Transglutaminase 2-targeted autoantibodies in celiac disease: Pathogenetic players in addition to diagnostic tools?

Expression of Elafin and CD200 as Immune Checkpoint Molecules Involved in Celiac Disease

We comprehensively evaluated the expression of therapeutically targetable immune checkpoint molecules involved in celiac disease (CD). We have focused on the alteration of the CD200/CD200R pathway and Elafin expression in celiac disease and discussed their roles in regulating the immune response. There are limited data related to the expression or function of these molecules in celiac disease. This finding could significantly contribute to the understanding of the clinical manifestation of CD. CD200, CD200R and Elafin distributions were determined by ELISA and immunohistochemistry analyses in serum and biopsies of CD patients. Analyses of Th1 and Th17 cytokines were determined. PCR amplification of a fragment of the PI3 gene was carried out using genomic DNA isolated from whole blood samples of the study subjects. Different aliquots of the PCR reaction product were subjected to RFLP analysis for SNP genotyping and detection. We characterized the expression and function of the CD200-CD200R axis and PI3 in celiac disease. A significantly higher level of soluble CD200 and CD200R and lower expression of PI3 in serum of CD patients was observed compared to healthy controls. Consistent with our results, CD200 expression is regulated by IFN-gamma. Interaction of CD200/CD200R leads to production of type-Th1 and -Th17 cytokines. Regarding the PI3 genotype, the CT genotype proportion SNP rs1733103 and the GG genotype SNP rs41282752 were predominant in CD patients. SNP rs1733103 showed a significant association between the SNP variables and CD. In celiac disease the immune checkpoint is compromised or dysregulated, which can contribute to inflammation and the autoimmunity process. The study of these checkpoint points will lead to the development of targeted therapies aimed at restoring immunological balance in CD. Specific coding regions of the PI3 gene-splice variants predispose the Elafin protein, both at the transcriptional and post-translational levels, to modify its expression and function, resulting in reduced differential functional protein levels in patients with active celiac disease.

Possible relationship between refractory celiac disease and malignancies

Celiac disease (CeD) is a chronic autoimmune disorder that is triggered by gluten in genetically susceptible individuals, and that is characterized by CeD-specific antibodies, HLA-DQ2 and/or HLA-DQ8 haplotypes, enteropathy and different clinical pictures related to many organs. Intestinal lymphoma may develop as a result of refractory CeD. If a patient diagnosed with CeD is symptomatic despite a strict gluten-free diet for at least 12 months, and does not improve with severe villous atrophy, refractory CeD can be considered present. The second of the two types of refractory CeD has abnormal monoclonal intraepithelial lymphocytes and can be considered as pre-lymphoma, and the next picture that will emerge is enteropathy-associated T-cell lymphoma. This manuscript addresses "CeD and malignancies" through a review of current literature and guidelines.

TG2-gluten complexes as antigens for gluten-specific and transglutaminase-2 specific B cells in celiac disease

A hallmark of celiac disease is the gluten-dependent production of antibodies specific for deamidated gluten peptides (DGP) and the enzyme transglutaminase 2 (TG2). Both types of antibodies are believed to result from B cells receiving help from gluten-specific CD4⁺ T cells and differentiating into antibody-producing plasma cells. We have here studied the collaboration between DGP- and TG2-specific B cells with gluten-specific CD4⁺ T cells using transgenic mice expressing celiac patient-derived T-cell and B-cell receptors, as well as between B-cell transfectants and patient-derived gluten-specific T-cell clones. We show that multivalent TG2-gluten complexes are efficient antigens for both TG2-specific and DGP-specific B cells and allow both types of B cells to receive help from gluten-specific T cells of many different specificities.

Can a Synbiotic Supplementation Contribute to Decreasing Anti-Tissue Transglutaminase Levels in Children with Potential Celiac Disease?

