Intestinal tissue transglutaminase in coeliac disease of children and adults: ultrastructural localization and variation in expression

Genetic and Environmental Contributors for Celiac Disease

PURPOSE OF REVIEW

Celiac disease (CD) is an autoimmune enteropathy triggered by gluten. The purpose of this review is to examine the major genetic and environmental factors that contribute to CD pathogenesis.

RECENT FINDINGS

We reviewed the current state of knowledge on the genetic and environmental components that play a role in CD onset. A genome-wide association study (GWAS) analysis has highlighted several genes other than HLA involved in CD. Recent studies have shown that HLA haplotype influences the microbiome composition in infants and that dysbiosis in the intestinal microflora, in turn, contributes to loss of tolerance to gluten. Recently, observational studies have discussed the hypothesis stating that breast-feeding had a protective role against CD onset. CD etiology is influenced by genetic and environmental factors. A better understanding of these components would deepen our knowledge on the mechanisms that lead to loss of tolerance and could help in developing a more "personalized medicine."

Involvement of cell surface TG2 in the aggregation of K562 cells triggered by gluten

Gluten-induced aggregation of K562 cells represents an in vitro model reproducing the early steps occurring in the small bowel of celiac patients exposed to gliadin. Despite the clear involvement of TG2 in the activation of the antigen-presenting cells, it is not yet clear in which compartment it occurs. Herein we study the calcium-dependent aggregation of these cells, using either cell-permeable or cell-impermeable TG2 inhibitors. Gluten induces efficient aggregation when calcium is absent in the extracellular environment, while TG2 inhibitors do not restore the full aggregating potential of gluten in the presence of calcium. These findings suggest that TG2 activity is not essential in the cellular aggregation mechanism. We demonstrate that gluten contacts the cells and provokes their aggregation through a mechanism involving the A-gliadin peptide 31-43. This peptide also activates the cell surface associated extracellular TG2 in the absence of calcium. Using a bioinformatics approach, we identify the possible docking sites of this peptide on the open and closed TG2 structures. Peptide docks with the closed TG2 structure near to the GTP/GDP site, by establishing molecular interactions with the same amino acids involved in stabilization of GTP binding. We suggest that it may occur through the displacement of GTP, switching the TG2 structure from the closed to the active open conformation. Furthermore, docking analysis shows peptide binding with the β-sandwich domain of the closed TG2 structure, suggesting that this region could be responsible for the different aggregating effects of gluten shown in the presence or absence of calcium. We deduce from these data a possible mechanism of action by which gluten makes contact with the cell surface, which could have possible implications in the celiac disease onset.

Immunological indicators of coeliac disease activity are not altered by long-term oats challenge

Coeliac disease is a gluten-sensitive enteropathy that develops in genetically susceptible individuals. The disease exhibits many features of an autoimmune disorder. These include the production of highly specific anti-endomysial autoantibodies directed against the enzyme tissue transglutaminase. It is well accepted that wheat-, barley- and rye-based foods should be excluded in the gluten-free diet. Although several studies report that oats ingestion is safe in this diet, the potential toxicity of oats remains controversial. In the current study, 46 coeliac patients ingested oats for 1 year and were investigated for a potential immunogenic or toxic effect. Stringent clinical monitoring of these patients was performed and none experienced adverse effects, despite ingestion of a mean of 286 g of oats each week. Routine histological analysis of intestinal biopsies showed improvement or no change in 95% of the samples examined. Furthermore, tissue transglutaminase expression in biopsy samples, determined quantitatively using the IN Cell Analyzer, was unchanged. Employing immunohistochemistry, oats ingestion was not associated with changes in intraepithelial lymphocyte numbers or with enterocyte proliferation as assessed by Ki-67 staining. Finally, despite the potential for tissue transglutaminase to interact with oats, neither endomysial nor tissue transglutaminase antibodies were generated in any of the patients throughout the study. To conclude, this study reaffirms the lack of oats immunogenicity and toxicity to coeliac patients. It also suggests that the antigenic stimulus caused by wheat exposure differs fundamentally from that caused by oats.

Celiac disease in patients with type 1 diabetes: a condition with distinct changes in intestinal immunity?

