Bacterial probiotic modulation of dendritic cells

Effect of probiotics Lactobacillus acidophilus on Citrobacter rodentium colitis: the role of dendritic cells

Modulation of the intestinal immune response early in life by administration of probiotic bacteria may be an effective strategy for preventing or attenuating infectious diarrhea. We preinoculated the mice early in life with the probiotic bacteria Lactobacillus acidophilus NCFM (La) at age 2 wk. Dendritic cells (DCs) were collected and purified from mesenteric lymph nodes (MLN) and spleens of the BalbC/ByJ mice. DC isolation and adoptive transfer was used to examine the function of probiotics. We demonstrated that when mice were adoptively transferred with La-primed DCs (t-LaDC) instead of oral consumption with La, there was a similar effect on fecal bacteria counts, IgA levels, and colonic histopathology, as well as cytokine levels in MLN when there was intestinal bacterial infection. The above findings suggest that DCs play a key role in probiotics attenuating Citrobacter rodentium (Cr) colitis. Moreover, the location of La-primed DC hints that there is interaction of DCs and T cells in the digestive system of the host. Up-regulated expression of a surface marker on DCs indicated that inoculation with probiotics will stimulate the function of DCs, thereby further increasing immune response triggered by DC.

Genetically engineered Lactococcus lactis secreting murine IL-10 modulates the functions of bone marrow-derived dendritic cells in the presence of LPS

Oral delivery of IL-10 by genetically modified Lactococcus lactis (LL-pTmIL10) has been shown to efficiently reduce intestinal inflammation in mice with chronic colitis, but the mechanisms involved have not been elucidated. It has been suggested that IL-10 controls intestinal inflammation by inhibiting microbe-induced activation of dendritic cells. We therefore investigated whether LL-pTmIL10 can modulate the functions of bone marrow-derived dendritic cells (BM-DC) responding to LPS. Incubation of these cells with LL-pTmIL10 or with the control strain LL-pTREX reduced their ability to activate allogeneic T-cell proliferation. However, in contrast to LL-pTREX, LL-pTmIL10 inhibited the LPS-stimulated secretion of MCP-1 by BM-DC and reduced the synergistic up-regulation of IL-12/IL-23p40. In addition, LL-pTmIL10 treatment of LPS-stimulated BM-DC significantly inhibited their capacity to induce strong secretion of IL-17 by CD4+ T cells. Our data suggest that the beneficial effects of LL-pTmIL10 treatment during chronic colitis might involve inhibition of CD4+ Th17 cells and a reduced accumulation of these cells as well as other immune cells at the site of inflammation.

Mechanisms of probiotic action: Implications for therapeutic applications in inflammatory bowel diseases

Probiotics are defined as nonpathogenic living microorganisms, including some commensal bacterial flora, which have beneficial effects on host health and disease prevention and/or treatment. Clinical trials have shown beneficial effects of probiotics on several human diseases, such as inflammatory bowel diseases (IBDs), which are among the most-studied diseases testing probiotics as a potential therapy. However, a significant question regarding clinical use of probiotics is the mechanism underlying the wide range of actions. Studies discussed in this review suggest 3 distinct cellular and molecular mechanisms for probiotic regulation in IBD therapy: 1) Probiotics block pathogenic bacterial effects by producing bactericidal substances and competing with pathogens and toxins for adherence to the intestinal epithelium; 2) Probiotics regulate immune responses by enhancing the innate immunity and modulating pathogen-induced inflammation via toll-like receptor-regulated signaling pathways; and 3) Probiotics regulate intestinal epithelial homeostasis by promoting intestinal epithelial cell survival, enhancing barrier function, and stimulating protective responses. Probiotics modulate host cell signaling pathways, including Akt, mitogen-activated protein kinases, and nuclear factor-kappaB to mediate these intestinal epithelial functions. It is hoped that developing a mechanistic understanding of probiotic action will provide the rationale to support the development of new hypothesis-driven studies to define the clinical efficacy in preventive, adjunctive, or alternative treatments for IBD.

Supernatant from bifidobacterium differentially modulates transduction signaling pathways for biological functions of human dendritic cells

Background

Probiotic bacteria have been shown to modulate immune responses and could have therapeutic effects in allergic and inflammatory disorders. However, the signaling pathways engaged by probiotics are poorly understood. We have previously reported that a fermentation product from Bifidobacterium breve C50 (BbC50sn) could induce maturation, high IL-10 production and prolonged survival of DCs via a TLR2 pathway. We therefore studied the roles of mitogen-activated protein kinases (MAPK), glycogen synthase kinase-3 (GSK3) and phosphatidylinositol 3-kinase (PI3K) pathways on biological functions of human monocyte-derived DCs treated with BbC50sn.

Methodology/Principal Findings

DCs were differentiated from human monocytes with IL-4 and GM-CSF for 5 days and cultured with BbC50sn, lipopolysaccharide (LPS) or Zymosan, with or without specific inhibitors of p38MAPK (SB203580), ERK (PD98059), PI3K (LY294002) and GSK3 (SB216763). We found that 1) the PI3K pathway was positively involved in the prolonged DC survival induced by BbC50sn, LPS and Zymosan in contrast to p38MAPK and GSK3 which negatively regulated DC survival; 2) p38MAPK and PI3K were positively involved in DC maturation, in contrast to ERK and GSK3 which negatively regulated DC maturation; 3) ERK and PI3K were positively involved in DC-IL-10 production, in contrast to GSK3 that was positively involved in DC-IL-12 production whereas p38MAPK was positively involved in both; 4) BbC50sn induced a PI3K/Akt phosphorylation similar to Zymosan and a p38MAPK phosphorylation similar to LPS.

Conclusion/Significance

We report for the first time that a fermentation product of a bifidobacteria can differentially activate MAPK, GSK3 and PI3K in order to modulate DC biological functions. These results give new insights on the fine-tuned balance between the maintenance of normal mucosal homeostasis to commensal and probiotic bacteria and the specific inflammatory immune responses to pathogen bacteria.

