Gliadin uptake in human enterocytes. Differences between coeliac patients in remission and control individuals

Gliadin effect on the oxidative balance and DNA damage: An in-vitro, ex-vivo study

BACKGROUND

Gliadins are involved in gluten-related disorders and are responsible for the alteration of the cellular redox balance. It is not clear if the gliadin-related oxidative stress can induce DNA damage in enterocytes.

AIM

To investigate any possible genotoxicity caused by gliadin and to assess its relationship with oxidative stress in vitro and ex vivo.

METHODS

Caco-2 cells were exposed for 6-12-24 h to increasing concentrations (250 μg/mL-1000 μg/mL) of digested gliadin. We investigated: cytotoxicity, oxidative balance (reactive oxygen species, ROS), DNA damage (comet assay and γ-H2AX detection), transglutaminase type 2 (TG2) activity and annexin V expression. H2AX and 8-OHG immunohistochemistry has been evaluated on duodenal biopsies of celiac subjects and controls.

RESULTS

Gliadin induced a significant increase (+50%) of ROS after 12 h of exposition starting with a 500 μg/mL dose of gliadin. Comet assay and γ-H2AX demonstrated DNA damage, evident at the gliadin concentration of 500 μg/mL after 24 h. TG2 activity increased in chromatin and cytoskeleton cellular compartments at different gliadin doses (250/500/1000 μg/mL). The γ-H2AX and 8-OHG immunohistochemistry was altered in the duodenal biopsies of celiac patients.

CONCLUSIONS

Gliadin induces cellular oxidative stress, DNA damage and pro-apoptotic stimulation in Caco-2 cells and in the duodenal mucosa of celiac patients.

Interactions among secretory immunoglobulin A, CD71, and transglutaminase-2 affect permeability of intestinal epithelial cells to gliadin peptides

BACKGROUND & AIMS

The transferrin receptor (CD71) is up-regulated in duodenal biopsy samples from patients with active celiac disease and promotes retrotransport of secretory immunoglobulin A (SIgA)-gliadin complexes. We studied intestinal epithelial cell lines that overexpress CD71 to determine how interactions between SIgA and CD71 promote transepithelial transport of gliadin peptides.

METHODS

We analyzed duodenal biopsy specimens from 8 adults and 1 child with active celiac disease. Caco-2 and HT29-19A epithelial cell lines were transfected with fluorescence-labeled small interfering RNAs against CD71. Interactions among IgA, CD71, and transglutaminase 2 (Tgase2) were analyzed by flow cytometry, immunoprecipitation, and confocal microscopy. Transcytosis of SIgA-CD71 complexes and intestinal permeability to the gliadin 3H-p31-49 peptide were analyzed in polarized monolayers of Caco-2 cells.

RESULTS

Using fluorescence resonance energy transfer and in situ proximity ligation assays, we observed physical interactions between SIgA and CD71 or CD71 and Tgase2 at the apical surface of enterocytes in biopsy samples and monolayers of Caco-2 cells. CD71 and Tgase2 were co-precipitated with SIgA, bound to the surface of Caco-2 cells. SIgA-CD71 complexes were internalized and localized in early endosomes and recycling compartments but not in lysosomes. In the presence of celiac IgA or SIgA against p31-49, transport of intact 3H-p31-49 increased significantly across Caco-2 monolayers; this transport was inhibited by soluble CD71 or Tgase2 inhibitors.

CONCLUSIONS

Upon binding to apical CD71, SIgA (with or without gliadin peptides) enters a recycling pathway and avoids lysosomal degradation; this process allows apical-basal transcytosis of bound peptides. This mechanism is facilitated by Tgase2 and might be involved in the pathogenesis of celiac disease.

Gliadin peptide P31-43 localises to endocytic vesicles and interferes with their maturation

BACKGROUND

Celiac Disease (CD) is both a frequent disease (1:100) and an interesting model of a disease induced by food. It consists in an immunogenic reaction to wheat gluten and glutenins that has been found to arise in a specific genetic background; however, this reaction is still only partially understood. Activation of innate immunity by gliadin peptides is an important component of the early events of the disease. In particular the so-called "toxic" A-gliadin peptide P31-43 induces several pleiotropic effects including Epidermal Growth Factor Receptor (EGFR)-dependent actin remodelling and proliferation in cultured cell lines and in enterocytes from CD patients. These effects are mediated by delayed EGFR degradation and prolonged EGFR activation in endocytic vesicles. In the present study we investigated the effects of gliadin peptides on the trafficking and maturation of endocytic vesicles.