PURPOSE

Synbiotics can alleviate some intestinal pathologies or prevent trigger mechanisms for some diseases such as celiac disease (CD). If patients with high levels of anti-tissue transglutaminase (anti-tTG) immunoglobulin A (IgA) antibodies have normal duodenal histology, they are followed as potential CD patients. The aim of this study was to investigate the effect of synbiotic use on the blood levels of anti-tTG antibodies in children.

METHODS

Eighty-two patients with high anti-tTG levels were included in this study. Patients were randomly divided into two groups. The synbiotic group was treated with a daily dose of a synbiotic including multi-strain probiotics for 20 days. The control group was not administered any medication. Anti-tTG values at baseline and repeat measurements and the percentage change in anti-tTG levels between groups were compared.

RESULTS

The anti-tTG level at baseline was 36 U/mL (interquartile range [IQR], 26.4-68 U/mL) in the synbiotic group, and it decreased significantly to 13 U/mL (IQR, 6.5-27.5 U/mL) after 20 days (p<0.05). The anti-tTG level at baseline was 46 U/mL (IQR, 31-89 U/mL) in the control group, which also decreased significantly to 23 U/mL (IQR, 7-41 U/mL) after 20 days (p<0.05). Anti-tTG levels exhibited 73% and 56% decreases in the synbiotic and control groups, respectively (p<0.05).

CONCLUSION

It may be speculated that a synbiotic supplementation can contribute to decreasing anti-tTG levels in children with potential CD.

Efficient T cell-B cell collaboration guides autoantibody epitope bias and onset of celiac disease

B cells play important roles in autoimmune diseases through autoantibody production, cytokine secretion, or antigen presentation to T cells. In most cases, the contribution of B cells as antigen-presenting cells is not well understood. We have studied the autoantibody response against the enzyme transglutaminase 2 (TG2) in celiac disease patients by generating recombinant antibodies from single gut plasma cells reactive with discrete antigen domains and by undertaking proteomic analysis of anti-TG2 serum antibodies. The majority of the cells recognized epitopes in the N-terminal domain of TG2. Antibodies recognizing C-terminal epitopes interfered with TG2 cross-linking activity, and B cells specific for C-terminal epitopes were inefficient at taking up TG2-gluten complexes for presentation to gluten-specific T cells. The bias toward N-terminal epitopes hence reflects efficient T-B collaboration. Production of antibodies against N-terminal epitopes coincided with clinical onset of disease, suggesting that TG2-reactive B cells with certain epitope specificities could be the main antigen-presenting cells for pathogenic, gluten-specific T cells. The link between B cell epitopes, antigen presentation, and disease onset provides insight into the pathogenic mechanisms of a T cell-mediated autoimmune condition.

Celiac Disease Autoimmunity

Celiac disease is an autoimmune condition triggered by the ingestion of gluten, the protein fraction of wheat, barley and rye. It is not simply an intestinal disease; it is multifactorial caused by many different genetic factors acting together with non-genetic causes. Similar to other autoimmune diseases, celiac disease is a polygenic disorder for which the major histocompatibility complex locus is the most important genetic factor, and is the result of an immune response to self-antigens leading to tissue destruction and the autoantibodies production. Celiac disease exemplifies how an illness can have autoimmune-like features having to be driven by exogenous antigen and how can be reasonably considered as a model of organ-specific autoimmunity.

Linear α-(1 → 6)-d-glucan from Bifidobacterium bifidum BIM В-733D is low molecular mass biopolymer with unique immunochemical properties

