Physiological Basis for Novel Drug Therapies Used to Treat the Inflammatory Bowel Diseases I. Pathophysiological basis and prospects for probiotic therapy in inflammatory bowel disease
Fergus Shanahan
Alimentary Pharmabiotic Centre, Department of Medicine, University College Cork, National University of Ireland, Cork, Ireland
 |
ABSTRACT
|
---|
Mechanisms underlying the conditioning influence of the intestinal flora on mucosal homeostasis, including development and function of immune responses, are attracting increasing scientific scrutiny. The intestinal flora is a positive asset to host defense, but some of its components may, in genetically susceptible hosts, become a risk factor for development of inflammatory bowel disease (IBD). It follows that strategies to enhance assets or offset microbial liabilities represent a therapeutic option; therein lies the rationale for manipulation of the flora in IBD. In addition, the diversity of regulatory signalling among the flora and host epithelum, lymphoid tissue, and neuromuscular apparatus is an untapped reservoir from which novel therapeutics may be mined. Moreover, the capacity to engineer food-grade or commensal bacteria to deliver therapeutic molecules to the intestinal mucosa promises to extend the scope of microbial manipulation for the benefit of mankind.
bacteria; intestinal flora; Crohn's disease; ulcerative colitis; mucosal immunity
THE CHRONIC INFLAMMATORY BOWEL DISEASES (IBD), which are comprised of Crohn's disease and ulcerative colitis, cause much personal suffering and disablement for patients and represent a substantial economic burden on healthcare resources. Of the three major contributory factors to the pathogenesis of IBD, genetic susceptibility, environmental triggers, and immune activation, only the latter is targeted by most current therapeutic strategies. Notwithstanding remarkable advances in biological and other immunomodulatory therapy over the past decade, the enthusiasm for such drugs is tempered by various issues such as expense, toxicity, and incomplete efficacy in many patients. Sustained therapeutic responses in IBD may require more comprehensive approaches including modification of the bacterial microenvironment.
The lesson of Helicobacter pylori and chronic peptic ulcer disease is a sobering reminder that the solution to some chronic disorders cannot be resolved by exclusive investigation of the host response. Lasting cure of peptic ulceration would never have been achieved by strategies directed solely at suppressing the host response with gastric acid suppressants. Rather, it was the host-Helicobacter interaction that held the answer. Similarly, host-flora interactions underpin the pathogenesis of chronic disorders such as IBD. In most instances, these appear to involve components of the normal commensal flora rather than infections with specific pathogens (4, 42).
Commensal bacteria within the human gastrointestinal tract vary widely in proinflammatory capacity, with some having apparent anti-inflammatory properties. Therefore, optimal modification of the intestinal ecosystem with probiotics has emerged as a realistic therapeutic opportunity for IBD (36, 41). Traditional descriptions of probiotics as "friendly" or "good" bacteria betray a naiveté that has been eroded by a more intriguing picture involving the host response and modification of mucosal immunoinflammatory responses to the microenvironment (13). Although there is mounting evidence from meta-analyses for probiotic efficacy in several clinical conditions, particularly in Clostridum difficile, rotavirus, and other mucosal infections (11), the evidence for efficacy in IBD is less clear and largely based on studies in pouchitis and experimental animal models. Nonetheless, there is intriguing circumstantial evidence for manipulation of the gut flora in IBD. The intent here is to present an overview of probiotic rationale and promise for the future in IBD; the emphasis is on current concepts of mechanisms and the potential for therapeutic "mining" of the flora. Other sources are recommended for reviews on clinical and experimental efficacy with probiotics (11, 36, 41).
 |
LIMITATIONS OF DEFINITION AND SELECTION CRITERIA FOR PROBIOTICS
|
---|
Definitions of probiotics are evolving as understanding of their effects on human physiology increases. At present, the term describes "live micro-organisms, which when consumed in adequate amounts, confer a health benefit on the host" (33, 51). However, this definition may be too restrictive. Live bacteria may not be an absolute requirement for therapeutic efficacy; bacterial constituents, such as CpG DNA, account for some of the anti-inflammatory effects of probiotics, whereas secreted metabolites, such antimicrobial peptides (bacteriocins), contribute to others. Although several authorities, including the Joint Food and Agricultural Organization of the United Nations and the World Health Organization (33, 51), have described selection criteria for probiotic organisms, it is noteworthy that there is currently no in vitro predictor of probiotic performance in vivo (18, 41). Lactobacilli and bifidobacteria have traditionally been the most common candidates, but nonpathogenic Escherichia coli and nonbacterial organisms, such as Saccharomyces boulardii, or even nematode parasites have been used for probiotic effect (40, 42).
