Enterocyte Proliferation and Signaling Are Constitutively Altered in Celiac Disease

Celiac disease (CD) occurs frequently, and is caused by ingestion of prolamins from cereals in subjects with a genetic predisposition. The small intestinal damage depends on an intestinal stress/innate immune response to certain gliadin peptides (e.g., A-gliadin P31-43) in association with an adaptive immune response to other gliadin peptides (e.g., A-gliadin P57-68). Gliadin and peptide P31-43 affect epithelial growth factor receptor (EGFR) signaling and CD enterocyte proliferation. The reason why the stress/innate immune and proliferative responses to certain gliadin peptides are present in CD and not in control intestine is so far unknown. The aim of this work is to investigate if, in CD, a constitutive alteration of enterocyte proliferation and signaling exists that may represent a predisposing condition to the damaging effects of gliadin. Immunofluorescence and immunohistochemistry were used to study signaling in CD fibroblasts and intestinal biopsies. Western blot (WB) analysis, immunoprecipitation, and quantitative PCR were also used. We found in CD enterocytes enhancement of both proliferation and Epidermal Growth Factor Receptor (EGFR)/ligand system. In CD enterocytes and fibroblasts we found increase of the phosphorylated downstream signaling molecule Extracellular Signal Regulated Kinase (ERK); block of the ERK activation normalizes enterocytes proliferation in CD mucosa. In conclusion the same pathway, which gliadin and gliadin peptide P31-43 can interfere with, is constitutively altered in CD cells. This observation potentially explains the specificity of the damaging effects of certain gliadin peptides on CD intestine.     

Interaction of ‘toxic’ and ‘immunogenic’ A‐gliadin peptides with a membrane‐mimetic environment

Celiac disease (CD) is characterized by abnormally high concentrations of certain peptides in the small bowel. These peptides can be grouped in ‘toxic’ and ‘immunogenic’ classes, which elicit an innate immune response and an HLA‐mediated adaptive response, respectively. It is not clear on which molecular mechanisms responses to these different classes are based, but the 31–43 (P31–43) and the 56–68 (P56–68) A‐gliadin fragments are usually adopted as sequence representatives of toxic and immunogenic peptides, respectively. Here we report fluorescence experiments aiming to mimic the interaction of these peptides with the cell membrane surface by using sodium dodecyl sulphate (SDS) as a membrane‐mimetic medium. We show that P31–43 is able to bind SDS micelles in a way that resembles mixed micelle formation. On the other hand, no binding at all could be detected for P56–68. This different behaviour could be related to the paracellular or transcellular route through which gluten peptides may cross the intestinal epithelium, and open new insights into the pathogenetic mechanisms of CD. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of a peptide from alpha-gliadin resistant to digestive enzymes: implications for celiac disease

Current knowledge indicates that both innate and adaptive immune responses are involved in Celiac disease (CD) driven by different gliadin peptides. By studying a representative recombinant alpha-gliadin form, a further 25-mer peptide resistant to gastric, pancreatic, and human intestinal brush-border membrane enzymes was detected. This peptide latter encompasses the sequence 31-43 known to elicit the innate immune response in CD. The resistance of 25-mer, as well as that of the already described 33-mer related to the CD adaptive immune response, was confirmed on a standard flour wheat sample representative of the most widespread European varieties.     

Gliadin Peptide P31-43 Localises to Endocytic Vesicles and Interferes with Their Maturation

Background

Celiac Disease (CD) is both a frequent disease (1∶100) and an interesting model of a disease induced by food. It consists in an immunogenic reaction to wheat gluten and glutenins that has been found to arise in a specific genetic background; however, this reaction is still only partially understood. Activation of innate immunity by gliadin peptides is an important component of the early events of the disease. In particular the so-called “toxic” A-gliadin peptide P31-43 induces several pleiotropic effects including Epidermal Growth Factor Receptor (EGFR)-dependent actin remodelling and proliferation in cultured cell lines and in enterocytes from CD patients. These effects are mediated by delayed EGFR degradation and prolonged EGFR activation in endocytic vesicles. In the present study we investigated the effects of gliadin peptides on the trafficking and maturation of endocytic vesicles.

