Uptake and transport of macromolecules by the intestine: possible role in clinical disorders (an update)

Neonatal maternal separation causes colonic dysfunction in rat pups including impaired host resistance

Previous studies have shown that early life stress in the form of intermittent maternal separation (MS) predisposes adult rats to develop stress-induced intestinal mucosal dysfunction and visceral hypersensitivity. However, the mechanism involved in the functional abnormalities is unclear. Our aim was to study immature animals during or shortly after exposure to MS to determine whether there are early pathophysiological changes in the gut. Sprague-Dawley rat pups were individually separated from the dam for 3 h/d from 4 to 21 d of age; nonseparated (NS) control pups remained in the home cage with the dam. On d 19-20, d 24-25, and d 29-30, blood was collected for corticosterone measurement, and colonic tissues were removed for functional and morphologic assessment. Corticosteroid levels were elevated in MS pups compared with NS, indicating that MS was indeed stressful. The distal colon demonstrated significantly enhanced ion secretion and macromolecular permeability at d 19-20 and d 24-25, returning to normal by d 29-30. Electron microscopy and bacterial culture studies indicated bacteria adhering to and penetrating into the colonic epithelium of the MS pups at all time points, while such events were rare in NS pups. The pathophysiological changes were inhibited by injecting pups sc with a corticotropin-releasing hormone (CRH) receptor antagonist daily during MS. Our studies indicate that early psychological trauma predisposes neonatal rats to develop persistent mucosal barrier dysfunction, including impaired host defense to luminal bacteria, by a mechanism involving peripheral CRH receptors.

Novel approaches to the nutritional management of the allergic infant

The increased prevalence of atopic diseases, i.e. atopic eczema, allergic rhinitis and asthma, has been described as the epidemic of the 21st century in Western societies. New approaches in the fight against allergic diseases are clearly called for, the target being the persistence of the allergic responder pattern beyond infancy. The advantage afforded by elimination diets lies in the silencing of specific allergic inflammation induced by an offending food. Novel nutritional approaches, beyond the treatment of food allergies, have recently attracted research interest subsequent to the identification of the immunomodulatory potential of specific dietary compounds. Dietary lipids as immunomodulators may prevent allergic sensitization by down-regulating inflammatory response whilst protecting the epithelial barrier. Probiotic bacteria have been shown to reinforce the different lines of gut defence: immune exclusion, immune elimination and immune regulation. On this basis, the strategy against allergic disease proposed here is based on the administration of tolerogenic gut-processed peptide fragments of a specific protein, in addition to the use of specific dietary compounds such as fatty acids and antioxidants, and introducing a microbial stimulus for the immature immune system by means of cultures of beneficial live micro-organisms characteristic of the healthy infant gut microbiota.

Review article: bifidobacteria as probiotic agents -- physiological effects and clinical benefits

Bifidobacteria, naturally present in the dominant colonic microbiota, represent up to 25% of the cultivable faecal bacteria in adults and 80% in infants. As probiotic agents, bifidobacteria have been studied for their efficacy in the prevention and treatment of a broad spectrum of animal and/or human gastrointestinal disorders, such as colonic transit disorders, intestinal infections, and colonic adenomas and cancer. The aim of this review is to focus on the gastrointestinal effects of bifidobacteria as probiotic agents in animal models and man. The traditional use of bifidobacteria in fermented dairy products and the GRAS ('Generally Recognised As Safe') status of certain strains attest to their safety. Some strains, especially Bifidobacterium animalis strain DN-173 010 which has long been used in fermented dairy products, show high gastrointestinal survival capacity and exhibit probiotic properties in the colon. Bifidobacteria are able to prevent or alleviate infectious diarrhoea through their effects on the immune system and resistance to colonization by pathogens. There is some experimental evidence that certain bifidobacteria may actually protect the host from carcinogenic activity of intestinal flora. Bifidobacteria may exert protective intestinal actions through various mechanisms, and represent promising advances in the fields of prophylaxis and therapy.

The role of enterocytes in the intestinal barrier function and antigen uptake

The intestinal epithelium is a critical interface between the organism and its environment. The cell polarity and structural properties of the enterocytes, limiting the amount of antigen reaching the epithelial surface, form the basis of the integrity of the epithelium. However, apart from their participation in digestive processes, the enterocytes perform more than just a passive barrier function. The resistance of the tight junctions regulates the paracellular transport of antigens. Furthermore, the enterocytes take up and process antigens, involving two functional pathways. In the major pathway, enzymes in the lysosomes degrade the antigens. In the minor direct transcytotic pathway, the antigens are not degraded and are released into the interstitial space. Moreover, the enterocytes can present processed antigens directly to T cells and are often directly involved in immune processes. In inflammatory conditions, the properties of the epithelial barrier and the outcome of the immune response to luminal antigens can be changed.

Gastrointestinal food allergy: new insights into pathophysiology and clinical perspectives

Adverse reactions to food that result in gastrointestinal symptoms are common in the general population; while only a minority of such individuals will have symptoms due to immunologic reactions to foods, gastrointestinal food allergies do exist in both children and adults. These immune reactions are mediated by immunoglobulin E-dependent and -independent mechanisms involving mast cells, eosinophils, and other immune cells, but the complexity of the underlying mechanisms of pathogenesis have yet to be fully defined. Knowledge of the spectrum of adverse reactions to foods that affect the digestive system, including gastrointestinal food allergy, is essential to correctly diagnose and manage the subset of patients with immunologically mediated adverse reactions to foods. Potentially fatal reactions to food necessitate careful instruction and monitoring on the part of health care workers involved in the care of individuals at risk of anaphylaxis. New methods of diagnosis and novel strategies for treatment, including immunologic modulation and the development of hypoallergenic foods, are exciting developments in the field of food allergy.

