Missing endomysial and reticulin binding of coeliac antibodies in transglutaminase 2 knockout tissues

Development of Cell-Assembled Human Endomysial-Type Biomatrix Substrate for the Detection of Celiac Disease Autoantibodies

The endomysial antibody (EMA) immunofluorescent test is a highly specific method to detect disease-specific autoantibodies in celiac disease (CD) by their binding to natural transglutaminase-2 autoantigen in tissue sections, and it is used as a compulsory confirmatory test in the non-invasive diagnosis of CD. The classical EMA substrates are the monkey esophagus and the human umbilical cord. It is increasingly difficult to use these tissues due to ethical concerns and animal welfare regulations. In this study, we developed, in cell culture, an endomysium-type extracellular biomatrix assembled by human umbilical cord vein-derived endothelial cells which binds CD antibodies in a similar pattern as monkey esophagus and has similar macromolecular composition. Evaluating retrospectively and prospectively tested patient cohorts, including 130 CD cases and 105 non-celiac controls, IgA-class celiac antibody detection on the biomatrix was equally specific (100%) as EMA testing on tissues, and had higher sensitivity (95.6% versus 91.2%). Both EMA tests were less sensitive, but more specific than transglutaminase-based ELISA measurements. The decellularization of the biomatrix improved sensitivity, enabled the detection of IgG-class celiac antibodies, and allowed for simple reading without previous training. This easily available cell-assembled biomatrix substrate may replace substrate tissues in diagnostic EMA testing in the future.

Small intestinal biopsy findings consistent with celiac disease in patients with idiopathic inflammatory myopathy: Review of existing literature

BACKGROUND

Case reports have described patients with idiopathic inflammatory myopathies (IIM) and a concurrent diagnosis of celiac disease (CeD) for whom the muscle inflammation (myositis) component of IIM improves after the patients start standard treatment with gluten-free diet (GFD). A connection between IIM and CeD is not commonly recognized.

AIM

In this first systematic review of the topic, we aimed to explore all peer-reviewed publications of IIM cases and concomitant small intestinal biopsy findings consistent with CeD, published after 1975.

METHODS

Systematic literature searches were performed in MEDLINE, PubMed, and EMBASE, supplemented by screening of references and non-systematic searches via Google and Google Scholar.

RESULTS

Altogether 30 cases published between 1976 and 2017 were uncovered. Information about gastrointestinal symptoms prior to CeD diagnosis was available for 19 patients, with 6/19 (32%) reporting no GI symptoms. CeD-related serological data were available in 23/30 patients. Endomysial antibodies were present in 10/18 (56%), while only 2/9 (22%) had antibodies against tissue transglutaminase. Serum antibodies to native gliadin were present in 16/18 (89%). Clinical effects of a GFD on the IIM were reported for 24 patients, with signs of improvement in 14/24 (58%), including three patients with otherwise therapy-resistant inclusion body myositis. Longitudinal follow-up data available from the published studies indicated that 7/24 (29%) remained in clinical IIM remission with GFD as the sole therapeutic intervention.

CONCLUSION

In the IIM cases presented here, duodenal biopsy findings consistent with celiac disease was sometimes present without classical CeD symptoms or positive traditional CeD serology, and in the majority of cases, the IIM improved after introduction of a gluten-free diet. While extra vigilance towards CeD in IIM patients seems warranted, there is need for more research to clarify if GFD has effects on organ systems other than the small intestine in patients with IIM and small intestinal biopsy findings consistent with CeD.

Current Concepts of Dermatitis Herpetiformis

Dermatitis herpetiformis (DH) is an autoimmune skin disease that causes itchy, blistering rash, typically on the elbows, knees and buttocks. DH and coeliac disease share the same genetic background, gluten-dependent enteropathy and antibody response against tissue transglutaminase. DH is currently considered a cutaneous manifestation of coeliac disease, and the prevailing hypothesis is that DH develops as a late manifestation of subclinical coeliac disease. The incidence of DH is decreasing contemporarily with the increasing incidence of coeliac disease. The IgA immune response in DH skin is directed against epidermal transglutaminase, while the autoantigen in the gut is tissue transglutaminase. Granular IgA deposition in the papillary dermis is pathognomonic for DH, and is a finding used to confirm the diagnosis. The treatment of choice for DH is a life-long gluten-free diet, which resolves the rash and enteropathy, increases quality of life, and offers a good long-term prognosis.

Changing Pattern of Childhood Celiac Disease Epidemiology: Contributing Factors

Up until the 1960s and 1970s, diarrhea, malabsorption syndrome, and failure to thrive were the presenting symptoms and signs of celiac disease (CD) in young infants; however this disease was also at the same time reported to be disappearing. Indeed, clinical childhood CD was seen to transform into a milder form, resulting in an upward shift in age at diagnosis during the 1970s (and years later for many countries). This changing pattern of CD presentation then altered the epidemiology of the disease, with major differences between and within countries observed. An awareness of the changing clinical nature of CD and use of case-finding tools to detect even clinically silent CD became an important factor in this changing epidemiology. Countries report both low and high prevalence but it seems to be on the increase resulting in a population-based level of 1-2%. This paper discusses the potential causes and environmental factors behind these observed clinical changes, identifying new clues from different studies published at the time this transformation took place. For instance, it was found that breastfeeding postponed the diagnosis of the disease but did not altogether prevent it. Moreover, gluten introduction at a young age, specifically at the mean age of 2 months, seemed to also have a clear impact in inducing malabsorption syndrome and failure to thrive in young infants in addition to other factors such as gluten intake volume and type of cereal present in the weaning food. Further, the impact of cow's milk and its high osmolarity might have played an important role; humanized milk formulas were not yet invented. Future epidemiological studies on the contributing environmental factors to the shift in CD presentation are thus recommended for countries in which these changing clinical features are still being observed.

Celiac-Related Autoantibodies and IL-17A in Bulgarian Patients with Dermatitis Herpetiformis: A Cross-Sectional Study

Background and objectives: Dermatitis herpetiformis (DH) is a blistering dermatosis, which shares common immunologic features with celiac disease (CD). The aim of the present study was to explore the performance of a panel of CD-related antibodies and IL-17A in Bulgarian patients with DH. Materials and Methods: Serum samples from 26 DH patients at mean age 53 ± 15 years and 20 healthy controls were assessed for anti-tissue transglutaminase (anti-tTG), anti-deamidated gliadin peptides (anti-DGP), anti-actin antibodies (AAA), and IL-17A by enzyme linked immuno-sorbent assay (ELISA), as well as anti-tTG, anti-gliadin (AGA), and anti-Saccharomyces cerevisiae antibodies (ASCA) using immunoblot. Results: The average serum levels of anti-tTG, anti-DGP, AGA, AAA, and the cytokine IL-17A were at significantly higher levels in patients with DH compared to the average levels in healthy persons which stayed below the cut-off value (p < 0.05). Anti-DGP and anti-tTG antibodies showed the highest diagnostic sensitivity and specificity, as well as acceptable positive and negative predictive value. None of the healthy individuals was found positive for the tested antibodies, as well as for ASCA within the DH group. All tests showed good to excellent correlations (r = 0.5 ÷ 0.9, p < 0.01). Conclusions: Although the diagnosis of DH relies on skin biopsy for histology and DIF, serologic testing of a panel of celiac-related antibodies could be employed with advantages in the diagnosing process of DH patients. Furthermore, DH patients who are positive for the investigated serologic parameters could have routine monitoring for gastrointestinal complications typical for the gluten-sensitive enteropathy.

