Exposing gliadin as a tasty food for lymphocytes

Features of ZED1227: The First-In-Class Tissue Transglutaminase Inhibitor Undergoing Clinical Evaluation for the Treatment of Celiac Disease

ZED1227 is a small molecule tissue transglutaminase (TG2) inhibitor. The compound selectively binds to the active state of TG2, forming a stable covalent bond with the cysteine in its catalytic center. The molecule was designed for the treatment of celiac disease. Celiac disease is an autoimmune-mediated chronic inflammatory condition of the small intestine affecting about 1–2% of people in Caucasian populations. The autoimmune disease is triggered by dietary gluten. Consumption of staple foods containing wheat, barley, or rye leads to destruction of the small intestinal mucosa in genetically susceptible individuals, and this is accompanied by the generation of characteristic TG2 autoantibodies. TG2 plays a causative role in the pathogenesis of celiac disease. Upon activation by Ca²⁺, it catalyzes the deamidation of gliadin peptides as well as the crosslinking of gliadin peptides to TG2 itself. These modified biological structures trigger breaking of oral tolerance to gluten, self-tolerance to TG2, and the activation of cytotoxic immune cells in the gut mucosa. Recently, in an exploratory proof-of-concept study, ZED1227 administration clinically validated TG2 as a “druggable” target in celiac disease. Here, we describe the specific features and profiling data of the drug candidate ZED1227. Further, we give an outlook on TG2 inhibition as a therapeutic approach in indications beyond celiac disease.

Diagnosis and Updates in Celiac Disease

Celiac disease is an autoimmune disorder induced by gluten in genetically susceptible individuals. It can result in intraintestinal and extraintestinal manifestations of disease including diarrhea, weight loss, anemia, osteoporosis, or lymphoma. Diagnosis of celiac disease is made through initial serologic testing and then confirmed by histopathologic examination of duodenal biopsies. Generally celiac disease is a benign disorder with a good prognosis in those who adhere to a gluten-free diet. However, in refractory disease, complications may develop that warrant additional testing with more advanced radiologic and endoscopic methods. This article reviews the current strategy to diagnose celiac disease and the newer modalities to assess for associated complications.

Celiac anti-type 2 transglutaminase antibodies induce differential effects in fibroblasts from celiac disease patients and from healthy subjects

Type 2 transglutaminase (TG2) has an important pathogenic role in celiac disease (CD), an inflammatory intestinal disease that is caused by the ingestion of gluten-containing cereals. Indeed, TG2 deamidates specific gliadin peptides, thus enhancing their immunogenicity. Moreover, the transamidating activity seems to provoke an autoimmune response, where TG2 is the main autoantigen. Many studies have highlighted a possible pathogenetic role of anti-TG2 antibodies, because they modulate TG2 enzymatic activity and they can interact with cell-surface TG2, triggering a wide range of intracellular responses. Autoantibodies also alter the uptake of the alpha-gliadin peptide 31-43 (p31-43), responsible of the innate immune response in CD, thus partially protecting cells from p31-43 damaging effects in an intestinal cell line. Here, we investigated whether anti-TG2 antibodies protect cells from p31-43-induced damage in a CD model consisting of primary dermal fibroblasts. We found that the antibodies specifically reduced the uptake of p31-43 by fibroblasts derived from healthy subjects but not in those derived from CD patients. Analyses of TG2 expression and enzymatic activity did not reveal any significant difference between fibroblasts from healthy and celiac subjects, suggesting that other features related to TG2 may be responsible of such different behaviors, e.g., trafficking or subcellular distribution. Our findings are in line with the concept that a "celiac cellular phenotype" exists and that TG2 may contribute to this phenotype. Moreover, they suggest that the autoimmune response to TG2, which alone may damage the celiac mucosa, also fails in its protective role in celiac cells.

Celiac anti-type 2 transglutaminase antibodies induce phosphoproteome modification in intestinal epithelial Caco-2 cells

BACKGROUND

Celiac disease is an inflammatory condition of the small intestine that affects genetically predisposed individuals after dietary wheat gliadin ingestion. Type 2-transglutaminase (TG2) activity seems to be responsible for a strong autoimmune response in celiac disease, TG2 being the main autoantigen. Several studies support the concept that celiac anti-TG2 antibodies may contribute to disease pathogenesis. Our recent findings on the ability of anti-TG2 antibodies to induce a rapid intracellular mobilization of calcium ions, as well as extracellular signal-regulated kinase phosphorylation, suggest that they potentially act as signaling molecules. In line with this concept, we have investigated whether anti-TG2 antibodies can induce phosphoproteome modification in an intestinal epithelial cell line.

METHODS AND PRINCIPAL FINDINGS

We studied phosphoproteome modification in Caco-2 cells treated with recombinant celiac anti-TG2 antibodies. We performed a two-dimensional electrophoresis followed by specific staining of phosphoproteins and mass spectrometry analysis of differentially phosphorylated proteins. Of 14 identified proteins (excluding two uncharacterized proteins), three were hypophosphorylated and nine were hyperphosphorylated. Bioinformatics analyses confirmed the presence of phosphorylation sites in all the identified proteins and highlighted their involvement in several fundamental biological processes, such as cell cycle progression, cell stress response, cytoskeletal organization and apoptosis.