Probiotics: potential to prevent HIV and sexually transmitted infections in women

Women are at significant risk of human immunodeficiency virus (HIV) and sexually transmitted infection (STI) acquisition with the genital mucosa serving as the main portal of infection. Exogenously supplied lactobacillus used as a probiotic may prove a cost-effective, female-initiated method to prevent HIV and STI infection in women. A probiotic may act indirectly through treating and preventing recurrent bacterial vaginosis or directly by secreting endogenous (e.g., hydrogen peroxide) and exogenous substances that block HIV and STI transmission. This review summarizes the preclinical and clinical studies that have been conducted so far to test probiotic bacteria for these purposes. Although significant progress has been made in this field, more fundamental research is required to better understand vaginal ecology to maximize probiotic formulations. Once identified, a suitable product will require testing in a well-designed, randomized, placebo-controlled trial to measure its effectiveness in augmenting antibiotic treatment to prevent bacterial vaginosis. If results from such a trial demonstrate efficacy, future studies should be designed to determine whether a probiotic can significantly lower the risk for HIV and STIs in at-risk female populations.

Probiotics, immunomodulation, and health benefits

Probiotics are defined as live microorganisms that, when administered in adequate amount, confer a health benefit on the host. Amongst the many benefits associated with the consumption of probiotics, modulation of the immune system has received the most attention. Several animal and human studies have provided unequivocal evidence that specific strains of probiotics are able to stimulate as well as regulate several aspects of natural and acquired immune responses. There is also evidence that intake of probiotics is effective in the prevention and/or management of acute gastroenteritis and rotavirus diarrhoea, antibiotic-associated diarrhoea and intestinal inflammatory disorders such as Crohn's disease and pouchitis, and paediatric atopic disorders. The efficacy of probiotics against bacterial infections and immunological disorders such as adult asthma, cancers, diabetes, and arthritis in humans remains to be proven. Also, major gaps exist in our knowledge about the mechanisms by which probiotics modulate immune function. Optimum dose, frequency and duration of treatment required for different conditions in different population groups also remains to be determined. Different probiotic strains vary in their ability to modulate the immune system and therefore efficacy of each strain needs to be carefully demonstrated through rigorously designed (randomised, double-blind, placebo-controlled) studies. This chapter provides an over view of the immunomodulatory effects of probiotics in health and disease, and discusses possible mechanisms through which probiotics mediate their disparate effects.

In vitro Th1 cytokine-independent Th2 suppressive effects of bifidobacteria

A comparison between 17 strains of lactic acid bacteria and 15 strains of bifidobacteria indicated that bifidobacteria induced significantly lower levels of interleukin-12 (IL-12) in murine splenic cells. The present study aims to evaluate the effect and mechanism of Bifidobacterium longum BB536, a probiotic strain, in suppressing antigen-induced Th2 immune response in vitro. BB536 suppressed immunoglobulin (Ig) E and IL-4 production by ovalbumin-sensitized splenic cells, but induction of Th1-inducing cytokine production, such as IL-12 and gamma interferon (IFN-gamma) tended to be lower compared with lactic acid bacteria. Neutralization with antibodies to IL-12, IFN-gamma, IL-10 and transforming growth factor beta indicated negative involvement of Th1-inducing cytokines and regulatory cytokines in the suppression of Th2 immune response by BB536, especially when treated at higher doses of BB536 (>10 microg cells/ml). Furthermore, BB536 induced the maturation of immature bone marrow-derived dendritic cells (BM-DCs), and suppressed antigen-induced IL-4 production mediated by BM-DCs. These results suggested that BB536 suppressed Th2 immune responses, partially independent of Th1-inducing cytokines and independent of regulatory cytokines, mediated by antigen-presenting cells such as dendritic cells.

Lactobacillus casei prevents the development of dextran sulphate sodium-induced colitis in Toll-like receptor 4 mutant mice

Probiotics, defined as live or attenuated bacteria or bacterial products, confer a significant health benefit to the host. Recently, they have been shown to be useful in the treatment of chronic inflammatory bowel disease and infectious colitis. In this study, we investigated the effect of probiotics on the development of experimental colitis using Toll-like receptor 4 (TLR-4) mutant (lps-/lps-) mice. TLR-4(lps-/lps-) and wild-type (WT) mice were given 2.5% dextran sulphate sodium (DSS) in drinking water to induce colitis with or without Lactobacillus casei pretreatment. Clinical and histological activity of DSS-colitis was attenuated markedly both in TLR-4(lps-/lps-) and WT mice pretreated with L. casei. Interestingly, histological activity was less severe in TLR-4(lps-/lps-) mice than in WT mice. The levels of myeloperoxidase activity and interleukin (IL)-12p40 were attenuated in pretreated TLR-4(lps-/lps-) mice after DSS administration. By contrast, transforming growth factor (TGF)-beta and IL-10 mRNA and protein expressions were increased markedly in pretreated TLR-4(lps-/lps-) mice. The current results suggest that L. casei has a preventive effect in the development of acute DSS-induced colitis and its action depends largely upon TLR-4 status. L. casei modulates the expression of inflammatory cytokines and down-regulates neutrophilic infiltration in the case of incomplete TLR-4 complex signalling.

