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Home , Adaptive immune system, Immune system, Mucosal immunology

European Review for Medical and Pharmacological Sciences 2013; 17: 323-333 The role of intestinal and the

F. PURCHIARONI, A. TORTORA, M. GABRIELLI, F. BERTUCCI, G. GIGANTE, G. IANIRO, V. OJETTI, E. SCARPELLINI, A. GASBARRINI

Department of Internal , School of Medicine, Catholic University of the Sacred , Gemelli Hospital, Rome, Italy

Abstract. – BACKGROUND: The gut Introduction is an ecosystem consisting of a great number of commensal living in symbiosis with the The intestinal microbiota is composed of 1013-14 host. Several data confirm that is engaged in a dynamic interaction with the in- (Figure 1), with at least 100 testinal innate and , af- times as many as our , the micro- fecting different aspects of its development and biome. Its composition is individual-specific, function. ranges among individuals and also within the AIM: To review the immunological functions same individual during . Many factors can in- of gut microbiota and improve knowledge of its fluence the gut flora composition, as diet, age, therapeutic implications for several intestinal , illness, and lifestyle. The gas- and extra-intestinal associated to dys- regulation of the immune system. trointestinal (GI) tract contains both “friendly” METHODS: Significant articles were identified bugs, such as Gram-positive Lactobacilli and Bi- by literature search and selected based on con- fidobacteria dominate (> 85% of total bacteria), tent, including atopic diseases, inflammatory and potential , coexisting in a bowel diseases and treatment of these condi- complex symbiosis. Several evidences show that tions with . intestinal microbiota supports energy metabolism RESULTS: Accumulating evidence indicates and immune and trophic functions in the host. that intestinal microflora has protective, meta- bolic, trophic and immunological functions and Furthermore, the concept of a “super-” is able to establish a “cross-talk” with the im- has emerged to reflect the physiologic impor- mune component of mucosal , compris- tance of mutually advantageous bidirectional ing cellular and soluble elements. When one or host-microbe interactions in the gut. When this more steps in this fine interaction fail, autoim- equilibrium is altered several gastrointestinal and mune or auto-inflammatory diseases may occur. extraintestinal diseases can occur. Furthermore, it results from the data that probi- otics, used for the treatment of the diseases Gut Microbiota and caused by the dysregulation of the immune sys- Intestinal Mucosa Development tem, can have a beneficial effect by different mechanisms. Intestinal microflora has protective, metabolic, CONCLUSIONS: Gut microbiota interacts with trophic and immunological functions. In fact, to- both innate and adaptive immune system, play- gether with digestive , mucins, peristal- ing a pivotal role in maintenance and disruption sis, epithelial barrier with tight junctions, micro- of gut immune quiescence. A cross talk between biota belongs to the so called non-immune com- the mucosal immune system and endogenous microflora favours a mutual growth, survival and ponent of mucosal immunity and is able to estab- inflammatory control of the intestinal ecosys- lish a “cross-talk” with the immune component tem. Based on these evidences, probiotics can of mucosal immunity, comprising cellular and be used as an ecological in the treat- soluble elements1. Commensal microbiota can ment of immune diseases. profoundly influence the development of the gut mucosal immune system and be crucial in pre- Key Words: venting exogenous intrusion, both by Gut microbiota, Intestinal immune system, Atopic direct interaction with pathogenic bacteria and by diseases, Inflammatory bowel , Probiotics. stimulation of the immune system. Comparative

Corresponding Author: Flaminia Purchiaroni, MD; e-mail: [email protected] 323 F. Purchiaroni, A. Tortora, M. Gabrielli, F. Bertucci, G. Gigante, G. Ianiro, et al.

