Emerging treatments for pemphigoid diseases

Current knowledge of immunomodulation strategies for chronic skin wound repair

In orchestrating the wound healing process, the immune system plays a critical role. Hence, controlling the immune system to repair skin defects is an attractive approach. The highly complex immune system includes the coordinated actions of several immune cells, which can produce various inflammatory and antiinflammatory cytokines and affect the healing of skin wounds. This process can be optimized using biomaterials, bioactive molecules, and cell delivery. The present review discusses various immunomodulation strategies for supporting the healing of chronic wounds. In this regard, following the evolution of the immune system and its role in the wound healing mechanism, the interaction between the extracellular mechanism and immune cells for acceleration wound healing will be firstly investigated. Consequently, the immune-based chronic wounds will be briefly examined and the mechanism of progression, and conventional methods of their treatment are evaluated. In the following, various biomaterials-based immunomodulation strategies are introduced to stimulate and control the immune system to treat and regenerate skin defects. Other effective methods of controlling the immune system in wound healing which is the release of bioactive agents (such as antiinflammatory, antigens, and immunomodulators) and stem cell therapy at the site of injury are reviewed.

Visualization of autoantibodies and neutrophils in vivo identifies novel checkpoints in autoantibody-induced tissue injury

In several autoimmune diseases, e.g., pemphigoid disease (PD), autoantibodies are the direct cause of pathology. Albeit key requirements for antibody-mediated diseases were identified, their interactions and exact temporal and spatial interactions remained elusive. The skin is easily accessible for imaging. Thus, we selected epidermolysis bullosa acquisita (EBA), a PD with autoantibodies to type VII collagen (COL7), to visualize interactions of autoantibodies, target tissue and effector cells (neutrophils). Following injection into mice, anti-COL7 IgG bound to the dermal-epidermal junction (DEJ) within minutes. We unexpectedly observed an inhomogeneous distribution of autoantibodies along the DEJ. Thus, we hypothesized that specific external triggers may affect autoantibody distribution. Indeed, mechanical irritation led to an increased autoantibody binding along the DEJ. Subsequently, anti-COL7 IgG was injected into mice expressing green fluorescent protein under the LysM promoter (LysM-eGFP) mice. This allows to visualize myeloid cells in vivo in these animals. Using multiphoton imaging, we observed a limited extravasation of LysM-eGFP⁺ cells into skin was observed within 24 hours. Intriguingly, LysM-eGFP⁺ cells did not immediately co-localize with autoantibodies, which was only noted at later time points. Of note, interactions of LysM-eGFP⁺ with the autoantibodies at the DEJ were short-lived. Collectively, our results define the following checkpoints for autoantibody-induced tissue injury: (i) autoantibody egress to target tissue influenced by mechanical trigger factors, (ii) neutrophil recruitment into the vicinity of autoantibody deposits and (iii) short-term neutrophil localization to these deposits, as well as (iv) delayed recruitment of neutrophils with subsequent autoantibody-induced inflammation.

Treatment with anti-neonatal Fc receptor (FcRn) antibody ameliorates experimental epidermolysis bullosa acquisita in mice

Background and Purpose

Pemphigus and pemphigoid diseases are characterized and caused predominantly by IgG autoantibodies targeting structural proteins of the skin. Their current treatment relies on general and prolonged immunosuppression that causes severe adverse events, including death. Hence, novel safe and more effective treatments are urgently needed. Due to its' physiological functions, the neonatal Fc receptor (FcRn) has emerged as a potential therapeutic target for pemphigus and pemphigoid, primarily because IgG is protected from proteolysis after uptake into endothelial cells. Thus, blockade of FcRn would reduce circulating autoantibody concentrations. However, long‐term effects of pharmacological FcRn inhibition in therapeutic settings of autoimmune diseases are unknown.

Experimental Approach

Therapeutic effects of FcRn blockade were investigated in a murine model of the prototypical autoantibody‐mediated pemphigoid disease, epidermolysis bullosa acquisita (EBA). B6.SJL‐H2s C3c/1CyJ mice with clinically active disease were randomized to receive either an anti‐FcRn monoclonal antibody (4470) or an isotype control over 4 weeks.