Prior stimulation of antigen-presenting cells with Lactobacillus regulates excessive antigen-specific cytokine responses in vitro when compared with Bacteroides

The development of allergy is related to differences in the intestinal microbiota. Therefore, it is suggested that the immune responses induced by different genera of bacteria might be regulated through adaptive as well as innate immunity. In this study, we examined whether antigen-specific immune responses were affected by stimulation with the different genera of intestinal bacteria in vitro. Mesenteric lymph node (MLN) cells isolated from germ-free ovalbumin (OVA)-specific T cell receptor transgenic (OVA-Tg) mice were stimulated with OVA and intestinal bacteria. Cecal contents from conventional mice but not germ-free mice could induce OVA-specific cytokine production. Among the murine intestinal bacteria, Bacteroides acidofaciens (BA) enhanced OVA-specific IFN-gamma and IL-10 production while Lactobacillus johnsonii (LA) increased OVA-specific IL-10 production only. The expression of cell surface molecules and cytokine production by antigen-presenting cells (APCs) from germ-free Balb/c mice were analyzed. BA increased the expression of MHC II and co-stimulatory molecules on APCs compared with LA. BA increased IL-6 and IL-10 production but induced less IL-12p40 than LA. To examine the effects of prior stimulation of APCs by intestinal bacteria on the induction of antigen-specific immune responses, cytokine production was determined following co-culture with OVA, CD4(+) T cells from OVA-Tg mice, and APCs which were pre-stimulated with the bacteria or not. APCs pre-stimulated with LA did not enhance OVA-specific cytokine production while BA stimulated OVA-specific IL-10 production. These results suggest that the prior stimulation of intestinal immunocytes by Lactobacillus might regulate excessive antigen-specific cytokine responses via APCs when compared with prior stimulation by Bacteroides.

Gene expression profiling of chicken lymphoid cells after treatment with Lactobacillus acidophilus cellular components

Lactobacillus acidophilus has been shown to exert immunostimulating activities in a number of species, including the chicken. To examine the molecular mechanisms of this phenomenon, we investigated spatial and temporal expression of immune system genes in chicken cecal tonsil and spleen mononuclear cells in response to structural constituents of L. acidophilus. Using a low-density chicken immune system microarray, we found that cecal tonsil cells responded more rapidly than spleen cells to the bacterial stimuli, with the most potent stimulus for cecal tonsil cells being DNA and for splenocytes being the bacterial cell wall components. We also discovered that in both splenocytes and cecal tonsil cells, STAT2 and STAT4 genes were highly induced. Given the close interactions between cecal tonsil cells and commensal bacteria, we further examined the involvement of STAT2 and STAT4 signaling pathways in cellular responses to bacterial DNA. Our results revealed that the expression of STAT2, STAT4, IL-18, MyD88, IFN-alpha, and IFN-gamma genes were up-regulated in cecal tonsil cells after treatment with L. acidophilus DNA.

IL-10-inducing adjuvants enhance sublingual immunotherapy efficacy in a murine asthma model

BACKGROUND

IL-10-inducing adjuvants could enhance the efficacy of allergy vaccines in establishing allergen-specific tolerance. The aim of this study was to identify such adjuvants using in vitro cultures of human and murine cells and to evaluate them in a therapeutic murine model of sublingual immunotherapy (SLIT).

METHODS

Adjuvants stimulating IL-10 gene expression by human or murine immune cells were tested sublingually in BALB/c mice sensitized to ovalbumin (OVA), assessing the reduction in airway hyperresponsiveness (AHR) by whole-body plethysmography. The induction of regulatory T cells (T(reg)) was evaluated using phenotypic and functional assays. T-cell proliferation in cervical lymph nodes (LNs) was assessed following intravenous transfer of CFSE-labelled OVA-specific T cells and FACS analysis.

RESULTS

A combination of 1,25-dihydroxyvitamin D3 plus dexamethasone (VitD3/Dex) as well as Lactobacillus plantarum were found to induce IL-10 production by human and murine dendritic cells (DCs). The former inhibits LPS-induced DC maturation, whereas L. plantarum induces DC maturation. Following stimulation with VitD3/Dex-pretreated DCs, CD4+ naïve T cells exhibit a T(reg) profile. In contrast, a Th1/T(reg) pattern of differentiation is observed in the presence of DCs treated with L. plantarum. Both adjuvants significantly enhance SLIT efficacy in mice, in association with either induction of Foxp3+ T(reg) cells (for VitD3/Dex) or proliferation of OVA-specific T cells in cervical LNs (for L. plantarum).

CONCLUSIONS

Both VitD3/Dex and L. plantarum polarize naïve T cells towards IL-10-expressing T cells, through distinct mechanisms. As adjuvants, they both enhance SLIT efficacy in a murine asthma model.

Probiotics for preventing relapse or recurrence in Crohn's disease involving the ileum: Are there reasons for failure?

In contrast to ulcerative colitis and pouchitis, benefits of probiotic therapy in preventing recurrence/relapse in Crohn's disease (mostly involving the ileum) are far from being proven. The lack of response in this setting does not seem attributable to a lower relevance of dysbiosis in ileal Crohn's disease, since this - or at least the presence of increased mucosal amounts of potentially pathogen bacteria - has been proven to occur in the ileum of Crohn's disease patients. Available data indicate that whereas in ulcerative colitis (and to a lesser extent in colonic Crohn's disease) the innate immune response is enhanced, it is constitutively depressed in ileal Crohn's disease. Therefore, attempts to modify the composition of intestinal microflora in colonic IBD or pouchitis by means of probiotics do make sense. In contrast, supplying additional bacteria (even being probiotics) to an ileum with decreased antibacterial defence does not seem reasonable. In fact, the presence of intestinal contents has been reported to be related to postoperative recurrence in ileo-caecal Crohn's disease, and antibiotic treatment in effective to prevent its development.

