Gluten induces an intestinal cytokine response strongly dominated by interferon gamma in patients with celiac disease

Potential and latent coeliac disease

This case report details a child with coeliac disease and giardiasis. Treatment of the infection without recourse to a gluten-free diet cured the symptoms of diarrhoea and returned the small intestinal morphology to normal. Thus, the patient moved from active to latent coeliac disease. Potential and latent forms of coeliac disease are being increasingly recognized, since markers have become available to identify patients and investigations developed to test for gluten sensitivity in the small intestinal mucosa. This case provides an opportunity to consider potential and latent forms of coeliac disease and how these impact on clinical practice and the wider understanding of the disorder.

Nature and function of gastrointestinal antigen-presenting cells

Antigen-presenting cells (APCs) of the human gut are heterogeneous, including both macrophages, a variety of dendritic cells and B cells. They are found both in gut-associated lymphoid tissue and in the mucosal lamina propria, especially beneath the surface epithelium. APCs have diverse phenotypes and therefore probably different functions in various locations; their expression levels of a variety of costimulatory molecules are most likely important for immunological decision making of stimulated T cells, either locally in the gut or in regional lymph nodes to which migrating APCs (dendritic cells) carry antigen. Thus, APCs are involved in active immunity as well as in induction of oral tolerance. However, their precise role in food allergy remains to be defined.

Heat-shock protein 70-1 and HLA class II gene polymorphisms associated with celiac disease susceptibility in Navarra (Spain)

Heat shock proteins (HSP) are thought to play a role in the immune response making probable their contribution to celiac disease (CD). We studied the polymorphisms in the 5' regulatory region of the HSP70-1 gene and performed genomic HLA-DQ and -DR typing in 128 CD patients and 94 healthy controls from Navarra (Spain). The frequency of the C allele of the HSP70-1, characterized by the intermediate electrophoretic mobility of DNA, was significantly increased among CD patients (64.5% vs 37.2%. p <1 x 10(-7)). When subjects were stratified by the HLA II genotype, differences were statistically significant between DR3-negative or DR3-DQB1*02-negative CD patients and matched controls. Homozygosity for the DQB1*02 allele was present in 48.4% of CD patients and 12.8% of controls (OR = 6.4; CI:3.1 to 13.8; p <1 x 10(-7)). Similar increased risk was observed for DQB1*02/*02, DRB1*03/-, or DRB1*03/07 patients. Furthermore, those individuals expressing the classical HLA alleles in CD (DQB1*02/*02, DRB1*03/*07) who also carried the HSP70-1 CC genotype were twelve times more likely to develop the disease than the matched controls. We therefore conclude that although HSP70-1 gene does not seem to be primarily associated with CD, it might be a component of the high risk haplotype, playing a role as an additional predisposing gene for the disease.

Interferon-alpha drives T cell-mediated immunopathology in the intestine

The ability of interferon (IFN)-alpha to induce autoimmunity and exacerbate Th1 diseases is well known. We have recently described enhanced expression of IFN-alpha in the mucosa of patients with celiac disease (CD), a gluten-sensitive Th1-mediated enteropathy, characterized by villous atrophy and crypt cell hyperplasia. Previous studies from this laboratory have shown that T cell activation in explant cultures of human fetal gut can also result in villous atrophy and crypt cell hyperplasia. We have, therefore, examined changes that take place in explant cultures of human fetal gut after activation of T cells with anti-CD3 and/or IFN-alpha. We show that activation of T cells with anti-CD3 alone elicits a small IFN-gamma and TNF-alpha response with no tissue injury. Similarly, no changes are seen in explants cultured with IFN-alpha alone. However, addition of IFN-alpha with anti-CD3 results in enhanced Th1 response and crypt cell hyperplasia. This is associated with enhanced phosphorylation of STAT1, STAT3, and Fyn, a Src homology tyrosine kinase, which interacts with both TCR and IFN-alpha signal components. Together these data indicate that IFN-alpha can facilitate activation of Th1-reactive cells in the gut and drive immunopathology.

