Epitopes of calreticulin recognised by IgA autoantibodies from patients with hepatic and coeliac disease

MAFLD and Celiac Disease in Children

Celiac disease (CD) is an immune-mediated systemic disorder elicited by the ingestion of gluten whose clinical presentation ranges from the asymptomatic form to clinical patterns characterized by multiple systemic involvement. Although CD is a disease more frequently diagnosed in patients with symptoms of malabsorption such as diarrhea, steatorrhea, weight loss, or failure to thrive, the raised rate of overweight and obesity among general pediatric and adult populations has increased the possibility to diagnose celiac disease in obese patients as well. Consequently, it is not difficult to also find obesity-related disorders in patients with CD, including "metabolic associated fatty liver disease" (MAFLD). The exact mechanisms linking these two conditions are not yet known. The going assumption is that a gluten-free diet (GFD) plays a pivotal role in determining an altered metabolic profile because of the elevated content of sugars, proteins, saturated fats, and complex carbohydrates, and the higher glycemic index of gluten-free products than gluten-contained foods, predisposing individuals to the development of insulin resistance. However, recent evidence supports the hypothesis that alterations in one of the components of the so-called "gut-liver axis" might contribute to the increased afflux of toxic substances to the liver triggering the liver fat accumulation and to the subsequent hepatocellular damage. The aim of this paper was to describe the actual knowledge about the factors implicated in the pathogenesis of hepatic steatosis in pediatric patients with CD. The presented review allows us to conclude that the serological evaluations for CD with anti-transglutaminase antibodies, should be a part of the general workup in the asymptomatic patients with "non-alcoholic fatty liver disease" (NAFLD) when metabolic risk factors are not evident, and in the patients with steatohepatitis when other causes of liver disease are excluded.

Contribution of Infectious Agents to the Development of Celiac Disease

The ingestion of wheat gliadin (alcohol-soluble proteins, an integral part of wheat gluten) and related proteins induce, in genetically predisposed individuals, celiac disease (CD), which is characterized by immune-mediated impairment of the small intestinal mucosa. The lifelong omission of gluten and related grain proteins, i.e., a gluten-free diet (GFD), is at present the only therapy for CD. Although a GFD usually reduces CD symptoms, it does not entirely restore the small intestinal mucosa to a fully healthy state. Recently, the participation of microbial components in pathogenetic mechanisms of celiac disease was suggested. The present review provides information on infectious diseases associated with CD and the putative role of infections in CD development. Moreover, the involvement of the microbiota as a factor contributing to pathological changes in the intestine is discussed. Attention is paid to the mechanisms by which microbes and their components affect mucosal immunity, including tolerance to food antigens. Modulation of microbiota composition and function and the potential beneficial effects of probiotics in celiac disease are discussed.

Characterization of a Synovial B Cell-Derived Recombinant Monoclonal Antibody Targeting Stromal Calreticulin in the Rheumatoid Joints

Rheumatoid arthritis (RA) is characterized by formation of synovial ectopic lymphoid structures (ELS) supporting B cell autoreactivity toward locally generated citrullinated (cit) antigens, including those contained in neutrophil extracellular traps (NETs). However, only a minority of RA-rmAbs from B cells isolated from ELS⁺ RA tissues react against NETs. Thus, alternative cellular sources of other potential autoantigens targeted by locally differentiated B cells remain undefined. RA fibroblast-like synoviocytes (FLS) have been implicated in the release of RA-associated autoantigens. In this study, we aimed to define stromal-derived autoantigens from RA-FLS targeted by RA-rmAbs. Seventy-one RA-rmAbs were screened toward RA-FLS by living-cell immunofluorescence (IF). Western blotting was used to identify potential autoantigens from RA-FLS protein extracts. Putative candidates were validated using colocalization immunofluorescence confocal microscopy, ELISA, immunoprecipitation assay, and surface plasmon resonance on unmodified/cit proteins. Serum immunoreactivity was tested in anti-citrullinated peptide/protein Abs (ACPA)⁺ versus ACPA^- RA patients. Ten out of 71 RA-rmAbs showed clear reactivity toward RA-FLS in immunofluorescence with no binding to NETs. One stromal-reactive RA-rmAb (RA057/11.89.1) decorated a ∼58-kDa band that mass spectrometry and Western blotting with a commercial Ab identified as calreticulin (CRT). Confocal microscopy demonstrated significant cellular colocalization between anti-CRT RA057/11.89.1 in RA-FLS. RA057/11.89.1 was able to immunoprecipitate rCRT. Deimination of CRT to cit-CRT moderately increased RA057/11.89.1 immunoreactivity. cit-CRT displayed increased blocking capacity compared with unmodified CRT in competitive binding assays. Finally, anti-cit-CRT Abs were preferentially detected in ACPA⁺ versus ACPA^- RA sera. We identified a synovial B cell-derived RA-rmAb locally differentiated within the ELS⁺ RA synovium reacting toward CRT, a putative novel autoantigen recently described in RA patients, suggesting that FLS-derived CRT may contribute to fuel the local autoimmune response.

