Inhibition of HLA-DQ2-mediated antigen presentation by analogues of a high affinity 33-residue peptide from alpha2-gliadin

Immune Modulation by Antigenic Peptides and Antigenic Peptide Conjugates for Treatment of Multiple Sclerosis

The immune system defends our body by fighting infection from pathogens utilizing both the innate and adaptive immune responses. The innate immune response is generated rapidly as the first line of defense. It is followed by the adaptive immune response that selectively targets infected cells. The adaptive immune response is generated more slowly, but selectively, by targeting a wide range of foreign particles (i.e., viruses or bacteria) or molecules that enter the body, known as antigens. Autoimmune diseases are the results of immune system glitches, where the body's adaptive system recognizes self-antigens as foreign. Thus, the host immune system attacks the self-tissues or organs with a high level of inflammation and causes debilitation in patients. Many current treatments for autoimmune diseases (i.e., multiple sclerosis (MS), rheumatoid arthritis (RA)) have been effective but lead to adverse side effects due to general immune system suppression, which makes patients vulnerable to opportunistic infections. To counter these negative effects, many different avenues of antigen specific treatments are being developed to selectively target the autoreactive immune cells for a specific self-antigen or set of self-antigens while not compromising the general immune system. These approaches include soluble antigenic peptides, bifunctional peptide inhibitors (BPI) including IDAC and Fc-BPI, polymer conjugates, and peptide-drug conjugates. Here, various antigen-specific methods of potential treatments, their efficacy, and limitations will be discussed along with the potential mechanisms of action.

Next generation strategies to recover immunological tolerance in celiac disease

Celiac disease (CD) is an autoimmune disease that occurs in genetically predisposed individuals following the ingestion of gluten. Its prevalence is rising worldwide. A gluten-free (GF) diet is mandatory for the management of CD. However, several issues persist regarding the nutritional quality of GF products. Importantly, deep knowledge about the pathogenic mechanisms in CD highlights the central role of CD4⁺ T cell-mediated immunity in CD. Furthermore, intestinal T regulatory cells are functional in CD, but cytokines such as IL-15, produced under inflammatory conditions, hamper their activity. This paves the way for the development of immunomodulatory strategies to the GF diet. From this perspective, microbiological approaches were considered able to modulate the gluten-specific immune response. Interestingly, gliadin peptide-based immunotherapy to abolish the inflammatory CD4⁺T cell-mediated response has been explored in CD patients. Furthermore, different biotechnological approaches based on the use of chemically/enzymatically modified gluten molecules have been proved effective in different models of CD. However, the choice of the right age in infants to introduce the antigen and thus induce tolerance still remains an important issue to solve. Addressing all these points should help to design an effective intervention strategy for preventing CD.

New agents for immunosuppression

The human abdomen harbors organs that the host's immune system can attack easily. This immunological storm front leads to diseases like Crohn's Disease, Ulcerative Colitis or Autoimmune Hepatitis. Serious symptoms like pain, diarrhea, fatigue, or malnutrition accompany these diseases. Moreover, many patients have an increased risk for developing special kind of malignancies and some autoimmune disease can show a high mortality. The key to treat them consists of a deep understanding of their pathophysiology. In vitro and especially in vivo basic research laid the foundation for our increasing knowledge about it during the past years. This enabled the development of new therapeutic approaches that interact directly with cytokines or immune cells instead of building the treatment on a total immunosuppression. Different kind of antibodies, kinase inhibitors, and regulatory T cells build the base for these approaches. This review shows new therapeutical approaches in gastrointestinal autoimmune diseases in context to their pathophysiological basis.

Dynamics-Based Peptide-MHC Binding Optimization by a Convolutional Variational Autoencoder: A Use-Case Model for CASTELO

An unsolved challenge in the development of antigen-specific immunotherapies is determining the optimal antigens to target. Comprehension of antigen-major histocompatibility complex (MHC) binding is paramount toward achieving this goal. Here, we apply CASTELO, a combined machine learning-molecular dynamics (ML-MD) approach, to identify per-residue antigen binding contributions and then design novel antigens of increased MHC-II binding affinity for a type 1 diabetes-implicated system. We build upon a small-molecule lead optimization algorithm by training a convolutional variational autoencoder (CVAE) on MD trajectories of 48 different systems across four antigens and four HLA serotypes. We develop several new machine learning metrics including a structure-based anchor residue classification model as well as cluster comparison scores. ML-MD predictions agree well with experimental binding results and free energy perturbation-predicted binding affinities. Moreover, ML-MD metrics are independent of traditional MD stability metrics such as contact area and root-mean-square fluctuations (RMSF), which do not reflect binding affinity data. Our work supports the role of structure-based deep learning techniques in antigen-specific immunotherapy design.

Toward Guided Mutagenesis: Gaussian Process Regression Predicts MHC Class II Antigen Mutant Binding

Antigen-specific immunotherapies (ASI) require successful loading and presentation of antigen peptides into the major histocompatibility complex (MHC) binding cleft. One route of ASI design is to mutate native antigens for either stronger or weaker binding interaction to MHC. Exploring all possible mutations is costly both experimentally and computationally. To reduce experimental and computational expense, here we investigate the minimal amount of prior data required to accurately predict the relative binding affinity of point mutations for peptide-MHC class II (pMHCII) binding. Using data from different residue subsets, we interpolate pMHCII mutant binding affinities by Gaussian process (GP) regression of residue volume and hydrophobicity. We apply GP regression to an experimental data set from the Immune Epitope Database, and theoretical data sets from NetMHCIIpan and Free Energy Perturbation calculations. We find that GP regression can predict binding affinities of nine neutral residues from a six-residue subset with an average R² coefficient of determination value of 0.62 ± 0.04 (±95% CI), average error of 0.09 ± 0.01 kcal/mol (±95% CI), and with an receiver operating characteristic (ROC) AUC value of 0.92 for binary classification of enhanced or diminished binding affinity. Similarly, metrics increase to an R² value of 0.69 ± 0.04, average error of 0.07 ± 0.01 kcal/mol, and an ROC AUC value of 0.94 for predicting seven neutral residues from an eight-residue subset. Our work finds that prediction is most accurate for neutral residues at anchor residue sites without register shift. This work holds relevance to predicting pMHCII binding and accelerating ASI design.

