Development of the intestinal mucosal barrier

Pro-inflammatory T cells-derived cytokines enhance the maturation of the human fetal intestinal epithelial barrier

Small intestine (SI) maturation during early life is pivotal in preventing the onset of gut diseases. In this study we interrogated the milestones of SI development by gene expression profiling and ingenuity pathway analyses. We identified a set of cytokines as main regulators of changes observed across different developmental stages. Upon cytokines stimulation, with IFNγ as the most contributing factor, human fetal organoids (HFOs) increase brush border gene expression and enzyme activity as well as trans-epithelial electrical resistance. Electron microscopy revealed developed brush border and loss of fetal cell characteristics in HFOs upon cytokine stimulation. We identified T cells as major source of IFNγ production in the fetal SI lamina propria. Co-culture of HFOs with T cells recapitulated the major effects of cytokine stimulation. Our findings underline pro-inflammatory cytokines derived from T cells as pivotal factors inducing functional SI maturation in vivo and capable of modulating the barrier maturation of HFOs in vitro.

Porcine kobuvirus enhances porcine epidemic diarrhea virus pathogenicity and alters the number of intestinal lymphocytes in piglets

Recent epidemiological studies have discovered that a lot of cases of porcine epidemic diarrhea virus (PEDV) infection are frequently accompanied by porcine kobuvirus (PKV) infection, suggesting a potential relationship between the two viruses in the development of diarrhea. To investigate the impact of PKV on PEDV pathogenicity and the number of intestinal lymphocytes, piglets were infected with PKV or PEDV or co-infected with both viruses. Our findings demonstrate that co-infected piglets exhibit more severe symptoms, acute gastroenteritis, and higher PEDV replication compared to those infected with PEDV alone. Notably, PKV alone does not cause significant intestinal damage but enhances PEDV's pathogenicity and alters the number of intestinal lymphocytes. These results underscore the complexity of viral interactions in swine diseases and highlight the need for comprehensive diagnostic and treatment strategies addressing co-infections.

The role of intestinal alkaline phosphatase in the development of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating neonatal disease that affects neonates worldwide and often leads to high morbidity and mortality rates. Despite extensive research, the cause of NEC remains unclear, and current treatment options are limited. An important novel finding is the potential role of intestinal Alkaline Phosphatase (IAP) in both pathogenesis and treatment of NEC. IAP can play a vital role in detoxifying liposaccharides (LPS), a key mediator of many pathological processes, thereby reducing the inflammatory response associated with NEC. Furthermore, IAP can help prevent dysbiosis, improve intestinal perfusion, and promote autophagy. In this comprehensive review, we present evidence of the possible connection between IAP and the LPS/Toll-like receptor 4 (TLR4) pathway, impaired gut immunity, and dysbiosis in the preterm gut. Based on these findings, the administration of exogenous IAP might provide promising preventive and therapeutic avenues for the management of NEC.

The role of neutrophil extracellular traps in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) continues to be one of the most common causes of mortality and morbidity in preterm infants. Although not fully elucidated, studies suggest that prematurity, formula feeding, imbalanced vascular supply, and altered bacterial colonization play major roles in the pathogenesis of NEC. NEC is characterized by increased cytokine release and leukocyte infiltration. Recent data from preterm infants and animal models of NEC suggest that neutrophil extracellular traps (NETs) are released in intestinal tissue. The contribution of NETs in the pathogenesis and/or prevention/treatment of this disease continues to be controversial. Here, we review the available data on NETs release in NEC in human patients and in different NEC models, highlighting their potential contribution to pathology and resolution of inflammation. Here, we review the available data on NETs release in NEC in human patients and the different NEC models, highlighting their potential contribution to pathology or resolution of inflammation.

A Human 2D Primary Organoid-Derived Epithelial Monolayer Model to Study Host-Pathogen Interaction in the Small Intestine

Gut organoids are stem cell derived 3D models of the intestinal epithelium that are useful for studying interactions between enteric pathogens and their host. While the organoid model has been used for both bacterial and viral infections, this is a closed system with the luminal side being inaccessible without microinjection or disruption of the organoid polarization. In order to overcome this and simplify their applicability for transepithelial studies, permeable membrane based monolayer approaches are needed. In this paper, we demonstrate a method for generating a monolayer model of the human fetal intestinal polarized epithelium that is fully characterized and validated. Proximal and distal small intestinal organoids were used to generate 2D monolayer cultures, which were characterized with respect to epithelial cell types, polarization, barrier function, and gene expression. In addition, viral replication and bacterial translocation after apical infection with enteric pathogens Enterovirus A71 and Listeria monocytogenes were evaluated, with subsequent monitoring of the pro-inflammatory host response. This human 2D fetal intestinal monolayer model will be a valuable tool to study host-pathogen interactions and potentially reduce the use of animals in research.

Beneficial Effect of Mildly Pasteurized Whey Protein on Intestinal Integrity and Innate Defense in Preterm and Near-Term Piglets

Background. The human digestive tract is structurally mature at birth, yet maturation of gut functions such as digestion and mucosal barrier continues for the next 1–2 years. Human milk and infant milk formulas (IMF) seem to impact maturation of these gut functions differently, which is at least partially related to high temperature processing of IMF causing loss of bioactive proteins and formation of advanced glycation end products (AGEs). Both loss of protein bioactivity and formation of AGEs depend on heating temperature and time. The aim of this study was to investigate the impact of mildly pasteurized whey protein concentrate (MP-WPC) compared to extensively heated WPC (EH-WPC) on gut maturation in a piglet model hypersensitive to enteral nutrition. Methods. WPC was obtained by cold filtration and mildly pasteurized (73 °C, 30 s) or extensively heat treated (73 °C, 30 s + 80 °C, 6 min). Preterm (~90% gestation) and near-term piglets (~96% gestation) received enteral nutrition based on MP-WPC or EH-WPC for five days. Macroscopic and histologic lesions in the gastro-intestinal tract were evaluated and intestinal responses were further assessed by RT-qPCR, immunohistochemistry and enzyme activity analysis. Results. A diet based on MP-WPC limited epithelial intestinal damage and improved colonic integrity compared to EH-WPC. MP-WPC dampened colonic IL1-β, IL-8 and TNF-α expression and lowered T-cell influx in both preterm and near-term piglets. Anti-microbial defense as measured by neutrophil influx in the colon was only observed in near-term piglets, correlated with histological damage and was reduced by MP-WPC. Moreover, MP-WPC stimulated iALP activity in the colonic epithelium and increased differentiation into enteroendocrine cells compared to EH-WPC. Conclusions. Compared to extensively heated WPC, a formula based on mildly pasteurized WPC limits gut inflammation and stimulates gut maturation in preterm and near-term piglets and might therefore also be beneficial for preterm and (near) term infants.

