Epidermolysis Bullosa Acquisita-Current and Emerging Treatments

Epidermolysis bullosa acquisita (EBA) is a rare chronic autoimmune subepidermal blistering disease of the skin and mucous membranes, usually beginning in adulthood. EBA is induced by autoantibodies to type VII collagen, a major component of anchoring fibrils in the dermal-epidermal junction (DEJ). The binding of autoantibodies to type-VII collagen subsequently leads to the detachment of the epidermis and the formation of mucocutaneous blisters. EBA has two major clinical subtypes: the mechanobullous and inflammatory variants. The classic mechanobullous variant presentation consists of skin fragility, bullae with minimal clinical or histological inflammation, erosions in acral distribution that heal with scarring, and milia formation. The inflammatory variant is challenging to differentiate from other autoimmune bullous diseases, most commonly bullous pemphigoid (BP) but also mucous membrane pemphigoid (MMP), Brunsting-Perry pemphigoid, and linear IgA dermatosis. Due to its recalcitrance conventional treatment of epidermolysis bullosa acquisita is shown to be demanding. Here we discuss novel therapeutic strategies that have emerged and which could potentially improve the quality of life in patients with EBA.

Pathological Relevance of Anti-Hsp70 IgG Autoantibodies in Epidermolysis Bullosa Acquisita

Stress-induced heat shock protein 70 (Hsp70) is a key intra- and extracellular molecular chaperone implicated in autoimmune processes. Highly immunogenic extracellular Hsp70 can activate innate and acquired (adaptive) immune responses driving the generation of anti-Hsp70 autoantibodies that are frequently observed in inflammatory/autoimmune disorders. We recently described the direct pathological role of extracellular Hsp70 in epidermolysis bullosa acquisita (EBA), an anti-type VII collagen autoantibody-mediated autoimmune blistering skin disease. Here, we determined the role of anti-Hsp70 autoantibodies in EBA. We observed that circulating anti-Hsp70 IgG autoantibodies were significantly elevated in EBA patients compared to healthy individuals and positively correlated with serum levels of pro-inflammatory interferon gamma (IFN-γ). The pathophysiological relevance of anti-Hsp70 IgG autoantibodies was demonstrated in an antibody transfer-induced EBA mouse model in which elevated serum levels of anti-Hsp70 IgG were found. In addition, anti-Hsp70 IgG-treated animals had a more intense clinical and histological disease activity, as well as upregulated nuclear factor kappa B (NF-κB) activation in skin biopsies compared to isotype-treated animals. Our results suggest that autoantibodies to Hsp70 may contribute to EBA development via enhanced neutrophil infiltration to the skin and activation of the NF-κB signaling pathway in an IFN-γ-associated manner.

NUTRITION AND BULLOUS DISEASES

Although relatively uncommon, autoimmune bullous diseases carry the risk of increased mortality and can significantly impact quality of life. This group of diseases is broad and encompasses subepidermal conditions like bullous pemphigoid, cicatricial pemphigoid, epidermolysis bullosa acquisita, dermatitis herpetiformis, and linear IgA bullous dermatosis, as well as intraepidermal conditions like pemphigus and its variants. The pathophysiology of each condition is incompletely understood but broadly involves the formation of autoantibodies targeting skin adhesion proteins, a process which relies on a complex interplay between a dysregulated immune system, genetic predisposition, and environmental factors. We review the impact of nutrition on pathogenesis, clinical course, and treatment of various autoimmune bullous diseases.

Epidermal Damage Induces Th1 Polarization and Defines the Site of Inflammation in Murine Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita is an autoimmune skin disease characterized by subepidermal blisters. The pathogenesis is mediated by deposits of autoantibodies directed against type VII collagen in the skin, but the sequence of events regulating the localization of skin blisters is not fully understood. In this study, using the immunization-induced mouse model of epidermolysis bullosa acquisita, we demonstrate that epidermal disruption induces not only an infiltration of CD4⁺ T cells but also a T helper type 1 phenotype as it has been described for delayed-type hypersensitivity reactions. This T helper type 1 reaction was not found when different antigens were applied. Deep T-cell receptor β profiling revealed shifts in the V/J gene usage only in epidermolysis bullosa acquisita, suggesting an infiltration of autoantigen-specific T cells. To target these autoantigen-specific T cells, we established an approach with which skin inflammation could be prevented without impairing the functionality of autoantibodies. We conclude that T-cell involvement in skin blistering diseases such as epidermolysis bullosa acquisita relates not only to T-cell help for B cells that produce pathogenic autoantibodies but also to autoreactive T helper type 1 effector cells that migrate into injured skin sites, exacerbate inflammation through production of inflammatory cytokines such as IFNγ, and prevent wound healing.