Two common chronic childhood diseases-celiac disease (CD) and type 1 diabetes (T1D)-result from complex pathological mechanisms where genetic susceptibility, environmental exposure, alterations in intestinal permeability and immune responses play central roles. In this study, we investigated whether these characteristics were universal for CD independently of T1D association. For this purpose, we studied 36 children with normal small-bowel mucosa and 26 children with active CD, including 12 patients with T1D. In samples from the small-bowel mucosa, we detected the lowest expression of tight junction protein 1 (TJP1) mRNA in CD patients with T1D, indicating an increase in intestinal permeability. Furthermore, these samples displayed the highest expression of forkhead box P3 (FoxP3) mRNA, a marker for regulatory T cells, as compared with other patient groups. At the same time, serum levels of IgA antibodies specific for the CD-related antigens deamidated gliadin and tissue transglutaminase (tTG) were the highest in CD patients with T1D. In contrast, no significant differences were found in IgA or IgG antibodies specific for bovine beta-lactoglobulin or Bifidobacterium adolescentis DSM 20083-derived proteins. There were also no differences in the transamidating activity of serum autoantibodies between patients and control individuals. Our results show that patients with T1D and newly detected CD exhibit severely altered intestinal permeability, strong local immune activation and increased immunoregulatory mechanisms in the small bowel. Further study is required to determine whether these extreme changes in this CD subgroup are due to some specific environmental factors (virus infections), unknown genetic effects or autoimmune reactions to antigenic targets in intracellular tight junctions.

[Dermatitis herpetiformis. An update of the pathogenesis]

The multifactorial pathogenesis of dermatitis herpetiformis is reviewed in light of current experimental data. Genetic background, gluten consumption, and abnormal immune and autoimmune reactions are the most important pathogenetic factors, but other agents also participate in the disease development. The predisposing and inducing factors are summarized, while the pathophysiological steps leading to the development of skin symptoms are detailed.

Genetics and pathogenesis of coeliac disease

Coeliac disease is a common complex disease caused by a dietary intolerance to wheat gluten. Susceptibility is determined by both environmental and genetic factors. Coeliac disease results from complex interactions between the innate immune system, an adaptive T and B cell response and the mucosal barrier where inflammation is ultimately manifested. Genetic variants within the HLA region are well established, while variants outside of the HLA region have recently been identified. These variants are beginning to enhance our understanding of the immunology of the condition. This review focuses on the immunological pathogenesis of coeliac disease with special reference to the influence of genetic susceptibility on disease development.

Deamidation of gliadin peptides in lamina propria: implications for celiac disease

Activation of small intestinal gluten-reactive CD4(+) T-cells is a critical event in celiac disease. Deamidation of specific glutamine residues by tissue transglutaminase enhances the binding of T-cell activating gliadin epitopes to DQ2, increasing T-cell recognition. Our purpose was to investigate whether deamidated gliadin epitopes can be generated in the small intestinal mucosa by tissue transglutaminase and to characterize the location of the process. Intestinal explants from pig intestine and frozen biopsy slices from human and rat intestine were incubated with alpha-gliadin peptides containing the immunodominant motif. Monoclonal antibodies specifically recognizing the non-deamidated and/or the deamidated epitope were used for immunofluorescence studies. We conclude that endogenous tissue transglutaminase can mediate extracellular deamidation of gliadin peptides in the lamina propria. Gliadin peptides with more than one recognition site can be simultaneously cross-linked and deamidated extracellularly in the lamina propria, and might be of importance for the antibody response seen in untreated celiac disease patients.

