The analysis of the fine specificity of celiac disease antibodies using tissue transglutaminase fragments

A Functional Idiotype/Anti-Idiotype Network Is Active in Genetically Gluten-Intolerant Individuals Negative for Both Celiac Disease-Related Intestinal Damage and Serum Autoantibodies

An unbalance between Abs that recognize an autoantigen (idiotypes; IDs) and Igs that bind such Abs (anti-IDs) is considered a functional event in autoimmune disorders. We investigated the presence of an ID/anti-ID network in celiac disease (CD), a condition in which antitissue transglutaminase 2 (TG2) Abs are suspected to contribute to CD pathogenesis. To characterize the ID side, we reproduced by in vitro yeast display the intestine-resident Abs from CD and control patients. These TG2-specific IDs were used to identify potential anti-IDs in the serum. We observed elevated titers of anti-IDs in asymptomatic patients with predisposition to CD and demonstrated that anti-ID depletion from the serum restores a detectable humoral response against TG2. Our study provides an alternative approach to quantify CD-related autoantibodies in cases that would be defined "negative serology" with current diagnostic applications. Therefore, we suggest that developments of this technology could be designed for perspective routine tests.

Anti-type 2 transglutaminase antibodies as modulators of type 2 transglutaminase functions: a possible pathological role in celiac disease

Auto-antibodies to the ubiquitous enzyme type-2 transglutaminase (TG2) are a specific hallmark of celiac disease (CD), a widely diffused, multi-factorial disease, affecting genetically predisposed subjects. In CD an inflammatory response, at the intestinal level, is triggered by diet consumption of gluten-containing cereals. Intestinal mucosa displays various degrees of atrophy and hyperplasia, with consequent global intestinal dysfunction and other relevant extra-intestinal symptoms. Through deamidation of specific glutamines of gluten-derived gliadin peptides, TG2 strongly enhances gliadin immunogenicity. In addition, TG2 cross-linking activity may generate complexes between TG2 itself and gliadin peptides, and these complexes seem to cause the auto-immune response by means of an apten-carrier-like mechanism of antigen presentation. Anti-TG2 antibodies can be early detected in the intestinal mucosa of celiac patients and are also abundantly present into the serum, thus potentially reaching other organs and tissues by blood circulation. Recently, the possible pathogenetic role of auto-antibodies to TG2 in CD has been investigated. Here, we report an overview about the genesis of these antibodies, their specificity, their modulating ability toward TG2 enzymatic or non-enzymatic activities and their biological effects exerted by interacting with extracellular TG2 or with cell-surface TG2. We also discuss the auto-immune response occurring in CD against other TG members (i.e. type 3 and type 6) and analyze the occurrence of anti-TG2 antibodies in other auto-immune CD-related diseases. Data now available let us to suppose that, even if antibodies to TG2 do not represent the triggering molecules in CD, they could be important players in disease progression and manifestations.

Mapping the minimum domain of the fibronectin binding site on transglutaminase 2 (TG2) and its importance in mediating signaling, adhesion, and migration in TG2-expressing cells

The interaction between the enzyme transglutaminase 2 (TG2) and fibronectin (FN) is involved in the cell-matrix interactions that regulate cell signaling, adhesion, and migration and play central roles in pathologic conditions, particularly fibrosis and cancer. A precise definition of the exact interaction domains on both proteins could provide a tool to design novel molecules with potential therapeutic applications. Although specific residues involved in the interaction within TG2 have been analyzed, little is known regarding the TG2 binding site on FN. This site has been mapped to a large internal 45-kDa protein fragment coincident with the gelatin binding domain (GBD). With the goal of defining the minimal FN interacting domain for TG2, we produced several expression constructs encoding different portions or modules of the GBD and tested their binding and functional properties. The results demonstrate that the I₈ module is necessary and sufficient for TG2-binding in vitro, but does not have functional effects on TG2-expressing cells. Modules I₇ and I₉ increase the strength of the binding and are required for cell adhesion. A 15-kDa fragment encompassing modules I_7-9 behaves as the whole 45-kDa GBD and mediates signaling, adhesion, spreading, and migration of TG2⁺ cells. This study provides new insights into the mechanism for TG2 binding to FN.-Soluri, M. F., Boccafoschi, F., Cotella, D., Moro, L., Forestieri, G., Autiero, I., Cavallo, L., Oliva, R., Griffin, M., Wang, Z., Santoro, C., Sblattero, D. Mapping the minimum domain of the fibronectin binding site on transglutaminase 2 (TG2) and its importance in mediating signaling, adhesion, and migration in TG2-expressing cells.

Epitope mapping of the N-terminal portion of tissue transglutaminase protein antigen to identify linear epitopes in celiac disease

Celiac disease (CD) is an autoimmune mediated disease with complex and multifactorial etiology. Gluten intake triggers a composite immune response involving T-cells and B-cells and leading to the secretion of autoantibodies if a genetic predisposition is present. Untreated CD patients show high levels of circulating autoantibodies directed to different auto-antigens present in the intestinal mucosa. The most important auto-antigen is the endomysial enzyme tissue transglutaminase (tTG). Both IgA and IgG antibody isotypes to tTG are known, but only the IgA antibodies demonstrate the highest disease specificity and thus are considered disease biomarkers. Because the pathogenicity and exact tTG binding properties of these autoantibodies are still unclear, the characterization of tTG antigenic domains is a crucial step in understanding CD onset and the autoimmune pathogenesis. Overlapping peptide libraries can be used for epitope mapping of selected protein portions to determine antigenic fragments contributing to the immunological activity and possibly develop innovative peptide-based tools with high specificity and sensitivity for CD. We performed an epitope mapping study to characterize putative linear auto-antigenic epitopes present in the tTG N-terminal portion (1-230). A library of 23 overlapping peptides spanning tTG(1-230) was generated by Fmoc/tBu solid-phase peptide synthesis and screened by immunoenzymatic assays employing patients' sera. The results indicate that four synthetic peptides, that is, Ac-tTG(1-15)-NH2 , Ac-tTG(41-55)-NH2 , Ac-tTG(51-65)-NH2 , and Ac-tTG(151-165)-NH2 , are recognized by IgA autoantibodies circulating in CD patients' sera. These results offer important insight on the nature of the antigen-antibody interaction.

