Intestinal anaphylaxis in the rat. Effect of chronic antigen exposure

5-HT 3 receptors mediate the time-dependent vagal afferent modulation of nociception during chronic food allergen-sensitized visceral hyperalgesia in rats

Converging lines of evidence demonstrate a vagally mediated antinociceptive pathway in animals undergoing acute visceral insults, the contribution of this system to visceral pain following chronic noxious stimuli is unknown. 5-HT(3) receptor (5-HT(3)Rs) on spinal afferents are crucially involved in nociceptive processing, the role of 5-HT(3)Rs on vagal afferents is unclear. The aim of the present study was to determine the contribution of vagal afferents to visceral nociception in rats undergoing chronic luminal allergen stimulation and whether it involves vagal 5-HT(3)Rs. Sensitized rats received chicken egg albumin (EA, 1 mg mL(-1)) in drinking water for 2 weeks (day 1-14). Visceromotor response (VMR) to colorectal distension [colorectal distension (CRD), 60 mmHg] and the levels of mRNA encoding 5-HT(3)R (including 3A and 3B subunits) in the nodose ganglia (NG) were evaluated on day 2, 4, 8 and 15. Chronic EA challenge induced gradually increased visceral nociception, with a peak on day 15. Subdiaphragmatic vagotomy or functional deafferentation with capsaicin abolished this time-dependent manner, inducing hyperalgesia from day 2, lasting to day 15. Intraluminal infusion of a 5-HT(3)R antagonist (granisetron), whether alone or infused after local mucosa anaesthetic with 1% lidocaine, mimicked the effects of vagotomy. The mRNA levels for 5-HT(3B) or 5-HT(3A) subunit in the NG showed an opposite time-course to that of visceral pain, which increased from day 2, then decreased gradually to levels lower than those of controls. Our results demonstrate a time-dependent vagal afferent modulation of chronic allergen-sensitized visceral hyperalgesia, which may involve a 5-HT(3)R pathway.

Murine model of food allergy after epicutaneous sensitization: role of mucosal mast cell protease-1

OBJECTIVE

Studies of the pathological mechanisms of food allergy have been impeded by the lack of relevant animal models. The purpose of this study was to develop a physiological model of food allergy that was not dependent on immunostimulatory adjuvants.

MATERIAL AND METHODS

Balb/c mice were epicutaneously sensitized four times at varying intervals over a 22-day period, and challenged orally from day 40, 6 times every 1-3 days with either saline or ovalbumin.

RESULTS

After sensitization (day 35) but before the oral challenges, the ovalbumin-sensitized groups showed increased specific IgE and IgG1 production when compared with the sham-sensitized groups. Mucosal mast cell protease-1 (MMCP-1) was undetectable in serum before the intragastric challenge. MMCP-1 concentrations were increased after the first ovalbumin dose, solely in the ovalbumin-sensitized and -challenged group. After the challenge period, the mean serum MMCP-1 concentration increased from an undetectable level in controls to an over 44-fold level in the ovalbumin-sensitized and -challenged mice. In this group, MMCP-1-positive cells were present in the small intestine and expressions of IFN-gamma and CXCL-9 mRNA were decreased in the ileum, suggesting an impaired Th-1-type response. Within one hour of the last ovalbumin challenge, 5 out of 6 mice developed diarrhea in the ovalbumin-sensitized and -challenged group, but there was no diarrhea in the other groups.

CONCLUSIONS

A murine model of food allergy based on sensitization via epicutaneous exposure to allergen without immunostimulatory adjuvants was developed. Effective production of MMCP-1 together with specific IgE and IgG1 suggests a breakdown in oral tolerance to the allergen. Intragastric challenges were accompanied by mast cell-dependent immunopathological changes and diarrhea.

Immunopathology of giardiasis: the role of lymphocytes in intestinal epithelial injury and malfunction

T lymphocyte-mediated pathogenesis is common to a variety of enteropathies, including giardiasis, cryptosporidiosis, bacterial enteritis, celiac's disease, food anaphylaxis, and Crohn's disease. In giardiasis as well as in these other disorders, a diffuse loss of microvillous brush border, combined or not with villus atrophy, is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water, which ultimately cause diarrheal symptoms. Other mucosal changes may include crypt hyperplasia and increased infiltration of intra-epithelial lymphocytes. Recent studies using models of giardiasis have shed new light on the immune regulation of these abnormalities. Indeed, experiments using an athymic mouse model of infection have found that these epithelial injuries were T cell-dependent. Findings from further research indicate that that the loss of brush border surface area, reduced disaccharidase activities, and increase crypt-villus ratios are mediated by CD8+ T cells, whereas both CD8+ and CD4+ small mesenteric lymph node T cells regulate the influx of intra-epithelial lymphocytes. Future investigations need to characterize the CD8+ T cell signaling cascades that ultimately lead to epithelial injury and malfunction in giardiasis and other malabsorptive disorders of the intestine.

Hypersensitivity to ovalbumin induces chronic intestinal dysmotility and increases the number of intestinal mast cells

Undiagnosed food allergies have been proposed as possible causes of promoting and perpetuating irritable bowel syndrome . Our aim was to find out if sensitization could induce chronic functional motor disturbances in the intestine and the mechanisms implicated. Rats were sensitized to ovalbumin (OVA) following three hypersensitivity induction protocols, two parenteral and one oral. Rat mast cell protease II (RMCP II) release in response to OVA challenge and immunoglobulin E (IgE) concentration were measured in serum. At least 1 week after challenge, small intestinal motility was evaluated using strain gauges. Intestinal tissue samples from orally sensitized rats were checked for in vitro stimulation with OVA. Mucosal mast cells were counted from duodenum sections. All sensitized rats showed intestinal hypermotility. Only rats sensitized by parenteral procedure showed an increase in RMCP II after OVA challenge in serum. IgEs increased only in the Bordetella pertussis sensitized group. Small intestine sections from orally sensitized rats released more RMCP II than sections from control rats. All sensitized rats showed an increase in the number of mucosal mast cells in duodenum. In conclusion, hypersensitivity to food proteins induces chronic motor alteration that persists long after antigen challenge and an excited/activated state of sensitized mucosal mast cells.