CONCLUSIONS

Identification of differentially phosphorylated proteins downstream of TG2-antibody stimulation suggests that in Caco-2 cells these antibodies perturb cell homeostasis by behaving as signaling molecules. We hypothesize that anti-TG2 autoantibodies may destabilize the integrity of the intestinal mucosa in celiac individuals, thus contributing to celiac disease establishment and progression. Since several proteins here identified in this study were already known as TG2 substrates, we can also suppose that transamidating activity and differential phosphorylation of the same targets may represent a novel regulatory mechanism whose relevance in celiac disease pathogenesis is still unexplored.

Gliadin peptides induce tissue transglutaminase activation and ER-stress through Ca2+ mobilization in Caco-2 cells

BACKGROUND

Celiac disease (CD) is an intestinal inflammatory condition that develops in genetically susceptible individuals after exposure to dietary wheat gliadin. The role of post-translational modifications of gliadin catalyzed by tissue transglutaminase (tTG) seems to play a crucial role in CD. However, it remains to be established how and where tTG is activated in vivo. We have investigated whether gliadin peptides modulate intracellular Ca(2+) homeostasis and tTG activity.

METHODS/PRINCIPAL FINDINGS

We studied Ca(2+) homeostasis in Caco-2 cells by single cell microfluorimetry. Under our conditions, A-gliadin peptides 31-43 and 57-68 rapidly mobilized Ca(2+) from intracellular stores. Specifically, peptide 31-43 mobilized Ca(2+) from the endoplasmic reticulum (ER) and mitochondria, whereas peptide 57-68 mobilized Ca(2+) only from mitochondria. We also found that gliadin peptide-induced Ca(2+) mobilization activates the enzymatic function of intracellular tTG as revealed by in situ tTG activity using the tTG substrate pentylamine-biotin. Moreover, we demonstrate that peptide 31-43, but not peptide 57-68, induces an increase of tTG expression. Finally, we monitored the expression of glucose-regulated protein-78 and of CCAAT/enhancer binding protein-homologous protein, which are two biochemical markers of ER-stress, by real-time RT-PCR and western blot. We found that chronic administration of peptide 31-43, but not of peptide 57-68, induces the expression of both genes.

CONCLUSIONS

By inducing Ca(2+) mobilization from the ER, peptide 31-43 could promote an ER-stress pathway that may be relevant in CD pathogenesis. Furthermore, peptides 31-43 and 57-68, by activating intracellular tTG, could alter inflammatory key regulators, and induce deamidation of immunogenic peptides and gliadin-tTG crosslinking in enterocytes and specialized antigen-presenting cells.

Dermatitis herpetiformis. Part I. Epidemiology, pathogenesis, and clinical presentation

Dermatitis herpetiformis (DH) is an autoimmune disease that is linked to gluten sensitivity and has a clear relationship to celiac disease. Both conditions are mediated by the IgA class of autoantibodies and the diagnosis of DH is dependent on detection of granular deposits of IgA in the skin. There is an underlying genetic predisposition to the development of DH but environmental factors are also important. Typically, young adults present with excoriations only, as the severe pruritus effectively destroys any primary lesions. Based upon our experience with DH and a comprehensive literature review, we provide an update of DH epidemiology, pathophysiology, and clinical presentation.

Update on mucosal immunoglobulin A in gastrointestinal disease

PURPOSE OF REVIEW

To review recent findings dealing with the involvement of mucosal immunoglobulin A (IgA) in the gut barrier function and various gastrointestinal diseases. New information will be discussed in the context of previous knowledge in this field.

RECENT FINDINGS

The epithelial barrier function seems to be central in many mucosal disorders because it is decisive for host-microbial interactions and penetration of soluble antigens into the lamina propria. Secretory IgA contributes to the barrier function and recent evidence strongly supports the notion that such antibodies are involved in immunological homeostasis.

SUMMARY

Inflammatory bowel disease involves a break of tolerance to the commensal microbiota. Aberrations in the mucosal IgA system may, therefore, be part of the inflammatory bowel disease pathogenesis. In gluten-induced enteropathy, however, it has been suggested that a mucosal IgA response may promote the progression of celiac disease and dermatitis herpetiformis by enhancing the uptake of gluten peptides and inhibiting the enzyme activity of tissue transglutaminase. A mucosal IgA response may also promote gastritis by protecting Helicobacter pylori from complement attack. In food allergy, several facets of the epithelial barrier function may show deficiency, including secretory IgA.

Tissue transglutaminase in celiac disease: role of autoantibodies

In celiac disease (CD), gluten, the disease-inducing toxic component in wheat, induces the secretion of IgA-class autoantibodies which target tissue transglutaminase (tTG). These autoantibodies are produced in the small-intestinal mucosa, and, during gluten consumption, they can also be detected in patients' serum but disappear slowly 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 finding of IgA deposits on extracellular tTG in the liver, kidney, lymph nodes and muscles of patients with CD indicates that tTG is accessible to the gut-derived autoantibodies. Although the specific autoantibody response directed against tTG is very characteristic in celiac patients, their role in the immunopathology of the celiac mucosal lesion is a matter of debate. Here we report a brief summary of anti-tTG antibody effects demonstrating that these antibodies are functional and not mere bystanders in the disease pathogenesis. In fact, they inhibit intestinal epithelial cell differentiation, induce intestinal epithelial cell proliferation, increase epithelial permeability and activate monocytes and disturb angiogenesis.

