Transglutaminases in autoimmune and inherited skin diseases: The phenomena of epitope spreading and functional compensation.

Transglutaminases (TGs) are structurally and functionally related enzymes that modify the post-translational structure and activity of proteins or peptides, and thus are able to turn on or switch off their function. Depending on location and activities, TGs are able to modify the signalling, the function and the fate of cells and extracellular connective tissues. Besides mouse models, human diseases enable us to appreciate the function of various TGs. In this study, skin diseases induced by genetic damages or autoimmune targeting of these enzymes will be discussed. TG1, TG3 and TG5 contribute to the cutaneous barrier and thus to the integrity and function of epidermis. TGM1 mutations related to autosomal recessive ichthyosis subtypes, TGM5 mutations to a mild epidermolysis bullosa phenotype and as novelty TGM3 mutation to uncombable hair syndrome will be discussed. Autoimmunity to TG2, TG3 and TG6 may develop in a few of those genetically determined individuals who lost tolerance to gluten, and manifest as coeliac disease, dermatitis herpetiformis or gluten-dependent neurological symptoms, respectively. These gluten responder diseases commonly occur in combination. In autoimmune diseases, the epitope spreading is remarkable, while in some inherited pathologies, a unique compensation of the lost enzyme function is noted.

Ex vivo Culture of Duodenal Biopsies from Patients with Dermatitis Herpetiformis Indicates that Transglutaminase 3 Antibody Production Occurs in the Gut.

Coeliac disease and dermatitis herpetiformis (DH) are characterized by autoantibodies targeting transglutaminase (TG)2 and TG3, respectively. Previous studies show that TG2 antibodies are produced in the gut and can be assessed in organ culture of small-intestinal biopsies from patients with coeliac disease. Thus far, no studies have investigated TG3 antibodies in organ culture of biopsies from patients with DH, or exploited the method in DH. The aim of this study was to investigate TG3 and TG2 antibody responses in serum and small-intestinal biopsies from patients with DH with active disease, and from those in remission. The majority of patients with DH were negative for both serum and organ culture medium TG2-targeting antibodies. Surprisingly, patients with active DH secreted TG3 antibodies into the culture medium despite seronegativity. In patients secreting high levels of TG3 antibodies into the culture medium, we also detected TG3-antibody-positive cells in the small-intestinal mucosa. These findings suggest that TG3 antibodies can be investigated in the organ culture system and that their secretion occurs in the small intestine, especially in active DH.

Mediators of mast cells in bullous pemphigoid and dermatitis herpetiformis.

Bullous pemphigoid (BP) and dermatitis herpetiformis (DH) are skin diseases associated with inflammation. However, few findings exist concerning the role of mast cells in autoimmune blistering disease. Skin biopsies were taken from 27 BP and 14 DH patients, as well as 20 healthy individuals. Immunohistochemistry was used to identify the localization and mast cell expression of TNFα and MMP9 in skin lesions and perilesional skin. The serum concentrations of TNFα, MMP9, chymase, tryptase, PAF, and IL-4 were measured by immunoassay. TNFα and MMP9 expression in the epidermis and in inflammatory influxed cells in the dermis was detected in skin biopsies from patients. Although these mediators were found to be expressed in the perilesional skin of all patients, the level was much lower than that in lesional skin. Increased serum PAF levels were observed in BP patients. Mast cells may play an essential role in activating inflammation, which ultimately contributes to the tissue damage observed in BP and DH. Our findings suggest that differences in the pattern of cytokine expression directly contribute to variations in cellular infiltration in DH and BP.

Transverse myelitis associated with an itchy rash and hyperckemia: neuromyelitis optica associated with dermatitis herpetiformis.

IMPORTANCE: Neuromyelitis optica is associated with severe neurodisability if not recognized and treated promptly. Several autoimmune disorders are associated with this condition and may vary in their presentation. It is essential that clinicians are aware of the uncommon presenting features of neuromyelitis optica and associated autoimmune conditions. OBSERVATIONS: A 53-year-old woman presented with nausea and vomiting and was noted to have an asymptomatic elevated creatinine kinase level, which improved with conservative management. She had a history of iron-deficiency anemia due to long-standing celiac disease that was managed with a gluten-free diet. She then presented with recurrent transverse myelitis and a vesicobullous rash over her arms and feet that was pruritic and excoriating. Skin biopsy results confirmed a clinical diagnosis of dermatitis herpetiformis and antibody test findings against aquaporin-4 were positive, leading to a diagnosis of neuromyelitis optica spectrum disorder. She was treated with methylprednisolone sodium succinate, plasma exchange, and azathioprine and has remained in remission. CONCLUSIONS AND RELEVANCE: This report highlights the association of neuromyelitis optica with dermatitis herpetiformis, which can present even without clinical features of celiac disease. Nausea, vomiting, and asymptomatic hyperCKemia should be recognized as rare presenting features of neuromyelitis optica.