Role of microorganisms in induction of/protection from autoimmune diseases is proven though molecular mechanisms and bacterial/viral/yeast biopolymers responsible for these effects are in the research stage. Autoantobodies (AAbs) to thyroid peroxidase (anti-TPO) and thyroglobulin (anti-Tg) as well as AAbs to transglutaminase 2 (anti-TG2) and antibodies to gliadins (anti-gliadins) are serological markers of autoimmune thyroid disease and celiac disease, respectively, and players in pathogenesis of these autoimmune diseases. In current study, biopolymer of Bifidobacterium bifidum BIM В-733D that interacts selectively with anti-gliadins (Bb-G_{anti-gliadins}) was isolated by affinity chromatography with anti-gliadins, purified by size exclusion chromatography on TSK 40 gel and identified by NMR as linear α-(1 → 6)-d-glucan with molecular mass about 5000 Da. It was proven that compounds Bb-G_{anti-gliadins} and Bb-G_anti-TPO/Bb-G_anti-Tg isolated early from the same strain [Kiseleva, E. P. et al., Benef Microbes.2013, 4, 375 -391] are the same substance designated G_Bb. Its unique immunochemical property is the ability to interact selectively with anti-TPO, anti-Tg, anti-TG2 and anti-gliadins in presence of no less than 10-fold excess of total immunoglobulins of class G (tIgG), as it was proven by ELISA. Synthesis of G_Bb-bovine serum albumin (G_Bb-BSA) conjugate is an example of increasing the reliability and reproducibility of ELISA results by mediated immobilization of a polysaccharide covalently attached to a well-adsorbed protein. Taking into account that there are population of bispecific anti-gliadins (anti-gliadins and anti-TG2 simultaneously) we regard our data as first argument in favor of hypothesis that G_Bb differentiates between human AAbs per se and other human Ig (e.g. antibodies to antigens of infectious agents) due to its binding with a yet unidentified site which is present in the molecules of all AAbs (independently on their specificity) and absent in other human Igs.

Anemia in Pediatric Celiac Disease: Association With Clinical and Histological Features and Response to Gluten-free Diet

GOALS

The aim of the present study was to compare clinical, serological, and histological manifestations between children with anemia and without anemia at celiac disease (CD) diagnosis.

BACKGROUND

Despite being a common finding, the association between the presence of anemia and clinicohistopathological presentation of CD in children remains obscure.

STUDY

A total of 455 patients with CD <18 years of age were divided into those with anemia and those without anemia at diagnosis. The groups underwent comparisons of a variety of clinical, serological, and laboratory parameters and severity of small-bowel mucosal damage. Furthermore, adherence and clinical and serological response to the gluten-free diet (GFD) were compared.

RESULTS

Anemia was detected in 18.0% of the patients. Children with anemia had higher values for transglutaminase 2 antibodies (120.0 U/L vs 88.0 U/L, P < 0.001) and, by definition, lower values for hemoglobin (10.5 g/dL vs 12.8 g/dL, P < 0.001) and other iron parameters. They were also less often screen-detected (13.4% vs 34.6%), had more severe histological damage (P = 0.048), and poorer dietary adherence (78.3% vs 87.5%, P = 0.035) than the patients without anemia. A total of 92% of the patients recovered from anemia after a median of 1 year on a GFD, but hemoglobin values remained significantly lower compared with the nonanemic group (12.5 g/dL vs 13.2 g/dL, P = 0.045). There was no difference between the groups in the clinical and serological response to the GFD (P = 0.318).

CONCLUSIONS

Anemia at CD diagnosis is associated with more severe histological and serological presentation in children. Furthermore, low hemoglobin may not fully recover even after a median of 1 year on a strict GFD.

Assessment of Endothelial Dysfunction With Adhesion Molecules in Patients With Celiac Disease

OBJECTIVES

Celiac disease (CD) is a systemic immune disorder. We assessed serum levels of adhesion molecules as a marker of endothelial dysfunction in patients with CD at first diagnosis and in those on a gluten-free diet.

METHODS

Sixty-five patients with CD (mean age 6.74 ± 4.6 years) and 51 age- and sex-matched control patients participated in the present case-controlled, prospective clinical study. Serum levels of vascular adhesion molecule-1, intercellular adhesion molecule-1, endothelial selectin, vascular endothelial cadherin, high-sensitivity C-reactive protein, and homocysteine levels were measured.