METHODS/PRINCIPAL FINDINGS

Both P31-43 and the control P57-68 peptide labelled with fluorochromes were found to enter CaCo-2 cells and interact with the endocytic compartment in pulse and chase, time-lapse, experiments. P31-43 was localised to vesicles carrying early endocytic markers at time points when P57-68-carrying vesicles mature into late endosomes. In time-lapse experiments the trafficking of P31-43-labelled vesicles was delayed, regardless of the cargo they were carrying. Furthermore in celiac enterocytes, from cultured duodenal biopsies, P31-43 trafficking is delayed in early endocytic vesicles. A sequence similarity search revealed that P31-43 is strikingly similar to Hrs, a key molecule regulating endocytic maturation. A-gliadin peptide P31-43 interfered with Hrs correct localisation to early endosomes as revealed by western blot and immunofluorescence microscopy.

CONCLUSIONS

P31-43 and P57-68 enter cells by endocytosis. Only P31-43 localises at the endocytic membranes and delays vesicle trafficking by interfering with Hrs-mediated maturation to late endosomes in cells and intestinal biopsies. Consequently, in P31-43-treated cells, Receptor Tyrosine Kinase (RTK) activation is extended. This finding may explain the role played by gliadin peptides in inducing proliferation and other effects in enterocytes from CD biopsies.

Visualization of transepithelial passage of the immunogenic 33-residue peptide from alpha-2 gliadin in gluten-sensitive macaques

Background

Based on clinical, histopathological and serological similarities to human celiac disease (CD), we recently established the rhesus macaque model of gluten sensitivity. In this study, we further characterized this condition based on presence of anti-tissue transglutaminase 2 (TG2) antibodies, increased intestinal permeability and transepithelial transport of a proteolytically resistant, immunotoxic, 33-residue peptide from α₂-gliadin in the distal duodenum of gluten-sensitive macaques.

Methodology/Principal Findings

Six rhesus macaques were selected for study from a pool of 500, including two healthy controls and four gluten-sensitive animals with elevated anti-gliadin or anti-TG2 antibodies as well as history of non-infectious chronic diarrhea. Pediatric endoscope-guided pinch biopsies were collected from each animal's distal duodenum following administration of a gluten-containing diet (GD) and again after remission by gluten-free diet (GFD). Control biopsies always showed normal villous architecture, whereas gluten-sensitive animals on GD exhibited histopathology ranging from mild lymphocytic infiltration to villous atrophy, typical of human CD. Immunofluorescent microscopic analysis of biopsies revealed IgG+ and IgA+ plasma-like cells producing antibodies that colocalized with TG2 in gluten-sensitive macaques only. Following instillation in vivo, the Cy-3-labeled 33-residue gluten peptide colocalized with the brush border protein villin in all animals. In a substantially enteropathic macaque with “leaky” duodenum, the peptide penetrated beneath the epithelium into the lamina propria.

Conclusions/Significance

The rhesus macaque model of gluten sensitivity not only resembles the histopathology of CD but it also may provide a model for studying intestinal permeability in states of epithelial integrity and disrepair.

Noninflammatory gluten peptide analogs as biomarkers for celiac sprue

New tools are needed for managing celiac sprue, a lifelong immune disease of the small intestine. Ongoing drug trials are also prompting a search for noninvasive biomarkers of gluten-induced intestinal change. We have synthesized and characterized noninflammatory gluten peptide analogs in which key Gln residues are replaced by Asn or His. Like their proinflammatory counterparts, these biomarkers are resistant to gastrointestinal proteases, susceptible to glutenases, and permeable across enterocyte barriers. Unlike gluten peptides, however, they are not appreciably recognized by transglutaminase, HLA-DQ2, or disease-specific T cells. In vitro and animal studies show that the biomarkers can detect intestinal permeability changes as well as glutenase-catalyzed gastric detoxification of gluten. Accordingly, controlled clinical studies are warranted to evaluate the use of these peptides as probes for abnormal intestinal permeability in celiac patients and for glutenase efficacy in clinical trials and practice.