Gluten Challenge Induces Skin and Small Bowel Relapse in Long-Term Gluten-Free Diet-Treated Dermatitis Herpetiformis

Dermatitis herpetiformis (DH) is an extraintestinal manifestation of celiac disease causing an itchy, blistering rash. Granular IgA deposits in the skin are pathognomonic for DH, and the treatment of choice is a lifelong gluten-free diet (GFD). Preliminary evidence suggests that there are patients with DH who redevelop gluten tolerance after adherence to a GFD treatment. To evaluate this, we performed a 12-month gluten challenge with skin and small-bowel mucosal biopsy samples in 19 patients with DH who had adhered to a GFD for a mean of 23 years. Prechallenge biopsy was negative for skin IgA and transglutaminase 3 deposits in 16 patients (84%) and indicated normal villous height-to-crypt depth ratios in the small bowel mucosa in all 19 patients. The gluten challenge caused a relapse of the rash in 15 patients (79%) in a mean of 5.6 months; of these 15 patients, 13 had skin IgA and transglutaminase 3 deposits, and 12 had small-bowel villous atrophy. In addition, three patients without rash or immune deposits in the skin developed villous atrophy, whereas one patient persisted without any signs of relapse. In conclusion, 95% of the patients with DH were unable to tolerate gluten even after long-term adherence to a GFD. Therefore, lifelong GFD treatment remains justified in all patients with DH.

Extra-Intestinal Manifestations of Coeliac Disease in Children: Clinical Features and Mechanisms

Celiac disease (CD) is a systemic autoimmune disease due to a dysregulated mucosal immune response to gluten and related prolamines in genetically predisposed individuals. It is a common disorder affecting ~1% of the general population, its incidence is steadily increasing. Changes in the clinical presentation have become evident since the 80s with the recognition of extra-intestinal symptoms like short stature, iron deficiency anemia, altered bone metabolism, elevation of liver enzymes, neurological problems. Recent studies have shown that the overall prevalence of extra-intestinal manifestations is similar between pediatric and adult population; however, the prevalence of specific manifestations and rate of improvement differ in the two age groups. For instance, clinical response in children occurs much faster than in adults. Moreover, an early diagnosis is decisive for a better prognosis. The pathogenesis of extra-intestinal manifestations has not been fully elucidated yet. Two main mechanisms have been advanced: the first related to the malabsorption consequent to mucosal damage, the latter associated with a sustained autoimmune response. Importantly, since extra-intestinal manifestations dominate the clinical presentation of over half of patients, a careful case-finding strategy, together with a more liberal use of serological tools, is crucial to improve the detection rate of CD.

Advances in celiac disease testing

Celiac disease (CD) is a T cell-mediated inflammatory autoimmune disorder of the upper small intestine caused by the ingestion of gluten. It is increasingly recognized as a global problem by experts and societies. The diagnosis of CD is of crucial importance because its delay strongly affects patient's health and quality of life. The diagnosis of CD is, however, complex and requires reliable, sensitive, specific, rapid, simple, and cost-effective, as well-as non-invasive analytical tools. There is also a high demand to develop simple point-of-care (POC) tests for non-specialists at home or in doctors' offices. Analytical techniques are now moving toward the development of fast, more simple, non-invasive, and POC analyses. The present review focuses on recent advances of CD biomarker detection in body fluids, concerning CD specific autoantibody detection in blood and saliva using electrochemical, optic-fiber, and piezoelectric biosensors and POC finger-prick tests, and identifying CD characteristic volatile organic compounds (VOCs) in urine and feces.

Autoantibodies in the Extraintestinal Manifestations of Celiac Disease

Increased antibody reactivity towards self-antigens is often indicative of a disruption of homeostatic immune pathways in the body. In celiac disease, an autoimmune enteropathy triggered by the ingestion of gluten from wheat and related cereals in genetically predisposed individuals, autoantibody reactivity to transglutaminase 2 is reflective of the pathogenic role of the enzyme in driving the associated inflammatory immune response. Autoantibody reactivity to transglutaminase 2 closely corresponds with the gluten intake and clinical presentation in affected patients, serving as a highly useful biomarker in the diagnosis of celiac disease. In addition to gastrointestinal symptoms, celiac disease is associated with a number of extraintestinal manifestations, including those affecting skin, bones, and the nervous system. Investigations of these manifestations in celiac disease have identified a number of associated immune abnormalities, including B cell reactivity towards various autoantigens, such as transglutaminase 3, transglutaminase 6, synapsin I, gangliosides, and collagen. Clinical relevance, pathogenic potential, mechanism of development, and diagnostic and prognostic value of the various identified autoantibody reactivities continue to be subjects of investigation and will be reviewed here.

Transglutaminase 2 in human diseases

Transglutaminase 2 (TG2) is an inducible transamidating acyltransferase that catalyzes Ca(2+)-dependent protein modifications. In addition to being an enzyme, TG2 also serves as a G protein for several seven transmembrane receptors and acts as a co-receptor for integrin β1 and β3 integrins distinguishing it from other members of the transglutaminase family. TG2 is ubiquitously expressed in almost all cell types and all cell compartments, and is also present on the cell surface and gets secreted to the extracellular matrix via non-classical mechanisms. TG2 has been associated with various human diseases including inflammation, cancer, fibrosis, cardiovascular disease, neurodegenerative diseases, celiac disease in which it plays either a protective role, or contributes to the pathogenesis. Thus modulating the biological activities of TG2 in these diseases will have a therapeutic value.

Transglutaminase 2 strongly binds to an extracellular matrix component other than fibronectin via its second C-terminal beta-barrel domain

Transglutaminase 2 (TG2) is a ubiquitous crosslinking enzyme present in both intra- and extracellular in many cell types and tissues. TG2 is upregulated upon cellular stress or injury, and extracellular TG2 is implicated in several human diseases, including celiac disease. However, incomplete knowledge about extracellular TG2 biology limits our understanding of how TG2 is involved in disease. Here, we demonstrate that binding of TG2 to the ECM of small intestinal tissue sections is the sum of binding to fibronectin (FN) via its N-terminal domain and binding to an abundant, novel extracellular matrix (ECM) interaction partner via its second C-terminal beta-barrel domain. The latter interaction dominates and gives rise to the characteristic reticular staining pattern of extracellular TG2. Of relevance for celiac disease, we show that self-multimerized TG2 does not efficiently deposit in the intestinal ECM, and TG2 complexes may thus become free-floating antigens in tissues in contrast to monomeric TG2 that would readily become sequestered by the ECM. Upon injection of monoclonal antibody targeting the FN-binding site, we observe antibody deposition on extracellular TG2 in cryosections, suggesting that the FN-binding site of TG2 is exposed in vivo. This would explain how and why celiac autoantibodies recognizing the FN-binding site of TG2 can bind TG2 in vitro, in situ as well as in vivo.

Adaptive diagnosis of coeliac disease

Coeliac disease has for a long time simply been regarded as a gluten-dependent enteropathy and a duodenal biopsy was required in all patients for the diagnosis. It is now accepted that autoimmunity against transglutaminase 2 is an earlier, more universal and more specific feature of coeliac disease than histologic lesions. Moreover, high serum levels of combined anti-transglutaminase 2 and anti-endomysium antibody positivity have excellent predictive value for the presence of enteropathy with villous atrophy. This makes the histology evaluation of the gut no longer necessary in well defined symptomatic paediatric patients with compatible HLA-DQ2 and/or DQ8 background. The biopsy-sparing diagnostic route is not yet recommended by gastroenterologists for adults, and certain clinical circumstances (immunodeficiency conditions, extraintestinal manifestations, type-1 diabetes mellitus, age less than 2 years) may require modified diagnostic approaches. Coeliac patients with preserved duodenal villous structure do exist and these need a more extended evaluation by immunologic and molecular biology tools.

A point-of-care test for facing the burden of undiagnosed celiac disease in the Mediterranean area: a pragmatic design study

BACKGROUND

We aimed at assessing the factors that can influence results of the dissemination of an already validated, new generation commercial Point-of-Care Test (POCT) for detecting celiac disease (CD), in the Mediterranean area, when used in settings where it was designed to be administered, especially in countries with poor resources.

METHODS

Pragmatic study design. Family pediatricians at their offices in Italy, nurses and pediatricians in Slovenia and Turkey at pediatricians', schools and university primary care centers looked for CD in 3,559 (1-14 yrs), 1,480 (14-23 yrs) and 771 (1-18 yrs) asymptomatic subjects, respectively. A new generation POCT detecting IgA-tissue antitransglutaminase antibodies and IgA deficiency in a finger-tip blood drop was used. Subjects who tested positive and those suspected of having CD were referred to a Celiac Centre to undergo further investigations in order to confirm CD diagnosis. POCT Positive Predictive Value (PPV) at tertiary care (with Negative Predictive Value) and in primary care settings, and POCT and CD rates per thousand in primary care were estimated.