Probiotics and prebiotics — renaissance of a therapeutic principle

Probiotics are nonpathogenic microorganisms mostly of human origin which, when administered in adequate amounts, confer a health benefit on the host and enable to prevent or improve some diseases. Probiotics may be a natural temporary constituent of the resident intestinal microflora, but their concentration is not sufficient for therapeutic purposes. The microbiota, the intestinal epithelium, and the mucosal immune system constitute the gastrointestinal ecosystem. All three components are essential for complete functional and developmental maturity of the system. The viability of intestinal microflora (including probiotic strains) requires the availability of nutritional substrates (prebiotics), i.e. various types of fiber and oligosaccharides. Prebiotics are cleaved by microbial enzymes to numerous substances (short-chain fatty acids, aminoacids, polyamines, growth factors, vitamins and antioxidants) indispensable for metabolic and functional activities of the intestinal mucosa. The principal probiotics in use include lactobacilli, bifidobacteria, some nonpathogenic strains of Escherichia coli, and Saccharomyces boulardii. These microbiota display favourable effects which qualify them for therapeutic use. For this purpose, probiotics have to fulfill a series of requirements verifying their efficacy and safety. Experimental and clinical studies examine the prerequisites for the administration of probiotics in digestive diseases, allergic and atopic affections, as well as in some extraintestinal conditions. Future goals of probiotic application include genomic analysis, controlled postnatal colonisation of the digestive tract, the use of probiotics as carriers of peroral vaccines, and recombinant probiotics with in-situ production and targeted application of therapeutic molecules.

[Probiotics and prebiotics in inflammatory bowel disease]

Multiple studies of the immune system in patients with inflammatory bowel disease (IBD) have demonstrated the presence of altered intestinal mucosal immunity, probably genetically determined, giving rise to increased immunoreactivity against elements of the commensal flora. The basic strategy in the treatment of IBD is aimed at suppressing inflammatory responses. With the exception of studies of antibiotic therapy, little attention has been paid to modifying intestinal flora. Modification of intestinal flora through probiotics provides the possibility of acting microbiologically as well as immunologically. From the physiopathological point of view, the use of probiotics in IBD is a good therapeutic alternative. However, at present, studies with probiotics have only yielded positive results in highly specific situations. Secondary physiopathological data from clinical trials suggest a beneficial effect. However, this effect should be confirmed either in studies with a larger number of patients or by applying strategies that more effectively modify the composition of intestinal flora.

Dendritic cell activation and maturation induced by mucosal fluid from women with bacterial vaginosis

Dendritic cells (DC) at mucosal surfaces mature when exposed to "danger" signals such as LPS. Bacterial vaginosis (BV) is a prevalent alteration of the vaginal bacterial flora associated with preterm childbirth and increased risk for HIV acquisition. We examined the effect of mucosal fluid from women with BV or healthy flora on DC function. IL-12, IL-23 and p40 production by monocyte-derived dendritic cells (MDDC) were all induced by BV samples. Activation/maturation markers HLA-DR, CD40 and CD83 on MDDC incubated with BV CVL were also induced. BV CVL also decreased the endocytic ability of MDDC and increased proliferation of T cells in allogeneic MLR. Plasmacytoid dendritic cell (pDC) CD86 expression was induced by BV CVL. Healthy flora CVL had little effect in any of the tests. This study suggests that BV, but not healthy flora, affects local dendritic cell function in vivo suggesting a mechanism through which BV affects mucosal immunity.

Selection of probiotic bacteria for prevention of allergic diseases: immunomodulation of neonatal dendritic cells

Modification of intestinal microbiota early in life by administration of probiotic bacteria may be a potential approach to prevent allergic disease. To select probiotic bacteria for in vivo purposes, we investigated the capacity of probiotic bacteria to interact with neonatal dendritic cells (DC) and studied the ensuing T cell polarizing effect. Immature DC were generated from cord blood-derived monocytes and maturation was induced by maturation factors (MF), lipopolysaccharide (LPS) plus MF and Bifidobacterium bifidum, B. infantis, Lactobacillus salivarius, Lactococcus lactis alone or combined with MF. After 12 days of co-culture with DC and Staphylococcus aureus enterotoxin B (SEB) as antigenic stimulus, cytokine production by autologous T cells was determined by intracellular cytokine staining. Additionally, cells were stimulated with CD3 and CD28 monoclonal antibodies and cytokines were measured in supernatants by multiplex assay. The probiotic strains induced partial maturation of DC. Full maturation of DC was induced for all strains tested when MF was added. The percentage of interleukin (IL)-4 producing T cells was lower in T cell cultures stimulated with B. bifidum matured DC compared to MF and LPS matured DC, which coincided with a higher percentage of interferon (IFN)-gamma-producing T cells. Furthermore, T cells stimulated by B. bifidum matured DC produced significantly more IL-10 compared to MF matured DC. Selected species of the Bifidobacterium genus prime in vitro cultured neonatal DC to polarize T cell responses and may therefore be candidates to use in primary prevention of allergic diseases.

Selection of probiotic bacteria for prevention of allergic diseases: immunomodulation of neonatal dendritic cells

Modification of intestinal microbiota early in life by administration of probiotic bacteria may be a potential approach to prevent allergic disease. To select probiotic bacteria for in vivo purposes, we investigated the capacity of probiotic bacteria to interact with neonatal dendritic cells (DC) and studied the ensuing T cell polarizing effect. Immature DC were generated from cord blood-derived monocytes and maturation was induced by maturation factors (MF), lipopolysaccharide (LPS) plus MF and Bifidobacterium bifidum, B. infantis, Lactobacillus salivarius, Lactococcus lactis alone or combined with MF. After 12 days of co-culture with DC and Staphylococcus aureus enterotoxin B (SEB) as antigenic stimulus, cytokine production by autologous T cells was determined by intracellular cytokine staining. Additionally, cells were stimulated with CD3 and CD28 monoclonal antibodies and cytokines were measured in supernatants by multiplex assay. The probiotic strains induced partial maturation of DC. Full maturation of DC was induced for all strains tested when MF was added. The percentage of interleukin (IL)-4 producing T cells was lower in T cell cultures stimulated with B. bifidum matured DC compared to MF and LPS matured DC, which coincided with a higher percentage of interferon (IFN)-gamma-producing T cells. Furthermore, T cells stimulated by B. bifidum matured DC produced significantly more IL-10 compared to MF matured DC. Selected species of the Bifidobacterium genus prime in vitro cultured neonatal DC to polarize T cell responses and may therefore be candidates to use in primary prevention of allergic diseases.