Key Results

While clinical disease continued to worsen in isotype control‐treated mice, overall disease severity continuously decreased in mice injected with 4470, leading to almost complete remission in over 25% of treated mice. These clinical findings were paralleled by a reduction of autoantibody concentrations. Reduction of autoantibody concentrations, rather than modulating neutrophil activation, was responsible for the observed therapeutic effects.

Conclusion and Implications

The clinical efficacy of anti‐FcRn treatment in this prototypical autoantibody‐mediated disease encourages further development of anti‐FcRn antibodies for clinical use in pemphigoid diseases and potentially in other autoantibody mediated diseases.

Consensus on the treatment of autoimmune bullous dermatoses: bullous pemphigoid, mucous membrane pemphigoid and epidermolysis bullosa acquisita - Brazilian Society of Dermatology

Bullous pemphigoid, mucous membrane pemphigoid and epidermolysis bullosa acquisita are subepidermal autoimmune blistering diseases whose antigenic target is located at the basement membrane zone. Mucous membrane pemphigoid and epidermolysis bullosa acquisita can evolve with cicatricial mucosal involvement, leading to respiratory, ocular and/or digestive sequelae with important morbidity. For each of these dermatoses, a literature review covering all therapeutic options was performed. A flowchart, based on the experience and joint discussion among the authors of this consensus, was constructed to provide treatment orientation for these diseases in Brazil. In summary, in the localized, low-risk or non-severe forms, drugs that have immunomodulatory action such as dapsone, doxycycline among others may be a therapeutic option. Topical treatment with corticosteroids or immunomodulators may also be used. Systemic corticosteroid therapy continues to be the treatment of choice for severe forms, especially those involving ocular, laryngeal-pharyngeal and/or esophageal mucosal involvement, as may occur in mucous membrane pemphigoid and epidermolysis bullosa acquisita. Several immunosuppressants are used as adjuvant alternatives. In severe and recalcitrant cases, intravenous immunoglobulin is an alternative that, while expensive, may be used. Immunobiological drugs such as rituximab are promising drugs in this area. Omalizumab has been used in bullous pemphigoid.

Meta-analysis of the clinical and immunopathological characteristics and treatment outcomes in epidermolysis bullosa acquisita patients

Background

Epidermolysis bullosa acquisita (EBA) is an orphan autoimmune disease. Several clinical phenotypes have been described, but subepidermal blistering is characteristic of all variants. Limited data on clinical and immunopathological characteristics and treatment outcomes in EBA are available. To fill this gap, we collected this information from EBA cases, meeting current diagnostic criteria, published between 1971 and 2016.

Results

We identified 1159 EBA cases. This number must be, however, interpreted with caution, as it is not possible to check for multiple reporting. The analysis of all cases indicated that EBA affects all age groups (median: 50 years, range: 1 to 94 years) at an equal gender distribution. Non-mechanobullous (non-MB) forms of EBA were observed in 55% of patients, whereas the mechanobullous variant (MB-EBA) or a combination of both variants was described in 38 or 7% of patients, respectively. Type VII collagen (COL7)-specific autoantibodies were primarily of the IgG isotype, but anti-COL7 IgA, IgM and IgE were also documented. Comparison of the 2 clinical EBA types showed a higher frequency of IgA deposits in non-MB EBA as opposed to MB EBA. Mucous membrane involvement was observed in 23% of patients, and 4.4% of cases were associated with other chronic inflammatory diseases. Of note, IgA deposits were more frequently observed in cases with mucous membrane involvement. Our analysis indicated that EBA is difficult to treat and that the choice of treatment varies widely. Chi square was applied to identify medications associated with complete remission (CR). Considering all EBA cases, intravenous immunoglobulin (IVIG, p = 0.0047) and rituximab (p = 0.0114) were associated with CR. Subgroup analysis demonstrated that no treatment was associated with CR for non-MB EBA, while IVIG (p = 0.003) was associated with CR in MB EBA.

Conclusions

Within the limitations of the study, we here document the clinical and immunopathological characteristics and treatment outcomes in a large cohort of EBA patients. The observed associations of single drugs with treatment outcome may serve as a guide to develop clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0896-1) contains supplementary material, which is available to authorized users.