Interferon-gamma released by gluten-stimulated celiac disease-specific intestinal T cells enhances the transepithelial flux of gluten peptides

Celiac sprue is a T-cell-mediated enteropathy elicited in genetically susceptible individuals by dietary gluten proteins. To initiate and propagate inflammation, proteolytically resistant gluten peptides must be translocated across the small intestinal epithelium and presented to DQ2-restricted T cells, but the effectors enabling this translocation under normal and inflammatory conditions are not well understood. We demonstrate that a fluorescently labeled antigenic 33-mer gluten peptide is translocated intact across a T84 cultured epithelial cell monolayer and that preincubation of the monolayer with media from gluten-stimulated, celiac patient-derived intestinal T cells enhances the apical-to-basolateral flux of this peptide in a dose-dependent, saturable manner. The permeability-enhancing activity of activated T-cell media is inhibited by blocking antibodies against either interferon-gamma or its receptor and is recapitulated using recombinant interferon-gamma. At saturating levels of interferon-gamma, activated T-cell media does not further increase transepithelial peptide flux, indicating the primacy of interferon-gamma as an effector of increased epithelial permeability during inflammation. Reducing the assay temperature to 4 degrees C reverses the effect of interferon-gamma but does not reduce basal peptide flux occurring in the absence of interferon-gamma, suggesting active transcellular transport of intact peptides is increased during inflammation. A panel of disease-relevant gluten peptides exhibited an inverse correlation between size and transepithelial flux but no apparent sequence constraints. Anti-interferon-gamma therapy may mitigate the vicious cycle of gluten-induced interferon-gamma secretion and interferon-gamma-mediated enhancement of gluten peptide flux but is unlikely to prevent translocation of gluten peptides in the absence of inflammatory conditions.

Antigen presentation in celiac disease

Celiac disease is caused by an inappropriate immune response to ingested gluten proteins. As a dietary antigen, gluten undergoes extensive but incomplete proteolytic digestion in the intestinal lumen. The resultant peptide fragments of gluten require deamidation, but not necessarily further intracellular processing for presentation. Recent studies reveal why the disease associated HLA-DQ2 molecule is particularly suited for binding proline-rich gluten peptides. In comparison, DQ8 exhibits different binding characteristics, which may explain the lesser risk for disease in association with this molecule.

The use of Cellomics to study enterocyte cytoskeletal proteins in coeliac disease patients

Coeliac disease is characterised by inflammation of small intestinal mucosa accompanied by abnormal villous architecture. It is now accepted that some patients with positive coeliac serology tests may have minor mucosal lesions that may not be apparent on routine histopathological analysis. The aim of the study was to perform detailed examination of enterocyte morphology and cytoskeletal structures using a high content analysis technology. Duodenal biopsies from 14 untreated and 10 treated coeliac patients and from 20 non-coeliac controls were examined. Tissue sections from six patients (study group subjects) before and after the development of gluten-sensitive enteropathy were also investigated. Immunohistochemical studies were performed on paraffin-embedded sections using an anti-α-tubulin antibody. Significant differences in enterocyte morphology and intracellular cytoskeletal structures were demonstrated in patients with proven coeliac disease and in the study group subjects. These changes were present in study group biopsies before evidence of enteropathy, as assessed by routine microscopy. This is the first study to demonstrate detailed characteristics of enterocyte morphology in coeliac patients using a high content analysis approach. The use of this technology allows a quantitative analysis of enterocyte intracellular structures from routine biopsy material and permits detection of subtle changes that precede the characteristic histological lesion.

Parallels between pathogens and gluten peptides in celiac sprue

Pathogens are exogenous agents capable of causing disease in susceptible organisms. In celiac sprue, a disease triggered by partially hydrolyzed gluten peptides in the small intestine, the offending immunotoxins cannot replicate, but otherwise have many hallmarks of classical pathogens. First, dietary gluten and its peptide metabolites are ubiquitous components of the modern diet, yet only a small, genetically susceptible fraction of the human population contracts celiac sprue. Second, immunotoxic gluten peptides have certain unusual structural features that allow them to survive the harsh proteolytic conditions of the gastrointestinal tract and thereby interact extensively with the mucosal lining of the small intestine. Third, they invade across epithelial barriers intact to access the underlying gut-associated lymphoid tissue. Fourth, they possess recognition sequences for selective modification by an endogenous enzyme, transglutaminase 2, allowing for in situ activation to a more immunotoxic form via host subversion. Fifth, they precipitate a T cell–mediated immune reaction comprising both innate and adaptive responses that causes chronic inflammation of the small intestine. Sixth, complete elimination of immunotoxic gluten peptides from the celiac diet results in remission, whereas reintroduction of gluten in the diet causes relapse. Therefore, in analogy with antibiotics, orally administered proteases that reduce the host's exposure to the immunotoxin by accelerating gluten peptide destruction have considerable therapeutic potential. Last but not least, notwithstanding the power of in vitro methods to reconstitute the essence of the immune response to gluten in a celiac patient, animal models for the disease, while elusive, are likely to yield fundamentally new systems-level insights.