Human breast milk exosomes attenuate intestinal damage

BACKGROUND

Human breast milk (HBM), which contains an abundant supply of exosomes, is known to prevent necrotizing enterocolitis (NEC). Preterm infants are commonly given pasteurized donor milk when HBM is unavailable. However, pasteurization can disrupt its components. This study investigates the effects of both raw and pasteurized HBM-derived exosomes on intestinal inflammation.

METHODS

HBM exosomes were isolated and characterized by positive CD63 and negative calnexin markers from western blot, nanoparticle tracking analysis and transmission electron microscopy. Mouse intestine organoids were established and treated with exosomes from raw or pasteurized HBM in healthy and injury conditions. Following ethical approval (#44032), mice pups were randomly assigned to (1) breastfed control; (2) NEC; (3) NEC receiving raw HBM exosomes; (4) NEC receiving pasteurized HBM exosomes. NEC was induced by hypoxia, gavage feeding and lipopolysaccharide (LPS). Ileum was evaluated. Data were analyzed using one-way ANOVA with Bonferroni post-test.

RESULTS

Both raw and pasteurized HBM exosomes decreased inflammation in hypoxia and LPS-treated organoids compared to control. In vivo, NEC-induced mucosal injury, inflammation and mucous production were improved by raw and pasteurized HBM-derived exosomes.

CONCLUSIONS

Exosomes derived from raw and pasteurized HBM equally reduced intestinal damage. Exosome administration in clinical practice requires further investigation.

Necrotizing enterocolitis: It's not all in the gut

Necrotizing enterocolitis is the leading cause of death due to gastrointestinal disease in preterm neonates, affecting 5–12% of neonates born at a very-low birth weight. Necrotizing enterocolitis can present with a slow and insidious onset, with some neonates displaying early symptoms such as feeding intolerance. Treatment during the early stages includes bowel rest and careful use of antibiotics, but surgery is required if pneumoperitoneum and intestinal perforation occur. Mortality rates among neonates requiring surgery are estimated to be 20–30%, mandating the development of non-invasive and reliable biomarkers to predict necrotizing enterocolitis before the onset of clinical signs. Such biomarkers would allow at-risk neonates to receive maximal preventative therapies such as careful nutritional consideration, probiotics, and increased skin-to-skin care.

Impact statement

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease; its high mortality rate mandates the development of non-invasive biomarkers to predict NEC before its onset. This review summarizes the pathogenesis, prevention, unresolved issues, and long-term outcomes of NEC.

Pancreatic Enzyme Supplementation in Patients with Atopic Dermatitis and Food Allergies: An Open-Label Pilot Study

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease that affects both patients and their families. Current therapies often alleviate symptoms but do not prevent or eradicate the disease.

OBJECTIVES

Our objective was to determine whether pancreatic enzyme supplementation is an effective and safe treatment in refractory pediatric AD associated with food allergies.

METHODS

We conducted an open-label pilot study using a case-control design. Patients with severe AD and known food allergies refractory to conventional therapies and exclusion diets were recruited and treated for 6 weeks with oral supplementation of pancreatic enzymes. The primary endpoint was the severity of AD, using the Scoring Atopic Dermatitis (SCORAD) index. Secondary measures included markers of intestinal permeability (urinary sucrose and lactulose/mannitol excretion).

RESULTS

A total of 11 patients met all eligibility criteria and completed the trial. Significant improvement in AD was observed after 6 weeks of pancreatic enzyme supplementation (SCORAD index 52.3 ± 5.5 vs. 34.6 ± 7.6; p = 0.0008). Beneficial effect was observed in 9 of 11 patients, without adverse events. Fractional urinary sucrose excretion improved to a level comparable to that of age-matched controls (p < 0.05). However, urinary lactulose:mannitol ratios remained abnormally high compared with those of controls (p = 0.01).

CONCLUSIONS

Pancreatic enzyme supplementation was associated with improved AD and gastroduodenal permeability. Additional randomized placebo-controlled studies are required before this treatment can be recommended in this clinical setting.

Role of intestinal Hsp70 in barrier maintenance: contribution of milk to the induction of Hsp70.2

BACKGROUND

Necrotizing enterocolitis (NEC) is a gastrointestinal disease of complex etiology resulting in devastating systemic inflammation and often death in premature newborns. We previously demonstrated that formula feeding inhibits ileal expression of heat shock protein-70 (Hsp70), a critical stress protein within the intestine. Barrier function for the premature intestine is critical. We sought to determine whether reduced Hsp70 protein expression increases neonatal intestinal permeability.

METHODS

Young adult mouse colon cells (YAMC) were utilized to evaluate barrier function as well as intestine from Hsp70-/- pups (KO). Sections of intestine were analyzed by Western blot, immunohistochemistry, and real time PCR. YAMC cells were sub-lethally heated or treated with expressed milk (EM) to induce Hsp70.

RESULTS

Immunostaining demonstrates co-localized Hsp70 and tight junction protein zona occludens-1 (ZO-1), suggesting physical interaction to protect tight junction function. The permeability of YAMC monolayers increases following oxidant injury and is partially blocked by Hsp70 induction either by prior heat stress or EM. RT-PCR analysis demonstrated that the Hsp70 isoforms, 70.1 and 70.3, predominate in WT pup; however, Hsp70.2 predominates in the KO pups. While Hsp70 is present in WT milk, it is not present in KO EM. Hsp70 associates with ZO-1 to maintain epithelial barrier function.

CONCLUSION

Both induction of Hsp70 and exposure to EM prevent stress-induced increased permeability. Hsp70.2 is present in both WT and KO neonatal intestine, suggesting a crucial role in epithelial integrity. Induction of the Hsp70.2 isoform appears to be mediated by mother's milk. These results suggest that mother's milk feeding modulates Hsp70.2 expression and could attenuate injury leading to NEC.

LEVEL OF EVIDENCE

Level III.

Human Ontogeny of Drug Transporters: Review and Recommendations of the Pediatric Transporter Working Group

The critical importance of membrane-bound transporters in pharmacotherapy is widely recognized, but little is known about drug transporter activity in children. In this white paper, the Pediatric Transporter Working Group presents a systematic review of the ontogeny of clinically relevant membrane transporters (e.g., SLC, ABC superfamilies) in intestine, liver, and kidney. Different developmental patterns for individual transporters emerge, but much remains unknown. Recommendations to increase our understanding of membrane transporters in pediatric pharmacotherapy are presented.