Transamidation Down-Regulates Intestinal Immunity of Recombinant α-Gliadin in HLA-DQ8 Transgenic Mice

Enzymatic transamidation of gliadins by microbial transglutaminase (mTG) inhibits interferon-γ (IFN-γ) secretion by intestinal T cell lines in patients with celiac disease (CD). To gain insight into the cellular mechanisms underlying the down-regulatory effects of transamidation, we tested a single recombinant α-gliadin (r-gliadin) harbouring two immunodominant peptides, p13 (aa. 120–139) and p23 (aa. 220–239), in HLA-DQ8 transgenic mice, a model of gluten sensitivity. Mice were intranasally immunised with r-gliadin or r-gliadin transamidated by mTG (K-r-gliadin) along with cholera toxin, and the response of mesenteric lymph node cells was analysed by cytokine multiplex assay. An in vitro challenge with r-gliadin was characterised by secretion of specific cytokines featuring both innate immunity and the Th1/Th2/Th17 pattern of the adaptive response. Notably, transamidation specifically down-regulated the Th1 response. Structural studies performed on K-r-gliadin confirmed that specific glutamine residues in p13 and p23, previously found to be deamidated by tissue transglutaminase, were also transamidated by mTG. In silico analysis, simulating p13 and p23 peptide binding to HLA-DQ8 showed that these glutamines, in the form of glutamate, could interact by means of salt bridges with peculiar amino acids of the alpha chain of HLA-DQ8, suggesting that their transamidation may influence the HLA-restricted recognition of these peptides. Thus, the structural findings provided a rationale to explain the down-regulation of the r-gliadin-specific Th1 response following transamidation.

Expanded Clinical Phenotype, Oncological Associations, and Immunopathologic Insights of Paraneoplastic Kelch-like Protein-11 Encephalitis

Importance

Recognizing the presenting and immunopathological features of Kelch-like protein-11 immunoglobulin G seropositive (KLHL11 IgG+) patients may aid in early diagnosis and management.

Objective

To describe expanding neurologic phenotype, cancer associations, outcomes, and immunopathologic features of KLHL11 encephalitis.

Design, Setting, and Participants

This retrospective tertiary care center study, conducted from October 15, 1998, to November 1, 2019, prospectively identified 31 KLHL11 IgG+ cases in the neuroimmunology laboratory. Eight were identified by retrospective testing of patients with rhomboencephalitis (confirmed by tissue-based-immunofluorescence and transfected-cell-based assays).

Main Outcomes and Measures

Outcome variables included modified Rankin score and gait aid use.

Results

All 39 KLHL11 IgG+ patients were men (median age, 46 years; range, 28-73 years). Initial clinical presentations were ataxia (n = 32; 82%), diplopia (n = 22; 56%), vertigo (n = 21; 54%), hearing loss (n = 15; 39%), tinnitus (n = 14; 36%), dysarthria (n = 11; 28%), and seizures (n = 9; 23%). Atypical neurologic presentations included neuropsychiatric dysfunction, myeloneuropathy, and cervical amyotrophy. Hearing loss or tinnitus preceded other neurologic deficits by 1 to 8 months in 10 patients (26%). Among patients screened for malignancy (n = 36), testicular germ-cell tumors (n = 23; 64%) or testicular microlithiasis and fibrosis concerning for regressed germ cell tumor (n = 7; 19%) were found in 83% of the patients (n = 30). In 2 patients, lymph node biopsy diagnosed metastatic lung adenocarcinoma in one and chronic lymphocytic leukemia in the other. Initial brain magnetic resonance imaging revealed T2 hyperintensities in the temporal lobe (n = 12), cerebellum (n = 9), brainstem (n = 3), or diencephalon (n = 3). Among KLHL11 IgG+ patients who underwent HLA class I and class II genotyping (n = 10), most were found to have HLA-DQB1*02:01 (n = 7; 70%) and HLA-DRB1*03:01 (n = 6; 60%) associations. A biopsied gadolinium-enhancing temporal lobe lesion demonstrated T cell-predominant inflammation and nonnecrotizing granulomas. Cerebellar biopsy (patient with chronic ataxia) and 2 autopsied brains demonstrated Purkinje neuronal loss and Bergmann gliosis, supporting early active inflammation and later extensive neuronal loss. Compared with nonautoimmune control peripheral blood mononuclear cells, cluster of differentiation (CD) 8+ and CD4+ T cells were significantly activated when patient peripheral blood mononuclear cells were cultured with KLHL11 protein. Most patients (58%) benefitted from immunotherapy and/or cancer treatment (neurological disability stabilized [n = 10] or improved [n = 9]). Kaplan-Meier curve demonstrated significantly higher probability of wheelchair dependence among patients without detectable testicular cancer. Long-term outcomes in KLHL11-IgG+ patients were similar to Ma2 encephalitis.

Conclusions and Relevance

Kelch-like protein-11 IgG is a biomarker of testicular germ-cell tumor and paraneoplastic neurologic syndrome, often refractory to treatment. Described expanded neurologic phenotype and paraclinical findings may aid in its early diagnosis and treatment.

Gliadin Sequestration as a Novel Therapy for Celiac Disease: A Prospective Application for Polyphenols

Celiac disease is an autoimmune disorder characterized by a heightened immune response to gluten proteins in the diet, leading to gastrointestinal symptoms and mucosal damage localized to the small intestine. Despite its prevalence, the only treatment currently available for celiac disease is complete avoidance of gluten proteins in the diet. Ongoing clinical trials have focused on targeting the immune response or gluten proteins through methods such as immunosuppression, enhanced protein degradation and protein sequestration. Recent studies suggest that polyphenols may elicit protective effects within the celiac disease milieu by disrupting the enzymatic hydrolysis of gluten proteins, sequestering gluten proteins from recognition by critical receptors in pathogenesis and exerting anti-inflammatory effects on the system as a whole. This review highlights mechanisms by which polyphenols can protect against celiac disease, takes a critical look at recent works and outlines future applications for this potential treatment method.

The HLA complex and coeliac disease

The Human Leukocyte Antigen (HLA) has a crucial role in the development and pathogenesis of coeliac disease (CD). The genes HLA-DQA1 and HLA-DQB1, both lying in this region and encoding the HLA-DQ heterodimer, are the main genetic predisposing factors to CD. Approximately 90% of CD patients carry the heterodimer HLA-DQ2.5, leaving only a small proportion of patients with lower risk heterodimers (HLA-DQ8, HLA-DQ2.2 or HLA-DQ7.5). These HLA-DQ molecules act as receptors present in the surface of antigen presenting cells and show high affinity for deamidated gluten peptides, which bind and present to CD4⁺ T cells. This triggers the immunological reaction that evolves into CD. Since specific HLA genetics is present in almost the totality of CD patients, HLA typing has a very high negative predictive value, and it can be used to support diagnosis in specific scenarios. HLA risk has been associated to different CD-related features, such as age at onset, clinical outcomes, antibody levels and grade of histological lesion; but further research is needed. HLA-DQ genotypes have been also suggested to modulate the composition of the gut microbiota.