Parallels between pathogens and gluten peptides in celiac sprue

Pathogens are exogenous agents capable of causing disease in susceptible organisms. In celiac sprue, a disease triggered by partially hydrolyzed gluten peptides in the small intestine, the offending immunotoxins cannot replicate, but otherwise have many hallmarks of classical pathogens. First, dietary gluten and its peptide metabolites are ubiquitous components of the modern diet, yet only a small, genetically susceptible fraction of the human population contracts celiac sprue. Second, immunotoxic gluten peptides have certain unusual structural features that allow them to survive the harsh proteolytic conditions of the gastrointestinal tract and thereby interact extensively with the mucosal lining of the small intestine. Third, they invade across epithelial barriers intact to access the underlying gut-associated lymphoid tissue. Fourth, they possess recognition sequences for selective modification by an endogenous enzyme, transglutaminase 2, allowing for in situ activation to a more immunotoxic form via host subversion. Fifth, they precipitate a T cell-mediated immune reaction comprising both innate and adaptive responses that causes chronic inflammation of the small intestine. Sixth, complete elimination of immunotoxic gluten peptides from the celiac diet results in remission, whereas reintroduction of gluten in the diet causes relapse. Therefore, in analogy with antibiotics, orally administered proteases that reduce the host's exposure to the immunotoxin by accelerating gluten peptide destruction have considerable therapeutic potential. Last but not least, notwithstanding the power of in vitro methods to reconstitute the essence of the immune response to gluten in a celiac patient, animal models for the disease, while elusive, are likely to yield fundamentally new systems-level insights.

Growth factor-like activity of gliadin, an alimentary protein: implications for coeliac disease

BACKGROUND

Gliadins, a family of wheat proteins, are central to the pathogenesis of celiac disease (CD). In addition to 'immunogenic' effects, gliadin directly affects cultured cells and intestine preparations, and produces damage in vivo, via a separate 'toxic' peptide, such as A-gliadin p31-43 (P31-43).

AIMS

Understanding the molecular mechanisms underlying direct non T-cell mediated effects of gliadin peptides, and assessing their potential role in promoting CD.

METHOD

Gliadin effects were tested on a number of cell lines and on cultured mucosa samples by evaluating cytoskeleton rearrangements, endocytosis, proliferation and apoptosis. Standard biochemical methods were used to assess prolonged epidermal growth factor receptor (EGFR) activation.

RESULTS

Crude gliadin peptic-tryptic peptides (PTG], or P31-43 alone, fully reproduce the effects of epidermal growth factor (EGF] on actin cytosketon, cell cycle and cell proliferation of various cell lines. Inhibitor studies demonstrate the role of EGFR in the early response to gliadin exposure, pointing to activation of the EGFR pathway. Peptide P31-43 is not similar to any EGFR ligand, but can delay inactivation of the EGFR interfering with its endocytosis. Gliadin-induced delay of EGFR endocytosis in cultured intestinal biopsies, together with S-phase entry of epithelial intestinal cells, confirm a role for EGFR activation in CD.

CONCLUSION

The ability of gliadin peptides to delay EGFR inactivation through interference with the endocytic pathway suggests a model where gliadin fragments amplify the effects of trace amounts of EGF, and possibly of other growth factors, by prolonging receptor activation. The results, using cultures of coeliac intestinal biopsies, highlight the role of the EGF pathway in establishing and maintaining the typical atrophic and proliferative alterations of the small intestine in CD.

Celiac sprue is primarily a disease of blocked cellular recognition

A key initial event is proposed for the pathogenesis of celiac sprue. The indigestible fragments generated from gluten are actively transported to the vicinity of sites which are critical for recognition of intestinal basement membrane by enterocytes. The fragments are attached in the vicinity of those sites by transamidation and make the recognition sites unavailable. Enterocytes are lost because they do not recognize that they are in the right place. Proliferation in the crypts of Lieberkühn and immune reactions in the epithelium are normal and appropriate. This hypothesis is shown to be compatible with a variety of observations, some of which are difficult to explain otherwise. Absence of a good animal model is laid to the sensitive site being a human peculiarity. The pattern of damage and the fact of recovery on a gluten-free diet are explained since the immune reactions and tissue remodeling observed are normal responses to tissue damage.

Rapid disruption of intestinal barrier function by gliadin involves altered expression of apical junctional proteins

Coeliac disease is a chronic enteropathy caused by the ingestion of wheat gliadin and other cereal prolamines derived from rye and barley. In the present work, we investigated the mechanisms underlying altered barrier function properties exerted by gliadin-derived peptides in human Caco-2 intestinal epithelial cells. We demonstrate that gliadin alters barrier function almost immediately by decreasing transepithelial resistance and increasing permeability to small molecules (4 kDa). Gliadin caused a reorganisation of actin filaments and altered expression of the tight junction proteins occludin, claudin-3 and claudin-4, the TJ-associated protein ZO-1 and the adherens junction protein E-cadherin.