Gut Microbiota and Immunity: Possible Role in Sudden Infant Death Syndrome

The gut microbiome influences the development of the immune system of young mammals; the establishment of a normal gut microbiome is thought to be important for the health of the infant during its early development. As the role of bacteria in the causation of sudden infant death syndrome (SIDS) is backed by strong evidence, the balance between host immunity and potential bacterial pathogens is likely to be pivotal. Bacterial colonization of the infant colon is influenced by age, mode of delivery, diet, environment, and antibiotic exposure. The gut microbiome influences several systems including gut integrity and development of the immune system; therefore, gut microflora could be important in protection against bacteria and/or their toxins identified in SIDS infants. The aims of the review are to explore (1) the role of the gut microbiome in relation to the developmentally critical period in which most SIDS cases occur; (2) the mechanisms by which the gut microbiome might induce inflammation resulting in transit of bacteria from the lumen into the bloodstream; and (3) assessment of the clinical, physiological, pathological, and microbiological evidence for bacteremia leading to the final events in SIDS pathogenesis.

Endoplasmic reticulum stress may not be involved in intestinal epithelial cell apoptosis in experimental acute pancreatitis

OBJECTIVES

To investigate whether endoplasmic reticulum (ER) stress is activated in the intestinal epithelium of acute pancreatitis (AP), and whether it is one of the inducing factors of the intestinal epithelial cell apoptosis in AP.

METHODS

Twenty-four rats were randomly divided into two groups. AP was induced via retrograde injection of 3 % sodium taurocholate into the pancreatic duct. As a control group, rats received a sham operation. Forty-eight hours after the operation, the ultrastructural changes of ileal epithelial cells were investigated by transmission electron microscope. The protein expressions of GRP78, CHOP, caspase-12, and JNK in the ileal epithelium were determined by immunohistochemistry, and apoptosis was determined by TdT-mediated dUTP nick end labeling. The mRNA expressions of GRP78, CHOP, caspase-12, and JNK in the ileal epithelium were determined using quantitative RT-PCR.

RESULTS

The ileal epithelium in rats with AP had significantly higher apoptotic cells compared with that of the control rats (P < 0.05). ER stress was activated in the ileal epithelium, which was characterized by dilated, irregular ER and upregulated expressions of GRP78 mRNA and protein. The mRNA and protein expressions of CHOP, caspase-12, and JNK in rats with AP were similar to that in the control rats (P > 0.05).

CONCLUSIONS

ER stress is induced in intestinal epithelium during AP; however, ER stress is not likely to be involved in the apoptosis of the intestinal epithelium during AP.

White and dark kidney beans reduce colonic mucosal damage and inflammation in response to dextran sodium sulfate

Common beans are a rich source of nondigestible fermentable components and phenolic compounds that have anti-inflammatory effects. We assessed the gut-health-promoting potential of kidney beans in healthy mice and their ability to attenuate colonic inflammation following dextran sodium sulphate (DSS) exposure (via drinking water, 2% DSS w/v, 7 days). C57BL/6 mice were fed one of three isocaloric diets: basal diet control (BD), or BD supplemented with 20% cooked white (WK) or dark red kidney (DK) bean flour for 3 weeks. In healthy mice, anti-inflammatory microbial-derived cecal short chain fatty acid (SCFA) levels (acetate, butyrate and propionate), colon crypt height and colonic Mucin 1 (MUC1) and Resistin-like Molecule beta (Relmβ) mRNA expression all increased in WK- and DK-fed mice compared to BD, indicative of enhanced microbial activity, gut barrier integrity and antimicrobial defense response. During colitis, both bean diets reduced (a) disease severity, (b) colonic histological damage and (c) increased mRNA expression of antimicrobial and barrier integrity-promoting genes (Toll-like Receptor 4 (TLR4), MUC1-3, Relmβ and Trefoil Factor 3 (TFF3)) and reduced proinflammatory mediator expression [interleukin (IL)-1β, IL-6, interferon (IFN)γ, tumor necrosis factor (TNF)α and monocyte chemoattractant protein-1], which correlated with reduced colon tissue protein levels. Further, bean diets exerted a systemic anti-inflammatory effect during colitis by reducing serum levels of IL-17A, IFNγ, TNFα, IL-1β and IL-6. In conclusion, both WK and DK bean-supplemented diets enhanced microbial-derived SCFA metabolite production, gut barrier integrity and the microbial defensive response in the healthy colon, which supported an anti-inflammatory phenotype during colitis. Collectively, these data demonstrate a beneficial colon-function priming effect of bean consumption that mitigates colitis severity.

The impact of immune dysregulation on the development of autoimmune gastrointestinal and liver disease

The intestinal epithelium plays an active immunologic role in preventing the uptake of foreign antigens. Additionally, the intestinal mucosa is an active site for immune suppression through the development of oral tolerance. Dysfunction of any aspect of the intestinal barrier, such as impairment of intestinal tight junctions, immunologic dysregulation or decreased oral tolerance will lead to overstimulation of the immune system upon exposure to foreign antigens and subsequent unregulated chronic intestinal inflammation. This persistent inflammatory activity may potentially predispose the patient to the development of intestinal autoimmune disease. An active immune response possibly directed against intestinal flora has been postulated to be the underlying etiology for inflammatory bowel disease. Failure of oral tolerance is thought predispose a patient to celiac disease and possibly eosinophilic esophagitis. Additionally, an active immunologic response to absorbed antigen may be the underlying etiology for the development of autoimmune liver disease.

Inhibition of p38 mitogen-activated protein kinase attenuates butyrate-induced intestinal barrier impairment in a Caco-2 cell monolayer model

OBJECTIVES

Butyrate is well known to induce apoptosis in differentiating intestinal epithelial cells. The present study was designed to examine the role of p38 mitogen-activated protein kinase (MAPK) in butyrate-induced intestinal barrier impairment.

METHODS

The intestinal barrier was determined by measuring the transepithelial electrical resistance (TER) in a Caco-2 cell monolayer model. The permeability was determined by measuring transepithelial passage of fluorescein isothiocyanate-conjugated inulin (inulin-FITC). The morphology of the monolayers was examined with scanning electron microscopy. The apoptosis status was determined by annexin V-FITC labeling and flow cytometry. The activity of p38 MAPK was determined by the phosphorylation status of p38 with Western blotting.