Functional and structural alterations of epithelial barrier properties of rat ileum following X-irradiation

Irradiation of the digestive system leads to alterations of the small intestine. We have characterized the disruption of the barrier integrity in rat ileum from 1 to 14 days following irradiation ranging from 6 to 12 Gy. The intestinal permeability to 14C-mannitol and 3H-dextran 70 000 was measured in vitro in Ussing chambers. In parallel to these functional studies, immunohistochemical analyses of junctional proteins (ZO-1 and beta-catenin) of ileal epithelium were performed by confocal microscopy. Irradiation with 10 Gy induced a marked decrease in epithelial tissue resistance at three days and a fivefold increase in mannitol permeability, without modifications of dextran permeability. A disorganization of the localization for ZO-1 and beta-catenin was also observed. At 7 days after irradiation, we observed a recovery of the organization of junctional proteins in parallel to a return of intestinal permeability to control value. In addition to these time-dependent effects, a gradual effect on epithelial integrity of the radiation doses was observed 3 days after irradiation. This study shows a disruption of the integrity of the intestinal barrier in rat ileum following abdominal X-irradiation, depending on the time postirradiation and on the delivered dose. The loss of barrier integrity was characterized by a disorganization of proteins of tight and adherent junctions, leading to increased intestinal permeability to mannitol.

Glucocorticoid responsiveness in developing human intestine: possible role in prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a major inflammatory disease of the premature human intestine that can be prevented by glucocorticoids if given prenatally before the 34th wk of gestation. This observation suggests that a finite period of steroid responsiveness exists as has been demonstrated in animal models. Human intestinal xenografts were used to determine whether a glucocorticoid responsive period exists in the developing human intestine. Developmental responsiveness was measured by lactase activity and inflammatory responsiveness by IL-8, IL-6, and monocyte chemotactic protein-1 (MCP-1) induction after an endogenous (IL-1 beta) or exogenous (LPS) proinflammatory stimulus, respectively. Functional development of ileal xenografts were monitored for 30 wk posttransplantation, and the lactase activity recapitulated that predicted by in utero development. Cortisone acetate accelerated the ontogeny of lactase at 20 wk (immature) but the effect was lost by 30 wk (mature) posttransplant. Concomitant with accelerated maturation, the IL-8 response to both IL-1 beta and LPS was significantly dampened (from 6- to 3-fold) by glucocorticoid pretreatment in the immature but not mature xenografts. The induction of IL-8 was reflected at the level of IL-8 mRNA, suggesting transcriptional regulation. The excessive activation of IL-8 in the immature gut was mediated by a prolonged activation of ERK and p38 kinases and nuclear translocation of NF-kappa B due to low levels of I kappa B. Steroid pretreatment in immature intestine dampens activation of all three signaling pathways in response to proinflammatory stimuli. Therefore, accelerating intestinal maturation by glucocorticoids within the responsive period by accelerating functional and inflammatory maturation may provide an effective preventive therapy for NEC.

Characterization of breast milk received by infants with gross blood in stools

OBJECTIVE

The aim of this study was to ascertain factors that might be protective of the appearance of gross blood in the stools of breast-fed infants.

METHODS

Logistic regression models were formed to search for variables possibly explaining the condition. In addition to the analyzed breast milk factors, mother's allergic disease was introduced into the models to control for its possible confounding effect. The breast milk samples, collected from mothers of infants with gross blood in stools (n = 23) and from mothers of healthy age-matched infants (n = 71), were analyzed for concentrations of transforming growth factor-beta2, tumor necrosis factor-alpha, interleukin (IL)-4, IL-10, prostaglandin (PG)E2, cysteinyl leukotrienes (Cys-LTs) and fatty acid composition.

RESULTS AND CONCLUSIONS

Increase in the concentrations of PGE2 and Cys-LTs in the breast milk together with mother's allergic disease reduced the likelihood of gross blood in stools in the breast-fed infant. The results suggest that no single factor, but a combination of immunomodulatory factors may protect the child from gross blood in the stools of breast-fed infants. Allergic disease was not a risk factor as mother's allergic disease appeared to counterbalance the gross blood in stools. Due to the preliminary nature of the study, the results need to be verified in a larger setting. The challenge for the future lies in identifying of such active compounds for dietary modification to enforce particularly the properties of the breast milk which are immunoprotective for the infant and to reduce the likelihood of intestinal disorders in at risk infants.

Isolation of tryptophan as an inhibitor of ovalbumin permeation and analysis of its suppressive effect on oral sensitization

Tryptophan was isolated from rat feces as an active compound against ovalbumin permeation in an in vitro Caco-2 cell model. Tryptophan dose-dependently inhibited ovalbumin permeation with accompanying increase in transepithelial electric resistance, and its inhibitory activity reached a plateau at 10 mM. Brown Norway rats were sensitized by intragastric administration of ovalbumin together with or without tryptophan. Antibody levels specific to ovalbumin in the sera and proliferative responses of spleen mononuclear cells to ovalbumin were significantly lower in rats administered ovalbumin plus tryptophan than those administered ovalbumin alone. These results suggest that tryptophan suppresses oral sensitization to ovalbumin, probably via suppression of ovalbumin absorption from the intestinal tract.

The hygiene hypothesis of atopic disease--an extended version

The hygiene hypothesis of atopic disease suggests that environmental changes in the industrialized world have lead to reduced microbial contact at an early age and thus resulted in the growing epidemic of atopic eczema, allergic rhinoconjunctivitis, and asthma. The epidemiological findings have been combined with the Th1/Th2 paradigm of immune responsiveness to provide a coherent theory. Recent advances in epidemiology and immunology demonstrate, however, that the hygiene hypothesis may need to be extended in three respects. First, the importance of infections in causing immune deviance may be outweighed by other sources of microbial stimulation, perhaps most importantly by the indigenous intestinal microbiota. Second, immunomodulatory and suppressive immune responses complement the Th1/Th2 paradigm. Third, in addition to protection against atopy, protection against infectious, inflammatory, and autoimmune diseases may also depend upon healthy host-microbe interactions implicated in the hygiene hypothesis.

Diarrhoea in children: an interface between developing and developed countries

Despite much progress in the understanding of pathogenesis and of management, diarrhoeal illnesses remain one of the most important causes of global childhood mortality and morbidity. Infections account for most illnesses, with pathogens employing ingenious mechanisms to establish disease. In the developed world, an upsurge in immune-mediated gut disorders might have resulted from a disruption of normal bacterial-epithelial cross-talk and impaired maturation of the gut's immune system. Oral rehydration therapies are the mainstay of management of gastroenteritis, and their composition continues to improve. Malnutrition remains the major adverse prognostic indicator for diarrhoea-related mortality, emphasising the importance of nutrition in early management. Drugs are of little use, except for specific indications although new agents that target mechanisms of secretory diarrhoea show promise, as do probiotics. However, preventive strategies on a global scale might ultimately hold the greatest potential to reduce the burden of diarrhoeal disease. These strategies include vaccines and, most importantly, policies to address persisting inequalities between the developed and developing worlds with respect to nutrition, sanitation, and access to safe drinking water.