Fcγ Receptor IIB Controls Skin Inflammation in an Active Model of Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita (EBA) is an autoimmune skin blistering disease characterized by IgG autoantibodies (aAb) against type VII collagen (COL7). The mechanisms controlling the formation of such aAbs and their effector functions in the skin tissue are incompletely understood. Here, we assessed whether the inhibitory IgG Fc receptor, FcγRIIB, controls the development of autoimmune skin blistering disease in an active model of EBA. For this purpose, we immunized congenic EBA-susceptible B6.SJL-H2s (B6.s) and B6.s-Fcgr2b^−/− mice with the immunodominant vWFA2 region of COL7. B6.s-Fcgr2b^−/− mice developed a strong clinical phenotype with 15 ± 3.3% of affected body surface area at week 4. In contrast, the body surface area in B6.s mice was affected to a maximum of 5% at week 6 with almost no disease signs at week 4. Surprisingly, we already found strong but similar COL7-specific serum IgG1 and IgG2b aAb production at week 2. Further, aAb and C3b deposition in the skin of B6.s and B6.s-Fcgr2b^−/− mice increased between weeks 2 and 6 after vWFA2 immunization. Importantly, neutrophil skin infiltration and activation was much stronger in B6s-Fcgr2b^−/− than in B6.s mice and already present at week 2. Also, the early aAb response in B6.s-Fcgr2b^−/− mice was more diverse than in wt B6.s mice. Reactive oxygen species (ROS) release from infiltrating neutrophils play a crucial role as mediator of skin inflammation in EBA. In line, sera from B6.s and B6.s-Fcgr2b^−/− mice induced strong ROS release from bone marrow-neutrophils in vitro. In contrast to the antibody-transfer-induced EBA model, individual targeting of FcγRIII or FcγRIV decreased ROS release to 50%. Combined FcγR blocking abrogated ROS release from BM neutrophils. Also, ROS release induced by COL7-specific serum IgG aAbs was significantly higher using BM neutrophils from B6.s-Fcgr2b^−/− than from B6.s mice. Together, our findings identified FcγRIIB as a suppressor of skin inflammation in the active EBA model through inhibition of early epitope spreading, protection from strong early neutrophil infiltration to and activation of neutrophils in the skin and suppression of FcγRIII activation by IgG1 aAbs which drive strong ROS release from neutrophils leading to tissue destruction at the dermal-epidermal junction.

From bench to bedside: evolving therapeutic targets in autoimmune blistering disease

Autoimmune blistering diseases comprise a group of heterogenous conditions characterized by the loss of tolerance and subsequent development of autoantibodies targeting epidermal and subepidermal adhesion proteins. Blisters and erosions form on the skin and mucous membranes leading to significant morbidity and mortality. Traditional therapies rely on systemic immunosuppression. Advancements in our understanding of the pathophysiology of pemphigus and pemphigoid have led to the development of molecules which target specific pathways involved in induction and perpetuation of disease. In this review, we outline the novel therapeutic strategies including B-cell depletion, T-regulatory cell repletion, cell signalling inhibitors and small molecular inhibitors, inhibitory monoclonal antibodies, as well as complement inhibition. We additionally review their current level of clinical evidence. We lastly review therapeutics targets gleaned from the experimental epidermolysis bullosa acquisita mouse model. These emerging treatments offer an exciting progression from basic science discoveries that have the potential to transform the treatment paradigm in autoimmune blistering diseases.

Unraveling the ECM-Immune Cell Crosstalk in Skin Diseases

The extracellular matrix (ECM) is a complex network of proteins and proteoglycans secreted by keratinocytes, fibroblasts and immune cells. The function of the skin ECM has expanded from being a scaffold that provides structural integrity, to a more dynamic entity that is constantly remodeled to maintain tissue homeostasis. The ECM functions as ligands for cell surface receptors such as integrins, dystroglycans, and toll-like receptors (TLRs) and regulate cellular signaling and immune cell dynamics. The ECM also acts as a sink for growth factors and cytokines, providing critical cues during epithelial morphogenesis. Dysregulation in the organization and deposition of ECMs lead to a plethora of pathophysiological conditions that are exacerbated by aberrant ECM-immune cell interactions. In this review, we focus on the interplay between ECM and immune cells in the context of skin diseases and also discuss state of the art therapies that target the key molecular players involved.