Most commercially available probiotics meet minimum selection criteria including acid and bile resistance and survival during gastrointestinal transit, but an ideal probiotic strain for any given indication has not been defined. In addition, rigorous strain-strain comparisons of probiotic performance have yet to be performed in a single disease setting. Different probiotics are unlikely to be equally suited to all indications; selection of strains for disease-specific indications will be required. Optimal selection of a probiotic may even need to take into account individual variations in host diet and composition of gut flora. In this respect, the apparent influence of human genetic variability on intestinal bacterial composition is particularly intriguing (47).
Finally, the likely emergence of genetically or otherwise-modified food-grade commensal bacteria may have to be accommodated into the probiotic concept, as discussed below. This, coupled with clarification of the molecular determinants and mechanisms of probiotic action, will hasten a transition "from bugs to drugs." Perhaps the neologism "pharmabiotic" may be a more appropriate generic or umbrella term to encompass any form of therapeutic exploitation of the commensal flora including the use of whole organisms (probiotics), food ingredients that influence the composition of the flora (prebiotics), combinations thereof (synbiotics), dead or live organisms, or biologically active bacterial metabolites.
 |
PROKARYOTIC-EUKARYOTIC SIGNALLING WITHIN THE GUT
|
---|
Because probiotics may be considered operationally as commensal organisms that can be exploited for health benefit, the mechanisms of probiotic action are likely to be reflected in the normal host-flora signalling processes. The most tangible evidence for bacterial-derived regulatory influences on intestinal structure and function have been derived from comparative studies of germ-free and colonized animals (42) (Table 1).
At birth, immunologic organs are developed, but mucosal immune responses require education and fine tuning of cytokine balances and T cell repertoires. This is achieved with microbial exposure by bacterial colonzisation and sporadic mucosal infections. Without the flora, mucosal lymphoid tissue is rudimentary; induction of mucosal immune responses and tolerance is suboptimal (42).
Although the molecular details underpinning the regulatory exchanges between the flora and mucosal structures are unclear, they can now be explored with modern technology such as laser microdissection and gene array analysis (15, 16). When applied to animals colonized with only a single bacterial strain, Bacteroides thetaiotaomicron, this combined approach has illustrated the impact of bacterial-derived signalling on the expression of host genes controlling mucosal barrier function, nutrient absorption, angiogenesis, and development of the enteric nervous system. Similarly, the sequencing of the bacterial genome for several commensal (52) and probiotic strains (30) will help reveal properties that are essential for desired probiotic effects on host function.
The incoming bacterial signals include secreted chemoattractants such as the formylated peptide f-met-leu-phe, cell wall constituents such as peptidoglycans and lipopolysaccharide, and bacterial nucleic acids (CpG DNA). These maintain the mucosal immune response in a state of "controlled" or physiological inflammation, a state of tolerance or constrained responsiveness to the commensal flora but on ready-alert for rapid response to episodic challenge with pathogens. This requires exquisitely precise regulation and accurate discriminatory responses to danger microbial signals versus those from harmless commensals. In this respect, the mucosal immune response is a sensory organ, the afferent and efferent limbs of which comprise a network of connectivity among lymphoid, epithelial, neuronal, stromal, and endocrine components of the intestine (39).
