Genetic and immunological processes in the pathomechanism of gluten-sensitive enteropathy and associated metabolic bone disorders

Celiac disease, or gluten sensitive enteropathy is a relatively common disease of the jejunum, leading to malabsorption. It is an immune mediated disease, induced by gluten on the grounds of a specific genetic makeup. After gluten exposition immune processes are induced mainly by T-cells, causing typical intestinal and extra intestinal manifestations. The diagnosis of celiac disease is based on jejunal biopsy histology and the presence of antibodies against endomysium and tissue transglutaminase. Genetically, celiac disease is associated with HLA DQ2/DQ8. Strict gluten-free diet improves the clinical, histological and serological picture and remission may be achieved. In the etiopathogenesis of celiac disease several genetic and immunological mechanisms have been recognized in the recent years. Concerning accompanying diseases/extraintestinal manifestations, several disorders have been shown, including rheumatological diseases. In celiac disease, bone metabolic changes are more frequent compared to the prevalence of inflammatory join disorders. In this review, we aim to give an overview on various aspects of the genetic and immunological processes in the pathomechanism of gluten-sensitive enteropathy and associated metabolic bone disorders.     

Is celiac disease an autoimmune disorder?

Celiac disease, which results from an immune reaction to ingested cereal gluten proteins, has several autoimmune features. In particular, celiac disease patients produce highly disease specific IgA and IgG autoantibodies to tissue transglutaminase when they are on a gluten-containing diet, and they have small intestinal intraepithelial lymphocytes which can mediate direct cytotoxicity of enterocytes expressing MIC molecules in an antigen non-specific manner. Similar to typical autoimmune disorders, celiac disease has a multifactorial aetiology with complex genetics, and several autoimmune diseases are commonly presented by patients with celiac disease. Much has been learned about the immunology of celiac disease in recent years, and there is overwhelming evidence that the immune response to gluten is central to the pathogenesis. In light of this, the many autoimmune phenomena associated with celiac disease are thought-provoking, and they challenge us to rethink the boundaries between autoimmunity and immunopathology.     

Celiac disease and transglutaminase 2: a model for posttranslational modification of antigens and HLA association in the pathogenesis of autoimmune disorders

Posttranslational modification (PTM) of antigen is a way to break T-cell tolerance to self-antigens and promote autoimmunity. However, the precise mechanisms by which modifications would facilitate autoimmune T-cell responses and how they relate to particular autoimmune-associated MHC molecules remain elusive. Celiac disease is a T-cell mediated enteropathy with a strong HLA association where the immune response is directed mainly against deamidated cereal gluten peptides that have been modified by the enzyme transglutaminase 2. The disease is further characterized by autoantibodies to transglutaminase 2 that have extraordinary high disease specificity and sensitivity. There have been important advances in the knowledge of celiac disease pathogenesis, and these insights may be applicable to other autoimmune disorders where PTM plays a role. This insight gives clues for understanding the involvement of PTMs in other autoimmune diseases.     

Update on the evaluation and diagnosis of celiac disease

PURPOSE OF REVIEW: Our understanding of the pathophysiology of celiac disease has advanced with associated improvement in diagnostic modalities. Recent studies have placed the prevalence of celiac disease in Western populations at between 1:250 and 1:67. Celiac disease is common throughout the world and most cases go undiagnosed. Understanding the risk factors, clinical presentations and diagnostic modalities is necessary to identify and treat patients with this commonly misdiagnosed disorder. RECENT FINDINGS: Increased prevalence of celiac disease in individuals with autoimmune diseases, reduced bone mineral density and undiagnosed liver disease have been confirmed. However, celiac disease may not be associated with Down's syndrome or epilepsy. Evidence supports high sensitivity and specificity of endomysial- and tissue transglutaminase-based tests in most settings. In children, high or low tissue transglutaminase levels may preclude the need for duodenal biopsy. Cost-effectiveness studies suggest using tissue transglutaminase or endomysial initially, while distal duodenal or jejunal biopsy may confirm celiac disease in the absence of proximal changes. SUMMARY: There is insufficient evidence to support mass screening for celiac disease. However, case finding in individuals with risk factors for celiac disease is recommended. Further study is necessary to define diagnostic algorithms and target populations likely to benefit from testing.     