An open-label randomised pilot trial on safety of wheat variety C273 in patients with adult celiac disease

BACKGROUND

The only effective treatment for celiac disease (CeD) is gluten free diet (GFD). However, GFD is restrictive and efforts are being made to explore alternative therapies including safer wheat varieties. Wheat variety C273 has been previously identified to have reduced load of intact T-cell stimulatory epitopes via in silico and in vitro analysis.

METHODS

Adult patients diagnosed with CeD and recovered on GFD were included in the study. Patients were randomised into two groups in a 2:1 ratio. Patients in group I had graded introduction of C273 wheat in diet, maintained for 24 weeks; in Group II, wheat was restricted with continuation of GFD. Clinical symptoms, serology [anti-tissue transglutaminase (anti-tTG), anti-endomysial antibody (anti-EMA)], circulating inflammatory biomarkers [intestinal fatty-acid binding protein (I-FABP), plasma citrulline, interferon-γ (IFN-γ)] and histology were evaluated periodically. Final evaluation was performed at week 28.

RESULTS

A total of 15 patients were enrolled (Group I: n = 10, Group II: n = 5). All patients except two in Group I remained compliant. None of the remaining eight patients in group I developed symptoms. No significant changes in serology (anti-tTG, anti-EMA) and histology were observed between the two groups at 28 weeks (p > 0.05). Significant changes in plasma citrulline(29.87 ± 8.98 versus 36.58 ± 3.09, p = 0.049) and IFN-γ (44.56 ± 9.74 versus 33.50 ± 3.68; p = 0.031) were observed in Group I.

CONCLUSION

Consumption of C273 wheat did not result in development of symptoms or evident changes in serology and histology at 28 weeks. However, variations in circulating inflammatory markers were noted. Larger randomised trials are needed to corroborate these findings.

CLINICAL TRIALS REGISTRY-INDIA

CTRI/2018/06/014521.

Therapeutic options for coeliac disease: What else beyond gluten-free diet?

Coeliac disease is a chronic and systemic autoimmune condition triggered by gluten ingestion in genetically predisposed subjects. Currently, the only effective treatment available is a strict, lifelong gluten-free diet. However, patients perceive gluten withdrawal as an unsustainable burden in their life and some of them can exhibit persistent symptoms despite a strict diet. Thus, gluten-free diet represents a challenge, leading scientists to look for alternative or complementary treatments. This review will focus on non-dietary therapies for coeliac disease highlighting six therapeutic strategies: (1) decreasing gluten immunogenic content before it reaches the intestine; (2) sequestering gluten in the gut lumen before absorption; (3) blocking the passage of gluten through a leaky intestinal barrier; (4) preventing the enhancement of immune response against gliadin; (5) dampening the downstream immune activation; (6) inducing immune tolerance to gluten. Most developing therapies are only in the pre-clinical phase with only a few being tested in phase 2b or 3 trials. Although new approaches raise the hope for coeliacs giving them a chance to come back to gluten, for the time being a cautionary appraisal of new therapies suggests that they may have a complementary role to gluten withdrawal, mainly to prevent inadvertent gluten contamination.

Microbial transglutaminase: A biotechnological tool to manage gluten intolerance

Celiac disease (CD) is a chronic immune-mediated disease in which gluten ingestion leads to damage of the small intestinal mucosa in genetically susceptible individuals. The enteropathy is mainly induced by the production of IFN-γ from intestinal CD4⁺T cells that recognise gliadin peptides following deamidation by tissue transglutaminase. The only available therapy is a strict, lifelong gluten-free diet (GFD). This diet is strongly demanding for patients, which justifies the search for alternative strategies. The enzyme approach is one promising strategy to address this issue. In particular, transamidation of wheat gliadin by microbial transglutaminase (mTG) was fully effective at inhibiting gliadin-specific IFN-γ secretion in intestinal T cells from CD patients. Furthermore, transamidated gliadin induced higher levels of the anti-inflammatory IL-10 than native gliadin in different in vitro models. These data suggest that a more balanced immune response could be induced by mTG-treated gliadin in the small intestine of celiac patients. Furthermore, the highlighted biological property of mTG-treated gliadin could be exploited to induce tolerance to native gliadin in at-risk individuals.

A multi-spectroscopic study on the interaction of food polyphenols with a bioactive gluten peptide: From chemistry to biological implications

This study aims to exploit the molecular and cellular mechanisms concerning the functionality of dietary polyphenols (catechin, procyanidin B3, procyanidin C2, epigallocatechin and epigallocatechin gallate) in a nutritional context to prevent Celiac Disease (CD). In that sense, the interaction between the main CD bioactive peptide (32-mer peptide) and some polyphenols was fully characterized at the intestinal level under near physiological conditions by means of different spectroscopic techniques and dynamic simulations. Accordingly, it is proposed that the primarily polyphenol-binding sites on the 32-mer peptide correspond to leucine, tyrosine and phenylalanine containing domains being this interaction entropy-driven. Although procyanidin B3 and trimer C2 had a similar low-affinity constant at 310 K, both procyanidins were able to reduce the 32-mer peptide apical-to-basolateral translocation in in vitro simulated intestinal epithelial barrier thus prospecting the occurrence of additional and still unexplored regulatory mechanisms by which dietary polyphenols might modulate the transepithelial transport of CD bioactive peptides.

Novel Nondietary Therapies for Celiac Disease

Celiac Disease (CeD) is defined as a chronic small intestinal immune-mediated enteropathy that is precipitated by exposure to dietary gluten in genetically predisposed individuals. CeD is one of the most common autoimmune disorders affecting around 1% of the population worldwide. Currently, the only acceptable treatment for CeD is strict, lifelong adherence to a gluten-free diet (GFD) which can often present a challenging task. A GFD alone is not sufficient to control symptoms and prevent mucosal damage that can result from unintentional gluten exposure. Moreover, long-term complications can occur in many patients. Consequently, there is an unmet need for non-dietary therapies for the management of CeD. Such therapies could serve as an adjunct to the GFD but eventually may replace it. This review will focus on and discuss non-dietary therapies currently in clinical development for the management of CeD. METHODOLOGY: We searched clinicaltrials.gov and PubMed to extract articles about celiac disease. We used keywords including, but not limited to, "celiac disease," "non-dietary," "therapeutics," "pathophysiology," "Endopeptidases," "tight junction modulators," "vaccine," and "Nexvax2". We focused mainly on articles that conducted pathophysiologic and therapeutic research in human trials.