Epidermolysis Bullosa Acquisita: The 2019 Update

Epidermolysis bullosa acquisita (EBA) is an orphan autoimmune disease. Patients with EBA suffer from chronic inflammation as well as blistering and scarring of the skin and mucous membranes. Current treatment options rely on non-specific immunosuppression, which in many cases, does not lead to a remission of treatment. Hence, novel treatment options are urgently needed for the care of EBA patients. During the past decade, decisive clinical observations, and frequent use of pre-clinical model systems have tremendously increased our understanding of EBA pathogenesis. Herein, we review all of the aspects of EBA, starting with a detailed description of epidemiology, clinical presentation, diagnosis, and current treatment options. Of note, pattern analysis via direct immunofluorescence microscopy of a perilesional skin lesion and novel serological test systems have significantly facilitated diagnosis of the disease. Next, a state-of the art review of the current understanding of EBA pathogenesis, emerging treatments and future perspectives is provided. Based on pre-clinical model systems, cytokines and kinases are among the most promising therapeutic targets, whereas high doses of IgG (IVIG) and the anti-CD20 antibody rituximab are among the most promising "established" EBA therapeutics. We also aim to raise awareness of EBA, as well as initiate basic and clinical research in this field, to further improve the already improved but still unsatisfactory conditions for those diagnosed with this condition.

Calcitriol Treatment Ameliorates Inflammation and Blistering in Mouse Models of Epidermolysis Bullosa Acquisita

A link between hypovitaminosis D and development of autoimmune bullous disorders has been suggested recently, but this association has not been elaborated experimentally. Here, the role of vitamin D was investigated in epidermolysis bullosa acquisita (EBA), an anti-type VII collagen autoantibody-induced blistering skin disease. Oral administration of the hormonally active vitamin D metabolite calcitriol ameliorated clinical disease severity and dermal neutrophil infiltration in both an antibody transfer- and immunization-induced EBA mouse model. Mechanistically, calcitriol hindered immune effector cell activation as evidenced by increased L-selectin expression on Gr-1⁺ cells in calcitriol-treated mice with antibody transfer-induced EBA, as well as suppressed in vitro immune complex-induced reactive oxygen species production in calcitriol-treated murine neutrophils. Additionally, calcitriol administration was associated with an increase of regulatory T (CD4⁺FoxP3⁺) and B (CD19⁺IL10⁺) cells as well as reduction of pro-inflammatory T helper 17 (CD4⁺IL-17⁺) cells in mice with immunization-induced EBA. In line, levels of circulating anti-type VII collagen autoantibodies were lower in mice that received calcitriol compared to solvent-treated animals. Together with the observed state of hypovitaminosis D in most cases of an analyzed EBA patient cohort, the results of this study support the use of vitamin D derivatives or analogs for patients with EBA and related diseases.

Immune mechanism-targeted treatment of experimental epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is an autoimmune bullous dermatosis characterized by chronic mucocutaneous blistering caused by autoantibodies directed against type VII collagen. EBA causes a high morbidity and is difficult to treat. Model systems have significantly broadened our understanding of EBA pathogenesis, leading to the identification of numerous therapeutic targets. Of these, so far, a few have been evaluated for their therapeutic potential in preclinical models. In mice, EBA can be induced by transfer of anti-type VII collagen antibodies or by immunization with the protein. The latter model, immunization-induced EBA, is ideal to test drugs for their therapeutic efficacy. Here, mice with already established disease can be treated for prolonged periods. Albeit time consuming, results from immunization-induced EBA will pave the way for clinical application in patients. As the key pathogenic principle, that is, autoantibody-induced, leukocyte-mediated tissue injury and inflammation, is shared by other diseases, these findings may have translational applications beyond EBA.

