Is celiac disease due to molecular mimicry between gliadin peptide-HLA class II molecule-T cell interactions and those of some unidentified superantigen?

[Infections in early life as risk factor for coeliac disease]

INTRODUCTION

Among the environmental factors that can affect the pathological response to gluten in coeliac disease (CD), the factors that influence the immune response, such as infections and use of antibiotics, are proposed. Our objective is to determine the relationship between infections in early life and the risk of CD.

PATIENTS AND METHODS

A retrospective case-control study, including patients aged 0-16 years with a diagnosis of CD was performed between the years 2014-2018. An analysis was made of documented infections in the first 6 months of life, types of infection (respiratory, gastrointestinal, urinary, others), microorganisms involved, and antibiotic therapy used.

RESULTS

A total of 93 coeliac patients, 93 controls, and 237 infectious episodes were registered. Documented infections affected 67.7% of coeliac patients and 50.5% of controls (P = .017), with a mean of 1.49 ± 1.53 episodes in the coeliac group and 1.05 ± 1.5 in the controls (P = .016). Documented infections in the first 6 months of life doubles the risk of developing CD (OR 2.05; 95% CI; 1.13-3.73), with this risk being higher for respiratory infections, which multiply the risk by 2.3 (OR 2.30, 95% CI; 1.28-4.14). Also, having 3 or more respiratory infections in the first 6 months of life multiplied the risk by 2.8 (OR 2.79, 95% CI; 1.03-7.54). No differences were found related to the types of involved microorganism or regarding the use of antibiotics.

CONCLUSIONS

Infections in the first 6 months of life increase the risk of developing CD, especially for respiratory infections and, to a greater extent, if 3 or more episodes occur. The use of antibiotics in this period of life has not been related to an increased risk of CD.

Transglutaminase 2 in human diseases

Transglutaminase 2 (TG2) is an inducible transamidating acyltransferase that catalyzes Ca(2+)-dependent protein modifications. In addition to being an enzyme, TG2 also serves as a G protein for several seven transmembrane receptors and acts as a co-receptor for integrin β1 and β3 integrins distinguishing it from other members of the transglutaminase family. TG2 is ubiquitously expressed in almost all cell types and all cell compartments, and is also present on the cell surface and gets secreted to the extracellular matrix via non-classical mechanisms. TG2 has been associated with various human diseases including inflammation, cancer, fibrosis, cardiovascular disease, neurodegenerative diseases, celiac disease in which it plays either a protective role, or contributes to the pathogenesis. Thus modulating the biological activities of TG2 in these diseases will have a therapeutic value.

Adult celiac disease in the elderly

There is an increased awareness that celiac disease may occur in the elderly although presentations with either diarrhea, weight loss or both may be less common causing delays in diagnosis for prolonged periods. Higher detection rates also seem evident owing to active case screening, largely through serodiagnostic measures. In some elderly patients who are genetically predisposed, it has been hypothesized that celiac disease might be precipitated late in life by an antigen, possibly from an infectious agent. As a result, peptide mimicry or other poorly-defined mechanisms may precipitate an autoimmune gluten-dependent clinical state. Although diarrhea and weight loss occur, only isolated iron deficiency anemia may be present at the time of initial diagnosis. In addition, the risk of other autoimmune disorders, particularly autoimmune thyroiditis, and bone disease, are increased. Osteopenia may also be associated with an increased risk of fractures. Finally, elderly celiacs have an increased risk of malignant intestinal disease, especially lymphoma.

Deamidated gliadin peptides form epitopes that transglutaminase antibodies recognize

OBJECTIVE

Deamidated gliadin peptides are efficient antigens in diagnostic tests for celiac disease, and results correlate better with transglutaminase 2-based assays than those with native gliadin. We investigated whether deamidated gliadin antigens are structurally similar to transglutaminase 2 or could mimic transglutaminase epitopes.