RESULTS

Average soluble vascular adhesion molecule-1 (CD vs control group: 1320 ± 308 vs 1120 ± 406 ng/mL, P = 0.006), soluble intercellular adhesion molecule-1 (336 ± 99 vs 263 ± 67 ng/mL, P = 0.025), and soluble endothelial selectin (113.9 ± 70 vs 76.9 ± 32 ng/mL, P = 0.007) levels were significantly higher in cases of newly diagnosed CD than in the control group. Soluble vascular adhesion molecule-1 (1050 ± 190 ng/mL) and soluble endothelial selectin (68.7 ± 45 ng/mL) levels in patients with CD, who were fully compliant with a gluten-free diet, were significantly lower than that in those newly diagnosed as having CD (P = 0.003 and P = 0.0012, respectively).

CONCLUSIONS

These results show that serum adhesion molecule levels are higher in patients with CD. Some of the risks associated with endothelial dysfunction may be related to CD and these risks can be reduced with an appropriate and fully controlled diet.

Immunopathogenesis and therapeutic approaches in pediatric celiac disease

Celiac Disease is an autoimmune enteropathy with increasing incidence worldwide in both adults and children. It occurs as an inflammatory condition with destruction of the normal architecture of villi on consumption of gluten and related protein products found in wheat, barley and rye. However, the exact pathogenesis is not yet fully understood. A gluten-free diet remains the main modality of therapy to date. While some patients continue to have symptoms even on a gluten-free diet, adherence to this diet is also difficult, especially for the children. Hence, there is continued interest in novel methods of therapy and the current research focus is on the promising novel non-dietary modalities of treatment. Here, we critically reviewed the existing literature regarding the pathogenesis of celiac disease in children including the role of in-utero exposure leading to neonatal and infant sensitization and its application for the development of new therapeutic approaches for these patients.

Novel diagnostic techniques for celiac disease

The diagnosis of celiac disease has long been based on the demonstration of gluten-induced small-bowel mucosal damage. However, due to the constantly increasing disease prevalence and limitations in the histology-based criteria there is a pressure towards more serology-based diagnostics. The serological tools are being improved and new non-invasive methods are being developed, but the constantly refined endoscopic and histologic techniques may still prove helpful. Moreover, growing understanding of the disease pathogenesis has led researchers to suggest completely novel approaches to celiac disease diagnostics regardless of disease activity. In this review, we will elucidate the most recent development and possible future innovations in the diagnostic techniques for celiac disease.

Celiac disease as an autoimmune condition

Autoimmune diseases have become a major medical problem of recent years. Celiac disease is an autoimmune disease model. The aim of our study was to follow the changes in the clinical autoimmunity picture of the celiac disease from recent years. The study of autoimmunity in celiac disease has focused on associated diseases with the aforementioned disease: type 1 diabetes mellitus, thyroid autoimmunity disease, Graves’ disease, Hashimoto's disease, systemic lupus erythematosus, systemic sclerosis, spondyloarthritis, hyperprolactinemia, Turner syndrome, Addison's disease, sensory neuronopathies. Immune reactivity to tissue transglutaminase targeted autoantibodies and other autoantigens, including transglutaminase 3, actin, ganglioside, collagen, calreticulin or zonulin which have been reported in the celiac disease. New research directions given by celiac disease autoimmunity, interleukin 1, interleukin 2, protein tyrosine phosphatase non-receptor type 22, CD4+CD25+ T lymphocytes, cytotoxic T-lymphocyte antigen 4, infection with Necator americanus and definitive identification of pathogenic T cell epitopes, seem to provide a solution in celiac disease treatment.

Microbial transglutaminase treatment in pasta-production does not affect the immunoreactivity of gliadin with celiac disease patients' sera

The effect of microbial transglutaminase (MTG)-treatment of pasta-dough on the immunoreactivity with celiac disease patient's sera has been investigated. Modification by MTG has been proven by determination of the MTG reaction product ε-(γ-glutamyl)lysine (3.63 μmol/g protein), which was not detectable in non-MTG-treated pasta. Antigenicity has been analyzed by immunoblotting and ELISA using gliadin-extracts from pasta and MTG-treated pasta. Immunoblotting showed that the antibody-population (antigliadin antibodies and antideamidated gliadin antibodies) of the sera is specific for every individual patient. Immunoblotting and ELISA showed that there is no difference in immunoreactivity of gliadin extracted from pasta and MTG-pasta. Recognition pattern and intensity in Western blot as well as antibody titer has also been identical even for sera with a high antideamidated gliadin antibody titer. These results indicate no difference between pasta-gliadin and MTG-pasta-gliadin and especially no increased deamidation in pasta-gliadin by MTG-treatment.