Effect of pH control during rice fermentation in preventing a gliadin P31-43 entrance in epithelial cells

Coeliac disease is an increasingly recognised pathology, induced by the ingestion of gluten in genetically predisposed patients. Undigested gliadin peptide can induce adaptive and innate immune response that unleash the typical intestinal mucosal alterations. A growing attention is paid to alternative therapeutic approaches to the gluten-free diet: one of these approaches is the use of probiotics and/or postbiotics. We performed lactic fermentation of rice flour with and without pH control, using Lactobacillus paracasei CBA L74 as fermenting strain. We evaluated bacterial growth, lactic acid production during fermentation and gliadin peptide P31-43 entrance in CaCo-2 cells with and without pH control. When pH control was applied no differences were observed in terms of bacterial growth; on the contrary, lactic acid production was greater, as expected. Both samples could inhibit the P31-43 entrance in CaCo-2 cells but the effect was significantly greater for samples obtained when the pH control was applied.

Epitope Selection for HLA-DQ2 Presentation: Implications for Celiac Disease and Viral Defense

We have reported that the major histocompatibility molecule HLA-DQ2 (DQA1*05:01/DQB1*02:01) (DQ2) is relatively resistant to HLA-DM (DM), a peptide exchange catalyst for MHC class II. In this study, we analyzed the role of DQ2/DM interaction in the generation of DQ2-restricted gliadin epitopes, relevant to celiac disease, or DQ2-restricted viral epitopes, relevant to host defense. We used paired human APC, differing in DM expression (DM^null versus DM^high) or differing by expression of wild-type DQ2, versus a DM-susceptible, DQ2 point mutant DQ2α+53G. The APC pairs were compared for their ability to stimulate human CD4⁺ T cell clones. Despite higher DQ2 levels, DM^high APC attenuated T cell responses compared with DM^null APC after intracellular generation of four tested gliadin epitopes. DM^high APC expressing the DQ2α+53G mutant further suppressed these gliadin-mediated responses. The gliadin epitopes were found to have moderate affinity for DQ2, and even lower affinity for the DQ2 mutant, consistent with DM suppression of their presentation. In contrast, DM^high APC significantly promoted the presentation of DQ2-restricted epitopes derived intracellularly from inactivated HSV type 2, influenza hemagglutinin, and human papillomavirus E7 protein. When extracellular peptide epitopes were used as Ag, the DQ2 surface levels and peptide affinity were the major regulators of T cell responses. The differential effect of DM on stimulation of the two groups of T cell clones implies differences in DQ2 presentation pathways associated with nonpathogen- and pathogen-derived Ags in vivo.

Tailoring the immune response to wheat gliadin by enzymatic transamidation

Enzymatic transamidation of wheat gliadin by microbial transglutaminase inhibits IFN-γ secretion by intestinal T cell lines from celiac disease (CD) patients. Here, we analysed its effects on intestinal biopsies from CD patients and studied the underlying mechanisms in HLA-DQ8 transgenic (tg) mice, a model of T-cell mediated gluten sensitivity. In vitro challenge with a soluble form of transamidated gliadin (spf) upregulated IL-10 transcript levels in human biopsy samples. Furthermore, the ratio of IL-10/IFN-γ transcripts was significantly increased following treatment with spf. In DQ8 tg mice, recall responses in vitro in the presence of dendritic cells pulsed with transamidated gliadin showed that gliadin-specific CD4⁺ T cells did not produce IFN-γ at any tested dose. On the contrary, spf-specific CD4⁺ T cells still secreted IFN-γ, but they also produced significant levels of IL-10 with both native and transamidated gliadin. Interestingly, this anti-inflammatory activity was restricted to a specific reverse-phase high-pressure liquid chromatography (RP-HPLC) fraction encompassing α-gliadins. These findings suggested an ability of transamidated gliadin to revert, as well as to prevent, the inflammatory phenotype triggered by native gliadin. This property was intrinsically associated with specific components of the α-gliadin fraction.

Physiopathology and Management of Gluten-Induced Celiac Disease

Proline- and glutamine-rich gluten proteins are one of the major constituents of cereal dietary proteins, which are largely resistant to complete cleavage by the human gastrointestinal (GI) digestive enzymes. Partial digestion of gluten generates approximately 35 amino acids (aa) immunomodulatory peptides which activate T-cell-mediated immune system, followed by immunological inflammation of mucosa leading to the onset of celiac disease (CD). CD is an autoimmune disease associated with HLA-DQ2/DQ8 polymorphism and dysbiosis of gut microbiota. CD is either diagnosed using duodenal mucosal biopsis or serological testing for transglutaminase 2 (TG2) specific antibodies (IgA and IgG). Current therapy for CD management is gluten-free diet, while other therapies like glutenase, probiotics, immunomodulation, jamming of HLA-DQ2, inhibition of TG2, and gluten tolerance aided by gluten tolerizing vaccines are being developed.

On Peptides and Altered Peptide Ligands: From Origin, Mode of Action and Design to Clinical Application (Immunotherapy)

T lymphocytes equipped with clonotypic T cell antigen receptors (TCR) recognize immunogenic peptides only when presented in the context of their own major histocompatibility complex (MHC) molecules. Peptide loading to MHC molecules occurs in intracellular compartments (ER for class I and MIIC for class II molecules) and relies on the interaction of the respective peptides and peptide binding pockets on MHC molecules. Those peptide residues not engaged in MHC binding point towards the TCR screening for possible peptide MHC complex binding partners. Natural or intentional modification of both MHC binding registers and TCR interacting residues of peptides - leading to the formation of altered peptide ligands (APLs) - might alter the way peptides interact with TCRs and hence influence subsequent T cell activation events, and consequently T cell effector functions. This review article summarizes how APLs were detected and first described, current concepts of how APLs modify T cellular signaling, which biological mechanisms might force the generation of APLs in vivo, and how peptides and APLs might be used for the benefit of patients suffering from allergic or autoimmune diseases.

Intestinal barrier dysfunction: implications for chronic inflammatory conditions of the bowel

The intestinal epithelium of adult humans acts as a differentially permeable barrier that separates the potentially harmful contents of the lumen from the underlying tissues. Any dysfunction of this boundary layer that disturbs the homeostatic equilibrium between the internal and external environments may initiate and sustain a biochemical cascade that results in inflammation of the intestine. Key to such dysfunction are genetic, microbial and other environmental factors that, singularly or in combination, result in chronic inflammation that is symptomatic of inflammatory bowel disease (IBD). The aim of the present review is to assess the scientific evidence to support the hypothesis that defective transepithelial transport mechanisms and the heightened absorption of intact antigenic proinflammatory oligopeptides are important contributing factors in the pathogenesis of IBD.