Figure 1. GUT microbiota composition and distribution. studies in germ-free and conventional favours a mutual growth, survival and inflamma- have established that the intestinal microflora is tory control of the intestinal ecosystem. A typi- essential for the development and function of the cal feature of innate immunity is the ability of mucosal immune system especially during early distinguishing between potentially pathogenic life, a process important to overall immunity in microbial components and harmless by adults2. Different studies over the time have “pattern recognition receptors” (PRRs) and demonstrated that the development of the ultra- among those toll-like receptors (TLRs) enable structure of the intestinal mucosa is dependent on mammalian cells to recognize conserved charac- luminal bacteria. For example, villus teristic present on microorganisms in germ-free mice develop poorly during wean- and described as pathogen-associated molecular ing and remain poorly developed until adulthood, patterns (PAMPs)9-11. Since these molecules e.g. indicating a microbial contribution in angiogene- , peptidoglycans, , sis of villus-core3-5. Germ-free animals show de- formylated peptides and others, are present also fects in the development of gut-associated lym- on commensal bacteria it seems more precise to phoid (GALT) and production, call them microbe-associated molecular patterns fewer cellular lymphoid follicles (Peyer’s patch- (MAMPs). In TLRs are present on es), reduced cellular lamina propria, and fewer , , dendritic cells (DCs), plasma cells in of the mesenteric intestinal epithelial cells (ECs) and other cells node (MLNs) compared with animals un- belonging to . Over the der conventional conditions6-8. The microbiota al- time, researches have led different studies so contributes to the development of intra-epithe- demonstrating that microbiota can regulate the lial (IEL). intestinal innate immune system by modulating TLRs expression on immunosensory cells sur- Gut Microbiota and Innate Immune System face through MAMPs; recognition of microbes A cross talk between the mucosal innate im- leads to of nuclear factor-kappa B mune system and endogenous microflora (NF-κB) signaling pathway and consequently

324 The role of intestinal microbiota and the immune system triggers production, up-regulation of tions by adhering to pathogens15,16 and protect co-stimulatory molecules on presenting against gastric and duodenal . The cells, leading to activation of T cells. Thus, in- also provide a medium in which bacterial- nate immunity is tightly linked to adaptive im- derived metabolites with signaling functions are munity9-11. secreted and concentrated. Thus, the mucus layer In physiological conditions, complex and may promote mutualism by keeping bacteria at poorly understood cell interactions regulate in bay and restricting overt immune stimulation the gut responses to antigens and to anti- while facilitating host-commensal or commensal- gens of the normal microflora in close proximity commensal cross-talk through the diffusion of to a large population of rapidly renewing ECs, bacterial products. specialized IELs and other immunologically ac- tive cells present in the mucosa. Cells of innate Gut Microbiota and immunity are able to produce essential Adaptative Immune System for inflammatory reactions as well as factors crit- An important immune compartment in the ical for the subsequent initiation of specific im- bowel is the lamina propria, where is present a munity. The contact with bacteria and their com- large number of macrophages, DCs, T cells, and ponents through the PRRs on their surface initi- IgA-secreting B cells. Acquired immune re- ates innate immunity responses11. So far, the ex- sponse is primarily imprinted in GALT (Peyer’s pression and modulation of TLRs on DCs (which patches (PPs) and MLNs)17-19. Indeed, regulatory represent the link between innate and adaptive cells are also present in the lamina propria where immunity) and on ECs play an active role during they maintain tolerance to and self-anti- interaction with external environment and in reg- gens. In the lamina propria are also present resi- ulating the mucosal immune responses. dent CD4, CD8 and B cells, while some CD8 ECs are perhaps the most important part of lymphocytes migrate to tip of the villous, where the innate defense mechanism of mucosal sur- they became IELs20,21. The B cells in the lamina faces. It has been recently shown that ECs are propria are activated and become IgA-producing directly involved in various immune processes, plasma cells. The IgA is transported across the in addition to their absorptive, digestive and se- epithelial layer and secreted in the gut lumen. cretory functions. For example, they show a pe- Antigens sampled in the lamina propria are taken culiar capacity of transporting secretory im- up by DCs and transported via draining lymphat- munoglobulins, produced by plasma cells in ic vessels to the MLNs and secondarily to the gut lamina propria, to the lumen, by binding these lymphoid tissue (PPs), to response to gut anti- to a of polymeric immunoglobulins gens. The important feature is the presence of (pIgR)12. There is also strong evidence that ECs specialized ECs, called microfold, or M cells. can present antigens13. ECs express numerous The M-cells sample the antigens in the gut lumen molecules involved in : and transport bacteria to professional antigen- transplantation antigens class I, both classic and presenting-cells, such as DCs on their basolateral non-classic (HLQ A-C, HLA E, CD1d, MI- surface22. CA/MICB), transplantation antigens class II. The larger part of the bacteria are killed by ECs can allow the interaction with other cells of macrophages, while those transferred by M-cells the immune system and participate to the in- to DCs can survive for several days. In healthy flammatory response to microbial invasion. Hu- individuals DCs sample the antigens and induce man intestinal ECs express an important T-cells unresponsiveness, probably by stimulat- -binding CD14 ing balanced differentiation of naïve T cells into that, together with TLRs, can maintain the intri- either effectors cells (Th1, Th2, Th17) or regula- cate balance between the self and the environ- tory T cells (Tr1, Th3), to maintain tolerance to- ment in the gut14. Furthermore, these cells re- ward commensal and food antigens. Specialized lease soluble form of CD14 which may be im- DCs in the lamina propria can sample luminal plicated in shaping the interaction between the antigens directly through extended cellular mucosal immune system and gut bacteria. processes that penetrate in the lumen. DCs con- Another mechanism for microbiota’s im- taining antigens and expressing CD103 migrate munomodulation is the capacity of regulating the to lymphoid tissue, where interact with naïve production of the mucins from intestinal goblet lymphocytes to generate primed effectors lym- cells. Mucins may directly limit intestinal infec- phocytes. DCs containing alive bacteria migrate