Effect of pharmacologically induced smooth muscle activation on permeability in murine colitis

BACKGROUND

Both intestinal permeability and contractility are altered in inflammatory bowel disease. Little is known about their mutual relation. Therefore, an in vitro organ bath technique was developed to investigate the simultaneous effects of inflammation on permeability and smooth muscle contractility in different segments of the colon.

METHODS AND MATERIALS

BALB/c mice were exposed to a 10% dextran sulphate sodium drinking water solution for 7 days to induce a mild colitis, while control mice received normal tap water. Intestinal segments were placed in an oxygenated organ bath containing Krebs buffer. Permeability was measured by the transport of the marker molecules 3H-mannitol and 14C-polyethyleneglycol 4000. Contractility was measured through a pressure sensor. Smooth muscle relaxation was obtained by salbutamol and l-phenylephrine, whereas contraction was achieved by carbachol and 1-(3-chlorophenyl)-biguanide.

RESULTS

The intensity of mucosal inflammation increased throughout the colon. Also, regional differences were observed in intestinal permeability. In both normal and inflamed distal colon segments, permeability was diminished compared with proximal colon segments and the non-inflamed ileum. Permeability in inflamed distal colon segments was significantly decreased compared with normal distal segments. Pharmacologically induced relaxation of smooth muscles did not affect this diminished permeability, although an increased motility positively affected permeability in inflamed and non-inflamed distal colon.

CONCLUSIONS

Inflammation and permeability is inversely related. The use of pro-kinetics could counteract this disturbed permeability and, in turn, could regulate the disturbed production of inflammatory mediators.

Current understanding of gastrointestinal immunoregulation and its relation to food allergy

Tolerance to food antigens induced via the gut ("oral tolerance") appears to be a rather robust adaptive immune mechanism. However, the neonatal period is particularly critical in terms of mucosal defense, with regard to infections and priming for allergic disease. This is so because the intestinal barrier function provided by secretory antibodies, as well as the immunoregulatory network, is poorly developed for a variable period after birth. Notably, the postnatal development of mucosal immune homeostasis depends on the establishment of a normal commensal microbial flora and also on adequate timing and dose of dietary antigens when first introduced. In this context, breastfeeding appears to exert both shielding and positive regulatory effects. Altogether, the intestinal immune system normally seems rather fit for tolerance induction against innocuous antigens because most children with food allergy "outgrow" their problems, whereas airway allergy tends to persist.

Electrical charge on protein regulates its absorption from the rat small intestine

The effect of the electrical charge on the intestinal absorption of a protein was studied in normal adult rats. Chicken egg lysozyme (Lyz), a basic protein with a molecular weight of 14,300, was selected and several techniques for chemical modification were applied. Then the intestinal absorption of Lyz derivatives was evaluated by measuring the radioactivity in plasma and tissues, after the administration of an (111)In-labeled derivative to an in situ closed loop of the jejunum. After the administration of (111)In-Lyz, the level of radioactivity in plasma was comparable with the lytic activity of Lyz, supporting the fact that the radioactivity represents intact Lyz. (111)In-cationized Lyz showed a 2-3 times higher level of radioactivity in plasma, whereas the radioactivity of (111)In-anionized Lyz was much lower. The absorption rate of (111)In-Lyz derivatives calculated by a deconvolution method was correlated for the strength of their positive net charge. A similar relationship was observed using superoxide dismutase. These findings indicate that the intestinal absorption of a protein is, at least partially, determined by its electrical charge.

Ultrastructural characteristics of distal duodenum mucosa in patients with cirrhosis

OBJECTIVES

Morphological abnormalities observed by light microscopy, such as oedema or vasodilatation, have been described in intestinal mucosa of patients with cirrhosis, but no information is available regarding the ultrastructural characteristics of the intestinal epithelial layer. The aim of this observational study was to investigate the ultrastructural characteristics of the intestinal epithelial layer of duodenum mucosa in patients with cirrhosis.

METHODS

Six patients with advanced cirrhosis and six control patients without liver disease were included in the study. Biopsies were obtained from the distal duodenum during upper diagnostic endoscopy, and ultrastructural characteristics were studied by means of electron microscopy.

RESULTS

A distended interenterocyte space with intestinal epithelial cells closely attached by morphologically intact tight junctions has been observed in cirrhotic patients, together with shorter and wider microvilli than in the control subjects.

CONCLUSIONS

The epithelial layers from cirrhotic patients show ultrastructural abnormalities. However, it is not known if the observed alterations are related to the presence of increased intestinal permeability or to bacterial translocation, which are frequently found in these patients.

In vitro presentation of gliadin-derived peptides by different cell lines

BACKGROUND

Gliadin peptide presentation and T-cell activation are critical events in the pathogenesis of celiac disease. Several studies have been performed to identify the toxic gliadin peptides but the complexity of the antigenic fraction makes this analysis difficult. In this work, an in vitro model for the analysis of gliadin peptide presentation is studied.

METHODS

The human cell lines U937 and THP-1 (monocytic), DUCAF and VAVY (immortalised B cells) and HT-29 and Caco-2 (intestinal epithelial cells) were incubated with biotin-labelled gliadin (bG). FITC-labelled streptavidin was used to detect biotinylated peptides at the cell surface by flow cytometry.

RESULTS

All cell lines tested showed a fluorescence signal derived from bG, that was highest when cells were stimulated with IFN-gamma for 48 h. Time course experiments performed using THP-1 cells showed that after 4-h incubation, almost a maximal signal can be reached. THP-1 cells incubated at 4 degrees C or after paraformaldehyde fixation showed a substantial signal reduction, suggesting that metabolic activity was necessary for the detection of the maximal fluorescence signal at the cell surface. The presence of HLA class II-bound biotinylated peptides was observed in cell lysates of THP-1 cells incubated with bG.