Transglutaminase 2-specific autoantibodies in celiac disease target clustered, N-terminal epitopes not displayed on the surface of cells

The gluten-sensitive enteropathy celiac disease is tightly associated with the production of autoantibodies specific for the enzyme transglutaminase 2 (TG2). The mechanisms underlying the activation of autoreactive B cells, however, are not well defined. To gain more insight into this autoimmune response we have characterized the binding of TG2 by a panel of human mAbs generated by expression cloning of Ig genes from single plasma cells of the celiac disease lesion. The Abs were highly specific to TG2 and bound preferentially to the open, Ca(2+)-activated enzyme conformation. Epitope mapping revealed that they recognize few distinct conformational epitopes that cluster in the N-terminal half of the enzyme. Two of the epitopes were overlapping with the fibronectin binding site in TG2, and none of the epitopes was accessible when TG2 was in a cell surface-bound form. Based on our findings, we propose that the autoantibodies are generated against the soluble, catalytically active enzyme, whereas Abs reactive with cell surface-associated TG2 are absent from the response due to negative selection of B cells recognizing membrane-bound self-Ag. The findings give insight into the mechanisms controlling the formation of anti-TG2 autoantibodies in celiac disease.

Anti-transglutaminase immunoreactivity and histological lesions of the duodenum in coeliac patients

Coeliac disease (CD) is characterized by several markers, including anti-transglutaminase auto-antibodies (tTGAb) directed against multiple epitopes of the gliadin protein. We aimed to investigate the correlation among CD duodenal lesions, tTGAb titres and the immunoreactivity against tTG constructs. A total of 345 CD patients (209 females, 136 males, overall median age: 7.3 years) were tested for full-length (fl) tTGAb with a fluid-phase radioimmunoassay. Out of the total, 231 patients were also tested for immunoreactivity against tTG fragments (F1: a.a. 227-687 and F2: a.a. 473-687). Patients were classified according to diffuse (D), patchy (P) or bulb (B) histological lesions. All sera were found fltTGAb positive. Patients with D, P and B lesions had a mean Ab index of 0.84±0.39, 0.57±0.39 and 0.45±0.24, respectively. Mean tTGAb titre varied between D and localized (P+B) patients (0.84±0.39 versus 0.52±0.34, P < 0.0001). Overall, 86.1% of patients were F1 auto-antibody (F1Ab) positive (D: 89%, P: 75%, B: 40%; D versus P+B: P = 0.004) and 49% of patients were F2 auto-antibody (F2Ab) positive (D: 53%, P: 19%, B: 10%; D versus P+B: P = 0.0006). Of the D patients 50.7% showed combined F1Ab-F2Ab (D versus P+B: P = 0.001), whereas 60% of B patients were negative for both F1Ab and F2Ab (B versus D: P < 0.0001). Coeliac-specific tTGAb immunoreactivity correlates with the grading and extension of histological duodenal lesions in CD patients at diagnosis. The immunoreactivity against single and combined tTG fragments is significantly higher in patients with D lesions. This is the first evidence of a distinct coeliac-specific immunoreactivity in patients with different duodenal involvement.

Binding of autoantibodies to the core region of tissue transglutaminase is a feature of paediatric coeliac disease

OBJECTIVES

Production of autoantibodies to the enzyme tissue transglutaminase (tTG) is a hallmark of coeliac disease (CD). We have previously demonstrated that the immumoglobulin (Ig) A response to tTG in adult CD specifically targets its catalytic core region, containing the active-site triad of amino acids. The aim of the present study was to investigate this phenomenon in paediatric patients with CD, and to elucidate the contribution of each active-site residue to epitopes recognised. The specificity of the IgG anti-tTG response was also investigated and compared with that of the IgA anti-tTG response, in both paediatric and adult patients with CD.

METHODS

Wild-type and novel variants of tTG were generated via site-directed mutagenesis and expressed as glutathione-S-transferase-fusion proteins in Escherichia coli BL-21. The mutagenic variants of tTG had substitutions of 1, 1, or all of the 3 of the catalytic triad amino acids. All of the recombinant tTGs were tested for their antigenicity in IgA and IgG enzyme-linked immunosorbent assays with cohorts of paediatric (n=63) and adult (n=30) CD sera.

RESULTS

Substitution of even 1 amino acid in the catalytic triad resulted in a significant reduction of CD IgA and IgG anti-tTG binding, with all of the mutant proteins displaying diminished antigenicity compared with the wild-type protein.

CONCLUSIONS

The core region of tTG is specifically targeted from early on in disease course by CD patient autoantibodies of both the IgA and IgG class.

The adaptive immune response in celiac disease

Compared to other human leukocyte antigen (HLA)-associated diseases such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, fundamental aspects of the pathogenesis in celiac disease are relatively well understood. This is mostly because the causative antigen in celiac disease-cereal gluten proteins-is known and the culprit HLA molecules are well defined. This has facilitated the dissection of the disease-relevant CD4+ T cells interacting with the disease-associated HLA molecules. In addition, celiac disease has distinct antibody responses to gluten and the autoantigen transglutaminase 2, which give strong handles to understand all sides of the adaptive immune response leading to disease. Here we review recent developments in the understanding of the role of T cells, B cells, and antigen-presenting cells in the pathogenic immune response of this instructive disorder.