Sampling of the microbial environment across the epithelial "barrier" occurs at three main sites. First, M cells that overlie lymphoid follicles transport particulate and some microbial antigens to subjacent antigen-presenting cells (dendritic cells, B cells, and macrophages). Second, surface enterocytes transport soluble antigens and serve as afferent sensors of danger within the luminal microenvironment by producing chemokines that alert the host innate and acquired immune responses and direct them to breaches in mucosal barrier with infection (21). A bidirectional IgG-dependent system transepithelial transport of antigen has recently been demonstrated (8). In addition, specialized Paneth cells within the epithelium may also exhibit microbial discriminatory responses in relation to production of defensins. Third, dendritic cells throughout the mucosa have a pivotal role in mucosal immunosensory functions (44). These antigen-presenting cells have been identified within intestinal epithelium in rodents (26), and in vitro modeling suggests that subepithelial dendritic cells extend into the lumen between the surface enterocytes without disrupting tight junctions (34).
Compelling evidence has shown that intestinal dendritic cells can ingest and retain intact live commensal bacteria and transit to the mesenteric lymph node where immune responses to commensals are induced locally (25). Thus the mesenteric lymph node acts as a gatekeeper, preventing access of commensal bacteria to the internal milieu and protecting the host from harmful systemic immune reactivity. As expected, the immunosensory function of dendritic cells exhibits marked plasticity and versatility of responses (17). Moreover, dendritic cells are heterogeneous, with tissue-specific specialization in the gut (19, 20). These cells are the decision makers determining the balance of T effector cell responses (TH1 and TH2 effectors) versus regulatory T cell responses (Treg/tolerance). Thus they provide the switch for the host response to danger from pathogens and determine the nature of that response (Fig. 1). The apparent paradox of probiotic efficacy in TH1- and TH2-mediated inflammatory disorders may be accounted for if the mechanism of probiotic action is activation of Treg cells.

View larger version (30K):
[in this window]
[in a new window]
|
Fig. 1. Immunosensory detection of the intestinal microbial environment. Sampling of the microbial environment within the lumen occurs across M cells via the surface enterocytes and by transepithelial processes of dendritic cells. Pathogen-associated molecular patterns (PAMPs) from episodic pathogens or commensals are recognized by pattern-recognition receptors on the surface of dendritic cells and epithelial cells. Discrimination between danger and nondanger signals depends on the nature of the PAMPs. The dendritic cell acts as the switch for immune responsiveness or tolerance and determines the nature of the response by promoting either TH1 or TH2 effector cells or regulatory T cells (T reg) and their associated cytokines.
|
|
In addition to presenting intact live bacteria to the immune system, dendritic cells respond rapidly to danger signals from the microbial environment via pattern recognition receptors (PPRs), which include Toll-like receptors (TLRs) (1) and C-type lectins. PPRs are also expressed on epithelial cells and may be differentially altered in ulcerative colitis and Crohn's disease (5, 6). Multiple TLRs are probably used simultaneously by immunocytes to recognize the features of a specific microbe. TLR2 recognizes lipoproteins and peptidoglycans and triggers the host response to gram-positive bacteria and yeast; TLR4 mediates responses to LPS primarily from gram-negative bacteria; TLR1 and TLR6 participate in activation of macrophages by gram-positive bacteria, whereas TLR5 and TLR9 recognize flagellin and bacterial (CpG) DNA, respectively. Bacterial DNA and oligonucleotides containing unmethylated CpG dinucleotides stimulate lymphocytes, whereas eukaryotic DNA and methylated oligonucleotides do not (49, 50).
 |
PROKARYOTIC-REGULATED EPITHELIAL ANTI-INFLAMMATORY RESPONSES
|
---|
A miscellany of host responses to commensal or probiotic bacteria has been observed in different experimental settings (Table 2). Some of these were expected, even predictable. Their therapeutic significance is uncertain. However, with the resurgence of interest in host-flora interactions, hitherto unknown anti-inflammatory mechanisms have emerged. Thus distinct mechanisms of bacterial regulation of epithelial responses in inflammation have been reported.