CONCLUSIONS

In all cell lines tested, a specific biotin-peptide-derived signal was observed. This was increased after IFN-gamma treatment and decreased after fixation or incubation at low temperature. The signal was higher in monocytic and B-cell lines than in the epithelial cell lines. The use of this procedure could be a useful tool to study the in vitro processing and presentation of naturally gliadin-derived peptides.

Nutritional factors and immune functions of gut epithelium

The intestinal epithelium acts as a barrier to the external environment contained within the lumen of the gut. It also transports solutes for nutrition and for immunological surveillance. The present review develops the hypothesis that changes in diet, through the composition of the lumen environment, alter the expression of genes in the epithelium. These genes include those that encode for proteins that signal to the mucosal immune system. Directly changing the expression of signalling molecules in the intestinal epithelium using transgenic techniques alters immune function. For example, up regulation of the chemokine macrophage inflammatory protein-2 increases neutrophil recruitment. Furthermore, lumen molecules such as short-chain fatty acids regulate chemokine expression by epithelial cells. By this means, the epithelium acts as a transducing monolayer signalling between the contents of the intestine and the mucosal immune system.

Permeability measurement of macromolecules and assessment of mucosal antigen sampling using in vitro converted M cells

INTRODUCTION

M cells are located in the epithelial layer covering the gut-associated lymphoid tissue and are responsible for delivery of macromolecules and microorganisms to the underlying lymphoid cells. It has been shown that the human colonic cell line Caco-2 can be converted to M cells in vitro following coculture with isolated lymphocytes from murine Peyer's patches. Studies were undertaken to evaluate and characterize the transepithelial transport of select macromolecules across these in vitro derived M cells.

METHODS

Caco-2 cells were converted to M cells as reported previously. The morphology of Caco-2 cells and M cells was compared by transmission electron microscopy (TEM). The transport properties of macromolecules such as horseradish peroxidase, FITC-conjugated polystyrene beads, and radiolabeled dextrans were examined. The activation of murine antigen-specific T cells following transport of the antigen ovalbumin across the M-cell barrier was assessed by measuring cytokine production.

RESULTS

M cells were shown to be irregular in shape and have fewer and shorter microvilli compared to the Caco-2 cell progenitors. These cells were still able to form tight junctions and monolayers on polycarbonate membranes. Time-course studies demonstrated that the transport of polystyrene beads and large-molecular-weight dextrans at physiological temperature across M-cell-containing monolayers was size dependent and more rapid than across Caco-2 cell monolayers. The transport of dextrans was also shown to be temperature and concentration dependent. Befitting the role of the M cell in mucosal defense, protein antigen could be delivered by these cells in order to be processed and presented to antigen-specific CD4+ T lymphocytes.

DISCUSSION

The M-cell permeability model is a functional and practical system for evaluating the transport properties of macromolecules and assessing the potential for intestinal mucosal antigen sampling to elicit immunological responses.

The intestinal mucosa as a target for dietary polyunsaturated fatty acids

Several studies have reported beneficial effects of dietary polyunsaturated fatty acids (PUFA) on various aspects of both human and animal health, and particular reference has been made to their effects on systemic immune responses. Both immune stimulation and immune suppression have been reported, with the outcome dependent on the type of PUFA, the target cell, as well as the immune competence of the cells before exposure. The systemic and the mucosal immune systems are discrete entities, which have evolved specific approaches in the defense of the host. The latter comprises several interconnected tissues, which communicate with one another through the action of soluble mediators and the trafficking of cellular components. After the oral mucosa, the intestinal epithelium and its associated gut-associated lymphoid tissue are the primary targets of dietary components. Absorption of dietary PUFA and its incorporation into intestinal tissues has been well studied, but the consequences of these events in relation to local immune responses have received little attention. This article describes some of the immune mechanisms operating at this barrier and, where possible, pinpoints areas for which a modulatory role for PUFA has already been demonstrated. Although not an exhaustive treatise of the subject, it is hoped that this review will foster research into the specific interaction between dietary PUFA and cell populations comprising the intestinal barrier.

Gastrointestinal permeability during exercise: effects of aspirin and energy-containing beverages

The purpose of this study was to determine whether aspirin (A) ingestion combined with prolonged exercise increases gastrointestinal permeability and whether consumption of a carbohydrate-containing (CHO) or a CHO + glutamine-containing (CHO+G) beverage would reduce this effect. Seventeen subjects completed six experiments. They ingested A (1,300 mg) or placebo (P) pills the evening before and before running 60 min at 70% maximal oxygen uptake. Also, before running they ingested a solution containing 5 g lactulose (L), 5 g sucrose (S), and 2 g rhamnose (R). During each trial, either a 6% CHO beverage, a 6% CHO+G (0.6%; 41 mM) beverage, or a water placebo (WP) was consumed. For 4 h after a run, all urine was collected to measure urinary excretion of L, R, and S. S excretion (percentage of dose ingested; measure of gastroduodenal permeability) was significantly greater (P < 0.05) during the A trial while the subjects drank the WP compared with all other trials. Administration of A also significantly increased L/R (measure of intestinal permeability) for the CHO and WP trials compared with all P trials. Ingestion the CHO or CHO+G beverages significantly reduced S excretion and L excretion when A was administered, but it did not reduce L/R. These results indicate that gastroduodenal and intestinal permeability increase after A ingestion during prolonged running and that ingestion of a CHO beverage attenuates the gastroduodenal effect but not the intestinal effect. Furthermore, addition of G to the CHO beverage provided no additional benefit in reducing gastroduodenal or intestinal permeability.