325 F. Purchiaroni, A. Tortora, M. Gabrielli, F. Bertucci, G. Gigante, G. Ianiro, et al. to the MLNs and induce IgA-producing plasma crobiota25-29 and this explains the remarkable in- cells. After the antigens is cleared, most effector ter-individual variability observed in the cells have died leaving a cohort of long-lived gut bacteria during the first months of life30. memory cells that can rapidly increase immunity Many studies suggest that the intestinal microflo- on reencounter with their cognate antigen. Once ra induces maturation of host immunity and a an antigen has been detected by DCs, it is “distortion” in any of its functions could poten- processed in its endoplasmic reticulum to form tially contribute to the development of allergic small peptides that can be presented on MHC diseases. This distortion comes from environ- class II molecules to lymphocytes in GALT. mental changes associated with western Most of DCs reside in the lamina propria and mi- lifestyles, including dietary changes, grate via afferent lymphatic to GALT. Entry of use and other medications, such as antiacids, pro- both DCs and lymphocytes into GALT is depen- ton pump inhibitors, and non-steroidal anti-in- dent on specific adhesion molecules (L-selectin, flammatory . In 1989, Strachan introduced CCR7 and L-selectin ligand, CCL21 interaction). the “”, which states that a lack DCs direct the lymphocytes location where the of microbial exposure during childhood results in antigen is most likely encountered by imprinting a perturbation in gut microbiota composition and tissue specificity. DCs also determine the nature in aberrant immune responses to innocuous anti- of : early production of IL-2 is gens later in the life31,32 with development of important for the development of an IFN-δ-se- atopic diseases, defined as chronic inflammatory creting Th1 response; Th17 response is driven by disorders caused by aberrant T-helper 2 (Th2)- IL-1, IL-6 and IL-23. Interaction with immature type immune responses against common innocu- DCs or the presence of IL-10 and TGF-beta can ous environmental antigens () in suscep- lead to induction of regulatory T cells with an an- tible individual33 (Figure 2). The initial immuno- ti-inflammatory response. Lymphocytes logical explanation for this hypothesis was a lack in the lymphoid tissue change adhesion mole- of microbial antigen-induced immune deviation cules expressions and lose the ability to enter from the Th2 cytokine profile to a Th1-type pro- lymphoid tissue by down regulation of CCR7 file, resulting in the development of enhanced and L-selectin expression, while gaining expres- Th2-cell responses to allergens34-36. However, this sion of new adhesion molecules that direct mi- explanation does not take into account that the gration to peripheral tissue. This essential feature prevalence of Th1-associated diseases, such as is called “homing”. Crohn’s disease, and multiple When one or more steps in this complex sys- sclerosis, was also increasing and that chronic tem fail, autoimmune or auto-inflammatory dis- (helminth) inducing eases may occur. strong Th2 responses and high IgE levels are not associated with an increased risk of allergy37. An Gut Microbiota and Atopic Diseases alternative interpretation conceives anti-inflam- The prevalence of allergic diseases (such as matory immune responses to be of fundamental eczema, food , hay and ) has importance in the development of mucosal and been increasing worldwide during the past 40 systemic tolerance38. These immunosuppressive years, especially in the western countries and mechanisms are managed by regulatory T-cell among children23. Although genetic susceptibili- classes (Treg cells) controlling through inter- ty plays a pivotal role in atopy changes, the leukin (IL)-10 and/or tumor prevalence of these diseases has been much (TGF)-β] both Th1 and Th2 responses and hence faster than any possible shift in genetic constitu- the development of both atopic and autoimmune tion. Therefore, accumulating evidence indicates diseases38,39. Indeed, the importance of a delicate that environmental factors in the gut, such as balance between -specific Treg cells and commensal bacteria, may play an important role allergen-specific Th2 cells in healthy and allergic in the maintenance and disruption of gut immune immune responses to common environmental al- quiescence24. The development of the intestinal lergens was demonstrated in a study conducted microflora starts immediately after birth and de- by Akdis et al40. Moreover, duodenal biopsies of pends on bacteria from the and the sur- healthy and infants with multiple food al- rounding environment; in particular, type of de- lergy showed that the dominant mucosal abnor- livery (vaginal or caesarian), -feeding, diet mality was not Th2 deviation but impaired gener- and country of birth influence the infant gut mi- ation of TGF-β-producing Treg cells41. The epi-

