Understanding the molecular basis of coeliac disease

Evidence for aberrant regulation of MAP kinase signal transduction pathway in peripheral blood mononuclear cells in patients with active celiac disease

BACKGROUND

Aberrant signaling via the p21/mitogen-activated proteins (MAP) kinase pathway has been described in lymphocytes of patients with various autoimmune diseases. There is little published data about the intracellular mediators and signals that regulate expression and activity of transcription factors and their effect on celiac disease induction and progression.

AIM

To investigate the possible involvement of MAP kinase pathway in peripheral blood mononuclear cells (PBMC) in celiac disease and its correlation with disease activity.

METHODS

Expression of the total and activated forms of two MAP kinases [extracellular response kinase (ERK) and c-Jun amino terminal kinase (JNK)] were studied by Western blots in PBMC of 17 untreated and 19 treated celiac patients, and 17 controls. Seven of these untreated celiac patients were studies before and after 6 months of gluten-free diet.

RESULTS

Phosphorylated ERK of active celiac disease patients was significantly lower compared with controls (P < 0.01) and was increased towards normal after 6 month of gluten-free diet (P < 0.01). Phosphorylated JNK was increased significantly in the untreated celiac group (P < 0.01) and normalized towards the control level after 6 months of gluten-free diet (P < 0.04).

CONCLUSIONS

Aberrant MAP-kinase pathway activity is associated with active celiac disease (CD). Further studies should examine the potential role of this aberration in pathogenesis of CD.

Extracts of wheat gluten activate complement via the alternative pathway

We studied the ability of wheat gluten and its subfractions to activate complement directly. A sensitive sandwich ELISA employing a monoclonal antibody (MoAb) to a C9 neoepitope exposed in the terminal complement complex (TCC), a functional haemolytic assay for C5b6 generation, and LaurelFs electrophoretic method of estimating C3 conversion to C3bi were used. On a weight-for-weight basis, enzyme solubilized Frazer's fraction three of gluten (Fill) produced approximately 75% of the complement activation seen with the potent activator zymosan. By contrast, activation with whole insoluble undigested gluten was very weak and similar to that seen with ovalbumin or β-lactoglobulin. The results were the same using normal human serum or sera from patients with coeliac disease, dermatitis herpetiformis, or hypogammaglobulinaemia as the complement source. Activation by both zymosan and Fill was blocked in 0.01 M EDTA, but not in 0.01 M EGTA with 0.0025 m magnesium chloride. Zymosan and Fill activated complement in a serum from a patient with an intact alternative pathway but classical pathway haemolytic activity (CH50) of zero. Preferential heat inactivation of the alternative pathway inhibited both zymosan- and Fill-induced activation. Our results confirm that Fill is a strong activator of the alternative pathway. We discuss how gluten enteropathy might be initiated by complement.

Coeliac disease, epilepsy and cerebral calcifications

Coeliac disease, epilepsy and cerebral calcifications (CEC) syndrome is a rare clinical condition. One hundred and seventy-one patients have been reported in the literature. Patients are mostly from Italy, Spain, and Argentina, suggesting a geographically restricted condition. Epilepsy is more frequently characterized by occipital seizures. It may be benign or drug-resistant, sometime evolving into severe epileptic encephalopathy. Gluten free diet (GFD) efficacy seems to be inversely related to the duration of epilepsy and the young age of the patient. Patients with cerebral calcifications (CC) and coeliac disease (CD) without epilepsy are considered as having an incomplete form of CEC syndrome. Some patients with epilepsy and CC without CD are supposed to have a CEC syndrome with silent or latent CD. Whether CEC syndrome is a genetic condition, or whether epilepsy and/or CC are a consequence of an untreated CD is unknown yet. Since histopathological findings seem to be the expression of vascular calcified malformation, CEC syndrome may be considered a genetically determined entity, such as a type of Sturge-Weber-like phacomatosis. Moreover, CEC, as well as CD, is associated with HLA-DQ2 and HLA-DQ8 phenotype and genotype. The progressive growth and late occurrence of CC before beginning a GFD, the demonstration of anti-gliadin antibodies in the cerebro-spinal fluid and the association with HLA class II genes, suggest that an immune reaction originating from the jejunal mucosa, triggered by gliadin in gluten intolerance predisposed subjects (HLA phenotype) may be responsible for seizures and CC. Moreover, a long-lasting untreated CD folic acid deficiency may cause calcifications. Probably, CEC is considered a genetic, non-inherited, ethnically and geographically restricted syndrome associated with environmental factors.

