Enzyme Tissue Transglutaminase Research Articles

Tissue Transglutaminase Does Not Affect Fibrotic Matrix Stability or Regression of Liver Fibrosis in Mice

The ubiquitous cross-linking enzyme tissue transglutaminase (TG2) has been implicated in irreversible collagen stabilization in liver fibrosis, although functional evidence is lacking. We studied the contribution of TG2 to hepatic fibrotic matrix stability, as well as liver fibrosis progression and regression in TG2-deficient mice. Advanced liver fibrosis was induced by carbon tetrachloride or thioacetamide in TG2(-/-) mice and their wild-type littermates to study fibrosis progression and its spontaneous regression for up to 36 weeks. Pattern and extent of fibrosis were analyzed by histology and hepatic hydroxyproline quantification. Dynamic changes in hepatic matrix cross-linking were assessed by stepwise collagen extraction. Expression of 7 TGs and fibrosis-related genes was determined by quantitative reverse-transcription polymerase chain reaction. Transglutaminase activity was increased in fibrosis, and the level of TG2 messenger RNA correlated with the expression of fibrosis-related genes. Biochemical analysis revealed progressive collagen stabilization, with an up to 6-fold increase in the highly cross-linked, pepsin-insoluble fraction (26%). In TG2(-/-) mice, hepatic TG activity was significantly decreased, but chronic administration of carbon tetrachloride or thioacetamide led to a comparable extent and pattern of liver fibrosis, as in wild-type mice. In TG2(-/-) mice, the composition of hepatic collagen fractions and levels of fibrosis-related transcripts were unchanged, and fibrosis reversal was not facilitated. TG2 and TG activity are up-regulated during hepatic fibrosis progression, but do not contribute to fibrogenesis or stabilization of the collagen matrix. TG2 deletion does not promote regression of liver fibrosis. TG2-independent collagen cross-linking is a remarkable feature of progressing hepatic fibrosis and represents an important therapeutic target for liver fibrosis.

Tissue transglutaminase antibodies in celiac disease: focus on the pediatric population

Celiac disease (CD) is an immune-mediated disorder induced by the ingestion of gluten in genetically susceptible individuals. The enzyme tissue transglutaminase (protein-glutamine gamma-glutamyltransferase 2; tTG) plays an important role in the pathogenesis of the disease and antibodies against tTG are used as serological markers for the diagnosis of CD. Discovery of tTG as the autoantigen for endomysial antibodies changed the diagnostic approach to patients with suspected CD and, importantly, made screening for CD more accurate and easier to perform. Studies in pediatric populations confirmed the high sensitivity and specificity of immunoglobulin A (IgA) tTG antibodies in the diagnosis of CD. The aim of this review is to summarize the data on the role of tTG in the pathogenesis of CD and to present current evidence on the accuracy of IgA tTG, IgG tTG and IgA tTG point-of-care tests in the diagnosis of CD in children. This review shows why IgA tTG antibodies replaced endomysial antibodies as the preferred serological marker due to the ease of their use, their high sensitivity and specificity, and the high correlation between high titers and intestinal mucosal lesions.

The role of tissue transglutaminase (TG2) in regulating the tumour progression of the mouse colon carcinoma CT26

The multifunctional enzyme tissue transglutaminase (TG2) is reported to both mediate and inhibit tumour progression. To elucidate these different roles of TG2, we established a series of stable-transfected mouse colon carcinoma CT26 cells expressing a catalytically active (wild type) and a transamidating-inactive TG2 (Cys277Ser) mutant. Comparison of the TG2-transfected cells with the empty vector control indicated no differences in cell proliferation, apoptosis and susceptibility to doxorubicin, which correlated with no detectable changes in the activation of the transcription factor NF-κB. TG2-transfected cells showed increased expression of integrin β3, and were more adherent and less migratory on fibronectin than control cells. Direct interaction of TG2 with β3 integrins was demonstrated by immunoprecipitation, suggesting that TG2 acts as a coreceptor for fibronectin with β3 integrins. All cells expressed the same level of TGFβ receptors I and II, but only cells transfected with active TG2 had increased levels of TGFβ1 and matrix-deposited fibronectin, which could be inhibited by TG2 site-directed inhibitors. Moreover, only cells transfected with active TG2 were capable of inhibiting tumour growth when compared to the empty vector controls. We conclude that in this colon carcinoma model increased levels of active TG2 are unfavourable to tumour growth due to their role in activation of TGFβ1 and increased matrix deposition, which in turn favours increased cell adhesion and a lowered migratory and invasive behaviour.