A single conformational transglutaminase 2 epitope contributed by three domains is critical for celiac antibody binding and effects

The multifunctional, protein cross-linking transglutaminase 2 (TG2) is the main autoantigen in celiac disease, an autoimmune disorder with defined etiology. Glutamine-rich gliadin peptides from ingested cereals, after their deamidation by TG2, induce T-lymphocyte activation accompanied by autoantibody production against TG2 in 1-2% of the population. The pathogenic role and exact binding properties of these antibodies to TG2 are still unclear. Here we show that antibodies from different celiac patients target the same conformational TG2 epitope formed by spatially close amino acids of adjacent domains. Glu153 and 154 on the first alpha-helix of the core domain and Arg19 on first alpha-helix of the N-terminal domain determine the celiac epitope that is accessible both in the closed and open conformation of TG2 and dependent on the relative position of these helices. Met659 on the C-terminal domain also can cooperate in antibody binding. This composite epitope is disease-specific, recognized by antibodies derived from celiac tissues and associated with biological effects when passively transferred from celiac mothers into their newborns. These findings suggest that celiac antibodies are produced in a surface-specific way for which certain homology of the central glutamic acid residues of the TG2 epitope with deamidated gliadin peptides could be a structural basis. Monoclonal mouse antibodies with partially overlapping epitope specificity released celiac antibodies from patient tissues and antagonized their harmful effects in cell culture experiments. Such antibodies or similar specific competitors will be useful in further functional studies and in exploring whether interference with celiac antibody actions leads to therapeutic benefits.

Development of phage-based single chain Fv antibody reagents for detection of Yersinia pestis

BACKGROUND

Most Yersinia pestis strains are known to express a capsule-like antigen, fraction 1 (F1)(.) F1 is encoded by the caf1 gene located on the large 100-kb pFra plasmid, which is found in Y. pestis but not in closely related species such as Yersinia enterocolytica and Yersinia pseudotuberculosis. In order to find antibodies specifically binding to Y. pestis we screened a large single chain Fv antibody fragment (scFv) phage display library using purified F1 antigen as a selection target. Different forms of the selected antibodies were used to establish assays for recombinant F1 antigen and Y. pestis detection.

METHODS

Phage antibody panning was performed against F1 in an automated fashion using the Kingfisher magnetic bead system. Selected scFvs were screened for F1-binding specificity by one-step alkaline phosphatase enzyme linked immunosorbant assay (ELISA), and assayed for binding to recombinant antigen and/or Y. pestis by flow cytometry and whole-cell ELISA.

RESULTS

Seven of the eight selected scFvs were shown to specifically bind both recombinant F1 and a panel of F1-positive Yersinia cells. The majority of the soluble scFvs were found to be difficult to purify, unstable and prone to cross-reactivity with F1-negative Yersinia strains, whereas phage displayed scFvs were found to be easy to purify/label and remarkably stable. Furthermore direct fluorescent labeling of phage displaying scFv allowed for an easy one-step flow cytometry assay. Slight cross-reactivity was observed when fixed cells were used in ELISA.

CONCLUSIONS

Our high throughput methods of selection and screening allowed for time and cost effective discovery of seven scFvs specifically binding Y. pestis F1 antigen. We describe implementation of different methods for phage-based immunoassay. Based on the success of these methods and the proven stability of phage, we indicate that the use of phage-displayed, rather than phage-free proteins, might generally overcome the shortcomings of scFv antibodies.

The use of phage display in neurobiology

Phage display has been extensively used to study protein-protein interactions, receptor- and antibody-binding sites, and immune responses, to modify protein properties, and to select antibodies against a wide range of different antigens. In the format most often used, a polypeptide is displayed on the surface of a filamentous phage by genetic fusion to one of the coat proteins, creating a chimeric coat protein, and coupling phenotype (the protein) to genotype (the gene within). As the gene encoding the chimeric coat protein is packaged within the phage, selection of the phage on the basis of the binding properties of the polypeptide displayed on the surface simultaneously results in the isolation of the gene encoding the polypeptide. This unit describes the background to the technique, and illustrates how it has been applied to a number of different problems, each of which has its neurobiological counterparts. Although this overview concentrates on the use of filamentous phage, which is the most popular platform, other systems are also described.

Celiac anti-tissue transglutaminase antibodies interfere with the uptake of alpha gliadin peptide 31-43 but not of peptide 57-68 by epithelial cells

Celiac disease is characterized by the secretion of IgA-class autoantibodies that target tissue transglutaminase (tTG). It is now recognized that anti-tTG antibodies are functional and not mere bystanders in the pathogenesis of celiac disease. Here we report that interaction between anti-tTG antibodies and extracellular membrane-bound tTG inhibits peptide 31-43 (but not peptide 57-68) uptake by cells, thereby impairing the ability of p31-43 to drive Caco-2 cells into S-phase. This effect did not involve tTG catalytic activity. Because anti-tTG antibodies interfered with epidermal growth factor endocytosis, we assume that they exert their effect by reducing peptide 31-43 endocytosis. Our results suggest that cell-surface tTG plays a hitherto unknown role in the regulation of gliadin peptide uptake and endocytosis.

Anti transglutaminase antibodies cause ataxia in mice

Background

Celiac disease (CD) is an autoimmune gastrointestinal disorder characterized by the presence of anti-transglutaminase 2 (TG2) and anti-gliadin antibodies. Amongst the neurological dysfunctions associated with CD, ataxia represents the most common one.

Methods

We analyzed by immunohistochemistry, the anti-neural reactivity of the serum from 20 CD patients. To determine the role of anti-TG2 antibodies in ataxia, two anti-TG2 single chain variable fragments (scFv), isolated from a phage-display IgA antibody library, were characterized by immunohistochemistry and ELISA, and injected in mice to study their effects on motor coordination. We found that 75% of the CD patient population without evidence of neurological involvement, has circulating anti-neural IgA and/or IgG antibodies. Two anti-TG2 scFvs, cloned from one CD patient, stained blood vessels but only one reacted with neurons. This anti-TG2 antibody showed cross reactivity with the transglutaminase isozymes TG3 and TG6. Intraventricular injection of the anti-TG2 or the anti-TG2/3/6 cross-reactive scFv provoked transient, equally intensive ataxia in mice.

Conclusion

The serum from CD patients contains anti-TG2, TG3 and TG6 antibodies that may potentially cause ataxia.