RESULTS

Butyrate at 5 mM increases the apoptosis rate of Caco-2 cells and induces impairment of intestinal barrier functions as determined by decreased TER and increased inulin-FITC permeability. Butyrate treatment activates p38 MAPK in a concentration- and time-dependent manner. SB203580, a specific p38 inhibitor, inhibits butyrate-induced Caco-2 cell apoptosis. Treatment of SB203580 significantly attenuates the butyrate-induced impairment of barrier functions in the Caco-2 cell monolayer model.

CONCLUSIONS

p38 MAPK can be activated by butyrate and is involved in the butyrate-induced apoptosis and impairment of intestinal barrier function. Inhibition of p38 MAPK can significantly attenuate butyrate-induced intestinal barrier dysfunction.

Management of breastfeeding during and after the maternity hospitalization for late preterm infants

Among infants born moderately and late preterm or early term, the greatest challenge for breastfeeding management is the late preterm infant (LPI) who is cared for with the mother in the maternity setting. Breastfeeding failure among LPIs and their mothers is high. Evidence-based strategies are needed to protect infant hydration and growth, and the maternal milk supply, until complete feeding at breast can be established. This article reviews the evidence for lactation and breastfeeding risks in LPIs and their mothers, and describes strategies for managing these immaturity-related feeding problems. Application to moderately and early preterm infants is made throughout.

The gut mucosal immune system in the neonatal period

Invasive sepsis in the newborn period is a major cause of childhood morbidity and mortality worldwide. The infant immune system undoubtedly differs intrinsically from the mature adult immune system. Current understanding is that the newborn infant immune system displays a range of competencies and is developing rather than deficient. The infant gut mucosal immune system is complex and displays a plethora of phenotypic and functional irregularities that may be clinically important. Various factors affect and modulate the infant gut mucosal immune system: components of the intestinal barrier, the infant gut microbiome, nutrition and the maternal-infant hybrid immune system. Elucidation of the phenotypic distribution of immune cells, their functional significance and the mucosa-specific pathways used by these cells is essential to the future of research in the field of infant immunology.

Molecular characterization of bacterial colonization in the preterm and term infant's intestine

OBJECTIVE

To further define patterns of colonising intestinal microflora in newborn infants utilising molecular methods.

METHODS

Ten term and 5 preterm (<32 wk) infants born at the Royal Hospital for Women, Sydney, Australia were enrolled in the present study and followed for 6 mo post partum. Serial stools were collected, DNA was extracted and subjected to PCR-Denaturing Gradient Gel Electrophoresis using a range of primers and sequencing. The effect of gestational length, feeding and delivery method was compared to the pattern of bacterial acquisition.

RESULTS

Intestinal bacterial diversity was lower in preterm compared with term infants. For term infants, bacterial DNA detection rates were not associated with feeding or delivery method, although Enterobacteria and Clostridia were commonly identified. The detection rate of Bifidobacteria was lower in preterm infants than term infants. Potential pathogens were detected in preterm infant samples.

CONCLUSIONS

Preterm infants frequently have aberrant bacterial colonization of the intestine. Further research is now required to determine if this may contribute to adverse health outcomes.

Isolation and characterization of human primary enterocytes from small intestine using a novel method

Cell culture studies of enterocytes are important in many fields. However, there are difficulties in obtaining cell lines from adult human intestine, such as microbial contamination of cultures from the tissue samples, short life span of enterocytes, overgrowth of mesenchymal cells, etc. Various model used to obtain adult intestinal cell lines are very complex requiring use of feeder layer or gel matrices. The aim of this study was to establish a novel method for the simple and reproducible isolation of human enterocytes. Enterocytes were isolated from SI samples (n = 5) obtained from cadaveric donors using a mechanical procedure, and separation with immunomagnetic beads coated with anti-EpCAM antibodies. Light and electron microscopy, flow cytometry and immunocytochemistry techniques were used to characterize the isolated cells. Immunohistochemical staining of normal SB biopsies confirmed that the cell cultures maintained an in vivo phenotype as reflected in cytokeratin expression CK18, CK20 and expression of intestine-specific markers such as sucrase isomaltase and maltase glucoamylase. Furthermore, the cells strongly expressed TLR-5, 6, 7, 8 and 10 and several molecules such as CD40, CD86, CD44, ICAM-1 and HLA-DR which are important in triggering cell-mediated immune responses. This novel technique provides a unique in vitro system to study the biology of enterocytes in normal conditions as well as to study inflammatory processes in various small bowel disorders.

Transfusion-related acute gut injury: feeding, flora, flow, and barrier defense

TRAGI (transfusion-related acute gut injury) is an acronym we proposed to characterize a severe neonatal gastrointestinal reaction temporally related to a transfusion of packed blood red cells (PRBCs) for anemia in very low birth weights. The following are in support of a causative relationship: (1) the timing of necrotizing enterocolitis after a PRBC transfusion not being random, (2) traditional risk factors for necrotizing enterocolitis are often absent, (3) significant anemia appears to be a universal finding, (4) the age of donor blood is often slightly older than controls, (5) TRAGI is not postnatal age dependent, and (6) TRAGI does not show a centering at 31 weeks' postconceptual age as does nontransfusion-related NEC. Although TRAGI is linked to the timing of PRBC transfusions, we propose a novel hypothesis that the convergence at 31 weeks' postconceptual age for classic NEC approximates the age of presentation of other oxygen delivery and neovascularization syndromes (eg, retinopathy of prematurity), suggesting its etiologic link to a generalized systemic maturational mechanism or another common developmental theme. This report will begin by reviewing the history of the clinical presentation and discovery of TRAGI and will then analyze various pathophysiologic mechanisms that may account for the phenomenon when clinicians render therapies. We will end by a call to action for randomized clinical trials to test various etiologic theories.