RESULTS

At tertiary care setting, PPV of the POCT and 95% CI were 89.5 (81.3-94.3) and 90 (56-98.5) with Negative Predictive Value 98.5 (94.2-99.6) and 98.7% (92-99.8) in children and adults, respectively. In primary care settings of different countries where POCT was performed by a different number of personnel, PPV ranged from 16 to 33% and the CD and POCT rates per thousand ranged from 4.77 to 1.3 and from 31.18 to 2.59, respectively.

CONCLUSIONS

Interpretation of POCT results by different personnel may influence the performance of POC but dissemination of POCT is an urgent priority to be implemented among people of countries with limited resources, such as rural populations and school children.

Gluten-related neurologic dysfunction

The term gluten-related disorders (GRD) encompasses a spectrum of systemic autoimmune diseases with diverse manifestations. GRD are characterized by abnormal immunological responsiveness to ingested gluten in genetically susceptible individuals. Celiac disease (CD) or gluten-sensitive enteropathy is only one of a number of GRD. Extraintestinal manifestations include dermatitis herpetiformis (DH) and neurologic dysfunction. Furthermore it is only recently that the concept of extraintestinal manifestations without enteropathy has become accepted. In this chapter we review the spectrum of neurologic manifestations in GRD, discuss recent advances in their diagnosis, and look at their possible pathophysiologic mechanisms.

Transglutaminase 2-specific autoantibodies in celiac disease target clustered, N-terminal epitopes not displayed on the surface of cells

The gluten-sensitive enteropathy celiac disease is tightly associated with the production of autoantibodies specific for the enzyme transglutaminase 2 (TG2). The mechanisms underlying the activation of autoreactive B cells, however, are not well defined. To gain more insight into this autoimmune response we have characterized the binding of TG2 by a panel of human mAbs generated by expression cloning of Ig genes from single plasma cells of the celiac disease lesion. The Abs were highly specific to TG2 and bound preferentially to the open, Ca(2+)-activated enzyme conformation. Epitope mapping revealed that they recognize few distinct conformational epitopes that cluster in the N-terminal half of the enzyme. Two of the epitopes were overlapping with the fibronectin binding site in TG2, and none of the epitopes was accessible when TG2 was in a cell surface-bound form. Based on our findings, we propose that the autoantibodies are generated against the soluble, catalytically active enzyme, whereas Abs reactive with cell surface-associated TG2 are absent from the response due to negative selection of B cells recognizing membrane-bound self-Ag. The findings give insight into the mechanisms controlling the formation of anti-TG2 autoantibodies in celiac disease.

Protein kinase C delta is a substrate of tissue transglutaminase and a novel autoantigen in coeliac disease

Post-translational modification of proteins by deamidation or transamidation by tissue transglutaminase (tTG) has been suggested as a possible mechanism for the development of autoimmunity. Sequence analysis of protein kinase C delta (PKCδ) identified an amino acid motif that suggested the possibility that PKCδ was a glutamine substrate of tTG and MALDI-TOF analysis of synthesised peptides from PKCδ proved that this was the case. Polymerisation experiments using recombinant tTG and biotinylated hexapeptide substrate incorporation assays demonstrated that PKCδ is a substrate for tTG-mediated transamidation. Elevated levels of anti-PKCδ antibodies were detected in sera from patients with coeliac disease (p<0.0001) but not from patients with other autoimmune disorders. These data suggest that a subset of patients with coeliac disease produce autoantibodies against PKCδ and that this response may stem from a tTG-PKCδ substrate interaction.

Accuracy of diagnostic antibody tests for coeliac disease in children: summary of an evidence report

OBJECTIVE

The aim of this study was to summarise the evidence from 2004 to September 2009 on the performance of laboratory-based serological and point of care (POC) tests for diagnosing coeliac disease (CD) in children using histology as reference standard.

PATIENTS AND METHODS

We searched MEDLINE and EMBASE for studies reporting on children for tests based on IgA and IgG anti-gliadin (AGA), endomysial (EmA), anti-transglutaminase-2 (TG2), and anti-deamidated gliadin peptides (DGP) antibodies or POC tests. For inclusion, histological analysis of duodenal biopsies and sensitivity and specificity for index tests had to be reported. Data were pooled and summary measures calculated for sensitivity, specificity, positive and negative likelihood ratios ("LR+", "LR-"), and diagnostic odds ratios (DOR). In case of elevated statistical heterogeneity, studies reaching 90% sensitivity or specificity were reported.

RESULTS

A total of 2510 articles were reviewed; 16 entered meta-analysis, reporting on 3110 patients (1876 with CD, 1234 without CD). For IgA-EmA, sensitivity was ≥90% in 7/11 studies and pooled specificity 98.2%. For IgA-anti-TG2, 11/15 studies yielded sensitivities ≥90% and 13/15 specificities ≥90%. For IgA-DGP, sensitivity ranged between 80.7% and 95.1% (specificity 86.3%-93.1%); for IgG-DGP between 80.1% and 98.6% (specificity 86.0-96.9%). IgA-EmA had the highest pooled DOR (554) and LR+ (31.8) for a laboratory test, followed by IgA-anti-TG2, IgG-DGP, IgA-DGP and IgA-AGA. POC tests showed a pooled sensitivity of 96.4% for IgA-TG2 (specificity 97.7%).

CONCLUSIONS

IgA-EmA and IgA-anti-TG2 tests appear highly accurate to diagnose CD. IgG-anti-DGP tests may help in excluding CD. IgA-AGA and IgA-DGP tests show inferior accuracy. POC tests may achieve high accuracy in the hands of experienced readers, but IgA-anti-TG2/EmA were superior.

Antibodies in celiac disease: implications beyond diagnostics

Celiac disease is a multisystemic dietary, gluten-induced autoimmune disorder characterized by the presence of transglutaminase (TG) 2 serum autoantibodies. Distinct autoantibodies targeting members of the TG family (TG2, TG3 and TG6) are found deposited in small-bowel mucosa and in extraintestinal tissues affected by the disease. Serum autoantibodies against other self-antigens also emerge in untreated celiac disease patients. Although villous atrophy and crypt hyperplasia in small-bowel biopsy samples are still the gold standards in diagnostics, celiac disease-specific antibodies are widely used as diagnostic aids. Gluten-induced small-bowel mucosal T-cell response is the cornerstone in the pathogenesis of the disorder, but humoral immunity may also play a central role. This review article is focused on the autoantibodies that occur in the context of celiac disease. The article summarizes the diagnostic utility of different celiac-related antibodies and discusses their roles in the pathogenesis of the disease.

Usefulness of small-bowel mucosal transglutaminase-2 specific autoantibody deposits in the diagnosis and follow-up of celiac disease

BACKGROUND

Diagnosis of celiac disease may be problematic in that small-bowel villous atrophy sometimes occurs in conjunction with other enteropathies, develops gradually and may be patchy. Furthermore, as the often compromised quality of biopsy specimens renders diagnosis difficult, new diagnostic tools are warranted.

GOALS

As the celiac disease-specific autoantibodies are found deposited at their production site, in the small-bowel mucosa, they may be useful in diagnostics, especially in problematic cases. We therefore systematically assessed the occurrence of celiac-specific autoantibody deposits in a large cohort of celiac patients, and established how IgA deposits decline after initiation of a gluten-free diet.

METHODS

Transglutaminase-2 specific mucosal IgA autoantibody deposits were determined from small-bowel mucosal biopsies in 261 untreated, 71 short-term (1 y), and 105 long-term (2 to 41 y) treated celiac disease patients and in 78 nonceliac controls. The presence of the deposits was compared with celiac serology, mucosal villous morphology and density of intraepithelial lymphocytes.

RESULTS

All untreated celiac disease patients had mucosal autoantibody deposits and their intensity was moderate or strong in 90% of cases. In contrast, 18% of the controls had weak depositions. During a gluten-free diet the intensity of the deposits diminished, but was still faintly positive in 56% of long-term treated celiac patients. The efficiency of the test in determining mucosal autoantibody deposits was superior to serology and inflammatory markers.