Therapeutic Effect of a Novel Phosphatidylinositol-3-Kinase δ Inhibitor in Experimental Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita (EBA) is a rare, but prototypical, organ-specific autoimmune disease, characterized and caused by autoantibodies against type VII collagen (COL7). Mucocutaneous inflammation, blistering, and scarring are the clinical hallmarks of the disease. Treatment of EBA is difficult and mainly relies on general immunosuppression. Hence, novel treatment options are urgently needed. The phosphatidylinositol-3-kinase (PI3K) pathway is a putative target for the treatment of inflammatory diseases, including EBA. We recently discovered LAS191954, an orally available, selective PI3Kδ inhibitor. PI3Kδ has been shown to be involved in B cell and neutrophil cellular functions. Both cell types critically contribute to EBA pathogenesis, rendering LAS191954 a potential drug candidate for EBA treatment. We, here, demonstrate that LAS191954, when administered chronically, dose-dependently improved the clinical phenotype of mice harboring widespread skin lesions secondary to immunization-induced EBA. Direct comparison with high-dose corticosteroid treatment indicated superiority of LAS191954. Interestingly, levels of circulating autoantibodies were unaltered in all groups, indicating a mode of action independent of the inhibition of B cell function. In line with this, LAS191954 also hindered disease progression in antibody transfer-induced EBA, where disease develops dependent on myeloid, but independent of B cells. We further show that, in vitro, LAS191954 dose-dependently impaired activation of human myeloid cells by relevant disease stimuli. Specifically, immune complex-mediated and C5a-mediated ROS release were inhibited in a PI3Kδ-dependent manner. Accordingly, LAS191954 also modulated the dermal–epidermal separation induced in vitro by co-incubation of immune complexes with polymorph nuclear cells, thus pointing to an important role of PI3Kδ in EBA effector functions. Altogether, these results suggest a new potential mechanism for the treatment of EBA and potentially also other autoimmune bullous diseases.

Specific Inhibition of Complement Activation Significantly Ameliorates Autoimmune Blistering Disease in Mice

Epidermolysis bullosa acquisita (EBA) is an antibody-mediated blistering skin disease associated with tissue-bound and circulating autoantibodies to type VII collagen (COL7). Transfer of antibodies against COL7 into mice results in a subepidermal blistering phenotype, strictly depending on the complement component C5. Further, activation predominantly by the alternative pathway is required to induce experimental EBA, as blistering was delayed and significantly ameliorated only in factor B^-/- mice. However, C5 deficiency not only blocked the activation of terminal complement components and assembly of the membrane attack complex (MAC) but also eliminated the formation of C5a. Therefore, in the present study, we first aimed to elucidate which molecules downstream of C5 are relevant for blister formation in this EBA model and could be subsequently pharmaceutically targeted. For this purpose, we injected mice deficient in C5a receptor 1 (C5aR1) or C6 with antibodies to murine COL7. Importantly, C5ar1^-/- mice were significantly protected from experimental EBA, demonstrating that C5a-C5aR1 interactions are critical intermediates linking pathogenic antibodies to tissue damage in this experimental model of EBA. By contrast, C6^-/- mice developed widespread blistering disease, suggesting that MAC is dispensable for blister formation in this model. In further experiments, we tested the therapeutic potential of inhibitors of complement components which were identified to play a key role in this experimental model. Complement components C5, factor B (fB), and C5aR1 were specifically targeted using complement inhibitors both prophylactically and in mice that had already developed disease. All complement inhibitors led to a significant improvement of the blistering phenotype when injected shortly before anti-COL7 antibodies. To simulate a therapeutic intervention, anti-fB treatment was first administered in full-blown EBA (day 5) and induced significant amelioration only in the final phase of disease evolution, suggesting that early intervention in disease development may be necessary to achieve higher efficacy. Anti-C5 treatment in incipient EBA (day 2) significantly ameliorated disease during the whole experiment. This finding is therapeutically relevant, since the humanized anti-C5 antibody eculizumab is already successfully used in patients. In conclusion, in this study, we have identified promising candidate molecules for complement-directed therapeutic intervention in EBA and similar autoantibody-mediated diseases.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Reduced skin blistering in experimental epidermolysis bullosa acquisita after anti-TNF treatment