Fate of five celiac disease-associated antibodies during normal diet in genetically at-risk children observed from birth in a natural history study

OBJECTIVES

To explore the natural history of antibodies against tissue transglutaminase (TGA), endomysium (EMA), reticulin (ARA), and gliadin (AGA-IgG and AGA-IgA) in children carrying HLA-conferred risk for celiac disease (CD) and observed frequently from birth.

METHODS

TGA was measured in serum samples obtained between years 2000 and 2003 from 1,320 children carrying genetic CD risk. If a sample was TGA positive, all five antibodies were analyzed in all banked and forthcoming samples from that child, and a duodenal biopsy was recommended. At the end of this observation, in August 2004, the age of the children was from 1 to 9.5 yr (mean 4.1 yr).

RESULTS

Forty-nine children (3.7%) were TGA positive. In these children, AGA-IgG had emerged at the mean age (+/- SD, range) of 2.0 +/- 1.5, 0.5-6.6 yr, while TGA, EMA, and ARA all emerged concurrently somewhat later (TGA at 3.2 +/- 1.5, 1.0-7.0 yr, P < 0.001 when compared to AGA-IgG). Despite continuing gluten exposure, positive TGA, EMA, ARA, AGA-IgA, and AGA-IgG values were spontaneously lost in 49%, 45%, 43%, 41%, and 32% of the children, respectively. CD was diagnosed by biopsy in 20 of the 26 TGA-positive children who consented to a biopsy.

CONCLUSIONS

Potential CD trigger(s) other than only gluten probably function before AGA-IgG emerges, i.e., > or =3 months earlier than the transglutaminase-associated antibodies appear. In a remarkable proportion of the children, antibodies disappear spontaneously suggesting that regulatory immune phenomena under favorable circumstances are able to extinguish incipient CD in genetically at-risk children even without exclusion of gluten from the diet.

Recent advances in the understanding of celiac disease: therapeutic implications for the management of pediatric patients

Celiac disease (CD) is an autoimmune condition occurring in genetically susceptible individuals characterized by inflammatory injury to the mucosa of the small intestine after the ingestion of wheat glutens or related barley and rye products. Originally thought to be highly prevalent only in Northern European populations, growing evidence indicates a much higher prevalence in many other regions, including the US as well as South America, North Africa, and Asia. The growing awareness that pediatric patients may present with quite diverse and protean manifestations and the significant impact of CD on childhood development has prompted efforts to increase CD awareness for the early diagnosis and treatment of this disease. The current diagnostic criteria for CD requires characteristic histologic findings in small bowel biopsies and clinical remission when placed on a gluten-free diet. Serologic testing for CD can provide additional support for the diagnosis of CD or a means to assess efficacy and adherence to a gluten-free diet. The mainstay of treatment remains the institution of a gluten-free diet. However, patients with refractory CD may require treatment with immunosuppressant medications. With the increased identification of specific gluten epitopes and understanding of the pathogenesis of CD, future therapies may rely on genetically altering gluten proteins, immunization techniques, or therapies focused on either the development of specific immune tolerance or regulation of mucosal inflammation.

Evidence of a selective epitope loss of anti-transglutaminase immunoreactivity in gluten-free diet celiac sera: A new tool to distinguish disease-specific immunoreactivities

The aim of the present study was to evaluate the epitope specific humoral human tissue transglutaminase (tTG) immunoreactivity against 3 different human recombinant tTG constructs [(full-length tTG (a.a. 1-687), tTG (a.a. 227-687); tTG (a.a. 473-687)] before and after the introduction of a gluten-free diet (GFD). To this end, sera from 64 celiac disease (CD) subjects on a gluten-containing diet (44 f, 20 m) and after 0.6 +/- 0.3 years and 2.1 +/- 1.3 years of GFD were studied using a quantitative radioimmunoprecipitation assay. All 64 CD patients at diagnosis were full-length anti-tTG (a.a. 1-687)Ab positive. These Abs significantly decreased in frequency and titer after 6 months and 2 years of GFD. However, at low titers, 64.1% (41/64) of CD patients were still fl-tTG (a.a. 1-687)Ab positive after 2 years of GFD. At disease diagnosis, 70.3% (45/64) of the CD patients had Abs directed against fragments (227-687) and/or (473-687) of the tTG protein. This percentage, after 2 years of GFD, significantly decreased to 18.7%, whereas almost 50% of GFD patients had no tTG (227-687) and tTG (473-687) fragment reactivity, but only persistent, low-titer full-length tTG (1-687)Abs. We suggest that the selective loss of immunoreactivity against tTG (227-687) and tTG (473-687) fragments in CD patients with a GFD, could be due to quantitative decrease of autoreactivity driven by tTG-gliadin interaction underlying celiac disease pathogenesis.