Celiac disease 2015 update: new therapies

Celiac disease (CD) is a chronic, small intestinal, immune-mediated enteropathy triggered by exposure to dietary gluten in genetically susceptible individuals. Currently, lifelong adherence to a gluten-free diet (GFD) is the only available treatment. However, GFD alone is not sufficient to relieve symptoms, control small intestinal inflammation and prevent long-term complications in many patients. The GFD has its challenges including issues related to adherence, lifestyle restrictions and cost. As a result, there is growing interest in and a need for non-dietary therapies to manage this condition. In recent years, different targets in the immune-mediated cascade of CD have been identified in clinical and pre-clinical trials for potential therapies. This review will discuss the latest non-dietary therapies in CD, including endopeptidases, modulators of enterocyte tight junctions and agents involved in gluten tolerization and immunomodulation. We will also discuss the potential implications of approved therapeutics on CD clinical practice.

The role of animal models in unravelling therapeutic targets in coeliac disease

Coeliac disease is a complex small intestinal enteropathy that develops consequently to a breach of tolerance to gliadin, a storage protein abundantly found in cereals such as wheat, rye and barley. The understanding of the mechanisms underlying the development of coeliac disease in HLA-DQ2 and HLA-DQ8 genetically susceptible individuals has greatly improved during the last decades but so far did not allow to develop curative therapeutics, leaving a long-life gluten free diet as the only treatment option for the patients. In order to bring new therapeutic targets to light and to test the safety and efficacy of putative drugs, animal models recapitulating features of the disease are needed. Here, we will review the existing animal models and the clinical features of coeliac disease they reflect and discuss their relevance for modelling immune pathways that may lead to potential therapeutic approaches.

Taming the TCR: antigen-specific immunotherapeutic agents for autoimmune diseases

Current treatments for autoimmune diseases are typically non-specific anti-inflammatory agents that affect not only the autoreactive cells but also the parts of the immune system that are required to maintain health. There is a need for the development of antigen-specific therapeutic agents that can effectively prevent the autoimmune attack while leaving the rest of the immune system functioning as normal. The simplest way to achieve this is using the autoantigen itself as a tolerizing agent; however, there is some risk involved with administering a potentially pathogenic antigen. In this review, we focus instead on the development and use of modified T cell receptor (TCR) ligands, in which the peptide ligand is modified to change the response by the T cell from a disease inducing to a protective response, and still retain the antigen-specificity necessary to target the autoreactive T cells. We review the use of modified TCR ligands as therapeutic agents in animal models of autoimmunity and in human autoimmune disease, and finally consider how they need to be improved in order to use them effectively in patients with autoimmune disease.

Vaccination and other antigen-specific immunomodulatory strategies in celiac disease

BACKGROUND

Celiac disease (CD) results from an alteration in the oral tolerance to dietary gluten. The response to gluten is normally tightly regulated and involves the secretion of TGF-β and IL-10 from different subtypes of regulatory T cells (Tregs). Interestingly, in addition to proinflammatory cytokines, the inflamed CD mucosa also contains high levels of T cell-derived IL-10 compared with treated CD patients or normal donors. Furthermore, most studies describe an increase in the number of Foxp3+ Tregs in the small intestinal mucosa in CD patients compared to controls. This paradoxical condition suggests that regulatory mechanisms might operate to counterbalance the abnormal gliadin-triggered immune activation in untreated mucosa. Indeed, addition of exogenous IL-10 to mucosal cultures from treated CD patients can suppress gliadin-induced T cell activation. Considering the central role of adaptive immunity in CD, the development of strategies to stimulate these mechanisms is a primary goal of efforts to restore gluten tolerance. Key Messages: Different immunomodulatory strategies have been explored. NexVax2, a desensitizing vaccine that uses three dominant gluten peptides administered subcutaneously to induce a tolerogenic response in CD patients, is under development. Alternatively, the potential of substituted, cyclic or dimeric peptide analogues as blockers to prevent HLA from binding to the immunodominant gliadin epitopes has been demonstrated in vitro. In line with these results, we recently found that modified (transamidated) gliadins influenced the immune response in intestinal biopsy samples from CD patients with overt disease by drastically reducing the production of IFN-γ. Notably, in a mouse model, transamidated gliadins reverted the phenotype of the gliadin-inducible immune response from an inflammatory phenotype to an anti-inflammatory phenotype.

CONCLUSIONS

Various approaches are currently under investigation to recover gluten tolerance based on the use of both modified and native antigen molecules. More specific studies are now required to test the efficacy of such strategies for preventing CD.

Current status of drugs in development for celiac disease

INTRODUCTION

Gluten is the main trigger for celiac disease, and the current treatment is based on its elimination from the diet. Although the symptoms usually disappear during the diet, it is restrictive and difficult to maintain. Further, despite a strict treatment the small-bowel mucosal damage does now always heal. Consequently, adherence is often poor and new treatment approaches are needed. With an increased understanding of the disease pathogenesis, several novel treatments have been suggested, and some of them have already entered Phase II clinical trials.

AREAS COVERED

This article reviews the latest status of the drugs in development for celiac disease. The article focuses mainly on synthetic drugs currently entering in clinical trials.

EXPERT OPINION

It is anticipated that some of the treatments under investigation will soon enter Phase III clinical trials, although challenges remain. For instance, histological studies are problematic in wide-scale clinical studies. On the other hand, the existing non-invasive serological methods and clinical outcome measures might be too insensitive for monitoring responses to the possible drug candidates. There is also no animal model which would accurately reflect celiac disease. Well-conducted basic and clinical research is required to develop better non-invasive surrogate markers and patient-related outcomes for future pharmacological studies.

Design of gliadin peptide analogues with low affinity for the celiac disease associated HLA–DQ2 protein

A computational study on the binding of celiac disease relevant epitopes and their analogues identified the di-hydroxylation of Pro residues as a promising functionalization to lower the affinity for HLA–DQ2.5.

Modeling of celiac disease immune response and the therapeutic effect of potential drugs

Background

Celiac disease (CD) is an autoimmune disorder that occurs in genetically predisposed people and is caused by a reaction to the gluten protein found in wheat, which leads to intestinal villous atrophy. Currently there is no drug for treatment of CD. The only known treatment is lifelong gluten-free diet. The main aim of this work is to develop a mathematical model of the immune response in CD patients and to predict the efficacy of a transglutaminase-2 (TG-2) inhibitor as a potential drug for treatment of CD.

Results

A thorough analysis of the developed model provided the following results:

1. TG-2 inhibitor treatment leads to insignificant decrease in antibody levels, and hence remains higher than in healthy individuals.

2. TG-2 inhibitor treatment does not lead to any significant increase in villous area.

3. The model predicts that the most effective treatment of CD would be the use of gluten peptide analogs that antagonize the binding of immunogenic gluten peptides to APC. The model predicts that the treatment of CD by such gluten peptide analogs can lead to a decrease in antibody levels to those of normal healthy people, and to a significant increase in villous area.