Methods/Principal Findings

Both P31-43 and the control P57-68 peptide labelled with fluorochromes were found to enter CaCo-2 cells and interact with the endocytic compartment in pulse and chase, time-lapse, experiments. P31-43 was localised to vesicles carrying early endocytic markers at time points when P57-68-carrying vesicles mature into late endosomes. In time-lapse experiments the trafficking of P31-43-labelled vesicles was delayed, regardless of the cargo they were carrying. Furthermore in celiac enterocytes, from cultured duodenal biopsies, P31-43 trafficking is delayed in early endocytic vesicles. A sequence similarity search revealed that P31-43 is strikingly similar to Hrs, a key molecule regulating endocytic maturation. A-gliadin peptide P31-43 interfered with Hrs correct localisation to early endosomes as revealed by western blot and immunofluorescence microscopy.

Conclusions

P31-43 and P57-68 enter cells by endocytosis. Only P31-43 localises at the endocytic membranes and delays vesicle trafficking by interfering with Hrs-mediated maturation to late endosomes in cells and intestinal biopsies. Consequently, in P31-43-treated cells, Receptor Tyrosin Kinase (RTK) activation is extended. This finding may explain the role played by gliadin peptides in inducing proliferation and other effects in enterocytes from CD biopsies.     

Gliadin-mediated proliferation and innate immune activation in celiac disease are due to alterations in vesicular trafficking

Background and Objectives

Damage to intestinal mucosa in celiac disease (CD) is mediated both by inflammation due to adaptive and innate immune responses, with IL-15 as a major mediator of the innate immune response, and by proliferation of crypt enterocytes as an early alteration of CD mucosa causing crypts hyperplasia. We have previously shown that gliadin peptide P31-43 induces proliferation of cell lines and celiac enterocytes by delaying degradation of the active epidermal growth factor receptor (EGFR) due to delayed maturation of endocytic vesicles. IL-15 is increased in the intestine of patients affected by CD and has pleiotropic activity that ultimately results in immunoregulatory cross-talk between cells belonging to the innate and adaptive branches of the immune response. Aims of this study were to investigate the role of P31-43 in the induction of cellular proliferation and innate immune activation.

Methods/Principal Findings

Cell proliferation was evaluated by bromodeoxyuridine (BrdU) incorporation both in CaCo-2 cells and in biopsies from active CD cases and controls. We used real-time PCR to evaluate IL-15 mRNA levels and FACS as well as ELISA and Western Blot (WB) analysis to measure protein levels and distribution in CaCo-2 cells.Gliadin and P31-43 induce a proliferation of both CaCo-2 cells and CD crypt enterocytes that is dependent on both EGFR and IL-15 activity. In CaCo-2 cells, P31-43 increased IL-15 levels on the cell surface by altering intracellular trafficking. The increased IL-15 protein was bound to IL15 receptor (IL-15R) alpha, did not require new protein synthesis and functioned as a growth factor.

Conclusion

In this study, we have shown that P31-43 induces both increase of the trans-presented IL-15/IL5R alpha complex on cell surfaces by altering the trafficking of the vesicular compartments as well as proliferation of crypt enterocytes with consequent remodelling of CD mucosa due to a cooperation of IL-15 and EGFR.     

Gliadin stimulation of murine macrophage inflammatory gene expression and intestinal permeability are MyD88-dependent: role of the innate immune response in Celiac disease