CONCLUSIONS

Mucosal transglutaminase-2 specific autoantibody deposits proved to be accurate gluten-dependent markers of celiac disease and would thus be of value in the diagnostics and dietary monitoring of this disorder.

Transglutaminase 2 is expressed and active on the surface of human monocyte-derived dendritic cells and macrophages

The multifunctional enzyme, transglutaminase 2 (TG2), can be found intracellularly, in the extracellular matrix and on the cell surface. Cell surface TG2 (csTG2) could not be detected by TG2-specific antibodies or autoantibodies on immunocompetent cells. A supposedly csTG2-specific antibody, 6B9, was recently shown to actually react with CD44. Though the importance of TG2-mediated deamidation of gluten in the pathogenesis of celiac disease has been well recognized, it is not known in which intestinal cells or cell compartment the deamidation occurs. Duodenal dendritic cells (DCs) can be directly involved in gluten-reactive T-cell activation. Here we use blood monocyte-derived dendritic cells (iDC) and macrophages (MPhi) as a model for intestinal antigen-presenting cells (APCs) and show that they contain large amounts of TG2. We found that TG100, a commercial TG2-specific monoclonal antibody can recognize TG2 on the surface of these cells, that is monocyte-derived APCs express surface-associated TG2. TG2 expression was found on the surface of individual tunica propria cells in frozen small bowel tissue sections from both normal and celiac subjects. We also demonstrate that the pool of TG2 on the surface of iDCs can be catalytically active, hence it might directly be involved in the deamidation of gliadin peptides. Bacterial lipopolysaccharide (LPS) increased the level of TG2 on the surface of maturing DCs, supporting the hypothesis that an unspecific inflammatory process in the gut may expose more transglutaminase activity.

Celiac disease IgA modulates vascular permeability in vitro through the activity of transglutaminase 2 and RhoA

Celiac disease is characterized by the presence of specific autoantibodies targeted against transglutaminase 2 (TG2) in untreated patients' serum and at their production site in the small-bowel mucosa below the basement membrane and around the blood vessels. As these autoantibodies have biological activity in vitro, such as inhibition of angiogenesis, we studied if they might also modulate the endothelial barrier function. Our results show that celiac disease patient autoantibodies increase endothelial permeability for macromolecules, and enhance the binding of lymphocytes to the endothelium and their transendothelial migration when compared to control antibodies in an endothelial cell-based in vitro model. We also demonstrate that these effects are mediated by increased activities of TG2 and RhoA. Since the small bowel mucosal endothelium serves as a "gatekeeper" in inflammatory processes, the disease-specific autoantibodies targeted against TG2 could thus contribute to the pathogenic cascade of celiac disease by increasing blood vessel permeability.

Transglutaminases and disease: lessons from genetically engineered mouse models and inherited disorders

The human transglutaminase (TG) family consists of a structural protein, protein 4.2, that lacks catalytic activity, and eight zymogens/enzymes, designated factor XIII-A (FXIII-A) and TG1-7, that catalyze three types of posttranslational modification reactions: transamidation, esterification, and hydrolysis. These reactions are essential for biological processes such as blood coagulation, skin barrier formation, and extracellular matrix assembly but can also contribute to the pathophysiology of various inflammatory, autoimmune, and degenerative conditions. Some members of the TG family, for example, TG2, can participate in biological processes through actions unrelated to transamidase catalytic activity. We present here a comprehensive review of recent insights into the physiology and pathophysiology of TG family members that have come from studies of genetically engineered mouse models and/or inherited disorders. The review focuses on FXIII-A, TG1, TG2, TG5, and protein 4.2, as mice deficient in TG3, TG4, TG6, or TG7 have not yet been reported, nor have mutations in these proteins been linked to human disease.

Diagnosing mild enteropathy celiac disease: a randomized, controlled clinical study

BACKGROUND & AIMS

The diagnostic criteria for celiac disease require small-bowel mucosal villous atrophy with crypt hyperplasia (Marsh III). However, mucosal damage develops gradually and patients may evince clinical symptoms before histologic changes appear. Endomysial antibodies are specific in predicting forthcoming villous atrophy. We hypothesized that patients with mild enteropathy but positive endomysial antibodies benefit from a gluten-free diet (GFD) similarly to patients with more severe enteropathy.

METHODS

Small-bowel endoscopy together with clinical evaluations was performed in all together 70 consecutive adults with positive endomysial antibodies. Of these, 23 had only mild enteropathy (Marsh I-II) and they were randomized either to continue on a gluten-containing diet or start a GFD. After 1 year, clinical, serologic, and histologic evaluations were repeated. A total of 47 participants had small-bowel mucosal lesions compatible with celiac disease (Marsh III), and these served as disease controls.

RESULTS

In the gluten-containing diet group (Marsh I-II) the small-bowel mucosal villous architecture deteriorated in all participants, and the symptoms and abnormal antibody titers persisted. In contrast, in the GFD group (Marsh I-II) the symptoms were alleviated, antibody titers decreased, and mucosal inflammation diminished equally to celiac controls (Marsh III). When the trial was completed, all participants chose to continue on a life-long GFD.

CONCLUSIONS

Patients with endomysial antibodies benefit from a GFD regardless of the degree of enteropathy. The diagnostic criteria for celiac disease need re-evaluation: endomysial antibody positivity without atrophy belongs to the spectrum of genetic gluten intolerance, and warrants dietary treatment.

Autoantibodies in gluten ataxia recognize a novel neuronal transglutaminase

OBJECTIVE

Gluten sensitivity typically presents as celiac disease, a chronic, autoimmune-mediated, small-intestinal disorder. Neurological disorders occur with a frequency of up to 10% in these patients. However, neurological dysfunction can also be the sole presenting feature of gluten sensitivity. Development of autoimmunity directed toward different members of the transglutaminase gene family could offer an explanation for the diversity in manifestations of gluten sensitivity. We have identified a novel neuronal transglutaminase isozyme and investigated whether this enzyme is the target of the immune response in patients with neurological dysfunction.

METHODS

Using recombinant human transglutaminases, we developed enzyme-linked immunosorbent assays and inhibition assays to analyze serum samples of patients with gluten-sensitive gastrointestinal and neurological disorders, and various control groups including unrelated inherited or immune conditions for the presence and specificity of autoantibodies.

RESULTS

Whereas the development of anti-transglutaminase 2 IgA is linked with gastrointestinal disease, an anti-transglutaminase 6 IgG and IgA response is prevalent in gluten ataxia, independent of intestinal involvement. Such antibodies are absent in ataxia of defined genetic origin or in healthy individuals. Inhibition studies showed that in those patients with ataxia and enteropathy, separate antibody populations react with the two different transglutaminase isozymes. Furthermore, postmortem analysis of brain tissue showed cerebellar IgA deposits that contained transglutaminase 6.

INTERPRETATION

Antibodies against transglutaminase 6 can serve as a marker in addition to human leukocyte antigen type and detection of anti-gliadin and anti-transglutaminase 2 antibodies to identify a subgroup of patients with gluten sensitivity who may be at risk for development of neurological disease.

Gluten-dependent small bowel mucosal transglutaminase 2-specific IgA deposits in overt and mild enteropathy coeliac disease

OBJECTIVES

In coeliac disease, immunoglobulin (Ig)A-class autoantibodies against transglutaminase-2 are produced in the small intestinal mucosa, where they are deposited extracellularly. It remains unclear whether positive intestinal transglutaminase-2-targeted IgA deposits in subjects having normal small bowel mucosal morphology are signs of early-stage coeliac disease. We evaluated the gluten dependency of these deposits in overt and mild enteropathy coeliac disease.

PATIENTS AND METHODS

All together 48 subjects suspected of coeliac disease but having normal small bowel mucosal villi were enrolled; 28 of them had latent coeliac disease. The remaining 20 having positive intestinal IgA deposits adopted a gluten-free diet before villous atrophy had developed. For comparison, 13 patients with overt coeliac disease and 42 noncoeliac controls were studied. Small bowel mucosal transglutaminase-2-specific autoantibodies were compared with villous morphology, intraepithelial lymphocyte densities, and serum coeliac autoantibodies.