Transglutaminase 2 is expressed and active on the surface of human monocyte-derived dendritic cells and macrophages

The multifunctional enzyme, transglutaminase 2 (TG2), can be found intracellularly, in the extracellular matrix and on the cell surface. Cell surface TG2 (csTG2) could not be detected by TG2-specific antibodies or autoantibodies on immunocompetent cells. A supposedly csTG2-specific antibody, 6B9, was recently shown to actually react with CD44. Though the importance of TG2-mediated deamidation of gluten in the pathogenesis of celiac disease has been well recognized, it is not known in which intestinal cells or cell compartment the deamidation occurs. Duodenal dendritic cells (DCs) can be directly involved in gluten-reactive T-cell activation. Here we use blood monocyte-derived dendritic cells (iDC) and macrophages (MPhi) as a model for intestinal antigen-presenting cells (APCs) and show that they contain large amounts of TG2. We found that TG100, a commercial TG2-specific monoclonal antibody can recognize TG2 on the surface of these cells, that is monocyte-derived APCs express surface-associated TG2. TG2 expression was found on the surface of individual tunica propria cells in frozen small bowel tissue sections from both normal and celiac subjects. We also demonstrate that the pool of TG2 on the surface of iDCs can be catalytically active, hence it might directly be involved in the deamidation of gliadin peptides. Bacterial lipopolysaccharide (LPS) increased the level of TG2 on the surface of maturing DCs, supporting the hypothesis that an unspecific inflammatory process in the gut may expose more transglutaminase activity.

Anti-transglutaminase antibodies in non-coeliac children suffering from infectious diseases

Anti-transglutaminase antibodies are the diagnostic markers of coeliac disease. A role is suggested for infectious agents in the production of anti-transglutaminase antibodies. The aim was to measure positive anti-transglutaminase antibody levels in children with infectious diseases and to compare immunological and biological characteristics of the anti-transglutaminase antibodies derived from these children with that from coeliac patients. Two hundred and twenty-two children suffering from infectious diseases were enrolled prospectively along with seven biopsy-proven coeliacs. Serum samples were tested for anti-transglutaminase antibodies and anti-endomysium antibodies; positive samples were tested for coeliac-related human leucocyte antigen (HLA)-DQ2/8 and anti-viral antibodies. Purified anti-transglutaminase antibodies from the two study groups were tested for urea-dependent avidity, and their ability to induce cytoskeletal rearrangement and to modulate cell-cycle in Caco-2 cells, using phalloidin staining and bromodeoxyuridine incorporation assays, respectively. Nine of 222 children (4%) tested positive to anti-transglutaminase, one of whom also tested positive for anti-endomysium antibodies. This patient was positive for HLA-DQ2 and was diagnosed as coeliac following intestinal biopsy. Of the eight remaining children, two were positive for HLA-DQ8. Levels of anti-transglutaminase returned to normal in all subjects, despite a gluten-containing diet. Purified anti-transglutaminase of the two study groups induced actin rearrangements and cell-cycle progression. During an infectious disease, anti-transglutaminase antibodies can be produced temporarily and independently of gluten. The infection-triggered anti-transglutaminase antibodies have the same biological properties as that of the coeliacs, with the same in-vivo potential for damage.

Autoantibodies in gluten ataxia recognize a novel neuronal transglutaminase

OBJECTIVE

Gluten sensitivity typically presents as celiac disease, a chronic, autoimmune-mediated, small-intestinal disorder. Neurological disorders occur with a frequency of up to 10% in these patients. However, neurological dysfunction can also be the sole presenting feature of gluten sensitivity. Development of autoimmunity directed toward different members of the transglutaminase gene family could offer an explanation for the diversity in manifestations of gluten sensitivity. We have identified a novel neuronal transglutaminase isozyme and investigated whether this enzyme is the target of the immune response in patients with neurological dysfunction.

METHODS

Using recombinant human transglutaminases, we developed enzyme-linked immunosorbent assays and inhibition assays to analyze serum samples of patients with gluten-sensitive gastrointestinal and neurological disorders, and various control groups including unrelated inherited or immune conditions for the presence and specificity of autoantibodies.

RESULTS

Whereas the development of anti-transglutaminase 2 IgA is linked with gastrointestinal disease, an anti-transglutaminase 6 IgG and IgA response is prevalent in gluten ataxia, independent of intestinal involvement. Such antibodies are absent in ataxia of defined genetic origin or in healthy individuals. Inhibition studies showed that in those patients with ataxia and enteropathy, separate antibody populations react with the two different transglutaminase isozymes. Furthermore, postmortem analysis of brain tissue showed cerebellar IgA deposits that contained transglutaminase 6.

INTERPRETATION

Antibodies against transglutaminase 6 can serve as a marker in addition to human leukocyte antigen type and detection of anti-gliadin and anti-transglutaminase 2 antibodies to identify a subgroup of patients with gluten sensitivity who may be at risk for development of neurological disease.

Radioimmunological detection of anti-transglutaminase autoantibodies in human saliva: a useful test to monitor coeliac disease follow-up

BACKGROUND

Serum radioimmunoassay (RIA) tissue transglutaminase autoantibodies (tTG-Abs) proved to be a sensitive test also during coeliac disease (CD) follow-up. We demonstrated that RIA tTG-Abs could be detected in human saliva.

AIM

To evaluate salivary RIA tTG-Abs in coeliac children on gluten-free diet (GFD).

METHODS

Saliva and serum samples from 109 coeliac children were evaluated at diagnosis (group 1: 71 females, median age 9.4 years) and 58 of them on GFD: 36 after 3-6 months (group 2a), 34 at 9 months or more (group 2b). Two gender- and age-matched control groups: 89 gastroenterological patients (group 3) and 49 healthy subjects (group 4) participated in the study. Saliva and serum tTG-Abs were detected by RIA and compared with serum tTG-Abs ELISA and IgA anti-endomysium antibodies (EMA).

RESULTS

Salivary RIA tTG-Abs were found in 94.5%, 66.7% and 50.0% of groups 1, 2a and 2b CD patients and in 98.2%, 72.2% and 50.0% of corresponding serum samples, respectively. tTG-Abs decreased with GFD progression and a correlation was found between saliva and serum titres (r = 0.75, P = 0.0001). During the CD follow-up, salivary and serum RIA sensitivities were comparable, and higher with respect to EMA and ELISA.

CONCLUSIONS

This study demonstrates that it is possible to detect salivary tTG-Abs with high sensitivity not only at CD diagnosis, but also during GFD.