The changing immunological paradigm in coeliac disease

When coeliac disease is referred to as an inflammatory disorder, this may detract from its true nature. Activation of innate and adaptive immunity takes place in the mucosal lesion, but the tissue reaction is not that of classical inflammation. In fact, coeliac disease contrasts strikingly with typical inflammatory bowel disorders such as ulcerative colitis and Crohn's disease. The coeliac lesion apparently reflects, in the main, immune-driven remodelling of mucosal architecture with only a minor inflammatory component - initially most likely resulting from innate signals. Complement split products might be one of several potential initial hits that lead to activation of lamina propria and epithelial cells with release of mediators such as interleukin-15. This cytokine appears to stimulate potentially pathogenic intraepithelial lymphocytes. In genetically susceptible individuals, such early innate events could turn into persistent pathogenic signalling with subsequent adaptive cellular and humoral immunopathology resulting in a chronic lesion. Nevertheless, mucosal homeostasis is surprisingly well preserved as signified by the remarkable dominance of plasma cells that produce dimeric immunoglobulin A as a basis for enhanced secretory immunity. This shows that the microvascular endothelium in the lesion largely maintains its 'gatekeeper' function for mucosal immune cells - in striking contrast to the 'promiscuous' situation in inflammatory bowel disease. Altogether, a two-signal model is emerging for the pathogenesis of coeliac disease - signal 1 generated by innate immunity and signal 2 by adaptive immunity. Hence, there is currently an increased focus on immune activation in the epithelial compartment rather than on changes in the microvasculature as a basis for classical inflammation.

How NKG2D ligands trigger autoimmunity?

The function of NK and CD8 T cells in the elimination of infected, transformed, or stressed cells occurs together with tolerance to self, a property that is essential to prevent autoimmunity. Inappropriate expression of NK receptor ligands, leading to activation of autoreactive effector cells, might therefore trigger or exacerbate autoimmunity. We review here some recent data on the activating receptor NKG2D and its MIC ligand, which are indicative of their detrimental roles in some autoimmune disorders.

[Genetics and immunopathogenics aspects of the celiac disease: a recent vision]

BACKGROUND

Celiac disease, or gluten-sensitive enteropathy, is a strongly inherited condition. Although the genetic association of CD with the DQ2 and DQ8 HLA haplotypes has been known for long, others HLA and non-HLA genes are also important in the development of the disease. Celiac disease results of the combined effect of different normally functioning genes' products. The tissue damage in celiac disease is immunologically mediated and several effector mechanisms are responsible for the disease expression. The interplay between genetic, immunological and environmental factors explains the large spectrum of clinical, histological and serological alterations observed in the different stages of the disease development, pointing out to the polygenic nature of celiac disease.

CONCLUSION

The recent advances in the understanding of the immunopathogenesis, genetics and diagnoses of celiac disease have allowed the revision of strict concepts and previous criteria and their adequation to the new evidences, aiming a better diagnostic and orientation to celiac patients and relatives.

Celiac disease-associated transglutaminase autoantibody target domains at diagnosis are age and sex dependent

The contribution of age and/or sex to the transglutaminase (tTG) autoantibody response in celiac disease (CD) is not known. To gain insights into transglutaminase humoral autoimmunity at CD diagnosis, our aim was to characterize the autoimmune response against three tTG constructs [(full-length tTG(a.a.1-687), tTG(a.a.227-687), and tTG(a.a.473-687)] and to investigate into its relationship with CD patients' age and sex. One hundred seventy-five newly diagnosed CD patients (115 females and 60 males), subdivided into different groups according to age and sex, were studied using a serum 35S-radioimmunoassay. We found that among full-length tTG autoantibody-positive CD subjects (175/175), 50.9% (89/175) and 83.4% (146/175) had autoantibodies against tTG(227-687) and tTG(473-687) domains, respectively. Female patients of less than 4 years expressed tTG(227-687)Abs in significantly higher percentage and mean autoantibody titers vs. all other groups investigated, and tTG(473-687)Abs in significantly higher titers with respect to adult female patients. Our data identify a subset of CD patients showing a strong humoral tTG immunoreactivity at diagnosis, thus suggesting that age and sex influence the anti-tTG autoantibody response.

Transforming growth factor-beta (TGF-beta) and tissue transglutaminase expression in the small intestine in children with coeliac disease

The production of cytokines from T cells and macrophages is of potential importance for the histological changes apparent in coeliac disease (CoD). Small intestinal biopsy specimens from children with CoD and disease control subjects were investigated for their content of cytokines and tissue transglutaminase (tTG). The transforming growth factor-beta1 (TGF-beta1) expression was increased in the lamina propria of children with villous atrophy. In contrast, TGF-beta3 was expressed at a higher level in the epithelium and the lamina propria of the disease control subjects. The tTG expression was increased in the small intestine of CoD patients as compared with that in subjects. Interleukin-4 (IL-4) was detected in the lamina propria of both CoD patients and controls, and some of the investigated biopsy specimens also showed IL-4 expression in the epithelium. We conclude that children with active CoD could have an altered expression of TGF-beta and tTG in the small intestine and that a disturbed regulation of TGF-beta may be of importance in the immune pathogenesis of CoD.

Candidate T cell epitopes of the human La/SSB autoantigen

OBJECTIVE

To identify T cell epitopes of the human La autoantigen involved in the generation of anti-Ro/La autoantibodies.

METHODS

Molecular techniques were used for HLA typing of 219 white patients with systemic lupus erythematosus and 125 white patients with primary Sjögren's syndrome. Anti-Ro/La antibody levels were measured by enzyme-linked immunosorbent assay. Peripheral blood mononuclear cell responses to an overlapping series of synthetic 15-mer peptides spanning the entire La sequence were examined in pools or individually in conventional 7-day proliferation assays.