Probiotics in human disease

Western civilization is facing a progressive increase in immune-mediated, gut-related health problems, such as allergies and autoimmune and inflammatory diseases, and genetic factors are an unlikely explanation for these rapid increases in disease incidence. Two environmental factors that relate to the modern lifestyle in Western societies are hygiene and nutrition. There has been a decline in the incidence of microbial stimulation by infectious diseases as a result of improved hygiene, vaccination, and antimicrobial medication. In the past, methods of food preservation involved either the natural fermentation or drying of foods; thus, the human diet once contained several thousand times more bacteria than it does today. The development of probiotic, functional foods aims to "kill two birds with one stone," which is accomplished by providing a microbial stimulus to the host immune system by means of beneficial live microorganism cultures that are characteristic of the healthy, human gut microflora, ie, probiotics. Probiotic bacteria were shown to reinforce the different lines of gut defense, which are immune exclusion, immune elimination, and immune regulation. They were also shown to stimulate nonspecific host resistance to microbial pathogens, thereby aiding in pathogen eradication. Consequently, the best documented clinical application of probiotics is in the treatment of acute diarrhea. In humans, documented effects were reported for the alleviation of intestinal inflammation, normalization of gut mucosal dysfunction, and down-regulation of hypersensitivity reactions. These data show that probiotics promote endogenous host defense mechanisms. Thus, modification of gut microflora by probiotic therapy may offer a therapeutic potential in clinical conditions associated with gut-barrier dysfunction and inflammatory response.

Induction of mucosal immune response after intranasal or oral inoculation of mice with Lactococcus lactis producing bovine beta-lactoglobulin

The bovine beta-lactoglobulin (BLG) is a major cow's milk allergen. Here, we evaluated the immune response against BLG induced in mice, using the organism Lactococcus lactis, which has GRAS ("generally regarded as safe") status, as a delivery vehicle. The cDNA of the blg gene, encoding BLG, was expressed and engineered for either intra- or extracellular expression in L. lactis. Using a constitutive promoter, the yield of intracellular recombinant BLG (rBLG) was about 20 ng per ml of culture. To increase the quantity of rBLG, the nisin-inducible expression system was used to produce rBLG in the cytoplasmic and extracellular locations. Although the majority of rBLG remained in the cytoplasm, the highest yield (2 microg per ml of culture) was obtained with a secreting strain that encodes a fusion between a lactococcal signal peptide and rBLG. Whatever the expression system, the rBLG is produced mostly in a soluble, intracellular, and denatured form. The BLG-producing strains were then administered either orally or intranasally to mice, and the immune response to BLG was examined. Specific anti-BLG immunoglobulin A (IgA) antibodies were detected 3 weeks after the immunization protocol in the feces of mice immunized with the secreting lactococcal strain. Specific anti-BLG IgA detected in mice immunized with lactococci was higher than that obtained in mice immunized with the same quantity of pure BLG. No specific anti-BLG IgE, IgA, IgG1, or IgG2a was detected in sera of mice. These recombinant lactococcal strains constitute good vehicles to induce a mucosal immune response to a model allergen and to better understand the mechanism of allergy induced by BLG.

Adherence of probiotic bacteria to human intestinal mucus in healthy infants and during rotavirus infection

The concentration of fecal mucin and the adhesion of specific probiotics and their combinations in the intestinal mucus of infants during and after rotavirus diarrhea and in healthy children were determined. Mucus was prepared from fecal samples from 20 infants during and after rotavirus diarrhea and from 10 healthy age-matched children. Mucin concentration was determined, and the adhesion of five probiotics-Lactobacillus rhamnosus GG, Lactobacillus casei Shirota, Lactobacillus paracasei F19, Lactobacillus acidophilus LA5, and Bifidobacterium lactis Bb12-and their combinations was tested in vitro. The mean concentrations of fecal mucin during and after rotavirus diarrhea, 15.2 and 14.1 mg/g, were comparable to that in healthy children, 14.9 mg/g. The adherence of probiotics ranged from 1 to 34% in healthy subjects as indicated for the following strains: L. rhamnosus GG, 34%; B. lactis Bb12, 31%; L. acidophilus LA5, 4%; L. paracasei F19, 3%; and L. casei Shirota, 1% (P = 0.0001). The distinctive pattern of probiotic adherence was not influenced by rotavirus diarrhea. The adhesion of Bb12 in the presence of GG increased from 31 to 39% in healthy infants (P = 0.018) and in episodes of diarrhea increased from 26 to 44% (P = 0.001). Rotavirus diarrhea does not decrease the production of fecal mucin or with respect to the adhesion of probiotic bacteria tested in vitro. Combination of specific probiotic strains may enhance adherence in a synergistic manner. Optimal clinical application of these interactions may offer novel therapeutic guidelines for the treatment and prevention of gastrointestinal infections.

Probiotics: effects on immunity

The gastrointestinal tract functions as a barrier against antigens from microorganisms and food. The generation of immunophysiologic regulation in the gut depends on the establishment of indigenous microflora. This has led to the introduction of novel therapeutic interventions based on the consumption of cultures of beneficial live microorganisms that act as probiotics. Among the possible mechanisms of probiotic therapy is promotion of a nonimmunologic gut defense barrier, which includes the normalization of increased intestinal permeability and altered gut microecology. Another possible mechanism of probiotic therapy is improvement of the intestine's immunologic barrier, particularly through intestinal immunoglobulin A responses and alleviation of intestinal inflammatory responses, which produce a gut-stabilizing effect. Many probiotic effects are mediated through immune regulation, particularly through balance control of proinflammatory and anti-inflammatory cytokines. These data show that probiotics can be used as innovative tools to alleviate intestinal inflammation, normalize gut mucosal dysfunction, and down-regulate hypersensitivity reactions. More recent data show that differences exist in the immunomodulatory effects of candidate probiotic bacteria. Moreover, distinct regulatory effects have been detected in healthy subjects and in patients with inflammatory diseases. These results suggest that specific immunomodulatory properties of probiotic bacteria should be characterized when developing clinical applications for extended target populations.

Small intestinal mucosal immunity and morphometry in luminal overgrowth of indigenous gut flora

OBJECTIVE

The aim of this study was to investigate the separate effects of indigenous oropharyngeal- and colonic-type flora on small intestinal mucosal immunity and morphometry in small intestinal bacterial overgrowth (SIBO).

METHODS

A duodenal aspirate and random biopsies of underlying mucosa were obtained from 52 adult subjects (age range, 18-90 yr; median, 60 yr) without disorders that may otherwise disturb small intestinal histology or mucosal immunity. Villus height, crypt depth, villus/crypt ratios, counts of intraepithelial lymphocytes (IELs) and lamina propria total mononuclear cells, IgA, IgM, and IgG plasma cells, mast cells, and B and T lymphocytes were determined in relation to the presence or absence of SIBO and the nature of the overgrowth flora in all subjects. CD4+ve and CD8+ve T-cell counts were determined in 24 subjects.