Toll-like receptor 2-mediated dendritic cell activation by a Porphyromonas gingivalis synthetic lipopeptide

A PG1828 gene-encoded triacylated lipoprotein was previously isolated from a Porphyromonas gingivalis lipopolysaccharide preparation as a Toll-like receptor (TLR) 2 agonist and its lipopeptide derivatives were synthesized based on the chemical structure. In the present study, granulocyte-macrophage colony stimulating factor-differentiated bone marrow-derived dendritic cells (BMDDCs) were stimulated separately with the P. gingivalis synthetic lipopeptide N-palmitoyl-S-[2-pentadecanoyloxy, 3-palmitoyloxy-(2R)-propyl]-l-Cys-Asn-Ser-Gln-Ala-Lys (PGTP2-RL) and its glyceryl stereoisomer (PGTP2-SL). Only PGTP2-RL activated BMDDCs from wild-type mice to secrete tumour necrosis factor-alpha, interleukin (IL)-6, IL-10 and IL-12p40, whilst PGTP2-RL-induced cytokine production was eliminated in TLR2 knockout (-/-) BMDDCs. BMDDCs from wild-type mice but not TLR2-/- mice responded to PGTP2-RL as well as Pam(3)CSK(4) by increasing the expression of maturation markers, including CD80 (B7-1), CD86 (B7-2), CD40, CD275 (B7RP-1/inducible T-cell co-stimulatory ligand) and major histocompatibility complex class II. Taken together, these results indicate that the fatty acid residue at the glycerol position in the P. gingivalis lipopeptide plays a pivotal role in TLR2-mediated dendritic cell activation.

Molecular and cellular basis of microflora-host interactions

Mucosal surfaces represent the main sites in which environmental microorganisms and antigens interact with the host. In particular the intestinal mucosal surfaces are in continuous contact with a heterogeneous population of microorganisms of the endogenous flora and are exposed to food and microbes. As a result, the immune system of the host has to discriminate between pathogenic and commensal microorganisms. This article reviews the types of sentinel cells that continuously sense the environment and coordinate immune defenses as well as the mechanisms of the innate and adaptive immune systems that are activated by bacterial and viral molecular patterns leading to inflammatory, allergic, or regulatory immune response with special emphasis on probiotic bacteria.

Impact of lactic Acid bacteria on dendritic cells from allergic patients in an experimental model of intestinal epithelium

Lactic acid bacteria (LAB) are Gram positive nonpathogenic commensal organisms present in human gastrointestinal tract. In vivo, LAB are separated from antigen-presenting cells such as dendritic cells (DC) by the intestinal epithelial barrier. In this study, the impact of one LAB strain (Lactobacillus casei ATCC393) on human monocyte-derived DC from allergic and healthy donors was assessed by using a polarized epithelium model. Confocal and flow cytometer analyses showed that immature DC efficiently captured FITC-labelled L. casei through the epithelial layer. After interaction with L. casei, DC acquired a partial maturation status (i.e., CD86 and CD54 increase) and increased their interleukin (IL)-10 and IL-12 production. Interestingly, after activation by L. casei in the presence of experimental epithelium, DC from allergic patients instructed autologous naïve CD4(+) T cells to produce more interferon-gamma than without the epithelium. Thus by modulating human DC reactivity, LAB and intestinal epithelium might modify T cell immune response and regulate the development of allergic reaction.

Oral feeding of Bifidobacterium bifidum (BGN4) prevents CD4(+) CD45RB(high) T cell-mediated inflammatory bowel disease by inhibition of disordered T cell activation

Probiotics have been considered as preventive agents for the control of inflammatory bowel disease (IBD). In this study, we assessed the immunomodulatory effect of Bifidobacterium bifidum BGN4 on the control of IBD using the CD4(+) CD45RB(high) T cell transfer disease model. The mice were fed for 4 weeks with either a conventional diet containing only skim milk or a diet containing skim milk with 0.3% (w/w) BGN4. The BGN4-fed mice showed normal weight growth, fewer clinical symptoms such as thickened wall and inflammatory cell infiltration, and lower levels of CD4(+) T lymphocyte infiltration and inflammatory cytokine productions than the skim milk-fed mice with IBD in the large intestine. Suppression of these cytokine productions, particularly IFN-gamma and MCP-1, through BGN4 treatment was also observed in the in vitro co-culture between intestinal epithelial cells and T cells. These findings suggested that a BGN4 supplemented diet could be helpful for the control of aberrant immune responses in the intestinal tissue.

Bioecological control of inflammatory bowel disease

It is today generally accepted, that the intestinal bacterial flora is deeply involved in the pathogenesis of human inflammatory bowel diseases (IBDs), although the exact presence of unwanted or lack of specific crucial bacteria are not yet known. Westerners lack to large extent important immunomodulatory and fibre-fermenting lactic acid bacteria (LAB), bacteria which are present in all with a more primitive rural lifestyle. Acute reduction of flora is observed in disease, including IBD, as well as in mental and physical stress. Some observations suggest the mucosa has lost its ability of holding back the pathogenic flora and prevent close contacts between resident microflora and the epithelial surface. Among the manifestations of IBD are increased inflammation and coagulability, impaired cellular membrane function, exaggerated nitric oxide production and impaired short-chain fatty acid production. Animal studies suggest, in addition to reduced flora, an intimate association with immunostimulatory DNA, malfunctioning trifoil factors, increased splanchnic metabolism and reduced availability of natural antioxidants. Treatment with plant fibres, antioxidants and sometimes probiotics have had limited success. The most dramatic effects are seen in the few cases where total faecal replacement (TFR) has been tried. The general experience this far is that the best effects are obtained with compositions of probiotics rather than with single LAB treatments.

