Coeliac disease: the paradox of diagnosing a food hypersensitivity disorder with autoantibodies

Serum antibodies to the autoantigen transglutaminase 2 (TG2) are increasingly harnessed to diagnose coeliac disease. Diagnostic guidelines for children give recommendation for a no-biopsy-based diagnosis through detection of high amounts of IgA anti-TG2 antibodies in serum with confirmation of positivity in a separate blood sample by characteristic autoantibody-staining of tissue. While measurement of IgA anti-TG2 also is important in the diagnostic workup of adults, the adult guidelines still mandate examination of gut biopsies. This requirement might well change in the future, as might the necessity for confirming autoantibody positivity by tissue staining. The key role of autoantibody serology for diagnosis of coeliac disease is paradoxical. Coeliac disease was considered, and still can be considered, a food intolerance disorder where autoantibodies at face value are out of place. The immunological mechanisms underlying the formation of autoantibodies in response to gluten exposure have been dissected. This review presents the current insights demonstrating that the autoantibodies in coeliac disease are intimately integrated in the maladapted immune response to gluten.

Review article: Diagnosis of coeliac disease: a perspective on current and future approaches

Diagnostics will play a central role in addressing the ongoing dramatic rise in global prevalence of coeliac disease, and in deploying new non-dietary therapeutics. Clearer understanding of the immunopathogenesis of coeliac disease and the utility of serology has led to partial acceptance of non-biopsy diagnosis in selected cases. Non-biopsy diagnosis may expand further because research methods for measuring gluten-specific CD4+ T cells and the acute recall response to gluten ingestion in patients is now relatively straightforward. This perspective on diagnosis in the context of the immunopathogenesis of coeliac disease sets out to highlight current consensus, limitations of current practices, gluten food challenge for diagnosis and the potential for diagnostics that measure the underlying cause for coeliac disease, gluten-specific immunity.

Antibody Responses to Transglutaminase 3 in Dermatitis Herpetiformis: Lessons from Celiac Disease

Dermatitis herpetiformis (DH) is the skin manifestation of celiac disease, presenting with a blistering rash typically on the knees, elbows, buttocks and scalp. In both DH and celiac disease, exposure to dietary gluten triggers a cascade of events resulting in the production of autoantibodies against the transglutaminase (TG) enzyme, mainly TG2 but often also TG3. The latter is considered to be the primary autoantigen in DH. The dynamics of the development of the TG2-targeted autoimmune response have been studied in depth in celiac disease, but the immunological process underlying DH pathophysiology is incompletely understood. Part of this process is the occurrence of granular deposits of IgA and TG3 in the perilesional skin. While this serves as the primary diagnostic finding in DH, the role of these immunocomplexes in the pathogenesis is unknown. Intriguingly, even though gluten-intolerance likely develops initially in a similar manner in both DH and celiac disease, after the onset of the disease, its manifestations differ widely.

Emergence of an adaptive immune paradigm to explain celiac disease: a perspective on new evidence and implications for future interventions and diagnosis

INTRODUCTION

Recent patient studies have shown that gluten-free diet is less effective in treating celiac disease than previously believed, and additionally patients remain vulnerable to gluten-induced acute symptoms and systemic cytokine release. Safe and effective pharmacological adjuncts to gluten-free diet are in preclinical and clinical development. Clear understanding of the pathogenesis of celiac disease is critical for drug target identification, establishing efficacy endpoints and to develop non-invasive biomarkers suitable to monitor and potentially diagnose celiac disease.

AREAS COVERED

The role and clinical effects of CD4+ T cells directed against deamidated gluten in the context of an "adaptive immune paradigm" are reviewed. Alternative hypotheses of gluten toxicity are discussed and contrasted. In the context of recent patient studies, implications of the adaptive immune paradigm for future strategies to prevent, diagnose, and treat celiac disease are outlined.

EXPERT OPINION

Effective therapeutics for celiac disease are likely to be approved and necessitate a variety of new clinical instruments and tests to stratify patient need, monitor remission, and confirm diagnosis in uncertain cases. Sensitive assessments of CD4+ T cells specific for deamidated gluten are likely to play a central role in clinical management, and to facilitate research and pharmaceutical development.