Celiac disease: how complicated can it get?

In the small intestine of celiac disease patients, dietary wheat gluten and similar proteins in barley and rye trigger an inflammatory response. While strict adherence to a gluten-free diet induces full recovery in most patients, a small percentage of patients fail to recover. In a subset of these refractory celiac disease patients, an (aberrant) oligoclonal intraepithelial lymphocyte population develops into overt lymphoma. Celiac disease is strongly associated with HLA-DQ2 and/or HLA-DQ8, as both genotypes predispose for disease development. This association can be explained by the fact that gluten peptides can be presented in HLA-DQ2 and HLA-DQ8 molecules on antigen presenting cells. Gluten-specific CD4+ T cells in the lamina propria respond to these peptides, and this likely enhances cytotoxicity of intraepithelial lymphocytes against the intestinal epithelium. We propose a threshold model for the development of celiac disease, in which the efficiency of gluten presentation to CD4+ T cells determines the likelihood of developing celiac disease and its complications. Key factors that influence the efficiency of gluten presentation include: (1) the level of gluten intake, (2) the enzyme tissue transglutaminase 2 which modifies gluten into high affinity binding peptides for HLA-DQ2 and HLA-DQ8, (3) the HLA-DQ type, as HLA-DQ2 binds a wider range of gluten peptides than HLA-DQ8, (4) the gene dose of HLA-DQ2 and HLA-DQ8, and finally,(5) additional genetic polymorphisms that may influence T cell reactivity. This threshold model might also help to understand the development of refractory celiac disease and lymphoma.

Decreased S -Nitrosylation of Tissue Transglutaminase Contributes to Age-Related Increases in Vascular Stiffness

Although an age-related decrease in NO bioavailability contributes to vascular stiffness, the underlying molecular mechanisms remain incompletely understood. We hypothesize that NO constrains the activity of the matrix crosslinking enzyme tissue transglutaminase (TG2) via S-nitrosylation in young vessels, a process that is reversed in aging. We sought to determine whether endothelium-dependent NO regulates TG2 activity by S-nitrosylation and whether this contributes to age-related vascular stiffness. We first demonstrate that NO suppresses activity and increases S-nitrosylation of TG2 in cellular models. Next, we show that nitric oxide synthase (NOS) inhibition leads to increased surface and extracellular matrix-associated TG2. We then demonstrate that endothelium-derived bioactive NO primarily mediates its effects through TG2, using TG2(-/-) mice chronically treated with the NOS inhibitor l-N(G)-nitroarginine methyl ester (L-NAME). We confirm that TG2 activity is modulated by endothelium-derived bioactive NO in young rat aorta. In aging rat aorta, although TG2 expression remains unaltered, its activity increases and S-nitrosylation decreases. Furthermore, TG2 inhibition decreases vascular stiffness in aging rats. Finally, TG2 activity and matrix crosslinks are augmented with age in human aorta, whereas abundance remains unchanged. Decreased S-nitrosylation of TG2 and increased TG activity lead to enhanced matrix crosslinking and contribute to vascular stiffening in aging. TG2 appears to be the member of the transglutaminase family primarily contributing to this phenotype. Inhibition of TG2 could thus represent a therapeutic target for age-associated vascular stiffness and isolated systolic hypertension.

Effects of phenyl saligenin phosphate on cell viability and transglutaminase activity in N2a neuroblastoma and HepG2 hepatoma cell lines

The main aim of this study was to determine whether sub-lethal concentrations of the organophosphate compound phenyl saligenin phosphate (PSP) could disrupt the activity of the Ca 2+-activated enzyme tissue transglutaminase (TGase 2) from cultured cell lines of neuronal (N2a) and hepatic (HepG2) origin. The results indicated that PSP added directly to cytosol extracts from healthy cells was able to inhibit TGase 2 activity by 40–60% of control levels at sub-lethal concentrations (⩾0.1 μM) that were approximately 100-fold lower than their IC 50 values in cytotoxicity assays. Following 24 h exposure of N2a cells to 0.3 and 3 μM PSP in situ, a similar reduction in activity was observed in subsequent assays of TGase 2 activity. However, significantly increased activity was observed following in situ exposure of HepG2 cells to PSP (ca. 4-fold at 3 μM). Western blotting analysis indicated slightly reduced levels of TGase 2 in N2a cells compared to the control, whereas an increase was observed in the level of TGase 2 in HepG2 cells. We suggest that TGase 2 represents a potential target of organophosphate toxicity and that its response may vary in different cellular environments, possibly affected by its expression pattern.