Review article: the intestinal lumen as a therapeutic target in inflammatory bowel disease

Undigested carbohydrates reaching the colon can act as competitors for epithelial bacterial receptors, making it difficult for noncommensal bacteria to adhere to them. On the contrary, fermentation of these carbohydrates by anaerobic flora produces - among other substrates - butyrate that is involved in numerous important metabolic processes. These include the provision of energy to the colonocytes, the enhancement of sodium and water absorption and the synthesis of mucus and cell membranes. In addition, butyrate inhibits the nuclear translocation of the transcription factor NFkappaB, which exerts a potent anti-inflammatory activity. Clinical experience with probiotics in inflammatory bowel disease (IBD) is controversial. Whereas some probiotic preparations appear to be useful in ulcerative colitis (UC) and pouchitis, most attempts to use probiotics for treating or preventing recurrence in Crohn's disease have failed. It should be pointed out that - unlike in the small bowel - the colon and ileal pouches are well-established microbiological ecosystems with increasing amounts of a wide variety of bacterial strains. These bacterial strains have a high degree of metabolic interaction with luminal nutrients and a greater probability of developing dysbiosis. With this in mind, the rationale for using pre- and probiotics appears to be stronger for colonic IBD (UC or Crohn's colitis) and pouchitis than for IBD mostly involving the small bowel.

Regulation of murine dendritic cell immune responses by Helicobacter felis antigen

Helicobacter infections are present in approximately 50% of humans, causing severe illnesses such as gastritis and malignancies. Dendritic cells (DC) are critical antigen-presenting cells which link innate and adaptive immune responses. The mechanism of dendritic cell regulation in Helicobacter-induced gastritis is poorly understood. These studies characterized DC isolated from the lamina propria of Helicobacter-infected mice and analyzed innate and adaptive immune responses elicited by Helicobacter antigen (Ag)-pulsed DC. The presence of DC was elevated in the gastric lamina propria infiltrate of infected mice in comparison with controls. After treatment with Helicobacter felis Ag, DC were polarized to secrete interleukin-6 as the dominant cytokine. In the presence of DC and Helicobacter Ag, responder allogeneic T cells in culture exhibited limited cell division. We suggest that the response of DC and T cells to Helicobacter Ag is critical to the chronic persistence of Helicobacter-induced gastritis.

Functional modulation of human intestinal epithelial cell responses by Bifidobacterium infantis and Lactobacillus salivarius

Intestinal epithelial cells (IECs) and dendritic cells (DCs) play a pivotal role in antigen sampling and the maintenance of gut homeostasis. However, the interaction of commensal bacteria with the intestinal surface remains incompletely understood. Here we investigated immune cell responses to commensal and pathogenic bacteria. HT-29 human IECs were incubated with Bifidobacterium infantis 35624, Lactobacillus salivarius UCC118 or Salmonella typhimurium UK1 for varying times, or were pretreated with a probiotic for 2 hr prior to stimulation with S. typhimurium or flagellin. Gene arrays were used to examine inflammatory gene expression. Nuclear factor (NF)-kappaB activation, interleukin (IL)-8 secretion, pathogen adherence to IECs, and mucin-3 (MUC3) and E-cadherin gene expression were assayed by TransAM assay, enzyme-linked immunosorbent assay (ELISA), fluorescence, and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), respectively. IL-10 and tumour necrosis factor (TNF)-alpha secretion by bacteria-treated peripheral blood-derived DCs were measured using ELISA. S. typhimurium increased expression of 36 of the 847 immune-related genes assayed, including NF-kappaB and IL-8. The commensal bacteria did not alter expression levels of any of the 847 genes. However, B. infantis and L. salivarius attenuated both IL-8 secretion at baseline and S. typhimurium-induced pro-inflammatory responses. B. infantis also limited flagellin-induced IL-8 protein secretion. The commensal bacteria did not increase MUC3or E-cadherin expression, or interfere with pathogen binding to HT-29 cells, but they did stimulate IL-10 and TNF-alpha secretion by DCs. The data demonstrate that, although the intestinal epithelium is immunologically quiescent when it encounters B. infantis or L. salivarius, these commensal bacteria exert immunomodulatory effects on intestinal immune cells that mediate host responses to flagellin and enteric pathogens.

Evaluation of immunomodulation by Lactobacillus casei Shirota: immune function, autoimmunity and gene expression

Lactic acid bacteria are claimed to have immunomodulating effects. Stimulation as well as suppression of T helper (Th)1 mediated immune responses, have been described for various strains. Experiments involving Lactobacillus casei Shirota (LcS) detected mainly enhancement of innate immune responses and promotion of Th1 mediated immune reactivity. To confirm and further investigate modulation of Th1 responses and development of autoimmune disease by LcS, the consequences of oral administration of LcS were assessed in several experiments. The effect of LcS varied between the different models. No modulation was found in the mitogen-induced cell proliferation and cytokine release assays in mesenteric lymph nodes of Wistar rats. LcS inhibited the Th1 mediated immune response in an adapted murine Local Lymph Node Assay (LLNA) in BALB/c mice, whereas experimental autoimmune encephalomyelitis (EAE) in Lewis rats was aggravated. These varying effects on Th1 responses indicate that beneficial as well as harmful effects on immune related disorders could occur after LcS consumption. Since microarray analysis is suggested to be more sensitive and predictive than functional tests, gene expression profiling was included as an alternative endpoint in the testing of immunomodulation. The detected gene expression profiles did not reflect the effects of LcS on the immune system. Microarray analysis may therefore have no more predictive value than immune function assays when investigating immunomodulation by probiotics. To gain further insight into effects of probiotics on immune function, experiments including cytokine assays and gene expression analysis combined with disease models could be useful.