Parenteral immunization to beta-lactoglobulin modifies the intestinal structure and mucosal electrical parameters in rabbit

Systemic and local immune responses and the intestinal structure were examined in parenterally beta-Lg-sensitized rabbits. Immunization led to high IgG titers against beta-Lg. In a Ussing chamber, a sensitized ileum had a higher short-circuit current (Isc) and potential difference (PD) than a control following in vitro beta-Lg challenge. Histological study indicated that presence of the sensitizing antigen affected and considerably modified the structure of the intestinal mucosa in sensitized rabbits when compared to controls. These alterations were revealed by active atrophy and marked infiltration of the lymphocytes. These findings indicate that antigen exposure results in morphological changes and abnormalities affecting the transport of water and electrolytes. This study provides a clearer understanding of the physiopathological mechanisms of allergy to cow's milk protein.

Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.

A model of chronic IgE-mediated food allergy in ovalbumin-sensitized mice

Food allergy is most frequently the result of IgE-mediated hypersensitivity reactions. Here, we describe a chronic model in which some of the intestinal and systemic consequences of continuous egg white solution ingestion by ovalbumin-sensitized eight-week-old BALB/c mice, 6 animals per group, of both sexes, were investigated. There was a 20% loss of body weight that began one week after antigen exposure and persisted throughout the experiment (3 weeks). The sensitization procedure induced the production of anti-ovalbumin IgG1 and IgE, which were enhanced by oral antigen exposure (129% for IgG1 and 164% for IgE, compared to sensitization values). Intestinal changes were determined by jejunum edema at 6 h (45% Evans blue extravasation) and by a significant eosinophil infiltration with a peak at 48 h. By day 21 of continuous antigen exposure, histological findings were mild, with mast cell hyperplasia (100%) and increased mucus production (483%). Altogether, our data clearly demonstrate that, although immune stimulation was persistently occurring in response to continuous oral antigen exposure, regulatory mechanisms were occurring in the intestinal mucosa, preventing overt pathology. The experimental model described here reproduces the clinical and pathological changes of mild chronic food allergy and may be useful for mechanistic studies of this common clinical condition.

Chronic allergy to dietary ovalbumin induces lymphocyte migration to rat small intestinal mucosa that is inhibited by MAdCAM-1

Few models have described a chronic food allergy with morphological changes in the intestinal mucosa. Here we established an ovalbumin (OVA)-induced, cell-mediated, allergic rat model and examined lymphocyte migration in the gut. Brown Norway rats were intraperitoneally sensitized to OVA and then given 10 mg OVA/day by gastric intubation for 6 wk. Lymphocyte subsets and adhesion molecules were examined immunohistochemically, and the migration of T lymphocytes to microvessels of Peyer's patches and villus mucosa was observed by using an intravital microscope. Serum OVA-specific IgG and IgE levels were increased in animals repeatedly exposed to OVA. Significant villus atrophy and increased crypt depth was accompanied by increased infiltration of T lymphocytes in the small intestinal mucosa of the group given OVA. Expression of rat mast cell protease II and of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was also increased in these groups. The administration of anti-MAdCAM-1 antibody significantly attenuated the OVA-induced changes in the mucosal architecture and in CD4 T lymphocyte infiltration. Intravital observation demonstrated that in rats with a chronic allergy, T lymphocytes significantly accumulated in villus microvessels as well as in Peyer's patches via a MAdCAM-1-dependent process. Our model of chronic food allergy revealed that lymphocyte migration was increased with MAdCAM-1 upregulation.

Alteration of CCK-induced satiety in post-Nippostrongylus brasiliensis-infected rats

In rats, the nematode Nippostrongylus brasiliensis induces an intestinal inflammation, but after the inflammation had resolved and the worm burden eliminated, morphological alterations of the intestinal wall, mainly consisting of mast cell hyperplasia and enteric nerve remodeling, persist for several weeks. Intestinal signals reaching the brain through the vagus nerve and involving neuropeptides such as CCK, play a role in the control of food intake. Our hypothesis was that neuroimmune alterations of the intestine may alter this control. This work was aimed to evaluate whether post-infection alterations of the intestinal wall may affect the satiety effects of CCK and further, the role of mast cells and their mediators, histamine and serotonin, in post-N. brasiliensis-infected rats. In basal conditions, food intake was not different in control and post-infected groups of rats. Post-infected rats were characterized by prolonged satiety effects of both CCK and histamine but not serotonin. The prolonged effect of CCK was reduced when mast cells were previously stabilized by ketotifen, which had no effect per se on food intake. No difference was observed in the increase of food intake induced by CCK-A and CCK-B receptor antagonists in both control and post-infected rats. Mast cell degranulation with compound 48/80 induced severe anorectic effects that lasted for less than 24h in post-infected rats and as long as 6 days in controls. Thus, in our experimental conditions, i.e., within 30-50 days post-N. brasiliensis infection, we observed an enhancement of the anorectic effect of exogenous CCK involving mast cell degranulation and histamine.

Giardia duodenalis trophozoites isolated from a parrot (Cacatua galerita) colonize the small intestinal tracts of domestic kittens and lambs

This study examines the ability of Giardia duodenalis trophozoites, isolated from a wild bird, to colonize the intestinal tracts of companion animals (kittens) and domestic ruminants (lambs). Trophozoites colonized the intestinal tracts of intraduodenally inoculated animals as demonstrated by increasing parasite burdens within the duodenum and jejunum and by fecal passage of cysts within 4 days post-inoculation. The pathogenesis of the trophozoites was further investigated in kittens. In these animals, infection significantly reduced jejunal brush border microvillous length and density, which resulted in a loss of overall epithelial brush border surface area. This injury was associated with the production of diarrhea in four of five infected kittens. These findings indicate that some bird species may carry G. duodenalis that represent a possible health threat to companion animals and livestock. Our results describe the first successful colonization of avian-derived G. duodenalis trophozoites in the small intestines of domestic kittens and lambs.