T Cell Response Toward Tissue-and Epidermal-Transglutaminases in Coeliac Disease Patients Developing Dermatitis Herpetiformis

The reason why only few coeliac patients develop the cutaneous manifestation of the disease, named dermatitis herpetiformis (DH), is still unknown. Epidermal transglutaminase (TG3) has been described as the main autoantigen of humoral immunity in DH but the mechanisms leading to this autoimmune response remain obscure. Here we characterized T cells from skin, gut and peripheral blood of DH and coeliac disease (CD) patients, evaluated the impact of the gluten-free diet on circulating T lymphocytes’ phenotype and investigated antigen specific T cell response toward epidermal and tissue transglutaminase (TG2). DH patients showed an increased frequency of skin-derived T cells producing TNFα when compared to CD patients. Moreover, circulating T cells producing TNFα and IL-17A positively correlated with clinical score of skin disease activity and decreased after gluten-free diet. Finally, TG2 and TG3-specific T cells resulted more reactive to antigens stimulation in DH patients and showed cross reactivity toward the two autoantigens in both the group of patients. Our data suggest a role of TNFα and IL-17A producing cells in the development of DH and, for the first time, show the existence of a crossed T cell response toward the two transglutaminases isoforms, thus suggesting new insights on T cells role in skin damage.

Coeliac Disease Pathogenesis: The Uncertainties of a Well-Known Immune Mediated Disorder

Coeliac disease is a common small bowel enteropathy arising in genetically predisposed individuals and caused by ingestion of gluten in the diet. Great advances have been made in understanding the role of the adaptive immune system in response to gluten peptides. Despite detailed knowledge of these adaptive immune mechanisms, the complete series of pathogenic events responsible for development of the tissue lesion remains less certain. This review contributes to the field by discussing additional mechanisms which may also contribute to pathogenesis. These include the production of cytokines such as interleukin-15 by intestinal epithelial cells and local antigen presenting cells as a pivotal event in the disease process. A subset of unconventional T cells called gamma/delta T cells are also persistently expanded in the coeliac disease (CD) small intestinal epithelium and recent analysis has shown that these cells contribute to pathogenic inflammation. Other unconventional T cell subsets may play a local immunoregulatory role and require further study. It has also been suggested that, in addition to activation of pathogenic T helper cells by gluten peptides, other peptides may directly interact with the intestinal mucosa, further contributing to the disease process. We also discuss how myofibroblasts, a major source of tissue transglutaminase and metalloproteases, may play a key role in intestinal tissue remodeling. Contribution of each of these factors to pathogenesis is discussed to enhance our view of this complex disorder and to contribute to a wider understanding of chronic immune-mediated disease.

T Cells in Celiac Disease

Celiac disease is a human T cell-mediated autoimmune-like disorder caused by exposure to dietary gluten in genetically predisposed individuals. This review will discuss how CD4 T cell responses directed against an exogenous Ag can cause an autoreactive B cell response and participate in the licensing of intraepithelial lymphocytes to kill intestinal epithelial cells. Furthermore, this review will examine the mechanisms by which intraepithelial cytotoxic T cells mediate tissue destruction in celiac disease.

Similar Responses of Intestinal T Cells From Untreated Children and Adults With Celiac Disease to Deamidated Gluten Epitopes

BACKGROUND & AIMS

Celiac disease is a chronic small intestinal inflammatory disorder mediated by an immune response to gluten peptides in genetically susceptible individuals. Celiac disease is often diagnosed in early childhood, but some patients receive a diagnosis late in life. It is uncertain whether pediatric celiac disease is distinct from adult celiac disease. It has been proposed that gluten-reactive T cells in children recognize deamidated and native gluten epitopes, whereas T cells from adults only recognize deamidated gluten peptides. We studied the repertoire of gluten epitopes recognized by T cells from children and adults.

METHODS

We examined T-cell responses against gluten by generating T-cell lines and T-cell clones from intestinal biopsies of adults and children and tested proliferative response to various gluten peptides. We analyzed T cells from 14 children (2-5 years old) at high risk for celiac disease who were followed for celiac disease development. We also analyzed T cells from 6 adults (26-55 years old) with untreated celiac disease. All children and adults were positive for HLA-DQ2.5. Biopsies were incubated with gluten digested with chymotrypsin (modified or unmodified by the enzyme transglutaminase 2) or the peptic-tryptic digest of gliadin (in native and deamidated forms) before T-cell collection.

RESULTS

Levels of T-cell responses were higher to deamidated gluten than to native gluten in children and adults. T cells from children and adults each reacted to multiple gluten epitopes. Several T-cell clones were cross-reactive, especially clones that recognized epitopes from γ-and ω-gliadin. About half of the generated T-cell clones from children and adults reacted to unknown epitopes.