Keratinocyte growth factor and coeliac disease

BACKGROUND

Coeliac disease is characterised by increased epithelial renewal associated with a mucosal T cell response to gliadin. Keratinocyte growth factor (KGF) is produced by cytokine activated gut stromal cells and may be a link between mucosal T cell activation in untreated coeliac disease and epithelial hyperplasia.

AIMS

To characterise expression of KGF in coeliac disease.

METHODS

KGF transcripts in coeliac disease were measured by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) and localised using in situ hybridisation. KGF production by gluten reactive CD4+ T cell clones was examined. In addition, KGF transcripts were measured following ex vivo challenge of coeliac biopsies with a peptic-tryptic digest of gliadin.

RESULTS

KGF transcripts were elevated in coeliac biopsies compared with normal controls but were not different from non-coeliac disease controls. By in situ hybridisation, KGF mRNA containing cells were present in the upper half of the lamina propria, most abundantly just under the epithelium. There was no signal from cells within the epithelium. Gluten reactive T cell clones did not make KGF. In vitro challenge of coeliac biopsies generated a strong interferon gamma response but a specific KGF response could not be detected because of an extremely high number of KGF transcripts in all cultured biopsies.

CONCLUSIONS

KGF is overexpressed in coeliac biopsies and in tissues with non-coeliac enteropathy. No evidence was found for KGF production by intraepithelial lymphocytes or lamina propria T cells.

Regulated production of interferon-inducible T-cell chemoattractants by human intestinal epithelial cells

BACKGROUND & AIMS

Human intestinal epithelial cells inducibly express neutrophil and monocyte chemoattractants, yet little is known about the regulated production of T-cell chemoattractants by the intestinal epithelium. IP-10, Mig, and I-TAC are 3 CXC chemokines that are known to act as CD4(+) T-cell chemoattractants.

METHODS

We studied constitutive chemokine expression in human colon, and defined the regulated expression of these chemokines by reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistology using cultured human intestinal epithelial cell lines and a novel adaptation of an in vivo human intestinal xenograft model.

RESULTS

IP-10 and Mig were constitutively expressed by normal human colon epithelium, and their cognate receptor, CXCR3, was expressed by mucosal mononuclear cells. Interferon (IFN)-gamma stimulation increased mRNA expression and the polarized basolateral secretion of these chemokines by human colon epithelial cell lines; infection with enteroinvasive bacteria, or stimulation with the proinflammatory cytokines tumor necrosis factor alpha and interleukin 1alpha, strongly potentiated IFN-gamma-induced epithelial cell IP-10, Mig, and I-TAC production. Epithelial cell mRNA and protein expression of IP-10, Mig, and I-TAC were rapidly up-regulated in human intestinal xenografts in response to stimulation with IFN-gamma alone or in combination with IL-1.

CONCLUSIONS

The constitutive and regulated production of the IFN-gamma-inducible chemokines IP-10, Mig, and I-TAC by human intestinal epithelium, and the expression of their cognate receptor, CXCR3, by mucosal mononuclear cells, suggest that the intestinal epithelium can play a role in modulating physiologic and pathologic T cell-mediated mucosal inflammation.

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.