Transduction of bacterial signals into host immune responses probably proceeds along several pathways, but the transcription factor, NF-kB, is the pivotal regulator of epithelial responses to invasive pathogens (42). Separate mechanisms of prokaryotic regulation of NF-
B-mediated responses within epithelial cells have recently been described for nonpathogenic and/or commensal bacteria (22, 28). For example, some nonpathogenic bacteria can attenuate inflammatory responses by delaying the degradation of I-
B, which is counterregulatory to NF-
B (28). Although conventional probiotic bifidobacteria and lactobacilli do not appear to use this mechanism, other signal-transduction pathways are likely to emerge to account for their anti-inflammatory effects. Thus the commensal anaerobe Bacteroides thetaiotaomicron has been shown to attenuate inflammation by antagonizing NF-
B within the epithelial cell, and this is achieved by enhancing the nuclear export of the transcriptionally active RelA subunit of NF-
B in a peroxisome proliferator-activated receptor
-dependent manner (22). As the molecular details of these prokaryotic regulated anti-inflammatory events become clear, they may be translated into new therapeutic targets.
 |
PROBIOTICS AND IMMUNITY
|
---|
Although the host immune modulation by probiotics may be expected to mimic some of the effects of the indigenous flora, several caveats of therapeutic relevance are noteworthy. First, probiotics are not a generic form of therapy (36); different probiotics have distinct properties, and not all models of experimental colitis respond to the same probiotics (11). In particular, different species of lactobacillus have been shown to exert distinct patterns of dendritic cell activation, and at least one species appears to inhibit dendritic cell activation by others within the same genus (7). This has implications for the therapeutic use of multispecies combinations of probiotics. Second, there appears to be regional variability in immunological effects of probiotic organisms. Although lactobacilli characteristically induce TH1-type cytokines, including IL-12 and TNF-
, from peripheral blood mononuclear cells (27), exposure of mucosal tissue ex vivo to different lactobacilli, but not other bacteria, led to downregulation of TNF-
production (3). Third, probiotics can attenuate inflammatory disease without any apparent impact on gut flora. This was shown by the efficacy of subcutaneously administered Lactobacillus salivarius 118 to IL-10 knockout mice (43). Moreover, the probiotic effect was not specific to colitis, and an anti-inflammatory effect was also observed in a murine model of arthritis after subcutaneous delivery of the probiotic. This emphasizes the role of the host response in determining probiotic efficacy and indicates that mucosal delivery may not be essential. Fourth, in certain murine models of IBD, bacterial CpG DNA mediates the anti-inflammatory effect of probiotics by signalling through host TLR9 receptors (31, 32). These studies question whether live organisms are an absolute requirement but, as pointed out by others (13), are not fully conclusive. Once again, bacteria vary and differ in immunostimulatory DNA content (13, 30). More importantly, CpG DNA motifs may have opposing effects in experimental models of intestinal inflammation depending on the timing of its administration. In contrast to the prophyactic effect of CpG DNA before the onset of inflammation, exposure to CpG DNA during acute inflammation has been shown to exacerbate disease in a murine model of IBD (29). Finally, although engagement with the host immune system is central to probiotic mechanisms, metabolites other than CpG nucleotides may influence selection criteria in certain settings. Bacterial production of short-chain fatty acids as nutrients for the colonic epithelium is well established but less well known is the production of conjugated linoleic acid (CLA) by some probiotic organisms. Among its health benefits, CLA has important anti-inflammatory properties (9).
 |
TURBO PROBIOTICS-ENGINEERING DESIRED FUNCTION
|
---|
The exploitation of microbes is no longer limited to their role as cell factories for production of human therapeutics. Commensal and food-grade bacteria can be engineered for delivery of anti-inflammatory cytokines or other biologically active molecules and vaccines to the gut. Proof of principle and efficacy have been demonstrated with Lactococcus lactis, engineered to secrete IL-10 locally within the gut in murine models of IBD (45). Other examples of genetically modified (GM) microbes include the delivery of single-chain antibodies for pathogen-specific passive immunity (2, 23) and bacterial-derived trefoil factors to promote healing and repair in the inflamed murine gut (48).