PATIENTS AND METHODS

Serum samples from 74 celiac and 65 control patients, and 13 different transglutaminase 2-specific monoclonal mouse antibodies were investigated for their binding to commercially available deamidated gliadin peptides using enzyme-linked immunosorbent assay, competition studies, and molecular modelling.

RESULTS

The enzyme-linked immunosorbent assay with deamidated gliadin peptides had 100% sensitivity and 98.5% specificity in patients. Deamidated gliadin epitopes also were recognized by 3 transglutaminase-specific monoclonal antibodies, and antibodies affinity-purified with deamidated gliadin peptides from celiac patient sera reacted with transglutaminase but did not show endomysial binding. The binding of the monoclonal antibodies to deamidated gliadin was inhibited dose dependently by full-length recombinant human transglutaminase, its fragments containing the binding sites of these monoclonal antibodies, or by celiac patient antibodies. Deamidated gliadin peptides decreased the binding of transglutaminase-specific monoclonal antibodies to transglutaminase. Three different cross-reacting transglutaminase epitopes were found, of which 2 are located in the C-terminal domain and 1 is conformational. The binding of celiac serum samples to deamidated gliadin peptides could not be abolished by transglutaminase or by any of the transglutaminase-specific monoclonals, indicating that celiac sera also contain additional antibodies to gliadin epitopes different from transglutaminase.

CONCLUSIONS

Certain deamidated gliadin-derived peptides and transglutaminase 2 epitopes have similar 3-dimensional appearance. This homology may contribute to the induction of transglutaminase autoantibodies by molecular mimicry.

Novel foods to treat food allergy and gastrointestinal infection

The gastrointestinal tract communicates directly with the external environment. Necessary nutrients must be absorbed and commensal bacteria tolerated, and foreign proteins, antigens, and pathogens must be simultaneously excluded or destroyed. Immaturity or disruption of the mucosal immune defenses increases vulnerability to food allergy, intolerance, and infectious disease. Diseases resulting from ingested foreign proteins and organisms are increasing and cause morbidity and mortality worldwide. There is no specific treatment for food allergy other than avoidance. Vaccination for infectious disease is limited by the cost and logistics of distribution and administration, particularly in developing countries. Novel strategies are being explored to modulate the gut mucosal immune system by altering protein expression in food. Crops are being developed to remove deleterious allergens to prevent immunogenic exposure while preserving nutritional quality. Local food plants that express protein fragments of pathogens might provide an effective means to stimulate gut mucosal immunity while increasing vaccine accessibility.

Anti-ganglioside antibodies in children with coeliac disease: correlation with gluten-free diet and neurological complications

BACKGROUND

Emerging evidence points to humoural mechanisms in neurological complications of coeliac disease. Immunoglobulin G anti-ganglioside antibodies have been reported in coeliac disease patients with neuropathy, suggesting an immune response to peripheral nerve antigens. No data are so far available on anti-ganglioside antibodies in coeliac disease children or on antibody modifications after gluten-free diet.

AIM

To evaluate the presence of antibodies to ganglioside antigens in children with coeliac disease, their modification after gluten-free diet, and possible correlations with neurological manifestations.

METHODS

Sera from 42 coeliac disease children, before and after gluten-free diet, were tested by enzyme-linked immunosorbent assay for the presence of antibodies (immunoglobulin M, immunoglobulin A, immunoglobulin G) to gangliosides. Thirty-five sera of age-matched children with dyspepsia were used as control.

RESULTS

High anti-ganglioside antibodies titres were present in two patients. In one patient, antibody titre reversed after gluten-free diet, whereas in the other one the titre increased after diet. Neither one complained of neurological symptoms.

CONCLUSIONS

Anti-ganglioside antibodies do not seem to correlate with gluten ingestion or with neurological manifestations in children with coeliac disease. Mechanisms different from gluten exposure may be implicated in the antibody production. An ongoing prospective study will help clarify the role, if any, of these antibodies in coeliac disease.