Up-regulation of the IL-12 receptor beta 2 chain in Crohn's disease

Crohn' s disease (CD) is a chronic intestinal inflammatory disorder characterized by aberrant mucosal Th1 cell activation and production of IL-12, the major Th1-driving factor. The T cell response to IL-12 is dependent on the expression of a specific receptor composed of two subunits, termed IL-12Rbeta1 and IL-12Rbeta2. The content of IL-12Rbeta2, as measured at the mRNA level, is crucial in regulating Th1 differentiation. In this study we therefore investigated IL-12Rbeta2 RNA transcripts in CD. IL-12Rbeta2 expression was increased in active CD as well as Helicobacter pylori (HP)-associated gastritis and Salmonella colitis compared with that in inactive CD, ulcerative colitis, noninflammatory controls, and celiac disease. In contrast, IL-12Rbeta1 transcripts were expressed at comparable levels in all samples. In CD, IL-12Rbeta2 expression strictly correlated with tyrosine phosphorylation of STAT4, a key component of the IL-12-dependent Th1 polarization. This was associated with a pronounced expression of IFN-gamma. Transcripts for IL-12/p40 were detected in CD, HP-positive, and Salmonella colitis patients, but not in celiac disease, indicating that IL-12Rbeta2 up-regulation occurs only in IL-12-associated Th1 gastrointestinal diseases. Finally, we showed that stimulation of lamina propria mononuclear cells with IL-12 enhanced IL-12Rbeta2, suggesting that IL-12 regulates IL-12Rbeta2 expression in human gastrointestinal mucosa. The data show that the signaling pathway used by IL-12 to induce Th1 differentiation is increased at the site of disease in CD, further supporting the view that IL-12/IL-12R signals contribute to the inflammatory response in this condition.

The effect of inflammation severity and of treatment on the production and release of TNFalpha by colonic explants in inflammatory bowel disease

BACKGROUND

Despite its pivotal role in mucosal inflammation, data on TNFalpha levels in inflammatory bowel diseases have been contradictory.

AIM

To examine TNFalpha production in relation to the type and severity of inflammation and therapy, using colonic explant cultures.

MATERIALS AND METHODS

Rectal mucosal biopsies from 271 paediatric patients (178 inflammatory bowel disease, 27 inflammatory controls, 66 normal) were cultured for 4 or 18 h. Basal TNFalpha tissue content and release into the medium were measured by ELISA and compared to histological severity and clinical parameters.

RESULTS

TNFalpha release as well as tissue-associated TNFalpha levels were significantly increased in rectal biopsies from involved inflammatory bowel disease tissue. The amount of TNFalpha correlated with inflammation severity scores. TNFalpha levels were higher at 18 compared to 4 h in all groups, whether inflamed or not. TNFalpha released from rectal biopsies was lower among treated patients at 18 h. The presence of proximal colonic involvement was associated with higher TNFalpha release by uninvolved Crohn's disease rectal biopsies compared to patients with ileitis alone.

CONCLUSIONS

TNFalpha production and release is increased in involved rectal explants from inflammatory bowel disease. Anti-inflammatory treatment diminishes this response.

Human Peyer's patch T cells are sensitized to dietary antigen and display a Th cell type 1 cytokine profile

Animal studies have demonstrated that feeding Ags induces regulatory (Th2, Th3) cells in Peyer's patches (PP), which migrate to the periphery and produce immunomodulatory cytokines such as IL-4, IL-10, or TGF-beta. In this work we have attempted to extend this paradigm to man by analyzing the response of human PP T cells to in vitro challenge with the common dietary Ag beta-lactoglobulin (betalg) of cow's milk. PP T cells stimulated with betalg showed enhanced proliferation compared with blood T cells from the same patient. Increased expression of CD25 and the Th1-associated chemokine receptor CCR5 was also seen on CD4(+) and CD8(+) PP T cells, but not blood T cells, stimulated with betalg. By enzyme-linked immunospot assay and RT-PCR, the PP T cell recall response to betalg and casein was dominated by IFN-gamma, with negligible IL-4, IL-5, IL-10, or TGF-beta. To help explain the PP T cell response to betalg, we examined IL-12 expression. Both IL-12p40 and -p35 transcripts were abundantly expressed in PP, but not in adjacent normal ileal mucosa. Immunoreactive IL-12p40-containing cells were present below the PP dome epithelium. Furthermore, in culture, PP, but not paired PBMC, spontaneously released IL-12p70. These results suggest that the human response to oral Ags in the gut may be different from that in rodents.

Interleukin 15 mediates epithelial changes in celiac disease

BACKGROUND & AIMS

Villous atrophy and crypt proliferation are key epithelial features of untreated celiac disease. We tried to define whether cytokines such as interleukin (IL)-15, IL-2, IL-4, and IL-7, which share chains of their receptors, could influence the epithelial modifications.