326 The role of intestinal microbiota and the immune system

Figure 2. Interactions between microbiota and immune cells in allergic diseases development. demiological findings and the experimental evi- particles, fluids and microbes are also swal- dence available so far suggest that both the re- lowed. Thus, the GI tract is exposed to any anti- duced immune suppression by T-reg cells and the gens as the . Since ingestion of lack of immune deviation from a Th2 to a Th1 antigens can induce tolerance to that antigen profile are involved42. Moreover, the impact of (oral tolerance), the GI tract may act as a “sen- the gut microbiota on the development of IgA an- sor” for the development of tolerance to inhaled tibody responses, which contribute to pathogen antigens46,47. In addition, induced regulatory T and allergen exclusion in the gut lumen, may also cells may move to other tissues throughout the be involved43. In fact, the effects of the gut mi- body as the respiratory tract48. crobiota on the immune system may not only be related to food antigens but also to aero-allergens and to the manifestation of allergic airway symp- Gut Microbiota and toms. Noverr et al44 developed a mouse model to Inflammatory Bowel Diseases demonstrate experimentally that antibiotic thera- The term inflammatory bowel disease (IBD) py leading to bacterial and fungal microbiota comprises two types of chronic intestinal disor- changes could predispose a host to allergic air- ders: Crohn’s disease (CD) and ulcerative colitis way diseases. In addition, oral treatment with (UC). CD is characterized by deep Lactobacillus reuterii has recently been shown to with , and may affect any part of the inhibit the allergic airway response in mices45. GI tract, although it most commonly affects the These results support the possibility that afferent distal and caecum. UC is largely limited events in allergic sensitization may occur outside to the colon, particularly the distal colon and the of and involve host-microbiota communi- rectum49, and causes more superficial ulceration. cation. The gut can affect the systemic immune The initial trigger responsible for the onset of system and local inflammation in remote tissues, IBD is not known yet but it seems that it in- such as the respiratory tract, remains to be deter- volves a complex interplay between the immune mined. However, it has been shown that inhaled system, environmental factors, such as stress, di-