Recent studies have demonstrated the importance of TLR signaling in intestinal homeostasis. Celiac disease (CD) is an autoimmune enteropathy triggered in susceptible individuals by the ingestion of gliadin-containing grains. In this study, we sought to test the hypothesis that gliadin initiates this response by stimulating the innate immune response to increase intestinal permeability and by up-regulating macrophage proinflammatory gene expression and cytokine production. To this end, intestinal permeability and the release of zonulin (an endogenous mediator of gut permeability) in vitro, as well as proinflammatory gene expression and cytokine release by primary murine macrophage cultures, were measured. Gliadin and its peptide derivatives, 33-mer and p31-43, were found to be potent inducers of both a zonulin-dependent increase in intestinal permeability and macrophage proinflammatory gene expression and cytokine secretion. Gliadin-induced zonulin release, increased intestinal permeability, and cytokine production were dependent on myeloid differentiation factor 88 (MyD88), a key adapter molecule in the TLR/IL-1R signaling pathways, but were neither TLR2- nor TLR4-dependent. Our data support the following model for the innate immune response to gliadin in the initiation of CD. Gliadin interaction with the intestinal epithelium increases intestinal permeability through the MyD88-dependent release of zonulin that, in turn, enables paracellular translocation of gliadin and its subsequent interaction with macrophages within the intestinal submucosa. There, the interaction of gliadin with macrophages elicits a MyD88-dependent proinflammatory cytokine milieu that facilitates the interaction of T cells with APCs, leading ultimately to the Ag-specific adaptive immune response seen in patients with CD.     

Modulatory Effect of Gliadin Peptide 10-mer on Epithelial Intestinal CACO-2 Cell Inflammatory Response

Celiac Disease (CD) is a chronic inflammatory enteropathy, triggered in genetically susceptible individuals by dietary gluten. Gluten is able to elicit proliferation of specific T cells and secretion of inflammatory cytokines in the small intestine. In this study we investigated the possibility that p10-mer, a decapeptide from durum wheat (QQPQDAVQPF), which was previously shown to prevent the activation of celiac peripheral lymphocytes, may exert an inhibitory effect on peptic-tryptic digested gliadin (PT-Gly)-stimulated intestinal carcinoma CACO-2 cells. In these cells, incubated with PT-Gly or p31-43 α-gliadin derived peptide in the presence or in the absence of p10-mer, IRAK1 activation and NF-kB, ERK1/2 and p38 MAPK phosphorylation were measured by immunoblotting, Cyclooxigenase 2 (COX-2) activity by PGE-2 release assay, and production of cytokines in the cell supernatants by ELISA. Our results showed that pre-treatment of CACO-2 cells with p10-mer significantly inhibited IRAK1 activation and NF-kB, ERK1/2 and p38 MAPK phosphorylation, as well as COX-2 activity (i.e. PGE-2 release) and production of the IL-6 and IL-8 pro-inflammatory cytokines, induced by gliadin peptides. These findings demonstrate the inhibitory effect of the p10-mer peptide on inflammatory response in CACO-2 cells. The results of the present study show that this p10-mer peptide can modulate "in vitro" the inflammatory response induced by gliadin peptides, allowing to move towards new therapeutic strategies. Turning off the inflammatory response, may in fact represent a key target in the immunotherapy of celiac disease.     

The toxic alpha‐gliadin peptide 31–43 enters cells without a surface membrane receptor

Alpha‐gliadin peptide 31–43 is considered to be the main peptide responsible for the innate immune response in celiac disease patients. Recent evidence indicates that peptide 31–43 rapidly enters cells and interacts with the early endocytic vesicular compartment. However, the mechanism of its uptake is not completely understood. Our aim is to characterize, isolate and identify possible cell surface proteins involved in peptide 31–43 internalization by Caco‐2 cells. In this study, we used a chemical cross‐linker to block peptide 31–43 on cell surface proteins, and pulled‐down peptide‐proteins complexes using antibodies raised against peptide 31–43. Through this experimental approach, we did not observe any specific complex between cell proteins and peptide 31–43 in Coomassie‐stained denaturating gels or by Western blotting. We also found that type 2 transglutaminase was not necessary for peptide 31–43 internalization, even though it had a regulatory role in the process. Finally, we demonstrated that peptide 31–43 did not behave as a classical ligand, indeed the labeled peptide did not displace the unlabeled peptide in a competitive binding assay. On the basis of these findings and of previous evidence demonstrating that peptide 31–43 is able to interact with a membrane‐like environment in vitro, we conclude that membrane composition and organization, rather than a specific receptor protein, may have a major role in peptide 31–43 internalization by cells.     