Celiac Disease and Liver Disorders: From Putative Pathogenesis to Clinical Implications

Immunologically mediated liver diseases belong to the common extraintestinal manifestations of celiac disease. We have reviewed the current literature that addresses the association between celiac disease and liver disorders. We searched relevant articles on MEDLINE/PubMed up to 15 June 2018. The objective of the article is to provide a comprehensive and up-to-date review on the latest hypotheses explaining the pathogenetic relationship between celiac disease and liver injury. Besides the involvement of gut–liver axis, tissue transglutaminase antibodies, and impairment of intestinal barrier, we integrate the latest achievements made in elucidation of the role of gut microbiota in celiac disease and liver disorders, that has not yet been sufficiently discussed in the literature in this context. The further objective is to provide a complete clinical overview on the types of liver diseases frequently found in celiac disease. In conclusion, the review highlights the clinical implication, recommend a rational approach for managing elevated transaminases in celiac patients, and underscore the importance of screening for celiac disease in patients with associated liver disease.

Heightened autoantibody immune response to citrullinated calreticulin in bronchiectasis: Implications for rheumatoid arthritis

Calreticulin (CRT) and citrullinated (citCRT) are implicated in rheumatoid arthritis (RA) pathology. citCRT binds to RA shared epitopes (SE) on HLA-DR molecules with high affinity and triggers pro-inflammatory events in adjacent cells. The aim of the study was to detect the presence of citCRT prior to developing RA and evaluate if citCT is a target for autoantibodies in RA cohorts with and without lung disease. Antibodies were assessed by ELISA against native CRT, citCRT and general protein citrullination, in sera from 50 RA patients without lung disease, 122 bronchiectasis (BR) patients, 52 bronchiectasis patients with RA (BRRA), 87 asthma patients and 77 healthy controls (HC). Serum citCRT was detected by immunoblotting and mass spectrometry. Genomic DNA was genotyped for HLA-DRB1 alleles. Patients were assessed for DAS28, rheumatoid factor, and anti-cyclic citrullinated peptide antibodies. Extracellular citCRT was detected in BR patients sera prior to them developing RA. A citCRT SE binding peptide GEWKPR_261citQIDNPDYK was identified. Anti-CRT antibodies were observed in 18% of BR patients with or without RA. Anti-citCRT antibodies were observed in ∼35% of BR or RA patients, increasing to 58% in BRRA patients. In the RA alone patients 7/20 (35%) who were negative for RF and anti-CCP were anti-CRT antibody positive and had higher DAS28 scores than triple negative RA alone patients. Three of the four BR patients who developed RA over 18 months were anti-citCRT+ve SE^+ve. The detection of citCRT in BR and development of anti-citCRT in BR patients suggests citCRT antigens are early targets of antigenicity in these patients, especially in SE^+ve patients prior to the onset of RA.

Anti-calreticulin antibodies and calreticulin in sera of patients diagnosed with dilated or hypertrophic cardiomyopathy

Distinct cellular level of the Ca²⁺-binding chaperone calreticulin (CRT) is essential for correct embryonal cardiac development and postnatal function. However, CRT is also a potential autoantigen eliciting formation of antibodies (Ab), whose role is not yet clarified. Immunization with CRT leads to cardiac injury, while overexpression of CRT in cardiomyocytes induces dilated cardiomyopathy (DCM) in animals. Hence, we analysed levels of anti-CRT Ab and calreticulin in the sera of patients with idiopatic DCM and hypertrophic cardiomyopathy (HCM). ELISA and immunoblot using human recombinant CRT and Pepscan with synthetic, overlapping decapeptides of CRT were used to detect anti-CRT Ab. Serum CRT concentration was tested by ELISA. Significantly increased levels of anti-CRT Ab of isotypes IgA (p < 0.001) and IgG (p < 0.05) were found in patients with both DCM (12/34 seropositive for IgA, 7/34 for IgG) and HCM (13/38 seropositive for IgA, 11/38 for IgG) against healthy controls (2/79 for IgA, 1/79 for IgG). Titration analysis in seropositive DCM and HCM patients documented anti-CRT Ab detected at 1/1600 dilution for IgG and 1/800 for IgA (and IgA1) and at least at 1/200 dilution for IgA2, IgG1, IgG2 and IgG3. Pepscan identified immunogenic CRT epitopes recognized by IgA and IgG Ab of these patients. Significantly increased levels of CRT relative to healthy controls were found in sera of patients with HCM (p < 0.01, 5/19). These data extend the knowledge of seroprevalence of anti-CRT Ab and CRT, and suggest possible involvement of autoimmune mechanisms directed to CRT in some forms of cardiomyopathies, which are clinically heterogeneous.