Human leukocyte antigen class II alleles in white Brazilian patients with celiac disease

BACKGROUND

Celiac disease (CD) is a permanent gluten intolerance disorder characterized by malabsorption, intestinal mucosa villus atrophy, and crypt hyperplasia. Clinical and histologic features improve in persons consuming a gluten free diet. The pathogenesis of CD involves environmental, genetic, and immunologic factors.

METHODS

The frequencies of human leukocyte antigen (HLA) class II alleles were evaluated in white Brazilian patients who had CD and compared with those observed in healthy individuals from the same geographical area (Ribeirão Preto, São Paulo) and of similar ethnic background. Twenty-five patients with CD, 11 females and 14 males, and 91 control individuals were studied. The HLA class II alleles were typed using amplified DNA hybridized with sequence-specific primers. Statistical analysis was performed using the two-tailed Fisher exact test. The relative risk (RR), etiologic fraction (EF), and preventive fraction (PF) were also estimated. The EF represents the attributable risk for the development of CD at the population level, whereas PF represents the protective risk.

RESULTS

The frequency of the HLA-DRB1*03, HLA-DRB1*07, and HLA-DQB1*02 alleles was significantly increased in patients. The RR conferred by these alleles was 5.35, 7.15, and 10.6, respectively, and the EF was 48.7%, 44.7%, and 76%, respectively. The frequency of HLA-DQB1*06 alleles was significantly decreased in CD patients, conferring an RR of 0.08 and a PF of 48%.

CONCLUSIONS

The results show that HLA-DRB1*03, HLA-DRB1*07, and HLA-DQB1*02 alleles conferred susceptibility to CD in Brazilian patients. In contrast, HLADQB1*06 alleles conferred protection against development of the disease.

Increased levels of circulating ICAM-1, E-selectin, and IL-2 receptors in celiac disease

Adhesive interactions between endothelium and circulating cells are crucial for the development of inflammatory reactions. We found significantly higher serum levels of soluble intracellular adhesion molecule-1 (sICAM-1, 492.5 +/- 22.1 ng/ml) in patients with active celiac disease (including IgA-deficient patients) than in patients on a gluten-free diet (335.7 +/- 20.0 ng/ml) (P < 0.001) and healthy controls (207.4 +/- 11.2 ng/ml) (P < 0.001). The concentration of soluble E-selectin in sera from celiac patients (37.2 +/- 3.4 ng/ml) was also higher (P < 0.001) than in sera from healthy controls (15.5 +/- 0.7 ng/ml) but, in contrast to sICAM-1, it remained high in the patients after treatment (30.2 +/- 2.7 ng/ml). Interestingly, the concentration of circulating soluble interleukin-2 receptors, molecules indicating lymphocyte activation, was only increased in sera from patients with active celiac disease (2943.0 +/- 214.1 pg/ml), and the level in sera from treated patients and healthy controls was comparable (1936 +/- 349 and 1416 +/- 111.7 pg/ml). The elevated serum level of soluble cell adhesion molecules could be used as a supplementary, noninvasive procedure for monitoring intestinal immune reactions.

No polymorphism in the tissue transglutaminase gene detected in coeliac disease patients

BACKGROUND

The autoantigen for the anti-endomysial antibody (AEA) found in coeliac disease has recently been reported to be the enzyme tissue transglutaminase (tTG). Polymorphisms in the gene for tTG would result in different enzymic isoforms being expressed. Certain isoforms may interact with gliadin to create antigenic neoepitopes, which could then generate an immune response in genetically predisposed individuals possessing major histocompatibility complex (MHC) class II DQ2.

METHODS

We have sequenced the coding region of tTG in coeliac patients and normal controls. Total RNA was extracted from mucosal biopsies from eight AEA-positive histologically proven coeliac disease patients and four control patients with a histologically normal duodenum and a negative AEA. The 2-kb coding region of tTG was amplified in overlapping fragments by reverse transcription polymerase chain reaction (PCR), using five sets of PCR primers. Each overlapping PCR fragment was sequenced using the fmol DNA sequencing system.

RESULTS

tTG transcripts were detected in all samples. There was no difference in the coding sequence of tTG between the four control and eight coeliac patients, even though we observed differences in sequence between our study and the original published sequence. These differences have also been reported in sequences published subsequent to the original description.

CONCLUSIONS

Polymorphisms in the tTG gene have not been observed in coeliac disease patients and therefore cannot explain the creation of neoepitopes.

Identification of common epitopes on gliadin, enterocytes, and calreticulin recognised by antigliadin antibodies of patients with coeliac disease

BACKGROUND

Sera of patients with coeliac disease, containing IgA and IgG antigliadin antibodies (AGA) and various IgA autoantibodies, react with isolated enterocytes. AGA cross react with enterocyte antigens, one of which has been identified as calreticulin.