Mucosal tissue transglutaminase expression in celiac disease

Tissue transglutaminase (tTG) plays an important role in celiac disease pathogenesis and antibodies to tTG are a diagnostic marker of gluten-sensitive enteropathy. The aim of this study was to investigate the localization of tTG in the duodenal mucosa in control tissues and in different histological stages of celiac disease by using a commercial and a novel set of anti-tTG monoclonal antibodies, to see whether this assessment can be useful for diagnostic purpose. The distribution of tTG was firstly evaluated in 18 untreated celiac patients by using a commercial monoclonal antibody (CUB7402) against tissue transglutaminase enzyme and directed against the loop-core region of the enzyme. Thereafter, in further 30 untreated celiac patients we employed three newly characterized anti-tTG monoclonal antibodies produced against recombinant human-tTG. The epitopes recognized are located in three distinct domains of the protein corresponding to the core, C1 and C2 protein structure. Eleven age- and sex-matched patients with chronic duodenitis acted as controls. All subjects underwent upper endoscopy to obtain biopsy samples from the duodenum. Overall, we found that (i) tTG is equally expressed in CD at different stages of disease; (ii) tTG is expressed, at similar level, in CD and controls with duodenitis. Assessment of tTG level in biopsy samples by immunohistochemical methods is not useful in the clinical diagnostic work-up of CD.

Transglutaminase and the pathogenesis of coeliac disease

In 1997, a German group demonstrated that the antigen of the biomarker EMA (endomysial antibodies) in coeliac disease is a calcium-dependent thiol enzyme, transglutaminase type 2 (TG2). This most important discovery opened up an exciting field of research aimed at a better understanding of the pathogenesis of coeliac disease, a T-cell-driven autoimmune disorder with a prevalence of about 1%. The accidental activation of TG2, possibly caused by a stress-induced local deficiency of zinc in the intestinal wall, might play a key role where the enzyme catalyzes an atypical deamidation of specific glutamine residues of food gliadins. The genetic contribution is HLA DQ2 or DQ8, which can form a complex with the TG2-modified gliadin residues, resulting in an immune response with the formation of antibodies against both gliadin and the enzyme. Indeed, the immunopathogenesis of coeliac disease can now be recognized partly at the molecular level. Progress has already improved the opportunities for laboratory diagnostics and, hopefully, new ways of treating and preventing coeliac disease will become available. These exciting developments might stimulate research within other fields of autoimmune disorders. With its focus on TG2, this review highlights some of the intriguing mechanisms of the pathogenesis of coeliac disease, such as the structure of the neo-antigen, the involvement of calcium and zinc, and the effects of coeliac antibodies on TG2 activity. Moreover, the many pitfalls due to dubious laboratory practice are addressed, as is the potential when a fundamental biological mechanism is understood at the molecular level.

Serum and intestinal dipeptidyl peptidase IV (DPP IV/CD26) activity in children with celiac disease

OBJECTIVE

Dipeptidyl peptidase IV (DPP IV/CD26) is involved in the degradation of proline-rich proteins such as gliadin and in modulation of the immune response. The aim of this study was to examine the possible causal connection between DPP IV enzyme activities and celiac disease (CD) in children.

PATIENTS AND METHODS

Intestinal mucosal biopsy specimens were obtained from 97 patients. The patients were divided into 3 groups: patients with active CD (n = 38), patients with malabsorption syndrome (MS) of other causes (n = 37), and control patients (n = 22). In addition, blood samples were collected from 48 patients with active CD and 50 control patients without gastrointestinal diseases. DPP IV enzyme activity was measured in the intestinal mucosal biopsy specimens and in the serum samples.

RESULTS

DPP IV activity in the small intestine correlated inversely with the grade of mucosal damage in the CD (r = -0.92, P < 0.001) and MS groups (r = -0.90, P < 0.001). Intestinal DPP IV activity was statistically significantly lower in the CD and MS groups than in the control group (P < 0.001). By contrast, serum DPP IV activity was not significantly different between the CD and control groups.

CONCLUSIONS

Our results suggest that the decrease in intestinal DPP IV activity is not specific to CD because it correlates with the level of mucosal damage in both patients with CD and those with MS. In addition, it seems that serum DPP IV activity cannot be used as a specific noninvasive diagnostic or prognostic marker of CD.