Tissue transglutaminase enhances collagen type II‐induced arthritis and modifies the immunodominant T‐cell epitope CII260‐270

The calcium-dependent enzyme tissue transglutaminase (tTG) is associated with diverse biological functions, such as induction of apoptosis, modeling of the extracellular matrix, receptor-mediated endocytosis, cell growth and differentiation, cell adhesion and signal transduction. Also, it may deamidate glutamine residues to glutamic acid and catalyze cross-linking of proteins. In this study, we have investigated the impact of tTG for posttranslational modifications and cross-linking of the immunodominant T-cell epitope CII260-270 and their effects on the collagen-induced arthritis, an animal model for rheumatoid arthritis. By using mass spectrometry analysis and hybridoma assays, we have demonstrated that tTG could perform both types of modifications (deamidation and cross-link formation) on the immunodominant T-cell epitope CII259-273. Replacement of the glutamine at position 267 with glutamic acid leads to a decreased binding affinity to MHC II. T cells recognized both non-modfied (Q(267)) and modified (E(267)) CII259-273-peptides. We also show that administration of tTG leads to increased incidence, severity and histopathological manifestations of collagen-induced arthritis in mice. Moreover, we conclude that both processes, deamidation and cross-linking, are involved in the tTG-catalyzed reactions, and in vivo administration of tTG enhances arthritis severity and joint destruction in mice.

The treatment of collagen fibrils by tissue transglutaminase to promote vascular smooth muscle cell contractile signaling

The enzyme tissue transglutaminase 2 (TG2) appears to play an important role in several physiological processes such as wound healing, the progression of cancer and of vascular disease. Additionally, TG2 has been proposed as a means of stabilizing collagen extracellular matrix (ECM) scaffolds for tissue engineering applications. In this report, we examined the effect of TG2 treatment on the mechanical properties of the ECM, and associated cell responses. Using a model ECM of fibrillar collagen, we quantitatively examined vascular smooth muscle cell (vSMC) response to untreated, or TG2 treated collagen. We show that cells respond to TG2 treated collagen with increased spreading, an increase in contractile response as indicated by elevated F-actin polymerization and myosin light chain phosphorylation, and increased proliferation, without apparent changes in integrin specificity or matrix topography. Comparative atomic force microscopy loading studies indicate that TG2 treated fibrils are 3 times more resistant to shearing force from an AFM tip than untreated fibrils. The data suggest that TG2 treatment of collagen increases matrix mechanical stiffness, which apparently alters the contractile and proliferative response of vSMC.

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.

Alterations in the Calcitonin and Calcitonin Modulated Proteins, E-Cadherin and the Enzyme Tissue Transglutaminase II during the Window of Implantation in a Baboon Model of Endometriosis

Endometriosis is a gynecological condition associated with infertility. We have previously demonstrated dysregulation of several molecular markers of uterine receptivity in a baboon model of induced endometriosis. Specifically, reduced levels of endometrial progesterone receptor (PR) and progesterone (P)-regulated genes, HOXA10 and FKBP52 were observed during the window of uterine receptivity in baboons with endometriosis, suggesting that this disease results in the development of an endometrial P resistance. In this study calcitonin (CALC) and CALC-modulated proteins, E-cadherin (E-Cad) and tissue Transglutaminase (tTgase-2) were evaluated in the eutopic endometrium of endometriotic animals throughout disease progression. Endometriosis was induced in normal cycling baboons by intraperitoneal inoculation of menstrual endometrium. Eutopic and ectopic endometrium was harvested consecutively from each animal at 1, 6 and 15 months of disease, during the window of receptivity. Control eutopic endometrium was similarly harvested from disease free baboons. Immunohistochemistry for CALC, E-cad and tTgase-2, was performed on formalin fixed tissues embedded in paraffin following antigen retrieval. CALC immunostaining was localized in the glandular and luminal epithelium as well as in the uterine stromal cells in disease free eutopic endometrium. However, in the eutopic endometrium from endometriotic baboons there was a reduction of CALC in the luminal and glandular epithelium as well as a reduction in the stromal cells. In the ectopic endometrium there was no immunostaining for the CALC protein. E-cad protein was immunolocalized primarily to the glandular epithelium of both control and endometriotic eutopic endometria. However, E-cad immunostaining was markedly increased in endometria of baboons with disease. The immunostaining was weak for E-Cad in the ectopic endometrial lesions regardless of color or location in the peritoneum. Strong immunostaining for tTgase-2 was observed in the stroma in disease free controls. Endometria from animals with endometriosis demonstrated a progressive loss of tTgase-2 immunostaining in the stroma throughout the time course of disease. There was strong immunostaining in the stroma of the ectopic endometrial collected throughout disease progression. The maintained levels of E-cad and reduced levels of tTgase-2 correlate with the reduction of CALC in eutopic endometria of baboons with endometriosis. These data suggest that the reduced fecundity associated with endometriosis is mediated, in part, by a progesterone resistance that affects not only genes directly regulated by progesterone, but those that are down-stream targets of progesterone regulated genes.

