Loss and Gain of Tolerance to Pancreatic Glycoprotein 2 in Celiac Disease

Coincidence of antibodies against Hwp1 and ASCA, two distinct molecular targets of Candida albicans, reinforces the link between this fungal species and coeliac disease

Candida albicans is an immunogen for anti-Saccharomyces cerevisiae antibodies (ASCA), a serological marker of Crohn's disease. ASCA has also been reported in other autoimmune diseases, including coeliac disease (CeD). A strong antibody response against Hwp1, a protein associated with invasive hyphal form of C. albicans which presents peptide sequence homologies with gliadin, has also been described in CeD. This observation supports the hypothesis that C. albicans hyphal transition in C. albicans may trigger CeD onset through a mechanism of molecular/antigenic mimicry. In this study, we assessed whether the anti-C. albicans oligomannose and anti-Hwp1 protein responses may be linked despite their different pathophysiological significance. The measurement of ASCA levels in a cohort of patients involved in our previous Hwp1 study showed a significant correlation between the two biomarkers. This new observation further reinforces the link between C. albicans and CeD.

Glycoprotein 2 as a gut gate keeper for mucosal equilibrium between inflammation and immunity

Glycoprotein 2 (GP2) is a widely distributed protein in the digestive tract, contributing to mucosal barrier maintenance, immune homeostasis, and antigen-specific immune response, while also being linked to inflammatory bowel disease (IBD) pathogenesis. This review sheds light on the extensive distribution of GP2 within the gastrointestinal tract and its intricate interplay with the immune system. Furthermore, the significance of GP2 autoantibodies in diagnosing and categorizing IBD is underscored, alongside the promising therapeutic avenues for modulating GP2 to regulate immunity and maintain mucosal balance.

Human glycoprotein-2 expressed in Brunner glands - A putative autoimmune target and link between Crohn's and coeliac disease

Glycoprotein 2 (GP2) is an autoantigen in Crohn's (CD) and coeliac disease (CeD). We assessed GP2-isoform (GP2_1-4)-expression in intestinal biopsies of paediatric patients with CD, CeD, ulcerative colitis (UC), and healthy children (HC). Transcription of GP2_1-4 was elevated in proximal small intestine in CeD and CD patients (only GP2_2/4) compared to jejunum (CeD/CD) and large bowel (CD). CeD patients demonstrated higher duodenal GP2_2/4-mRNA levels compared to HC/UC patients whereas CD patients showed higher GP2₄-mRNA levels compared to UC patients. Duodenal synthesis of only small GP2 isoforms (GP2_3/4) was demonstrated in epithelial cells in patients/HC and in Brunner glands (also large isoforms) with a more frequent apical location in CD/CeD patients. All four GP2 isoforms interacted with gliadin and phosphopeptidomannan. Gliadin digestion improved binding to GP2 isoforms. GP2_1-4 binding to CeD/CD-related antigens, elevated duodenal GP2_1-4-mRNA transcription, and GP2-protein secretion in Brunner glands of CeD/CD patients suggest an autoimmune CeD/CD link.

The search for the Holy Grail: autoantigenic targets in primary sclerosing cholangitis associated with disease phenotype and neoplasia

Unlike in other autoimmune liver diseases such as autoimmune hepatitis and primary biliary cholangitis, the role and nature of autoantigenic targets in primary sclerosing cholangitis (PSC), a progressive, chronic, immune-mediated, life threatening, genetically predisposed, cholestatic liver illness, is poorly elucidated. Although anti-neutrophil cytoplasmic antibodies (ANCA) have been associated with the occurrence of PSC, their corresponding targets have not yet been identified entirely. Genome-wide association studies revealed a significant number of immune-related and even disease-modifying susceptibility loci for PSC. However, these loci did not allow discerning a clear autoimmune pattern nor do the therapy options and the male gender preponderance in PSC support a pathogenic role of autoimmune responses. Nevertheless, PSC is characterized by the co-occurrence of inflammatory bowel diseases (IBD) demonstrating autoimmune responses. The identification of novel autoantigenic targets in IBD such as the major zymogen granule membrane glycoprotein 2 (GP2) or the appearance of proteinase 3 (PR3) autoantibodies (autoAbs) have refocused the interest on a putative association of loss of tolerance with the IBD phenotype and consequently with the PSC phenotype. Not surprisingly, the report of an association between GP2 IgA autoAbs and disease severity in patients with PSC gave a new impetus to autoAb research for autoimmune liver diseases. It might usher in a new era of serological research in this field. The mucosal loss of tolerance against the microbiota-sensing GP2 modulating innate and adaptive intestinal immunity and its putative role in the pathogenesis of PSC will be elaborated in this review. Furthermore, other potential PSC-related autoantigenic targets such as the neutrophil PR3 will be discussed. GP2 IgA may represent a group of new pathogenic antibodies, which share characteristics of both type 2 and 3 of antibody-mediated hypersensitive reactions according to Coombs and Gell.