RESULTS

HLA typing confirmed that the HLA-DR3/DQ2 haplotype is closely associated with the occurrence of anti-Ro/La antibodies, and that the frequency of HLA-DR1 and DR4 haplotypes is reduced among antibody-positive patients. We identified 3 regions of the La sequence likely to contain T cell epitopes and 1 peptide, La 49-63, that generated a low-level but clear-cut T cell proliferative response. The HLA restrictions of these responses mirrored the HLA association data from the cohort study. Among individuals who were HLA-DR3 positive, there was no difference between patients and controls in the proliferative response to the La 49-63 peptide.

CONCLUSION

Our data suggest that these are naive T cell responses, and that the identification of T cell epitopes involved in the generation of anti-Ro/La autoantibodies should focus on alternative candidate antigens.

Coeliac disease: the cause of the various associated disorders?

The advent of the endomysial antibody test has allowed the true association between coeliac disease and at least 12 other disorders to be established. There is evidence suggesting that coeliac disease is a cause of these disorders; a mechanism for this is proposed.

IgA anti-tissue transglutaminase: setting the stage for coeliac disease screening

Coeliac disease is triggered in genetically predisposed individuals by the ingestion of wheat and related cereals. Affected persons raise an intestinal mucosal T-cell response against the gluten fraction of these cereals. Furthermore, they produce characteristic circulating IgA antibodies to a self-antigen present in the extracellular matrix that can be detected on tissue sections. The positive predictive value of these endomysial, reticular or umbilical cord antibodies for coeliac disease comes close to 100%. Recently, the enzyme tissue transglutaminase was identified as the main, if not sole, endomysial autoantigen in coeliac disease. Enzyme-linked immunosorbent assay tests with tissue transglutaminase from guinea pig or the recombinant human enzyme have been established that allow a standardized and quantitative determination of IgA anti-tissue transglutaminase titres. While the published assay variants report high positive and negative predictive values for coeliac disease, they were applied to preselected patients from mostly single centres. Therefore, validation and in part cross-validation of a standardized assay based on guinea pig tissue transglutaminase in 38 European and non-European centres is timely. With a sensitivity of 90% and specificity of 96% relative to local diagnostic standards the assay performed well. Considering further improvement by the use of recombinant human tissue transglutaminase as the antigen and central re-evaluation of the local standards for confirmation of coeliac disease, this enzyme-linked immunosorbent assay promises to become the primary tool for non-invasive diagnosis, therapy control and screening of coeliac disease. However, with an estimated prevalence of 1:100-1:200 of mostly atypical and subclinical coeliacs in Western populations, we are confronted with the question of how far mass screening is ethically feasible and cost effective.

Role of anti-transglutaminase (anti-tTG), anti-gliadin, and anti-endomysium serum antibodies in diagnosing celiac disease: a comparison of four different commercial kits for anti-tTG determination

The aims of this study were: (1) to compare the diagnostic efficacy for celiac disease (CD) diagnosis of serum determination of anti-gliadin (AG) (IgA and IgG) and anti-endomysium (AE) with that of anti-transglutaminase (AtTG); and (2) to compare the accuracy of four different assays to measure AtTG. We studied 72 children: the histological diagnosis of CD was made in 38 cases and excluded in the remaining 34 children. In fasting sera we measured AE, AG-IgA and IgG, and AtTG, the latter with four different commercial kits (Eurospital, Medipan, Inova, Arnika). Moreover AtTG was measured in a group of 58 CD children after a gluten-free diet. AE was positive in all but 1 case of CD patients (sensitivity = 97%); false positive results were found in 1/34 controls (specificity = 97%). When a specificity of 95% was fixed, the sensitivities were 97% for AE, 83% for AG-IgA, and 63% for AG-IgG; the sensitivities of anti-tTG were 90, 84, 84, and 75% when measured with Eurospital, Medipan, Inova, and Arnika kits respectively. The new AtTG seems to be accurate enough to be proposed as a noninvasive diagnostic tool for CD diagnosis; the 4 kits analyzed showed similar diagnostic efficacy.

The high prevalence of autoantibodies to tissue transglutaminase in first-degree relatives of patients with type 1 diabetes is not associated with islet autoimmunity

OBJECTIVE

To determine the extent of celiac autoimmunity in type 1 diabetic patients and the overlap between islet and celiac autoimmunity in their nondiabetic relatives.

RESEARCH DESIGN AND METHODS

IgA antibodies to tissue transglutaminase were determined in serum taken from 433 type 1 diabetic patients and 1,442 nondiabetic first-degree relatives. Samples with transglutaminase antibodies above the 97.5th percentile of 347 schoolchildren were also assayed for IgA anti-endomysial antibodies (EMAs). Markers of islet autoimmunity (islet cell antibodies and autoantibodies to insulin, glutamate decarboxylase. and protein tyrosine phosphatase IA-2) had previously been measured in all relatives.

RESULTS

In the absence of known celiac disease, the prevalence of transglutaminase antibody levels above the 97.5th percentile of the schoolchildren was 13.4% in diabetic patients and 7.0% in nondiabetic relatives. ENMAs were found in addition to transglutaminase antibodies in 2.6% of probands and in 1.9% of first-degree relatives, but none of the schoolchildren. Transglutaminase antibodies were found to persist in 10 of 30 patients and in 30 of 59 relatives with follow-up samples taken at least 2 years after the initial sample. Of 186 nondiabetic relatives with islet autoantibodies, only 10 also had transglutaminase antibodies.