Epidermolysis bullosa acquisita (EBA) is a difficult-to-treat subepidermal autoimmune blistering skin disease (AIBD) with circulating and tissue-bound anti-type VII collagen antibodies. Different reports have indicated an increased concentration of tumor necrosis factor alpha (TNF) in the serum and blister fluid of patients with subepidermal AIBDs. Furthermore, successful anti-TNF treatment has been reported for individual patients with AIBDs. Here, we show that in mice, induction of experimental EBA by repeated injections of rabbit-anti mouse type VII collagen antibodies led to increased expression of TNF in skin, as determined by real-time PCR and immunohistochemistry. To investigate if the increased TNF expression is of functional relevance in experimental EBA, we inhibited TNF function using the soluble TNF receptor fusion protein etanercept (Enbrel®) or a monoclonal antibody to murine TNF. Interestingly, mice receiving either of these two treatments showed significantly milder disease progression than controls. In addition, immunohistochemical staining demonstrated reduced numbers of macrophages in lesional skin in mice treated with TNF inhibitors compared to controls. Furthermore, etanercept treatment significantly reduced the disease progression in immunization-induced EBA. In conclusion, the increased expression of TNF in experimental EBA is of functional relevance, as both the prophylactic blockade of TNF and the therapeutic use of etanercept impaired the induction and progression of experimental EBA. Thus, TNF is likely to serve as a new therapeutic target for EBA and AIBDs with a similar pathogenesis.

T cells mediate autoantibody-induced cutaneous inflammation and blistering in epidermolysis bullosa acquisita

T cells are key players in autoimmune diseases by supporting the production of autoantibodies. However, their contribution to the effector phase of antibody-mediated autoimmune dermatoses, i.e., tissue injury and inflammation of the skin, has not been investigated. In this paper, we demonstrate that T cells amplify the development of autoantibody-induced tissue injury in a prototypical, organ-specific autoimmune disease, namely epidermolysis bullosa acquisita (EBA) – characterized and caused by autoantibodies targeting type VII collagen. Specifically, we show that immune complex (IC)-induced inflammation depends on the presence of T cells – a process facilitated by T cell receptor (TCR)γδ and NKT cells. Because tissue damage in IC-induced inflammation is neutrophil-dependent, we further analyze the interplay between T cells and neutrophils in an experimental model of EBA. We demonstrate that T cells not only enhance neutrophil recruitment into the site of inflammation but also interact with neutrophils in lymphatic organs. Collectively, this study shows that T cells amplify the effector phase of antibody-induced tissue inflammation.

Macropinocytosis of type XVII collagen induced by bullous pemphigoid IgG is regulated via protein kinase C

Macropinocytosis is an endocytic pathway that is involved in the nonselective fluid uptake of extracellular fluid. Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies to type XVII collagen (COL17), which is a component of hemidesmosome. When keratinocytes are treated with BP-IgG, COL17 internalizes into cells by way of the macropinocytosis. We investigated the mechanism of COL17 macropinocytosis using DJM-1 cells, a cutaneous squamous cell carcinoma cell line. First, non-hemidesmosomal COL17 was preferentially depleted by stimulation with the BP-IgG in the DJM-1 cells. To investigate the signaling involved in COL17-macropinocytosis, the inhibition of small GTPase family members Rac1 and Cdc42 was found to strongly repress COL17 internalization; in addition, the Rho inhibitor also partially blocked that internalization, suggesting these small GTPases are involved in signaling to mediate COL17-macropinocytosis. Western blotting using Phostag-SDS-PAGE demonstrated high levels of COL17 phosphorylation in DJM-1 cells under steady-state condition. Treatment with BP-IgG increased the intracellular calcium level within a minute, and induced the overabundant phosphorylation of COL17. The overabundant phosphorylation of COL17 was suppressed by a protein kinase C (PKC) inhibitor. In addition, PKC inhibitor repressed COL17 endocytosis using cell culture and organ culture systems. Finally, the depletion of COL17 was not observed in the HEK293 cells transfected COL17 without intracellular domain. These results suggest that COL17 internalization induced by BP-IgG may be mediated by a PKC pathway. In summary, BP-IgG initially binds to COL17 distributed on the plasma membrane, and COL17 may be internalized by means of a macropinocytic pathway related to the phosphorylation of the intracellular domain by PKC.