Current Paediatric Coeliac Disease Screening Strategies and Relevance of Questionnaire Survey

Coeliac disease (CD) is an autoimmune enteropathy triggered by the ingestion of gluten-containing grains in genetically predisposed individuals. Identification of CD in clinical practice is often difficult due to the manifestation of non-specific symptoms and signs, so a relatively significant proportion of CD cases remain undiagnosed. Timely detection of the disease is necessary to provide an appropriate approach to control of the disease treatment, in order to avoid potential complications. This is even more important in the case of children and adolescents, to ensure their proper growth and development. In this review, we discuss the data on the current strategies for CD detection among paediatric populations and the role of questionnaire-based discovery of CD cases in the area of interest. We assume that mass screening is a preferable strategy for finding CD cases within the paediatric population because this could uncover symptomatic, oligosymptomatic, and asymptomatic CD cases. However, under conditions of limited financial resources, screening for CD in risk groups, members of which can be identified using questionnaires, is essential. The pros and cons of CD screening in paediatric populations are presented. These depend on a number of situational criteria (cost-effectiveness, lack of awareness), but screening is designed to improve the detection of the disease and therefore improve the quality of life of patients.

Next-Generation Autoantibody Testing by Combination of Screening and Confirmation-the CytoBead® Technology

Occurrence of autoantibodies (autoAbs) is a hallmark of autoimmune diseases, and the analysis thereof is an essential part in the diagnosis of organ-specific autoimmune and systemic autoimmune rheumatic diseases (SARD), especially connective tissue diseases (CTDs). Due to the appearance of autoAb profiles in SARD patients and the complexity of the corresponding serological diagnosis, different diagnostic strategies have been suggested for appropriate autoAb testing. Thus, evolving assay techniques and the continuous discovery of novel autoantigens have greatly influenced the development of these strategies. Antinuclear antibody (ANA) analysis by indirect immunofluorescence (IIF) on tissue and later cellular substrates was one of the first tests introduced into clinical routine and is still an indispensable tool for CTD serology. Thus, screening for ANA by IIF is recommended to be followed by confirmatory testing of positive findings employing different assay techniques. Given the continuous growth in the demand for autoAb testing, IIF has been challenged as the standard method for ANA and other autoAb analyses due to lacking automation, standardization, modern data management, and human bias in IIF pattern interpretation. To address these limitations of autoAb testing, the CytoBead® technique has been introduced recently which enables automated interpretation of cell-based IIF and quantitative autoAb multiplexing by addressable microbead immunoassays in one reaction environment. Thus, autoAb screening and confirmatory testing can be combined for the first time. The present review discusses the history of autoAb assay techniques in this context and gives an overview and outlook of the recent progress in emerging technologies.

Diagnostic value of the antiglycoprotein-2 antibody for Crohn's disease: a PRISMA-compliant systematic review and meta-analysis

OBJECTIVES

To perform a meta-analysis to evaluate the diagnostic performance of the antiglycoprotein-2 (GP2) antibody for Crohn's disease (CD).

METHODS

Three databases (EMBASE, ISI Web of Knowledge and PubMed) were systematically searched. There were 17 eligible studies included in the meta-analysis. A total of 2439 patients with CD and 3184 controls were involved in these studies. STATA V.11.2 and Meta-DiSc V.1.4 were used to perform the meta-analysis.

RESULTS

The area under the summary receiver operating characteristic curve was 0.68-0.72. The pooled diagnostic sensitivity of the anti-GP2 antibody ranged from 14% to 24%, and the specificity was 96%-98%.

CONCLUSIONS

The anti-GP2 antibody is a specific biomarker for CD, and further exploration of its prevalence among different clinical phenotypes of CD will provide a better understanding of its diagnostic performance.