METHODS

Duodenal biopsy specimens (14 treated and 13 untreated celiac patients, 7 controls) were cultured in vitro for 24 hours with or without gliadin (1 mg/mL), IL-15, IL-7, IL-4, or IL-2 (10 ng/mL). Tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma were also used in some specimens of untreated celiacs. Epithelial expression of Ki67, FAS, and transferrin receptor (TFR) was detected by immunohistochemistry, and apoptosis by TUNEL technique (percentage of positive enterocytes). IL-15-positive cells were detected by immunohistochemistry in celiac disease and control biopsy specimens; presence of IL-15 was also determined by semiquantitative polymerase chain reaction.

RESULTS

Only IL-15 induced enterocyte expression of Ki67, TFR, and FAS in treated celiac (P<0.01 vs. medium) and enterocyte apoptosis in untreated celiac disease specimens. Anti-IL-15 monoclonal antibodies neutralized gliadin-induced enterocyte TFR and FAS expression in treated celiac and enterocyte apoptosis in untreated celiac disease specimens (P<0.05 vs. gliadin). IL-15-positive cells were increased in untreated celiacs (P<0.001 vs. treated celiacs and controls).

CONCLUSIONS

IL-15 is involved in the modulation of epithelial changes in celiac disease, indicating that this cytokine has an unforeseen role in the pathologic manifestations of celiac disease.

Molecular basis of celiac disease

Celiac disease (CD) is an intestinal disorder with multifactorial etiology. HLA and non-HLA genes together with gluten and possibly additional environmental factors are involved in disease development. Evidence suggests that CD4(+) T cells are central in controlling an immune response to gluten that causes the immunopathology, but the actual mechanisms responsible for the tissue damage are as yet only partly characterized. CD provides a good model for HLA-associated diseases, and insight into the mechanism of this disease may well shed light on oral tolerance in humans. The primary HLA association in the majority of CD patients is with DQ2 and in the minority of patients with DQ8. Gluten-reactive T cells can be isolated from small intestinal biopsies of celiac patients but not of non-celiac controls. DQ2 or DQ8, but not other HLA molecules carried by patients, are the predominant restriction elements for these T cells. Lesion-derived T cells predominantly recognize deamidated gluten peptides. A number of distinct T cell epitopes within gluten exist. DQ2 and DQ8 bind the epitopes so that the glutamic acid residues created by deamidation are accommodated in pockets that have a preference for negatively charged side chains. Evidence indicates that deamidation in vivo is mediated by the enzyme tissue transglutaminase (tTG). Notably, tTG can also cross-link glutamine residues of peptides to lysine residues in other proteins including tTG itself. This may result in the formation of complexes of gluten-tTG. These complexes may permit gluten-reactive T cells to provide help to tTG-specific B cells by a mechanism of intramolecular help, thereby explaining the occurrence of gluten-dependent tTG autoantibodies that is a characteristic feature of active CD.

Differing patterns of transforming growth factor-beta expression in normal intestinal mucosa and in active celiac disease

BACKGROUND

Growth-inhibitory autocrine polypeptides such as transforming growth factor (TGF)-beta may play a role in the control of normal epithelial cell proliferation and differentiation. In addition, TGF-beta has a central role in extracellular matrix homeostasis and regulates the immune response at the local level. In this study immunohistochemistry was used to examine the pattern of TGF-beta protein distribution and quantitative reverse transcription-polymerase chain reaction (RT-PCR) to determine levels of TGF-beta messenger RNA expression in normal intestinal mucosa and in the flat mucosa of children with celiac disease.

METHODS

Small intestinal biopsies were performed in children with active celiac disease and in histologically normal control subjects. Frozen sections were single stained using an anti-TGF-beta monoclonal antibody and were double stained for TGF-beta and T cell, macrophages, and the activation marker CD25. Total RNA was extracted from frozen specimens and competitive quantitative RT-PCR performed for TGF-beta mRNA using internal synthetic standard RNA.