CONCLUSIONS

T-cell responses to different gluten peptides appear to be similar between adults and children at the time of diagnosis of celiac disease.

The Role of T-Cell Subsets in Chronic Inflammation in Celiac Disease and Inflammatory Bowel Disease Patients: More Common Mechanisms or More Differences?

Background

Chronic intestinal inflammation due to noninfectious causes represents a growing health issue all over the world. Celiac disease as well as inflammatory bowel diseases (IBD) like Crohn's disease and ulcerative and microscopic colitis involve uncontrolled T-cell activation and T-cell-mediated damage as common denominators. Therefore, diagnosis and treatment decisions clearly benefit from the knowledge of the intricacies of the systemic and the local T-cell activity.

Summary

Depending on the cytokine milieu, CD4⁺ T cells can differentiate into proinflammatory T helper 1 (Th1), anti-inflammatory Th2, antimicrobial Th17, pleiotropic Th9, tissue-instructing Th22 cells, and in the regulatory compartment forkhead box protein 3⁺ Treg, suppressive Tr1 or Th3 cells. Additionally, follicular Th cells provide B-cell help in antibody class switching; cytotoxic CD8⁺ T cells target virus-infected or tumor cells. This review discusses our current knowledge on the contribution of defined T-cell subpopulations to establishing and maintaining chronic intestinal inflammation in either of the above entities. It also puts emphasis on the differences in the prevalence of these diseases between Eastern and Western countries.

Key Messages

In celiac disease, the driving role of T cells in the lamina propria and in the epithelium mainly specific for two defined antigens is well established. Differences in genetics and lifestyle between Western and Eastern countries were instrumental in understanding underlying mechanisms. In IBD, the vast amount of potential antigens and the corresponding antigen-specific T cells makes it unlikely to find universal triggers. Increased mucosal CD4⁺ regulatory T cells in all four entities fail to control or abrogate local inflammatory processes. Thus, prevailing differences in the functional T-cell subtypes driving chronic intestinal inflammation in celiac disease and IBD at best allow some overlap in the treatment options for either disease.

Characterisation of tissue transglutaminase-reactive T cells from patients with coeliac disease and healthy controls

Previous studies have shown evidence for T lymphocytes specific for tissue transglutaminase (tTG) in the periphery of coeliac disease (CD) patients. These cells could play a role in disease pathogenesis and may be involved in providing help for the production of anti-tTG autoantibodies. The objective of this study was to further investigate the presence of tTG-specific T cells in patients with treated and untreated CD, and normal controls. Positive proliferative responses to three different commercial tTG antigens were detected in all groups tested, occurring more frequently and at higher levels in untreated CD patients. The addition of antibodies to HLA-DQ and HLA-DR caused a significant reduction in the proliferative response to tTG. T cell lines specific for tTG and composed predominantly of CD4-positive T cells were generated from responsive CD and control individuals, and were found to produce large amounts of interferon-γ, as well as interleukins 10, 17A, and 21.

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.

Tissue-infiltrating lymphocytes analysis reveals large modifications of the duodenal "immunological niche" in coeliac disease after gluten-free diet

OBJECTIVES

The role of T lymphocytes in the pathogenesis of Celiac disease (CD) is well established. However, the mechanisms of T-cell involvement remain elusive. Little is known on the distribution of T subpopulations: T-regulatory (Treg), Th17, CD103, and CD62L cells at disease onset and after gluten-free diet (GFD). We investigated the involvement of several T subpopulations in the pathogenesis of CD.

METHODS

We studied T cells both in the peripheral blood (PB) and the tissue-infiltrating lymphocytes (TILs) from the mucosa of 14 CD patients at presentation and after a GFD, vs. 12 controls.

RESULTS

Our results extend the involvement of Treg, Th1, and Th17 cells in active CD inflammation both in the PB and at the TILs. At baseline, Tregs, Th1, and Th17 cells are significantly higher in active CD patients in TILs and PB. They decreased after diet. Moreover, CD62L+ TILs were increased at diagnosis as compared with GFD patients.

CONCLUSIONS

Our data show significant modifications of the above-mentioned subpopulations both in the PB and TILs. The increase of suppressive Tregs in active CD both in the PB and TILs is intriguing. T lymphocytes are known to have a crucial role in the pathogenesis of CD. We have shown that gluten trigger results in systemic recruitment of T lymphocytes, the unbalance between pro-inflammatory and anti-inflammatory populations and the increase of CD62L+ T cells in TILs. Our results delineate a more complete picture of T-cell subsets in active vs. GFD disease. Our data of T-cell subpopulations, combined with known data on cytokine production, support the concept that duodenal micro-environment acts as an immunological niche and this recognition may have an important role in the diagnosis, prognosis and therapeutical approach of CD.