CONCLUSIONS

We found a high prevalence of celiac autoimmunity in patients and first-degree relatives of children with type 1 diabetes, but we found limited overlap between islet and celiac autoimmunity in nondiabetic relatives. The high prevalence of celiac autoimmunity may be explained by shared genetic susceptibility and identifies a population within which screening for the disease may be justified.

Antibodies to tissue transglutaminase: comparison of ELISA and immunoprecipitation assay in the presence and in the absence of calcium ions

Endomysial antibodies are characteristic of coeliac disease and tissue transglutaminase (tTG) has been identified as a major component of the endomysial antigen. tTG autoantibodies were measured in sera from patients with coeliac disease using ELISA based on guinea pig tTG and immunoprecipitation assay (IPA) based on 35S-labelled human tTG produced in an in vitro transcription/translation system. In addition, the effect of calcium ions on the interaction between tTG autoantibodies in the two assays was studied. Under standard (i.e. Ca2+-free) conditions, 36/39 (92%) coeliac sera were positive for IgA tTG antibodies by ELISA and 34/39 (87%) sera were positive by IPA. Comparison of ELISA and IPA results showed three sera positive by ELISA but negative by IPA and one serum which was positive by IPA but negative by ELISA. Bland and Altman analysis of the correlation between the ELISA and IPA showed that the results for 37 out of 39 samples were in the agreement. The results by ELISA carried out without and with Ca2+ were in good agreement (r=0.99; n=39). IPA using Ca2+ containing buffer detected fewer samples compared to IPA using standard assay buffer however the results of the two assays also showed a good agreement (r=0.93; n=39). Our studies confirm that antibodies to tTG are good markers of coeliac disease and indicate that the autoantibody binding sites on tTG are formed in a way which is essentially independent of Ca2+.

Interleukin 15 mediates epithelial changes in celiac disease

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Human genome search in celiac disease using gliadin cDNA as probe

Celiac disease is a wheat gliadin-promoted disorder that displays a complex genetic susceptibility associated with HLA-DQ2, and one or more unknown factor(s), possibly gliadin-like. The presence of mammalian proteins with partial gliadin similarity was suggested by transglutaminase-independent multi-tissue reactivity of gliadin-immunopurified antibodies from celiac patients. No non-plant sequence, however, was identified in gliadin peptide epitope searches of non-redundant and EST databanks via TBLASTN, BLASTP and FASTA, even at E values as high as 20. Therefore, an alpha-gliadin cDNA screen of human cDNA and genomic libraries was undertaken, an approach in keeping with positive human Northern and Southern analyses with the same probe. Four distinct cDNA clones were obtained, the most stringent of which (3.2 and 5.1 kb) were novel, and featured potential open reading frames with high gliadin domain II and domain IV homologies (BestFit quality scores >/=295 and 322, respectively, versus random value 126-127). Both were also homologous to ESTs. An additional 5' gliadin oligonucleotide screen identified the widely distributed cytoplasmic protein acyl coA hydrolase whose homology was restricted to the oligonucleotide probe (BestFit quality=215 versus 100 for random); and achaete-scute homologous protein, which displays particularly high gliadin domain II homology (BestFit quality 316 versus 111 for random). Genomic screening uncovered 16 positives, one of which was the ALR gene, whose similarity to three of gliadin's five domains (I, II and IV; BestFit quality 322-473 versus 121-154 for random) was remarkable. More extensive was novel genomic clone 2, with fragments hybridizing to cDNA probes approximating gliadin domains I, II+IV, V and the gliadin 5' untranslated region, and mapping by FISH to 19q13.11-13. 12. Two fragments were sequenced; one was exonic, as predicted by four different programs; and test oligonucleotides suggested widespread 4 and/or 2 kb mRNA expression, even at high stringency (t(m)-8.8 deg. C). Taken together, it is apparent that several genes with partial gliadin homology exist in the human genome. Many bear gliadin-like T-cell epitopes, are expressed in intestine and, like transglutaminase, are cytoplasmic. Glutamine to glutamic acid or other mutation within such epitopes followed by injury or infection-related release could explain enhanced disease susceptibility in affected families.

Antibody reactivity against human and guinea pig tissue transglutaminase in children with celiac disease

BACKGROUND

Highly discriminatory markers for celiac disease are needed to identify children with early mucosal lesions. The purposes of this study were to evaluate the clinical potential of circulating anti-tissue transglutaminase (tTG) immunoglobulin (Ig)A antibodies in the diagnosis of childhood celiac disease and to investigate the extent of autoreactivity of these antibodies.

METHODS

Included in this retrospective study were samples from 22 children with biopsy-verified celiac disease, 23 control subjects with disease, and 22 healthy control subjects without any known gastrointestinal or inflammatory disorders. An enzyme-linked immunosorbent assay (ELISA) was used to measure the serum levels of IgA antibodies specific for human and guinea pig tTGs. All samples were also analyzed for antibodies to gliadin and endomysium (EMA).