Public health concerns about the release of GM organisms into the environment have replaced technological constraints as the major hurdles to be overcome with GM bacteria (14). One approach to contain GM bacteria after their excretion from the host is to substitute the therapeutic transgene for the thymidylate synthase (thy A) gene within the bacterial genome (46). Because this enzyme is required for DNA biosynthesis by methylating uracil or uridine to make thymine or thymidine, the organism becomes dependent on the latter, which are available within the gut but not within the external environment. This leads to bacterial cell death and containment of the GM organism outside the host. An appealing aspect of this strategy is the elimination of the transgene from the bacterial genome in the event of the engineered organism reacquiring the thy A gene from the wild-type strain. The importance of this type of biocontainment for avoiding unforeseen consequences of transgenic organisms escaping into the environment has been empasized in a recent report by the National Academics Research Council (reviewed in Ref. 14).
In conclusion, the metabolic activity of the indigenous gut flora represents a rich repository from which novel therapeutic agents can be "mined." Therapeutic manipulation of the intestinal flora with any form of pharmabiotic is, at present, suboptimal because of incomplete understanding of the normal flora and host-flora interactions. Although the antimicrobial actions of probiotics and their prophylactic efficacy against infectious diseases are now well established, the anti-inflammatory properties of the indigenous commensal/probiotic flora are perhaps more intriguing. Mechanisms of probiotic action vary depending on the experimental or clinical context and depending on differences in the host and in the bacterial strain, but engagement with host immunity is central to probiotic action in IBD.
 |
DISCLOSURES
|
---|
The author has been affiliated with a multidepartmental university campus company (Alimentary Health), which investigates host-flora interactions and the therapeutic manipulation of these interactions in various human and animal disorders. The content of this article was neither influenced nor constrained by this fact.
 |
GRANTS
|
---|
The author is supported in part by Science Foundation Ireland in the form of a center grant (Alimentary Pharmabiotic Centre), by the Health Research Board of Ireland, the Higher Education Authority of Ireland, and the European Union (PROGID QLK-2000-00563).
 |
FOOTNOTES
|
---|
Address for reprint requests and other correspondence: F. Shanahan, Alimentary Pharmabiotic Centre, Dept. of Medicine, Clinical Science Bldg., Cork Univ. Hospital, Cork, Ireland (E-mail F.Shanahan{at}ucc.ie)
 |
REFERENCES
|
---|
- Akira S, Takeda K, and Kaisho T. Toll-like receptors: critical proteins linking innate and acquired immunity. Nat Immun 2: 675680, 2001.[CrossRef][ISI]
- Beninati C, Oggioni MR, Boccanera M, Spinosa MR, Maggi T, Conti S, Magliani W, De Bernardis F, Teti G, Cassone A, Pozzi G, and Polonelli L. Therapy of mucosal candidiasis by expression of an anti-idiotype in human commensal bacteria. Nat Biotechnol 18: 10601064, 2000.[CrossRef][ISI][Medline]
- Borruel N, Carol M, Casellas F, Antolin M, de Lara F, Espin E, Naval J, Guarner F, and Malagelada JR. Increased mucosal tumour necrosis factor alpha production in Crohn's disease can be downregulated ex vivo by probiotic bacteria. Gut 51: 659664, 2002.[Abstract/Free Full Text]
- Bouma G and Strober W. The immunological and genetic basis of inflammatory bowel disease. Nat Rev Immunol 3: 521533, 2003.[CrossRef][ISI][Medline]