Small bowel transglutaminase 2-specific IgA deposits in dermatitis herpetiformis.

Dermatitis herpetiformis (DH) is an extraintestinal manifestation of coeliac disease. Untreated coeliac disease patients are known to have transglutaminase 2 (TG2)-targeted IgA deposits in the small bowel mucosa. To evaluate whether similar intestinal IgA deposits are also present in DH and whether the deposits disappear with gluten-free diet, 47 untreated and 27 treated DH patients were studied. Seventy-nine percent of untreated and 41% of the treated DH patients had TG2-specific IgA deposits in the small bowel, and the presence of the deposits showed a significant association with the degree of small bowel villous atrophy (p < 0.001). Other coeliac-disease related inflammatory markers were also investigated, and the density of small bowel mucosal intraepithelial γδ(+) T cells was increased in 91% of untreated and 73% of treated DH patients. The results show that the majority of untreated DH patients have similar gluten-dependent TG2-specific IgA deposits the small bowel mucosa as coeliac disease patients.

Association study of FUT2 (rs601338) with celiac disease and inflammatory bowel disease in the Finnish population.

Homozygosity for a nonsense mutation in the fucosyltransferase 2 (FUT2) gene (rs601338G>A) leads to the absence of ABH blood groups (FUT2 non-secretor status) in body fluids. As the secretor status has been shown to be a major determinant for the gut microbial spectrum, assumed to be important in the gut immune homeostasis, we studied the association of rs601338-FUT2 with celiac disease (CelD) and inflammatory bowel disease (IBD) in the Finnish population. Rs601338 was genotyped in CelD (n = 909), dermatitis herpetiformis (DH) (n = 116), ulcerative colitis (UC) (n = 496) and Crohn's disease (CD) (n = 280) patients and healthy controls (n = 2738). CelD showed significant genotypic [P = 0.0074, odds ratio (OR): 1.28] and recessive (P = 0.015, OR: 1.28) association with the rs601338-AA genotype. This was also found in the combined CelD+DH dataset (genotype association: P = 0.0060, OR: 1.28; recessive association: P < 0.011, OR: 1.28). The A allele of rs601338 showed nominal association with dominant protection from UC (P = 0.044, OR: 0.82) and UC+CD (P = 0.035, OR: 0.84). The frequency of non-secretors (rs601338-GG) in controls, CelD, DH, UC and CD datasets was 14.7%, 18%, 18.1%, 14.3% and 16.1%, respectively. No association was evident in the DH or CD datasets alone. In conclusion, FUT2 non-secretor status is associated with CelD susceptibility and FUT2 secretor status may also play a role in IBD in the Finnish population.

Autoimmunity-driven enzymatic remodeling of the dermal-epidermal junction in bullous pemphigoid and dermatitis herpetiformis.

Pathogenesis of blister formation in bullous pemphigoid (BP) and dermatitis herpetiformis (DH) is associated with destruction of numerous components of the dermal--epidermal junction. Proteolytic enzymes (PE) are involved in a multitude of physiological reactions and may have impact on the epidermal--dermal integrity. Involvement of various PE in inflammation and blister formation in BP and DH is intensively investigated using both morphologic and functional approaches, particularly in BP. The development into the full-blown stage in BP and DH may be caused by an impairment of the human Fc receptor regulatory system that may cause the inefficiently controlled activation of inflammatory cells and subsequent secretion of various proteases.

Dermatitis herpetiformis sera or goat anti-transglutaminase-3 transferred to human skin-grafted mice mimics dermatitis herpetiformis immunopathology.