Contribution of humoral immune responses to the antitumor effects mediated by anthracyclines

Immunogenic cell death induced by cytotoxic compounds contributes to the success of selected chemotherapies by eliciting a protective anticancer immune response, which is mediated by CD4(+) and CD8(+) T cells producing interferon-γ. In many instances, cancer progression is associated with high titers of tumor-specific antibodies, which become detectable in the serum, but whose functional relevance is elusive. Here, we explored the role of humoral immune responses in the anticancer efficacy of anthracyclines. Chemotherapy reduced the number of tumor-infiltrating B cells, and failed to promote humoral responses against immunodominant tumor antigens. Although anthracycline-based anticancer chemotherapies failed in T cell-deficient mice, they successfully reduced the growth of cancers developing in mice lacking B lymphocytes (due to the injection of a B-cell-depleting anti-CD20 antibody), immunoglobulins (Igs) or Ig receptors (Fc receptor) due to genetic manipulations. These results suggest that the humoral arm of antitumor immunity is dispensable for the immune-dependent therapeutic effect of anthracyclines against mouse sarcoma. In addition, we show here that the titers of IgA and IgG antibodies directed against an autoantigen appearing at the cell surface of tumor cells post chemotherapy (calreticulin, CRT) did not significantly increase in patients treated with anthracyclines, and that anti-CRT antibodies had no prognostic or predictive significance. Collectively, our data indicate that humoral anticancer immune responses differ from cellular responses in, thus far, that they do not contribute to the success of anthracycline-mediated anticancer therapies in human breast cancers and mouse sarcomas.

Celiac disease markers in patients with liver diseases: A single center large scale screening study

AIM: To study the coincidence of celiac disease, we tested its serological markers in patients with various liver diseases.

METHODS: Large-scale screening of serum antibodies against tissue transglutaminase (tTG), and deamidated gliadin using enzyme-linked immunosorbent assay and serum antibodies against endomysium using immunohistochemistry, in patients with various liver diseases (n = 962) and patients who underwent liver transplantation (OLTx, n = 523) was performed. The expression of tTG in liver tissue samples of patients simultaneously suffering from celiac disease and from various liver diseases using immunohistochemistry was carried out. The final diagnosis of celiac disease was confirmed by histological analysis of small-intestinal biopsy.

RESULTS: We found that 29 of 962 patients (3%) with liver diseases and 5 of 523 patients (0.8%) who underwent OLTx were seropositive for IgA and IgG anti-tTG antibodies. However, celiac disease was biopsy-diagnosed in 16 patients: 4 with autoimmune hepatitis type I, 3 with Wilson's disease, 3 with celiac hepatitis, 2 with primary sclerosing cholangitis, 1 with primary biliary cirrhosis, 1 with Budd-Chiari syndrome, 1 with toxic hepatitis, and 1 with non-alcoholic steatohepatitis. Unexpectedly, the highest prevalence of celiac disease was found in patients with Wilson's disease (9.7%), with which it is only rarely associated. On the other hand, no OLTx patients were diagnosed with celiac disease in our study. A pilot study of the expression of tTG in liver tissue using immunohistochemistry documented the overexpression of this molecule in endothelial cells and periportal hepatocytes of patients simultaneously suffering from celiac disease and toxic hepatitis, primary sclerosing cholangitis or autoimmune hepatitis type I.

CONCLUSION: We suggest that screening for celiac disease may be beneficial not only in patients with associated liver diseases, but also in patients with Wilson's disease.

Overexpression of calreticulin in malignant and benign breast tumors: relationship with humoral immunity

OBJECTIVE

Calreticulin is a multicompartmental protein which regulates many important cellular responses. The aim of this study was to elucidate whether the intensity and location of calreticulin overexpression in tumor cells are related to the elevated humoral immunity to calreticulin in patients with benign or malignant breast disease.

METHODS

This study involved 27 patients with benign and 58 patients with malignant breast tumors before surgical resection and 38 healthy volunteers. Cytoplasmatic or membranous calreticulin overexpression in malignant or benign cells in paraffin-embedded tissues was determined using immunohistochemistry. Levels of the serum anti-calreticulin autoantibodies were detected by ELISA.