327 F. Purchiaroni, A. Tortora, M. Gabrielli, F. Bertucci, G. Gigante, G. Ianiro, et al. et and enteric infections caused by some lated of IL-10. Oral administration of (i.e. Mycobacterium avium subspecies either live F. prausnitzii or its supernatant re- paratuberculosis, Clostridium difficile, entero- duced the severity of TNBS (2,4,6-trinitroben- toxigenic Bacteroides fragilis, adherent/invasive zenesulfonic acid) colitis and corrected the asso- E. coli, Campylobacter spp, spp.), ciated dysbiosis. In parallel, the abundance of E. and host genotype. Accumulating evidence sug- coli is increased in IBD. E coli isolated from CD gests that IBD results from an inappropriate in- patients express uropathic-like virulence factors flammatory response to intestinal microbes in a that are postulated to facilitate mucosal inva- genetically susceptible host. The role of the mi- sion56. Compositional changes of the microbiota crobiota in IBD has been inferred by the follow- (dysbiosis) in IBD subsets may contribute to dis- ing experiments: (1) suppressing micro-- ease severity, since abnormal corre- isms (using or gnotoxenic animals); lated with the occurrence of in CD pa- (2) adding micro- or microbial compo- tients, and IBD patients with dysbiosis under- nents (e.g. probiotics, CpG-DNA, culture super- went surgery at a younger age than those with natants); (3) altering the composition of the mi- normal microbiotas54. crobiota using substrates; (4) studies in knockout animals lacking receptors to specific Treatment of Atopic Dieases: Probiotics microbial signals50. These experiments have Probiotics such as Lactobacilli spp., certain shown microbial and host specificity50. Studies types of , and Bifidobacteria spp in knockout animals have revealed cross talk be- are alive microorganisms with a vast array of tween the intestinal microbes and the host. Mi- therapeutic potential. Probiotics have a beneficial crobial molecules such as lipopolysaccharide, effect on intestinal mucosa via several proposed peptidoglycans, and bacterial DNA, mechanisms that include suppression of the are recognised by specific receptors on intestinal growth and binding of pathogenic bacteria, im- and/or immune cells. These receptors comprise provement of the barrier function of the epitheli- the TLRs and nucleotide oligomerisation bind- um, and alteration of the immune activity of the ing domains (NOD)-like receptors. Noticeably, host57,58. Probiotics secrete short chain fatty polymorphisms of some of these receptors with decrease of luminal pH and production of [NOD2, TLR4 and others, such as caspase re- bactericidal proteins58. , a byproduct cruitment domain family, member 15 of bacterial fermentation of fiber, has been (CARD15)] are associated with an increased risk shown to nourish colonic enterocytes enhancing of IBD in models and in humans51. On mucosal integrity59,60. The DNA of or- the other hand, the normal intestine secretes var- ganisms may also inhibit of ECs61,62. In ious peptides with anti-microbial properties, in- addition, probiotics may improve bowel dys- cluding , , cathelicidins and motility59. secretory immunoglobulins. Defensins are syn- The “hygiene hypothesis” provides a rationale thesised in Paneth cells and released in the in- for using probiotics in order to modify gut micro- testinal crypts and (other ones) at the epithelial biota and thereby shaping the immune response surface and trapped in the mucus layer. Notice- of the host especially during infancy. Several ably again, several studies have shown a reduced studies demonstrated that the composition of the expression of α-defensins in ileal CD and an at- gut microbiota differs between healthy and aller- tenuated induction of β-defensins in the colon of gic infants, as in countries with a high and low patients with colonic IBD. Moreover, reports on prevalence of allergies63-67. In particular, main faecal samples using modern molecular tech- microfolra composition changes associated with niques have shown that, as compared with con- allergic trait are represented by less frequent col- trol subjects, patients with CD and those UC onization with Lactobacilli and lower counts of have depletion of and reduced diversity in both Bifidobacteria63-66. According to these evidences, faeces and mucosa-associated phyla Firmicutes probiotics are potentially able to modulate and and Bacteroidetes52-55, which promote GI health reconstitute the microbiota of allergic patients. in multiple ways53. Researchers have led studies Although this area of research is relatively new which shown that in vitro peripheral (the first probiotic intervention trial dates back to mononuclear cell stimulation by F. prausnitzii (a 1997), several potential targets for the probiotics major member of the family Firmicutes) de- can be identified, such as degradation of enteral creased IL-12 and IFN-γ production and stimu- antigens, normalization of the properties of aber-