Dermatitis herpetiformis (DH) is characterized by deposition of IgA in the papillary dermis. However, indirect immunofluorescence is routinely negative, raising the question of the mechanism of formation of these immune deposits. Sárdy et al. (2002. J. Exp. Med. 195: 747-757) reported that transglutaminase-3 (TG3) colocalizes with the IgA. We sought to create such deposits using passive transfer of Ab to SCID mice bearing human skin grafts. IgG fraction of goat anti-TG3 or control IgG were administered i.p. to 20 mice. Separately, sera from seven DH patients and seven controls were injected intradermally. Biopsies were removed and processed for routine histology as well as direct immunofluorescence. All mice that received goat anti-TG3 produced papillary dermal immune deposits, and these deposits reacted with both rabbit anti-TG3 and DH patient sera. Three DH sera high in IgA anti-TG3 also produced deposits of granular IgA and TG3. We hypothesize that the IgA class anti-TG3 Abs are directly responsible for the immune deposits and that the TG3 is from human epidermis, as this is its only source in our model. These deposits seem to form over weeks in a process similar to an Ouchterlony immunodiffusion precipitate. This process of deposition explains the negative indirect immunofluorescence results with DH serum.

Gluten T cell epitope targeting by TG3 and TG6; implications for dermatitis herpetiformis and gluten ataxia.

Transglutaminase 2 (TG2) is well characterized as the main autoantigen of celiac disease. The ability of TG2 to deamidate and crosslink gluten peptides is essential for the gluten-dependent production of TG2 specific autoantibodies. In patients with primarily extraintestinal manifestation of gluten sensitivity the repertoire of autoantibodies may be different. In dermatitis herpetiformis (DH), TG3 appears to be the target autoantigen whereas in gluten ataxia (GA) autoantibodies reactive with TG6 are present. A functional role for TG3 and TG6 in these diseases has yet to be described. It is also not known whether these enzymes can use gluten peptides implicated in the pathology as substrates. We here report that similar to TG2, TG3 and TG6 can specifically deamidate gluten T cell epitopes. However, the fine specificities of the enzymes were found to differ. TG2 can form covalent complexes with gluten by iso-peptide and thioester bonds. We found that both TG3 and TG6 were able to complex with gluten peptides through thioester linkage although less efficiently than TG2, whereas TG6 but not TG3 was able to form iso-peptide linked complexes. Our findings lend credence to the notion that TG3 and TG6 are involved in the gluten-induced autoimmune responses of DH and GA.

Prediction of clinical and mucosal severity of coeliac disease and dermatitis herpetiformis by quantification of IgA/IgG serum antibodies to tissue transglutaminase.

OBJECTIVES: We analysed whether the quantification of autoantibodies against tissue transglutaminase could be used to predict mucosal destruction and disease severity in patients with gluten sensitivity. PATIENTS AND METHODS: One hundred seventy patients with coeliac disease (CD), comprising 52 children with severe malabsorption (group I), 59 children with mild symptoms (group II), 59 adults (group III), 134 patients with dermatitis herpetiformis (DH), and 131 disease controls, were studied. Serial serum samples of patients in groups I and II on a gluten-free diet were also included. Serum levels of antibodies against recombinant tissue transglutaminase were determined with ELISA using standard curves for quantification of antibodies. RESULTS: Immunoglobulin (Ig)A antibodies against tissue transglutaminase (IgA-TGA) were detected in all of the patients with CD and in 95% of the DH patients. The IgA-TGA and IgG-TGA levels were higher in group I (P < 0.001). The IgG-TGA levels and positivity rate in group I (100%) were higher than in group II (81%), group III (73%), and the DH group (67%). Elevated IgA-TGA and IgG-TGA levels in combination predicted a more severe small intestinal atrophy (P < 0.0001) with a specificity of 99% for Marsh IIIb-IIIc (flat) lesions. The kinetics of the IgA-TGA decrease during diet differed between groups I and II. CONCLUSIONS: High levels of IgA-TGA and IgG-TGA antibodies were associated with the grade of mucosal villous atrophy and a more severe clinical presentation. The combined measurement of IgA-TGA and IgG-TGA enables a noninvasive prediction of small intestinal villous atrophy with high accuracy, and may reduce the need for a biopsy in patients with suspected CD.

Elevation of IgA anti-epidermal transglutaminase antibodies in dermatitis herpetiformis.