Intestinal infection with Giardia spp. reduces epithelial barrier function in a myosin light chain kinase-dependent fashion

BACKGROUND & AIMS

Giardiasis causes malabsorptive diarrhea, and symptoms can be present in the absence of any significant morphologic injury to the intestinal mucosa. The effects of giardiasis on epithelial permeability in vivo remain unknown, and the role of T cells and myosin light chain kinase (MLCK) in altered intestinal barrier function is unclear. This study was conducted to determine whether Giardia spp. alters intestinal permeability in vivo, to assess whether these abnormalities are dependent on T cells, and to assess the role of MLCK in altered epithelial barrier function.

METHODS

Immunocompetent and isogenic athymic mice were inoculated with axenic Giardia muris trophozoites or sterile vehicle (control), then assessed for trophozoite colonization and gastrointestinal permeability. Mechanistic studies using nontransformed human duodenal epithelial monolayers (SCBN) determined the effects of Giardia on myosin light chain (MLC) phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, cytoskeletal F-actin, tight junctional zonula occludens-1 (ZO-1), and MLCK.

RESULTS

Giardia infection caused a significant increase in small intestinal, but not gastric or colonic, permeability that correlated with trophozoite colonization in both immunocompetent and athymic mice. In vitro, Giardia increased permeability and phosphorylation of MLC and reorganized F-actin and ZO-1. These alterations were abolished with an MLCK inhibitor.

CONCLUSIONS

Disruption of small intestinal barrier function is T cell independent, disappears on parasite clearance, and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1 in an MLCK-dependent fashion.

Examination of oral sensitization with ovalbumin in Brown Norway rats and three strains of mice

We studied the conditions needed to sensitize animals to the oral feeding of food allergens, without induction of tolerance, in order to investigate the allergenicity of orally ingested food proteins. Brown Norway (BN) rats were sensitized by daily OVA (ovalbumin)-gavage or by drinking OVA containing water ad libitum and the ASA (active systemic anaphylaxis) response, as the immediate hypersensitivity response to antigen stimulation after oral sensitization, was examined. The oral administration of OVA by gavage produced a higher OVA-specific IgE response and an increase in serum histamine after antigen challenge, as compared to those produced by drinking water. Next, we examined the effect of murine age, the oral feeding technique and the oral feeding dose on sensitization using BALB/c, B10A and ASK mice. Twenty-week-old mice showed the strongest OVA-specific IgE and IgG1 responses and ASA-associated serum histamine contents increased with gavage in the three different age groups of BALB/c mice. Administering 0.1 mg of OVA by gavage daily for 9 weeks appeared to induce a higher response than administering 1 mg of OVA, in terms of OVA-specific IgE and IgG1 antibody responses and ASA responses. Among the three strains of mice, B10A mice exhibited the highest response in terms of OVA-specific IgE and IgG1 antibody and ASA responses. These findings suggested BN rats and B10A mice were suitable models for oral sensitization with antigen protein and that oral sensitization in mice requires low dose, intermittent antigen intakes.

Mast cells in the rat liver are phenotypically heterogeneous and exhibit features of immaturity

Gastrointestinal hypersensitivity to food allergens is a significant but relatively poorly understood allergic disease. Recent evidence from a rat model of IgE-mediated gastrointestinal hypersensitivity has suggested that hepatic mast cells (HMC) may play an important role in such reactions. The present study was undertaken to better define their phenotype. Livers from Australian albino Wistar (AaW), Brown Norway (BN) and PVG/c rats were examined using traditional histological techniques and reverse transcription-polymerase chain reaction (RT-PCR). Hepatic mast cells were overwhelmingly Alcian blue positive, sensitive to formalin fixation and predominantly rat mast cell protease (RMCP) 1+/2- (AaW 57%; BN 53%). Such a phenotype has previously been associated with an immature mast cell phenotype. A significant number of HMC also stained RMCP 1-/2+ (AaW 15%; BN 19%) or were RMCP 1+/2+ (AaW 24%; BN 26%). In contrast to previous reports, RT-PCR showed that the liver expressed mRNA of other mast cell proteases, including the chymase RMCP 5 as well as two tryptases, RMCP 6 and RMCP 7. These results suggest that HMC are a heterogeneous population of mast cells with some characteristics previously associated with immature cells.

Giardia lamblia rearranges F-actin and alpha-actinin in human colonic and duodenal monolayers and reduces transepithelial electrical resistance

The mechanisms of epithelial injury in giardiasis remain unknown. The effects of live Giardia lamblia on cellular G-actin, F-actin, alpha-actinin, and electrical resistance of human intestinal epithelial monolayers were investigated using SCBN and Caco2 cell lines grown on chamber slides or Transwell filter membranes. In separate experiments, some monolayers were also exposed to sonicated trophozoites, some to supernatant from live G. lamblia cultures, and some with or without the Ca2+ channel blocker verapamil. After 2, 24, or 48 hr of coincubation with G. lamblia, monolayers were assessed for cytoskeletal arrangement under fluorescence and confocal laser microscopy, and transepithelial electrical resistance was measured. Exposure to live G. lamblia trophozoites induced localized condensation of F-actin and loss of perijunctional alpha-actinin while G-actin remained unchanged. Confocal laser microscopy indicated that F-actin rearrangement was not affected by verapamil and was localized within the terminal web area. Coincubation of monolayers with G. lamblia lysates or with spent medium alone similarly rearranged F-actin. Verapamil alone did not alter F-actin. Electrical resistance of SCBN and Caco2 monolayers exposed to G. lamblia was significantly decreased versus controls regardless of whether live or lysed trophozoite samples were used. The results indicate that G. lamblia-induced epithelial injury is associated with F-actin and alpha-actinin rearrangements in the terminal web area via mechanisms independent of extracellular Ca2+. These alterations are associated with reduced transepithelial electrical resistance and are due at least in part to trophozoite products.