Mucosal tissue transglutaminase expression in celiac disease

Tissue transglutaminase (tTG) plays an important role in celiac disease pathogenesis and antibodies to tTG are a diagnostic marker of gluten-sensitive enteropathy. The aim of this study was to investigate the localization of tTG in the duodenal mucosa in control tissues and in different histological stages of celiac disease by using a commercial and a novel set of anti-tTG monoclonal antibodies, to see whether this assessment can be useful for diagnostic purpose. The distribution of tTG was firstly evaluated in 18 untreated celiac patients by using a commercial monoclonal antibody (CUB7402) against tissue transglutaminase enzyme and directed against the loop-core region of the enzyme. Thereafter, in further 30 untreated celiac patients we employed three newly characterized anti-tTG monoclonal antibodies produced against recombinant human-tTG. The epitopes recognized are located in three distinct domains of the protein corresponding to the core, C1 and C2 protein structure. Eleven age- and sex-matched patients with chronic duodenitis acted as controls. All subjects underwent upper endoscopy to obtain biopsy samples from the duodenum. Overall, we found that (i) tTG is equally expressed in CD at different stages of disease; (ii) tTG is expressed, at similar level, in CD and controls with duodenitis. Assessment of tTG level in biopsy samples by immunohistochemical methods is not useful in the clinical diagnostic work-up of CD.

Deamidated gliadin peptides form epitopes that transglutaminase antibodies recognize

OBJECTIVE

Deamidated gliadin peptides are efficient antigens in diagnostic tests for celiac disease, and results correlate better with transglutaminase 2-based assays than those with native gliadin. We investigated whether deamidated gliadin antigens are structurally similar to transglutaminase 2 or could mimic transglutaminase epitopes.

PATIENTS AND METHODS

Serum samples from 74 celiac and 65 control patients, and 13 different transglutaminase 2-specific monoclonal mouse antibodies were investigated for their binding to commercially available deamidated gliadin peptides using enzyme-linked immunosorbent assay, competition studies, and molecular modelling.

RESULTS

The enzyme-linked immunosorbent assay with deamidated gliadin peptides had 100% sensitivity and 98.5% specificity in patients. Deamidated gliadin epitopes also were recognized by 3 transglutaminase-specific monoclonal antibodies, and antibodies affinity-purified with deamidated gliadin peptides from celiac patient sera reacted with transglutaminase but did not show endomysial binding. The binding of the monoclonal antibodies to deamidated gliadin was inhibited dose dependently by full-length recombinant human transglutaminase, its fragments containing the binding sites of these monoclonal antibodies, or by celiac patient antibodies. Deamidated gliadin peptides decreased the binding of transglutaminase-specific monoclonal antibodies to transglutaminase. Three different cross-reacting transglutaminase epitopes were found, of which 2 are located in the C-terminal domain and 1 is conformational. The binding of celiac serum samples to deamidated gliadin peptides could not be abolished by transglutaminase or by any of the transglutaminase-specific monoclonals, indicating that celiac sera also contain additional antibodies to gliadin epitopes different from transglutaminase.

CONCLUSIONS

Certain deamidated gliadin-derived peptides and transglutaminase 2 epitopes have similar 3-dimensional appearance. This homology may contribute to the induction of transglutaminase autoantibodies by molecular mimicry.

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.

Gluten ataxia: passive transfer in a mouse model

Gluten sensitivity is an autoimmune disease that usually causes intestinal atrophy resulting in a malabsorption syndrome known as celiac disease. However, gluten sensitivity may involve several organs and is often associated with extraintestinal manifestations. Typically, patients with celiac disease have circulating anti-tissue transglutaminase and anti-gliadin antibodies. When patients with gluten sensitivity are affected by other autoimmune diseases, other autoantibodies may arise like anti-epidermal transglutaminase in dermatitis herpetiformis, anti-thyroid peroxidase antibodies in thyroiditis, and anti-islet cells antibodies in type 1 diabetes. The most common neurological manifestation of gluten sensitivity is ataxia, the so-called gluten ataxia (GA). In patients with GA we have demonstrated that anti-gliadin and anti-tissue transglutaminase antibodies cross-react with neurons but that additional anti-neural antibodies are present. The aim of the present article is to review the knowledge on animal models of gluten sensitivity, as well as reviewing the role of anti-neural antibodies in GA.

Construction of miniantibodies for the in vivo study of human autoimmune diseases in animal models

Background

Phage display antibody libraries have been made from the lymphocytes of patients suffering from autoimmune diseases in which the antibodies are known to play a role in the pathogenesis or are important for the diagnosis of the disease. In the case of Celiac Disease, the immune response is directed against the autoantigen tissue transglutaminase. However, despite numerous studies, the role of these antibodies in the pathogenesis of this disease has not been elucidated.

Results

We were able to engineer specific anti-transglutaminase antibody fragments in the form called "miniantibody". These are produced by genetic fusion of anti-tTG scFv to Human, Mouse or Rat Fc domains, making them suitable for in vivo expression. The results obtained here indicate that the miniantibody molecule is efficiently secreted, and that the reactivity to the antigen is retained even after fusion to heterologous Fc domains. Further analysis demonstrate that the molecule is secreted as homodimeric, mimicking original antibody structure. Finally, the in vivo expression in mice leads to detectable serum levels with no apparent gross immune response by the host.

Conclusion

In this work we demonstrated the usefulness of a method for the in vivo expression of miniantibodies specific to transglutaminase, corresponding to the autoimmune specificity of Celiac Disease. This can be proposed as a general method to study the pathogenic role of autoimmune antibodies in autoimmune diseases.

Humoral immune response to tissue transglutaminase is related to epithelial cell proliferation in celiac disease

BACKGROUND & AIMS

Tissue transglutaminase (tTG) autoantibodies are markers of celiac disease, and the enzyme is required for several crucial biological processes. The aim of this study was to determine whether these autoantibodies are involved in the pathogenesis of the mucosal lesion typical of celiac disease.

METHODS

Using rhodamine-conjugated phalloidin staining, we evaluated whether tTG antibodies, both commercially available and cloned from patients with celiac disease, cause cytoskeletal changes in Caco-2, MCF7, and NIH 3T3 cells. We monitored cell levels of bromodeoxyuridine incorporation to determine whether tTG autoantibodies are able to induce NIH 3T3 fibroblasts and epithelial mucosal cells into S phase.