Transglutaminase 2 cross-linking of matrix proteins: biological significance and medical applications

This review summarises the functions of the enzyme tissue transglutaminase (TG2) in the extracellular matrix (ECM) both as a matrix stabiliser through its protein cross-linking activity and as an important cell adhesion protein involved in cell survival. The contribution of extracellular TG2 to the pathology of important diseases such as cancer and fibrosis are discussed with a view to the potential importance of TG2 as a therapeutic target. The medical applications of TG2 are further expanded by detailing the use of transglutaminase cross-linking in the development of novel biocompatible biomaterials for use in soft and hard tissue repair.

Use of tissue transglutaminase and fibronectin to influence osteoblast responses to tricalcium phosphate scaffolds

To explore the possibility of controlling cell interaction with biomaterials, tricalcium phosphate scaffolds were modified using the enzyme tissue transglutaminase (tTgase) in conjunction with fibronectin. Previous reports in the literature have highlighted a number of favourable responses that this protein-enzyme complex can stimulate, including enhancing both cell adhesion, and mineralisation. Fibronectin and tTgase alone were used as controls, and a series of different concentrations of tTgase and fibronectin in combination were assessed. Cell metabolic activity, alkaline phosphatase production, and collagen content were all measured in cultures up to 28 days. Using tetracycline labelling, calcium containing multilayered regions were imaged and quantified. Addition of 6 microg fibronectin resulted in increased alkaline phosphatase activity in all combinations, while increased transglutaminase resulted in more collagen in the cell lysates. Samples treated with fibronectin produced many small mineralised areas, those with 6 microg fibronectin and transglutaminase produced numerous large mineralised areas. The mixture of fibronectin and transglutaminase may prove to be a useful treatment for producing increased osteoblast differentiation on scaffolds.

Tissue transglutaminase modulates α‐synuclein oligomerization

We have studied the interaction of the enzyme tissue transglutaminase (tTG), catalyzing cross-link formation between protein-bound glutamine residues and primary amines, with Parkinson's disease-associated alpha-synuclein protein variants at physiologically relevant concentrations. We have, for the first time, determined binding affinities of tTG for wild-type and mutant alpha-synucleins using surface plasmon resonance approaches, revealing high-affinity nanomolar equilibrium dissociation constants. Nanomolar tTG concentrations were sufficient for complete inhibition of fibrillization by effective alpha-synuclein cross-linking, resulting predominantly in intramolecularly cross-linked monomers accompanied by an oligomeric fraction. Since oligomeric species have a pathophysiological relevance we further investigated the properties of the tTG/alpha-synuclein oligomers. Atomic force microscopy revealed morphologically similar structures for oligomers from all alpha-synuclein variants; the extent of oligomer formation was found to correlate with tTG concentration. Unlike normal alpha-synuclein oligomers the resultant structures were extremely stable and resistant to GdnHCl and SDS. In contrast to normal beta-sheet-containing oligomers, the tTG/alpha-synuclein oligomers appear to be unstructured and are unable to disrupt phospholipid vesicles. These data suggest that tTG binds equally effective to wild-type and disease mutant alpha-synuclein variants. We propose that tTG cross-linking imposes structural constraints on alpha-synuclein, preventing the assembly of structured oligomers required for disruption of membranes and for progression into fibrils. In general, cross-linking of amyloid forming proteins by tTG may prevent the progression into pathogenic species.