RESULTS

The concentrations of IgA specific for human and guinea pig tTGs correlated with the small intestinal villous structure and the serum levels of IgA EMA. The tTG ELISAs exhibited a high specificity and sensitivity for detection of untreated celiac disease. The human erythrocyte IgA tTG ELISA had the highest sensitivity (100%) and a specificity of 98%. The IgA EMA method had a sensitivity of 95% and the highest specificity (100%) of all tests.

CONCLUSIONS

Our results provide additional support to the concept that anti-tTG IgA antibodies can be used as a highly discriminatory serologic marker for celiac disease and that measurements of these autoreactive antibodies may in the future be used as an alternative to the EMA test.

Food-induced malabsorption syndromes

A syndrome of chronic diarrhea, vomiting, and failure to thrive was described 35 years ago. The syndrome was caused by damage in the jejunum after ingestion of cow's milk. Symptoms appeared in young infants shortly after introduction of cow's milk formula. Patients had moderate steatorrhea, decreased absorption of D-xylose, and, often, iron-deficiency anemia and hypoproteinemia. They had strong IgA and IgG antibodies to cow's milk. IgE antibodies to cow's milk were negative, as a rule. Indicators of cell-mediated immune reaction to cow's milk proteins were often positive. Patients were tolerant to cow's milk by the age of 3 years. Malabsorption was due to damage to the jejunal mucosa: Varying villus atrophy was associated with inflammation in surface epithelium and lamina propria. The epithelial cell renewal rate increased. Surface epithelial cells decreased in height, with short, furry microvilli and large aggregates of lysozymes. The number of intraepithelial lymphocytes was markedly increased, but normalized during cow's milk elimination. Most of these lymphocytes had alpha/beta T-cell receptors, and many were cytotoxic. Some specimens had an increase in gamma/delta T-cell receptor-bearing cells. In the lamina propria, CD4+ cells predominated, and some of them were activated. IgA- and IgM-containing cells were markedly increased during cow's milk exposure, but IgE cells were not abnormal. The density of eosinophils was moderately increased. Secretion of interferon-gamma by cells isolated from patients' intestines was markedly increased. Morphologic and immunologic findings suggest that T-cell-mediated reaction to proteins in cow's milk is present in the small intestines of patients with this syndrome and causes this enteropathy.

Circulating autoantibodies to tissue transglutaminase differentiate patients with dermatitis herpetiformis from those with linear IgA disease

BACKGROUND

Dermatitis herpetiformis (DH) is highly associated with celiac disease. Recently, tissue transglutaminase (tTG) was identified as the autoantigen of IgA antibodies in celiac disease. The prevalence of antibodies to tTG in DH patients is not known.

OBJECTIVE

The purpose of this study was to determine whether DH patients show circulating IgA autoantibodies to tTG, to compare their serum levels with those from patients with other subepidermal autoimmune bullous diseases, and to correlate levels of antibodies to tTG with the extent of small bowel disease.

METHODS

Sera were obtained from consecutive patients with DH (n = 11), linear IgA disease (n = 15), bullous pemphigoid (n = 10), and epidermolysis bullosa acquisita (n = 6) and were studied by indirect immunofluorescence on monkey esophagus and NaCl-split human skin. IgA reactivity to tTG was measured by enzyme-linked immunosorbent assay. The extent of mucosal involvement in jejunal biopsy specimens was assessed according to the grading of Marsh.

RESULTS

All untreated DH patients showed circulating IgA autoantibodies to tTG. One DH patient already undergoing therapy, the 15 patients with linear IgA disease, and all other controls revealed no autoantibodies to tTG. In addition, serum levels of IgA anti-tTG antibodies reflected the degree of histopathologic changes in jejunal mucosa from biopsy specimens in DH patients.

CONCLUSION

Our results show that circulating IgA autoantibodies to tTG are detectable in DH but not in linear IgA disease or other subepidermal autoimmune bullous diseases. The levels of IgA anti-tTG antibodies reflect the extent of histopathologic changes of the jejunal mucosa in DH.

Transglutaminase and coeliac disease: endomysial reactivity and small bowel expression

This study was aimed at verifying whether tissue transglutaminase (tTG) is the sole autoantigen eliciting anti-endomysial antibodies in coeliac disease (CoD) and investigating tTG expression in normal and coeliac mucosa. Twelve anti-endomysial-positive coeliac sera and 12 anti-endomysial-negative control sera (10 microl, diluted 1:5-1:400 in PBS pH 7.3) were preincubated with 10, 20 or 50 microg guinea pig liver tTG at 4 degrees C overnight. Monkey oesophagus tissue slides were then tested with tTG-preincubated and non-preincubated sera to search for IgA anti-endomysial reactivity by indirect immunofluorescence. Moreover, six sections of monkey oesophagus were incubated with an anti-tTG mouse MoAb, six sections with an anti-cytokeratin mouse MoAb and six sections with only 3% bovine serum albumin. Finally, endoscopic duodenal biopsy sections obtained from 12 patients affected by untreated CoD, six patients affected by treated CoD and 10 biopsied controls were immunohistochemically stained with a peroxidase-conjugated anti-tTG MoAb. Our results show that (i) preincubation with tTG abolished endomysial immunofluorescence in most, but not in all, coeliac sera; (ii) the incubation of anti-tTG MoAb with sections of monkey oesophagus resulted in an immunofluorescence staining pattern similar but not identical to that of anti-endomysial-positive coeliac sera; (iii) although tTG expression was present at muscularis mucosae and pericryptal fibroblast in both normal and coeliac mucosa, it was slightly more marked and evident in the latter. Although our absorption experiment was performed with guinea pig liver tTG, we confirm that tTG is the predominant antigen of endomysial antibodies, but we speculate that, at least in some patients, it is not the only one.