Serological and clinical comparison of children and adults with anti-endomysial antibodies

We compared serological and clinical presentation of 38 adults (5 males, 33 females) and 37 children (15 boys, 22 girls) with anti-endomysial antibodies (AEA).AEA, antinuclear (ANA), anti-parietal (APA), anti-thyroid microsomal (ATMA), anti-thyreoglobulin (ATGA), anti-smooth muscle (SMA) and anti-mitochondrial (AMA) antibodies were detected by IIF. Anti-tissue transglutaminase (tTG), anti-extractable nuclear antigens (ENA) and anti-actin (AAA) antibodies were studied by ELISA. There were no differences in frequency of ANA, APA, ATGA, SMA, AMA and AAA in children and adults. ATMA (p < 0.001) and anti-ENA (p < 0.05) positivity were more frequently found in adults. Anti-Ro/SSA had 7/38 adults and 1/37 children (p < 0.05). Adults had more frequently silent form of celiac disease associated with autoimmune diseases (p < 0.001). We are the first to demonstrate that in spite of no difference in ANA positivity in adults and children, ANA in adults more frequently target ENA, especially Ro/SSA antigen. The reason for this ANA specificity could be the longer gluten exposure in adults.

Coeliac disease: a diverse clinical syndrome caused by intolerance of wheat, barley and rye

Coeliac disease is a lifelong intolerance to the gluten found in wheat, barley and rye, and some patients are also sensitive to oats. The disease is genetically determined, with 10% of the first-degree relatives affected and 75% of monozygotic twins being concordant. Of the patients with coeliac disease 95% are human leucocyte antigen (HLA)-DQ2 or HLA-DQ8 positive. Characteristically, the jejunal mucosa becomes damaged by a T-cell-mediated autoimmune response that is thought to be initiated by a 33-mer peptide fragment in A2 gliadin, and patients with this disorder have raised levels of anti-endomysium and tissue transglutaminase antibodies in their blood. Coeliac disease is the major diagnosable food intolerance and, with the advent of a simple blood test for case finding, prevalence rates are thought to be approximately 1:100. Classically, the condition presented with malabsorption and failure to thrive in infancy, but this picture has now been overtaken by the much more common presentation in adults, usually with non-specific symptoms such as tiredness and anaemia, disturbance in bowel habit or following low-impact bone fractures. Small intestinal biopsy is necessary for diagnosis and shows a characteristically flat appearance with crypt hypoplasia and infiltration of the epithelium with lymphocytes. Diet is the key to management and a gluten-free diet effectively cures the condition. However, this commitment is lifelong and many aisles in the supermarket are effectively closed to individuals with coeliac disease. Compliance can be monitored by measuring antibodies in blood, which revert to negative after 6-9 months. Patients with minor symptoms, who are found incidentally to have coeliac disease, often ask whether it is necessary to adhere to the diet. Current advice is that dietary adherence is necessary to avoid the long-term complications, which are, principally, osteoporosis and small bowel lymphoma. However, risk of these complications diminishes very considerably in patients who are on a gluten-free diet.

Increased prevalence of anti-gliadin IgA-antibodies with aberrant duodenal histopathological findings in patients with IgA-nephropathy and related disorders

BACKGROUND

Antibodies present in coeliac disease may occur in IgA-nephropathy. This raises the question of food intolerance in the disease. Evidence for a true correlation between the two disorders has however been scarce.

DESIGN

Sera from 89 patients with IgA-nephropathy and 13 other patients with IgA deposits in the glomeruli of kidney biopsies were analysed for IgA-antibodies to gliadin, endomysium and tissue transglutaminase (92/102 patients).

RESULTS

Eleven out of 89 (12.4%) of the patients with IgA-nephropathy and five of the 13 others (38%) had elevated titres of IgA-antibodies to gliadin but, in all cases but one, normal IgA-antibodies to endomysium. Patients with IgA-nephropathy and elevated IgA-antibodies to gliadin had elevated total serum IgA more frequently than patients who had not (p<0.01). Two patients with IgA-nephropathy and one with Hennoch Schönlein's purpura had elevated IgA-antibodies to tissue transglutaminase. Small bowel biopsy in 7 out of 11 IgA-antibodies to gliadin positive patients with IgA-nephropathy was pathologic in three cases (two with Marsh I) . One patient with chronic glomerulnephritis also had Marsh I.

CONCLUSIONS

We found no increased frequency of verified coeliac disease in 89 patients with IgA-nephropathy. Two patients with IgA-nephropathy and one patient with chronic glomerulonephritis with IgA deposits in the kidney biopsy had a Marsh I histopathology. The findings suggest a possible link of celiac disease to IgA-nephropathy and a role for antibodies to food antigens in this disorder.