RESULTS

Intestinal IgA deposits were seen in all but 1 of the patients with latent coeliac disease, when the morphology was still intact; the intensity of these deposits increased as villous atrophy developed and decreased again on a gluten-free diet. In 20 patients with intestinal IgA deposits in normal villi, the intensity of the deposits decreased with the diet similarly to that seen in patients with overt coeliac disease. Mucosal IgA deposits were seen initially only in 5% of noncoeliac controls and in 8% after extended gluten consumption.

CONCLUSIONS

The response of small bowel mucosal transglutaminase-2-specific IgA deposits for dietary intervention was similar in overt and mild enteropathy coeliac disease. Detection of such IgA deposits thus offers a good diagnostic tool to uncover early-stage coeliac disease.

Elevated serum anti-Saccharomyces cerevisiae, anti-I2 and anti-OmpW antibody levels in patients with suspicion of celiac disease

OBJECTIVES

Expression of anti-Saccharomyces cerevisiae antibodies (ASCA) identifies patients and individuals at risk for Crohn's disease and has also been reported in 40-60% of celiac disease (CD) cases, suggesting a role of host response to enteric microbiota in the development of inflammatory lesions. In this prospective study in patients with suspicion of CD, we evaluate the frequency and association of ASCA to serological responses for other host microbial targets formally associated with Crohn's disease, including the Pseudomonas fluorescens associated sequence I2 and a Bacteroides caccae TonB-linked outer membrane protein, OmpW.

METHODS

Small bowel mucosal biopsies were taken from 242 patients with suspicion of CD, their sera were tested for antibodies to tissue transglutaminase (tTG), ASCA, I2, and OmpW. Eighty adult healthy blood donors were used as controls.

RESULTS

The diagnosis of CD was confirmed on biopsy in 134 cases. The occurrence of ASCA and I2 positivity was significantly higher in adult CD patients than in patients with non-CD disease. Anti-I2 levels in the sera were significantly higher in adult CD patients than in non-CD disease or the controls and anti-OmpW levels in CD and non-CD patients when compared to controls. Positive seroreactivity to OmpW seemed to increase with age. Of the CD patients, 90% were seropositive for at least one microbial antigen tested.

CONCLUSIONS

This study demonstrates a mosaic of disease-related serological responses to microbial antigens in patients with CD. Immune responses to commensal enteric bacteria may play a role in the small intestine mucosal damage in CD.

Extracellular transglutaminase 2 is catalytically inactive, but is transiently activated upon tissue injury

Transglutaminase 2 (TG2) is a multifunctional mammalian protein with transamidase and signaling properties. Using selective TG2 inhibitors and tagged nucleophilic amine substrates, we show that the majority of extracellular TG2 is inactive under normal physiological conditions in cell culture and in vivo. However, abundant TG2 activity was detected around the wound in a standard cultured fibroblast scratch assay. To demonstrate wounding-induced activation of TG2 in vivo, the toll-like receptor 3 ligand, polyinosinic-polycytidylic acid (poly(I:C)), was injected in mice to trigger small intestinal injury. Although no TG2 activity was detected in vehicle-treated mice, acute poly(I:C) injury resulted in rapid TG2 activation in the small intestinal mucosa. Our findings provide a new basis for understanding the role of TG2 in physiology and disease.

Transepithelial transport and enzymatic detoxification of gluten in gluten-sensitive rhesus macaques

BACKGROUND AND AIMS

In a previous report, we characterized a condition of gluten sensitivity in juvenile rhesus macaques that is similar in many respects to the human condition of gluten sensitivity, celiac disease. This animal model of gluten sensitivity may therefore be useful toward studying both the pathogenesis and the treatment of celiac disease. Here, we perform two pilot experiments to demonstrate the potential utility of this model for studying intestinal permeability toward an immunotoxic gluten peptide and pharmacological detoxification of gluten in vivo by an oral enzyme drug candidate.

METHODS

Intestinal permeability was investigated in age-matched gluten-sensitive and control macaques by using mass spectrometry to detect and quantify an orally dosed, isotope labeled 33-mer gluten peptide delivered across the intestinal epithelium to the plasma. The protective effect of a therapeutically promising oral protease, EP-B2, was evaluated in a gluten-sensitive macaque by administering a daily gluten challenge with or without EP-B2 supplementation. ELISA-based antibody assays and blinded clinical evaluations of this macaque and of an age-matched control were conducted to assess responses to gluten.

RESULTS

Labeled 33-mer peptide was detected in the plasma of a gluten-sensitive macaque, both in remission and during active disease, but not in the plasma of healthy controls. Administration of EP-B2, but not vehicle, prevented clinical relapse in response to a dietary gluten challenge. Unexpectedly, a marked increase in anti-gliadin (IgG and IgA) and anti-transglutaminase (IgG) antibodies was observed during the EP-B2 treatment phase.

CONCLUSIONS

Gluten-sensitive rhesus macaques may be an attractive resource for investigating important aspects of celiac disease, including enhanced intestinal permeability and pharmacology of oral enzyme drug candidates. Orally dosed EP-B2 exerts a protective effect against ingested gluten. Limited data suggest that enhanced permeability of short gluten peptides generated by gastrically active glutenases may trigger an elevated antibody response, but that these antibodies are not necessarily causative of clinical illness.

Tissue transglutaminase: a novel pharmacological target in preventing toxic protein aggregation in neurodegenerative diseases

Alzheimer's disease, Parkinson's disease and Huntington's disease are neurodegenerative diseases, characterized by the accumulation and deposition of neurotoxic protein aggregates. The capacity of specific proteins to self-interact and form neurotoxic aggregates seems to be a common underlying mechanism leading to pathology in these neurodegenerative diseases. This process might be initiated and/or accelerated by proteins that interact with these aggregating proteins. The transglutaminase (TG) family of proteins are calcium-dependent enzymes that catalyze the formation of covalent epsilon-(gamma-glutamyl)lysine isopeptide bonds, which can result in both intra- and intermolecular cross-links. Intramolecular cross-links might modify self-interacting proteins, and make them more prone to aggregate. In addition, intermolecular cross-links could link self-aggregating proteins and thereby initiate and/or stimulate the aggregation process. So far, increased levels and activity of tissue transglutaminase (tTG), the best characterized member of the TG family, have been observed in many neurodegenerative diseases, and the self-interacting proteins, characteristic of Alzheimer's disease, Parkinson's disease and Huntington's disease, are known substrates of tTG. Here, we focus on the role of tTG in the initiation of the aggregation process of self-interacting proteins in these diseases, and promote the notion that tTG might be an attractive novel target for treatment of neurodegenerative diseases.

Deamidated gliadin peptides form epitopes that transglutaminase antibodies recognize

OBJECTIVE

Deamidated gliadin peptides are efficient antigens in diagnostic tests for celiac disease, and results correlate better with transglutaminase 2-based assays than those with native gliadin. We investigated whether deamidated gliadin antigens are structurally similar to transglutaminase 2 or could mimic transglutaminase epitopes.

PATIENTS AND METHODS

Serum samples from 74 celiac and 65 control patients, and 13 different transglutaminase 2-specific monoclonal mouse antibodies were investigated for their binding to commercially available deamidated gliadin peptides using enzyme-linked immunosorbent assay, competition studies, and molecular modelling.

RESULTS

The enzyme-linked immunosorbent assay with deamidated gliadin peptides had 100% sensitivity and 98.5% specificity in patients. Deamidated gliadin epitopes also were recognized by 3 transglutaminase-specific monoclonal antibodies, and antibodies affinity-purified with deamidated gliadin peptides from celiac patient sera reacted with transglutaminase but did not show endomysial binding. The binding of the monoclonal antibodies to deamidated gliadin was inhibited dose dependently by full-length recombinant human transglutaminase, its fragments containing the binding sites of these monoclonal antibodies, or by celiac patient antibodies. Deamidated gliadin peptides decreased the binding of transglutaminase-specific monoclonal antibodies to transglutaminase. Three different cross-reacting transglutaminase epitopes were found, of which 2 are located in the C-terminal domain and 1 is conformational. The binding of celiac serum samples to deamidated gliadin peptides could not be abolished by transglutaminase or by any of the transglutaminase-specific monoclonals, indicating that celiac sera also contain additional antibodies to gliadin epitopes different from transglutaminase.