Effects of PEMF on microcirculation and angiogenesis in a model of acute hindlimb ischemia in diabetic rats

Hindlimb ischemia is a major complication of diabetic patients due to poor neovascularization. Therapy with pulsed electromagnetic fields (PEMF) can promote angiogenesis in ischemic lesions. However, the efficacy and therapeutic mechanisms of PEMF in diabetes‐related hindlimb ischemia are unclear. Sprague–Dawley rats were injected with streptozocin to induce diabetes, and 10 weeks later diabetic rats were subjected to surgical induction of acute hindlimb ischemia. The rats were randomized and treated with PEMF, and the blood perfusion of individual rats was determined longitudinally by laser Doppler perfusion imaging (LDPI). The neovascular density was examined using immunofluorescent analysis of CD31 expression and alkaline phosphatase (AP) staining. The levels of VEGF, VEGFR, FGF‐2, and FGFR1 expression, and ERK 1/2 and P38 phosphorylation in the muscles were characterized using enzyme‐linked immunosorbent assay (ELISA) and Western blot assays. The values of LDPI in the PEMF‐treated rats at 14 and 28 days post surgery were significantly greater than those in the controls, accompanied by significantly elevated levels of anti‐CD31 and AP staining. The relative levels of FGF‐2 and FGFR1, but not VEGF and VEGFR expression, and ERK1/2, but not P38 phosphorylation, in the muscles of the PEMF‐treated rats were significantly higher than those in the controls. Our data indicated that PEMF enhanced acute hindlimb ischemia‐related perfusion and angiogenesis, associated with up‐regulating FGF‐2 expression and activating the ERK1/2 pathway in diabetic rats. Therefore, PEMF may be valuable for the treatment of diabetic patients with ischemic injury. Bioelectromagnetics 34:180–188, 2013. © 2012 Wiley Periodicals, Inc.     

Celiac disease‐associated Neisseria flavescens decreases mitochondrial respiration in CaCo‐2 epithelial cells: Impact of Lactobacillus paracasei CBA L74 on bacterial‐induced cellular imbalance

We previously identified a Neisseria flavescens strain in the duodenum of celiac disease (CD) patients that induced immune inflammation in ex vivo duodenal mucosal explants and in CaCo‐2 cells. We also found that vesicular trafficking was delayed after the CD‐immunogenic P31‐43 gliadin peptide‐entered CaCo‐2 cells and that Lactobacillus paracasei CBA L74 (L. paracasei‐CBA) supernatant reduced peptide entry. In this study, we evaluated if metabolism and trafficking was altered in CD‐N. flavescens‐infected CaCo‐2 cells and if any alteration could be mitigated by pretreating cells with L. paracasei‐CBA supernatant, despite the presence of P31‐43. We measured CaCo‐2 bioenergetics by an extracellular flux analyser, N. flavescens and P31‐43 intracellular trafficking by immunofluorescence, cellular stress by TBARS assay, and ATP by bioluminescence. We found that CD‐N. flavescens colocalised more than control N. flavescens with early endocytic vesicles and more escaped autophagy thereby surviving longer in infected cells. P31‐43 increased colocalisation of N. flavescens with early vesicles. Mitochondrial respiration was lower (P < .05) in CD‐N. flavescens‐infected cells versus not‐treated CaCo‐2 cells, whereas pretreatment with L. paracasei‐CBA reduced CD‐N. flavescens viability and improved cell bioenergetics and trafficking. In conclusion, CD‐N. flavescens induces metabolic imbalance in CaCo‐2 cells, and the L. paracasei‐CBA probiotic could be used to correct CD‐associated dysbiosis.     