RESULTS

In normal intestinal mucosa, by immunohistochemistry, TGF-beta expression was most prominent in the villous tip epithelium, whereas in the lamina propria, weak immunoreactivity was present. The celiac mucosa showed weak and patchy epithelial TGF-beta immunoreactivity. In contrast, an intense staining positivity was present in the lamina propria localized mostly in the subepithelial region where T cells, macrophages, and CD25+ cells were detected by double staining. By quantitative RT-PCR, levels of TGF-beta mRNA transcripts appeared to be increased in celiac intestinal mucosa compared with that in control subjects, although the difference did not reach statistical significance.

CONCLUSIONS

These observations suggest that TGF-beta expression is associated with differentiated enterocyte function. In celiac disease the lower TGF-beta epithelial cell expression could be a consequence of the preponderance of a less differentiated epithelial cell phenotype also present in the surface epithelium. In contrast, the prominent TGF-beta positivity of the subepithelial lamina propria suggests an association with the local immune and inflammatory response, as well as a potential role of these peptides in mesenchymal-epithelial cell interaction.

Cyclooxygenase-2-dependent arachidonic acid metabolites are essential modulators of the intestinal immune response to dietary antigen

Intestinal inflammatory diseases are mediated by dysregulated immune responses to undefined luminal antigens. Feeding hen egg-white lysozyme to mice expressing a transgenic T-cell receptor that recognizes hen egg-white lysozyme peptide 46-61 resulted in no intestinal pathology; however, simultaneous administration of cyclooxygenase-2 inhibitors and dietary hen egg-white lysozyme resulted in increased proliferation of lamina propria mononuclear cells and crypt epithelial cells, crypt expansion and villus blunting. Lamina propria mononuclear cells produce high levels of cyclooxygenase-2-dependent arachidonic acid metabolites, which act as immunomodulators in the immune response to dietary antigen. These findings establish that cyclooxygenase-2-dependent arachidonic acid metabolites are essential in the development and maintenance of intestinal immune homeostasis.

Intravenous or intranasal administration of gliadin is able to down-regulate the specific immune response in mice

The mucosal lesion in coeliac disease (CD) represents an immunologically mediated injury triggered by gliadin and is restricted by a particular assortment of major histocompatibility complex (MHC) class II genes. Therefore, immunomodulatory strategies to tolerize gliadin-specific, class II-restricted T-cell responses could represent an alternative to current treatments of CD, which are based on a gluten-free diet. In this study, BALB/c mice derived from a gluten-free diet colony were tolerized by either intranasal (i.n.) or intravenous (i.v.) administration of single or multiple doses of gliadin. While a single dose failed to induce tolerance, a significant decrease in gliadin-specific T-cell proliferation was detected (P < 0.001) after multiple i.n. or i.v. administrations. No significant difference in antibody titre was detected for antigen-specific immunoglobulin G (IgG) or the IgG1 subclass, but a lower IgG2a-specific titre was observed. Both interferon-gamma (IFN-gamma) and interleukin (IL)-2 expression, measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR), were reduced on antigen administration, both i.v. and i.n. Neither regimen showed a regulatory effect on IL-4 production. As T helper 1 (Th1) cytokines seem to be important in the pathogenesis of CD, our data therefore highlight the potential of i.n. and i.v. routes for the design of useful immunomodulatory strategies for CD.

