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

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.

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 progression of coeliac disease: its neurological and psychiatric implications

The aim of the paper is to show the various neurological and psychiatric symptoms in coeliac disease (CD). CD is a T cell-mediated, tissue-specific autoimmune disease which affects genetically susceptible individuals after dietary exposure to proline- and glutamine-rich proteins contained in certain cereal grains. Genetics, environmental factors and different immune systems, together with the presence of auto-antigens, are taken into account when identifying the pathogenesis of CD. CD pathogenesis is related to immune dysregulation, which involves the gastrointestinal system, and the extra-intestinal systems such as the nervous system, whose neurological symptoms are evidenced in CD patients. A gluten-free diet (GFD) could avoid cerebellar ataxia, epilepsy, neuropathies, migraine and mild cognitive impairment. Furthermore, untreated CD patients have more symptoms and psychiatric co-morbidities than those treated with a GFD. Common psychiatric symptoms in untreated CD adult patients include depression, apathy, anxiety, and irritability and schizophrenia is also common in untreated CD. Several studies show improvement in psychiatric symptoms after the start of a GFD. The present review discusses the state of the art regarding neurological and psychiatric complications in CD and highlights the evidence supporting a role for GFD in reducing neurological and psychiatric complications.

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.