Novel foods to treat food allergy and gastrointestinal infection

The gastrointestinal tract communicates directly with the external environment. Necessary nutrients must be absorbed and commensal bacteria tolerated, and foreign proteins, antigens, and pathogens must be simultaneously excluded or destroyed. Immaturity or disruption of the mucosal immune defenses increases vulnerability to food allergy, intolerance, and infectious disease. Diseases resulting from ingested foreign proteins and organisms are increasing and cause morbidity and mortality worldwide. There is no specific treatment for food allergy other than avoidance. Vaccination for infectious disease is limited by the cost and logistics of distribution and administration, particularly in developing countries. Novel strategies are being explored to modulate the gut mucosal immune system by altering protein expression in food. Crops are being developed to remove deleterious allergens to prevent immunogenic exposure while preserving nutritional quality. Local food plants that express protein fragments of pathogens might provide an effective means to stimulate gut mucosal immunity while increasing vaccine accessibility.

Clinical features of coeliac disease today

Coeliac disease is an inflammatory disorder of the small intestine induced by dietary gluten. This frequently results in malabsorption of a range of important nutrients including iron, folic acid, calcium and fat-soluble vitamins. Coeliac disease in now considered to be a common disorder, possibly affecting 1:300 of the general population. Many patients present in adulthood, have minimal symptoms, and gastrointestinal manifestations are frequently absent. The diagnosis and screening for coeliac disease has been dramatically facilitated by testing for endomysial autoantibodies, although biopsy and demonstration of a characteristic histological lesion remains the definitive diagnostic investigation. Treatment with a gluten-free diet is effective but requires good patient compliance and monitoring to succeed.

Enhanced peptide-binding capacities of small intestinal brush border membranes in celiac disease

In pathogenesis of celiac disease, the significance of prolamin peptide interactions with enterocytes is controversial. Changes in cellular metabolism induced by gliadin peptides, as well as uptake and presentation by enterocytes, are discussed. We analyzed peptide binding to enterocytic membranes as a potential key event. Binding capacities of brush border membranes isolated from small intestinal biopsies of untreated (n = 49) and treated celiac patients on a gluten-free diet (n = 30), as well as control subjects (n = 43), were measured with a dot blot chemiluminescence assay. Synthetic gliadin peptides comprising amino acid position 8-19 (G XIV) and 30-41 (G XI) of alpha-gliadins, a peptic-tryptic digest of gliadin (PT-GLI), and a synthetic zein peptide were used. Comparing treated celiac patients with controls, we observed significantly enhanced membrane-binding of PT-GLI [mean 122.4 densitometric units/microg (95% confidence interval 116.0-128.9) vs 108.9 (102.1-115.7)] and of zein peptide [50.2 (38.4-61.9) vs 28.8 (13.4-44.2)], but only slightly increased binding of the synthetic gliadin peptides G XIV [65.5 (60.6-70.5) vs 62.4 (56.3-68.5) and G XI [75.2 (69.8-80.6) vs 65.9 (55.2-76.5)]. Independent of patient group, membrane-binding capacities for celiac-active gliadin peptides exceeded those of the zein peptide. Thus, interaction of gliadin peptides with the apical enterocytic membrane was not found exclusively in celiac disease. Furthermore, increased binding capacities in treated celiac disease were not confined to celiac-active peptides. Quantitative differences in gliadin peptide binding as a primary characteristic in celiac disease might contribute to pathogenetic effects exerted on small intestinal epithelial cells.

Superantigens and autoimmune disease: are they involved?

In over 10 years since the definition of superantigens, much has been learned about host cell-superantigen interactions. The initial simple set of rules used to define these interactions has given way to a more complex system, in which the activation of multiple cell types can occur as a consequence of superantigen-cell interactions or as a result of bystander effects based on the induction of a specific cytokine milieu. As a consequence, our ideas concerning the ways in which superantigens might be involved in disease are also expanding rapidly. This review highlights some of the many different pathways of superantigen-associated pathogenesis currently under investigation.