A subset of anti-rotavirus antibodies directed against the viral protein VP7 predicts the onset of celiac disease and induces typical features of the disease in the intestinal epithelial cell line T84

Celiac disease (CD) is an autoimmune disorder of the small intestine triggered by environmental factors in genetically predisposed individuals. A strong association between type 1 diabetes (T1DM) and CD has been reported. We have previously shown that rotavirus infection may be involved in the pathogenesis of CD through a mechanism of molecular mimicry. Indeed, we identified a subset of anti-transglutaminase IgA antibodies that recognize the rotavirus viral protein VP7. In this study, we aimed at evaluating whether such antibodies may predict the onset of CD in children affected by T1DM. Moreover, to further analyze the link between rotavirus infection and pathogenesis of CD, we analyzed the effect of anti-rotavirus VP7 antibodies on T84 intestinal epithelial cells using the gene-array technique, complemented by the analysis of molecules secreted in the supernatant of stimulated cells. We found that anti-rotavirus VP7 antibodies are present in the vast majority (81%) of T1DM-CD tested sera, but are detectable also in a fraction (27%) of T1DM children without CD. Moreover, we found that anti-rotavirus VP7 antibodies are present before the CD onset, preceding the detection of anti-tTG and anti-endomysium antibodies. The gene-array analysis showed that purified anti-rotavirus VP7 antibodies modulate genes that are involved in apoptosis, inflammation, and alteration of the epithelial barrier integrity in intestinal epithelial cells, all typical features of CD. Taken together, these new data further support the involvement of rotavirus infection in the pathogenesis of CD and suggest a predictive role of anti-rotavirus VP7 antibodies.

Advances in the treatment of coeliac disease: an immunopathogenic perspective

Coeliac disease is a common and fairly well-characterized systemic disorder that mainly affects the small intestine, but also has extraintestinal manifestations. The environmental trigger (gluten derived from wheat, rye and barley), the genetic predisposition conferred by the HLA-DQ2 and HLA-DQ8 haplotypes and many steps in the disease pathogenesis are known. This knowledge has enabled researchers to suggest novel alternative treatments or adjunctive therapies to the gluten-free diet, which is currently the only available and effective treatment for the condition. This Review focuses on emerging and potential treatment strategies that are based on the current concept of the disease pathophysiology. The search for novel future treatment modes, including nonpharmacological and pharmacological approaches, is also outlined. The potential pitfalls associated with the various research avenues are also discussed.

Alcohol induces sensitization to gluten in genetically susceptible individuals: a case control study

BACKGROUND

The mechanisms of cerebellar degeneration attributed to prolonged and excessive alcohol intake remain unclear. Additional or even alternative causes of cerebellar degeneration are often overlooked in suspected cases of alcohol-related ataxia. The objectives of this study were two fold: (1) to investigate the prevalence of gluten-related serological markers in patients with alcohol-related ataxia and; (2) to compare the pattern of brain involvement on magnetic resonance imaging between patients with alcohol and gluten ataxias.

MATERIALS & METHODS

Patients diagnosed with alcohol and gluten ataxias were identified from a retrospective review of patients attending a tertiary clinic. HLA genotype and serological markers of gluten-related disorders were recorded. Cerebellar volumetry, MR spectroscopy and voxel-based morphometric analyses were performed on patients and compared with matched control data.

