contains significant secretory immunoglobulin A (sIgA), most of its protective factors are constitutively expressed. Multifunctional milk components are nutrients whose partial digestion products inhibit pathogens. Cytokines, cytokine receptors, TLR agonists and antagonists, hormones, anti-inflammatory agents, and nucleotides in milk modulate inflammation. Human milk is rich in glycans (complex carbohydrates): As prebiotics, indigestible glycans stimulate colonization by probiotic organisms, modulating mucosal immunity and protecting against pathogens. Through structural homology to intestinal cell surface receptors, glycans inhibit pathogen binding, the essential first step of pathogenesis. Bioactive milk components comprise an innate immune system of human milk whereby the mother protects her nursing infant. Interactions between human milk glycans, intestinal microflora, and intestinal mucosa surface glycans underlie ontogeny of innate mucosal immunity, pathobiology of enteric infection, and inflammatory bowel diseases.

Addressing the "New" NEC: Part I: rediscovering the basics

Epithelial cell functions ultimately define the ability of the extremely low birth weight human fetus to survive outside of the uterus. These specialized epithelial cell capacities manage all human interactions with the ex utero world including: (i) lung mechanics, surface chemistry and gas exchange, (ii) renal tubular balance of fluid and electrolytes, (iii) barrier functions of the intestine and skin for keeping bacteria out and water in, plus enabling intestinal digestion, as well as (iv) maintaining an intact neuroepithelium lining of the ventricles of the brain and retina. In Part I of this two part review, the authors describe why the gut barrier is a clinically relevant model system for studying the complex interplay between innate and adaptive immunity, dendritic &epithelial cell interactions, intraepithelial lymphocytes, M-cells, as well as the gut associated lymphoid tissues where colonization after birth, clinician feeding practices, use of antibiotics as well as exposure to prebiotics, probiotics and maternal vaginal flora all program the neonate for a life-time of immune competence distinguishing "self" from foreign antigens. These barrier defense capacities become destructive during disease processes like necrotizing enterocolitis (NEC) when an otherwise maturationally normal, yet dysregulated and immature, immune defense system is associated with high levels of certain inflammatory mediators like TNFa. In Part II, the authors will discuss the theoretical advantages of using rhG-CSF in managing NEC or sepsis by augmenting neonatal neutrophil number and killing capacity including an unexpected, paradoxical and potent anti-TNFa function that may serve to limit extension of tissue destruction without impairing bacterial killing capacity. The authors conclude by arguing that NEC may be the ideal disease process for testing whether a clearly defined clinical benefit of cytokine therapy can prove beneficial.

Recent understanding of IBD pathogenesis: implications for future therapies

The inflammatory bowel diseases (IBD) are comprised of two major phenotypes, Crohn's disease (CD) and ulcerative colitis (UC). Research over the last couple of years has led to great advances in understanding the inflammatory bowel diseases and their underlying pathophysiologic mechanisms. From the current understanding, it is likely that chronic inflammation in IBD is due to aggressive cellular immune responses to a subset of luminal bacteria. Susceptibility to disease is thereby determined by genes encoding immune responses which are triggered by environmental stimuli. Based on extensive research over the last decade, there are several new and novel pathways and specific targets on which to focus new therapeutics. The following review summarizes the current view on the four basic tenets of the pathophysiological basis of IBD and its implications for therapies of IBD: genetics, immune dysregulation, barrier dysfunction and the role of the microbial flora.

Circadian oscillation of innate immunity components in mouse small intestine

The digestive system is a major port of entry for pathogens. To detect and combat pathogens, the innate immunity in the gut utilizes pattern recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) proteins, and broad-spectrum anti-bacterial polypeptides, such as defensins. We have previously shown that mouse enteric defensins (cryptdins) oscillate around the circadian cycle and peak at the end of the dark phase suggesting control by the biological clock. As the core mechanism of the biological clock has never been studied in the small intestine, our objective was to determine whether the biological clock is functional in mouse jejunum and examine whether mTlr and mNod2 mRNAs, similarly to cryptdins, oscillate throughout the circadian cycle. Mouse jejunum and Paneth-enriched crypt base cells were isolated around the circadian day and the levels of clock (mClock, mBmal1, mPer1, mPer2, mCry1) and innate immunity component (mTlr2, mTlr3, mTlr4, mTlr5, mTlr9, mNod2) genes were measured by real-time PCR. Analysis of mouse jejunum and Paneth-enriched crypt base cells revealed that all clock genes exhibited circadian oscillation. Similarly to cryptdins, mTlr2, mTlr3, mTlr4, mTlr5 displayed circadian rhythmicity in mouse jejunum. Although no circadian oscillation could be detected for mTlr9 and mNod2 in the whole jejunum, these genes oscillated in Paneth-enriched crypt base cells. In addition, mTlr3 exhibited the highest expression level. As the clock regulates intestinal motility and function, resetting of the clock in the small intestine may help not only to restore activity but also to gain better protection against pathogens.