RESULTS

Statistically significant differences between serum levels of IgA of anti-calreticulin antibodies in controls and patients with breast tumors, and between controls and patients with nonmalignant breast diseases were found, but no statistically significant differences were found between levels of serum IgG anti-calreticulin antibodies. Humoral immunity to calreticulin developed against cytoplasmatic and co-localized membranous calreticulin was not correlated to the intensity of its overexpression and was present even in the absence of its membranous localization.

CONCLUSIONS

The degree of calreticulin overexpression in lobular breast carcinoma is lower than in ductal breast carcinoma. Elevated concentrations of anti-calreticulin IgA antibodies were present more frequently in patients with metastasis in locoregional lymph nodes in comparison to anti-calreticulin IgG antibodies.

Similarity of fine specificity of IgA anti-gliadin antibodies between patients with celiac disease and humanized α1KI mice

Gliadins, and primarily α-gliadins containing several sequences such as aa 31-49, aa 56-88 (33-mer), aa 57-68, and aa 69-82, are critical in the induction of immune response or toxic reaction leading to the development of celiac disease (CLD). The role of IgA anti-gliadin antibodies (IgA AGA) is unknown. To this end, we prepared several humanized monoclonal IgA AGA using transgenic α1KI mice. Employing Pepscan with overlapping decapeptides of α-gliadin we observed a robust similarity between the specificity of humanized mouse monoclonal IgA AGA and IgA AGA from patients with florid CLD. The common immunodominant region included several sequential epitopes localized in the N-terminal part of α-gliadin (QFQGQQQPFPPQQPYPQPQPFP, aa 29-50, and QPFPSQQPYLQL, aa 47-58). Notably, IgA AGA produced by clones 8D12, 15B9, 9D12, and 18E2 had significant reactivity against sequences localized in the 33-mer, LQLQPFPQPQ (aa 56-65) and PQLPYPQPQPFL (aa 69-80). Humanized mouse monoclonal IgA AGA that have a known specificity are suitable as standard in ELISAs to detect serum IgA AGA of CLD patients and for studying the AGA pathogenic role in CLD, especially for analyzing the translocation of complex of specific IgA antibodies and individual gliadin peptides through enterocyte barrier.

Calreticulin is a B cell molecular target in some gastrointestinal malignancies

Calreticulin, upon translocation to the cell surface, plays a critical role in the recognition of tumour cells and in experimentally induced cellular anti-tumour immunity. However, less is known about anti-calreticulin antibodies and their role in malignancies. Using enzyme-linked immunosorbent assay (ELISA), we found immunoglobulin (Ig)A and/or IgG anti-calreticulin antibodies in sera of approximately 63% of patients with hepatocellular carcinoma (HCC), 57% of patients with colorectal adenocarcinoma (CRA) and 47% of patients with pancreatic adenocarcinoma (PACA), while healthy controls, patients with viral hepatitis C and with chronic pancreatitis reached only 2%, 20% and 31% seropositivity, respectively. We found significantly elevated mean levels of IgA anti-calreticulin antibodies (P < 0.001) in patients with HCC (78.7 +/- 52.3 AU, mean +/- standard deviation), PACA (66.5 +/- 30.9 AU) and CRA (61.8 +/- 25.8 AU) when compared to healthy controls (41.4 +/- 19.2 AU). Significantly elevated mean levels of IgG anti-calreticulin antibodies (P < 0.001) were detected in patients with HCC (121.9 +/- 94.2 AU), gall bladder adenocarcinoma (118.4 +/- 80.0 AU) and PACA (88.7 +/- 55.6 AU) when compared to healthy controls (56.7 +/- 22.9 AU). Pepscan analysis revealed a large number of antigenic epitopes of calreticulin recognized by both IgA and IgG antibodies of patients with HCC and PACA, indicating robust systemic immune response. Moreover, significantly elevated levels of antibodies against peptide KGEWKPRQIDNP (P < 0.001) in these patients, tested by ELISA, confirmed the distinct character of antibody reactivity against calreticulin. The high occurrence and specificity of serum anti-calreticulin autoantibodies in the majority of patients with some gastrointestinal malignancies provide the evidence for their possible clinical relevance.