The function of tissue transglutaminase in celiac disease

Celiac disease is a chronic small bowel disorder caused by an abnormal immune response to an array of epitopes of wheat gluten and related proteins of rye and barley in genetically susceptible individuals who express the HLA-DQ2/-DQ8 haplotype. Gluten peptides are efficiently presented by celiac disease-specific HLA-DQ2- and HLA-DQ8-positive antigen presenting cells to CD4(+) T-cells that, once activated, drive a T helper cell type 1 response leading to the development of the typical celiac lesion-villous atrophy, crypt hyperplasia and intraepithelial and lamina propria infiltration of inflammatory cells. Tissue transglutaminase (tTG) is a calcium dependent ubiquitous enzyme which catalyses posttranslational modification of proteins and is released from cells during inflammation. tTG is suggested to exert at least two crucial roles in celiac disease: as a deamidating enzyme, that can enhance the immunostimulatory effect of gluten, and as a target autoantigen in the immune response. Since glutamine-rich gliadin peptides are excellent substrates for tTG, and the resulting deamidated and thus negatively charged peptides have much higher affinity for the HLA-DQ2 and HLA-DQ8 molecules, the action of tTG is believed to be a key step in the pathogenesis of celiac disease. This review is focused on the function of tTG in celiac disease, although it also deals with novel advances in tTG-based therapies.

Cholesterol: An Inflammatory Compound

Obesity is one of the main rising causes of health problems in modern society and is correlated to type 2 diabetes mellitus, hypertension, heart disease and atherosclerosis. Bacterial products, endogenous substances such as oxidized LDL (ox-LDL) and heat shock proteins mediate activation of Toll-like receptors and reinforce the view that the innate immune system plays a key role in the genesis of atherosclerosis. In addition, natural killer T (NKT) cells respond to lipids presented via CD1d on APCs, and may also be able to affect atherosclerosis. All the main cell types involved in atherosclerosis such as endothelial cells, macrophages, T cells, smooth muscle cells and platelets express proinflammatory cytokines. In addition, CD4 ligation triggers the expression of adhesion molecules, cytokines and matrix metalloprotinease. IL-6 cytokines travels to the liver where it elicits acute phase response resolving in the release of serum amyloid-A C-reactive protein, fibrogen and plasminogen activator inhibitor-1. Therefore increasing body fat mass is associated with high levels of inflammatory cytokines such as IL-1 and TNF. In this study we revisit the interrelationship between fat and inflammation.

Characterization of gliadin-specific Th17 cells from the mucosa of celiac disease patients

OBJECTIVES

Celiac disease (CD) is a disorder characterized by a deregulated immune response to ingested wheat gluten and related cereal proteins in susceptible individuals. It has been considered that the onset of CD is mediated by a skewed Th1 response. However, the participation of Th17 cells in the pathogenesis of the disease, a key cell population in other autoimmune disorders, has not been studied in detail. We have investigated the presence of Th17 cells in the mucosa of active CD patients and their functional implications in the pathogenesis of the disease.

METHODS

T cells obtained from duodenum biopsies from 15 untreated patients and 11 control individuals were characterized by flow cytometry, immunoassays, and real-time PCR.

RESULTS

We found gliadin-specific CD4(+) interleukin (IL)-17A-producing T cells in the mucosa of CD patients with a phenotype consisting of TCR (T-cell receptor)αβ(+) CD45RO(+) CD161(+) CCR6(+) (C-C chemokine receptor type 6) and IL-23R(+). Functional analysis showed that Th17 cells from CD patients are different from those of control individuals in terms of cytokines production. Th17 cells from CD patients, but not from controls, simultaneously express transforming growth factor-β (TGFβ). Th17 CD cells also produce interferon-γ (IFNγ), IL-21, and IL-22. The analysis of the transcription factors revealed a high expression of interferon regulatory factor-4 as a feature of gliadin-specific cells from CD patients with respect to controls.

CONCLUSIONS

Gliadin-specific Th17 cells are present in the mucosa of CD patients having a dual role in the pathogenesis of the disease as they produce proinflammatory cytokines (such as IL-17, IFNγ, IL-21), mucosa-protective IL-22, and regulatory TGFβ, which actively modulates IL-17A production by T cells in the celiac mucosa.