Necrotising enterocolitis

Necrotising enterocolitis is one of the most common gastrointestinal emergencies in newborn infants. Here we review the epidemiology, clinical presentation, and pathophysiology of the disease, as well as strategies for diagnosis, management, and prevention. Necrotising enterocolitis is one of the most devastating and unpredictable diseases affecting premature infants. Despite decades of research, its pathogenesis remains unclear; diagnosis can be difficult; and treatment is challenging. We will need to improve our understanding of intestinal defences in premature infants, dietary and bacterial factors, and genetic effects that could predispose infants to necrotising enterocolitis before we can develop new strategies for prevention and treatment.

Contribution of polymeric immunoglobulin receptor to regulation of intestinal inflammation in dextran sulfate sodium-induced colitis

BACKGROUND

Inflammatory bowel disease (IBD) affects approximately 4 million people worldwide and can be caused by dysregulated mucosal immune responses to the intestinal commensal microflora. Immunoglobulin A (IgA) is considered to be the principal antibody in intestinal secretions and functions to prevent commensals and pathogenic organisms from gaining access to epithelial cell surfaces. Immunoglobulin A deficiency in humans has been associated with celiac disease and ulcerative colitis. However, the precise role of IgA in the pathogenesis of these disorders is yet to be fully understood.

METHODS

Mice with a targeted disruption in IgA production (IgA(-/-) mice) and polymeric immunoglobulin receptor (pIgR(-/-) mice) were analyzed for the contribution of secretory immunity in the pathogenesis of dextran sulfate sodium (2.5%)-induced colitis.

RESULTS

It was found that dextran sulfate sodium-treated pIgR(-/-) mice displayed greater loss of bodyweight and had severe clinical illness compared to similarly treated IgA(-/-) mice and wild-type animals. Additionally, colonic tissues from the pIgR(-/-) mice exhibited progressively and significantly greater degrees of mucosal edema, ulceration, crypt abscesses and macrophage infiltration when compared to similarly treated IgA(-/-) mice and wild-type animals.

CONCLUSIONS

The results indicate that secretory immunoglobulins contribute to protection of the colonic mucosa against dextran sulfate sodium-induced epithelial injury, although the isotype of the secretory immunoglobulin (IgA or IgM) may not be a decisive factor in such protection. Collectively, the pIgR and/or the secretory component are important for the maintenance of epithelial integrity and mucosal homeostasis in the colonic epithelium.

The oligopeptide transporter hPepT1: gateway to the innate immune response

Bacterial products that are normally present in the lumen of the colon, such as N-formylated peptides and muramyl-dipeptide, are important for inducing the development of mucosal inflammation. The intestinal dipeptide transporter, hPepT1, which is expressed in inflamed but not in noninflamed colonic epithelial cells, mediates the transport of these bacterial products into the cytosol of colonic epithelial cells. The small bacterial peptides subsequently induce an inflammatory response, including the induction of MHC class I molecules expression and cytokines secretion, via the activation of nucleotide-binding site and leucine-rich repeat (NBS-LRR) proteins, for example NOD2, and activation of NF-kappaB. Subsequent secretion of chemoattractants by colonic epithelial cells induces the movement of neutrophils through the underlying matrix, as well as across the epithelium. These bacterial products can also reach the lamina propria through the paracellular pathway and across the basolateral membrane of epithelial cells. As a consequence, small formylated peptides can interact directly with immune cells through specific membrane receptors. Since immune cells, including macrophages, also express hPepT1, they can transport small bacterial peptides into the cytosol where these may interact with the NBS-LRR family of intracellular receptors. As in intestinal epithelial cells, the presence of these small bacterial peptides in immune cells may trigger immune response activation.