Biomarkers to Monitor Gluten-Free Diet Compliance in Celiac Patients

Gluten-free diet (GFD) is the only treatment for celiac disease (CD). There is a general consensus that strict GFD adherence in CD patients leads to full clinical and histological remission accompanied by improvement in quality of life and reduced long-term complications. Despite the importance of monitoring the GFD, there are no clear guidelines for assessing the outcome or for exploring its adherence. Available methods are insufficiently accurate to identify occasional gluten exposure that may cause intestinal mucosal damage. Serological tests are highly sensitive and specific for diagnosis, but do not predict recovery and are not useful for follow-up. The use of serial endoscopies, it is invasive and impractical for frequent monitoring, and dietary interview can be subjective. Therefore, the detection of gluten immunogenic peptides (GIP) in feces and urine have been proposed as new non-invasive biomarkers to detect gluten intake and verify GFD compliance in CD patients. These simple immunoassays in human samples could overcome some key unresolved scientific and clinical problems in CD management. It is a significant advance that opens up new possibilities for the clinicians to evaluate the CD treatment, GFD compliance, and improvement in the quality of life of CD patients.

Simultaneous detection of celiac disease-specific IgA antibodies and total IgA

Purpose

Celiac disease (CD) serology requires analysis of tissue transglutaminase type-2 (TG2autoAbs), deamidated gliadin (DGAbs), and as reference endomysial autoantibodies (EmA). Total IgA assessment helps to determine IgA-deficient CD patients. The novel multiplex indirect immunofluorescence (IIF) technique CytoBead was used to develop the first quantitative one-step serological CD assay comprising both simultaneous IgA autoAb and total IgA testing.

Methods

CytoBead CeliAK detecting TG2autoAb, DGAb, EmA, and simultaneously total IgA uses fluorescent microparticles for antigen and antibody immobilization along with monkey-esophagus tissue sections on glass slides. The assay was interpreted visually by classical fluorescent microscopy and digital IIF using AKLIDES^®. Overall, 380 samples (155 CD patients, 5 with IgA deficiency, 68 with cystic fibrosis, 59 with eye disease, 93 blood donors) were run for performance analysis. Data were compared with classical IgA autoAb analysis by ELISA and IIF.

Results

Comparing CD-specific IgA autoAb testing by CytoBead with classical IIF and ELISA, very good agreements for EmA, TG2autoAb, and DGAb were determined (Cohen’s κ = 0.98, 0.96, 0.85, respectively). The difference between multiplex and single testing revealed a significant difference for TG2autoAb testing only (McNemar, p = 0.0078). Four CD patients and 4 controls demonstrated TG2autoAb positivity by ELISA but were negative by CytoBead. Further, 140/155 (90.9 %) CD patients demonstrated TG2autoAb levels above ten times the upper normal and all five IgA-deficient samples IgA levels <0.2 g/L by CytoBead.

Conclusions

The novel multiplex CytoBead CeliAK enables simultaneous CD-specific autoAb and IgA deficiency analyses comparable with classical testing by single-parameter assays. Thus, comprehensive CD serology by CytoBead can alleviate the workload in routine laboratories.

Electronic supplementary material

The online version of this article (doi:10.1007/s13317-016-0073-2) contains supplementary material, which is available to authorized users.

Autoimmunity in Crohn's Disease-A Putative Stratification Factor of the Clinical Phenotype

Inflammation in inflammatory bowel diseases (IBD) has been linked to a loss of tolerance to self-antigens suggesting the existence of autoantibodies in specific disease phenotypes. However, the lack of clearly defined autoantigenic targets has slowed down research. Genome-wide association studies have identified an impressive number of immune-related susceptibility loci for IBD with no clearly discernible pattern among them. Growing evidence supports the hypothesis that innate immune responses to a low-diversity and impaired gut microbiota may be of key importance in initiating and perpetuating chronic inflammation in IBD. Increasing evidence suggests that reduced microbial diversity and microbial-mucosal epithelium interaction (including adhesion and clearance) are critically involved in IBD pathogenesis. Along these lines the discovery of autoantigenic targets in Crohn's disease (CD) has refocused research in IBD on the possible role of autoimmune responses. The identification of the major zymogen granule membrane glycoprotein 2 (GP2) as an autoantigen in CD patients and its proposed role in the sensing of the microbiota lends credence to this trend. Loss of tolerance to GP2 occurs in up to 40% of patients with CD. Corresponding autoantibodies appear to be associated with distinct disease courses (types or phenotypes) in CD. Here, we critically review autoantibodies in CD for their impact on clinical practice and future IBD research. The immunomodulatory role of GP2 in innate and adaptive intestinal immunity is also discussed.