AIMS

To characterise the antigenic structures of gliadin, enterocytes, and calreticulin recognised by AGA from patients with active coeliac disease.

METHODS

AGA were isolated from sera of nine patients by affinity chromatography and tested by competitive ELISA using 40 alpha-gliadin synthetic dodecapeptides (A1-F6).

RESULTS

Reactivity of gliadin with all purified AGA tested was inhibited by peptide A4 at the N-terminal region; by C2, C3, and D4 at the central region; and by F3 and F4 at the C-terminal region of the gliadin molecule. AGA cross reactivity with enterocytes was inhibited by peptides A4, D1-D4, and F6 and with calreticulin by peptides A4, D3, and D4. As dominant epitopes AGA of coeliac patients recognise similar structures corresponding to peptides A4, D3, D4, and F6 present on gliadin, enterocytes, and calreticulin. Substitution of glutamine in the A4 peptide by glutamic acid caused loss of inhibitory capacity. Shortening of peptide A4 on the N-terminal by three amino acids increased its inhibitory effect.

CONCLUSIONS

AGA of patients with coeliac disease react with similar structures on gliadin and potential autoantigens on enterocytes.

New clinical issues in celiac disease

Celiac disease is a chronic disorder of gluten sensitivity associated with a spectrum of mucosal lesions termed preinfiltrative, infiltrative, hyperplastic, destructive, and atrophic. The symptoms are not related to the degree of mucosal pathology but to the extent of the mucosal lesion. Neoplasms constitute the major complication of celiac disease, and EATCL is the most common neoplasm in this category. There is evidence that a strict gluten-free diet is protective against the complications of celiac disease; hence it is important that even the subclinical forms be diagnosed early. Small bowel biopsy remains the gold standard for diagnosis of celiac disease; however, antibody tests are a useful adjunct in deciding whom to biopsy and for screening groups at high risk before initiating a lifelong gluten-free diet.

Abnormal intestinal intraepithelial lymphocytes in refractory sprue

BACKGROUND & AIMS

The etiology of refractory sprue is unclear. To gain insight into its pathogenesis, the phenotype and T-cell receptor (TCR) gene rearrangement status of intestinal lymphocytes were analyzed in a group of patients with clinical or biological features of celiac disease but either initially or subsequently refractory to a gluten-free diet.

METHODS

Intestinal biopsy specimens were obtained from 26 adults: 6 patients with refractory sprue, 7 patients with active celiac disease, and 13 normal controls. The phenotype of intestinal lymphocytes was studied by immunohistochemistry and, in 3 patients with refractory sprue, by cytometry of lymphocytes purified from intestinal biopsy specimens. TCR rearrangements were assessed by studying TCRgammaV-J junctional regions from DNA extracted from intestinal biopsy specimens and purified intestinal lymphocytes.

RESULTS

In the 6 patients with refractory sprue, but not in normal controls or patients with active celiac disease, the intestinal epithelium was massively infiltrated by small lymphocytes that lacked CD8, CD4, and TCR, contained intracytoplasmic but not surface CD3epsilon chains, and exhibited restricted TCRgamma gene rearrangements.

CONCLUSIONS

Refractory sprue is associated with an abnormal subset of intraepithelial lymphocytes containing CD3epsilon and restricted rearrangements of the TCRgamma chain but lacking surface expression of T-cell receptors.

Anti-gliadin antibodies in patients with celiac disease cross-react with enterocytes and human calreticulin

One of the characteristic features of celiac disease is an increase in anti-gliadin antibodies (Abs). Recently we found that some of the monoclonal Abs to gliadin cross-react with molecules on rat enterocytes. One of these cross-reacting molecules was identified as rat calreticulin. This study shows that the levels of serum IgA Abs to gliadin, rat, and human enterocytes; purified enterocyte antigens; and calreticulin in sera from patients with active disease were significantly higher than in patients on a gluten-free diet and healthy controls (P < 0.001). Anti-gliadin Abs were isolated by affinity chromatography from the sera of six active celiac patients. The reactivity of these anti-gliadin Abs was demonstrated to be significantly higher (P < 0.05) with human enterocytes and human calreticulin than with other antigens tested. Furthermore, using isolated patients' anti-gliadin Abs bound to Sepharose 2B, two main proteins of molecular mass 62 and 66 kDa were purified from a lysate of human enterocytes. The 62-kDa enterocyte antigen was identified as human calreticulin. These findings suggest that anti-gliadin Abs may play a pathogenic role in celiac disease by cross-reacting with enterocytes. Calreticulin in enterocytes may be one of the putative targets for autoimmune reactions.