Pathogenesis and Clinical Significance of Liver Injury in Celiac Disease

Abnormalities of liver function are one of the manifold extraintestinal manifestations of celiac disease. Although the spectrum of liver manifestations associated with celiac disease is particularly wide, two main forms of liver damage namely, cryptogenic and autoimmune, appear to be strictly related to gluten-sensitive enteropathy. The most frequent finding is represented by a cryptogenic hypertransaminasemia, observed in about a half of untreated celiac patients, as an expression of a mild liver dysfunction with a histological picture of nonspecific reactive hepatitis (celiac hepatitis) reverting to normal after 6–12 months of a strict gluten-free diet. In a few cases, when celiac disease is diagnosed, a more severe liver injury, characterized by a cryptogenic chronic hepatitis or liver cirrhosis, is present. In these patients, liver damage can still improve after a gluten-free diet institution. Moreover, a close association between celiac disease and autoimmune liver disorders has been widely demonstrated. Indeed, celiac disease has been found in 3–7% of patients with primary biliary cirrhosis, in 3–6% with autoimmune hepatitis, and in 2–3% with primary sclerosing cholangitis. Differently from cryptogenic liver injury, autoimmune liver dysfunction, found in celiac disease, does not usually improve after a gluten-free diet. Presently, it is difficult to establish if the two main kinds of liver injury found in celiac disease (cryptogenic and autoimmune) are discrete entities with a different pathogenesis or if they are an expression of the same disorder where genetic factors and the duration of gluten exposure may determine the severity and the pattern of liver injury.     

Contribution of celiac disease autoantibodies to the disease process

Transglutaminase 2 is a multifunctional protein involved in cellular adhesion. Moreover, transglutaminase 2 has been identified as the autoantigen in celiac disease, and in untreated celiac disease, in addition to being present in the serum, the transglutaminase 2-targeted autoantibodies are bound to their antigen in the basement membrane underlining the small-bowel mucosal epithelium. Furthermore, the disease-specific transglutaminase 2-targeted autoantibodies have been experimentally shown to exert various biological effects on different cell types. Using Caco-2 intestinal epithelial cells, it has now also been demonstrated that serum transglutaminase 2-targeted autoantibodies from untreated celiac patients inhibit the adhesion of these cells. These findings provide an important direction for future research to improve our general understanding of celiac disease pathogenesis and especially the role of the disease-specific autoantibodies during the progression of the disorder.     

Celiac disease: diagnosis,autoimmune mechanisms and treatment

Celiac disease is a systemic autoimmune disorder triggered by the ingestion of gluten found in wheat and related grains. Once considered rare, celiac disease is now thought to affect more than one in 100 individuals, and is commonly associated with other autoimmune disorders. It predisposes patients to an increased risk of malignancy if left untreated. Celiac disease is HLA restricted as only HLA-DQ2 and -DQ8 are able to bind deamidated gluten with sufficient affinity to trigger an immune response. Both cellular and humoral immune activation occur, leading to local tissue damage and antibody formation. These antibodies, primarily to tissue transglutaminase, are the basis for highly accurate serologic testing, although the gold standard for celiac disease diagnosis remains small intestinal biopsy. Currently, the only treatment for celiac disease is a life-long gluten-free diet, although multiple novel therapeutic modalities are being studied. Although most individuals with celiac disease respond completely to gluten withdrawal, 10–20% have persistent symptoms at some point during their course and less than 1% develop refractory celiac disease, an entity of substantial morbidity.     