T cell proliferation, MHC class II restriction and cytokine products of gliadin-stimulated peripheral blood mononuclear cells (PBMC)

The immune response of PBMC to gliadin was investigated in patients with coeliac disease (CoD) by examining proliferation, MHC restriction and cytokine production. Gliadin induced low levels of proliferation in 63% of eight untreated patients, 32% of 28 treated patients and 35% of 31 healthy control subjects. In MHC restriction studies, the proliferative response to gliadin was inhibited (range 47-98% inhibition) in the presence of a MoAb to HLA-DR in each of three coeliac and three control donors studied. Using flow cytometry, increased expression of activation markers (HLA-DR and IL-2R) was demonstrated on gliadin-stimulated T cells from four of nine coeliac patients and three of seven healthy control donors. Cytokines were studied in culture supernatants using ELISA. Gliadin was a potent inducer of IL-6 and IL-10 in 100% of coeliac patients and controls, whereas IL-4 was not produced in either subject group. Gliadin induced IL-2 production in 40% of untreated patients, 42% of treated patients and 35% of healthy control donors. Interferon-gamma (IFN-gamma) in gliadin-stimulated cultures was found only in coeliac patients, observed in 33% of untreated patients and 25% of treated patients. Spontaneous secretion of both IL-2 and IFN-gamma was found more frequently in patients with untreated disease (87% of cases versus 21% of controls for IFN-gamma and 40% versus 0% for IL-2). These results suggest, as manifest by IFN-gamma production, that gliadin stimulates a Th1/Th0-like response in coeliac patients and a Th0-like response in healthy controls.

Cytokine profile in coeliac disease

Coeliac disease (CD), an inflammatory enteropathy, is believed to be caused by immune sensitivity to ingested gluten. T-cell activation appears to be implicated in the disease although little is known regarding the role of T-cell subsets, Th1/Th2, and the cytokines they secrete. Reverse transcription-polymerase chain reaction was used to examine the mRNA expression of a wide profile of cytokines in intestinal and peripheral samples taken from active and inactive CD paediatric patients. Differential mRNA expression was observed for cytokines, between CD patients and controls, in both compartments. The percentage of samples expressing interleukin (IL)-2, interferon (IFN)-gamma, tumor necrosis factor (TNF)-beta, IL-10, IL-1beta, TNF-alpha and transforming growth factor (TGF)-beta mRNA from active CD patients was higher than from controls. A prominent finding was the expression of both Th1 (IFN-gamma, IL-2) and Th2 (IL-4, IL-10)-associated cytokine transcripts in the same biopsies and peripheral blood cells from patients with active CD implying activation of Th0 cells. The expression of IL-2 and IL-4 mRNA was not observed in peripheral blood samples from inactive CD patients associating them with disease activity. These results are important to the understanding of the inflammatory process in CD while cytokine levels may prove to be relevant markers of disease activity.

Celiac disease

There continues to be much research interest in celiac disease, with well over 200 papers published in the year under review, covering a multitude of areas from population screening to the molecular immunology of disease pathogenesis. The high prevalence of "silent" disease again has been demonstrated, and there is continued emphasis on the increasingly wide recognized range of associated conditions and extraintestinal manifestations. The case for the safety of oats is further strengthened by a study involving patients with dermatitis hepetiformis. One of the most significant scientific advances has been the discovery of a potential role for tissue transglutaminase, recently found to be the autoantigen of antiendomysial antibodies, in disease pathogenesis, by enhancing gliadin peptide class II binding and consequent T-cell activation. However, the very central role of T cells has been thrown into doubt with an elegant study that assessed the effect of blocking costimulation in T-cell activation.

Different regulatory pathways employed in cytokine-enhanced expression of secretory component and epithelial HLA class I genes