RESULTS

Treatment with tTG antibodies caused a dose-dependent increase of membrane ruffling in Caco-2, MCF7, and NIH 3T3 cells. It also dose-dependently induced G(0)-synchronized NIH 3T3 fibroblasts into S phase but did not affect the rate of apoptosis. Similarly, tTG antibodies induced S-phase entry of epithelial cells in cultured intestinal biopsy specimens from patients with celiac disease. They did not affect biopsy specimens from patients without celiac disease.

CONCLUSIONS

Our results suggest that tTG autoantibodies per se, by interacting with the extracellular membrane-bound transglutaminase, may play an important role in epithelial cell proliferation in celiac disease.

Deamidated Gliadin Peptides as Targets for Celiac Disease‐Specific Antibodies

Celiac disease (CD) is an (auto)immunologically mediated intestinal intolerance against proteins from wheat (gluten) and related cereal proteins. Tissue transglutaminase (tTG) has been identified as the autoantigen in CD. Although ultimate diagnosis is based on histological analysis of small intestinal mucosa obtained via tissue biopsy, assessment of autoantibodies can provide substantial help in the evaluation of CD. Gliadin antibodies are directed against the native disease-provoking cereal proteins. Despite their initial usefulness, these antibodies have lost diagnostic importance due to their poor specificity and sensitivity as CD markers. Recently, it was found, however, that gliadin antibodies from sera of patients with active CD preferentially recognized deamidated gliadin peptides. The use of deamidated gliadin peptides in immunoassays has significantly improved the usefulness of gliadin antibodies in diagnosis of CD to that observed with autoantibody assay methods (endomysium antibodies, antibodies against tTG). The antibody epitopes (B-cell epitopes) reflect substrate specificity of tTG and resemble peptide sequences known to be strongly T-cell stimulatory (T-cell epitopes) in CD. The assay applying deamidated gliadin peptides measures a new species of antibodies, which is different from conventional gliadin antibodies as well as from autoantibodies and will likely provide new information on pathophysiological mechanisms of CD.

Evidence of a selective epitope loss of anti-transglutaminase immunoreactivity in gluten-free diet celiac sera: A new tool to distinguish disease-specific immunoreactivities

The aim of the present study was to evaluate the epitope specific humoral human tissue transglutaminase (tTG) immunoreactivity against 3 different human recombinant tTG constructs [(full-length tTG (a.a. 1-687), tTG (a.a. 227-687); tTG (a.a. 473-687)] before and after the introduction of a gluten-free diet (GFD). To this end, sera from 64 celiac disease (CD) subjects on a gluten-containing diet (44 f, 20 m) and after 0.6 +/- 0.3 years and 2.1 +/- 1.3 years of GFD were studied using a quantitative radioimmunoprecipitation assay. All 64 CD patients at diagnosis were full-length anti-tTG (a.a. 1-687)Ab positive. These Abs significantly decreased in frequency and titer after 6 months and 2 years of GFD. However, at low titers, 64.1% (41/64) of CD patients were still fl-tTG (a.a. 1-687)Ab positive after 2 years of GFD. At disease diagnosis, 70.3% (45/64) of the CD patients had Abs directed against fragments (227-687) and/or (473-687) of the tTG protein. This percentage, after 2 years of GFD, significantly decreased to 18.7%, whereas almost 50% of GFD patients had no tTG (227-687) and tTG (473-687) fragment reactivity, but only persistent, low-titer full-length tTG (1-687)Abs. We suggest that the selective loss of immunoreactivity against tTG (227-687) and tTG (473-687) fragments in CD patients with a GFD, could be due to quantitative decrease of autoreactivity driven by tTG-gliadin interaction underlying celiac disease pathogenesis.

Reduction of tissue transglutaminase autoantibody levels by gluten-free diet is associated with changes in subsets of peripheral blood lymphocytes in children with newly diagnosed coeliac disease

Tissue transglutaminase (tTG) autoantibodies decline after gluten-free diet in patients with coeliac disease. We tested the hypothesis that gluten-free diet-induced change in tTG autoantibody levels affects subsets of peripheral blood lymphocytes. Peripheral blood was obtained from 20 children with biopsy-proven active coeliac disease. Gluten-free diet was initiated and the children examined again after three and six months. tTG autoantibodies were measured in radioligand binding assays and lymphocyte subsets by flow cytometry. IgA-tTG levels at diagnosis, 2204 U/ml (median, range 113-24990), were reduced over six months to 76 U/ml (median, range 1-1261) (P < 0.001). At six months, 12/20 (60%) children had reduced their IgA-tTG levels to < 100 U/ml and these children showed a decrease in B cells (mean change -3.8%, P = 0.014), CD4+ T cells (mean -4.32%, P = 0.011) and CD4+ T cells expressing CD25high (mean change -0.62%, P = 0.036). In contrast, the CD4+CD25(high)CCR4+ T cell population increased during the same period (mean change 11.5%, P = 0.0036). The decline in IgA-tTG levels correlated to the decrease in B cells (r = 0.56, P = 0.01), CD4+ T cells (r = 0.66, P = 0.004) as well as CD4+CD25high T cells (r = 0.59, P = 0.01). A negative correlation was found between the decline in IgA-tTG and CD4+CD25high T cells expressing CD45RO (r = -0.49, P = 0.03) and CCR4 (r = -0.54, P = 0.01). This is the first observational study on the effect of gluten-free diet on concurrent changes of tTG autoantibodies and specific peripheral blood lymphocyte subsets. Our data suggest that flow cytometry may be a useful complement to tTG autoantibodies when studying the effects of gluten-free diet in children with coeliac disease.

Characterizing monoclonal antibody epitopes by filtered gene fragment phage display

In the present paper, we describe a novel approach to map monoclonal antibody epitopes, using three new monoclonal antibodies that recognize h-TG2 (human transglutaminase 2) as an example. The target gene was fragmented and cloned upstream of an antibiotic-resistance gene, in the vector pPAO2, to select for in-frame polypeptides. After removal of the antibiotic-resistance gene by Cre/Lox recombination, an antigen fragment phage display library was created and selected against specific monoclonal antibodies. Using the h-TG2 fragment library, we were able to identify epitopes. This technique can also be broadly applied to the study of protein-protein interactions.