Diagnostic sérologique de la maladie cœliaque

Screening studies using high-sensitivity and specificity markers indicate a prevalence of celiac disease of up to 1% in European and North-American populations. Celiac disease is a frequent condition that has become an important public health issue. Yet the majority of cases remain undiagnosed due to the polymorphism of its clinical manifestations. The new insight in the pathogenesis of celiac disease has lead to the development of new diagnostic tools. Early screening of symptomatic patients and pre-identified at-risk groups significantly improves the quality of life while reducing morbidity and mortality. However, prophylactic benefits of early diagnosis by assessing the general population have not been shown in any study. French and Northern American scientific societies have introduced serological testing in their newly revised strategies to diagnose celiac disease. Older markers judged insufficiently accurate like anti-gliadin and anti-reticulin antibodies have recently been withdrawn from the list of reimbursed medical expenses in France. Anti-endomysium and tissue transglutaminase IgA antibodies have proven to be at this day the most sensitive and specific markers for the diagnosis and follow-up of patients on gluten-free diet, at the exception of IgA-deficient patients. Assays testing for IgG antibodies are recommended upon IgA-deficiency. Although very accurate, a better standardisation of current assays may enable serological testing to replace in a near future histological confirmation brought by small bowel biopsies which remains today the gold standard test to diagnose celiac disease. Indeed, serological testing represents and attractive alternative as it is less invasive, less expansive, laboursaving and more objective in interpretation.     

Contribution of celiac disease autoantibodies to the disease process

Evaluation of: Teesalu K, Panarina M, Uibo O, Uibo R, Utt M. Autoantibodies from patients with celiac disease inhibit transglutaminase 2 binding to heparin/heparan sulfate and interfere with intestinal epithelial adhesion. Amino Acids doi:10.1007/s00726-011-1020-1 (2011) (Epub ahead of print).

Transglutaminase 2 is a multifunctional protein involved in cellular adhesion. Moreover, transglutaminase 2 has been identified as the autoantigen in celiac disease, and in untreated celiac disease, in addition to being present in the serum, the transglutaminase 2-targeted autoantibodies are bound to their antigen in the basement membrane underlining the small-bowel mucosal epithelium. Furthermore, the disease-specific transglutaminase 2-targeted autoantibodies have been experimentally shown to exert various biological effects on different cell types. Using Caco-2 intestinal epithelial cells, it has now also been demonstrated that serum transglutaminase 2-targeted autoantibodies from untreated celiac patients inhibit the adhesion of these cells. These findings provide an important direction for future research to improve our general understanding of celiac disease pathogenesis and especially the role of the disease-specific autoantibodies during the progression of the disorder.     

Celiac disease and endocrine autoimmunity – the genetic link

Celiac disease is a small intestinal inflammatory disease with autoimmune features that is triggered and maintained by the ingestion of the storage proteins (gluten) of wheat, barley and rye. The prevalence of celiac disease is increased in patients with monoglandular and/or polyglandular autoimmunity and their relatives. Between 10 and 30% of patients with celiac disease are thyroid and/or type 1 diabetes antibody positive, while around 5 to 7% of patients with autoimmune thyroid disease and/or type 1 diabetes are IgA anti-tissue transglutaminase antibody positive. The close relationship between celiac disease and endocrine autoimmunity is largely explained by sharing a common genetic background. The HLA antigens DQ2 (DQA1*0501-DQB1*0201) and/or DQ8 (DQA1*0301-DQB1*0302), that are tightly linked to DR3 and DR4, respectively, are the major common genetic predisposition. Moreover, functional single nucleotide polymorphisms of various genes that are involved in immune regulation have been identified as “overlap” susceptibility genes for both celiac disease and monoglandular or polyglandular autoimmunity. While plausible, it remains to be established how far a gluten free diet may prevent or ameliorate glandular autoimmunity. In conclusion, all patients with celiac disease should be screened for type 1 diabetes and/or autoimmune thyroid disease. Conversely, patients with the above autoimmune endocrine disorders should be also screened for celiac disease.     

Diagnostic immunology in celiac disease

Serum autoantibodies to transglutaminase and endomysium are found in the majority of patients with celiac disease, an autoimmune multisystem disorder affecting approximately 1% of Western and Middle-Eastern populations. Detection of these antibodies plays a crucial role in the diagnosis of celiac disease. The aim of this review is to summarize recent publications in this field, with particular focus on the applications and limitations of celiac autoantibody testing in routine clinical practice.     