328 The role of intestinal microbiota and the immune system rant indigenous microbiota and of gut barrier oping allergic diseases later. No differences in functions, regulation of the secretion of inflam- the frequency of allergic diseases and sensitiza- matory mediators, and promotion of the develop- tion were shown between the probiotic mixture ment of the immune system. The probiotics’ ef- (LGG, Lactobacillus rhamnosus, Bifidobacteri- fects are strain-specific: different bacteria or um breve, and propionibacteria) and placebo components have defined adherence sites, im- groups after 5 years of follow-up in Kuitunen munologic effects, and varied effects in the study72. In this latter, 1223 with infants healthy versus inflamed mucosal milieu. at high risk for allergy were randomized to re- Over the time, different studies have been led ceive the probiotic mixture or placebo during the with the aim of demonstrating probiotics’ benefi- last month of and their infants to addi- cial effect in several allergic conditions. In the tionally receive prebiotic galactoligosaccharide, Majamaa study68, the clinical and immunologic from birth until the age of 6 months. However, effects of cow’s milk elimination without and less IgE-associated allergic diseases occurred in with the addition of the Lactobacillus GG (LGG) cesarean-delivered children receiving a probi- in an extensively hydrolyzed whey formula in otics mixture. The study by Taylor et al73 showed children with atopic eczema and cow’s milk al- an opposite effect. In 178 newborns of allergic lergy were evaluated. The second part of the women, Lactobacillus acidophilus supplementa- study involved 10 breast-fed infants who had tion for the first 6 months of life failed to reduce atopic eczema and cow’s ; in this the risk of and increased the group, LGG was given to nursing mothers. These risk of allergen sensitisation. studies showed a significant change in the SCO- Thus, these results suggest that further studies RAD (a scoring system which combines an as- are needed to better understand the mechanisms sessment of disease extent using the rule of nines of allergic disorders and the role of probiotics in with six clinical features of disease intensity: . erythema/darkening, oedema/papulation, ooz- ing/crust, excoriation, lichenification/prurigo and Treatment of IBD: Probiotics dryness) after intervention in infants receiving Probiotics can be used as “ecological treat- LGG and no significant change in the other ments” even in IBD. The rationale of using them group. In the breast-fed infants the SCORAD in IBD has been validated by different studies, score improved statistically after 1 month of which focused on their mechanism of action. In treatment. To test the effect of probiotics in the particular, it has been shown that: primary prevention of atopic disease, Kalliomaki et al69 assigned 159 mothers to receive placebo or 1. certain probiotic strains can induce the secre- LGG daily for 4 weeks before expected delivery. tion of peptides by intestinal After delivery, LGG or placebo were taken post- cells. can be secreted natally for 6 months. In children aged 2 years, either by bacteria (bacteriocins), or specialized the frequency of atopic eczema in the probiotic epithelial Paneth cells (defensins) and can reg- group was half that of the placebo group. The 7- ulate the bacterial load to the mucosa74. It has year follow-up visit confirmed that the cumula- been shown that CD is associated with a defect tive risk of developing eczema during the first 7 in defensins75, and probiotics, which could en- years of life was significantly lower in the LGG hance these peptides, thus appear as attractive group than in the placebo group. However, atopic candidates; sensitization was similar between groups, sug- 2. some probiotics can reinforce the integrity of gesting that the preventive effect on eczema was the intestinal barrier. It is well-known that an not IgE-mediated70. increase in intestinal permeability is suspected The clinical studies do not completely agree as a major factor in the of IBD59. about the efficacy of probiotics in allergic dis- Thus, probiotics seem to be able to normalize eases. In the Abrahamsson et al study71, the cu- intestinal permeability and some Lactobacilli mulative prevalence of eczema was similar in ba- can inhibit pathogen adhesion inducing ex- bies receiving Lactobacillus reuteri before deliv- pression of mucins; ery and up to 12 months old and in the control 3. some probiotics seem to have an immunomod- group. The L. reuteri group had a lower impact ulatory action, since they can stimulate innate of IgE-associated eczema during the second year immunity and educate adaptive immunity to- and, therefore, possibly a reduced risk of devel- wards Th1, Th2 or Th3 (tolerance) responses.