Blistering disease: insight from the hemidesmosome and other components of the dermal-epidermal junction

The hemidesmosome is a specialized transmembrane complex that mediates the binding of epithelial cells to the underlying basement membrane. In the skin, this multiprotein structure can be regarded as the chief adhesion unit at the site of the dermal-epidermal junction. Focal adhesions are additional specialized attachment structures located between hemidesmosomes. The integrity of the skin relies on well-assembled and functional hemidesmosomes and focal adhesions (also known as integrin adhesomes). However, if these adhesion structures are impaired, e.g., as a result of circulating autoantibodies or inherited genetic mutations, the mechanical strength of the skin is compromised, leading to blistering and/or tissue inflammation. A particular clinical presentation emerges subject to the molecule that is targeted. None of these junctional complexes are simply compounds of adhesion molecules; they also play a significant role in signalling pathways involved in the differentiation and migration of epithelial cells such as during wound healing and in tumour invasion. We summarize current knowledge about hereditary and acquired blistering diseases emerging from pathologies of the hemidesmosome and its neighbouring proteins as components of the dermal-epidermal junction.

Effects of intravenous immunoglobulins on mice with experimental epidermolysis bullosa acquisita

Although well-designed prospective trials are generally lacking, intravenous immunoglobulins (IVIG) seem an effective adjuvant treatment for autoimmune bullous skin diseases. Here, efficacy of IVIG monotherapy was compared with corticosteroid treatment in mice with immunization-induced experimental epidermolysis bullosa acquisita (EBA), an autoimmune bullous skin disease characterized by autoantibodies against type VII collagen. We found that IVIG significantly ameliorated clinical disease severity and skin neutrophil infiltration compared with vehicle-treated mice, whereas methylprednisolone showed comparatively less pronounced effects. Efficacy of IVIG was accompanied by reduced levels of autoantibodies, a shift toward noncomplement-fixing autoantibodies, and lower complement deposition at the dermal-epidermal junction. In addition, peripheral Gr-1-positive cells of IVIG-treated animals showed reduced expression of the activating Fcγ receptor IV, which we recently described as a major mediator of tissue injury in experimental EBA. These data show that treatment with IVIG is superior to systemic corticosteroids in experimental EBA and that the effects of IVIG are pleiotropic involving modulation of both the adaptive and innate immune response, although the detailed mode of action of IVIG in this model remains in need of further elucidation.

Blister-inducing antibodies target multiple epitopes on collagen VII in mice

Epidermolysis bullosa acquisita (EBA) is an autoimmune subepidermal blistering disease of mucous membranes and the skin caused by autoantibodies against collagen VII. In silico and wet laboratory epitope mapping studies revealed numerous distinct epitopes recognized by EBA patients' autoantibodies within the non-collagenous (NC)1 and NC2 domains of collagen VII. However, the distribution of pathogenic epitopes on collagen VII has not yet been described. In this study, we therefore performed an in vivo functional epitope mapping of pathogenic autoantibodies in experimental EBA. Animals (n = 10/group) immunized against fragments of the NC1 and NC2 domains of collagen VII or injected with antibodies generated against the same fragments developed to different extent experimental EBA. Our results demonstrate that antibodies targeting multiple, distinct epitopes distributed over the entire NC1, but not NC2 domain of collagen VII induce blistering skin disease in vivo. Our present findings have crucial implications for the development of antigen-specific B- and T cell-targeted therapies in EBA.

Persistent autoantibody-production by intermediates between short-and long-lived plasma cells in inflamed lymph nodes of experimental epidermolysis bullosa acquisita

Autoantibodies are believed to be maintained by either the continuous generation of short-lived plasma cells in secondary lymphoid tissues or by long-lived plasma cells localized in bone marrow and spleen. Here, we show in a mouse model for the autoimmune blistering skin disease epidermolysis bullosa acquisita (EBA) that chronic autoantibody production can also be maintained in inflamed lymph nodes, by plasma cells exhibiting intermediate lifetimes. After EBA induction by immunization with a mCOL7c-GST-fusion protein, antigen-specific plasma cells and CD4 T cells were analyzed. Plasma cells were maintained for months in stable numbers in the draining lymph nodes, but not in spleen and bone marrow. In contrast, localization of mCOL7c-GST -specific CD4 T cells was not restricted to lymph nodes, indicating that availability of T cell help does not limit plasma cell localization to this site. BrdU-incorporation studies indicated that pathogenic mCOL7c- and non-pathogenic GST-specific plasma cells resemble intermediates between short-and long-lived plasma cells with half-lives of about 7 weeks. Immunization with mCOL7c-GST also yielded considerable numbers of plasma cells neither specific for mCOL7c- nor GST. These bystander-activated plasma cells exhibited much shorter half-lives and higher population turnover, suggesting that plasma cell lifetimes were only partly determined by the lymph node environment but also by the mode of activation. These results indicate that inflamed lymph nodes can harbor pathogenic plasma cells exhibiting distinct properties and hence may resemble a so far neglected site for chronic autoantibody production.