Jejunal brush border microvillous alterations in Giardia muris-infected mice: role of T lymphocytes and interleukin-6

Intestinal colonization with the protozoan Giardia causes diffuse brush border microvillous alterations and disaccharidase deficiencies, which in turn are responsible for intestinal malabsorption and maldigestion. The role of T cells and/or cytokines in the pathogenesis of Giardia-induced microvillous injury remains unclear. The aim of this study was to assess the role of T cells and interleukin-6 (IL-6) in the brush border pathophysiology of acute murine giardiasis in vivo. Athymic nude (nu(-)/nu(-)) CD-1 mice and isogenic immunocompetent (nu(+)/nu(+)) CD-1 mice (4 weeks old) received an axenic Giardia muris trophozoite inoculum or vehicle (control) via orogastric gavage. Weight gain and food intake were assessed daily. On day 6, segments of jejunum were assessed for parasite load, brush border ultrastructure, IL-6 content, maltase and sucrase activities, villus-crypt architecture, and intraepithelial lymphocyte (IEL) infiltration. Despite similar parasitic loads on day 6, infected immunocompetent animals, but not infected nude mice, showed a diffuse loss of brush border microvillous surface area, which was correlated with a significant reduction in maltase and sucrase activities and a decrease in jejunal IL-6 concentration. In both athymic control and infected mice, jejunal brush border surface area and disaccharidases were high, but levels of tissue IL-6 were low and comparable to the concentration measured in immunocompetent infected animals. In both immunocompetent and nude mice, infection caused a small but significant increase in the numbers of IELs. These findings suggest that the enterocyte brush border injury and malfunction seen in giardiasis is, at least in part, mediated by thymus-derived T lymphocytes and that suppressed jejunal IL-6 does not necessarily accompany microvillous shortening.

Chronic stress impairs rat growth and jejunal epithelial barrier function: role of mast cells

We examined the impact of chronic stress on rat growth rate and intestinal epithelial physiology and the role of mast cells in these responses. Mast cell-deficient (Ws/Ws) rats and +/+ littermate controls were submitted to water avoidance stress or sham stress, 1 h/day, for 5 days. Seven hours after the last sham or stress session, jejunal segments were mounted in Ussing chambers, in which secretion and permeability were measured. Body weight (as a growth index) and food intake were determined daily. Stress increased baseline jejunal epithelial ion secretion (indicated by short-circuit current), ionic permeability (conductance), and macromolecular permeability (horseradish peroxidase flux) in +/+ rats, but not in Ws/Ws rats, compared with nonstressed controls. Stress induced weight loss and reduced food intake similarly in the groups. In +/+ rats, these parameters remained altered 24-72 h after the cessation of stress. Modulation of stress-induced mucosal mast cell activation may help in the management of certain intestinal conditions involving epithelial pathophysiology.

An oral sensitization model in Brown Norway rats to screen for potential allergenicity of food proteins

We developed an oral sensitization protocol for food proteins for the rat. Young Brown Norway (BN) rats were exposed to 1 mg ovalbumin (OVA) by daily gavage dosing for 42 days without the use of an adjuvant. OVA-specific IgE and IgG responses were determined by ELISA. On an oral challenge with OVA some clinical symptoms of food allergy-like effects on the respiratory system, blood pressure, and permeability of the gastrointestinal barrier were studied. In addition, BN rats were orally exposed to a total hen egg white protein (HEW) extract and cow's milk (CM) and the specificities of induced antibody responses were compared with the specificities of antibodies in sera from egg- and milk-allergic patients using immunoblotting. Animals orally exposed to the allergens developed specific IgE and IgG antibodies which recognized the same proteins compared with antibodies from egg- or CM-allergic patients. Among the various clinical symptoms of food allergy, gut permeability was increased after an oral challenge. In addition, some animals demonstrated a temporary decrease in breathing frequency or systolic blood pressure. The results obtained show that the Brown Norway rat is a suitable animal model for inducing specific IgG and IgE responses on daily intragastric dosing of OVA without the use of an adjuvant. Moreover, local immune-mediated effects on oral challenge are observed. The observation that enterally exposed BN rats and food-allergic patients demonstrate antibody responses to a comparable selection of proteins on exposure to different protein mixtures (HEW and CM) further supports the suitability of the BN rat as an animal model for food allergy research and for the study of the allergenicity of (novel) food proteins.

Humoral and cellular immune responses in different rat strains on oral exposure to ovalbumin

No adequate enteral sensitization models are available to study food allergy and allergenicity of food proteins. Using a previously described oral sensitization protocol to sensitize Brown Norway rats (BN) to food proteins, the influence of genetically-based strain-specific characteristics of the immune system on the outcome of oral sensitization studies was investigated. BN, Hooded Lister (HL), Piebald Virol Glaxo (PVG) and Wistar rats were daily administered 1 mg of ovalbumin (OVA) by gavage dosing for 42 days without the use of an adjuvants. The highest OVA-specific IgG responses were detected in the BN rats followed by Wistar, HL and PVG rats. OVA-specific IgE responses were only detectable in the BN rats. The cellular immune response was examined by determination of delayed-type hypersensitivity (DTH) reactions in the animals. The response was most pronounced in the HL and Wistar rats. PVG and BN rats showed comparable DTH responses but the responses were significantly weaker than those observed in HL and Wistar rats. It was concluded that the genetic make-up of different rat strains influences the outcome of oral sensitization studies. In addition, using the described oral sensitization protocol, the BN rat seems to be the most suitable strain for inducing oral sensitization.

A role for the hepatobiliary system in IgE-mediated intestinal inflammation in the rat

BACKGROUND

For many years the central focus of research into gastrointestinal hypersensitivity reactions has been the mast cell population of the intestinal lamina propria. Since bile is known to deliver immunological mediators to the gastrointestinal tract, the possibility arises that extra-intestinal populations of mast cells may also contribute to IgE-mediated intestinal damage.

OBJECTIVES

To characterize hepatic mast cells in the rat and to investigate the role of the hepatobiliary system in a model of IgE-mediated reactivity to dietary antigen.

METHODS

Wistar rats were passively sensitized with monoclonal antidinitrophenyl (DNP) IgE antibodies, and were later challenged orogastrically with DNP-HSA. Additional animals were sensitized, then bile duct-cannulated prior to antigen challenge. At various time points, liver and intestinal samples were collected for histological examination, and bile was collected and assayed for histamine and TNFalpha.