CONCLUSIONS

Certain deamidated gliadin-derived peptides and transglutaminase 2 epitopes have similar 3-dimensional appearance. This homology may contribute to the induction of transglutaminase autoantibodies by molecular mimicry.

Secretion of celiac disease autoantibodies after in vitro gliadin challenge is dependent on small-bowel mucosal transglutaminase 2-specific IgA deposits

Background

In celiac disease gluten, the disease-inducing toxic component in wheat, induces the secretion of autoantibodies which are targeted against transglutaminase 2 (TG2). These autoantibodies are produced in the small-intestinal mucosa, where they can be found deposited extracellularly below the epithelial basement membrane and around mucosal blood vessels. In addition, during gluten consumption these autoantibodies can also be detected in patients' serum but disappear from the circulation on a gluten-free diet. Interestingly, after adoption of a gluten-free diet the serum autoantibodies disappear from the circulation more rapidly than the small-intestinal mucosal autoantibody deposits. The toxicity of gluten and the secretion of the disease-specific autoantibodies have been widely studied in organ culture of small-intestinal biopsy samples, but results hitherto have been contradictory. Since the mucosal autoantibodies disappear slowly after a gluten-free diet, our aim was to establish whether autoantibody secretion to organ culture supernatants in treated celiac disease patient biopsies is related to the duration of the diet and further to the pre-existence of mucosal TG2-specific IgA deposits in the cultured biopsy samples.

Results

In the organ culture system conducted with biopsies derived from treated celiac disease patients, gliadin induced secretion of autoantibodies to culture supernatants, reduced epithelial cell height and increased the density of lamina proprial CD25+ cells. However, these changes could be demonstrated only in biopsies from short-term treated celiac disease patients, where the small-intestinal mucosal TG2-specific IgA autoantibody deposits were still present. Furthermore, in these biopsies autoantibody secretion could be stimulated fully only after a 48-hour gliadin challenge.

Conclusion

Our results show that studies focusing on the toxic effects of gliadin in the organ culture system should be carried out with biopsy samples from short-term treated celiac disease patients who are likely still to have mucosal IgA deposits present. In addition to providing an explanation for the discrepancies in previous publications, the present study also enables further validation of the organ culture method.

Coeliac disease-specific autoantibodies targeted against transglutaminase 2 disturb angiogenesis

Coeliac disease is characterized by immunoglobulin-A (IgA)-class autoantibodies targeted against transglutaminase 2 (TG2), a multi-functional protein also with a role in angiogenesis. These antibodies are present in patient serum but are also found bound to TG2 below the epithelial basement membrane and around capillaries in the small intestinal mucosa. Based on these facts and the information that the mucosal vasculature of coeliac patients on a gluten-containing diet is disorganized, we studied whether the coeliac disease-specific autoantibodies targeted against TG2 would disturb angiogenesis. The effects of coeliac disease-specific autoantibodies on in vitro angiogenesis were studied in angiogenic cell cultures. The binding of the antibodies to cells, endothelial sprouting, migration of both endothelial and vascular mesenchymal cells, the integrity of the actin cytoskeleton in both cell types and the differentiation of vascular mesenchymal cells were recorded. In vitro, IgA derived from coeliac disease patients on a gluten-containing diet binds to surface TG2 on endothelial and vascular mesenchymal cells and this binding can be inhibited by the removal of TG2. In addition, coeliac disease-specific autoantibodies targeting TG2 disturb several steps of angiogenesis: endothelial sprouting and the migration of both endothelial and vascular mesenchymal cells. Furthermore, the autoantibodies cause disorganization of the actin cytoskeleton in both capillary cell types that account most probably for the defective cellular migration. We conclude that coeliac disease-specific autoantibodies recognizing TG2 inhibit angiogenesis in vitro. This disturbance of the angiogenic process could lead in vivo to the disruption of the mucosal vasculature seen in coeliac disease patients on a gluten-containing diet.

Autoantibodies in celiac disease

Autoantibody production is an important feature of many autoimmune disorders, signifying a breakdown of immune tolerance to self-antigens. In celiac disease, an autoimmune enteropathy with multiple extra-intestinal manifestations, autoantibody reactivity to transglutaminase 2 (TG2) has been shown to closely correlate with the acute phase of the disease. It serves as a specific and sensitive marker of celiac disease, and is highly useful in aiding diagnosis and follow-up. Immune reactivity to other autoantigens, including transglutaminase 3, actin, ganglioside, collagen, calreticulin and zonulin, among others, has also been reported in celiac disease. The clinical significance of these antibodies is not known, although some may be associated with specific clinical presentations or extra-intestinal manifestations of celiac disease. This review examines the presence of anti-TG2 and other autoantibodies in celiac disease, discussing their diagnostic value, their potential role in disease pathogenesis and current hypotheses that explain how their release may be triggered.

Antitissue transglutaminase antibodies in acute coronary syndrome: an alert signal of myocardial tissue lesion?

BACKGROUND AND AIM

Antitransglutaminase, previously considered identical to antiendomysial in coeliac sprue (CS), have been reported in end-stage heart failure. To clarify the above-mentioned data, we evaluated these antibodies in a cohort of cardiological patients with respect to troponin I, creatine kinase (CK), MB fraction creatine kinase (CK-MB mass) and myoglobin.

METHODS

Forty-one patients with acute coronary syndrome (ACS), 39 with dilated cardiomyopathy (DCM), 45 with CS and 58 blood donors (BDs) were evaluated. Antitransglutaminase and antiendomysial antibodies were tested in serum of the patients being studied.

RESULTS

High-positive antitransglutaminase values were found in CS, whilst low-positive values were also found in ACS and DCM. In patients at the second ACS, antibody levels were higher than in those at the first cardiac event. In patients with infarct Q, antitransglutaminase were higher than those in infarct non-Q, in which antibody levels were higher than those in unstable angina. A correlation between antitransglutaminase and troponin I, CK, CK-MB mass and myoglobin was found. Finally, antibody levels rose to reach a peak at 30 days from the cardiac event, whereas after further 150 days, approached the values of BDs. Antiendomysial were detectable only in CS.

CONCLUSIONS

Data highlight that antitransglutaminase can occur in cardiological patients, and that these antibodies are related to the severity/extent of the myocardial tissue lesion. This feature suggests a loss of specificity for antitransglutaminase in CS. Furthermore, the possibility of employing these antibodies in the long-term follow-up of ACS, could become an object of interesting discussion.

Transglutaminase 2 inhibitors and their therapeutic role in disease states

Transglutaminase 2 (TG2) is a multi-domain, multi-functional enzyme that post-translationally modifies proteins by catalyzing the formation of intermolecular isopeptide bonds between glutamine and lysine side-chains. It plays a role in diverse biological functions, including extracellular matrix formation, integrin-mediated signaling, and signal transduction involving 7-transmembrane receptors. While some of the roles of TG2 under normal physiological conditions remain obscure, the protein is believed to participate in the pathogenesis of several unrelated diseases, including celiac sprue, neurodegenerative diseases, and certain types of cancer. A variety of small molecule and peptidomimetic inhibitors of the TG2 active site have been identified. Here, we summarize the biochemistry, biology, pharmacology and medicinal chemistry of human TG2.

Surface Expression of Transglutaminase 2 by Dendritic Cells and its Potential Role for Uptake and Presentation of Gluten Peptides to T Cells

Celiac disease is a chronic small intestinal inflammation driven by gluten-reactive T cells of the intestinal mucosa. These T cells are HLA-DQ2 or -DQ8 restricted, and predominantly recognize gluten peptides that are deamidated by the enzyme transglutaminase 2 (TG2). Our recent results strongly suggest that duodenal CD11c(+) dendritic cells (DC) are directly involved in T cell activation in the celiac lesion. The aim of this study was to investigate whether surface-associated TG2 could be involved in receptor-mediated endocytosis of gluten peptides, a process that may contribute to the preferential recognition of deamidated peptides. We found that both monocyte-derived DC and local CD11c(+) DC in the duodenal mucosa expressed cell surface-associated TG2. As phenotypic characterization of CD11c(+) DC in the celiac lesion suggests that these cells may be derived from circulating monocytes, we used monocyte-derived DC in functional in vitro studies. Using a functional T cell assay, we obtained evidence that cell surface-associated TG2 is endocytosed by monocyte-derived DC. However, we were unable to obtain evidence for a role of surface TG2 in the loading and subsequent generation of deamidated gluten peptides in these cells.