Prevalence of specific anti-skin autoantibodies in a cohort of patients with inherited epidermolysis bullosa

Background

Inherited epidermolysis bullosa (EB) is a group of skin diseases characterized by blistering of the skin and mucous membranes.

There are four major types of EB (EB simplex, junctional EB, dystrophic EB and Kindler syndrome) caused by different gene mutations. Dystrophic EB is derived from mutations in the type VII collagen gene (COL7A1), encoding a protein which is the predominant component of the anchoring fibrils at the dermal-epidermal junction.

For the first time in literature, we have evaluated the presence of anti-skin autoantibodies in a wider cohort of patients suffering from inherited EB and ascertained whether they may be a marker of disease activity.

Methods

Sera from patients with inherited EB, 17 with recessive dystrophic EB (RDEB), 10 with EB simplex (EBS) were analysed. As much as 20 patients with pemphigus vulgaris, 21 patients with bullous pemphigoid and 20 healthy subjects were used as controls.

Anti-skin autoantibodies were tested in all samples with the Indirect Immunofluorescence (IIF) method and the currently available ELISA method in order to detect anti-type VII collagen, anti-BP180 and anti-BP230 autoantibodies.

Results

The mean concentrations of anti-type VII collagen autoantibodies titres, anti-BP180 and anti-BP230 autoantibodies were statistically higher in RDEB patients than in EBS patients.

The sensitivity and specificity of the anti-type VII collagen ELISA test were 88.2% and 96.7%. The Birmingham Epidermolysis Bullosa Severity score, which is used to evaluate the severity of the disease, correlated with anti-skin autoantibodies titres.

Conclusions

The precise pathogenic role of circulating anti-skin autoantibodies in RDEB is unclear. There is a higher prevalence of both anti-type VII collagen and other autoantibodies in patients with RDEB, but their presence can be interpreted as an epiphenomenon.

Clinical presentation, pathogenesis, diagnosis, and treatment of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. The pathogenic relevance of autoantibodies targeting type VII collagen (COL7) has been well-documented. Therefore, EBA is a prototypical autoimmune disease with a well-characterized pathogenic relevance of autoantibody binding to the target antigen. EBA is a rare disease with an incidence of 0.2 new cases per million and per year. The current treatment of EBA relies on general immunosuppressive therapy, which does not lead to remission in all cases. Therefore, there is a high, so far unmet medical need for the development of novel therapeutic options. During the last 10 years, several novel in vitro and in vivo models of EBA have been established. These models demonstrated a critical role of the genetic background, T cells, and cytokines for mediating the loss of tolerance towards COL7. Neutrophils, complement activation, Fc gamma receptor engagement, cytokines, several molecules involved in cell signaling, release of reactive oxygen species, and matrix metalloproteinases are crucial for autoantibody-induced tissue injury in EBA. Based on this growing understanding of the diseases' pathogenesis, several potential novel therapeutic targets have emerged. In this review, the clinical presentation, pathogenesis, diagnosis, and current treatment options for EBA are discussed in detail.

Epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic autoimmune subepidermal bullous disease with clinical features similar to the genetic form of dystrophic epidermolysis bullosa. EBA is characterized by the presence of autoantibodies against type VII collagen which is a major component of the anchoring fibrils at the dermal-epidermal junction. EBA can be divided into two main clinical types; mechanobullous and inflammatory EBA. Mechanobullous EBA, referred to as classic EBA, presents with skin fragility, blisters and dystrophic changes on trauma-prone areas. Inflammatory EBA resembles other autoimmune subepidermal bullous diseases. Compelling evidence from mouse models supports a pathogenic role of autoantibodies against type VII collagen in EBA. Treatment of EBA is often unsatisfactory. The most widely used systemic treatment is corticosteroids. Colchicine and dapsone have been reported to be good treatment modalities when combined with corticosteroids. Some intractable cases of EBA have successfully been treated with intravenous immunoglobulin or rituximab.