The transmembrane secretory component (SC, or pIg receptor) plays a crucial role in mucosal immunity by translocating dimeric IgA and pentameric IgM through exocrine epithelia. This receptor is up-regulated by cytokines in parallel with increased epithelial HLA expression. By use of the human epithelial cell line HT-29m3, we show that IFN-gamma, TNF-alpha and IL-4 activate transcription of the SC gene. This activation was slow, suggesting mediation via newly synthesized protein factors. IFN-gamma and TNF-alpha, but not IL-4, also up-regulated expression of HLA class I genes. However, this gene induction was rapid and did not depend on new protein synthesis. Nuclear run-on experiments showed that the transcription rate of HLA class I genes nearly peaked after only 30 min of IFN-gamma or TNF-alpha stimulation, whereas the SC transcription rate did not peak until after 20-36 h of IFN-gamma, TNF-alpha or IL-4 stimulation. Gel electrophoresis mobility shift assays demonstrated binding of nuclear proteins from cytokine-stimulated HT-29 cells to consensus elements in the promoter of the SC gene, involving the binding site for the nuclear factor-kappaB p50 subunit after TNF-alpha stimulation, and IFN-stimulated response element after IFN-gamma stimulation (and weakly after TNF-alpha. Our observations in vitro likely parallel events in vivo by which activated mucosal T cells and macrophages enhance pIg receptor-mediated external transport of secretory IgA and IgM and up-regulate epithelial HLA expression.

T cell immunity to oral allergens

Considerable light has been thrown on the mechanisms of oral tolerance (or, more correctly, orally-induced systemic tolerance) in the past 12-18 months. While it is very clear that T cell anergy and apoptosis can occur after being fed antigen, a major pathway that has been described in different models is the induction of regulatory T cells which secrete transforming growth factor beta. These cells have been designated Th3 cells but their relation to the in-vitro-generated Tr cells, which inhibit tissue-damaging T cell responses in the gut mucosa, is not known. An important discovery is that food antigens have major systemic effects on T cells, similar in many ways to those seen following intravenous injection of soluble antigens. This conceptually moves us away from the notion that there is something special about mucosal (compared to systemic) lymphoid tissue to the notion that it is the type of antigens seen in the gut (i.e. digested, soluble polypeptides) which dictates the types of response seen there. After initial excitement, clinical trials using oral tolerance to treat autoimmune disease have been somewhat disappointing.

HLA restriction patterns of gliadin- and astrovirus-specific CD4+ T cells isolated in parallel from the small intestine of celiac disease patients

Celiac disease is a common HLA-DQ2-associated enteropathy caused by an abnormal T-cell-mediated immune response to ingested wheat gliadin proteins. We have previously isolated in situ activated mucosal T cells from celiac disease patients and demonstrated that these T cells were gliadin specific and predominantly DQ2 restricted. In contrast to this, gliadin-specific T cells isolated from peripheral blood display a variable HLA restriction pattern, thereby indicating that the skewed DQ restriction of T cells resident in the celiac lesions could be dictated by a preference for DQ-mediated antigen presentation in the mucosa of CD patients. To address this, we analyzed the HLA restriction of T cells recognizing astrovirus, a common gastroentetitis virus, isolated from intestinal mucosa of six celiac disease patients. As an internal control, gliadin-specific T cells were isolated and analyzed in parallel. The gliadin-specific mucosal T cells were marked in their DQ2 restriction, whereas the parallel astrovirus-specific T cells were predominantly restricted by DR molecules. Our data indicate that the repertoire of T cells present in celiac lesions is determined by the priming antigen(s) and not by a skewing in the expression of functional HLA class II isotypes in the disease affected small intestinal mucosa.

Mechanisms of gastrointestinal reactions to food

Much of the genetic information that modulates mucosal immune responses was encoded several million years ago and has subsequently been subjected to modifications selected by the impact of microorganisms and food antigens. Confronted with these challenges, the intestinal immune system has developed two arms: (1) immune exclusion performed mainly by secretory IgA antibodies to inhibit colonization of pathogenic microorganisms and penetration of harmful antigens; and (2) down-regulatory mechanisms to avoid local and peripheral overreaction (hypersensitivity) towards innocuous substances. The latter phenomenon is called oral tolerance and apparently explains why most individuals show no adverse immune reactions food. When the mucosal barrier function is insufficient, tolerance to dietary antigens is abrogated in genetically susceptible individuals. This is most likely to occur during the vulnerable period after birth before the immunoregulatory network has been established. Breast-feeding appears to be immunologically important during this period, not only to substitute for the infant's lacking secretory antibodies but also because of its immune-modulating effects.