- Cario E and Podolsky DK. Differential alteration in intestinal epithelial cell expression of toll-like receptor 3 (TLR3) and TLR4 in inflammatory bowel disease. Infect Immun 68: 70107017, 2000.[Abstract/Free Full Text]
- Cario E, Rosenberg IM, Brandwein SL, Beck PL, Reinecker HC, and Podolsky DK. Lipopolysaccharide activates distinct signaling pathways in intestinal epithelial cell lines expressing Toll-like receptors. J Immunol 164: 966972, 2000.[Abstract/Free Full Text]
- Christensen HR, Frokiaer H, and Pestka JJ. Lactobacilli differentially modulate expression of cytokines and maturation surface markers in murine dendritic cells. J Immunol 168: 171178, 2002.[Abstract/Free Full Text]
- Claypool SM, Dickinson BL, Wagner JS, Johansen FE, Venu N, Borawski JA, Lencer WI, and Blumberg RS. Bidirectional transepithelial IgG transport by a strongly polarized basolateral membrane Fc-receptor. Mol Biol Cell 15: 17461759, 2004.[Abstract/Free Full Text]
- Coakley M, Ross RP, Nordgren M, Fitzgerald G, Devery R, and Stanton C. Conjugated linoleic acid biosynthesis by human-derived Bifidobacterium species. J Appl Microbiol 94: 138145, 2003.[CrossRef][ISI][Medline]
- Collins JK, Dunne C, Murphy L, Morrissey D, O'Mahony L, O'Sullivan E, Fitzgerald G, Kiely B, O'Sullivan GC, Daly C, Marteau P, and Shanahan F. A randomised controlled trial of a probiotic Lactobacillus strain in healthy adults: assessment of its delivery, transit, and influence on microbial flora and enteric immunity. Microbial Ecol Health Disease 14: 8189, 2002.[CrossRef]
- Fedorak RN and Madsen KL. Probiotics and prebiotics in gastrointestinal disorders. Curr Opin Gastroenterol 20: 146155, 2004.[CrossRef][ISI][Medline]
- Flynn S, Van Sinderen D, Thornton GM, Holo H, Nes IF, and Collins JK. Characterisation of the genetic locus responsible for the production of A.BP-118, a novel bacteriocin produced by the probiotic bacterium Lactobacillus salivarius subsp. Salivarius UCC118. Microbiology 148: 973984, 2002.[ISI][Medline]
- Ghosh S, van Heel D, and Playford RJ. Probiotics in inflammatory bowel disease: is it all gut flora manipulation? Gut 53: 620622, 2004.[Free Full Text]
- Hampton T. Prevent genetically modified organisms from escaping into nature, report urges. JAMA 291: 1055, 2004.[Free Full Text]
- Hooper LV, Midvedt T, and Gordon JI. How host-microbial interactions shape the nutrient environment of the mammalian intestine. Annu Rev Nutr 22: 283307, 2002.[CrossRef][ISI][Medline]
- Hooper LV, Wong MH, Thelin A, Hansson L, Falk PG, and Gordon JI. Molecular analysis of commensal host-microbial relationships in the intestine. Science 291: 881884, 2001.[Abstract/Free Full Text]
- Huang Q, Liu D, Majewski P, Schulte LC, Korn JM, Young RA, Lander ES, and Hacohen N. The plasticity of dendritic cell responses to pathogens and their components. Science 294: 870875, 2001.[Abstract/Free Full Text]
- Ibnou-Zekri N, Blum S, Schiffrin EJ, and von der Weid T. Divergent patterns of colonization and immune response elicited from two intestinal Lactobacillus strains that display similar properties in vitro. Infect Immun 71: 428436, 2003.[Abstract/Free Full Text]
- Iwasaki A and Kelsall BL. Freshly isolated Peyer's Patch but not spleen, dendritic cells produce interleukin 10 and induce the differentiation of T helper type 2 cells. J Exp Med 190: 229239, 1999.[Abstract/Free Full Text]
- Kadowaki N, Ho S, Antonenko S, Malefyt RW, Kastelein RA, Bazan F, and Liu YJ. Subsets of human dendritic cell precursors express different toll-like receptors and respond to different microbial antigens. J Exp Med 194: 863869, 2001.[Abstract/Free Full Text]
- Kagnoff MF and Eckmann L. Epithelial cells as sensors for microbial infection. J Clin Invest 100: 610, 1997.[Free Full Text]