RESULTS

Hepatic mast cells display a mucosal mast cell-like phenotype, and are closely associated with the vessels of the portal triads. Orogastric antigen challenge led to a rapid and significant decline (P<0.0001) in detectable mast cells as a result of anaphylactic degranulation. The median number of granulated mast cells associated with each portal triad in liver sections declined from six per portal triad to one per portal triad post-antigen challenge. After 15 min, biliary histamine concentrations rose above background levels (P<0.01). TNFalpha was also detectable in the majority (4/6) of bile samples within 15 min of challenge. Histological examination of the gastrointestinal mucosa revealed disruption to the villous epithelium ranging from oedematous changes to gross destruction. Such damage was not seen in animals in which bile had been externally drained.

CONCLUSION

The data indicate that biliary products are major contributors to the gastrointestinal damage arising from IgE-mediated hypersensitivity reactions in the rat, and such hypersensitivity reactions may involve a population of mast cells which reside in the liver.

Chronic oral antigen exposure induces lymphocyte migration in anaphylactic mouse intestine

Persistent diarrhea, vomiting, and dehydration are symptoms often seen in patients suffering from food allergy after chronic antigen exposure; however, the precise mechanisms involved have not been well defined. In an effort to clarify the mechanisms of the chronic intestinal changes attributable to genuine IgE-mediated anaphylactic reactions induced by orally administered antigen, a mouse model was established by s.c. implantation of a murine hybridoma capable of producing monoclonal anti-trinitrophenyl IgE antibody, and the morphologic and immunologic changes occurring in the intestine upon chronic antigen exposure were investigated. In the early stage after ingestion of the antigen, diarrhea and noticeable infiltration of mast cells as well as eosinophils into the lamina propria were observed. A substantial increase in serum histamine levels as well as an increase in leukotriene C4 synthesis in the jejunal mucosa were observed 1 h after antigen challenge. Also, the synthesis of leukotriene B4 was significantly elevated for up to 9 h after antigen challenge. The expression of both intercellular adhesion molecule-1 (ICAM-1) on mucosal vascular endothelial cells and IAd on epithelial cells was markedly enhanced, and noticeable infiltration of eosinophils and lymphocytes was also confirmed in the mouse model after chronic antigen exposure. These findings suggest that oral antigen exposure induces anaphylactic reactions in the intestine mediated by mast cells and eosinophils in response to the IgE-antigen complex in the early phase, and also induces lymphocyte migration after chronic antigen exposure.

Effects of orally administered epidermal growth factor on enteropathogenic Escherichia coli infection in rabbits

The increased intestinal absorption induced by epidermal growth factor (EGF) is associated with diffuse lengthening of brush border microvilli. The aim of this study was to examine the in vivo effects of oral administration of EGF during infection with enteropathogenic Escherichia coli. New Zealand White rabbits (4 weeks old) received orogastric EGF daily starting 3 days prior to infection with enteropathogenic E. coli RDEC-1 and were compared with sham-treated infected animals and uninfected controls. Weight gain, food intake, fecal E. coli, and stool consistency were assessed daily. On day 10, segments of jejunum, ileum, proximal, and distal colon were assessed for gram-negative bacterial colonization, disaccharidase activities, and epithelial ultrastructure. Effects of EGF on E. coli RDEC-1 proliferation were studied in vitro. E. coli RDEC-1 caused diarrhea and reduced weight gain. Seven days postinfection, the small and large intestines were colonized with numerous bacteria, brush border microvilli were disrupted, and maltase and sucrase activities were significantly reduced in the jejunum. Daily treatment with EGF prevented the occurrence of diarrhea and reduction of weight gain. These effects were associated with significant inhibition of E. coli colonization in the small and large intestine, improved jejunal maltase and sucrase activities and reduced microvillous injury. EGF did not affect the proliferation of E. coli in vitro. The findings suggest that EGF protects the gastrointestinal tract against colonization by enteropathogenic E. coli.

Nuclear Translocation of Upstream Stimulating Factor 2 (USF2) in Activated Mast Cells: A Possible Role in Their Survival

Multiple transcription factors are activated in the cytoplasm and translocated to the nucleus where they exert positive or negative control over cellular genes. Such subcellular traffic of transcription factors usually requires the presence of a positively charged nuclear localization sequence (NLS). Upstream stimulating factor 2 (USF2) is one of the few transcription factors that contain two potential domains for nuclear localization. In addition to the conventional basic NLS, USF2 contains a highly conserved USF-specific region that is involved in its nuclear translocation. In the present work, the induction of translocation of USF2 into the mast cell nucleus was observed and found to be dependent on activation of the cells either by IL-3 or IgE-Ag. It was also observed that the prevention of the translocation of USF2 to the nucleus, using a peptide derived from the specific USF-NLS region, significantly inhibited their IL-3-mediated survival. Thus, our findings show a direct connection between mast cell surface receptor-mediated USF2 nuclear translocation and cell viability.

Oral sensitization to food proteins: a Brown Norway rat model

BACKGROUND

Although several in vivo antigenicity assays using parenteral immunization are operational, no adequate enteral sensitization models are available to study food allergy and allergenicity of food proteins.

OBJECTIVE

This paper describes the development of an enteral model for food allergy research in the Brown Norway (BN) rat.

METHODS

The animals were exposed to ovalbumin either ad libitum via the drinking water (0.002 to 20 mg/mL) continuously for 6 weeks or by gavage (1 mg/mL per rat). Gavage dosing was performed either daily, twice a week, once a week or once every 2 weeks during a period of 6 weeks. No adjuvants were used during the sensitization studies.

RESULTS

After intra-gastric administration of ovalbumin once or twice a week or once every two weeks, no or only a very low frequency of ovalbumin-specific antibody responses were detected. Daily intra-gastric dosing with ovalbumin resulted in antigen-specific IgG as well as IgE responses in almost all animals tested. Upon ad libitum exposure, ovalbumin-specific IgG but no ovalbumin-specific IgE was detected. The cellular response was examined by determination of delayed-type hypersensitivity (DTH) reactions in the animals dosed by daily gavage and in the ad libitum exposed rats. Both sensitization protocols sensitized for DTH. The response was most pronounced in ad libitum exposed rats at day 28 of exposure.