Enterocolite necrosante em recém-nascidos de muito baixo peso em uma unidade neonatal de alto risco do Nordeste do Brasil (2003-2007)

OBJETIVOS: avaliar a incidência de enterocolite necrosante (ECN), no período de 2003 a 2007, em crianças nascidas com muito baixo peso e descrever as características da assistência prestada a esses recém-nascidos. MÉTODOS: estudo longitudinal retrospectivo conduzido em uma unidade neonatal de alto risco com uma amostra de 1028 recém-nascidos de muito baixo peso, excluindo-se os menores de 750 g. A frequência de ECN foi observada do primeiro até o trigésimo dia de vida, ou até a sua ocorrência ou óbito, considerando-se o que ocorresse primeiro em um período de cinco anos. ECN foi definida pelo critério de Bell (estágio ≥2). Utilizou-se o qui-quadrado de tendência para avaliar o comportamento das variáveis categóricas ao longo dos cinco anos. RESULTADOS: ECN ocorreu em 55 dos 1028 recém-nascidos (5,3%). Observou-se maior incidência de ECN no ano de 2005 (19/204) com uma significante redução no ano de 2007 (8/195), entretanto, essa variação não caracterizou uma tendência (p=0,45). Observou-se aumento significante do uso de antibióticos,de nutrição parenteral, de corticóide antenatal e do consumo de leite materno e uma redução na média da idade gestacional de 2,4 semanas entre 2003 e 2007. CONCLUSÕES: a incidência de ECN foi variável, sem tendência de ascensão ou queda. Observou-se um incremento na cobertura de corticoide antenatal, aumento na utilização de leite materno e redução no consumo de fórmula. Mais estudos são necessários para melhor avaliar a contribuição dessas medidas na não progressão da incidência da ECN, apesar de tratar-se de uma população com risco elevado para essa doença.

Active transport of bile acids decreases mucin 2 in neonatal ileum: implications for development of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency of premature infants, but its etiology remains unclear. We have previously shown that mucin 2 (Muc2) positive goblet cells are significantly decreased in NEC. We have also shown that ileal bile acids (BAs) are significantly increased during the development of this disease. Because BAs can affect mucins, we hypothesized that elevated ileal BAs contribute to decreased Muc2 in experimental NEC. The role of Muc2 in NEC was evaluated in Winnie +/+ mice, a strain that produces aberrant Muc2. Muc2 and trefoil factor 3 (Tff3) were assessed in neonatal rats subjected to the NEC protocol when bile acids were removed, and in ileal explants from newborn and older rats cultured with and without BAs. Further, the role of active transport of BAs was determined using neonatal rats given the apical sodium dependent bile acid transporter (Asbt) inhibitor SC-435 and in neonatal Asbt knockout mice subjected to the NEC protocol. Mice with aberrant Muc2 had significantly greater incidence and severity of NEC. Using both in vivo and ex vivo techniques, we determined that BAs decrease Muc2 positive cells in neonatal but not older ileum. However, Tff3 positive cells are not decreased by BAs. In addition, active transport of BAs is required for BAs to decrease Muc2 in immature ileum. These data show that functional Muc2 plays a critical role in the prevention of NEC and BAs can potentiate the decreased Muc2 in disease development. Further, BAs have a more profound effect on Muc2 in immature versus older ileum, which may explain at least in part why NEC occurs almost exclusively in premature infants.

Mother's milk-induced Hsp70 expression preserves intestinal epithelial barrier function in an immature rat pup model

Preterm infants face many challenges in transitioning from the in utero to extrauterine environment while still immature. Failure of the preterm gut to successfully mature to accommodate bacteria and food substrate leads to significant morbidity such as neonatal necrotizing enterocolitis. The intestinal epithelial barrier plays a critical role in gut protection. Heat shock protein 70 (Hsp70) is an inducible cytoprotective molecule shown to protect the intestinal epithelium in adult models. To investigate the hypothesis that Hsp70 may be important for early protection of the immature intestine, Hsp70 expression was evaluated in intestine of immature rat pups. Data demonstrate that Hsp70 is induced by exposure to mother's milk. Hsp70 is found in mother's milk, and increased Hsp70 transcription is induced by mother's milk. This Hsp70 colocalizes with the tight junction protein ZO-1. Mother's milk-induced Hsp70 may contribute to maintenance of barrier function in the face of oxidant stress. Further understanding of the means by which mother's milk increases Hsp70 in the ileum will allow potential means of strengthening the intestinal barrier in at-risk preterm infants.

Transfusion-related acute gut injury: necrotizing enterocolitis in very low birth weight neonates after packed red blood cell transfusion

OBJECTIVE

This is a repeat cohort study in which we sought to determine whether an association of necrotizing enterocolitis (NEC) <48 hours of a packed red blood cells (PRBC) transfusion was a prior sampling artifact.

STUDY DESIGN

All very low birth weight neonates with NEC Stage ≥ IIB admitted over an 18-month period were categorized for NEC: (1) <48 hours after a PRBC transfusion; (2) unrelated to the timing of PRBCs; and (3) never transfused.

RESULTS

Eight hundred eighty-three admissions over 18 months were reviewed; 256 were very low birth weight that resulted in 36 NEC cases and 25% were associated with PRBC (n = 9). PRBC-associated cases had lower birth weight, hematocrit, and rapid onset of signs (<5 hours). The timing of association of PRBC transfusion and NEC differed from random, showing a distribution that was not uniform over time (χ(2) = 170.7, df = 40; P < .000001) consistent with the possibility of a causative relationship in certain cases of NEC. Current weight at onset of NEC did not differ; however, the more immature the neonate the later the onset of NEC creating a curious centering of occurrence at a median of 31 weeks postconceptual age.

CONCLUSIONS

We conclude that PRBC-related NEC exists. Transfusion-related acute gut injury is an acronym we propose to characterize a severe neonatal gastrointestinal reaction proximal to a transfusion of PRBCs for anemia. The convergence at 31 weeks postconceptual age approximates the age of presentation of other O(2) delivery and neovascularization syndromes, suggesting a link to a generalized systemic maturational mechanism.

Efficacy of Bifidobacterium breve and Lactobacillus casei oral supplementation on necrotizing enterocolitis in very-low-birth-weight preterm infants: a double-blind, randomized, controlled trial

BACKGROUND

Probiotics are used for the prevention of necrotizing enterocolitis (NEC) because of their positive effects on intestinal motor function, modulation of inflammatory response, and mucosal barrier function.

OBJECTIVE

The objective was to assess whether the combined use of Lactobacillus casei and Bifidobacterium breve may prevent the occurrence of NEC stage ≥ 2 by the criteria of Bell in very-low-birth-weight preterm infants.

DESIGN

A double-blind, randomized, controlled clinical trial was conducted in 231 preterm infants weighing from 750 to 1499 g at birth. The intervention group was composed of 119 infants who received human milk with probiotic supplementation (B. breve and L. casei) and a control group of 112 infants who received human milk containing no probiotics. The primary outcome was the occurrence of NEC stage ≥ 2 as defined by Bell's modified criteria.

RESULTS

Four confirmed cases of NEC stage ≥ 2 by Bell's criteria occurred only in the control group.

CONCLUSIONS

Oral supplementation of B. breve and L. casei reduced the occurrence of NEC (Bell's stage ≥ 2). It was considered that an improvement in intestinal motility might have contributed to this result. This trial was registered at www.isrctin.org as number 67165178 (International Standard Randomized Controlled Trial).