329 F. Purchiaroni, A. Tortora, M. Gabrielli, F. Bertucci, G. Gigante, G. Ianiro, et al.

Probiotics have been assessed in animal mod- teractions and the availability of novel techniques els and some clinical trials. Oral administration that are able to finely identify microbiota modifi- of the VSL#3 consortium of probiotics76 was cations in different clinical subsets seem to be shown to normalize barrier function in IL-10 -/- the key to the success of effective probiotics mouse model of IBD77. VSL#3 is a probiotic treatment in IBD patients. cocktail consisting of eight different gram-posi- tive organisms: Bifidobacterium longum, Bifi- dobacterium infantis, Bifidobacterium breve, References Lactobacillus acidophilus, Lattobacillus casei, Lattobacillus delbrueckii spp. bulgaricus, Latto- 1) LIU Z, LI N, NEU J. Tight junctions, leaky intestines, bacillus plantarum, and Streptococcus salivarius and pediatric diseases. Acta Pediatr 2005; 94: spp. Thermophilus77. The characteristics of pro- 386-393. biotic bacteria suggest that some bacterial 2) SRIKANTH CV, MC CORMICK BA. Interactions of the in- species may be effective in the treatment of IBD testinal epithelial with the pathogen and the in- digenous microbiota: a three-way crosstalk. Inter- by strengthening the epithelial barrier. For exam- discip Perspect Infect Dis 2008; 2008: 626827. - - ple, VSL#3 treatment of IL-10 / mice with IBD Epub 2008 Oct 29. resulted in a normalization of colonic physiologi- 3) NEU J. Perinatal and neonatal manipulation of the cal function and barrier integrity along with a re- intestinaln microbiome: a note of caution. Nutr duction in mucosal levels of pro-inflammatory Rev 2007; 65(6 Pt 1): 282-285. cytokines and a significant improvement in histo- 4) STAPPENBECK TS, HOOPER LV, GORDON JI. Develop- logical disease by secretion of soluble factors en- mental regulation of intestinal angiogenesis by in- hancing the barrier integrity77. Other studies have digenous microbes via Paneth cells. Proc Natl Acad Sci USA 2002; 99: 15451-15455. confirmed that probiotic bacteria may enhance 5) CONROY ME, WALKER WA. Intestinal immune health. the integrity of the tight junctions between the in- Nestle Nutr Workshop Ser Pediatr Program 2008; testinal epithelial cells during infections or in- 62: 111-121; discussion 121-5. 78 flammatory conditions . Thus, colonization with 6) RAKOFF-NAHOUM S, PAGLINO J, ESLAMI-VARZANEH F, probiotic bacteria may lead to decreased expo- EDBERG S, MEDZHITOV R. Recognition of commen- sure of immune cells to the bacterial antigens sal microflora by toll-like receptors is required that are believed to drive IBD. Rachmiliwitz et for intestinal homeostasis. Cell 2004; 118: 229- al79 showed that protective effects of probiotic 241. microorganisms (VSL#3) in a dextran sulfate 7) MACPHERSON AJ, HARRIS NL. Interactions between commensal intestinal bacteria and the immune sodium model of experimental colitis are mediat- system. Nat Rev Immunol 2004; 4: 478-485. ed by DNA that was recognized by the mucosal 8) FALK PG, HOOPER LV, MIDTVEDT T, G ORDON JI. Creat- TLR9 receptor. This interaction subsequently led ing and maintaining the gastrointestinal ecosys- to an increased endogenous production of β-de- tem: what we know and need to know from gnoto- fensins, antibacterial peptides that regulate bacte- biology. Microbiol Mol Biol Rev 1998; 62: 1157- rial survival. Additionally, it was reported that 1170. the treatment of cultured intestinal epithelial cells 9) ULEVITCH RJ. Endotoxin opens the Tollgates to in- with VSL#3 led to an increase of the transepithe- nate immunity. Nat Med 1999; 5: 144-145. lial electrical resistance, a change that correlates 10) MEDZHITOV R, JANEWAY C JR. Innate immune recog- 80 nition: mechanisms and pathways. Immunol Rev with decreased permeability . In that study, in- 2000; 173: 89-97. cubation of intestinal epithelial cells with this 11) AKIRA S, HEMMI H. Recognition of pathogen-associ- probiotic consortium also induced the expression ated molecular patterns by TLR family. Immunol of several mucins, leading to decreased adhesion Lett 2003; 85: 85-95. of microorganisms and their components to the 12) STROBER W, F USS IJ, BLUMBERG RS. The epithelial surface. of mucosal models of inflammation. Annu Rev Im- All the above mentioned evidences suggest munol 2002; 20: 495-549. that probiotics may play an important role in the 13) BLAND PW. Mucosal –epithelial cell interac- management of IBD in the future, although cur- tions. Chem Immunol 1998; 71: 40-63. rent clinical trials lack statistical power, probably 14) FUNDA DP, TUÈKOVÁ L, FARRE MA, IWASE T, M ORO I, due to their limited number. In addition, treat- TLASKALOVÁ-HOGENOVÁ H. CD14 is expressed and released as soluble CD14 by human intestinal ep- ments need to be individualized based on compo- ithelial cells in vitro: lipopolysaccharide activation sitional alterations in patient subsets. A better un- of epithelial cells revisited. Infect Immun 2001; 69: derstanding of bacterial and host mutualistic in- 3772-3781.

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