RESULTS

SIBO was present in 26 of 52 (50%) subjects. Overgrowth flora included colonic-type bacteria in 20 subjects and oropharyngeal-type flora alone in 6 subjects. Lamina propria IgA plasma cell counts were significantly increased in subjects with SIBO, irrespective of whether the overgrowth flora comprised oropharyngeal-type flora alone or included colonic-type bacteria. Neither villus height, crypt depth, villus/crypt ratios, nor total or other mononuclear cell counts in lamina propria differed significantly between subjects with and without SIBO, irrespective of the nature of the overgrowth flora. IEL counts were significantly higher than in culture-negative subjects only when the overgrowth flora included colonic-type bacteria. Even then, IEL counts were within a range currently considered normal. A significant, inverse correlation between advancing age and IEL counts became apparent after adjusting for the effect of SIBO of colonic-type flora.

CONCLUSIONS

SIBO of oropharyngeal- and colonic-type flora are associated with differing disturbances of local duodenal mucosa. Nonetheless, these would not be readily apparent during routine histological assessment. Old age independently influences duodenal IEL counts.

Horseradish peroxidase binding to intestinal brush-border membranes of Cyprinus carpio. Identification of a putative receptor

Morphologic studies have shown that the classic endocytosis tracer horseradish peroxidase (HRP) is actively internalized by vesicular transport in the carp intestine, suggesting the existence of specific binding sites in the apical membrane of enterocytes. The aim of the present study was to develop an in vitro binding assay using isolated carp intestinal brush-border membranes (BBM) to demonstrate and characterize these specific HRP binding sites. The results obtained show that HRP binding to BBM exhibits a saturable mode and high affinity (K(d) = 22 nM). In addition, HRP binding sites are highly enriched in BBM compared to basolateral membranes. On the other hand, HRP interaction with these sites is apparently of an ionic character because binding increased concomitantly with decreasing NaCl concentrations in the assay, reaching a maximum in the absence of NaCl. Other proteins that are also internalized in carp intestine did not significantly inhibit HRP binding to BBM. A lectin-type of interaction was discarded because neither manan nor ovoalbumin inhibited HRP binding. Proteinase K treatment of BBM reduced HRP binding by 70%, suggesting a proteic nature for this binding site. Finally, ligand blotting assays showed that HRP binds specifically to a 15.3-kDa protein. Taken together, these results are consistent with the existence of a functional receptor for HRP in carp intestinal mucosa that could mediate its internalization.

Enhanced intestinal transepithelial antigen transport in allergic rats is mediated by IgE and CD23 (FcepsilonRII)

We previously reported that active sensitization of rats resulted in the appearance of a unique system for rapid and specific antigen uptake across intestinal epithelial cells. The current studies used rats sensitized to horseradish peroxidase (HRP) to define the essential components of this antigen transport system. Sensitization of rats to HRP stimulated increased HRP uptake into enterocytes (significantly larger area of HRP-containing endosomes) and more rapid transcellular transport compared with rats sensitized to an irrelevant protein or naive control rats. Whole serum but not IgE-depleted serum from sensitized rats was able to transfer the enhanced antigen transport phenomenon. Immunohistochemistry demonstrated that sensitization induced expression of CD23, the low-affinity IgE receptor (FcepsilonRII), on epithelial cells. The number of immunogold-labeled CD23 receptors on the enterocyte microvillous membrane was significantly increased in sensitized rats and was subsequently reduced after antigen challenge when CD23 and HRP were localized within the same endosomes. Finally, pretreatment of tissues with luminally added anti-CD23 antibody significantly inhibited both antigen transport and the hypersensitivity reaction. Our results provide evidence that IgE antibodies bound to low-affinity receptors on epithelial cells are responsible for the specific and rapid nature of this novel antigen transport system.

Development of intestinal transport function in mammals

Considerable progress has been made over the last decade in the understanding of mechanisms responsible for the ontogenetic changes of mammalian intestine. This review presents the current knowledge about the development of intestinal transport function in the context of intestinal mucosa ontogeny. The review predominantly focuses on signals that trigger and/or modulate the developmental changes of intestinal transport. After an overview of the proliferation and differentiation of intestinal mucosa, data about the bidirectional traffic (absorption and secretion) across the developing intestinal epithelium are presented. The largest part of the review is devoted to the description of developmental patterns concerning the absorption of nutrients, ions, water, vitamins, trace elements, and milk-borne biologically active substances. Furthermore, the review examines the development of intestinal secretion that has a variety of functions including maintenance of the fluidity of the intestinal content, lubrication of mucosal surface, and mucosal protection. The age-dependent shifts of absorption and secretion are the subject of integrated regulatory mechanisms, and hence, the input of hormonal, nervous, immune, and dietary signals is reviewed. Finally, the utilization of energy for transport processes in the developing intestine is highlighted, and the interactions between various sources of energy are discussed. The review ends with suggestions concerning possible directions of future research.

Mucosal in vitro permeability in the intestinal tract of the pig, the rat, and man: species- and region-related differences

BACKGROUND

The barrier properties of the gastrointestinal mucosa may be studied by measuring its permeability to different-sized marker molecules. Owing to difficulties in obtaining human tissue it is, however, often necessary to extrapolate findings from experimental animals to man. The aim of the present study was to compare regional intestinal mucosal permeability in man, the rat, and the pig, using the same marker molecules and in vitro technique.

METHODS

Segments from jejunum, ileum, colon, and rectum were mounted in Ussing diffusion chambers, and the mucosa-to-serosa passage of 14C-mannitol, fluorescein isothiocyanate (FITC)-dextran 4,400, alpha-lactalbumin, ovalbumin, and FITC-dextran 70,000 was studied.

RESULTS

Irrespective of species or intestinal region an inverse relationship between the molecular weight of the markers and the permeability was seen. The mannitol permeability was higher in the small intestine than in the colon in man, whereas the rat showed a higher permeability in the ileum than in the jejunum and colon. The FITC-dextran 4,400 permeability was higher in all intestinal regions in the rat than in man and the pig. The macromolecules showed low permeability with no regional differences.