HLA-DQ determines the response to exogenous wheat proteins: a model of gluten sensitivity in transgenic knockout mice

We have investigated the genetic basis of the immune response to dietary gluten in HCD4/DQ8 and HCD4/DQ6 double transgenic mice. Mice were immunized with gluten i.p. or individual peptides s.c. and spleen or draining lymph node T cells were challenged in vitro. Strong proliferative responses to gluten were seen in the HCD4/DQ8 mice, whereas the HCD4/DQ6 mice responded to gluten poorly. A series of overlapping peptides spanning gliadin were synthesized. The HCD4/DQ8 mice reacted to many of the individual peptides of gliadin, while the HCD4/DQ6 mice were relatively unresponsive. T cells isolated from HCD4/DQ8 mice also responded well to modified (deamidated) versions of the gliadin peptides, whereas HCD4DQ6 mice did not. The T cell response to gluten was CD4 dependent and DQ restricted and led to the production of cytokines IL-6, TGF-beta, and IL-10. Finally, intestinal lymphocytes isolated from gluten-fed HCD4/DQ8 mice displayed an activated phenotype. These data suggest that this HLA class II transgenic murine model of gluten sensitivity may provide insight into the initiation of the MHC class II-restricted gluten sensitivity in celiac disease.     

Functionality of lactic acid bacteria peptidase activities in the hydrolysis of gliadin‐like fragments

Aims: To evaluate the role of the peptidase activities from sourdough lactic acid bacteria (LAB) in the degradation of α‐gliadin fragments. Methods and Results: Different proline‐containing substrates were hydrolysed by LAB indicating pro‐specific peptidase activities. Lactobacillus plantarum CRL 775 and Pediococcus pentosaceus CRL 792 displayed the highest tri‐ and di‐peptidase activities, respectively. Lactobacillus plantarum strains hydrolysed more than 60%α‐gliadin fragments corresponding to the 31–43 and 62–75 amino acids in the protein after 2 h. None of the LAB strains alone could hydrolyse 57–89 α‐gliadin peptide; however, the combination of L. plantarum CRL 775 and P. pentosaceus CRL 792 led to hydrolysis (57%) of this peptide in 8 h. Conclusions: The capacity of LAB strains to degrade α‐gliadin fragments was not correlated to individual peptidase activities. Several strains separately degraded the 31–43 and 62–75 α‐gliadin fragments, while the 57–89 peptide degradation was associated with the combination of peptidase profiles from pooled LAB strains. This is the first report on the peptide hydrolase system of sourdough pediococci and its ability to reduce α‐gliadin fragments. Significance and Impact of the Study: This study contributes to a better knowledge of sourdough LAB proteolytic system and its role in the degradation of proline‐rich α‐gliadin peptides involved in celiac disease.     

Gliadin-specific type 1 regulatory T cells from the intestinal mucosa of treated celiac patients inhibit pathogenic T cells

Celiac disease (CD) results from a permanent intolerance to dietary gluten and is due to a massive T cell-mediated immune response to gliadin, the main component of gluten. In this disease, the regulation of immune responses to dietary gliadin is altered. Herein, we investigated whether IL-10 could modulate anti-gliadin immune responses and whether gliadin-specific type 1 regulatory T (Tr1) cells could be isolated from the intestinal mucosa of CD patients in remission. Short-term T cell lines were generated from jejunal biopsies, either freshly processed or cultured ex vivo with gliadin in the presence or absence of IL-10. Ex vivo stimulation of CD biopsies with gliadin in the presence of IL-10 resulted in suppression of Ag-specific proliferation and cytokine production, indicating that pathogenic T cells are susceptible to IL-10-mediated immune regulation. T cell clones generated from intestinal T cell lines were tested for gliadin specificity by cytokine production and proliferative responses. The majority of gliadin-specific T cell clones had a Th0 cytokine production profile with secretion of IL-2, IL-4, IFN-gamma, and IL-10 and proliferated in response to gliadin. Tr1 cell clones were also isolated. These Tr1 cells were anergic, restricted by DQ2 (a CD-associated HLA), and produced IL-10 and IFN-gamma, but little or no IL-2 or IL-4 upon activation with gliadin or polyclonal stimuli. Importantly, gliadin-specific Tr1 cell clones suppressed proliferation of pathogenic Th0 cells. In conclusion, dietary Ag-specific Tr1 cells are present in the human intestinal mucosa, and strategies to boost their numbers and/or function may offer new therapeutic opportunities to restore gut homeostasis.     