Duration of exposure to gluten and risk for autoimmune disorders in patients with celiac disease. SIGEP Study Group for Autoimmune Disorders in Celiac Disease

BACKGROUND & AIMS

The relationship between celiac disease and many autoimmune disorders has been explained by the sharing of a common genetic factor. In a multicenter national study, we examined the relationship between the prevalence of autoimmune disorders in celiac disease and the duration of exposure to gluten.

METHODS

Over a 6-month period, 909 patients with celiac disease (group A; mean age, 16.1 +/- 3.8 years; grouped according to age at diagnosis into three subgroups [group A1, <2 years; group A2, 2-10 years; and group A3, >10 years]), 1268 healthy controls (group B; mean age, 20.8 +/- 4.5 years), and 163 patients with Crohn's disease (group C; mean age, 28.8 +/- 10 years) were evaluated for the presence of autoimmune disorders.

RESULTS

Prevalence of autoimmune disorders in group A was significantly higher than in group B (14% vs. 2.8%; P < 0.000001) but not higher than in group C (12.9%). Prevalence of autoimmune disorders in celiac disease increased with increasing age at diagnosis: 5.1% in group A1, 17% in group A2, and 23.6% in group A3 (P = 0.000001). In group A3, the prevalence of autoimmune disorders was significantly higher than in group C. In a logistic regression model, age at diagnosis was the only significant predictor variable of the odds of developing an autoimmune disorder (r = 0.3; P < 0.000001).

CONCLUSIONS

Our data show for the first time that the prevalence of autoimmune disorders in celiac disease is related to the duration of exposure to gluten.

Antibodies to tissue transglutaminase as serologic markers in patients with dermatitis herpetiformis

Dermatitis herpetiformis is a gluten-sensitive disease with a symmetrically distributed blistering over extensor surfaces. The association with celiac disease is further supported by the high rate of immunoglobulin A autoantibodies to endomysium in patients with dermatitis herpetiformis, which are highly specific and sensitive indicators of celiac disease. Therefore, we determined immunoglobulin A antibodies to tissue transglutaminase, the recently discovered endomysial autoantigen in celiac disease, in patients with dermatitis herpetiformis and controls. Sera of 61 patients with dermatitis herpetiformis, as characterized by granular immunoglobulin A deposits in the subepidermal basement membrane and known endomysial antibody titers (determined by indirect immunofluorescence) as well as 84 control sera of patients with dermal or intestinal diseases unrelated to dermatitis herpetiformis, were analyzed for circulating immunoglobulin A antibodies to tissue transglutaminase by enzyme-linked immunosorbent assay. Immunoglobulin A anti-tissue transglutaminase titers in patients with dermatitis herpetiformis were significantly elevated above the controls. Furthermore, the immunoglobulin A anti-tTG titers showed a positive correlation with semiquantitative endomysial antibody data. Compared with endomysial antibodies, determination of immunoglobulin A anti-tissue transglutaminase reached a specificity and sensitivity of 97.6% and 89.1%. Patients with dermatitis herpetiformis have elevated immunoglobulin A autoantibodies to tissue transglutaminase, confirming its pathogenic relation with celiac disease and further supporting the usefulness of this novel assay for screening and therapy control.

Autoantibodies to tissue transglutaminase as predictors of celiac disease

BACKGROUND & AIMS

Immunoglobulin A (IgA) autoantibodies to endomysium (EMA) are highly specific and sensitive markers for celiac disease. Recently, we identified tissue transglutaminase (tTG) as the major if not sole endomysial autoantigen.

METHODS

An enzyme-linked immunosorbent assay (ELISA) was established to measure IgA anti-tTG titers in serum samples from 106 celiac patients with partial or subtotal villous atrophy, 43 celiac patients on a gluten-free diet, and 114 diseased and healthy controls. Results were correlated with clinical and histological data and with EMA titers.

RESULTS

In patients with biopsy-proven celiac disease consuming a normal, gluten-containing diet, 98.1% of the serum samples had elevated IgA titers against tTG, whereas 94.7% of the control sera were negative. IgA anti-tTG correlated positively with semiquantitative IgA EMA titers (r = 0.862; P < 0.0001).

CONCLUSIONS

An ELISA based on tTG allows diagnosis of celiac disease with a high sensitivity and specificity. IgA anti-tTG and IgA EMA show an excellent correlation, further confirming the enzyme as the celiac disease autoantigen. Because the assay is quantitative, not subjected to interobserver variation, and easy to perform, it will be a useful tool for population screening of a hitherto underdiagnosed disease.

Identification of the autoantigen of celiac disease

Tissue transglutaminase is demonstrated to be the unknown endomysial autoantigen by means of immunoprecipitations from a fibrosarcoma cell culture. A novel hypothesis for the pathogenesis of celiac disease is formulated: The mainly intracellular tissue transglutaminase is released from cells during wound healing where it aids in stabilizing the wound area by cross-linking a small set of extracellular matrix components.