CONCLUSIONS

The results showed differences between intestinal regions and between species. Permeability data from the pig correlated fairly well with those of man, whereas the rat differed, making it difficult to extrapolate from the rat to man.

Bioactive molecules in milk and their role in health and disease: the role of transforming growth factor-beta

Human breast milk is rich in nutrients, hormones, growth factors and immunoactive molecules, which influence the growth, development and immune status of the newborn infant. Although several of these factors are also present in bovine milk, the greater susceptibility of the formula-fed infant to infection and disease and the development of allergy is often attributed to the reduced level of protective factors in milk formulas. Nevertheless, modifying manufacturing processes may preserve the biological activity of some bioactive molecules in end products. Transforming growth factor (TGF)-beta is one such molecule. TGF-beta is a polypeptide, which has been described in both human and bovine milk. It is implicated in many processes, including epithelial cell growth and differentiation, development, carcinogenesis and immune regulation. The present article discusses the biological activity of TGF-beta2 that has been preserved and activated in a cow's milk-based product. More specifically, it addresses possible mechanisms of action in the intestinal lumen and speculates on how milk products containing naturally occurring TGF-beta2 could be exploited in functional foods for the infant or as therapies for specific intestinal diseases.

Food protein-induced enterocolitis syndrome: laboratory perspectives

The expression of food protein allergy in man is very heterogeneous, varies with the age of the subject and is to a certain extent genetically determined. Skin prick tests with standardized food extracts are a sensitive method for detection of immunoglobulin E bound to reactive cells such as mast cells. Various tests on cellular immunity have been developed, especially because T-cell mediated reactions are considered to play a role in mainly delayed gastrointestinal reactions to cow's milk proteins. Food allergy may involve the entire gut, from mouth to rectum, including the esophagus. Abnormalities in intestinal permeability are the hallmarks of the inflamed gut, and may contribute to diagnosis of food induced enteropathy. What determines the characteristics of the intestinal inflammatory response is largely the cytokine responses triggered by the pathologic mechanism, whatever its origin, in the stomach, the small intestine, and the colon. A so-called T-helper type 2 response is characteristic of the allergic subject. A secretion of tumor necrosis factor-alpha alpha by blood cells of children allergic to milk was shown. All means of investigation may help in analyzing food substitutes for allergic infants.

Modulation of antigen trafficking to MHC class II-positive late endosomes of enterocytes

BACKGROUND & AIMS

Oral tolerance is recognized as a central immunoregulatory phenomenon. The mechanisms of its induction remain unclear, and the role of the intestinal epithelial cells that are able to present antigens to T lymphocytes is poorly understood. In this report, we analyze under in vivo conditions the intracellular targeting of mucosally administered ovalbumin (OVA) to major histocompatibility complex (MHC) class II antigen containing compartments of enterocytes and compare these pathways between BALB/c and SCID mice, the latter being unable to generate a transferable tolerogenic moiety after a feed of OVA.

METHODS

OVA, lysosome-associated membrane proteins (LAMP-1), and MHC class II antigens were localized in jejunal biopsy specimens of BALB/c and SCID mice at 0, 5, 10, 20, 40, 60, and 120 minutes after a single feed with OVA by fluorescence and electron microscopy.

RESULTS

Ten minutes after oral administration, OVA was transported to the proximity of MHC class II antigens within LAMP-1-positive vacuoles and to the basolateral membrane of enterocytes from BALB/c strain mice. However, in SCID mice, OVA reached the paracellular spaces during the same time period through LAMP-1-negative vacuoles of enterocytes, which lacked MHC class II antigens.

CONCLUSIONS

Orally administered OVA is rapidly targeted to late endosomes containing LAMP-1 and MHC class II antigens in enterocytes of BALB/c mice but not in SCID mice bred on a BALB/c background. We suggest that this targeting process within the enterocytes is one of the requirements for the induction of oral tolerance.

The intestinal epithelial cell: processing and presentation of antigen to the mucosal immune system

The immunologic tone of the intestinal tract is one of suppressed or highly regulated responses. While there are several components (intrinsic and extrinsic to the gut-associated lymphoid tissue) responsible for this immunologically suppressed tone, the intestinal epithelial call (IEC) has been proposed as a key player in this process. IECs can take up and process antigen but distinct surface molecules and restriction elements allow them to present these antigens to unique regulatory T cells. These include the expression of the class Ib molecule CD1d as well as a novel CD8 ligand, gp180. These molecules come together to activate a subpopulation of CD8+ regulatory cells whose function is to suppress immune responses in an antigen non-specific fashion most likely through cognate interactions. This form of regulation may be unique to the gut-associated lymphoid tissue which is consistent with the unusual demands upon this part of the immune system.

Total parenteral nutrition alters molecular and cellular indices of intestinal inflammation in neonatal piglets

BACKGROUND

The adverse effects of TPN on systemic immunity are well-documented; however, the impact of IV feeding on neonatal intestinal immunity is unknown.

METHODS

A piglet TPN model was used to compare immune cell composition within the intestinal epithelium and lamina propria of parenterally and orally fed piglets.

RESULTS

Small intestinal weight of piglets maintained intravenously was reduced 50% after 7 days. Intestinal atrophy in piglets fed parenterally was evidenced by decreased width of intestinal villi and colon cuffs and reduced intestinal crypt depth. The numbers of CD4+ and CD8+ T lymphocytes were threefold greater within the lamina propria of jejunal and ileal villi of piglets supported intravenously. Inverse correlations were observed between villus height or width and T-lymphocyte numbers (r = -.80; p < .05). Major histocompatibility complex class II mRNA expression, an indicator of localized inflammation, was increased in the ileum and colon of piglets receiving parenteral nutrition. Goblet cell numbers were two-fold greater in jejunal and ileal villi, and mast cells were more abundant in the colon of piglets fed parenterally. Furthermore, jejunal T-lymphocyte numbers were correlated with goblet cell numbers (r = .80; p = .01).

CONCLUSIONS

These data identify molecular and cellular indices of intestinal inflammation that are responsive to IV feeding in neonates and provide a novel framework to investigate mechanisms underlying gut atrophy during TPN.