Bifidobacterium bifidum improves intestinal integrity in a rat model of necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is a major cause of morbidity and mortality in premature infants. Oral administration of probiotics has been suggested as a promising strategy for prevention of NEC. However, little is known about the mechanism(s) of probiotic-mediated protection against NEC. The aim of this study was to evaluate the effects of Bifidobacterium bifidum treatment on development of NEC, cytokine regulation, and intestinal integrity in a rat model of NEC. Premature rats were divided into three groups: dam fed (DF), hand fed with formula (NEC), or hand fed with formula supplemented with 5 x 10(6) CFU B. bifidum per day (B. bifidum). All groups were exposed to asphyxia and cold stress to develop NEC. Intestinal injury, mucin and trefoil factor 3 (Tff3) production, cytokine levels, and composition of tight junction (TJ) and adherens junction (AJ) proteins were evaluated in the terminal ileum. B. bifidum decreased the incidence of NEC from 57 to 17%. Increased levels of IL-6, mucin-3, and Tff3 in the ileum of NEC rats was normalized in B. bifidum treated rats. Reduced mucin-2 production in the NEC rats was not affected by B. bifidum. Administration of B. bifidum normalized the expression and localization of TJ and AJ proteins in the ileum compared with animals with NEC. In conclusion, administration of B. bifidum protects against NEC in the neonatal rat model. This protective effect is associated with reduction of inflammatory reaction in the ileum, regulation of main components of mucus layer, and improvement of intestinal integrity.

Butyrate enhances the intestinal barrier by facilitating tight junction assembly via activation of AMP-activated protein kinase in Caco-2 cell monolayers

Butyrate, one of the SCFA, promotes the development of the intestinal barrier. However, the molecular mechanisms underlying the butyrate regulation of the intestinal barrier are unknown. To test the hypothesis that the effect of butyrate on the intestinal barrier is mediated by the regulation of the assembly of tight junctions involving the activation of the AMP-activated protein kinase (AMPK), we determined the effect of butyrate on the intestinal barrier by measuring the transepithelial electrical resistance (TER) and inulin permeability in a Caco-2 cell monolayer model. We further used a calcium switch assay to study the assembly of epithelial tight junctions and determined the effect of butyrate on the assembly of epithelial tight junctions and AMPK activity. We demonstrated that the butyrate treatment increased AMPK activity and accelerated the assembly of tight junctions as shown by the reorganization of tight junction proteins, as well as the development of TER. AMPK activity was also upregulated by butyrate during calcium switch-induced tight junction assembly. Compound C, a specific AMPK inhibitor, inhibited the butyrate-induced activation of AMPK. The facilitating effect of butyrate on the increases in TER in standard culture media, as well as after calcium switch, was abolished by compound C. We conclude that butyrate enhances the intestinal barrier by regulating the assembly of tight junctions. This dynamic process is mediated by the activation of AMPK. These results suggest an intriguing link between SCFA and the intracellular energy sensor for the development of the intestinal barrier.

Effects of indomethacin on the rat small intestinal mucosa: immunohistochemical and biochemical studies using anti-mucin monoclonal antibodies

BACKGROUND

The luminal surface of the gastrointestinal tract is covered by a viscoelastic gel layer that acts as a protective barrier against the intraluminal environment. Because the situation of the small intestine has not been elucidated to the same degree as other sections, in this study, we investigated the effects of indomethacin on the rat small intestinal mucosa.

METHODS

Male Wistar rats were given indomethacin 10 mg/kg s-c and sacrificed 1, 3, 7, or 14 days later. The small intestine was opened along the anti-mesenteric side, and examined macroscopically. Total mucin content in the small intestinal epithelium was measured and immunoreactivity was examined using anti-mucin monoclonal antibodies HCM31 and PGM34.

RESULTS

Indomethacin caused punched out and linear ulcers located mostly along the mesenteric margin of the distal jejunum with sparing of the ileum. Histological examination showed sialomucin recognized by HCM31 increased on day 3 especially in the regenerating epithelium around the ulcer edge. Furthermore, the surface mucous gel layer displayed a multilaminated pattern, consisting of non-sulfated sialomucin-rich layers and sulfated mucin-rich layers, where both mucins had the common core protein, MUC2. Biochemical measurements also showed the total mucin content of the jejunum increased transiently and HCM31-positive mucin increased approximately 4 times greater than baseline on day 3, but no marked changes were observed in the ileum, with few ulcers observed.

CONCLUSIONS

Indomethacin administration causes quantitative and qualitative change in jejunal mucin. In particular, sialomucin plays an important role in regenerating epithelium during the healing process following indomethacin-induced mucosal damage.

Small intestinal MUC2 synthesis in human preterm infants

Mucin 2 (MUC2) is the structural component of the intestinal protective mucus layer, which contains high amounts of threonine in its peptide backbone. MUC2 synthesis rate might be a potential parameter for intestinal barrier function. In this study, we aimed to determine whether systemic threonine was used for small intestinal MUC2 synthesis and to calculate the MUC2 fractional synthetic rate (FSR) in human preterm infants. Seven preterm infants with an enterostomy following bowel resection for necrotizing enterocolitis received intravenous infusion of [U-(13)C]threonine to determine incorporation of systemic threonine into secreted MUC2 in intestinal outflow fluid. Small intestinal MUC2 was isolated using cesium chloride gradient ultracentrifugation and gravity gel filtration chromatography. MUC2-containing fractions were identified by SDS-PAGE/periodic acid-Schiff staining and Western blot analysis and were subsequently pooled. Isotopic enrichment of threonine, measured in MUC2 using gas chromatography isotopic ratio mass spectrometry, was used to calculate the FSR of MUC2. Systemically derived threonine was indeed incorporated into small intestinal MUC2. Median FSR of small intestinal MUC2 was 67.2 (44.3-103.9)% per day. Systemic threonine is rapidly incorporated into MUC2 in the small intestine of preterm infants, and thereby MUC2 has a very high synthesis rate.

Detection of galectin-3 in patients with inflammatory bowel diseases: new serum marker of active forms of IBD?

OBJECTIVE

It is an open question whether multifunctional galectin-3 can be a serum marker in inflammatory bowel disease.

METHODS

Western blots and commercial ELISA detected and quantitated the lectin immunocytochemistry using double labeling localized it in tissue sections.

RESULTS

Serum concentrations were significantly increased in specimen of patients with active and remission-stage ulcerative colitis and Crohn's disease, associated with emerging positivity of CD14(+) cells.