BACKGROUND: Dermatitis herpetiformis (DH) is a papulovesicular eruption caused by ingestion of gluten. It is characterized by the deposition of IgA in the dermal papillae. IgA antibodies directed at tissue transglutaminase (TG2) are elevated in gluten-sensitive diseases including DH and coeliac disease (CD). More recently, antibodies directed at epidermal transglutaminase (TG3) were identified in patients with DH, and this may be the dominant autoantigen in this disease. OBJECTIVES: To measure IgA antibodies to TG3 and TG2 in patients with DH and CD, and control populations. METHODS: Serum IgA antibodies against TG2 and TG3 were measured from adults with DH, adults and children with CD, patients with psoriasis, adult Red Cross blood donors, and paediatric controls. RESULTS: Patients with DH and CD had elevated levels of IgA anti-TG2 antibodies compared with control populations. The levels in the patients with DH and adults with CD were similar. IgA anti-TG2 antibodies were higher in the children with CD compared with adults with DH and CD, and with control populations. Patients with DH and adults with CD had elevated levels of IgA anti-TG3 antibodies compared with children with CD and control populations. There was a trend towards higher levels in the patients with DH compared with adults with CD. CONCLUSIONS: IgA antibodies to TG3 are elevated in patients with DH and adults with CD. The progressive expansion of the epitope-binding profile of IgA antitransglutaminase antibodies in patients with CD may explain the development of DH in patients with undiagnosed CD during their adult life.

Increased protein expression of matrix metalloproteinases -1, -3, and -9 and TIMP-1 in patients with gluten-sensitive enteropathy.

Gluten-sensitive enteropathy is characterized by small intestinal damage. The pathogenic mechanisms involved are not precisely understood. There is recent interest in the possibility that matrix metalloproteinases might play a pathogenic role. Using immunohistochemistry technique, we examined the protein expression of matrix metalloproteinases-1, -3, and -9 and the tissue inhibitor metalloproteinase-1 in duodenal biopsies from 30 patients with celiac disease and dermatitis herpetiformis. We demonstrated that the percentage of cells expressing these enzymes and their inhibitor in all patients was significantly greater than in the normal controls (P < 0.0001). This was evident even in patients with a minimal lesion but was most marked in patients with severe damage, mirroring the degree of inflammation in the small intestinal tissue. The increased expression of these enzymes and their inhibitor in the duodenal mucosa of patients with gluten-sensitive enteropathy suggests a role for these enzymes in the tissue remodeling which is a feature of these disorders.

Immunoglobulin, complement and epidermal transglutaminase deposition in the cutaneous vessels in dermatitis herpetiformis.

BACKGROUND: Recently, epidermal transglutaminase (TG) has been identified within the papillary IgA granules in dermatitis herpetiformis (DH). Although IgA type autoantibodies to tissue and epidermal TGs are characteristic serological markers for DH, these antibodies do not bind to normal papillary skin structures. AIMS: To test the possibility of IgA immune complex precipitation within the vessel walls as a first step in the pathogenesis of skin symptoms, we analysed immunoglobulin, complement, and epidermal TG deposition along the vascular system of DH skin. METHODS: Punch biopsy specimen were taken from 116 DH patients' skin, and evaluated for the presence of vascular immune precipitates by direct immunofluorescence. Skin samples from 16 DH patients were also studied for tissue and epidermal TGs. RESULTS: In 74 (64%) of the 116 DH skin studied, significant vascular staining accompanied the DH-specific granular IgA fluorescence (IgA and C3 in 39 patients; IgA alone in 18; IgA, C3 and IgM together in five; IgM alone in 12). In most cases (92%), the precipitates were detected in the small vessels of the papillary dermis; however, a subpapillary vascular fluorescence was also observed in a few patients (8%). Skin IgA colocalized with epidermal TG in the vessel walls and within the scattered papillary peri- and intervascular DH bodies. Tissue TG did not colocalize either with the immunoglobulins or with the complement precipitates of the dermis. Furthermore, we could not detect keratinocyte TG in the DH bodies nor in the vessel walls. CONCLUSIONS: These findings support possible immune complex precipitation in the vessel walls of DH skin and further confirm the significance of epidermal but not tissue TG in the pathomechanism of skin symptoms.

The imbalance between metalloproteinases and their tissue inhibitors is involved in the pathogenesis of dermatitis herpetiformis.

Dermatitis herpetiformis (DH) is a subepidermal autoimmune disease characterized by skin and intestinal lesions consistent with coeliac disease. There are also some data that metalloproteinases (MMPs) are involved in the development of skin lesions in DH, however their exact role in this process is not fully understood. The aim of the study was to investigate whether MMPs and their inhibitors are involved in pathogenesis of DH. Skin biopsies were taken from 13 patients with active DH and from 10 healthy subjects. The localization and expression of MMPs and TIMPs were examined by immunohistochemistry. MMPs expression was detected in basal keratinocytes and in the whole epidermis in all of the DH subjects. Neutrophils in microabscesses and in blister fluid were also positive for MMPs. Expression of TIMPs was moderate or weak in all examined biopsies. Our results allow us to conclude that imbalance between these enzymes takes an important role in the pathogenesis of DH.