RESULTS

Of 904 registered patients, 104 had alcohol ataxia and 159 had gluten ataxia. 61% of the alcohol ataxia group and 70% of the gluten ataxia group had HLA DQ2/DQ8 genotype compared to 30% in healthy local blood donors. 44% of patients with alcohol ataxia had antigliadin antibodies compared to 12% in the healthy local population and 10% in patients with genetically confirmed ataxias. None of the patients with alcohol ataxia and antigliadin antibodies had celiac disease compared to 40% in patients with gluten ataxia. The pattern of structural brain abnormality in patients with alcohol ataxia who had antigliadin antibodies differed from gluten ataxia and was identical to that of alcohol ataxia.

CONCLUSIONS

Alcohol related cerebellar degeneration may, in genetically susceptible individuals, induce sensitization to gluten. Such sensitization may result from a primary cerebellar insult, but a more systemic effect is also possible. The duration and amount of exposure to alcohol may not be the only factors responsible for the cerebellar insult.

Thioredoxin is involved in endothelial cell extracellular transglutaminase 2 activation mediated by celiac disease patient IgA

Purpose

To investigate the role of thioredoxin (TRX), a novel regulator of extracellular transglutaminase 2 (TG2), in celiac patients IgA (CD IgA) mediated TG2 enzymatic activation.

Methods

TG2 enzymatic activity was evaluated in endothelial cells (HUVECs) under different experimental conditions by ELISA and Western blotting. Extracellular TG2 expression was studied by ELISA and immunofluorescence. TRX was analysed by Western blotting and ELISA. Serum immunoglobulins class A from healthy subjects (H IgA) were used as controls. Extracellular TG2 enzymatic activity was inhibited by R281. PX12, a TRX inhibitor, was also employed in the present study.

Results

We have found that in HUVECs CD IgA is able to induce the activation of extracellular TG2 in a dose-dependent manner. Particularly, we noted that the extracellular modulation of TG2 activity mediated by CD IgA occurred only under reducing conditions, also needed to maintain antibody binding. Furthermore, CD IgA-treated HUVECs were characterized by a slightly augmented TG2 surface expression which was independent from extracellular TG2 activation. We also observed that HUVECs cultured in the presence of CD IgA evinced decreased TRX surface expression, coupled with increased secretion of the protein into the culture medium. Intriguingly, inhibition of TRX after CD IgA treatment was able to overcome most of the CD IgA-mediated effects including the TG2 extracellular transamidase activity.

Conclusions

Altogether our findings suggest that in endothelial cells CD IgA mediate the constitutive activation of extracellular TG2 by a mechanism involving the redox sensor protein TRX.

Fetal and neonatal outcome in celiac disease

Celiac disease (CD) is characterized by an abnormal immune response in susceptible individuals to dietary gluten derived from wheat, rye and barley. The disease affects not only the small bowel mucosa, but also many other extraintestinal organs resulting bone, liver, neurologic, skin and reproductive system disorders. The details of the pathogenic mechanism are not perfectly clear yet, but it is now proved that both humoral and cellular immune responses are triggered and autoimmune mechanisms are implicated. Studies have shown association of different pregnancy outcomes with maternal celiac disease. In this review, the most frequent fetal and neonatal outcome related to CD are presented, with a special focus on intrautherine growth restriction (IUGR) and prematurity. The need of active case finding of CD is discussed.

Pathophysiology of celiac disease

Celiac disease results from the interplay of genetic, environmental, and immunologic factors. An understanding of the pathophysiology of celiac disease, in which the trigger (wheat, rye, and barley) is known, will undoubtedly reveal basic mechanisms that underlie other autoimmune diseases (eg, type 1 diabetes) that share many common pathogenic perturbations. This review describes seminal findings in each of the 3 domains of the pathogenesis of celiac disease, namely genetics, environmental triggers, and immune dysregulation, with a focus on newer areas of investigation such as non-HLA genetic variants, the intestinal microbiome, and the role of the innate immune system.

Recent advances in the development of new treatments for celiac disease

INTRODUCTION

Celiac disease is a common autoimmune condition induced by dietary gluten in genetically susceptible individuals. So far, the only available treatment for the disorder is a lifelong strict gluten-free diet, because of which small intestinal histological changes recover and symptoms disappear. However, gluten-free dieting is restrictive, and nutritionally less than optimal, and gluten is difficult to avoid.