CONCLUSION

Enhanced concentration of galectin-3 in serum reflects presence of disease and points to its involvement in the pathogenesis.

Oral probiotics prevent necrotizing enterocolitis in very low birth weight preterm infants: a multicenter, randomized, controlled trial

OBJECTIVE

The goal was to investigate the efficacy of orally administered probiotics in preventing necrotizing enterocolitis for very low birth weight preterm infants.

METHODS

A prospective, blinded, randomized, multicenter controlled trial was conducted at 7 NICUs in Taiwan, to evaluate the beneficial effects of probiotics in necrotizing enterocolitis among very low birth weight infants (birth weight: <1500 g). Very low birth weight infants who survived to start enteral feeding were eligible and were assigned randomly to 2 groups after parental informed consent was obtained. Infants in the study group were given Bifidobacterium bifidum and Lactobacillus acidophilus, added to breast milk or mixed feeding (breast milk and formula), twice daily for 6 weeks. Infants in the control group were fed with breast milk or mixed feeding. The clinicians caring for the infants were blinded to the group assignment. The primary outcome measurement was death or necrotizing enterocolitis (Bell's stage >or=2).

RESULTS

Four hundred thirty-four infants were enrolled, 217 in the study group and 217 in the control group. The incidence of death or necrotizing enterocolitis (stage >or=2) was significantly lower in the study group (4 of 217 infants vs 20 of 217 infants). The incidence of necrotizing enterocolitis (stage >or=2) was lower in the study group, compared with the control group (4 of 217 infants vs 14 of 217 infants). No adverse effect, such as sepsis, flatulence, or diarrhea, was noted.

CONCLUSION

Probiotics, in the form of Bifidobacterium and Lactobacillus, fed enterally to very low birth weight preterm infants for 6 weeks reduced the incidence of death or necrotizing enterocolitis.

The nutritional modulation of the evolving intestine

Nutrition plays a major role in the modulation of the evolving human gut influencing all the main components of the intestinal ecosystem. The regulatory role of nutrition is particularly crucial in the early postnatal period but it continues also in subsequent ages when the development of the gastrointestinal tract is completed. Recent data support the hypothesis that nutrition can affect some inherited disorders of gastrointestinal tract. These "epigenetic" mechanisms are involved in the development of intestinal enzymes, hormones, transporters, and immunity. This is an expanding research area related to the possible nutritional intervention in selected clinical condition. This paper is focused on the main components and mechanisms of action of the nutritional modulation on intestinal development.

Probiotics: role in pathophysiology and prevention in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory bowel disease largely affecting low birth weight, premature infants. Once acquired, NEC is accompanied by significant mortality and morbid sequelae. Our understanding of the pathophysiology of NEC continues to evolve, and the development of NEC is likely multifactorial with resultant bowel injury mediated through a final, common inflammatory pathway. The predisposition for NEC appears to involve the interplay between intestinal integrity and function, enteral feeding and bacterial colonization, and regulation of the gastrointestinal and systemic inflammatory response. Commensal organisms or probiotics have been shown to be crucial in the development and modulation of each of these factors within the intestinal epithelium. As a result, probiotic supplementation has been proposed as a promising new intervention for the prevention of NEC. To understand the potential utility of probiotics in NEC, we will discuss: the components of gut defense; the role of the intestinal ecosystem in modulating immunity and inflammation; bacterial colonization patterns in the preterm infant compared with patterns seen in the healthy, full-term infant; the evidence for probiotic use in other populations and diseases; and finally, the evidence of probiotic use specific to the preterm infant and NEC.

Neonatal sublingual vaccination with Salmonella proteins and adjuvant cholera toxin or CpG oligodeoxynucleotides induces mucosal and systemic immunity in mice

OBJECTIVES

Salmonella enteritidis is one of the most common enteric pathogens that cause acute gastroenteritis. A vaccine that can induce systemic and mucosal immune responses by a simple, noninvasive pathway and provide protection against this mucosal pathogen is needed.

MATERIALS AND METHODS

Newborn BALB/c mice were sublingually vaccinated daily for the first 3 days with sonicated Salmonella proteins (SSP) only, or SSP combined with adjuvant CpG or cholera toxin (CT). A booster vaccination was given 7 weeks after the last treatment. Serum and saliva antibody responses, cytokine profiles of spleen cells, survival rate, and intestinal morphology after live S enteritidis challenge were investigated.

RESULTS

Saliva-specific secretory IgA (SIgA) antibody responses were markedly enhanced by neonatal sublingual vaccination with SSP together with adjuvant CpG or CT. Whereas vaccination with SSP and CpG enhanced spleen cell interferon-gamma production and serum-specific IgG2a antibody responses, vaccination with SSP and CT increased spleen cell interleukin (IL)-4, IL-5, IL-6, and interferon-gamma production and serum-specific IgG1 and IgG2a antibody responses. Vaccination with SSP and CpG or CT protected against intestinal necrosis and was associated with a higher survival rate after oral challenge with live S enteritidis. The vaccinated mice with higher specific IgG and saliva-specific secretory IgA antibody levels had a better survival rate.

CONCLUSIONS

Neonatal sublingual vaccination with adjuvant CpG or CT can induce both mucosal and systemic immunity and may play a crucial role in protection against enteric pathogens.

Bovine whey protein concentrate supplementation modulates maturation of immune system in suckling rats

During neonatal life, challenges from breast milk and microbial flora promote immune system maturation. Immunonutrition in these stages may become an important way to increase natural defence systems. The aim of this study was to determine the effect of a daily bovine milk whey protein concentrate (WPC) supplement on the intestinal and systemic immune systems in suckling rats. The composition of intraepithelial and lamina propria lymphocytes (IEL and LPL) was analysed by flow cytometry. Systemic and intestinal humoral immune responses were determined by sera Ig levels and Ig-secreting cell quantification by ELISA and ELISPOT, respectively. From birth, suckling Wistar rats were supplemented with WPC or standard infant formula (SIF). The WPC group showed the same proportion of most of the main mucosal cell subsets as the reference animals. However, in the first days of life WPC enhanced the innate immunity by increasing the NK cell proportion in both epithelial and lamina propria (LP) compartments. A rise in intestinal CD8alphaalpha+ IEL was also induced by WPC supplementation. A time-course of sera Ig levels and spontaneous IgA, IgM and IgG production by LPL and mononuclear cells from blood and spleen, in the WPC group, exhibited a similar pattern to those pups fed only by dam's milk. In summary, the present results show the effects of WPC on enhancing mucosal innate immunity during early life.