Conclusions

The developed mathematical model of immune response in CD allows prediction of the efficacy of TG-2 inhibitors and other possible drugs for the treatment of CD: their influence on the intestinal villous area and on the antibody levels. The model also allows to understand what processes in the immune response have the strongest influence on the efficacy of different drugs. This model could be applied in the pharmaceutical R&D arena for the design of drugs against autoimmune small intestine disorders and on the design of their corresponding clinical trials.

Latest in vitro and in vivo models of celiac disease

INTRODUCTION

Currently, the only treatment for celiac disease is a gluten-free diet, and there is an increased desire for alternative therapies. In vitro and in vivo models of celiac disease have been generated in order to better understand the pathogenesis of celiac disease, and this review will discuss these models as well as the testing of alternative therapies using these models.

AREAS COVERED

The research discussed describes the different in vitro and in vivo models of celiac disease that currently exist and how they have contributed to our understanding of how gluten can stimulate both innate and adaptive immune responses in celiac patients. We also provide a summary on the alternative therapies that have been tested with these models and discuss whether subsequent clinical trials were done based on these tests done with these models of celiac disease.

EXPERT OPINION

Only a few of the alternative therapies that have been tested with animal models have gone on to clinical trials; however, those that did go on to clinical trial have provided promising results from a safety standpoint. Further trials are required to determine if some of these therapies may serve as an effective adjunct to a gluten-free diet to alleviate the adverse affects associated with accidental gluten exposure. A "magic-bullet" approach may not be the answer to celiac disease, but possibly a future cocktail of these different therapeutics may allow celiac patients to consume an unrestricted diet.

Review article: coeliac disease, new approaches to therapy

BACKGROUND

Coeliac disease is managed by life-long gluten withdrawal from the diet. However, strict adherence to a gluten-free diet is difficult and is not always effective. Novel therapeutic approaches are needed to supplement or even replace the dietary treatment.

AIM

To review recent advances in new therapeutic options for coeliac disease.

METHODS

A literature search was performed on MEDLINE, EMBASE, Web of Science, Scopus, DDW.org and ClinicalTrials.gov for English articles and abstracts. The search terms used included, but not limited to, 'Celiac disease', 'new', 'novel', 'Advances', 'alternatives' and 'Drug therapy'. The cited articles were selected based on the relevancy to the review objective.

RESULTS

Several new therapeutic approaches for coeliac disease are currently under development by targeting its underlying pathogenesis. Alternative therapies range from reproduction of harmless wheat strains to immunomodulatory approaches. Some of these therapies such as enzymatic cleavage of gluten and permeability inhibitors have shown promise in clinical studies.

CONCLUSIONS

Gluten-free diet is still the only practical treatment for patients with coeliac disease. Novel strategies provide promise of alternative adjunctive approaches to diet restriction alone for patients with this disorder.

Resolving multiple protein-peptide binding events: implication for HLA-DQ2 mediated antigen presentation in celiac disease

Techniques that can effectively separate protein-peptide complexes from free peptides have shown great value in major histocompatibility complex (MHC)-peptide binding studies. However, most of the available techniques are limited to measuring the binding of a single peptide to an MHC molecule. As antigen presentation in vivo involves both endogenous ligands and exogenous antigens, the deconvolution of multiple binding events necessitates the implementation of a more powerful technique. Here we show that capillary electrophoresis coupled to fluorescence detection (CE-FL) can resolve multiple MHC-peptide binding events owing to its superior resolution and the ability to simultaneously monitor multiple emission channels. We utilized CE-FL to investigate competition and displacement of endogenous peptides by an immunogenic gluten peptide for binding to HLA-DQ2. Remarkably, this immunogenic peptide could displace CLIP peptides from the DQ2 binding site at neutral but not acidic pH. This unusual ability of the gluten peptide supports a direct loading mechanism of antigen presentation in extracellular environment, a property that could explain the antigenicity of dietary gluten in celiac disease.

Interferon-γ activates transglutaminase 2 via a phosphatidylinositol-3-kinase-dependent pathway: implications for celiac sprue therapy

The mechanism for activation of extracellular transglutaminase 2 (TG2) in the small intestine remains a fundamental mystery in our understanding of celiac sprue pathogenesis. Using the T84 human enterocytic cell line, we show that interferon-γ (IFN-γ), the predominant cytokine secreted by gluten-reactive T cells in the celiac intestine, activates extracellular TG2 in a dose-dependent manner. IFN-γ mediated activation of TG2 requires phosphatidylinositol-3-kinase (PI3K) activity, but is uninfluenced by a number of other kinases reported to be active in T84 cells. Pharmacological inhibition of PI3K in the presence of IFN-γ prevents TG2 activation as well as the previously characterized increase in transepithelial permeability. Our findings therefore establish PI3K as an attractive target for celiac sprue therapy, a possibility that is underscored by the encouraging safety profiles of several PI3K inhibitors undergoing human clinical trials.

Transglutaminase 2: biology, relevance to neurodegenerative diseases and therapeutic implications

Neurodegenerative disorders are characterized by progressive neuronal loss and the aggregation of disease-specific pathogenic proteins in hallmark neuropathologic lesions. Many of these proteins, including amyloid Αβ, tau, α-synuclein and huntingtin, are cross-linked by the enzymatic activity of transglutaminase 2 (TG2). Additionally, the expression and activity of TG2 is increased in affected brain regions in these disorders. These observations along with experimental evidence in cellular and mouse models suggest that TG2 can contribute to the abnormal aggregation of disease causing proteins and consequently to neuronal damage. This accumulating evidence has provided the impetus to develop inhibitors of TG2 as possible neuroprotective agents. However, TG2 has other enzymatic activities in addition to its cross-linking function and can modulate multiple cellular processes including apoptosis, autophagy, energy production, synaptic function, signal transduction and transcription regulation. These diverse properties must be taken into consideration in designing TG2 inhibitors. In this review, we discuss the biochemistry of TG2, its various physiologic functions and our current understanding about its role in degenerative diseases of the brain. We also describe the different approaches to designing TG2 inhibitors that could be developed as potential disease-modifying therapies.

New clues in celiac disease epidemiology, pathogenesis, clinical manifestations, and treatment

Celiac disease (CD) is an immune-mediated enteropathy triggered by the ingestion of gluten in genetically susceptible individuals. It is one of the most common lifelong disorders on a worldwide basis. Celiac enteropathy is the final consequence of an abnormal immune reaction, showing features of both an innate and an adaptive response to gluten prolamins. The clinical spectrum is wide, including cases with either typical intestinal or atypical extraintestinal features, and silent forms. The only available treatment consists in dietary exclusion of grains containing gluten. New pharmacological treatment are currently under scrutiny.