AREAS COVERED

With improving insight into the pathogenesis of celiac disease, several possible drug targets have been suggested. The new strategies include degradation of gluten intraluminally, reduction of mucosal permeability, inhibition of the transglutaminase 2 enzyme, blocking antigen presentation by HLA-DQ2 or HLA-DQ8, modulation of the immune responses of many cytokines, and vaccination.

EXPERT OPINION

Non-dietary treatment options are warranted either as adjunctive therapy together with dieting or to replace the gluten-free diet. The key question is whether the envisaged novel drug is able to prevent gluten-induced small intestinal mucosal injury as efficiently as a strict gluten-free diet, alleviating symptoms and signs of the disease. Furthermore, the gluten dose that can be detoxified, if at all, must be established. The new drug should also be as safe as dietary treatment. Several novel treatment options are under development.

Future treatment strategies for celiac disease

INTRODUCTION

Ingestion of dietary gluten in wheat, rye and barley by celiac patients leads to small-bowel mucosal villous atrophy, crypt hyperplasia and massive inflammation, often coupled with clinical symptoms and signs. Currently, the only effective treatment is a strict life-long gluten-free diet excluding all gluten-containing food products. In view of the extremely restricted nature of the diet, new treatment options would clearly be desirable.

AREAS COVERED

The improved understanding of celiac disease pathogenesis has enabled researchers to suggest alternative strategies to treat the disorder. This review covers current approaches toward developing an appropriate drug and discusses the possible problems associated with these approaches.

EXPERT OPINION

Phase II clinical trials are already ongoing to test the efficacy of novel alternative treatments for celiac disease. Before any of the candidates can enter Phase III trials, however, researchers must develop novel reliable non-invasive surrogate markers for intestinal injury and disease activity which also accurately reflect patient-related outcomes. Any novel medication for celiac disease should be as effective and safe as the gluten-free diet, and this constitutes a challenge for drug development. It is thus likely that the first medication entering the market will be supplementary to rather than substitute the gluten-free diet.

Transglutaminase 2 promotes both caspase-dependent and caspase-independent apoptotic cell death via the calpain/Bax protein signaling pathway

Transglutaminase 2 (TG2) is a versatile protein that is implicated in significant biological processes, including cell death and degenerative diseases. A possible role of TG2 in the apoptotic death of cancer cells induced by photodynamic therapy (PDT) was suggested recently; however, the mechanism by which TG2 regulates apoptotic responses to PDT remains to be elucidated. In this study, we investigated the key signaling pathways stimulated during apoptotic cell death following PDT and whether inhibition of TG2 activation using pharmacological approaches and siRNAs affects the signaling pathways. PDT caused the release of both cytochrome c and apoptosis-inducing factor (AIF) by damaging mitochondria, which resulted in caspase-dependent and caspase-independent apoptotic cell death, respectively. Released AIF translocated to the nucleus and, synergistically with the caspase-dependent pathway, led to apoptotic cell death. Both the caspase cascade and the activation of AIF following PDT were mediated by TG2 activation. In addition, PDT-activated calpain was responsible for the sequential events of Bax translocation, the collapse of ΔΨ(m), caspase-3 activation, and AIF translocation, all of which were provoked by TG2 activation. Together, these results demonstrate that PDT with a chlorin-based photosensitizer targets TG2 by activating calpain-induced Bax translocation, which induces apoptotic cell death through both caspase-dependent and AIF-mediated pathways. Moreover, these results indicate that TG2 may be a possible therapeutic target for PDT treatment of cancer.

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.