Colitogenic and non-colitogenic commensal bacteria differentially trigger DC maturation and Th cell polarization: An important role for IL-6

We investigated whether commensal bacteria modulate activation and maturation of bone marrow-derived DC and their ability to prime CD4(+) T cells. We used Escherichia coli mpk, which induces colitis in gnotobiotic IL-2-deficient (IL-2(-/-)) mice, and Bacteroides vulgatus mpk, which prevents E. coli-induced colitis. Stimulation of DC with E. coli induced TNF-alpha, IL-12 and IL-6 secretion and expression of activation markers. Moreover, stimulation of DC with E. coli increased T cell activation and led to Th1 polarization. Stimulation with B. vulgatus led only to secretion of IL-6, and DC were driven into a semi-mature state with low expression of activation markers and did not promote Th1 responses. B. vulgatus-induced semi-mature DC were non-responsive to stimulation by E. coli in terms of maturation, T cell priming and TNF-alpha but not IL-6 production. The non-responsiveness of B. vulgatus-stimulated DC was abrogated by addition of anti-IL-6 mAb or mimicked with rIL-6. These data suggest that B. vulgatus-induced IL-6 drives DC into a semi-mature state in which they are non-responsive to proinflammatory activation by E. coli. This in vitro mechanism might contribute to the prevention of E. coli-triggered colitis development by B. vulgatus in vivo; high IL-6 mRNA expression was consistently found in B. vulgatus-colonized or B. vulgatus/E. coli co-colonized IL-2(-/-) mice and was associated with absence of colitis.

Anti-inflammatory effect of Lactobacillus casei on Shigella-infected human intestinal epithelial cells

Shigella invades the human intestinal mucosa, thus causing bacillary dysentery, an acute recto-colitis responsible for lethal complications, mostly in infants and toddlers. Conversely, commensal bacteria live in a mutualistic relationship with the intestinal mucosa that is characterized by homeostatic control of innate responses, thereby contributing to tolerance to the flora. Cross-talk established between commensals and the intestinal epithelium mediate this active process, the mechanisms of which remain largely uncharacterized. Probiotics such as Lactobacillus casei belong to a subclass of these commensals that modulate mucosal innate responses and possibly display anti-inflammatory properties. We analyzed whether L. casei could attenuate the pro-inflammatory signaling induced by Shigella flexneri after invasion of the epithelial lining. Cultured epithelial cells were infected with L. casei, followed by a challenge with S. flexneri. Using macroarray DNA chips, we observed that L. casei down-regulated the transcription of a number of genes encoding pro-inflammatory effectors such as cytokines and chemokines and adherence molecules induced by invasive S. flexneri. This resulted in an anti-inflammatory effect that appeared mediated by the inhibition of the NF-kappaB pathway, particularly through stabilization of I-kappaBalpha. In a time-course experiment using GeneChip hybridization analysis, the expression of many genes involved in ubiquitination and proteasome processes were modulated during L. casei treatment. Thus, L. casei has developed a sophisticated means to maintain intestinal homeostasis through a process that involves manipulation of the ubiquitin/proteasome pathway upstream of I-kappaBalpha.

Probiotics and the immune response

Beneficial effects exerted by probiotic bacteria in the treatment of human disease may be broadly classified as those effects which arise due to activity in the large intestine and are related to colonization or inhibition of pathogen growth; and those effects which arise in both the small and large intestine, and are related to enhancement of the host immune response and intestinal barrier function. In a strain dependent fashion, probiotic bacteria can enhance intestinal barrier function and modulate signal transduction pathways and gene expression in epithelial and immune cells. Oral administration of live probiotics and bacterial structural components can also differentially modulate dendritic cells resulting in an increased production of IL-10 and regulatory T cells. Both innate and adaptive immune responses can be modulated by probiotic bacteria.

Induction of systemic and mucosal immune response and decrease in Streptococcus pneumoniae colonization by nasal inoculation of mice with recombinant lactic acid bacteria expressing pneumococcal surface antigen A

Mucosal epithelia constitute the first barriers to be overcome by pathogens during infection. The induction of protective IgA in this location is important for the prevention of infection and can be achieved through different mucosal immunization strategies. Lactic acid bacteria have been tested in the last few years as live vectors for the delivery of antigens at mucosal sites, with promising results. In this work, Streptococcus pneumoniae PsaA antigen was expressed in different species of lactic acid bacteria, such as Lactococcus lactis, Lactobacillus casei, Lactobacillus plantarum, and Lactobacillus helveticus. After nasal inoculation of C57Bl/6 mice, their ability to induce both systemic (IgG in serum) and mucosal (IgA in saliva, nasal and bronchial washes) anti-PsaA antibodies was determined. Immunization with L. lactis MG1363 induced very low levels of IgA and IgG, possibly by the low amount of PsaA expressed in this strain and its short persistence in the nasal mucosa. All three lactobacilli persisted in the nasal mucosa for 3 days and produced a similar amount of PsaA protein (150–250 ng per 10⁹ CFU). However, L. plantarum NCDO1193 and L. helveticus ATCC15009 elicited the highest antibody response (IgA and IgG). Vaccination with recombinant lactobacilli but not with recombinant L. lactis led to a decrease in S. pneumoniae recovery from nasal mucosa upon a colonization challenge. Our results confirm that certain Lactobacillus strains have intrinsic properties that make them suitable candidates for mucosal vaccination experiments.

Living drugs for gastrointestinal diseases: the case for probiotics

Nonpathogenic micro-organisms may contain or produce molecules of potential therapeutic interest. This led to the concept of using ingested living micro-organisms to produce and transport these molecules to targets in the proximal or distal intestine. Several characteristics of this pharmacological approach are very original: potential for in vivo production of active molecules, for targeting immune cells, for presenting immunogenic molecules in a microbial context, for duodenal delivery using bile sensitivity. Probiotics have been studied for some decades and more recently worm eggs have also received some interest. This paper summarizes facts (especially results of randomized controlled trials and pharmacokinetic studies), and ideas about the use of probiotics to treat or prevent gastrointestinal diseases. The safety of this approach (exceptional cases of infections have been observed), and the potential for using new agents or genetically modified micro-organisms (ongoing trials in humans with Crohn's disease) are also discussed.