Prevention measures and exploratory pharmacological treatments of celiac disease

Increasing prevalence, protean clinical manifestations, and lack of pharmacological therapy make celiac disease (CD) a complex and highly relevant illness in gastroenterology. This chronic inflammatory disorder of the small intestine is caused by the ingestion of gluten containing cereals in genetically susceptible individuals, leading to a variety of gastrointestinal (GI) and non-GI manifestations. Awareness among physicians is growing due to accessible and highly accurate diagnostic and screening methods. Recent evidence suggests a possible rising incidence of CD. Environmental factors such as early life gluten exposure, intestinal infections, short duration of breast-feeding, and changes in intestinal microbiota have been proposed to have a role in CD pathogenesis. Thus, prevention approaches to diminish the rising prevalence of CD are currently being evaluated. Still, the cornerstone treatment of CD remains a strict gluten-free diet. This nutritional regime is demanding, and non-adherence is common because of social isolation, financial issues, or restriction of food diversity. Allowing patients to occasionally consume small amounts of gluten would greatly improve their quality of life. Owing to recent advances in the understanding of the pathogenesis of CD, different targets have been identified and have motivated the development of several experimental therapeutic strategies. The main goal of this review is to discuss the mechanisms that can be exploited therapeutically to prevent or delay CD, disease associations and its complications. Current treatments for complications of CD, including refractory CD and malignancy, are beyond the scope of this review.

Celiac disease: prevention and treatment

Celiac disease is a common multisystemic disorder that may be diagnosed at any age. Owing to the increasing prevalence, prevention strategies, including encouragement of breastfeeding and introduction of small amounts of gluten whereas still on breastfeeding at fourth to sixth month of age, become more important than before. For avoiding complications of celiac disease, a strict gluten-free diet is essential. A lifelong gluten-free diet may bring about difficulties as avoiding gluten completely is problematic owing to the contamination with gluten of presumably gluten free foods. New therapeutic approaches include enzyme supplementation, correction of the intestinal barrier defect against gluten entry, blocking of gliadin presentation by human leukocyte antigen blockers and tissue transglutaminase inhibitors.

Noninflammatory gluten peptide analogs as biomarkers for celiac sprue

New tools are needed for managing celiac sprue, a lifelong immune disease of the small intestine. Ongoing drug trials are also prompting a search for noninvasive biomarkers of gluten-induced intestinal change. We have synthesized and characterized noninflammatory gluten peptide analogs in which key Gln residues are replaced by Asn or His. Like their proinflammatory counterparts, these biomarkers are resistant to gastrointestinal proteases, susceptible to glutenases, and permeable across enterocyte barriers. Unlike gluten peptides, however, they are not appreciably recognized by transglutaminase, HLA-DQ2, or disease-specific T cells. In vitro and animal studies show that the biomarkers can detect intestinal permeability changes as well as glutenase-catalyzed gastric detoxification of gluten. Accordingly, controlled clinical studies are warranted to evaluate the use of these peptides as probes for abnormal intestinal permeability in celiac patients and for glutenase efficacy in clinical trials and practice.

Design, synthesis and evaluation of high-affinity binders for the celiac disease associated HLA-DQ2 molecule

Celiac disease is caused by uncontrolled CD4 T-cell responses directed to wheat-derived gluten peptides bound to the disease predisposing HLA-DQ molecules. The only available treatment is a life-long gluten-free diet which is complicated by the widespread use of wheat-derived gluten in the food industry. As the binding of gluten-derived peptides is a prerequisite for the induction of the inflammatory T-cell response, blockers that would prevent gluten peptide binding to the HLA-DQ molecules might be used as an alternative to the gluten-free diet. In the present study we have analyzed the binding properties of a set of previously identified natural ligands for HLA-DQ2, the primary disease predisposing allele. An in silico method, Epibase, ranked these peptides and the top one, a peptide with a nine amino acid core FVAEYEPVL, was measured among these peptides as the peptide with the highest binding affinity for HLA-DQ2. In a stepwise approach we subsequently tested the impact of N-terminal extensions and systematic single amino acid substitutions within the core of this peptide which revealed that an N-terminal extension with the tripeptide sequence ADA increased binding affinity 5- to 6-fold. In addition the substitution analysis indicated which amino acids were most preferred at anchor residues in the lead peptide, generally leading to an increase of binding affinity with a factor of 2. Next we tested which combinations of such preferred amino acids yielded the best results. The combined results indicate that a peptide with sequence ADAYDYESEELFAA (core in bold) had superior binding properties. This peptide was chosen as a lead peptide for further optimization with non-natural amino acids at the p1 position, since molecular modeling indicated that none of the natural amino acids is able to optimally occupy the p1 pocket. A set of 8 non-proteinogenic amino acids was designed, synthesized and incorporated in the lead peptide (and in two control peptides) and tested for binding to HLA-DQ2. The results indicate that the effect of the incorporation of these non-proteinogenic amino acids depended on the peptide in which they were incorporated and that the maximum increase in binding affinity obtained was approximately 2-fold. Altogether lead sequences were obtained that have a binding affinity for HLA-DQ2 that is 100- to 200-fold higher compared to that of the gluten-derived peptide that has the highest affinity for HLA-DQ2. Such peptides are candidate lead peptides for further optimization. Our results, however, also indicate that in order to obtain further significant increases in binding affinity alternative approaches will have to be explored.

Celiac disease: from pathogenesis to novel therapies

Celiac disease has become one of the best-understood HLA-linked disorders. Although it shares many immunologic features with inflammatory bowel disease, celiac disease is uniquely characterized by (1) a defined trigger (gluten proteins from wheat and related cereals), (2) the necessary presence of HLA-DQ2 or HLA-DQ8, and (3) the generation of circulating autoantibodies to the enzyme tissue transglutaminase (TG2). TG2 deamidates certain gluten peptides, increasing their affinity to HLA-DQ2 or HLA-DQ8. This generates a more vigorous CD4(+) T-helper 1 T-cell activation, which can result in intestinal mucosal inflammation, malabsorption, and numerous secondary symptoms and autoimmune diseases. Moreover, gluten elicits innate immune responses that act in concert with the adaptive immunity. Exclusion of gluten from the diet reverses many disease manifestations but is usually not or less efficient in patients with refractory celiac disease or associated autoimmune diseases. Based on the advanced understanding of the pathogenesis of celiac disease, targeted nondietary therapies have been devised, and some of these are already in phase 1 or 2 clinical trials. Examples are modified flours that have been depleted of immunogenic gluten epitopes, degradation of immunodominant gliadin peptides that resist intestinal proteases by exogenous endopeptidases, decrease of intestinal permeability by blockage of the epithelial ZOT receptor, inhibition of intestinal TG2 activity by transglutaminase inhibitors, inhibition of gluten peptide presentation by HLA-DQ2 antagonists, modulation or inhibition of proinflammatory cytokines, and induction of oral tolerance to gluten. These and other experimental therapies will be discussed critically.