Antibodies from inflamed central nervous system tissue recognize myelin oligodendrocyte glycoprotein

Autoantibodies to myelin oligodendrocyte glycoprotein (MOG) can induce demyelination and oligodendrocyte loss in models of multiple sclerosis (MS). Whether anti-MOG Abs play a similar role in patients with MS or inflammatory CNS diseases by epitope spreading is unclear. We have therefore examined whether autoantibodies that bind properly folded MOG protein are present in the CNS parenchyma of MS patients. IgG was purified from CNS tissue of 14 postmortem cases of MS and 8 control cases, including cases of encephalitis. Binding was assessed using two independent assays, a fluorescence-based solid-phase assay and a solution-phase RIA. MOG autoantibodies were identified in IgG purified from CNS tissue by solid-phase immunoassay in 7 of 14 cases with MS and 1 case of subacute sclerosing panencephalitis, but not in IgG from noninflamed control tissue. This finding was confirmed with a solution-phase RIA, which measures higher affinity autoantibodies. These data demonstrate that autoantibodies recognizing MOG are present in substantially higher concentrations in the CNS parenchyma compared with cerebrospinal fluid and serum in subjects with MS, indicating that local production/accumulation is an important aspect of autoantibody-mediated pathology in demyelinating CNS diseases. Moreover, chronic inflammatory CNS disease may induce autoantibodies by virtue of epitope spreading.

Autoantibodies against soluble and immobilized human recombinant tissue transglutaminase in children with celiac disease

OBJECTIVES

The conformation of tissue transglutaminase might influence the performance of immunoassays to detect autoantibodies from patients with celiac disease. The present study investigated how the exposure of tissue transglutaminase kept in a liquid phase and fixed to a solid support affected the binding of immunoglobulin (Ig)A and IgG autoantibodies in children with untreated and treated celiac disease.

METHODS

Included were 73 untreated celiac disease children, 50 controls and 80 children with treated celiac disease. IgA and IgG antitissue transglutaminase were measured with solid phase enzyme-linked immunoassay (ELISA) and liquid phase radioligand binding assays. For IgG antitissue transglutaminase detection with radioligand binding assays antihuman IgG and protein A were used. IgA endomysial autoantibodies were measured by indirect immunofluorescence.

RESULTS

Both ELISA and radioligand binding assays detected IgA antitissue transglutaminase in 65 of 73 untreated celiac disease children and in 2 of 50 controls. One additional control child was detected with radioligand binding assays. Endomysial autoantibodies were present in 62 of 73 celiac disease children and in 2 of 50 controls. IgG antitissue transglutaminase was detected with both ELISA and radioligand binding assays in 40 of 73 untreated celiac disease children and in 2 of 50 controls. Radioligand binding assays using protein A detected 20 of 73 additional untreated celiac disease children and one control child with increased IgG antitissue transglutaminase. In treated celiac disease children, 21 of 80 were IgA antitissue transglutaminase positive with radioligand binding assays, 3 of 80 with ELISA, whereas none had endomysial autoantibodies.

CONCLUSIONS

No qualitative differences between radioligand binding assays and ELISA in IgA or IgG antitissue transglutaminase binding from untreated celiac disease children was demonstrated. However, discrepancies in the binding of IgA antitissue transglutaminase from a subgroup of treated celiac disease children indicated that alterations of tissue transglutaminase might occur on fixation of the antigen. Protein A used for radioligand binding assays seemed not to assess IgG autoantibodies exclusively. IgA antitissue transglutaminase detection in screening of childhood celiac disease can be performed either by ELISA or radioligand binding assays because the two assays are interchangeable.

Multiple sclerosis

Multiple sclerosis (MS) is a complex genetic disease associated with inflammation in the central nervous system (CNS) white matter and is thought to be mediated by autoimmune processes. Clonal expansion of B cells, their antibody products, and T cells, hallmarks of inflammation in the CNS, are found in MS. The association of the disease with major histocompatibility complex genes, the inflammatory white matter infiltrates, similarities with animal models, and the observation that MS can be treated with immunomodulatory and immunosuppressive therapies support the hypothesis that autoimmunity plays a major role in the disease pathology. This review discusses the immunopathology of MS with particular focus given to regulatory T cells and the role of B cells and antibodies, immunomodulatory therapeutics, and finally new directions in MS research, particularly new methods to define the molecular pathology of human disease with high-throughput examination of germline DNA haplotypes, RNA expression, and protein structures that will allow the generation of a new series of hypotheses that can be tested to develop better understandings and therapies for this disease.

Immunoglobulin G (IgG) anti-tissue transglutaminase antibodies used as markers for IgA-deficient celiac disease patients

The role of immunoglobulin A (IgA) anti-tissue transglutaminase antibodies (IgA-tTG) as predictors of untreated celiac disease (CoD) is well documented, and the presence and levels of these antibodies are most accurately monitored with native or recombinant human antigens. However, IgA-deficient CoD patients are not identified by IgA serology, and conflicting results concerning the diagnostic validity of IgG antibodies against gliadin (IgG-AGA), endomysium (IgG-EmA), and tTG (IgG-tTG) have been reported. The aim of the present study was to evaluate the utility of IgG-tTG for the detection of CoD in IgA-deficient patients. Samples from 115 IgA-deficient and 200 IgA-sufficient subjects were collected and tested for the presence of IgA and IgG antibodies against tTG, EmA, and AGA. Antibodies against tTG were measured by an enzyme-linked immunosorbent assay based on recombinant human tTG, and antibodies against EmA were determined by immunofluorescence. The values for IgG-tTG showed a higher correlation (correlation coefficient [r] = 0.91) with those for IgG-EmA for the IgA-deficient subjects than for the IgA-sufficient subjects (r = 0.88). The overall concordance of the positive and negative results between IgG-tTG and IgG-EmA was 97%, and the IgG-tTG assay discriminated between IgG-EmA-positive and -negative subjects with IgA deficiency at a rate of 100%. Elevated levels of IgG-tTG and IgG-EmA were measured in 70% of the IgA-sufficient subjects. IgG-tTG detection with recombinant human tTG is a good alternative to IgG-EmA detection, and the addition of IgG-tTG assessment to present screening methods may improve the ability to identify IgA-deficient subjects with CoD.