Limited efficiency of prolyl-endopeptidase in the detoxification of gliadin peptides in celiac disease

BACKGROUND & AIMS

The resistance of prolamines to digestive enzymes is thought to be a key contributor to the pathogenesis of celiac disease by promoting the intestinal entrance of peptides able to trigger inflammation in at-risk individuals. Oral administration of a bacterial prolyl-endopeptidase (PEP) therefore was proposed as a treatment for celiac disease. To delineate the feasibility of this treatment, the effect of PEP on gliadin peptides was assessed in vitro, and ex vivo during their transport across intestinal biopsy specimens of active celiac disease patients.

METHODS

In vitro degradation by PEP of 3H-labeled gliadin peptides 56-88 (33-mer) and 31-49, was analyzed by radio-reverse-phase high-performance liquid chromatography and mass spectrometry. For ex vivo studies, PEP and 3H-peptides were added together onto the mucosal side of duodenal biopsy specimens mounted in Ussing chambers, and peptide transport and digestion were assessed by radio-reverse-phase high-performance liquid chromatography.

RESULTS

Gliadin peptides were degraded partly by 20 mU/mL PEP both in vitro and ex vivo. This concentration of PEP decreased the amount of intact peptides 31-49 and 56-88 crossing the intestinal biopsy specimens of celiac disease patients, but could not prevent the intestinal passage of toxic or immunostimulatory metabolites. PEP concentrations of at least 500 mU/mL for 3 hours were required to achieve full detoxification of peptides and to prevent intestinal transport of active fragments.

CONCLUSIONS

After prolonged exposure to high concentrations of PEP, the amount of immunostimulatory gliadin peptides reaching the local immune system in celiac patients is decreased. These results provide a basis to establish whether such conditions are achievable in vivo.

Alterations of the intestinal transport and processing of gliadin peptides in celiac disease

BACKGROUND & AIMS

The hypothesis of a defect in the intestinal transport and processing of toxic (31-49) or immunostimulant (57-68 and the 33-mer 56-89) gliadin peptides was tested in patients with active celiac disease (ACD), patients with treated celiac disease (TCD), and controls.

METHODS

Using duodenal biopsy specimens mounted in Ussing chambers, we measured electrical resistance, mucosal-to-serosal radiolabeled-peptide fluxes, and peptide processing during transport using radio-reverse-phase high-performance liquid chromatography.

RESULTS

Peptide 31-49 fluxes (24.7 microg x 3 h(-1). cm(-2)) were increased in patients with ACD compared with controls and patients with TCD (12.7 and 12.3 microg x 3 h(-1). cm(-2); P < 0.01). In contrast, no increase was observed for peptide 57-68 or 56-89 (33-mer). Electrical resistance was decreased in patients with ACD versus controls (15.3 vs. 23.9 ohms. cm(2); P < 0.001). Peptide 57-68 was partially degraded by brush-border peptidases in controls but not in patients with celiac disease. However, it was totally degraded after intestinal transport both in controls and patients with celiac disease. Peptides 31-49 and 56-89 were resistant to brush-border peptidases in all groups of patients but were totally degraded during intestinal transport in controls and patients with TCD. In patients with ACD, however, 50% of peptide 31-49 was delivered intact into the serosal compartment and only partial degradation of the 33-mer was observed. These abnormalities were not related to a nonspecific paracellular leakage.

CONCLUSIONS

Our data indicate that gliadin peptides, although poorly or not digested by intraluminal enzymes, can be fully digested by enterocytes in controls and patients with TCD. In patients with ACD, incomplete degradation of the 33-mer and protected transport of the peptide 31-49 might favor their respective immunostimulatory and toxic effects.

Coeliac disease--all questions answered?

Gliadin specific T cells in the small intestines of coeliac disease patients use the disease associated human leukocyte antigen-DQ2 molecules in their antigen recognition. In an exciting interplay with tissue transglutaminase, the immune system recognises modified gliadin peptides and mounts a phlogistic response. Moreover, the role for autoimmune phenomena and the mechanism of breaking of immunological tolerance remain elusive.