Gliadin fragments promote migration of dendritic cells

In genetically predisposed individuals, ingestion of wheat gliadin provokes a T‐cell‐mediated enteropathy, celiac disease. Gliadin fragments were previously reported to induce phenotypic maturation and Th1 cytokine production by human dendritic cells (DCs) and to boost their capacity to stimulate allogeneic T cells. Here, we monitor the effects of gliadin on migratory capacities of DCs. Using transwell assays, we show that gliadin peptic digest stimulates migration of human DCs and their chemotactic responsiveness to the lymph node‐homing chemokines CCL19 and CCL21. The gliadin‐induced migration is accompanied by extensive alterations of the cytoskeletal organization, with dissolution of adhesion structures, podosomes, as well as up‐regulation of the CC chemokine receptor (CCR) 7 on cell surface and induction of cyclooxygenase (COX)‐2 enzyme that mediates prostaglandin E2 (PGE₂) production. Blocking experiments confirmed that gliadin‐induced migration is independent of the TLR4 signalling. Moreover, we showed that the α‐gliadin‐derived 31–43 peptide is an active migration‐inducing component of the digest. The migration promoted by gliadin fragments or the 31–43 peptide required activation of p38 mitogen‐activated protein kinase (MAPK). As revealed using p38 MAPK inhibitor SB203580, this was responsible for DC cytoskeletal transition, CCR7 up‐regulation and PGE₂ production in particular. Taken together, this study provides a new insight into pathogenic features of gliadin fragments by demonstrating their ability to promote DC migration, which is a prerequisite for efficient priming of naive T cells, contributing to celiac disease pathology.     

Role of non-phosphorylated activation loop residues in determining ERK2 dephosphorylation, activity, and subcellular localization

Extracellular signal-regulated kinases (ERKs) activity is regulated by MAPK/ERK kinases (MEKs), which phosphorylate the regulatory Tyr and Thr residues in ERKs activation loop, and by various phosphatases that remove the incorporated phosphates. Although the role of the phosphorylated residues in the activation loop of ERKs is well studied, much less is known about the role of other residues within this loop. Here we substituted several residues within amino acids 173-177 of ERK2 and studied their role in ERK2 phosphorylation, substrate recognition, and subcellular localization. We found that substitution of residues 173-175 and particularly Pro(174) to alanines reduces the EGF-induced ERK2 phosphorylation, without modifying its in vitro phosphorylation by MEK1. Examining the ability of these mutants to be dephosphorylated revealed that 173-5A mutants are hypersensitive to phosphatases, indicating that these residues are important for setting the phosphorylation/dephosphorylation balance of ERKs. In addition, 173-5A mutants reduced ERK2 activity toward Elk-1, without affecting the activity of ERK2 toward MBP, while substitution of residues 176-8 decreased ERK2 activity toward both substrates. Substitution of Asp(177) to alanine increased nuclear localization of the construct in MEK1-overexpressing cells, suggesting that this residue together with His(176) is involved in the dissociation of ERK2 from MEKs. Combining CRS/CD motif and the activation loop mutations revealed that these two regions cooperate in determining the net phosphorylation of ERK2, but the role of the CRS/CD motif predominates that of the activation loop residues. Thus, we show here that residues 173-177 of ERK2 join other regulatory regions of ERKs in governing ERK activity.     

Gliadin Peptides Induce Tissue Transglutaminase Activation and ER-Stress through Ca2+ Mobilization in Caco-2 Cells

Background

Celiac disease (CD) is an intestinal inflammatory condition that develops in genetically susceptible individuals after exposure to dietary wheat gliadin. The role of post-translational modifications of gliadin catalyzed by tissue transglutaminase (tTG) seems to play a crucial role in CD. However, it remains to be established how and where tTG is activated in vivo. We have investigated whether gliadin peptides modulate intracellular Ca²⁺ homeostasis and tTG activity.