Intestinal barrier failure during experimental necrotizing enterocolitis: protective effect of EGF treatment

Necrotizing enterocolitis (NEC) is the most common intestinal disease of premature infants. Although increased mucosal permeability and altered epithelial structure have been associated with many intestinal disorders, the role of intestinal barrier function in NEC pathogenesis is currently unknown. We investigated the structural and functional changes of the intestinal barrier in a rat model of NEC. In addition, the effect of EGF treatment on intestinal barrier function was evaluated. Premature rats were divided into three groups: dam fed (DF), formula fed (NEC), or fed with formula supplemented with 500 ng/ml EGF (NEC + EGF); all groups were exposed to asphyxia/cold stress to develop NEC. Intestinal permeability, goblet cell density, mucin production, and composition of tight junction (TJ) proteins were evaluated in the terminal ileum, the site of NEC injury, and compared with the proximal jejunum, which was unaffected by NEC. Animals with NEC had significantly increased intestinal paracellular permeability compared with DF pups. Ileal goblet cell morphology, mucin production, and TJ composition were altered in animals with NEC. EGF treatment significantly decreased intestinal paracellular permeability, increased goblet cell density and mucin production, and normalized expression of two major TJ proteins, occludin and claudin-3, in the ileum. In conclusion, experimental NEC is associated with disruption of the intestinal barrier. EGF treatment maintains intestinal integrity at the site of injury by accelerating goblet cell maturation and mucin production and normalizing expression of TJ proteins, leading to improved intestinal barrier function.

Intestinal immune defences and the inflammatory response in necrotising enterocolitis

Necrotising enterocolitis is a devastating neonatal gastrointestinal emergency predominantly affecting low birth weight, premature infants and is accompanied by significant mortality and morbid sequelae. The pathophysiology remains obscure and the management of infants with necrotising enterocolitis has not changed since the recognition of this disease. Necrotising enterocolitis is most likely the clinical culmination of multiple different risk factors interacting with each other to produce bowel injury through a final, common inflammatory pathway. Here, we review intestinal immunity and the specific inflammatory mediators involved in this disease process.

Increase of faecal bifidobacteria due to dietary oligosaccharides induces a reduction of clinically relevant pathogen germs in the faeces of formula-fed preterm infants

In a previous study on formula-fed preterm infants, we were able to demonstrate that dietary oligosaccharides (a mixture of 90% galacto-oligosaccharides and 10% fructo-oligosaccharides in a concentration of 1 g/dl) stimulate the growth of faecal bifidobacteria. In the present explorative analysis of this study, we focus on the effect of the dominance of bifidobacteria on the presence of clinically relevant pathogens (Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Pseudomonas aeruginosa, Enterobacter, Klebsiella, Proteus, Streptococcus group B, Clostridium difficile, Bacillus subtilis and Acinetobacter).

CONCLUSION

The data demonstrate that stimulation of bifidobacteria by prebiotic oligosaccharides reduces the presence of clinically relevant pathogens in the faecal flora, indicating that prebiotic substances might have the capacity to protect against enteral infections.

The effect of protective nutrients on mucosal defense in the immature intestine

Oral nutrition plays a dual role in the gut, providing nutrition to the body while affecting the function of the gastrointestinal tract. The exposure of the gut to food antigens, in the form of either beneficial or harmful nutritional substances, contributes to a vast array of physiological and pathologic gastrointestinal responses with secondary systemic implications. The immune system of the gastrointestinal tract is always involved in the first line of defense, and its actions are particularly important in the early period of life as maturation takes place. From maturation, a balance ensues in the regulatory mechanism of host defense, ultimately leading to either tolerance or immune reaction. This paper emphasizes how some nutrients may beneficially affect the gastrointestinal immune system's maturation in both term and especially premature neonates.

Commensal bacteria (normal microflora), mucosal immunity and chronic inflammatory and autoimmune diseases

Commensal microflora (normal microflora, indigenous microbiota) consists of those micro-organisms, which are present on body surfaces covered by epithelial cells and are exposed to the external environment (gastrointestinal and respiratory tract, vagina, skin, etc.). The number of bacteria colonising mucosal and skin surfaces exceeds the number of cells forming human body. Commensal bacteria co-evolved with their hosts, however, under specific conditions they are able to overcome protective host responses and exert pathologic effects. Resident bacteria form complex ecosystems, whose diversity is enormous. The most abundant microflora is present in the distal parts of the gut; the majority of the intestinal bacteria are Gram-negative anaerobes. More than 50% of intestinal bacteria cannot be cultured by conventional microbiological techniques. Molecular biological methods help in analysing the structural and functional complexity of the microflora and in identifying its components. Resident microflora contains a number of components able to activate innate and adaptive immunity. Unlimited immune activation in response to signals from commensal bacteria could pose the risk of inflammation; immune responses to mucosal microbiota therefore require a precise regulatory control. The mucosal immune system has developed specialised regulatory, anti-inflammatory mechanisms for eliminating or tolerating non-dangerous, food and airborne antigens and commensal micro-organisms (oral, mucosal tolerance). However, at the same time the mucosal immune system must provide local defense mechanisms against environmental threats (e.g. invading pathogens). This important requirement is fulfilled by several mechanisms of mucosal immunity: strongly developed innate defense mechanisms ensuring appropriate function of the mucosal barrier, existence of unique types of lymphocytes and their products, transport of polymeric immunoglobulins through epithelial cells into secretions (sIgA) and migration and homing of cells originating from the mucosal organised tissues in mucosae and exocrine glands. The important role of commensal bacteria in development of optimally functioning mucosal immune system was demonstrated in germ-free animals (using gnotobiological techniques). Involvement of commensal microflora and its components with strong immunoactivating properties (e.g. LPS, peptidoglycans, superantigens, bacterial DNA, Hsp) in etiopathogenetic mechanism of various complex, multifactorial and multigenic diseases, including inflammatory bowel diseases, periodontal disease, rheumatoid arthritis, atherosclerosis, allergy, multiorgan failure, colon cancer has been recently suggested. Animal models of human diseases reared in defined gnotobiotic conditions are helping to elucidate the aetiology of these frequent disorders. An improved understanding of commensal bacteria-host interactions employing germ-free animal models with selective colonisation strategies combined with modern molecular techniques could bring new insights into the mechanisms of mucosal immunity and also into pathogenetic mechanisms of several infectious, inflammatory, autoimmune and neoplastic diseases. Regulation of microflora composition (e.g. by probiotics and prebiotics) offers the possibility to influence the development of mucosal and systemic immunity but it can play a role also in prevention and treatment of some diseases.

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