The major complications of coeliac disease

Neoplasms constitute the major complication of coeliac disease, and high-grade T-cell lymphoma of the small intestine (enteropathy-associated T-cell lymphoma) is the most common neoplasm in this category. HLA genotyping indicates that in patients with enteropathy-associated T-cell lymphoma have the coeliac disease associated DQA1*0501, DQB1*0201 phenotype, although additional HLA-DR/DQ alleles may represent risk factors for lymphoma development. Molecular biological and immunohistochemical studies have shown that the intestinal mucosa distant from the tumour contains clonal populations of small T cells, often of the same clone as the high-grade T-cell lymphoma. These findings suggest that enteropathy-associated T-cell lymphoma arises in the setting of coeliac disease and evolves from reactive intraepithelial lymphocytes through a low-grade lymphocytic neoplasm to a high-grade tumour, which is usually the cause of the presenting symptoms. Most cases of chronic ulcerative enteropathy (ulcerative jejunitis) are probably part of the same disease process. If the ulceration occurs at a time when the neoplastic T-cells are of a low grade, morphological recognition of tumour cells in the ulcers may be impossible. Carcinoma of the pharynx and oesophagus, and adenocarcinoma of the small intestine, are increased in frequency in patients with coeliac disease. The increased risk of carcinoma of the oesophagus may be related to vitamin A deficiency. A number of reports have indicated an increased prevalence of various types of chronic hepatitis in patients with coeliac disease, but no coherent view of the cause of this association has emerged. Similarly, patients with coeliac disease have been reported to have various forms of fibrosing lung disease of uncertain causation. In recent years, there have been several reports, mainly from Italy, of a syndrome of epilepsy and bilateral brain calcification occurring in coeliac patients. The pathogenesis of this condition is not known and its prevalence in other communities is uncertain. Splenic atrophy occurs frequently in patients with coeliac disease and is related to the severity of the disease and degree of dietary control. Splenic atrophy predisposes to infection with capsulated bacteria, although mortality studies indicate that infection with these organisms is not a major cause of death in patients with coeliac disease.

Extracts of wheat gluten activate complement via the alternative pathway

We studied the ability of wheat gluten and its subfractions to activate complement directly. A sensitive sandwich ELISA employing a monoclonal antibody (MoAb) to a C9 neoepitope exposed in the terminal complement complex (TCC), a functional haemolytic assay for C5b6 generation, and Laurell's electrophoretic method of estimating C3 conversion to C3bi were used. On a weight-for-weight basis, enzyme solubilized Frazer's fraction three of gluten (FIII) produced approximately 75% of the complement activation seen with the potent activator zymosan. By contrast, activation with whole insoluble undigested gluten was very weak and similar to that seen with ovalbumin or beta-lactoglobulin. The results were the same using normal human serum or sera from patients with coeliac disease, dermatitis herpetiformis, or hypogammaglobulinaemia as the complement source. Activation by both zymosan and FIII was blocked in 0.01 M EDTA, but not in 0.01 M EGTA with 0.0025 M magnesium chloride. Zymosan and FIII activated complement in a serum from a patient with an intact alternative pathway but classical pathway haemolytic activity (CH50) of zero. Preferential heat inactivation of the alternative pathway inhibited both zymosan- and FIII-induced activation. Our results confirm that FIII is a strong activator of the alternative pathway. We discuss how gluten enteropathy might be initiated by complement.

Asp57-negative HLA DQ beta chain and DQA1*0501 allele are essential for the onset of DQw2-positive and DQw2-negative coeliac disease

The genetic predisposition to coeliac disease is associated with the HLA DQw2 allele. Coeliac patients lacking the DQw2 allele are very rare and always exhibit the DR4-DQw3 haplotype. We performed oligotyping of polymerase chain reaction (PCR)-amplified DQA1 and DQB1 genes in six DQw2-negative and 30 DQw2-positive coeliac patients. The DQB analysis showed that all six DQw2-negative patients possessed the DQB1*0302 allele. The other DQB alleles found in five of these patients were DQB1*0501, DQB1*0604 and DQB1*0302. The DQ beta chains encoded from all these alleles have the replacement of aspartic acid residue at position 57 (Asp57), as well as the DQB1*0201 allele which was found in all 30 DQw2-positive coeliac patients. The DQw2-negative proband who lacked the homozygous Asp57 replacement exhibited the DQA1*0501 allele in the DQA1 gene. The DQA1*0501 allele was also found in 27 of the 30 DQw2-positive coeliac patients. Among this group of coeliacs, the four cases lacking the DQA1*0501 allele exhibited the homozygous Asp57 replacement in the DQ beta chain. Our results indicate that Asp57-negative DQ beta alleles are involved in both DQw2-positive and -negative coeliac patients. Moreover, when the Asp57-negative DQ beta chain is encoded from only one of the two DQB1 genes the DQA1*0501 allele is always present.