Tissue transglutaminase ELISA positivity in autoimmune disease independent of gluten-sensitive disease

BACKGROUND

Our aim was to understand why some sera from patients with a broad spectrum of autoimmune diseases or non-autoimmune diseases involving enhanced apoptosis, cell lysis and/or putative secondary autoimmune processes show reactions in the tissue transglutaminase (TGc) ELISA used for diagnosis of gluten-sensitive disease.

METHODS

Sera were compared from groups of patients with autoimmune diseases, diseases involving organ specific enhanced cell death, celiac disease or dermatitis herpetiformis, diseases of non-autoimmune origin, and a group without known disease. IgA antibodies against TGc were detected using human antigen (produced recombinantly in bacterial or human cells) in different systems (non-commercial ELISA with buffers of differing NaCl concentrations, and anti-TGc sandwich ELISA). Anti-gliadin and anti-endomysium antibodies were also determined.

RESULTS

Many sera from patients with autoimmune disorders gave a positive signal in the human TGc ELISAs. The signal appeared related to minor impurities in the recombinant human TGc used and to raised serum IgA antibody levels rather than to the occurrence of TGc specific antibodies in these patients.

CONCLUSIONS

No association of anti-TGc Abs and autoimmune conditions independent of gluten-sensitive disease could be shown. Care should be taken to exclude copurification of chaperones, like heat shock protein 70, where preparing antigens for TGc ELISAs.

Endomysial antibody-negative coeliac disease: clinical characteristics and intestinal autoantibody deposits

BACKGROUND

Some patients with untreated coeliac disease are negative for serum endomysial autoantibodies (EmA) targeted against transglutaminase 2 (TG2).

AIMS

To evaluate the clinical and histological features of EmA-negative coeliac disease, and to examine whether EmA-equivalent autoantibodies against TG2 can be seen in the small-bowel mucosa when absent in serum.

PATIENTS

Serum EmA was studied in 177 biopsy-proved specimens from adult patients with coeliac disease. 20 patients with intestinal diseases served as non-coeliac controls; three had autoimmune enteropathy with villous atrophy.

METHODS

Clinical manifestations, small-bowel mucosal morphology, intraepithelial inflammation and TG2-specific extracellular immunoglobulin A (IgA) deposits were investigated in both serum EmA-negative and EmA-positive patients.

RESULTS

22 patients with IgA-competent coeliac disease were negative for serum EmA. Three of these had small-bowel lymphoma. Patients with EmA-negative coeliac disease were older, had abdominal symptoms more often, and the density of gammadelta+ intraepithelial lymphocytes in their intestinal mucosa was lower than in EmA-positive patients; otherwise the histology was similar. All serum EmA-negative patients with coeliac disease, but none of the disease controls, had gluten-dependent mucosal IgA deposits alongside TG2 in the small-bowel mucosal specimens. In vivo deposited IgA was shown to be TG2-specific by its ability to bind recombinant TG2.

CONCLUSIONS

Negative serum EmA might be associated with advanced coeliac disease. TG2-targeted autoantibodies were deposited in the small-bowel mucosa even when absent in serum. This finding can be used in the diagnosis of seronegative coeliac disease when the histology is equivocal. It may also be helpful in the differential diagnosis between autoimmune enteropathy and coeliac disease.

Diagnostic significance of HLA-DQ typing in patients with previous coeliac disease diagnosis based on histology alone

BACKGROUND

Coeliac disease is strongly associated with human leukocyte antigen (HLA)-DQ2 or DQ8 genotypes. The diagnosis is based on demonstrating crypt-hyperplastic villous atrophy, endomysial or transglutaminase antibodies and correlation of disease activity with gluten intake.

AIM

To evaluate the clinical utility of HLA-DQ typing, when coeliac disease diagnosis had previously been established solely by histology.

METHODS

HLA-DQ alleles, endomysial and transglutaminase antibodies were investigated and histology slides reviewed in 70 patients diagnosed 2-25 years earlier by small-intestinal biopsy but without measuring endomysial or transglutaminase antibodies. Patients without DQ2 or DQ8 or without unequivocal villous atrophy were followed-up on free diet by using serology and biopsies.

RESULTS

All 40 endomysial/transglutaminase antibodies positive patients carried DQ2 or DQ8, and 39 of them had severe villous atrophy. Only 56% of patients without endomysial or transglutaminase antibodies positivity had DQ2 or DQ8 (P < 0.001). Seropositivity and relapse developed in 4 of 11 DQ2 positive but in none of 15 DQ2 and DQ8 negative patients on long-term gluten exposure.

CONCLUSIONS

Coeliac disease diagnosis based solely on histology is not always reliable. HLA-DQ typing is important in identifying DQ2 and DQ8 negative subjects who need revision of their diagnosis, but it does not have additive diagnostic value if endomysial positivity is already known.

Immunoglobulin A autoantibodies against transglutaminase 2 in the small intestinal mucosa predict forthcoming coeliac disease

BACKGROUND

Reliable markers of early developing coeliac diseases are needed. Coeliac autoantibodies in the serum or Marsh I inflammation may be indicators of subsequent coeliac disease.

AIM

To investigate whether determination of intestinal transglutaminase 2-targeted autoantibody deposits would detect early developing coeliac disease better than previous methods.

METHODS

The study investigated patients previously excluded for coeliac disease: 25 had positive serum coeliac autoantibodies (endomysial), 25 antibody-negative had Marsh I, and 25 antibody-negative had Marsh 0 finding. Seven (median) years after baseline investigation, new coeliac cases were recorded, and small bowel biopsy was offered to the rest of the patients. Serum and intestinal coeliac autoantibodies and intraepithelial lymphocytes were assessed as indicators of developing coeliac disease.

RESULTS

Seventeen patients had developed coeliac disease: 13 in the autoantibody-positive group, three in the Marsh I group and one in the Marsh 0 group. At baseline, intestinal coeliac autoantibody deposits had a sensitivity and specificity of 93% and 93% in detecting subsequent coeliac disease, CD3+ 59% and 57%, gammadelta+ 76% and 60%, and villous tip intraepithelial lymphocytes 88% and 71%, respectively.

CONCLUSIONS

Endomysial antibodies with normal histology indicates early developing coeliac disease. Transglutaminase 2-targeted intestinal autoantibody deposits proved the best predictor of subsequent coeliac disease.

Celiac sprue (the great modern-day imposter)

PURPOSE OF REVIEW

To review the current epidemiological information on celiac disease and the various presentations and associated.

RECENT FINDINGS

Epidemiologic studies reveal celiac disease to be common, occurring in approx. 1% of the population. It is being diagnosed worldwide, even in developing countries. The classic mode of presentation has become less common, with diarrhea or a malabsorption syndrome as the mode of presentation in fewer than 50% of individuals. The other major modes of presentation are iron-deficiency anemia, osteoporosis, screening of family members, or incidentally at endoscopy done for dyspepsia or reflux. Neurological presentations may include peripheral neuropathy or ataxia. Arthritis is commonly found in patients with celiac disease when systematically sought. Patients often have a previous diagnosis of irritable bowel syndrome. Autoimmune diseases occur more frequently (three to ten times more) in those with celiac disease than the general population. However, this increased incidence of autoimmune diseases is not prevented by early diagnosis of celiac disease.

SUMMARY

We will review the various associated diseases/presentations of celiac disease. The heterogeneity of the symptoms can make the diagnosis challenging and certainly the great modern-day imposter.

Coeliac disease case finding and diet monitoring by point-of-care testing

BACKGROUND

Immunoglobulin A class transglutaminase autoantibodies are highly predictive markers of active coeliac disease, a disorder difficult to recognize solely on clinical grounds.