Anti-idiotypic response in mice expressing human autoantibodies

Celiac disease is an autoimmune illness characterized by intestinal mucosal injury and malabsorption precipitated by dietary exposure to gluten of some cereals. The immune response is based on both cellular and humoral components, although the former seem to be more important in the pathogenesis. The autoantibody response is directed at the enzyme tissue transglutaminase, tTG or TG2, which possibly play a role in the onset of the disease. In this study we sought to develop an animal model in which to analyze the immunological regulation and significance of anti-TG2 antibodies, by expressing specific human single-chain antibody fragments in mice using adeno-associated virus vectors. Upon vector injection in the skeletal muscles, high and persistent systemic levels of anti-TG2 antibodies were obtained. Mice injected with vectors encoding antibodies also recognizing rodent TG2, also developed a strong anti-idiotypic response. This finding raises the question of whether an anti-idiotypic response to anti-TG2 antibodies is a factor associated with celiac disease.

Tissue transglutaminase and the stress response

The expression of the protein crosslinking enzyme tissue transglutaminase (TG2, tTG), the ubiquitous member of transglutaminase family, can be regulated by multiple factors. Although it has been suggested that TG2 can be involved in apoptotic cell death, high levels of enzyme have also been associated with cell survival in response to different stimuli. Furthermore, evidence indicates that increases in TG2 production cause enzyme translocation to cell membrane. Cell stress can also lead to TG2 accumulation on the cell surface and in the extracellular matrix resulting in changes in cell-matrix interactions.Here, we discuss the underlying mechanisms of TG2 up-regulation induced by various stimuli including glutamate exposure, calcium influx, oxidative stress, UV, and inflammatory cytokines. These findings agree with a postulated role for transglutaminases in molecular mechanisms involved in several diseases suggesting that cross-linking reactions could be a relevant part of the biochemical changes observed in pathological conditions.

AGA Institute Medical Position Statement on the Diagnosis and Management of Celiac Disease

Celiac disease is a permanent intolerance to gluten, a term that is broadly used to describe the storage proteins in wheat, rye, and barley. Celiac disease is characterized by a chronic inflammatory state of the proximal small intestinal mucosa, which can impair digestion and absorption of macronutrients and micronutrients and results in increased net secretion of water and solute. Celiac disease can present with intestinal symptoms, can present with extraintestinal symptoms (including the intensely pruritic skin rash dermatitis herpetiformis), or may be detected in individuals who are asymptomatic as part of the screening of populations at increased risk for celiac disease. There is a spectrum of small intestinal mucosal injury that ranges from minimal with an increase in intraepithelial lymphocytes to total villous atrophy. However, most symptomatic patients with celiac disease have some degree of villous atrophy. The HLA class II DQ molecules DQ2 or DQ8 are necessary, although not sufficient, for the phenotypic expression of celiac disease.

Tissue transglutaminase serves as an inhibitor of apoptosis by cross-linking caspase 3 in thapsigargin-treated cells.

Thapsigargin (THG) is an inhibitor of the endoplasmic reticulum Ca2+-ATPase that induces caspase 3 activation and apoptosis in HCT116 cells through a Bax-dependent pathway. In Bax-deficient HCT116 cells, however, THG specifically generates two additional species of caspase 3, termed p40 and p64, with molecular masses of approximately 40 and 64 kDa, respectively, through unknown mechanisms. Here, we report that the Ca2+-dependent protein cross-linking enzyme tissue transglutaminase (tTGase) is involved in THG-induced p40 and p64 formation by catalyzing caspase 3 cross-linking reactions, thereby inactivating caspase 3 and apoptosis in Bax-deficient cells. Overexpression of tTGase increases p40 and p64 in THG-treated cells, and purified tTGase catalyzes procaspase 3 cross-linking in vitro. Inhibition of tTGase activity by either the tTGase inhibitor monodansylcadaverine or short-hairpin RNA reduces the cross-linked species p40 and p64 and restores caspase 3 activation in response to THG treatment. Moreover, prolonged exposure to THG results in a decrease in protein levels of XIAP and cIAP-1, which is subsequently followed by an increase in tTGase protein expression and activity. Expression of cytosolic Smac sensitizes Bax-deficient cells to THG-induced apoptosis; however, this effect is diminished by coexpression of tTGase. Taken together, these results suggest a novel role for tTGase as a new type of caspase 3 inhibitor in THG-mediated apoptosis.