Probiotics: facts and myths

In recent years there has been a significant upsurge in research on the characterisation and verification of the potential health benefits associated with the use of probiotics. In addition, the market for probiotics continues to expand exponentially as consumers (mostly healthy individuals) rely on health claims made by manufacturers to make their choices. This review appraises the available evidence for and against the health claims associated with probiotics. The use of probiotics in promoting gastrointestinal health and immunity, and their use in the prevention of urogenital infections, allergies and cancer are reviewed. Furthermore, issues surrounding the use of probiotics in healthy individuals, the safety of probiotics and regulatory concerns are addressed. There is scientific evidence that specific strains of probiotic microorganisms confer health benefits on the host and are safe for human use. However, this evidence cannot be extrapolated to other strains, as these effects are strain-specific. Probiotics have potential health benefits for conditions such as gastrointestinal infections, genitourinary infections, allergies and certain bowel disorders, all of which afflict a considerable proportion of the global population. However, considerable work is still needed to confirm these potential health benefits.

Mucosal immunity and allergic responses: lack of regulation and/or lack of microbial stimulation?

Allergic hyperreactivity is defined as an exaggerated immune response [typically immunoglobulin E (IgE) but also non-IgE mediated] toward harmless antigenic stimuli. The prevalence of allergic disease has increased dramatically during the last 20 years, especially in developed countries. Both genetic and environmental factors contribute to susceptibility to allergy. Evidence has emerged supporting the hypothesis that a reduction in antigenic stimulation brought about by widespread vaccination, improvements in standards of hygiene, and extensive use of antibiotics has contributed to the dysregulation of T-helper 2 cell (Th2) type responsiveness that typifies allergy. Regulation of the inherently Th2-biased mucosal immune response is crucial both to the maintenance of homeostasis at this strategic defensive barrier and to the prevention of allergic disease. The ability of Th1 responses to counter-regulate Th2 reactivity is well characterized. More recently, interest has centered on regulatory T cells, which can suppress both Th1 and Th2 cells through the secretion of immunosuppressive cytokines such as interleukin-10 and transforming growth factor-beta. In this review, we discuss the basic cellular mechanisms of allergic diseases at mucosal surfaces, focusing on allergic responses to food, before examining newer work that suggests the induction of allergic hyperreactivity is due to a deficient immunoregulatory network, a lack of microbial stimulation, or both.

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.

Probiotics ameliorate recurrent Th1-mediated murine colitis by inducing IL-10 and IL-10-dependent TGF-beta-bearing regulatory cells

Recent studies of murine models of mucosal inflammation suggest that, whereas some kinds of bacterial microflora are inducers of disease, others, known as probiotics, prevent disease. In the present study, we analyzed the regulatory cytokine and cell response to probiotic (VSL#3) administration in the context of the Th1 T cell colitis induced by trinitrobenzene sulfonic acid treatment of SJL/J mice. Daily administration of probiotics for 3 wk to mice during a remission period between a first and second course of colitis induced by trinitrobenzene sulfonic acid, resulted in a milder form of recurrent colitis than observed in mice administered PBS during this same period. This protective effect was attributable to effects on the lamina propria mononuclear cell (LPMC) population, because it could be transferred by LPMC from probiotic-treated mice to naive mice. Probiotic administration was associated with an early increase in the production of IL-10 and an increased number of regulatory CD4+ T cells bearing surface TGF-beta in the form of latency-associated protein (LAP) (LAP+ T cells). The latter were dependent on the IL-10 production because administration of anti-IL-10R mAb blocked their appearance. Finally, the LAP+ T cells were essential to the protective effect of probiotics because administration of anti-IL-10R or anti-TGF-beta at the initiation of recurrent colitis induction or depletion of LAP+ T cells from LPMC abolished the latter's capacity to transfer protection to naive recipients. These studies show that probiotic (VSL#3) administration during a remission period ameliorates the severity of recurrent colitis by inducing an immunoregulatory response involving TGF-beta-bearing regulatory cells.

Lactobacilli activate human dendritic cells that skew T cells toward T helper 1 polarization

Professional antigen-presenting dendritic cells (DCs) are critical in regulating T cell immune responses at both systemic and mucosal sites. Many Lactobacillus species are normal members of the human gut microflora and most are regarded as safe when administered as probiotics. Because DCs can naturally or therapeutically encounter lactobacilli, we investigated the effects of several well defined strains, representing three species of Lactobacillus on human myeloid DCs (MDCs) and found that they modulated the phenotype and functions of human MDCs. Lactobacillus-exposed MDCs up-regulated HLA-DR, CD83, CD40, CD80, and CD86 and secreted high levels of IL-12 and IL-18, but not IL-10. IL-12 was sustained in MDCs exposed to all three Lactobacillus species in the presence of LPS from Escherichia coli, whereas LPS-induced IL-10 was greatly inhibited. MDCs activated with lactobacilli clearly skewed CD4(+) and CD8(+) T cells to T helper 1 and Tc1 polarization, as evidenced by secretion of IFN-gamma, but not IL-4 or IL-13. These results emphasize a potentially important role for lactobacilli in modulating immunological functions of DCs and suggest that certain strains could be particularly advantageous as vaccine adjuvants, by promoting DCs to regulate T cell responses toward T helper 1 and Tc1 pathways.

Commensal bacteria in the gut: learning who our friends are

PURPOSE OF REVIEW

Recent evidence has shown that commensal bacteria regulate intestinal physiology, development, and function. This review focuses on new insights into the effects of these organisms on health and disease.

RECENT FINDINGS

Gastrointestinal tract development and function is determined by communication between the intestinal epithelium and commensal bacteria. Important regulatory interactions between these cells are being defined with early evidence indicating both beneficial and harmful consequences to the host. A subgroup of these bacteria overlaps with probiotic organisms that have preventative and therapeutic potential for diarrhea, inflammatory bowel disease (IBD), atopy, and other diseases, whereas evidence indicates some "nonpathogenic" commensal bacteria may promote an environment conducive to IBD, cancer, and other diseases.

SUMMARY

Progress in understanding the relation between commensal bacteria and human health is likely to promote the identification of new approaches to disease prevention and treatment.