Characterization of the anti-tissue transglutaminase antibody response in nonobese diabetic mice

Type 1 diabetes mellitus is an autoimmune disorder characterized by destruction of insulin-producing pancreatic beta cells by T lymphocytes. In nonobese diabetic (NOD) mice, a role has been hypothesized for dietary gluten proteins in the onset of diabetes, and because gluten dependence is the major feature of celiac disease, together with production of Abs to the autoantigen tissue transglutaminase (tTG), we looked for the presence of anti-tTG Abs in the serum of NOD mice and, to establish their origin, analyzed the Ab repertoire of NOD mice using phage display Ab libraries. We found significant levels of serum anti-tTG Abs and were able to isolate single-chain Ab fragments to mouse tTG mainly from the Ab libraries made from intestinal lymphocytes and to a lesser extent from splenocytes. Data from NOD mice on a gluten-free diet suggest that the anti-tTG response is not gluten-dependent. The intestinal Ab response to tTG is a feature of NOD mice, but the underlying mechanisms remain obscure.

Tissue transglutaminase autoantibody detection in human saliva: a powerful method for celiac disease screening

OBJECTIVE

To test the possibility of detecting tissue transglutaminase autoantibodies (tTG-Abs) in saliva with a novel sensitive fluid-phase radioimmunoassay (RIA).

STUDY DESIGN

Paired saliva and serum samples from 39 patients with celiac disease (CD), at the first biopsy (Group 1: 28 females, mean age 11.5 +/- 11.1 years); 32 controls with a normal duodenal mucosa (Group 2: 18 females, mean age 8.1 +/- 3.6 years); and 32 healthy volunteers (Group 3: 21 females, mean age 31.7 +/- 9.8 years) were studied for tTG-Ab presence. Limit of positivity for salivary assay was calculated according to the 99th percentiles of Group 2 control children and was expressed as an autoantibody (Ab) index.

RESULTS

Salivary tTG-Abs were found in 97.4% of the patients with CD and in 100% of the corresponding serum samples. All Group 3 subjects were negative with both saliva and serum assays. A correlation between saliva and serum tTG-Ab titers was found (r=0.826, P=.0014).

CONCLUSIONS

This study demonstrates that it is possible to detect salivary tTG-Abs in CD with a non-invasive, simple to perform, reproducible and sensitive method.

One-step cloning of anti tissue transglutaminase scFv from subjects with celiac disease

Celiac disease is characterized by intestinal mucosal injury and malabsorption precipitated by dietary exposure to gluten of some cereals with a prominent role being played by gliadins, specific antigenic determinants found in wheat gluten. Patients suffering from celiac disease have serum antibodies recognizing gliadin, as well as the endomysial autoantigen tissue transglutaminase. Phage display antibody libraries have revealed ectopic production of anti-transglutaminase antibodies by intestinal lymphocytes with a biased use of the VH5 antibody gene family. Here we report a study on the pairing of VH and VL families in the antibodies to transglutaminase. Our results led to the construction of small phage display antibody libraries based on the amplification of the two genes in the VH5 family from intestinal lymphocytes. This method can be used for the rapid characterization of the anti-transglutaminase response in a potentially large number of subjects including asymptomatic patients whose serum antibodies may be undetectable.

Celiac disease-associated transglutaminase autoantibody target domains at diagnosis are age and sex dependent

The contribution of age and/or sex to the transglutaminase (tTG) autoantibody response in celiac disease (CD) is not known. To gain insights into transglutaminase humoral autoimmunity at CD diagnosis, our aim was to characterize the autoimmune response against three tTG constructs [(full-length tTG(a.a.1-687), tTG(a.a.227-687), and tTG(a.a.473-687)] and to investigate into its relationship with CD patients' age and sex. One hundred seventy-five newly diagnosed CD patients (115 females and 60 males), subdivided into different groups according to age and sex, were studied using a serum 35S-radioimmunoassay. We found that among full-length tTG autoantibody-positive CD subjects (175/175), 50.9% (89/175) and 83.4% (146/175) had autoantibodies against tTG(227-687) and tTG(473-687) domains, respectively. Female patients of less than 4 years expressed tTG(227-687)Abs in significantly higher percentage and mean autoantibody titers vs. all other groups investigated, and tTG(473-687)Abs in significantly higher titers with respect to adult female patients. Our data identify a subset of CD patients showing a strong humoral tTG immunoreactivity at diagnosis, thus suggesting that age and sex influence the anti-tTG autoantibody response.

Transglutaminases: nature's biological glues

Transglutaminases (Tgases) are a widely distributed group of enzymes that catalyse the post-translational modification of proteins by the formation of isopeptide bonds. This occurs either through protein cross-linking via epsilon-(gamma-glutamyl)lysine bonds or through incorporation of primary amines at selected peptide-bound glutamine residues. The cross-linked products, often of high molecular mass, are highly resistant to mechanical challenge and proteolytic degradation, and their accumulation is found in a number of tissues and processes where such properties are important, including skin, hair, blood clotting and wound healing. However, deregulation of enzyme activity generally associated with major disruptions in cellular homoeostatic mechanisms has resulted in these enzymes contributing to a number of human diseases, including chronic neurodegeneration, neoplastic diseases, autoimmune diseases, diseases involving progressive tissue fibrosis and diseases related to the epidermis of the skin. In the present review we detail the structural and regulatory features important in mammalian Tgases, with particular focus on the ubiquitous type 2 tissue enzyme. Physiological roles and substrates are discussed with a view to increasing and understanding the pathogenesis of the diseases associated with transglutaminases. Moreover the ability of these enzymes to modify proteins and act as biological glues has not gone unnoticed by the commercial sector. As a consequence, we have included some of the present and future biotechnological applications of this increasingly important group of enzymes.