Toll-like receptor 4 contributes to colitis development but not to host defense during Citrobacter rodentium infection in mice

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) are noninvasive bacterial pathogens that infect their hosts' intestinal epithelium, causing severe diarrheal disease. These infections also cause intestinal inflammation, although the mechanisms underlying the inflammatory response, as well as its potential role in host defense, are unclear. Since these bacteria are gram-negative, Toll-like receptor 4 (TLR4), the innate receptor for bacterial lipopolysaccharide may contribute to the host response; however, the role of TLR4 in the gastrointestinal tract is poorly understood, and its impact has yet to be tested against this family of enteric bacterial pathogens. Since EPEC and EHEC are human specific, we infected mice with Citrobacter rodentium, a mouse-adapted attaching and effacing (A/E) bacterium that infects colonic epithelial cells, causing colitis and epithelial hyperplasia, using a similar array of virulence proteins as EPEC and EHEC. We demonstrated that C. rodentium activates TLR4 and rapidly induced NF-kappaB nuclear translocation in host cells in a partially TLR4-dependent manner. Infection of TLR4-deficient mice revealed that TLR4-dependent responses mediate much of the inflammation and tissue pathology seen during infection, including the induction of the chemokines MIP-2 and MCP-1, as well as the recruitment of macrophages and neutrophils into the infected intestine. Surprisingly, spread of C. rodentium through the colon was delayed in TLR4-deficient mice, whereas the duration of the infection was unaffected, indicating that TLR4-mediated responses against this A/E pathogen are not host protective and are ultimately maladaptive to the host, contributing to both the morbidity and the pathology seen during infection.

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes

Here, we examined hPepT1 expression in the monocytic cell line, KG-1. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that hPepT1 is expressed in KG-1 cells, while cDNA cloning and direct sequencing confirmed the sequence of KG-1 hPepT1 (accession number, AY634368). Immunoblotting of cell lysates from KG-1 cells or macrophages isolated from human peripheral blood revealed a approximately 100 kDa immunoreactive band mainly present in the membrane fraction. Uptake experiments showed that the transport of 20 microM radiolabeled Gly-Sarcosine ([14C]Gly-Sar) in KG-1 cells was Na+, Cl- dependent and disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS)-sensitive. In addition, hPepT1 activity was likely to be coupled to a Na+/H+ exchanger, as evidenced by the fact that [14C]Gly-Sar uptake was not affected by the absence of Na+ when cells were incubated at low pH (5.2). Interestingly, hPepT1-mediated transport was reduced in KG-1 cells incubated at low pH as it was also observed in nonpolarized Caco2-BBE cells. This pattern of pH-dependence is due to a disruption of the driving force of hPepT1-mediated transport events. This was supported by our finding that nonpolarized cells, Caco2-BBE cells and KG-1 cells, have an increased permeability to H+ when compared to polarized Caco2-BBE cells. Finally, we showed that hPepT1 is responsible for transporting fMLP into undifferentiated and differentiated (macrophage-like) KG-1 cells. Together, these results show that hPepT1 is expressed in nonpolarized immune cells, such as macrophages, where the transporter functions best at the physiological pH 7.2. Furthermore, we provide evidence for hPepT1-mediated fMLP transport, which might constitute a novel immune cell activation pathway during intestinal inflammation.

Environment as a Critical Factor for the Pathogenesis and Outcome of Gastrointestinal Disease: Experimental and Human Inflammatory Bowel Disease and Helicobacter-Induced Gastritis

Environmental factors play an important role in the manifestation, course, and prognosis of diseases of the gastrointestinal tract such as inflammatory bowel disease (IBD) and Helicobacter pylori-induced gastritis. These two disease complexes were chosen for a discussion of the contribution of environmental factors to the disease outcome in humans and animal models. Dissecting complex diseases like IBD and Helicobacter-induced gastritis has shown that the outcome of disease depends on the allelic constellation of a host and the microbial and physical environments. Host alleles predisposing to a disease in one genomic and/or environmental milieu may not be deleterious in other constellations; on the other hand, microbes can have different effects in different hosts and under different environmental conditions. The impact of the complex interaction between host genetics and environmental factors, particularly microflora, also underlines the importance of a defined genetic background and defined environments in animal studies and is indicative of the difficulties in analyzing complex diseases in humans.