Induction of experimental epidermolysis bullosa acquisita by immunization with murine collagen VII

Epidermolysis bullosa acquisita (EBA) is an autoimmune subepidermal blistering disease caused by an autoreactive response against collagen VII, the major constituent of the anchoring fibrils at the epidermal basement membrane. The pathogenic relevance of collagen VII-specific autoantibodies has been conclusively demonstrated ex vivo and in experimental animals using antibody passive transfer models. To study the mechanisms of autoantibody production and tissue damage an animal model reproducing both the autoimmune response and the active skin disease is needed. In the present protocol, we describe the induction of an autoimmune response and active disease by immunizing mice with recombinant murine collagen VII and the analysis of the induced disease phenotype. The humoral and cellular immune response elicited in mice by immunization with the autoantigen, as well as the induced skin pathology replicate the features of the human disease at the clinical, histo- and immunopathological levels. Thus, this model is an excellent tool for investigating the mechanisms underlying pathogenic autoantibody production, the autoantibody-mediated tissue injury, and for the development of more effective therapeutic strategies in autoimmune diseases.

Evidence for pathogenicity of autoreactive T cells in autoimmune bullous diseases shown by animal disease models

Autoimmune bullous diseases (AIBDs) are characterized by blisters and erosions on the skin and/or mucous membranes, which are caused by autoantibodies directed to structural proteins of the epidermis and the epidermal basement membrane zone. This Viewpoint Essay discusses the contribution by autoreactive T cells to the pathogenesis of bullous pemphigoid, pemphigus and epidermolysis bullosa acquisita, with an emphasis on studies using active animal mouse models for these diseases. Previous studies have demonstrated that cytokines produced by autoreactive T cells, the interaction between antigen-specific T cells and B cells and the function of regulatory T cells are likely related to the pathogenesis of AIBDs. In interpreting the experimental results, the limitations of those animal models should be considered. Further understanding of the pathogenicity of autoreactive CD4(+) T cells may lead to disease-specific treatments.

Prevalence of collagen VII-specific autoantibodies in patients with autoimmune and inflammatory diseases

Background

Autoimmunity to collagen VII is typically associated with the skin blistering disease epidermolysis bullosa acquisita (EBA), but also occurs occasionally in patients with systemic lupus erythematosus or inflammatory bowel disease. The aim of our present study was to develop an accurate immunoassay for assessing the presence of autoantibodies against collagen VII in large cohorts of patients and healthy donors.

Methods

Based on in silico antigenic analysis and previous wetlab epitope mapping data, we designed a chimeric collagen VII construct containing all collagen VII epitopes with higher antigenicity. ELISA was performed with sera from patients with EBA (n = 50), Crohn's disease (CD, n = 50), ulcerative colitis (UC, n = 50), bullous pemphigoid (BP, n = 76), and pemphigus vulgaris (PV, n = 42) and healthy donors (n = 245).

Results

By ELISA, the receiver operating characteristics analysis yielded an area under the curve of 0.98 (95% CI: 0.9638-1.005), allowing to set the cut-off at 0.32 OD at a calculated specificity of 98% and a sensitivity of 94%. Running the optimized test showed that serum IgG autoantibodies from 47 EBA (94%; 95% CI: 87.41%-100%), 2 CD (4%; 95% CI: 0%-9.43%), 8 UC (16%; 95% CI: 5.8%-26%), 2 BP (2.63%; 95% CI: 0%-6.23%), and 4 PV (9.52%; 95% CI: 0%-18.4%) patients as well as from 4 (1.63%; 95% CI: 0%-3.21%) healthy donors reacted with the chimeric protein. Further analysis revealed that in 34%, 37%, 16% and 100% of sera autoantibodies of IgG1, IgG2, IgG3, and IgG4 isotype, respectively, recognized the recombinant autoantigen.

Conclusions

Using a chimeric protein, we developed a new sensitive and specific ELISA to detect collagen specific antibodies. Our results show a low prevalence of collagen VII-specific autoantibodies in inflammatory bowel disease, pemphigus and bullous pemphigoid. Furthermore, we show that the autoimmune response against collagen VII is dominated by IgG4 autoantibodies. The new immunoassay should prove a useful tool for clinical and translational research and should improve the routine diagnosis and disease monitoring in diseases associated with collagen VII-specific autoimmunity.