IgG subclass profile of serum antigliadin antibodies and antibody-dependent cell-mediated cytotoxicity in young children with coeliac disease

Recently, sera from children with active coeliac disease were found to efficiently induce antibody-dependent cell-mediated cytotoxicity (ADCC) of gliadin-coated cells. In the present study, the subclass profile of immunoglobulin (Ig)G antigliadin antibodies in sera from young children, with or without coeliac disease, was determined and related to the ADCC-mediating capacity of the same sera. In addition, IgG subclasses were selectively depleted from sera and the effect on ADCC-mediating was studied. Children with untreated coeliac disease had high antigliadin antibody activities of all four IgG subclasses. However, they had a particularly high proportion of IgG1 antigliadin antibodies (ratio IgG1/IgG) compared with healthy references or coeliac children in remission. In contrast, children who had high serum antigliadin antibody activity but no histological signs of enteropathy (disease references), showed significantly lower proportions of antigliadin antibodies of the IgG1 as well as the IgG3 subclass compared with healthy references or untreated coeliac children. Regression analysis showed that IgG1 and IgG3 antigliadin antibody activity correlated positively to ADCC-mediating capacity, and depletion of IgG1 from sera profoundly diminished ADCC. The results suggest that gliadin-specific antibodies of predominantly the IgG1 subclass mediate tissue-damaging immune reactions like ADCC, and may, thus, contribute to the disease process of coeliac disease.

Celiac disease

Increased awareness of the high prevalence of celiac disease and the degree of underdiagnosis has led to calls for routine screening in certain groups. The potential consequences of underdiagnosis have been the subject of several studies. Where there is a delay in diagnosis, there may be an increased risk of associated autoimmune diseases. Alternatively, there may be marked neurological complications, or fetal growth retardation where pregnancy preceeds diagnosis. Once a diagnosis is obtained, treatment may become easier with further evidence that oats are well tolerated by most people with celiac disease. Screening will be facilitated by the development of highly sensitive and specific enzyme-linked immunosorbent assays for tissue transglutaminase. Further insights into the genetics of the condition have been gained with the discovery of a new human leukocyte antigen susceptibility type, plus a possible non-human-leukocyte antigen susceptibility gene.

Enhanced peptide-binding capacities of small intestinal brush border membranes in celiac disease

In pathogenesis of celiac disease, the significance of prolamin peptide interactions with enterocytes is controversial. Changes in cellular metabolism induced by gliadin peptides, as well as uptake and presentation by enterocytes, are discussed. We analyzed peptide binding to enterocytic membranes as a potential key event. Binding capacities of brush border membranes isolated from small intestinal biopsies of untreated (n = 49) and treated celiac patients on a gluten-free diet (n = 30), as well as control subjects (n = 43), were measured with a dot blot chemiluminescence assay. Synthetic gliadin peptides comprising amino acid position 8-19 (G XIV) and 30-41 (G XI) of alpha-gliadins, a peptic-tryptic digest of gliadin (PT-GLI), and a synthetic zein peptide were used. Comparing treated celiac patients with controls, we observed significantly enhanced membrane-binding of PT-GLI [mean 122.4 densitometric units/microg (95% confidence interval 116.0-128.9) vs 108.9 (102.1-115.7)] and of zein peptide [50.2 (38.4-61.9) vs 28.8 (13.4-44.2)], but only slightly increased binding of the synthetic gliadin peptides G XIV [65.5 (60.6-70.5) vs 62.4 (56.3-68.5) and G XI [75.2 (69.8-80.6) vs 65.9 (55.2-76.5)]. Independent of patient group, membrane-binding capacities for celiac-active gliadin peptides exceeded those of the zein peptide. Thus, interaction of gliadin peptides with the apical enterocytic membrane was not found exclusively in celiac disease. Furthermore, increased binding capacities in treated celiac disease were not confined to celiac-active peptides. Quantitative differences in gliadin peptide binding as a primary characteristic in celiac disease might contribute to pathogenetic effects exerted on small intestinal epithelial cells.

Targeting of gliadin peptides, CD8, alpha/beta-TCR, and gamma/delta-TCR to Golgi complexes and vacuoles within celiac disease enterocytes