Anti-calreticulin immunoglobulin A (IgA) antibodies in refractory coeliac disease

Refractory coeliac disease (RCD) is a very rare and dangerous form of CD, in which gluten-free diet loses its therapeutic effect and the damage of intestinal mucosa persists. Because of the adherence to the diet, serological markers of CD [immunoglobulin A (IgA) antibodies against gliadin, tissue transglutaminase (tTG) and endomysium] are often missing in RCD patients. We found substantially elevated levels of IgA anti-calreticulin (CRT) antibodies in the sera of almost all RCD patients tested. These sera were negative for IgA antibodies to gliadin and tTG and only some of them showed IgA antibodies to enterocytes. Analysis of patients' IgA reactivity to CRT fragments (quarters and halves) by Western blotting revealed differences in the specificity of IgA antibodies between RCD and CD patients. We therefore used the Pepscan technique with synthetic overlapping decapeptides of CRT to characterize antigenic epitopes recognized by serum IgA antibodies of RCD patients. Employing this method we demonstrated several dominant antigenic epitopes recognized by IgA antibodies of RCD patients on the CRT molecule. Epitope GVTKAAEKQMKD was recognized predominantly by serum IgA of RCD patients. Our results suggest that testing for serum IgA antibodies against CRT and its selected peptide could be a very useful tool in RCD differential diagnosis.

Autoantibodies in celiac disease

Autoantibody production is an important feature of many autoimmune disorders, signifying a breakdown of immune tolerance to self-antigens. In celiac disease, an autoimmune enteropathy with multiple extra-intestinal manifestations, autoantibody reactivity to transglutaminase 2 (TG2) has been shown to closely correlate with the acute phase of the disease. It serves as a specific and sensitive marker of celiac disease, and is highly useful in aiding diagnosis and follow-up. Immune reactivity to other autoantigens, including transglutaminase 3, actin, ganglioside, collagen, calreticulin and zonulin, among others, has also been reported in celiac disease. The clinical significance of these antibodies is not known, although some may be associated with specific clinical presentations or extra-intestinal manifestations of celiac disease. This review examines the presence of anti-TG2 and other autoantibodies in celiac disease, discussing their diagnostic value, their potential role in disease pathogenesis and current hypotheses that explain how their release may be triggered.

Associated autoantibodies in celiac disease

Celiac disease (CD) is a life-long inflammatory autoimmune condition of the gastrointestinal tract affecting genetically susceptible individuals. Several autoimmune disorders are more prevalent in patients and their close relatives and that risk is gluten exposure duration related. The most frequent reported CD associated conditions are type 1 diabetes mellitus and autoimmune thyroiditis. Associated autoimmune antibodies are frequent in CD and their first-degree relatives, spanning anti-endocrine, anti-gastrointestinal, anti-nuclear, anti-cytoskeleton and anti-neurological antibodies. More specifically, antibodies against thyroid and the endocrine pancreas, anti-gastric and liver, anti-nuclear constituents, anti-reticulin, actin, smooth muscle, calreticulin, desmin, collagens and bone, anti-brain, ganglioside, neuronal and blood vessel were described in sera of the patients in numerous studies. The common immunogenetic theories for the above associations are: sharing common HLA and non-HLA genes, antigenic mimicry, damage-induced neoantigen exposure, altered intestinal permeability, idiotype network dysregulation and epitope spreading. The CD associated autoantibodies enigma, being an epiphenomenon or pathogenic, remains unresolved and presents a challenging area for future research.

Anti-calreticulin antibodies in patients with inflammatory bowel disease

PURPOSE

Although the pathogenesis of inflammatory bowel disease (IBD) is unclear, autoimmune processes seem to play roles in IBD because several types of autoantibodies have been found in it. Calreticulin (CRT) is a soluble Ca2+ binding protein which is present in a wide variety of cells. CRT is localized mainly in the endoplasmic reticulum and is often a target for autoantibodies. The aim of this study was to evaluate the clinical significance of anti-CRT antibodies measured by enzyme-linked immunosorbent assay (ELISA) using the sera of patients with ulcerative colitis (UC) and Crohn's disease (CD).

METHODS

We measured the serum anti-CRT antibodies of 31 Japanese patients with UC and 24 with CD by ELISA. The controls were 105 subjects: 30 healthy persons, 44 patients with primary biliary cirrhosis (PBC), 21 with systemic lupus erythematosus (SLE) and 10 with acute colitis (AC).

RESULTS

The mean titer of anti-CRT antibodies was significantly higher in patients with UC than in healthy individuals (p <0.05). The prevalence of anti-CRT antibodies in these patients was significantly higher during the initial phase than during the passing phase (p <0.05). In patients with CD, the mean titer of anti-CRT antibodies was not significantly higher than in healthy individuals. The positivity for anti-CRT antibodies, however, was about 30% in those patients, which was as high as in patients with UC, SLE and PBC. In patients with AC, anti-CRT antibodies were all negative.

CONCLUSIONS

The positivity of anti-CRT antibodies may have a diagnostic value for IBD, especially in the initial phase of UC.