Transglutaminases as diagnostically relevant autoantigens in patients with gluten sensitivity.

BACKGROUND: Patients with gluten sensitivity, i. e. celiac disease and dermatitis herpetiformis have anti-endomysial antibodies recognizing transglutaminases, which are usually detected on appropriate tissue sections. It would be desirable to have available a reliable, tissue-independent serological diagnostic tool. We compared disease-specificity and sensitivity of tTG versus eTG-based detection systems for the diagnosis of anti-endomysial IgA-antibodies. PATIENTS AND METHODS: We examined 204 serum samples in duplicates with commercial human ELISA-kits: 54 healthy blood donors, 20 celiac disease, 29 dermatitis herpetiformis and 101 with other autoimmune dermatoses. RESULTS: The tTG-based ELISA proved to be very disease-specific (100 %) and sensitive for the diagnosis of gluten sensitivity (95 % celiac disease; 96.6 % dermatitis herpetiformis). The eTG-based ELISA was also perfectly specific (100 %), but only 15 % of celiac disease-sera and 44.8 % of dermatitis herpetiformis-sera yielded positive results. CONCLUSIONS: The human tTG-ELISA fulfills all criteria of a screening test and, because of being investigator-independent, inexpensive and highly reproducible, compares favorably with the current diagnostic gold standard (indirect immunofluorescence and biopsy) of celiac disease and dermatitis herpetiformis. The low sensitivity of the eTG-ELISA may have technical reasons, but could theoretically also be linked to disease activity or indicate the existence of an as yet undefined disease subset. Studies are currently under way to address these issues.

Serum eosinophil cationic protein, myeloperoxidase, tryptase, eotaxin and Th2-L-like cytokines in Dermatitis herpetiformis.

BACKGROUND: Dermatitis herpetiformis (DH) is a subepidermal bullous disease characterized by a neutrophilic and eosinophilic infiltrate, together with activated lymphocytes that show preferential polarization towards the Th2-like phenotype. To date, the role of neither soluble mediators, such as cytokines, nor serum levels of myeloperoxidase (MPO), eosinophil cationic protein (ECP) and tryptase (TRY) have been studied in the peripheral blood of DH. In this study we investigated 40 DH subjects for possible alterations in MPO, ECP, TRY, eotaxin, interleukin (IL) 4 and IL-5 concentrations to evaluate the role of neutrophils, eosinophils and mast cells in the induction of skin lesions. Sera from 20 healthy subjects were tested as controls. METHODS: Eotaxin, IL-4 and IL-5 serum contents were determined by a solid-phase enzyme-linked immunosorbent assay. A double antibody radioimmunoassay was used to measure serum levels of MPO, ECP and TRY. RESULTS: Normal levels of eotaxin and IL-4 were found in all DH subjects; increased IL-5 levels were found only in 1 subject. The MPO levels were significantly higher in DH subjects than in healthy controls (p < 0.01). There was also a significant difference between the serum ECP levels of DH and healthy controls (p < 0.05). TRY was not revealed in the serum of DH subjects. CONCLUSIONS: The determination of Th2-like cytokines and TRY serum levels is not important in quantifying the involvement of activated lymphocytes and mast cells in DH; however, the finding of high MPO and ECP serum levels seems to confirm that these products are good markers of the presence of activated neutrophils and eosinophils.

Epidermal transglutaminase (TGase 3) is the autoantigen of dermatitis herpetiformis.

Gluten sensitivity typically presents as celiac disease, a common chronic small intestinal disorder. However, in certain individuals it is associated with dermatitis herpetiformis, a blistering skin disease characterized by granular IgA deposits in the papillary dermis. While tissue transglutaminase has been implicated as the major autoantigen of gluten sensitive disease, there has been no explanation as to why this condition appears in two distinct forms. Here we show that while sera from patients with either form of gluten sensitive disease react both with tissue transglutaminase and the related enzyme epidermal (type 3) transglutaminase, antibodies in patients having dermatitis herpetiformis show a markedly higher avidity for epidermal transglutaminase. Further, these patients have an antibody population specific for this enzyme. We also show that the IgA precipitates in the papillary dermis of patients with dermatitis herpetiformis, the defining signs of the disease, contain epidermal transglutaminase, but not tissue transglutaminase or keratinocyte transglutaminase. These findings demonstrate that epidermal transglutaminase, rather than tissue transglutaminase, is the dominant autoantigen in dermatitis herpetiformis and explain why skin symptoms appear in a proportion of patients having gluten sensitive disease.