LACK OF CORRELATION OF COPY NUMBER OF HLA DQA1A*05 DQB1*02 AND TISSUE TRANSGLUTAMINASE LEVELS IN UNTREATED CELIAC DISEASE

Background: Celiac Disease is an autoimmune disorder of the small intestine characterized by intolerance to gluten. More than 90% of the patients with celiac disease have the human leukocyte antigen DQA1*05 DQB1*02. A gene dosage effect has been proposed for this high-risk genotype. In CD, there is an autoimmune response to the enzyme tissue transglutaminase, causing the production of immunoglobulin A autoantibodies, which are quantitative and resolve with improvement of intestinal inflammation after adherence to a gluten-free diet. Methods: Blood samples were collected from relatives of patients with known celiac disease as part of a family study to identify genes for celiac disease. These patients were screened for immunogloglobulin A endomysial antibodies. Positive sera were then evaluated for quantitative levels of immunoglobulin A tissue transglutaminase antibodies and HLA genotyping was performed. Results: One hundred sixteen family members were found to be positive for immunoglobulin A endomysial antibodies. Tissue transglutaminase levels for this group had a mean of 111 (±SD 93) with a range of 4-258. There was no correlation between IgA tTG levels and age or sex of the patients. Twelve patients had no copies of DQA1*05DQB1*02,82 had 1 copy, and 22 had 2 copies. The means for IgA tTG Ab levels for the 3 groups were (1) zero copies, mean = 129 Units (2) one copy, mean = 111 units (3) two copies, mean = 100 units. There were no statistical differences between the IgA tTG Ab levels in the 3 groups or when or when the presence of the DQB1*02 genotype alone was evaluated. Conclusion: HLA genotype, although it is strongly correlated with CD and does not correlate with the level of IgA tTG Ab.

The diagnostic accuracy of serologic tests for celiac disease: A systematic review

Clinicians are increasingly utilizing noninvasive serologic tests for the diagnosis and screening of celiac disease (CD). The aim of this study was to conduct a systematic review of the diagnostic performance of serologic tests for the diagnosis and screening of CD. Standard systematic review methodology was used. A literature search was conducted in MEDLINE (1966 to October 2003) and EMBASE (1974 to December 2003) databases. A weighted mean of the sensitivity and specificity along with 95% confidence intervals and summary receiver operating characteristic (ROC) curves were calculated. The pooled specificity of endomyseal antibody (EMA)-monkey esophagus (ME) or EMA-human umbilical cord (HU) was close to 100% in adults and children. The pooled specificity of transglutaminase antibody (tTG)-guinea pig (GP) and tTG-human recombinant (HR) were between 95% and 99%. IgA-EMA-ME demonstrated sensitivities of 96% and 97% in children and adults, respectively. EMA-HU demonstrated a similar sensitivity of 97% in children but 90% in adults. The pooled sensitivity of tTG-GP in adults and children was 90% and 93%, respectively. The sensitivity of tTG-HR was 98% and 96%, respectively. The performance of antigliadin antibody was inferior to that of EMA and tTG. EMA and tTG offer high sensitivity and specificity. The sensitivity of these tests appears to be lower than reported when milder histologic grades are used to define CD (below 90%). If true, the nearly perfect negative predictive value of these tests would drop. The positive predictive value of these tests is likely lower than reported when the tests are applied in low-prevalence populations.

Tissue Transglutaminase-Mediated Formation and Cleavage of Histamine-Gliadin Complexes: Biological Effects and Implications for Celiac Disease

Celiac disease is an HLA-DQ2-associated disorder characterized by an intestinal T cell response. The disease-relevant T cells secrete IFN-gamma upon recognition of gluten peptides that have been deamidated in vivo by the enzyme tissue transglutaminase (transglutaminase 2 (TG2)). The celiac intestinal mucosa contains elevated numbers of mast cells, and increased histamine secretion has been reported in celiac patients. This appears paradoxical because histamine typically biases T cell responses in the direction of Th2 instead of the Th1 pattern seen in the celiac lesions. We report that histamine is an excellent substrate for TG2, and it can be efficiently conjugated to gluten peptides through TG2-mediated transamidation. Histamine-peptide conjugates do not exert agonistic effects on histamine receptors, and scavenging of biologically active histamine by gluten peptide conjugation can have physiological implications and may contribute to the mucosal IFN-gamma response in active disease. Interestingly, TG2 is able to hydrolyze the peptide-histamine conjugates when the concentrations of substrates are lowered, thereby releasing deamidated gluten peptides that are stimulatory to T cells.