Lack of cellular and humoral immunological responses to oats in adults with coeliac disease

Gliadin T cell epitope selection by tissue transglutaminase in celiac disease. Role of enzyme specificity and pH influence on the transamidation versus deamidation process

Tissue transglutaminase (TG2) can modify proteins by transamidation or deamidation of specific glutamine residues. TG2 has a major role in the pathogenesis of celiac disease as it is both the target of disease-specific autoantibodies and generates deamidated gliadin peptides that are recognized by CD4(+), DQ2-restricted T cells from the celiac lesions. Capillary electrophoresis with fluorescence-labeled gliadin peptides was used to separate and quantify deamidated and transamidated products. In a competition assay, the affinity of TG2 to a set of overlapping gamma-gliadin peptides was measured and compared with their recognition by celiac lesion T cells. Peptides differed considerably in their competition efficiency. Those peptides recognized by intestinal T cell lines showed marked competition indicating them as excellent substrates for TG2. The enzyme fine specificity of TG2 was characterized by synthetic peptide libraries and mass spectrometry. Residues in positions -1, +1, +2, and +3 relative to the targeted glutamine residue influenced the enzyme activity, and proline in position +2 had a particularly positive effect. The characterized sequence specificity of TG2 explained the variation between peptides as TG2 substrates indicating that the enzyme is involved in the selection of gluten T cell epitopes. The enzyme is mainly localized extracellularly in the small intestine where primary amines as substrates for the competing transamidation reaction are present. The deamidation could possibly take place in this compartment as an excess of primary amines did not completely inhibit deamidation of gluten peptides at pH 7.3. However, lowering of the pH decreased the reaction rate of the TG2-catalyzed transamidation, whereas the rate of the deamidation reaction was considerably increased. This suggests that the deamidation of gluten peptides by TG2 more likely takes place in slightly acidic environments.

Coeliac disease

In the last few decades, the comprehension of epidemiological, pathogenic and clinical aspects of coeliac disease has increasingly improved. Serological screening studies on the general population have shown that the true coeliac disease prevalence in Europe is higher than previously reported. It has become clear that tissue transglutaminase has a crucial role in the pathogenesis of coeliac disease pathogenesis, and there is evidence that substitution of deamidated amino acidic residues at a critical position along the gliadin sequence dramatically increases immunological activation. The toxicity of many gluten epitopes has been investigated, so far, but recent studies have indicated the region 57-75 of alpha gliadin as a possible candidate epitope in the pathogenesis of coeliac disease. However, the wide heterogeneity of gliadin and glutenin molecules complicate any attempts to identify the toxic epitope, and the fascinating idea to produce detoxified grains will represent a great challenge in the near future. From a clinical point of view, there is now evidence of a broad spectrum of gluten conditions. Extra-intestinal signs, i.e., alopecia, unexplained neurological disorders, cryptic hypertransaminasaemia, increased red cell width, frequently constitute the only clinical manifestation at the diagnosis.

Specificity of tissue transglutaminase explains cereal toxicity in celiac disease

Celiac disease is caused by a selective lack of T cell tolerance for gluten. It is known that the enzyme tissue transglutaminase (tTG) is involved in the generation of T cell stimulatory gluten peptides through deamidation of glutamine, the most abundant amino acid in gluten. Only particular glutamine residues, however, are modified by tTG. Here we provide evidence that the spacing between glutamine and proline, the second most abundant amino acid in gluten, plays an essential role in the specificity of deamidation. On the basis of this, algorithms were designed and used to successfully predict novel T cell stimulatory peptides in gluten. Strikingly, these algorithms identified many similar peptides in the gluten-like hordeins from barley and secalins from rye but not in the avenins from oats. The avenins contain significantly lower percentages of proline residues, which offers a likely explanation for the lack of toxicity of oats. Thus, the unique amino acid composition of gluten and related proteins in barley and rye favors the generation of toxic T cell stimulatory gluten peptides by tTG. This provides a rationale for the observation that celiac disease patients are intolerant to these cereal proteins but not to other common food proteins.