Methods/Principal Findings

We studied Ca²⁺ homeostasis in Caco-2 cells by single cell microfluorimetry. Under our conditions, A-gliadin peptides 31–43 and 57–68 rapidly mobilized Ca²⁺ from intracellular stores. Specifically, peptide 31–43 mobilized Ca²⁺ from the endoplasmic reticulum (ER) and mitochondria, whereas peptide 57–68 mobilized Ca²⁺ only from mitochondria. We also found that gliadin peptide-induced Ca²⁺ mobilization activates the enzymatic function of intracellular tTG as revealed by in situ tTG activity using the tTG substrate pentylamine-biotin. Moreover, we demonstrate that peptide 31–43, but not peptide 57–68, induces an increase of tTG expression. Finally, we monitored the expression of glucose-regulated protein-78 and of CCAAT/enhancer binding protein-homologous protein, which are two biochemical markers of ER-stress, by real-time RT-PCR and western blot. We found that chronic administration of peptide 31–43, but not of peptide 57–68, induces the expression of both genes.

Conclusions

By inducing Ca²⁺ mobilization from the ER, peptide 31–43 could promote an ER-stress pathway that may be relevant in CD pathogenesis. Furthermore, peptides 31–43 and 57–68, by activating intracellular tTG, could alter inflammatory key regulators, and induce deamidation of immunogenic peptides and gliadin–tTG crosslinking in enterocytes and specialized antigen-presenting cells.     

Celiac disease: risk assessment, diagnosis, and monitoring

Celiac disease is an autoimmune disorder occurring in genetically susceptible individuals, triggered by gluten and related prolamins. Well identified haplotypes in the human leukocyte antigen (HLA) class II region (either DQ2 [DQA*0501-DQB*0201] or DQ8 [DQA*0301-DQB1*0302]) confer a large part of the genetic susceptibility to celiac disease.Celiac disease originates as a result of a combined action involving both adaptive and innate immunity. The adaptive immune response to gluten has been well described, with the identification of specific peptide sequences demonstrating HLA-DQ2 or -DQ8 restrictive binding motifs across various gluten proteins. As for innate immunity, through specific natural killer receptors expressed on their surface, intra-epithelial lymphocytes recognize nonclassical major histocompatibility complex (MHC)-I molecules such as MICA, which are induced on the surface of enterocytes by stress and inflammation, and this interaction leads to their activation to become lymphokine-activated killing cells. Four possible presentations of celiac disease are recognized: (i) typical, characterized mostly by gastrointestinal signs and symptoms; (ii) atypical or extraintestinal, where gastrointestinal signs/symptoms are minimal or absent and a number of other manifestations are present; (iii) silent, where the small intestinal mucosa is damaged and celiac disease autoimmunity can be detected by serology, but there are no symptoms; and, finally, (iv) latent, where individuals possess genetic compatibility with celiac disease and may also show positive autoimmune serology, that have a normal mucosa morphology and may or may not be symptomatic.The diagnosis of celiac disease still rests on the demonstration of changes in the histology of the small intestinal mucosa. The classic celiac lesion occurs in the proximal small intestine with histologic changes of villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytosis. Currently, serological screening tests are utilized primarily to identify those individuals in need of a diagnostic endoscopic biopsy. The serum levels of immunoglobulin (Ig)A anti-tissue transglutaminase (or TG2) are the first choice in screening for celiac disease, displaying the highest levels of sensitivity (up to 98%) and specificity (around 96%). Anti-endomysium antibodies-IgA (EMA), on the other hand, have close to 100% specificity and a sensitivity of greater than 90%. The interplay between gliadin peptides and TG2 is responsible for the generation of novel antigenic epitopes, the TG2-generated deamidated gliadin peptides. Such peptides represent much more celiac disease-specific epitopes than native peptides, and deamidated gliadin antibodies (DGP) have shown promising results as serological markers for celiac disease. Serology has also been employed in monitoring the response to a gluten-free diet.Despite the gluten-free diet being so effective, there is a growing demand for alternative treatment options. In the future, new forms of treatment may include the use of gluten-degrading enzymes to be ingested with meals, the development of alternative, gluten-free grains by genetic modification, the use of substrates regulating intestinal permeability to prevent gluten entry across the epithelium, and, finally, the availability of different forms of immunotherapy.