CONCLUSIONS

These studies show that the BN rat may provide a suitable animal model for inducing specific IgG and IgE responses as well as specific T-cell mediated hypersensitivity (DTH) to ovalbumin upon exposure via the enteral route without the use of adjuvants.

Time course of changes in the intestinal permeability of food-sensitized rats after oral allergen challenge

Rats were sensitized with ovalbumin (OVA) with a molecular weight of 45 kd, challenged with OVA orally, followed by orally administered beta-lactoglobulin (BLG) as an intestinal permeability marker. BLG is a macro-molecular protein with a molecular weight of 18 kd. Blood BLG concentrations were measured (by ELISA) serially over 4 hours following BLG administration, which in turn was given 1 hour after OVA challenges. The maximum BLG concentration was at 2 hours. BLG was then administered orally 1, 3, 6, 12 and 24 hours after oral OVA challenge, and the serum BLG concentration at 2 hours after BLG administration was compared among the five groups. BLG appeared in the circulation of the animals 1, 6 and 24 hours after allergen challenge, but not after 3 and 12 hours. The serum BLG concentration was not significantly different at 1, 6 and 24 hours. Histopathological examinations of the intestines showed mast cell infiltration of the intestinal mucosa at 1 hour, remarkable edema of villi at 3 hours, eosinophil infiltration at 6 hours, an increase of goblet cells at 12 hours and villous atrophy and lymphocyte infiltration at 24 hours. The appearance in the serum of three BLG peaks of comparable heights suggested that the intestinal absorption of BLG may be related to a late and delayed phase as well as the immediate IgE-dependent phase response.

Food allergy: predictive testing of food products

Food allergy is a substantial cause of distress in humans. Several biotechnological techniques can be applied to reduce the antigenicity of food proteins to produce for instance hypoallergenic infant formulas. Biotechnological techniques synthesizing new proteins or new biological varieties for applications in food are also available. For such biotechnologically for derived protein products (novel foods), allergenicity may also pose a major concern. For safety reasons, it is of importance to evaluate the residual antigenicity of modified protein products, to screen for possible cross-reactivity to prevent reactions in previously sensitized individuals, and to test for sensitizing properties of new and/or modified protein products. Besides physico-chemical and immunochemical analyses, several in vitro and in vivo bioassays may be applied in studying the antigenic or allergenic properties of (new or modified) food proteins. In this paper, an overview of several available assays and new developments for determining the antigenic or allergenic properties of dietary proteins, as well as their possible applications and limitations is presented. Special attention is paid to the role of the gastro-intestinal tract physiology in food allergy and in the evaluation of the allergenic potential of food proteins and to the possible applications of animal models in food allergy research and in the evaluation of the allergenicity of food proteins.

The frequency of cells secreting interferon-gamma and interleukin-4, -5, and -10 in the blood and duodenal mucosa of children with cow's milk hypersensitivity

Enzyme-linked immunoabsorbant spots (ELISPOTs) have been used to analyze the frequency of cells spontaneously secreting interferon-gamma (INF-gamma), IL-4, IL-5, or IL-10 in mononuclear cells isolated from the blood of children with cow's milk-sensitive enteropathy (CMSE), cow's milk allergy (CMA), and age-matched controls. In addition, cytokine profiles of duodenal lamina propria lymphocytes were compared in patients with CMSE and control subjects. In blood, spontaneous cytokine-secreting cells were uncommon, but there was significantly increased IFN-gamma, IL-4, IL-5, and IL-10 ELISPOTs in children with CMSE and CMA compared with control subjects. IL-4 ELISPOTs were significantly greater in the blood of children with CMA compared with those with CMSE. In the lamina propria the frequencies of spontaneous cytokine-secreting cells were high compared with that in blood. Significantly increased ELISPOTs for IFN-gamma and IL-4 were found in CMSE compared with controls. IL-5 ELISPOTs were unchanged, and IL-10 ELISPOTs were reduced in CMSE compared with controls. These results show a general enhancement of Th1 and Th2-type cytokine-secreting cells in the blood of children with cow's milk hypersensitivity, although the increased IL-4-secreting cells in blood in CMA may be of relevance in view of the fact that this disease is IgE-mediated. In the lamina propria, there is also enhancement of IFN-gamma- and IL-4-secreting cells in CMSE compared with control subjects; however, cells secreting IFN-gamma are 10 times more numerous than cells secreting IL-4, showing a dominance of Th1-type responses in both controls and CMSE patients.

Enhanced tissue responsiveness in colonic ion transport of cow's milk-sensitized guinea pigs

The effects of leukotriene D4 (LTD4) on ion transport were investigated in submucosa/mucosa colonic segments from guinea pigs sensitized to cow's milk and in age-matched, non-immune animals. Mediators released from mast cells in immune animals challenged with beta-lactoglobulin evoked an increase in short-circuit current that was reduced by SK&F 102922, a peptidoleukotriene antagonist. Serosal addition of LTD4 (0.15-1 microM) evoked a concentration-dependent, bumetanide-sensitive increase in short-circuit current which was greater in immune than non-immune controls. In the absence of ongoing neural activity, 1 microM LTD4 evoked an 8-20 microA/cm2 increase in short-circuit current which was increased 8-13-fold when ongoing neural activity was present. In tissues with ongoing activity, the response to 0.15 microM LTD4 was reduced by SK&F 102922, tetrodotoxin and atropine. LTD4 enhanced the responsiveness of the tissue to carbachol by a factor of two, but did not affect responses of T84 colonic epithelial cell monolayers to this agent. These results show enhanced secretory function for LTD4 in animals with allergy to cow's milk. They suggest that the level of ongoing neural activity in the enteric neural microcircuits is one of the major determinants of colonic secretory capacity.

Exposure of the rat small intestine to raw kidney beans results in reorganization of absorptive cell microvilli

BACKGROUND/AIMS

A single exposure to raw kidney beans (RKB) results in vesiculation, shortening, and then regrowth of microvilli in the rat small intestine. This study investigated changes that occur in the structure of microvilli 2-10 hours after RKB exposure.