Functional recombinant MHC class II molecules and high-throughput peptide-binding assays

BACKGROUND

Molecules of the class II major histocompability complex (MHC-II) specifically bind and present exogenously derived peptide epitopes to CD4+ T helper cells. The extreme polymorphism of the MHC-II hampers the complete analysis of peptide binding. It is also a significant hurdle in the generation of MHC-II molecules as reagents to study and manipulate specific T helper cell responses. Methods to generate functional MHC-II molecules recombinantly, and measure their interaction with peptides, would be highly desirable; however, no consensus methodology has yet emerged.

RESULTS

We generated alpha and beta MHC-II chain constructs, where the membrane-spanning regions were replaced by dimerization motifs, and the C-terminal of the beta chains was fused to a biotinylation signal peptide (BSP) allowing for in vivo biotinylation. These chains were produced separately as inclusion bodies in E. coli , extracted into urea, and purified under denaturing and non-reducing conditions using conventional column chromatography. Subsequently, diluting the two chains into a folding reaction with appropriate peptide resulted in efficient peptide-MHC-II complex formation. Several different formats of peptide-binding assay were developed including a homogeneous, non-radioactive, high-throughput (HTS) binding assay. Binding isotherms were generated allowing the affinities of interaction to be determined. The affinities of the best binders were found to be in the low nanomolar range. Recombinant MHC-II molecules and accompanying HTS peptide-binding assay were successfully developed for nine different MHC-II molecules including the DPA1*0103/DPB1*0401 (DP401) and DQA1*0501/DQB1*0201, where both alpha and beta chains are polymorphic, illustrating the advantages of producing the two chains separately.

CONCLUSION

We have successfully developed versatile MHC-II resources, which may assist in the generation of MHC class II -wide reagents, data, and tools.

Polymeric binders suppress gliadin-induced toxicity in the intestinal epithelium

BACKGROUND & AIMS

Celiac disease is a prevalent immune disorder caused by the ingestion of gliadin-containing grains. We investigated the ability of a polymeric binder to reverse the toxic effects induced by gliadin in human intestinal cells and gliadin-sensitive HCD4-DQ8 mice.

METHODS

Gliadin was neutralized by complexation to a linear copolymer of hydroxyethylmethacrylate (HEMA) and sodium 4-styrene sulfonate (SS). The ability of the polymeric binder to abrogate the damaging effect of gliadin on cell-cell contact was investigated in IEC-6, Caco-2/15, and primary cultured differentiated enterocytes. The efficacy of the polymeric binder in preventing gliadin-induced intestinal barrier dysfunction was assessed using gliadin-sensitive HLA-HCD4/DQ8 transgenic mice.

RESULTS

Poly(hydroxyethylmethacrylate-co-styrene sulfonate) [P(HEMA-co-SS)] complexed with gliadin in a relatively specific fashion. Intestinal cells exposed to gliadin underwent profound alterations in morphology and cell-cell contacts. These changes were averted by complexing the gliadin with P(HEMA-co-SS). More importantly, the P(HEMA-co-SS) hindered the digestion of gliadin by gastrointestinal enzymes, thus minimizing the formation of immunogenic peptides. Coadministration of P(HEMA-co-SS) with gliadin to HLA-HCD4/DQ8 mice attenuated gliadin-induced changes in the intestinal barrier and reduced intraepithelial lymphocyte and macrophage cell counts.

CONCLUSIONS

Polymeric binders can prevent in vitro gliadin-induced epithelial toxicity and intestinal barrier dysfunction in HCD4/DQ8 mice. They have a potential role in the treatment of patients with gluten-induced disorders.

Soluble HLA-DQ2 expressed in S2 cells copurifies with a high affinity insect cell derived protein

We here describe that soluble HLA-DQ2 (sDQ2) molecules, when expressed in Drosophila melanogaster S2 insect cells without a covalently tethered peptide, associate tightly with the D. melanogaster calcium binding protein DCB-45. The interaction between the proteins is stable in S2 cell culture and during affinity purification, which is done at high salt concentrations and pH 11.5. After affinity purification, the sDQ2/DCB-45 complex exists in substantial quantities next to a small amount of free heterodimeric sDQ2 and large amounts of aggregated sDQ2 free of DCB-45. Motivated by the stable complex formation and our interest in the development of reagents which inhibit HLA-DQ2 peptide binding, we have further characterized the sDQ2/DCB-45 interaction. Several lines of evidence indicate that an N-terminal fragment of DCB-45 is involved in the interaction with the peptide binding groove of sDQ2. Further mapping of this fragment of 54 residues identified a pentadecapeptide with high affinity for sDQ2 which may serve as a lead compound for the design of HLA-DQ2 blockers.

Parallels between pathogens and gluten peptides in celiac sprue

Pathogens are exogenous agents capable of causing disease in susceptible organisms. In celiac sprue, a disease triggered by partially hydrolyzed gluten peptides in the small intestine, the offending immunotoxins cannot replicate, but otherwise have many hallmarks of classical pathogens. First, dietary gluten and its peptide metabolites are ubiquitous components of the modern diet, yet only a small, genetically susceptible fraction of the human population contracts celiac sprue. Second, immunotoxic gluten peptides have certain unusual structural features that allow them to survive the harsh proteolytic conditions of the gastrointestinal tract and thereby interact extensively with the mucosal lining of the small intestine. Third, they invade across epithelial barriers intact to access the underlying gut-associated lymphoid tissue. Fourth, they possess recognition sequences for selective modification by an endogenous enzyme, transglutaminase 2, allowing for in situ activation to a more immunotoxic form via host subversion. Fifth, they precipitate a T cell–mediated immune reaction comprising both innate and adaptive responses that causes chronic inflammation of the small intestine. Sixth, complete elimination of immunotoxic gluten peptides from the celiac diet results in remission, whereas reintroduction of gluten in the diet causes relapse. Therefore, in analogy with antibiotics, orally administered proteases that reduce the host's exposure to the immunotoxin by accelerating gluten peptide destruction have considerable therapeutic potential. Last but not least, notwithstanding the power of in vitro methods to reconstitute the essence of the immune response to gluten in a celiac patient, animal models for the disease, while elusive, are likely to yield fundamentally new systems-level insights.