A Difficult and Rare Diagnosis of Autoimmune Enteropathy in a Patient Affected by Down Syndrome

Patients with Down syndrome are more susceptible to autoimmune pathologies, in particular endocrine or digestive diseases such as celiac disease. Autoimmune enteropathy is another form of digestive autoimmune disease, non-gluten-dependant, more often diagnosed in male neonates with immunodysregulation and polyendocrinopathy such as the Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked syndrome. It also exists in the adult, but this pathology is less known and therefore frequently under-diagnosed. Clinical manifestations are similar to celiac disease, but not improved after a gluten-free diet. Autoimmune enteropathy is frequently associated with other autoimmune diseases, such as thyroiditis, myasthenia gravis, lupus or immune deficiencies, as Common Variable Immunodeficiency. Pathological analysis of intestinal biopsies can frequently distinguish autoimmune enteropathy and celiac disease. Autoimmune enteropathy usually has an important lymphoplasmacytic infiltration of the mucosa and a lack of intraepithelial lymphocytes in the gastrointestinal mucosal surface, while celiac disease usually has a polymorph infiltration of the mucosa and an important intraepithelial lymphocytes infiltration. Nevertheless, the two pathological patterns may overlap. Here we report the first case of a patient with Down syndrome associated to autoimmune enteropathy (initially diagnosed as celiac disease), chronic pancreatitis and cutaneous lupus erythematosus. Even if autoimmune pathologies are much more common in patients with Down syndrome, we would like to report on this rare and original association found in our patient.     

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.     

Celiac disease: diagnostic criteria in progress

Until a few years ago, celiac disease (CD) was thought to be a rare food intolerance that was confined to childhood and characterized by severe malabsorption and flat intestinal mucosa. Currently, CD is regarded as an autoimmune disorder that is common in the general population (affecting 1 in 100 individuals), with possible onset at any age and with many possible presentations. The identification of CD is challenging because it can begin not only with diarrhea and weight loss but also with atypical gastrointestinal (constipation and recurrent abdominal pain) and extra-intestinal symptoms (anemia, raised transaminases, osteoporosis, recurrent miscarriages, aphthous stomatitis and associated autoimmune disorders), or it could be completely symptomless. Over the last 20 years, the diagnostic accuracy of serology for CD has progressively increased with the development of highly reliable tests, such as the detection of IgA tissue transglutaminase and antiendomysial and IgG antideamidated gliadin peptide antibodies. The routine use of antibody markers has allowed researchers to discover a very high number of 'borderline' cases, characterized by positive serology and mild intestinal lesions or normal small intestine architecture, which can be classified as potential CD. Therefore, it is evident that the 'old celiac disease' with flat mucosa is only a part of the spectrum of CD. It is possible that serology could identify CD in its early stages, before the appearance of severe intestinal damage. In cases with a positive serology but with mild or absent intestinal lesions, the detection of HLA-DQ2 and HLA-DQ8 can help reinforce or exclude the diagnosis of gluten sensitivity.     

An Update on the Diagnostics of Celiac Disease

In celiac disease, highly sensitive and specific serum endomysial and transglutaminase 2 antibody tests are widely used in identifying patients for diagnostic endoscopy and small-bowel biopsy. In addition, the recently developed deamidated gliadin peptide antibody tests show promise in celiac disease diagnostics. In view of these apparent problems attending the diagnostic gold standard, gluten-induced small-bowel mucosal villous atrophy with crypt hyperplasia, other diagnostic approaches beyond conventional histology have been introduced. Furthermore, the diagnostic criteria for celiac disease are currently under revision with an eye also to noninvasive diagnostic strategies.     

An update on the diagnostics of celiac disease

In celiac disease, highly sensitive and specific serum endomysial and transglutaminase 2 antibody tests are widely used in identifying patients for diagnostic endoscopy and small-bowel biopsy. In addition, the recently developed deamidated gliadin peptide antibody tests show promise in celiac disease diagnostics. In view of these apparent problems attending the diagnostic gold standard, gluten-induced small-bowel mucosal villous atrophy with crypt hyperplasia, other diagnostic approaches beyond conventional histology have been introduced. Furthermore, the diagnostic criteria for celiac disease are currently under revision with an eye also to noninvasive diagnostic strategies.     