Abnormally differentiated subsets of intestinal macrophage play a key role in Th1-dominant chronic colitis through excess production of IL-12 and IL-23 in response to bacteria

Disorders in enteric bacteria recognition by intestinal macrophages (Mphi) are strongly correlated with the pathogenesis of chronic colitis; however the precise mechanisms remain unclear. The aim of the current study was to elucidate the roles of Mphi in intestinal inflammation by using an IL-10-deficient (IL-10-/-) mouse colitis model. GM-CSF-induced bone marrow-derived Mphi (GM-Mphi) and M-CSF-induced bone marrow-derived Mphi (M-Mphi) were generated from bone marrow CD11b+ cells. M-Mphi from IL-10-/- mice produced abnormally large amounts of IL-12 and IL-23 upon stimulation with heat-killed whole bacteria Ags, whereas M-Mphi from wild-type (WT) mice produced large amounts of IL-10 but not IL-12 or IL-23. In contrast, IL-12 production by GM-Mphi was not significantly different between WT and IL-10-/- mice. In ex vivo experiments, cytokine production ability of colonic lamina propria Mphi (CLPMphi) but not splenic Mphi from WT mice was similar to that of M-Mphi, and CLPMphi but not splenic Mphi from IL-10-/- mice also showed abnormal IL-12p70 hyperproduction upon stimulation with bacteria. Surprisingly, the abnormal IL-12p70 hyperproduction from M-Mphi from IL-10-/- mice was improved by IL-10 supplementation during the differentiation process. These results suggest that CLPMphi and M-Mphi act as anti-inflammatory Mphi and suppress excess inflammation induced by bacteria in WT mice. In IL-10-/- mice, however, such Mphi subsets differentiated into an abnormal phenotype under an IL-10-deficient environment, and bacteria recognition by abnormally differentiated subsets of intestinal Mphi may lead to Th1-dominant colitis via IL-12 and IL-23 hyperproduction. Our data provide new insights into the intestinal Mphi to gut flora relationship in the development of colitis in IL-10-/- mice.

Regulation of mammalian defensin expression by Toll-like receptor-dependent and independent signalling pathways

The immune system consists of innate and adaptive immune responses. The innate immune system confers non-specific protection against a large number of pathogens, hence, serving as the first line of defence. The innate immune system utilizes Toll-like receptors (TLRs) to recognize and bind pathogen-associated molecular patterns (PAMPs). Binding of PAMPs leads to TLR activation, which, in turn, initiates MAPK- or NF-kappaB-dependent cascades that culminate in a proinflammatory response. This response involves the secretion of cytokines, chemokines and broad-spectrum antibacterial substances, such as defensins. Increased defensin synthesis is also mediated by the activation of receptors other than TLRs, such as NOD2, IL-17R and PAR-2. This review summarizes the recently characterized signalling pathways leading to increased defensin synthesis as well as the pathway by which defensins activate TLRs on immature dendritic and memory T cells. Thus, not only do defensins eliminate pathogens, but they also recruit the adaptive immune system in instances of infection and/or inflammation.

Development of intestinal M cells

Intestinal epithelium contains several specialized cell types including M cells, which can be found in the follicle-associated epithelium (FAE) or occasionally on the villi. M cells are critical for sampling of intestinal flora and for transferring pathogens across the epithelial barrier for recognition by the immune system. Development of M cells on the villi (M(v)) is independent of the presence of lymphocytes, while development of the FAE and M cells within the FAE (M(f)) is dependent on B lymphocytes. Here, the concept is discussed that B cells are not required for induction of M(f) differentiation but are required for transition to and maintenance of the mature M(f) phenotype. Signaling pathways possibly involved in the B-cell-independent stages of M-cell development are also discussed.

Place of probiotics

PURPOSE OF REVIEW

This review reports on the recent progress understanding mechanisms of action and clinical applications of probiotics.

RECENT FINDINGS

New insights on regulating mechanisms of intestinal commensal bacteria to prevent and treat different gastrointestinal diseases have been reported. Some probiotics, though not all, exert beneficial effects by modulating the mucosal barrier function and immune activity. It seems that a combination of different probiotics is more effective than a single strain. It was demonstrated that not only viable bacteria administered to the intestinal tract but also isolated probiotic DNA is active, even if injected subcutaneously. There is reasonable evidence to recommend probiotics in infectious diarrhoea for prevention and treatment (mainly in children) and to prevent antibiotic-induced gastrointestinal side effects. Furthermore, probiotics are effective in maintaining remission in ulcerative colitis and preventing and treating pouchitis. Promising positive effects were published in major surgery patients (gastric resection, pancreatic resection, liver transplantation) and in severe necrotising acute pancreatitis.

SUMMARY

Increasing knowledge on probiotics is exciting, but in the near future it must be defined which probiotics (single strains or a combination) are most effective in specific diseases. Well-designed, randomized clinical trials are still required to further define the role of probiotics as preventive and therapeutic agents.