- Kelly D, Campbell JI, King TP, Grant G, Jansson EA, Coutts AG, Pettersson S, and Conway S. Commensal anaerobic gut bacteria attenuate inflammation by regulating nuclear-cytoplasmic shuttling of PPAR-gamma and RelA. Nat Immun 5: 104112, 2004.[CrossRef][ISI]
- Kruger C, Hu Y, Pan Q, Marcotte H, Hultberg A, Delwar D, van Dalen PJ, Pouwels PH, Leer RJ, Kelly CG, van Dollenweerd C, Ma JK, and Hammarstrom L. In situ delivery of passive immunity by lactobacilli producing single-chain antibodies. Nat Biotechnol 20: 702726, 2002.[CrossRef][ISI][Medline]
- McCarthy J, O'Mahony L, O'Callaghan L, Sheil B, Vaughan EE, Fitzsimons N, Fitzgibbon J, O'Sullivan GC, Kiely B, Collins JK, and Shanahan F. Double blind, placebo controlled trial of two probiotic strains in interleukin 10 knockout mice and mechanistic link with cytokine balance. Gut 52: 975980, 2003.[Abstract/Free Full Text]
- Macpherson AJ and Uhr T. Induction of protective IgA by intestinal dendritic cells carrying commensal bacteria. Science 303: 16621665, 2004.[Abstract/Free Full Text]
- Maric L, Holt PG, Perdue MH, and Bienenstock J. Class II MHC antigen (Ia)-bearing dendritic cells in the epithelium of the rat intestine. J Immunol 156: 14081414, 1996.[Abstract]
- Miettinen M, Matikainen S, Vuopio-Varkila J, Pirhonen J, Varkila K, Kurimoto M, and Julkunen I. Lactobacilli and streptococci induce interleukin-12 (IL-12), IL-18, and gamma interferon production in human peripheral blood mononuclear cells. Infect Immun 66: 60586062, 1998.[Abstract/Free Full Text]
- Neish AS, Gewirtz AT, Zeng H, Young AN, Hobert ME, Karmali V, Rao AS, and Madara JL. Prokaryotic regulation of epithelial responses by inhibition of I&B-
ubiquitination. Science 289: 15601563, 2000.[Abstract/Free Full Text]
- Obermeier F, Dunger N, Strauch UG, Grunwald N, Herfarth H, Scholmerich J, and Falk W. Contrasting activity of cytosin-guanosin dinucleotide oligonucleotides in mice with experimental colitis. Clin Exp Immunol 134: 217224, 2003.[CrossRef][ISI][Medline]
- Pena JA, Li SY, Wilson PH, Thibodeau SA, Szary AJ, and Versalovic J. Genotypic and phenotypic studies of murine intestinal lactobacilli: species differences in mice with and without colitis. Appl Environ Microbiol 70: 558568, 2004.[Abstract/Free Full Text]
- Rachmilewitz D, Karmeli F, Takabayashi K, Hayashi T, Leider-Trejo L, Lee J, Leoni LM, and Raz E. Immunostimulatory DNA ameliorates experimental and spontaneous murine colitis. Gastroenterology 122: 14281441, 2002.[ISI][Medline]
- Rachmilewitz D, Katakura K, Karmeli F, Hayashi T, Reinus C, Rudensky B, Akira S, Takeda K, Lee J, Takabayashi K, and Raz E. Toll-like receptor 9 signaling mediates the anti-inflammatory effects of probiotics in murine experimental colitis. Gastroenterology 126: 520528, 2004.[CrossRef][ISI][Medline]
- Report of a Joint F.A.O./W.H.O. Expert Consultation. Health and Nutritional Properties of Probiotics in Food Including Powder Milk and Live Lactic Acid Bacteria. http://www.fao.org/es/ESN/Probio/report, 2001.
- Rescigno M, Urbano M, Valzasina B, Francolini M, Rotta G, Bonasio R, Granucci F, Kraehenbuhl JP, and Ricciardi-Castagnoli P. Dendritic cells express tight junction proteins and penetrate gut epithelial monolayers to sample bacteria. Nat Immun 2: 361367, 2001.[CrossRef][ISI]
- Resta-Lenert S and Barrett KE. Live probiotics protect intestinal epithelial cells from the effects of infection with enteroinvasive Escherichia coli (EIEC). Gut 52: 988997, 2003.[Abstract/Free Full Text]
- Sartor RB. Therapeutic manipulation of the enteric flora in inflammatory bowel diseases: antibiotics, probiotics and prebiotics. Gastroenterology 126: 16201633, 2004.[ISI][Medline]
- Servin AL. Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens. FEMS Micribiol Rev, 28: 405440, 2004.