The flavonoid luteolin inhibits Fcγ-dependent respiratory burst in granulocytes, but not skin blistering in a new model of pemphigoid in adult mice

Bullous pemphigoid is an autoimmune blistering skin disease associated with autoantibodies against the dermal-epidermal junction. Passive transfer of antibodies against BP180/collagen (C) XVII, a major hemidesmosomal pemphigoid antigen, into neonatal mice results in dermal-epidermal separation upon applying gentle pressure to their skin, but not in spontaneous skin blistering. In addition, this neonatal mouse model precludes treatment and observation of diseased animals beyond 2-3 days. Therefore, in the present study we have developed a new disease model in mice reproducing the spontaneous blistering and the chronic course characteristic of the human condition. Adult mice were pre-immunized with rabbit IgG followed by injection of BP180/CXVII rabbit IgG. Mice pre-immunized against rabbit IgG and injected 6 times every second day with the BP180/CXVII-specific antibodies (n = 35) developed spontaneous sustained blistering of the skin, while mice pre-immunized and then treated with normal rabbit IgG (n = 5) did not. Blistering was associated with IgG and complement C3 deposits at the epidermal basement membrane and recruitment of inflammatory cells, and was partly dependent on Ly-6G-positive cells. We further used this new experimental model to investigate the therapeutic potential of luteolin, a plant flavonoid with potent anti-inflammatory and anti-oxidative properties and good safety profile, in experimental BP. Luteolin inhibited the Fcγ-dependent respiratory burst in immune complex-stimulated granulocytes and the autoantibody-induced dermal-epidermal separation in skin cryosections, but was not effective in suppressing the skin blistering in vivo. These studies establish a robust animal model that will be a useful tool for dissecting the mechanisms of blister formation and will facilitate the development of more effective therapeutic strategies for managing pemphigoid diseases.

Noncollagenous 16A domain of type XVII collagen-reactive CD4+ T cells play a pivotal role in the development of active disease in experimental bullous pemphigoid model

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is caused by autoantibodies against type XVII collagen (COL17). We recently demonstrated that CD4+ T cells were crucial for the production of anti-COL17 IgG and for the development of the BP phenotype by using a novel active BP mouse model by adoptively transferring immunized splenocytes into immunodeficient COL17-humanized mice. Noncollagenous 16A (NC16A) domain of COL17 is considered to contain the main pathogenic epitopes of BP, however, the pathogenicity of COL17 NC16A-reactive CD4+ T cells has never been elucidated. To address this issue, we modulated the immune responses against COL17 in active BP model by using anti-CD40 ligand (CD40L) monoclonal antibody MR1, an inhibitor of the CD40-CD40L interaction, in various ways. First, we show the essential role of CD4+ T cells in the model by showing that CD4+ T cells isolated from wild-type mice immunized with human COL17 enabled naïve B cells to produce anti-COL17 NC16A IgG in vivo. Second, we show that the activation of anti-COL17 NC16A IgG-producing B cells via CD40-CD40L interaction was completed within 5 days after the adoptive transfer of immunized splenocytes. Notably, a single administration of MR1 at day 0 was enough to inhibit the production of anti-COL17 NC16A IgG and to diminish skin lesions despite the presence of restored anti-COL17 IgG at the later stage. In contrast, the delayed administration of MR1 failed to inhibit the production of anti-COL17 NC16A IgG and the development of the BP phenotype. These results strongly suggest that COL17 NC16A-reactive CD4+ T cells play a pivotal role in the production of pathogenic autoantibodies and in the development of active disease in experimental BP model.

Complement-fixing anti-type VII collagen antibodies are induced in Th1-polarized lymph nodes of epidermolysis bullosa acquisita-susceptible mice

The environment encountered in secondary lymphoid organs (e.g., lymph nodes) influences the outcome of immune responses. Immunization of mice with type VII collagen, an adhesion protein expressed at the cutaneous basement membrane, induces experimental epidermolysis bullosa acquisita (EBA). In this model, clinical disease is associated with the H2s haplotype of the MHC found in SJL/J mice. Most other strains (e.g., BALB/c, C57BL/6, NZM2410/J) are resistant to clinical disease, despite autoantibody production. Comparison of autoantibody response in EBA-resistant and -susceptible mice showed an IgG2-dominated response in the latter. We hypothesized that EBA susceptibility is due to specific cytokine gene expression in draining lymph nodes (dLN). To challenge this hypothesis, EBA-susceptible (SJL/J) and -resistant (BALB/c, C57BL/6) mice were immunized with type VII collagen, followed by analysis of clinical phenotype, subclasses of circulating and tissue-bound autoantibodies, complement activation, and cytokine gene expression in dLN. Disease manifestation was associated with induction of complement-fixing autoantibodies, confirming previous observations. Furthermore, however, IFN-γ/IL-4 ratio in dLN of EBA-susceptible mice was significantly increased compared with EBA-resistant strains, suggesting a Th1 polarization. Immunization of H2s-congenic C57BL/6 mice (B6.SJL-H2s) led to Th1 polarization in dLN and clinical disease. In addition to their cytokine milieu, EBA-susceptible and -resistant mice also differed regarding the expression of FcγR on peripheral leukocytes, in which a higher FcγRIV expression in SJL/J and B6.SJL-H2s mice, compared with C57BL/6, was associated with skin lesions. In summary, blistering in experimental EBA is regulated by both adaptive (divergent class switch recombination due to polarized cytokine expression) and innate (FcγR expression) immune mechanisms.