Phenotype and activation of milk-derived and peripheral blood lymphocytes from normal and coeliac subjects

The phenotype of milk-derived and peripheral blood lymphocytes from normal and coeliac subjects was assessed for CD3, alpha beta-TcR (T cell receptor), gamma delta-TcR, CD4, CD8, HML-1 (human mucosal lymphocyte) determinants, and activation was measured by interleukin-2 receptor (IL-2R) expression. Milk cells from normal and coeliac subjects were analysed by manual immunofluorescence and milk and blood cells from normal subjects were analysed by flow cytometry. Milk cells from two coeliac subjects were tested for proliferation to gluten antigen. The CD4:CD8 ratio of milk lymphocytes from both normal and coeliac subjects was similar (0.78-1.1), but lower than that present in blood (1.5-2.1). The IL-2R expression of milk lymphocytes from both coeliac and normal subjects was increased by 3-6 times compared with peripheral blood cells. For example, IL-2R was present on 27.3% of milk CD3+ lymphocytes and on 8.0% of blood CD3+ lymphocytes from normal subjects. gamma delta- and HML-1+ T cells were increased 4.2-fold and 12-fold respectively compared with blood lymphocytes. Milk cells from coeliac subjects showed specific proliferation to gluten but not to soya bean antigen. We conclude that milk cells have a 'mucosal' phenotype, with increased gamma delta-TcR, CD8+ and HML-1+ T cells, and have an increased proportion of activated cells. Milk cells from coeliac subjects have no 'toxic' phenotype, but show functional reactivity by specific proliferation to gluten antigen.

Molecular analysis of HLA DP and DQ genes associated with dermatitis herpetiformis

HLA class II DQ and DP genes from dermatitis herpetiformis patients were amplified and analyzed using molecular probes and compared to those from celiac disease patients and to an HLA and ethnically matched control group. In dermatitis herpetiformis, as in celiac disease, the strongest association of disease was with the DQ subregion alleles DQB1*0201 and DQA1*0501 that are linked to the DRB1*0301 allele. DQB1*0201 determines the DQw2 serologic marker whereas DRB1*0301 determines the DRw17 serologic marker (formerly termed DR3). A DP subregion allele DPB1*0301 was increased and a constellation of DPB1 alleles that included DPB1*0202, *0901, and *1301 was decreased in dermatitis herpetiformis. DPB1*0101, an allele reported to be increased in celiac disease, was not increased in dermatitis herpetiformis. DP beta chains that lack a negatively charged amino acid residue at position 69 of the DP beta chain are significantly over-represented both in dermatitis herpetiformis and celiac disease patients with the DRw17, DQw2 haplotype, compared to healthy controls with that haplotype. These data favor a multigenic model for the contribution of HLA class II D region genes to dermatitis herpetiformis susceptibility. Further, they indicate that a specific DQ molecule, when present in combination with the product of one of several different DPB1 alleles, may contribute to susceptibility to the intestinal lesion, which is common to dermatitis herpetiformis and celiac disease.

Expression of HLA-DQ antigens in the small-intestinal mucosa of patients with coeliac disease

Studies at the DNA and product level of B-cell lines of coeliac patients have shown a strong association between coeliac disease and the HLA-DQ alpha 2.3 and HLA-DQ beta 2.7 alleles. The monoclonal antisera SFR20-DQ alpha 5 and XIII-358.4, which specifically react with HLA-DQ alpha 2.3 and with HLA-DQ beta 2.3 and -DQ beta 2.7, respectively, have been used to detect the expression of these specificities in the small-intestinal mucosa of 7 coeliac patients and 11 non-coeliac persons. An immunoperoxidase technique on frozen tissue sections of jejunal biopsy specimens was used. Positive specimens showed immunoperoxidase staining of lymphocytes and histiocytes in the lamina propria. The epithelial cells showed no immunoperoxidase staining. Positive results at the intestinal level correlated with the HLA typing of the patients and controls. The distribution found for the HLA-DQ alleles in the intestinal mucosa makes the role of a HLA-DQ alpha/beta dimer as gliadin receptor at the epithelial cell less probable, but it is compatible with the hypothesis that these DQ molecules are involved in the regulation of the intestinal immune response to gluten.