Celiac disease prevalence and predisposing-HLA in a cohort of 93 Williams-Beuren syndrome patients

Williams-Beuren syndrome is considered to be at increased risk for celiac disease, as for recent literature data and celiac disease guidelines, despite pathogenic mechanisms are still unclear. Our study analyzed the prevalence of autoimmune disorders, HLA DQ2 and/or DQ8 haplotypes, of transglutaminase antibodies and of diagnosis of celiac disease in a cohort of 93 Williams-Beuren syndrome's patients (mean age 21.26 years). Our study showed an increased prevalence of celiac disease equal to 10.8% (10/93 patients). We did not find a significant different frequency of predisposing HLA in subjects with Williams-Beuren syndrome compared to literature data in the general population (49.5% vs. 42.9%, with p > .1), nor a susceptibility to autoimmunity. This suggests that the increased prevalence of celiac disease in Williams-Beuren syndrome cannot be ascribed to HLA haplotype and may be related to other factors that still need to be identified in these patients.     

Celiac disease: from gluten to autoimmunity

Celiac disease, also known as gluten-sensitive enteropathy and nontropical sprue, is a prevalent autoimmune disorder that is triggered by the ingestion of wheat gluten and related proteins of rye and barley in genetically susceptible individuals. The immune response in celiac disease involves the adaptive, as well as the innate, and is characterized by the presence of anti-gluten and anti-transglutaminase 2 antibodies, lymphocytic infiltration in the epithelial membrane and the lamina propria, and expression of multiple cytokines and other signaling proteins. The disease leads to inflammation, villous atrophy, and crypt hyperplasia in the small intestine. In addition to the intestinal symptoms, celiac disease is associated with various extra-intestinal complications, including bone and skin disease, anemia, endocrine disorders, and neurologic deficits. Gluten-free diet is currently the only effective mode of treatment for celiac disease, but better understanding of the mechanism of the disease is likely to add other choices for therapy in the future.     

Candida albicans in celiac disease: A wolf in sheep’s clothing

Candida albicans is a commensal fungus with a potential pathogenicity and celiac disease is an autoimmune condition. Both share multiple pathophysiological junctions, including serological markers against cell-wall proteins of Candida, anti-gliadin antibodies are positive in both entities, gluten and a candidal virulence factor share sequence similarity and the autoantigen of celiac disease, the tissue transglutaminase, is pivotal in Candida albicans commensalism and hostile behavior and its covalently cross linked products are stable and resistant to breakdown in the two entities. Those autoimmune/infectious cross roads are the basis for the hypothesis that Candida albicans is an additional environmental factor for celiac disease autoimmunogenesis.     

IgA cross-reactivity between a nuclear autoantigen and wheat proteins suggests molecular mimicry as a possible pathomechanism in celiac disease

Celiac disease patients display IgA antibody reactivity to wheat as well as to human proteins. We used serum IgA from celiac patients and, for control purposes, from patients with Crohn's disease, ulcerative colitis and from healthy individuals to identify celiac disease-specific IgA autoantigens in nitrocellulose-blotted extracts from various human cell types (epithelial, endothelial, intestinal cells, fibroblasts). The pattern, recognition intensity and time course of IgA autoreactivity was monitored using serial serum samples obtained from celiac children before and under gluten-free diet. By immunoblot inhibition and subcellular (cytosolic, nuclear) cell fractionation we identified a 55 kDa nuclear autoantigen expressed in intestinal, endothelial cells and in fibroblasts which was recognized by IgA antibodies of approximately half of the celiac disease patients and cross-reacted with wheat proteins. IgA reactivity to the 55 kDa autoantigen disappeared during gluten-free diet and was inhibited after pre-absorption of sera with wheat proteins but not with tissue transglutaminase, previously reported as the unique celiac disease-specific autoantigen. In conclusion, we defined a novel 55 kDa celiac disease-specific nuclear IgA autoantigen which shares epitopes with wheat proteins and which is different from tissue transglutaminase and calreticulin. Although the newly defined autoantigen was recognized much less frequently than tissue transglutaminase, our data suggest molecular mimicry between wheat and human proteins as a possible pathomechanism for the induction and/or maintenance of mucosal tissue damage in celiac disease.