- Servin AL and Coconnier MH. Adhesion of probiotic strains to the intestinal mucosa and interaction with pathogens. Best Pract Res Clin Gastroenterol 17: 741754, 2003.[CrossRef][ISI][Medline]
- Shanahan F. Nutrient Tasting and Signaling Mechanisms in the Gut. V. Mechanisms of immunologic sensation of intestinal contents. Am J Physiol Gastrointest Liver Physiol 278: G191G1896, 2000.[Abstract/Free Full Text]
- Shanahan F. Probiotics in inflammatory bowel disease: is there a scientific rationale? Inflamm Bowel Dis 6: 107115, 2000.[ISI][Medline]
- Shanahan F. Probiotics in inflammatory bowel disease-therapeutic rationale and role. Adv Drug Delivery Res 56: 809818, 2004.[CrossRef][ISI][Medline]
- Shanahan F. Host-flora interactions in inflammatory bowel disease. Inflamm Bowel Dis 10, Suppl 1: S16S24, 2004.[CrossRef]
- Sheil B, McCarthy J, O'Mahony L, Bennett MW, Ryan P, Fitzgibbon JJ, Kiely B, Collins JK, and Shanahan F. Is the mucosal route of administration essential for probiotic function? Subcutaneous administration is associated with attenuation of murine colitis and arthritis. Gut 53: 694700, 2004.[Abstract/Free Full Text]
- Stagg AJ, Hart AL, Knight SC, and Kamm MA. The dendritic cell: its role in intestinal inflammation and relationship with gut bacteria. Gut 52: 15221529, 2003.[Abstract/Free Full Text]
- Steidler L, Hans W, Schotte L, Neirynck S, Obermeier F, Falk W, and Remaut E. Treatment of murine colitis by Lactococcus lactis secreting interleukin-10. Science 289: 13521355, 2000.[Abstract/Free Full Text]
- Steidler L, Neirynck S, Huyghebaert N, Snoeck V, Vermeire A, Goddeeris B, Cox E, Remon JP, and Remaut E. Biological containment of genetically modified Lactococcus lactis for intestinal delivery of human interleukin 10. Nat Biotechnol 21: 785789, 2003.[CrossRef][ISI][Medline]
- Van de Merwe JP, Stegeman JH, and Hazenberg MP. The resident faecal flora is determined by genetic characteristics of the host. Implications for Crohn's disease? Antonie Van Leeuwenhoek 49: 119124, 1983.[CrossRef][Medline]
- Vandenbroucke K, Hans W, Van Huysse J, Neirynck S, Demetter P, Remaut E, Rottiers P, and Steidler L. Active delivery of trefoil factors by genetically modified Lactococcus lactis prevents and heals acute colitis in mice. Gastroenterology, 127: 502513, 2004.[CrossRef][ISI][Medline]
- Wagner H. Bacterial CpG-DNA activates immune cells to signal infectious danger. Adv Immunol 73: 329368, 1999.[ISI][Medline]
- Wagner H. Toll meets bacterial CpG-DNA. Immunity 14: 499502, 2001.[CrossRef][ISI][Medline]
- Working Group Report. Guidelines for the evaluation of probiotics in food. Joint Food and Agriculture Organization of the United Nations and The World Health Organization, London, Ontario, Canada April 30 and May 1, 2002. http://www.fao.org/es/ESN/Probio/probio.htm.
- Xu J, Bjursell MK, Himrod J, Deng S, Carmichael LK, Chiang HC, Hooper LV, and Gordon JI. A genomic view of the human bacteroides thetaiotaomicron symbiosis. Science 299: 20742076, 2003.[Abstract/Free Full Text]
- Yan F and Polk DB. Probiotic bacterium prevents cytokine-induced apoptosis in intestinal epithelial cells. J Biol Chem 277: 5095950965, 2002.[Abstract/Free Full Text]