The B-cell system of human mucosae and exocrine glands

The mucosae and exocrine glands harbour the largest activated B-cell system of the body, amounting to some 80-90% of all immunoglobulin (Ig)-producing cells. The major product of these immunocytes is polymeric (p)IgA (mainly dimers) with associated J chain. Both pIgA and pentameric IgM contain a binding site for the polymeric Ig receptor (pIgR), or secretory component (SC), which is a requirement for their active external transport through secretory epithelia. The pIgR/SC binding site depends on covalent incorporation of the J chain into the quaternary structure of the polymers when they are produced by the local immunocytes. This important differentiation characteristic appears to be sufficient functional justification for the J chain to be expressed also by most B cells terminating at secretory effector sites with IgD or IgG production; they probably represent a "spin-off" from sequential downstream CH switching on its way to pIgA expression, thus apparently reflecting a maturational stage of effector B-cell clones compatible with homing to these sites. Observations in IgA-deficient individuals suggest that the magnitude of this homing is fairly well maintained even when the differentiation pathway to IgA is blocked. Certain microenvironmental elements such as specific cytokines and dendritic cells appear to be required for induction of IgA synthesis, but it remains virtually unknown why this isotype normally is such a dominating product of local immunocytes and why they have such a high level of J chain expression. Also, despite the recent identification of some important requirements in terms of adhesion molecules (e.g. integrin alpha 4 beta 7 and MAdCAM-1) that explain the "gut-seeking" properties of enterically induced B cells, the origin of regionalized homing of B cells to secretory effector sites outside the gut remains elusive. Moreover, little is known about immune regulation underlying the striking disparity of both the class (IgD, IgM) and subclass (IgA1, IgA2, IgG1, IgG2) production patterns shown by local immunocytes in various regions of the body, although the topical microbiota and other environmental stimuli might be important. Rational design of local vaccines will depend on better knowledge of both inductive and migratory properties of human mucosal B cells.

Adherent surface mucus gel restricts diffusion of macromolecules in rat duodenum in vivo

The aim of this study was to investigate the permeability of the adherent mucus gel layer in rat duodenum in vivo to macromolecules applied in the lumen. Rats were anesthetized with thiobarbiturate, and the duodenum was perfused with isotonic NaCl solution containing large-molecular-size secretagogues. Effects on mucosal HCO(-)(3) secretion and blood-to-lumen (51)chromium-labeled EDTA clearance were used as indexes that compounds had migrated across the mucus layer. Exposure to a low concentration of papain (10 U/100 ml) for 30 min removed the mucus layer without damage to the epithelium and induced or markedly enhanced HCO(-)(3) secretory responses to cholera toxin (molecular mass of 85 kDa) or glucagon (3.5 kDa). Water extracts from a VacA cytotoxin (89 kDa) producing Helicobacter pylori strain, but not from a toxin-negative isogenic mutant, caused a small increase in HCO(-)(3) secretion but only after the mucus layer had been removed by papain. The duodenal surface mucus gel thus significantly restricts migration of macromolecules to the duodenal surface. Release of bacterial toxins at the cell-mucus interface may enhance or be a prerequisite for their effects on the gastrointestinal mucosa.

Epithelial permeability to proteins in the noninflamed ileum of Crohn's disease?

BACKGROUND & AIMS

Crohn's disease (CD) is associated with a disturbed intestinal barrier. Permeability studies have focused on inert molecules, but little is known about transepithelial transport of macromolecules with antigenic potential in humans. The aim of this study was to quantify permeation and to characterize passage routes for macromolecules in ileal mucosa in CD.

METHODS

Noninflamed and inflamed ileal mucosa specimens from patients with CD (n = 12) and ileal specimens from patients with colon cancer (n = 7) were studied regarding transmucosal permeation of ovalbumin, dextran (mol wt, 40,000), and 51Cr-EDTA for 90 minutes in vitro in Ussing chambers. Transepithelial passage routes for fluorescent ovalbumin and dextran 40,000 were investigated by confocal microscopy.

RESULTS

Noninflamed ileum from CD patients showed increased permeation of ovalbumin compared with ileum from colon cancer patients (P < 0.05). Dextran permeation was equal in the three groups, whereas 51Cr-EDTA permeability was increased in inflamed ileum. Ovalbumin passed both transcellularly and paracellularly, but dextran followed a strictly paracellular route. Both markers were subsequently endocytosed by cells of the lamina propria.

CONCLUSIONS

Noninflamed ileal mucosa from patients with CD shows increased epithelial permeability to ovalbumin, probably by augmented transcytosis. This increase in antigen load to the lamina propria could be an initiating pathogenic event in CD.

Small bowel T cells, HLA class II antigen DR, and GroEL stress protein in IgA nephropathy

BACKGROUND

Previous studies suggest that intestinal mucosa may be involved in the pathogenesis of IgA nephropathy (IgAN). To further clarify this involvement, we investigated whether or not IgAN patients have small bowel mucosal findings suggestive of inflammation and stress.

METHODS

Seventeen patients with IgAN underwent gastroscopic examination. Fresh small bowel biopsy specimens were frozen, and in cryosections, the proportion of alphabeta and gammadelta receptors bearing T cells and CD3+ T cells were quantitated immunohistochemically. The expression of HLA class II antigen DR (HLA-DR) and human GroEL stress-protein homologue was similarly quantitated. In an avidin-biotin peroxidase technique, the following monoclonal primary antibodies were used: anti-beta-chain (betaF1), anti-delta-chain (TCRdelta1), anti-CD3 (Leu4), anti-constant fragment of HLA-DR (L243), and anti-GroEL (ML30). Twenty-nine patients who had undergone gastroscopy because of dyspepsia served as controls.

RESULTS

In all specimens, the mucosal architecture was normal. The amount of gammadelta T cells and the total amount of T cells, as indicated by CD3+ positivity, were both significantly increased in IgAN. The number of alphabeta T cells was also higher in the IgAN patients. Villous epithelium of the IgAN patients disclosed a significant increase in the expression of HLA-DR antigen and GroEL stress protein.

CONCLUSIONS

Our results suggest that ongoing small bowel inflammation and stress are present in IgAN. Despite normal morphology, there is reason to believe that the small bowel mucosa is involved in the pathogenesis of IgAN.