In vitro models for gluten toxicity: relevance for celiac disease pathogenesis and development of novel treatment options

In genetically predisposed individuals, dietary gluten in wheat, rye and barley triggers celiac disease, a systemic autoimmune disorder hallmarked by an extensive small-bowel mucosal immune response. The current conception of celiac disease pathogenesis is that it involves components of both innate and adaptive immunity whose activation typically leads to small-bowel villous atrophy with crypt hyperplasia. Currently, the only effective treatment for celiac disease is a strict lifelong gluten-free diet excluding all wheat-, rye- and barley-containing food products. During the diet, the clinical symptoms improve and the small-bowel mucosal damage recovers, while re-introduction of gluten into the diet leads to re-appearance of the symptoms and deterioration of the small-bowel mucosal architecture. In view of the restricted nature of the diet, alternative treatment is warranted. Improved understanding of the molecular basis of celiac disease has enabled researchers to suggest other therapeutic approaches. Although there is no animal model reproducing all features of celiac disease, the use of in vitro approaches including a variety of cell lines and the celiac patient small-bowel mucosal biopsy organ culture has generated knowledge about pathogenesis of celiac disease. In these culture systems, gluten induces different effects that can be quantified, thus also enabling studies concerning the efficacy of candidate therapeutic compounds for celiac disease. This review describes the intestinal epithelial cell models, celiac patient T-cell lines and clones, as well as the small-bowel mucosal organ culture methods widely used in studies of celiac disease, and summarizes the major findings obtained with these systems.

Gluten-sensitive hypertransaminasemia in celiac disease: an infrequent and often subclinical finding

OBJECTIVES

Earlier studies suggest that 40-50% of untreated celiac disease patients have elevated transaminase levels. Celiac disease can also be the underlying reason for unexplained hypertransaminasemia or even liver failure. We investigated the prevalence and gluten dependency of hypertransaminasemia in celiac patients also diagnosed with minor or atypical symptoms.

METHODS

In the cross-sectional study, serum aspartate (AST) and alanine (ALT) transaminase levels were measured in 313 untreated and 339 treated adult celiac patients and 237 non-celiac controls. In the prospective part, transaminase levels were investigated in 130 celiac patients at diagnosis and after 1 year on a gluten-free diet and in 25 treated celiac patients in clinical remission before and after gluten challenge.

RESULTS

The proportion of subjects with elevated serum AST values in the untreated celiac disease group (11%) did not differ significantly from that in the treated celiac disease (8%) or non-celiac control groups (9%) (P=0.587). Although the serum transaminase values were within normal range in the majority of untreated patients, initially normal liver enzyme levels decreased significantly on a gluten-free diet. In treated celiac disease, gluten challenge led to mild and transient hypertransaminasemia.

CONCLUSIONS

In our area, where the prevalence of celiac disease is high, hypertransaminasemia is less frequent in untreated celiac disease patients than previously reported. The regular screening of transaminases in celiac disease needs to be re-evaluated. Although the liver enzyme levels were within the reference values in the majority of celiac patients, an obvious gluten dependence of transaminase levels was observed even in these subjects.

Autoimmunity in 2010

There is now growing evidence that autoimmunity is the common trait connecting multiple clinical phenotypes albeit differences in tissue specificity, pathogenetic mechanisms, and therapeutic approaches cannot be overlooked. Over the past years we witnessed a constant growth of the number of publications related to autoimmune diseases in peer-reviewed journals of the immunology area. Original data referred to factors from common injury pathways (i.e. T helper 17 cells, serum autoantibodies, or vitamin D) and specific diseases such as multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. As an example, the issue of a latitudinal gradient in the prevalence and incidence rates has been proposed for all autoimmune diseases and was recently coined as geoepidemiology to suggest new environmental triggers for tolerance breakdown. The present article is aimed at reviewing the articles that were published over the past year in the major autoimmunity and immunology journals.

Celiac disease: a model disease for gene-environment interaction

Celiac sprue remains a model autoimmune disease for dissection of genetic and environmental influences on disease progression. The 2010 Congress of Autoimmunity included several key sessions devoted to genetics and environment. Several papers from these symposia were selected for in-depth discussion and publication. This issue is devoted to this theme. The goal is not to discuss genetic and environmental interactions, but rather to focus on key elements of diagnosis, the inflammatory response and the mechanisms of autoimmunity.