METHODS

Circumferences of microvilli from absorptive cells obtained sequentially after challenge with RKB or chow were assigned to one of three groups: small, intermediate, or large. The distribution and concentration of actin in intact mucosae or isolated epithelial sheets were determined by confocal laser scanning microscopy, immunocytochemistry, and immunoblot analysis with specific probes.

RESULTS

Six hours after exposure to RKB, most microvilli were large, abnormal in shape, and contained significantly more actin filaments than large microvilli from control rats. In addition, the fluorescence intensity of F-actin increased within injured microvilli without changes in the total intracellular actin concentration. By 8-10 hours after challenge with RKB, some microvilli remained larger than those of control rats but had resumed their normal shape and contained fewer actin filaments than at 6 hours.

CONCLUSIONS

Exposure of the rat small intestine to RKB results in enlargement of absorptive cell microvilli and reorganization of membrane and core actin filaments without changes in intracellular actin concentration. Enlarged microvilli are rapidly repaired.

Proliferation of mast cells in the smooth muscle of denervated rat jejunum

Mast cell hyperplasia and changes in phenotypic characteristics subsequent to myenteric and extrinsic denervation of a segment of rat jejunum were studied. The myenteric plexus and extrinsic nerves were ablated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride. There was a four-fold increase in the number of mast cells in the smooth muscle layers 15 days after denervation. This increase was sustained for at least 90 days after treatment. No increase in mast cell number was observed in the villus-crypt axis of the jejunum. Berberine sulfate fluorescent detection of heparin-containing mast cells demonstrated that a change in mast cell phenotype occurred between 20 and 90 days after the denervation procedure. The fact that myeloperoxidase activity was the same in denervated and control tissue within 5 days of denervation demonstrates the lack of a chronic inflammatory reaction. Our results suggest that mast cells might play a role in the gut wall re-modeling processes.

Intestinal epithelial function: the case for immunophysiological regulation. Implications for disease (2)

Substantial amounts of data have been reported showing a role for immunomodulation of epithelial function (particularly ion secretion and permeability) using animal models of anaphylactic reactions. In part one of this review we outlined the main immune cell types and mediators/cytokines that are currently known to influence epithelial physiology either directly, or indirectly via an intermediate cell type. Here we will expand on the significance of these studies and show how antigenic activation of the mucosal immune system can evoke changes in epithelial function that may be beneficial to the host by mediating loss/inactivation of the antigen. However, a continued and inappropriate immune stimulation can lead to pathophysiological reactions and disease. Thus, we will present data on immune regulation of epithelial function with direct applicability to understanding the mechanism underlying human intestinal inflammatory and secretory disease. Finally, we highlight key strategic points in the cascade of immune events that can control epithelial function and thus may be of relevance in the formulation of new therapeutic approaches to intestinal inflammation.

Adaptation of the small intestine in desert-dwelling animals: morphology, ultrastructure and electrolyte transport in the jejunum of rabbits, rats, gerbils and sand rats

1. The aim of this study was to characterize adaptive alterations of the small intestine in desert-dwelling animals by comparing jejunal morphology, ultrastructure and function in mammalian species with or without desert habitat origins. 2. Crypt-villus architecture, brush border surface area, and electrolyte transport were measured and compared in the jejunum of rabbits (Oryctolagus cuniculus), rats (Rattus rattus), gerbils (Meriones unguiculatus) and sand rats (Psammomys obesus). 3. In addition, transport of 3-0-methyl-D-glucose was compared in rats, rabbits and gerbils. 4. Gerbils and sand rats had significantly longer microvilli and villi (P < 0.01), increased brush border surface area (P < 0.01), and greater absorption of Na+ and Cl- (P < 0.05) than rabbits and rats. 5. Absorption of 3-0-methyl-D-glucose was also significantly (P < 0.05) greater in gerbils than in rabbits or rats. 6. The findings demonstrate enhanced small intestinal absorption of electrolytes and nutrients in desert-dwelling animals. 7. This increase was associated with an enlarged mucosal absorptive surface area. 8. The findings suggest that intestinal mucosal adaptation allows desert-dwelling animals to compensate for the limited availability of water and nutrients in an arid environment.

Cow's milk provocation induces an immune response to unrelated dietary antigens

The activation of immune mechanisms was evaluated by the solid phase enzyme linked immunoassay of immunoglobulin and specific antibody secreting cells in 27 patients (aged from nine to 69 months), subjected to a diagnostic cow's milk challenge or a rechallenge. A significant rise in the total number of immunoglobulin secreting cells was associated with clinically positive (n = 17), but not a negative (n = 10) cow's milk challenge in all immunoglobulin isotypes. The number of specific antibody secreting cells against beta lactoglobulin, mean (95% confidence interval), increased from 4.8 (1.4, 15.8) to 16.9 (5.5, 52.7) specific antibody secreting cells/10(6) cells, p = 0.02, and against casein from 2.2 (0.8, 6.1) to 7.5 (2.5, 22.5) specific antibody secreting cells/10(6) cells, p = 0.01, in patients positive to challenge in the IgM class only, indicating defective immune elimination of milk antigens. In addition to the specific immune response to cow's milk antigens, an increase in IgM specific antibody secreting cells against an unrelated dietary antigen, gliadin, from 8.2 (2.1, 31.1) to 31.0 (14.2, 67.6) specific antibody secreting cells/10(6) cells, p = 0.01, was observed. These results indicate that cow's milk challenge, in patients who have cow's milk allergy, induces a strong non-antigen specific immune response that includes a response against unrelated antigens concomitantly present in the intestinal lumen. Activation of such immune mechanisms may hence reflect increased antigenic load caused by the immune mediated lesion in the gut mucosa.

Gastrointestinal food hypersensitivity: basic mechanisms of pathophysiology

Gastrointestinal symptoms occur in a large number of patients with food allergies. Immediate hypersensitivity mechanisms may give rise to the nausea, vomiting, abdominal pain, and diarrhea experienced by these patients. However, there are limited human data about the pathophysiological basis for these symptoms. Most of the available information comes from a variety of animal models. This article reviews the literature using models of intestinal food hypersensitivity, as well as human studies, that have contributed to our understanding of the pathophysiological mechanisms in gastrointestinal food hypersensitivity.