Specificity of tissue transglutaminase explains cereal toxicity in celiac disease

Celiac disease is caused by a selective lack of T cell tolerance for gluten. It is known that the enzyme tissue transglutaminase (tTG) is involved in the generation of T cell stimulatory gluten peptides through deamidation of glutamine, the most abundant amino acid in gluten. Only particular glutamine residues, however, are modified by tTG. Here we provide evidence that the spacing between glutamine and proline, the second most abundant amino acid in gluten, plays an essential role in the specificity of deamidation. On the basis of this, algorithms were designed and used to successfully predict novel T cell stimulatory peptides in gluten. Strikingly, these algorithms identified many similar peptides in the gluten-like hordeins from barley and secalins from rye but not in the avenins from oats. The avenins contain significantly lower percentages of proline residues, which offers a likely explanation for the lack of toxicity of oats. Thus, the unique amino acid composition of gluten and related proteins in barley and rye favors the generation of toxic T cell stimulatory gluten peptides by tTG. This provides a rationale for the observation that celiac disease patients are intolerant to these cereal proteins but not to other common food proteins.

No harm from five year ingestion of oats in coeliac disease

BACKGROUND

Six to 12 months of ingestion of moderate amounts of oats does not have a harmful effect in adult patients with coeliac disease. As the safety of long term intake of oats in coeliac patients is not known, we continued our previous 6-12 month study for five years.

AIM

To assess the safety of long term ingestion of oats in the diet of coeliac patients.

PATIENTS

In our previous study, the effects of a gluten free diet and a gluten free diet including oats were compared in a randomised trial involving 92 adult patients with coeliac disease (45 in the oats group, 47 in the control group). After the initial phase of 6-12 months, patients in the oats group were allowed to eat oats freely in conjunction with an otherwise gluten free diet. After five years, 35 patients in the original oats group (23 still on an oats diet) and 28 in the control group on a conventional gluten free diet were examined.

METHODS

Clinical and nutritional assessment, duodenal biopsies for conventional histopathology and histomorphometry, and measurement of antiendomysial, antireticulin, and antigliadin antibodies.

RESULTS

There were no significant differences between controls and those patients consuming oats with respect to duodenal villous architecture, inflammatory cell infiltration of the duodenal mucosa, or antibody titres after five years of follow up. In both groups histological and histomorphometric indexes improved equally with time.

CONCLUSIONS

This study provides the first evidence of the long term safety of oats as part of a coeliac diet in adult patients with coeliac disease. It also appears that the majority of coeliac patients prefer oats in their diet.

Celiac Disease

Individuals with celiac disease present with a wide array of symptoms and signs. Celiac disease can result in substantial injury to the small intestine, deleterious effects on other organ systems, and an overall doubling of mortality. The role of the gastroenterologist is primarily to make the diagnosis and then to ensure that patients with celiac disease receive up-to-date and accurate instructions on diet. It is our opinion that gastroenterologists should participate in the follow-up of what is in fact a form of inflammatory bowel disease. The failure to identify and treat patients with substantial problems may result in an excess of preventable morbidity and mortality. Intestinal biopsy is the definitive method of making the diagnosis of celiac disease, provided the patient has not excluded gluten from his or her diet, because exclusion of gluten results in negative serologic test results and normal small intestinal biopsy samples. The removal of gluten from the diet can result in a total recovery of gut function and a correction of most other consequences. The response is usually so complete that patients should consider themselves to be basically healthy as long as they stay away from the offending foods. However, the execution and maintenance of the "theoretically simple" exclusion of gluten is difficult. The condition is permanent and mandates adherence to a lifelong gluten-free diet; even small amounts of gluten can result in injury to the intestinal lining. The diet is restrictive and requires the patient to be careful about food choices. Therefore, patient education and motivation are crucial to a successful outcome. The correction of vitamin and mineral deficiencies may be helpful in aiding recovery; vitamin D and calcium supplementation often is recommended. No drug therapy has been proven to suppress the disease.