Celiac disease (CD) is characterized by autodestruction of enterocytes after exposure of genetically susceptible individuals to dietary gluten. To define the transport pathways of proteins involved in the celiac immune response, we wished to determine the subcellular compartments of the intestinal mucosa where wheat gliadin peptides colocalize with receptors of T lymphocytes, including alpha/beta-TCR, gamma/delta-TCR, and CD8. Semithin and ultrathin frozen section of jejunal biopsies from CD patients and controls were used to perform immunofluorescence and immunogold labeling as well as in situ hybridization experiments. In patients with active CD, we detected gliadin peptides in vacuoles and Golgi complexes of enterocytes. CD8, alpha/beta-TCR, and gamma/delta-TCR were found in vacuoles and Golgi complexes within these gliadin-containing enterocytes in addition to the surface of intraepithelial and mucosal T lymphocytes. In contrast, we observed that the localization of CD4, CD3, T cell-restricted intracellular antigen (TIA), and leukocyte common antigen (LCA) was restricted to lymphocytes in CD patients. We further detected labeling signals for gliadin peptides, CD8, alpha/beta-TCR, and gamma/delta-TCR at the basal membrane of enterocytes that were interdigitated by extensions of lymphocytes. In situ hybridization experiments revealed that CD8 and gamma/delta-TCR were not expressed by CD enterocytes. We conclude that CD8, alpha/beta-TCR, and gamma/delta-TCR are targeted to Golgi complexes and vacuoles of small intestinal enterocytes in active CD. The observed process may be involved in the pathogenesis of CD enterocytes. We propose a mechanism for the uptake of CD8, alpha/beta-TCR, and gamma/delta-TCR by the basolateral membrane of small intestinal enterocytes.

Antibody-dependent cell-mediated cytotoxicity to gliadin-coated cells with sera from children with coeliac disease

Antibody-dependent cell-mediated cytotoxicity (ADCC) has been suggested as a contributing immunological mechanism in the disease process of coeliac disease. In the present study, sera from coeliac children were examined for their capacity to mediate ADCC against gliadin-coated target cells. The ADCC-mediating efficacy of sera were tested using monocytes from healthy adults as effector cells and gliadin-coated erythrocytes from the same donor as targets. Using monocytes as effector cells, sera from children with active coeliac disease (untreated or challenged), demonstrated significantly higher ADCC-mediating capacity than sera from healthy and disease references as well as children with treated coeliac disease. A positive correlation was found between the ADCC-mediating capacity and serum IgG as well as IgA anti-gliadin antibody levels. The results suggest that an antibody-dependent monocyte/macrophage-induced cytotoxic reaction might be involved in the disease process of coeliac disease.

Effect of gamma-interferon on binding of gliadin and other food peptides to the human intestinal cell line HT-29

gamma-Interferon is one of the main cytokines released during activation of intestinal lymphocytes in coeliac patients. The question has never been addressed whether gamma-interferon influences binding of gliadin and other food peptides to human enterocytes. Therefore, the human intestinal epithelial cell line HT-29 was cultured with gliadin, casein, beta-lactoglobulin and ovalbumin, with or without gamma-interferon, and peptide binding to cells was determined by flow cytometry and fluorescence microscopy. gamma-Interferon stimulated gliadin binding by a factor of 4. Binding was saturable with half maximal binding at 0.15 mg/ml. For maximal binding, an incubation of at least 24 h was necessary. gamma-Interferon increased binding of beta-lactoglobulin and casein, too, but inhibited that of ovalbumin. Binding of gliadin was inhibited by the other peptides. Under the conditions of ongoing mucosal inflammatory reactions and release of gamma-interferon, enhanced binding may trigger intestinal lymphocytes, increase secretion of cytokines and thus induce a vicious circle.

Changes in jejunal mucosa after long-term feeding of germfree rats with gluten

BACKGROUND

Coeliac disease (CD) or gluten-sensitive enteropathy is a chronic gastrointestinal disease of children and adults. An experimental model using inbred germfree rats has been developed to study the effects of intragastric gliadin application on intestinal mucosa.

METHODS

AVN strain Wistar rats (inbred F 87)-germfree were used. Gliadin was applied by intragastric probe from birth until day 63 (0.5-5 mg of gliadin per immunization). Intraepithelial lymphocytes (IEL) were separated from the jejunum, and surface marker characterization was performed using flow cytometry. Isolated IEL were labelled with fluorescein isothiocyanate and injected into control jejunal loops. After 1 h and 6 h the abdominal cavity was reopened. The samples of jejunum were fixed.

RESULTS

Prolonged application of gliadin led to the shortening of jejunal villi, crypt hyperplasia, increased number of mitoses in the crypt epithelium, and increased number of IEL-characteristic CD8+, RGL-1+, and TcR alpha/beta +. Transfer of IEL separated from rats fed with gliadin into the intestinal loops of untreated rats led to tight junctions in the enterocytes of the intestinal loops. The IEL isolated from controls (albumin-treated) induced no mucosal changes in intestinal loops.

CONCLUSION

These data suggest that IEL isolated from gliadin-treated rats transfer mucosal damage and that gluten-induced enteropathy has an autoimmune component.