Pathophysiology of small intestinal malabsorption in gerbils infected with Giardia lamblia

Mongolian gerbils were infected with a human pathogenic Giardia lamblia strain and compared with sham-treated control animals 6 days after inoculation. Infection resulted in crypt hyperplasia associated with an increased enterocyte migration rate. Villus height was decreased in the duodenum, unchanged in the jejunum, and increased in the ileum of infected animals. Epithelial microvilli were markedly shortened, and brush border surface area decreased in the jejunum and ileum of infected animals. Thymidine kinase activity was increased in isolated duodenal villus enterocytes but did not differ in the jejunum and ileum. In vitro and in vivo experiments showed that the infection resulted in decreased jejunal glucose-stimulated electrolyte, water, and 3-O-methyl-D-glucose absorption, whereas in the ileum in vitro electrolyte and 3-O-methyl-D-glucose absorption was similar in infected and control animals. Thus, in the jejunum infection causes electrolyte, solute, and fluid malabsorption associated with decreased brush border surface area. The results indicate that the diarrhea associated with giardiasis is caused by malabsorption rather than active secretion.

Identical intestinal permeability changes in children with different clinical manifestations of cow's milk allergy

To determine the relationship between clinical symptoms of cow's milk allergy (CMA) and intestinal permeability, 51 children (mean age, 13 months) were studied during a diagnostic milk provocation test. Intestinal permeability was assessed by orally administered lactulose (4 gm) and mannitol (0.8 gm) immediately before (day 0) the milk challenge and 3 days later (day 3). Twenty-four patients evinced cutaneous symptoms and 27, gastrointestinal symptoms. The mean (95% confidence interval) urinary lactulose/mannitol recovery ratios before the milk challenge were, in both groups of patients, comparable to the level of that of control patients, 0.02 (0.01 and 0.03). A rise in lactulose/mannitol excretion ratios followed cow's milk administration by day 3 in patients with skin symptoms, 0.06 (0.03 and 0.13), as well as in patients with gastrointestinal symptoms, 0.08 (0.04, 0.17). These levels were significantly different from the control level, p = 0.003, and the prechallenge level, p = 0.01. This difference was caused by a concomitant increase in urinary recovery of lactulose and a decrease of mannitol. These results indicate that the intestinal barrier is equally altered in patients with different clinical manifestations of CMA and further suggest that enhancement of mucous membrane permeability is not a primary defect in the pathogenesis of CMA but rather a secondary phenomen, possibly caused by a hypersensitivity reaction in the intestinal mucosa.

Growth, activities of enzymes in the small intestine, and ultrastructure of microvillous border in gerbils infected with Giardia duodenalis

The aim of this study was to assess and correlate changes in weight gain, food intake, small intestinal disaccharidase activities and microvillous border surface area over the course of a primary Giardia duodenalis infection in weanling Mongolian gerbils (Meriones unguiculatus). Weight gain in infected animals was significantly impaired between days 8 and 20 postinoculation when compared to age- and weight-matched controls. No difference in food intake was observed between groups. Trophozoite population in the small intestine was maximal on day 4 and 6 of infection, and colonization persisted in the duodenum throughout the experiment (30 days). In infected gerbils, mucosal sucrase and maltase activities were significantly depressed in the duodenum and jejunum on day 4 and in all areas of the small intestine by day 6. Eight and 25 days postinoculation, disaccharidase activities had recovered in the jejunum and distal small intestine but remained depressed in the duodenum, the area where trophozoite colonization persisted. Diffuse loss of microvillous border surface area was observed in the duodenum and jejunum after 6 days of infection. Eight days postinoculation, microvillus surface area had returned to normal in the jejunum, but not in the duodenum. Our findings demonstrate that acute giardiasis in weanling gerbils impairs weight gain, depresses disaccharidase activities, and diffusely reduces mucosal microvillous border surface area.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal protozoa and epithelial cell kinetics, structure and function

Intestinal protozoa are not only common enteric pathogens in the tropics but also the high incidence of infection among immunocompromised patients in northern countries has evoked an increased interest in these parasites. Although enteric protozoa are a major cause of diarrhea and malabsorption in humans and other animals, the pathophysiology of gut disturbances caused by them remains poorly understood. Clinical signs related to enteric protozoan disease commonly involve malabsorption, diarrhea, weight loss or retarded weight gain and anorexua. Since these infections are most prevalent and most severe in the young, this may translate into considerable illness among children and significant loss to the agricultural economy where domestic animals are prone to infection. In this review we describe the effects of intestinal protozoan diseases on the structure, kinetics and function of absorptive intestinal cells and other epithelial cells, and correlate morphological injury with physiological alterations in the parasitized gut. Some of the interactions between immune responses and pathophysiology will be discussed, but in-depth discussion of intestinal immunity has recently been undertaken by other authors.

Effect of acute Yersinia enterocolitica infection on small intestinal ultrastructure

The purpose of this study was to assess the jejunal and ileal brush border injury caused by Yersinia enterocolitica and to correlate these alterations with functional abnormalities. Weanling rabbits infected with 10(10) organisms of a human pathogenic Y. enterocolitica strain were compared with control and pair-fed, sham-treated animals. On day 6, infection resulted in a diffuse decrease in brush border enzyme activities in the small intestine and villus atrophy and crypt hyperplasia in the ileum. By day 14, ileal architecture and jejunal disaccharidases had returned to normal, but enzyme abnormalities persisted in the ileum. Ultrastructural studies showed decreased brush border surface area in the jejunum and ileum on day 6 and in the ileum on day 14 of infection. Abnormalities of brush border function caused by infection correlated with the changes in microvillus surface area. In pair-fed animals on day 6, brush border surface area was slightly decreased in the ileum but increased in the jejunum, suggesting that the brush border injury resulted from infection rather than from malnutrition alone. The findings indicate that Y. enterocolitica inflicts a diffuse brush border injury that is in keeping with the generalized defect in brush border enzyme activity and transport function.