The changing face of celiac disease

The face of celiac disease has changed significantly over the past 50 years. With the advent of new noninvasive and more sensitive screening tools, it has become increasingly apparent that this disease presents in a heterogeneous fashion, with symptomatic disease only occurring in a small number of patients. Furthermore, great insights have been made into the disease's genetic and immunological components, thus increasing the medical community's understanding of the disease. The current gold standard for diagnosis is histological confirmation, and the cornerstone of therapy is lifelong elimination of gluten. Further advances in immunobiological techniques will most likely aid in earlier detection and commencement of the appropriate diet, thus preventing the development of associated complications.

Immunologic evidence of no harmful effect of oats in celiac disease

BACKGROUND

It was recently shown that antiendomysial antibodies (EMAs), which are highly sensitive and specific for celiac disease, are produced by intestinal mucosa. Furthermore, EMAs were detected previously in supernatant fluid from cultured duodenal mucosa specimens collected from untreated celiac disease patients and in culture media of biopsy specimens collected from treated celiac disease patients after an in vitro challenge with gliadin. Moreover, it was recently shown in vivo that oats are not toxic to celiac disease patients, suggesting the safety of oats in a gluten free-diet.

OBJECTIVE

The objective was to better define the controversial role of oats in celiac disease to determine whether oats can be safely included in a gluten-free diet.

DESIGN

We used an in vitro model to test whether oats induce EMA production in supernatant fluid from cultured duodenal mucosa specimens collected from 13 treated celiac disease patients. The biopsy specimens were cultured with and without peptic-tryptic digest (PT) of gliadin and avenin (from oats) and in medium alone. Samples from 5 of the 13 patients were cultured with the C fraction of PT-avenin. Indirect immunofluorescence was used to detect EMAs.

RESULTS

EMAs were detected in specimens from all 13 patients after the challenge with gliadin but not after culture in medium alone. By contrast, no EMAs were detected in any of the specimens cultured with PT-avenin and its C fraction.

CONCLUSIONS

Because the in vitro challenge with PT-avenin and its C fraction did not induce EMA production in treated celiac disease patients, it appears that oats have no harmful effect on celiac disease. Therefore, oats can be safely included in a gluten-free diet.

Celiac disease

Celiac disease is more prevalent than it was previously thought to be, and screening of selected population groups may reveal many new cases. Tissue transglutaminase appears to have a significant role in the degradation of gliadin and antigen production. Specific gliadin epitopes have been defined using T-cell responses. Bone disease is a significant problem for patients with celiac disease but management guidelines are being developed. Refractory sprue (nonresponsive celiac disease) appears to be a manifestation of enteropathy-associated T-cell lymphoma in most cases.

Coeliac disease and Type 1 diabetes mellitus - the case for screening

AIM

To review the relationship between coeliac disease and Type 1 diabetes mellitus with emphasis on prevalence of coeliac disease, presentation and implications for screening.

METHODS

Papers collected over many years by the author have been included in the review and a literature search employing Medline was undertaken to August 2000. Search words used were coeliac disease and diabetes mellitus.

RESULTS

Twenty papers exploring the prevalence of coeliac disease by serological screening of Type 1 diabetes in children, eight in adults and two including both groups were found. An additional 48 papers are included and relate to serological screening tests for coeliac disease, expressions and complications of coeliac disease, the value of GFD and the genetics of the two conditions. Unless formal screening studies are undertaken coeliac disease will not be diagnosed because patients are asymptomatic, have atypical symptoms or even in those with symptoms the diagnosis is overlooked. Based on small bowel biopsy, diagnosis the prevalence of coeliac disease in Type 1 diabetes in children is 1:6 to 1:103 and in adults 1:16 to 1:76. Patients may improve following the start of a gluten-free diet (GFD) in terms of symptoms, growth in children, serum antibody levels, haematological and biochemical indices, morphology of the small intestinal mucosa and control of diabetes.

CONCLUSION

Coeliac disease commonly occurs in Type 1 diabetes. It is recommended that screening for coeliac disease should be part of the routine investigation and offered to all patients because of the high prevalence and the potential benefits of treatment with a GFD. This includes control of symptoms, stabilization of diabetes and prevention of complications associated with coeliac disease. The cost per patient diagnosed with coeliac disease from the existing population with Type 1 diabetes would be pound860 and for those newly arising pound950.