Peptic-tryptic digests of gliadin: contaminating trypsin but not pepsin interferes with gastrointestinal protein binding characteristics

For many years, peptic-tryptic digests of gliadin, known as Frazer's fraction III, have been used in investigations of gliadin effects. Potential contamination by the proteases pepsin and trypsin, however, was not considered. To investigate the influence of contaminating proteases on binding of gliadin peptides to rat small intestinal brush border membranes we compared binding characteristics of different gliadin digests. Binding of biotinylated probes was studied in dot blots and Western blots with an enhanced chemiluminescence system. In gliadin peptide preparations only contaminating trypsin, but not pepsin, was detectable by specific antisera. Digestion with insoluble proteases attached to cross-linked beaded agarose yielded gliadin peptides free of contaminating pepsin and trypsin. These peptides bound 30% less to brush border membranes. Using these peptides, there was no trypsin-typical binding pattern to low molecular mass membrane proteins in contrast to peptide preparations which contained contaminating trypsin. In conclusion contaminating trypsin might alter gliadin peptide binding characteristics by direct binding to brush border membranes and by interfering with interactions between gliadin peptides and brush border membranes.

Crypt-villus differentiation reflected by lectin and protein binding to rat small intestinal brush border membranes

To compare differentiation along the crypt-villus axis in adult rats with changes observed in postnatal maturation with respect to binding capacities for lectins and food proteins, crypts and villi were isolated by in vivo perfusion and in vitro incubation. Brush border membranes were prepared from adults and newborns, and binding of 125I-labeled lectins and food proteins was assessed by airfuge ultracentrifugation. Crypt and villus membrane protein patterns looked almost identical, unlike newborn membranes. Considerable shifts in lectin binding to membranes were observed during postnatal maturation, but not in crypt-villus differentiation. For instance, fucose-specific lectin binding patterns in both preparations resembled the general adult mode. Contrary to differences in food protein binding between newborn and adult membranes, food protein binding did not show a consistent significant difference between membranes of crypt and villus origin in adult animals. In conclusion, membrane differentiation along the crypt-villus axis was found to follow a pattern dissimilar from neonatal maturation as far as protein and carbohydrate composition and food protein binding were concerned.

Translocation of gliadin into HLA-DR antigen containing lysosomes in coeliac disease enterocytes

Coeliac disease is triggered by ingestion of wheat gliadin and is probably immune mediated. There is evidence by light microscopy that expression of class II major histocompatibility complex (MHC) molecules is increased in the small intestinal epithelium of patients with untreated coeliac disease and that gliadin can be taken up by small intestinal enterocytes. The pathway by which gliadin is transported to class II MHC proteins has not been demonstrated. Using an immunogold technique and thin frozen sections of jejunal biopsy specimens, gliadin, HLA-DR antigens, and IgA were localised at an ultrastructural level in the jejunal epithelium of patients with both untreated and treated coeliac disease and controls. Cathepsin D was used as a marker for late endosomes or lysosomes. The results show that gliadin is translocated into vacuoles positive for HLA-DR antigens as well as cathepsin D in jejunal enterocytes of patients with untreated coeliac disease. Secretory IgA may have a role in this translocation of gliadin, which is a specific event that occurred only in jejunal enterocytes from patients with untreated coeliac disease but not in a patient maintained on a gluten free diet or in controls. These results support a central role for epithelial cells of the human intestinal mucosa in the transport of gliadin to an HLA-DR positive compartment which precedes antigen presentation of gliadin to antigen sensitive T lymphocytes.

Polymorphism of antigen processing (TAP, LMP) and HLA class II genes in celiac disease

Susceptibility to CD is strongly associated with particular HLA class II molecules. However, additive genetic factors are likely to be required for the development of the disease. The polymorphic TAP and LMP genes, located within the HLA class II region, are involved in the antigen presentation pathway and thus represent candidate susceptibility genes. HLA class II DRB1, DRB3, DQA1, DQB1, and DPB1 as well as TAP1, TAP2, and LMP2 polymorphism was studied in 80 Caucasian CD patients and 213 normal controls by DNA oligotyping. The DQB1*0201 allele was found in 96.3% of CD patients and provided the highest risk (RR = 50), whereas only 89% of CD patients carried the DQ alpha 501/beta 201 heterodimer (RR = 30). The participation of the DRB3 and DPB1 locus was ruled out as it was attributed to a linkage disequilibrium on the DR3 haplotype. TAP1 and LMP2 allelic distribution was not significantly different among CD patients and controls. The TAP2-C allele was completely absent from the CD population, while it was found in 22.5% of controls. Although linkage disequilibrium between TAP2 and class II loci clearly exists in some haplotypes, TAP could act as additional susceptibility genes.