AIMS

To develop and evaluate a simple rapid test for point-of-care detection of coeliac autoantibodies.

METHODS

The novel whole blood test utilizes the patient's endogenous transglutaminase in red blood cells for detection of transglutaminase-specific immunoglobulin A antibodies present in the blood sample, with normal plasma immunoglobulin A detection as positive test control. We evaluated 284 patients under suspicion of coeliac disease and undergoing jejunal biopsy, and 263 coeliac patients on a gluten-free diet, 383 being tested prospectively in a point-of-care setting. Results were compared with histology, conventional serum autoantibody results and dietary adherence.

RESULTS

The rapid test showed 97% sensitivity and 97% specificity for untreated coeliac disease, and identified all immunoglobulin A-deficient samples. Point-of-care testing found new coeliac cases as efficiently as antibody tests in laboratory. Coeliac autoantibodies were detected onsite in 21% of treated patients, while endomysial and transglutaminase antibodies were positive in 20% and 19%, respectively. The positivity rate correlated with dietary lapses and decreased on intensified dietary advice given upon positive point-of-care test results.

CONCLUSIONS

Point-of-care testing was accurate in finding new coeliac cases and helped to identify and decrease dietary non-compliance.

Tissue transglutaminase antibodies in celiac disease, comparison of an enzyme linked immunosorbent assay and a dot blot assay

AIMS

The purpose of our study is to determine the sensitivity, specificity and predictive values of an enzyme linked immunosorbent assay (ELISA) and a dot blot assay for the detection of IgA class anti-tissue transglutaminase antibodies (IgA-AtTGA) and to compare these results with those of IgA class anti-endomysium antibodies (IgA-AEA), IgA class anti-reticulin antibodies (IgA-ARA) and IgA class anti-gliadin antibodies (IgA-AGA).

PATIENTS

Serum samples from 143 patients (97 children, 46 adults) with untreated celiac disease (CD) confirmed by intestinal biopsy and 74 disease controls (64 children, 10 adults) were studied. Methods. - The anti-tissue transglutaminase antibodies were detected by dot blot assay and an ELISA using guinea pig tissue transglutaminase (gp-tTG) as antigen. The anti-endomysium antibodies were detected by an indirect immunofluorescence technique on cryostat sections of human umbilical cord. The anti-reticulin antibodies were also investigated by indirect immunofluorescence on cryostat sections of kidney, liver and stomach of rat. The anti-gliadin antibodies were determined by an ELISA.

RESULTS

The sensitivity of an ELISA for the detection of anti-tissue transglutaminase antibodies was 86% in children and 87% in adults and the sensitivity of dot blot assay was 57% in children and 54% in adults. The specificity of an ELISA and dot blot for the detection for anti-tissue transglutaminase antibodies was, respectively, 96% and 88% lower than that of anti-endomysium antibodies (100%). The sensitivity of anti-gliadin antibodies was 97% in children and 91% in adults and their specificity was 85%. The sensitivity of anti-reticulin antibodies was 94% in children and 87% in adults. Their specificity was 100%.

CONCLUSIONS

The sensitivity and specificity of an ELISA for the detection of anti-tissue transglutaminase antibodies were better than that of dot blot assay. However, this dot blot assay could screen four celiac patients who have not had anti-tissue transglutaminase antibodies by an ELISA. The sensitivity of anti-endomysium antibodies was better than that of anti-tissue transglutaminase antibodies, anti-reticulin antibodies and anti-gliadin antibodies but in children aged less than 2 years, the sensitivity of anti-gliadin antibodies was better than that of anti-tissue transglutaminase antibodies.

Gliadin as a stimulator of innate responses in celiac disease

In celiac disease (CD) we have the prototype of an immune mediated response dominated by the activation of the adaptive immune system and in particular of CD4+ HLA class II restricted T cells. Various seminal studies have established the precise mechanism of how antigen (prolamine) specific activation of CD4+ mucosal T cells occurs. Thus, CD is a condition in which T cells and their activation is the essential hinge in the pathogenic process. These functional studies have provided the explanation for the genetic association between CD and certain HLA alleles (HLA DQ2 and DQ8). These genetic, molecular and functional studies have permitted the clarification of a powerful Th1 dominated pro-inflammatory response that characterises the small intestine of active CD patients. Despite this unassailable set of information and reports there are some intriguing points that have been raised by a series of studies which have indicated that CD is not only defined by an aberrant prolamine-induced activation of the adaptive immune system. New evidence and re-assessments of old studies, point to a more complex pathogenic cascade, which may help to unravel some of the residual obscure points of CD pathogenesis. Here, we outline the current concepts that indicate a direct involvement of the adaptive immune system and we discuss all the evidence supporting a direct activation of the innate immune system by fragments of prolamines, which are not recognized T cell epitopes and how they could influence CD. The gliadin-induced activation of the 'innate' immune system might also have a significant role in the induction and persistence of many CD complications and most definitively for the most aggressive one, namely mucosal T cell lymphomas. We further suggest a novel way to harness the unwanted immune response to toxic prolamine, and thus indicate new potential therapeutic strategies to treat or at least control CD.

Narrative review: celiac disease: understanding a complex autoimmune disorder

Celiac disease is a common autoimmune disorder that has genetic, environmental, and immunologic components. It is characterized by an immune response to ingested wheat gluten and related proteins of rye and barley that leads to inflammation, villous atrophy, and crypt hyperplasia in the intestine. The disease is closely associated with genes that code for human leukocyte antigens DQ2 and DQ8. Transglutaminase 2 appears to be an important component of the disease, both as a deamidating enzyme that can enhance the immunostimulatory effect of gluten and as a target autoantigen in the immune response. Sensitive and specific serologic tests, including those for anti-transglutaminase antibody, are facilitating fast and noninvasive screening for celiac disease. Thus, they are contributing to a more accurate estimate of the prevalence of the disease and its association with other disorders. Celiac disease is associated with increased rates of anemia, osteoporosis, cancer, neurologic deficits, and additional autoimmune disorders. A gluten-free diet is the mainstay of safe and effective treatment of celiac disease, although its effect on some of the extraintestinal manifestations of the disease remains to be determined.

Immunoglobulin Isotype Profile of Tissue Transglutaminase Autoantibodies is Correlated with the Clinical Presentation of Coeliac Disease

Coeliac disease (CD) is characterized by the appearance of autoantibodies against tissue transglutaminase (tTG-Ab). Immunoglobulin A (IgA) tTG-Ab have been described as excellent diagnostic markers, but the Ig subclass distribution and the importance of isotype tTG-Ab have not yet been established. In this study, using newly developed isotype- and subclass-specific radioligand assays, we examined anti-tTG IgA1, IgA2, IgG1, IgG4 and IgE antibodies in 30 symptomatic, untreated patients with CD and 22 subjects suspected to suffer from silent CD (sCD). Among 30 patients with CD, 27 (90.0%) were positive for IgA1 tTG-Ab, whereas only 12 (40.0%) had autoantibodies of the IgA2 subclass (P <0.001). IgG1, IgG4 and IgE tTG-Ab were detected in 17 (56.6%), 0 and 3 (10.0%) individuals, respectively. IgA1 was also the predominant anti-tTG subclass in patients with sCD (n=20, 90.1%), followed by IgA2 antibodies (n=7, 31.8%), IgG1 antibodies (n=4, 18.2%), IgG4 antibodies (n=1, 4.5%) and IgE antibodies (n=1, 4.5%). The comparison between both groups revealed a significantly higher prevalence of IgG1 antibodies in patients with symptomatic CD (P <0.01). In 10 of 11 subjects undergoing an intestinal biopsy, the diagnosis of an sCD was confirmed. In this subgroup, there was a positive association between the presence of IgA2 and IgG1 tTG-Ab and severe (Marsh 2-3) mucosal abnormalities. In conclusion, patients with symptomatic and sCD predominantly have IgA1 tTG-Ab. IgG1 tTG-Ab are associated with symptomatic disease and, when present in patients with sCD, are correlated with a severe mucosal destruction. These data suggest that tTG-Ab subclasses could reflect inflammatory events associated with epithelial destruction.