Model systems duplicating epidermolysis bullosa acquisita: a methodological review

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease, in which generation of autoantibodies to type VII collagen (COL7) is the key factor for pathogenesis. Much of this current understanding of EBA pathogenesis has been obtained through the development and further application of respective model systems. In vitro model systems of EBA duplicate neutrophil activation by immune complexes of COL7 and anti-COL7 antibodies. Blister induction by anti-COL7 antibodies can be reproduced ex vivo by incubation of cryosections of human skin with anti-COL7 antibodies and neutrophils. Furthermore, EBA can be induced in mice by transfer of human or rabbit anti-COL7 IgG into adult mice, or by immunization of susceptible mouse strains with an immunodominant fragment within the non-collagenous 1 domain of COL7. However, our understanding of EBA pathogenesis is largely limited to mechanisms in autoantibody-induced tissue injury. Furthermore, these model systems of EBA have not been used to a large extent to evaluate the potential of novel treatment options. To foster a broader use of these elaborate model systems to specifically address these open issues, this review focuses on a detailed description of model systems for EBA, which should allow for a broad use of these models. This will hopefully lead to a better understanding of EBA pathogenesis, as well to a benefit in patient care.

Heat-shock protein 90 inhibition in autoimmunity to type VII collagen: evidence that nonmalignant plasma cells are not therapeutic targets

Blocking heat-shock protein 90 (Hsp90) induces death of malignant plasma cells by activation of the unfolded protein response, a signaling pathway activated by accumulation of misfolded proteins within the endoplasmic reticulum. We hypothesized that nontransformed plasma cells are also hypersensitive to Hsp90 inhibition because of their high amount of protein biosynthesis. To investigate this hypothesis, 2 different Hsp90 inhibitors, the geldanamycin derivative 17-DMAG and the nontoxic peptide derivative TCBL-145, were applied to mice with experimental epidermolysis bullosa acquisita, an autoimmune bullous disease characterized by autoantibodies against type VII collagen of the dermal-epidermal junction. Both inhibitors ameliorated clinical disease of type VII collagen-immunized mice, suppressed auto-antibody production, and reduced dermal neutrophilic infiltrate. Interestingly, total plasma cell numbers, type VII collagen-specific plasma cells, and germinal center B cells were unaffected by anti-Hsp90 treatment in vivo. However, T-cell proliferation was potently inhibited, as evidenced by the reduced response of isolated lymph node cells from immunized mice to in vitro restimulation with anti-CD3/CD28 antibody or autoantigen in the presence of Hsp90 inhibitors. Our results suggest that Hsp90 blockade has no impact on normal or autoreactive plasma cells in vivo and indentify T cells as targets of anti-Hsp90 treatment in autoimmunity to type VII collagen.

Autoimmunity against type VII collagen in inflammatory bowel disease

Autoimmunity against type VII collagen, an adhesion molecule of the extracellular matrix in epithelial basement membranes, is causing the rare organ-specific epidermolysis bullosa acquisita (EBA). An intriguing association between EBA and inflammatory bowel disease (IBD) has been extensively documented over the last decades, but, because of the very low incidence of EBA, received little attention from physicians involved in the care of patients with IBD. More recently, autoantibodies against type VII collagen have been detected in up to 68% of IBD patients. Although these findings suggest that chronic intestinal inflammation in IBD predisposes for autoimmunity against type VII collagen, their relevance for the pathogenesis of both IBD and EBA is still unclear. In this review article, the main features of the association between IBD and EBA are presented and pathomechanistic hypotheses as well as future lines of investigation in this area are discussed. Future research should provide new pathomechanistic insights and will likely facilitate the development of more specific and effective immunotherapeutic strategies for both conditions.