Cytoskeletal Regulation of Inflammation and Its Impact on Skin Blistering Disease Epidermolysis Bullosa Acquisita

Actin remodelling proteins regulate cytoskeletal cell responses and are important in both innate and adaptive immunity. These responses play a major role in providing a fine balance in a cascade of biological events that results in either protective acute inflammation or chronic inflammation that leads to a host of diseases including autoimmune inflammation mediated epidermolysis bullosa acquisita (EBA). This review describes the role of the actin cytoskeleton and in particular the actin remodelling protein called Flightless I (Flii) in regulating cellular inflammatory responses and its subsequent effect on the autoimmune skin blistering disease EBA. It also outlines the potential of an antibody based therapy for decreasing Flii expression in vivo to ameliorate the symptoms associated with EBA.

Dimethylfumarate Impairs Neutrophil Functions

Host defense against pathogens relies on neutrophil activation. Inadequate neutrophil activation is often associated with chronic inflammatory diseases. Neutrophils also constitute a significant portion of infiltrating cells in chronic inflammatory diseases, for example, psoriasis and multiple sclerosis. Fumarates improve the latter diseases, which so far has been attributed to the effects on lymphocytes and dendritic cells. Here, we focused on the effects of dimethylfumarate (DMF) on neutrophils. In vitro, DMF inhibited neutrophil activation, including changes in surface marker expression, reactive oxygen species production, formation of neutrophil extracellular traps, and migration. Phagocytic ability and autoantibody-induced, neutrophil-dependent tissue injury ex vivo was also impaired by DMF. Regarding the mode of action, DMF modulates-in a stimulus-dependent manner-neutrophil activation using the phosphoinositide 3-kinase/Akt-p38 mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 pathways. For in vivo validation, mouse models of epidermolysis bullosa acquisita, an organ-specific autoimmune disease caused by autoantibodies to type VII collagen, were employed. In the presence of DMF, blistering induced by injection of anti-type VII collagen antibodies into mice was significantly impaired. DMF treatment of mice with clinically already-manifested epidermolysis bullosa acquisita led to disease improvement. Collectively, we demonstrate a profound inhibitory activity of DMF on neutrophil functions. These findings encourage wider use of DMF in patients with neutrophil-mediated diseases.

Role of IgE in autoimmunity

There is accumulating evidence to suggest that IgE plays a significant role in autoimmunity. The presence of circulating self-reactive IgE in patients with autoimmune disorders has been long known but, at the same time, largely understudied. However, studies have shown that the increased IgE concentration is not associated with higher prevalence for atopy and allergy in patients with autoimmune diseases, such as systemic lupus erythematosus. IgE-mediated mechanisms are conventionally known to facilitate degranulation of mast cells and basophils and promote TH2 immunity, mechanisms that are not only central to mounting an appropriate defense against parasitic worms, noxious substances, toxins, venoms, and environmental irritants but that also trigger exuberant allergic reactions in patients with allergies. More recently, IgE autoantibodies have been recognized to participate in the self-inflicted damaging immune responses that characterize autoimmunity. Such autoimmune responses include direct damage on tissue-containing autoantigens, activation and migration of basophils to lymph nodes, and, as observed most recently, induction of type 1 interferon responses from plasmacytoid dendritic cells. The importance of IgE as a central pathogenic mechanism in autoimmunity has now been clinically validated by the approval of omalizumab, an anti-IgE mAb, for patients with chronic spontaneous urticaria and for the clinical benefit of patients with bullous pemphigoid. In this review we summarize recent reports describing the prevalence of self-reactive IgE and discuss novel findings that incriminate IgE as central in the pathogenesis of inflammatory autoimmune disorders.

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.

A recombinant fusion protein derived from dog hookworm inhibits autoantibody-induced dermal-epidermal separation ex vivo

The proteins secreted by parasitic nematodes are evolutionarily optimized molecules with unique capabilities of suppressing the immune response of the host organism. Neutrophil inhibitory factor (NIF), which is secreted by the dog hookworm Ancylostoma caninum, binds to the β2 integrin CD11b/CD18, which is expressed on human neutrophils, eosinophils, monocytes and macrophages and inhibits neutrophil-dependent lung injury and neutrophil invasion of ischaemic brain tissue. Neutrophils are key players in the pathogenesis of subepidermal autoimmune blistering diseases (sAIBDs), and their pathogenic activities are crucially dependent on β2 integrin functionality. Based on the template of single-stranded, dimerizing antibody derivatives, which are already used in cancer treatment, we designed a novel biologic, NIF-IGHE-CH4, comprising NIF and the dimerizing but otherwise inert constant heavy subdomain 4 (CH4) of human IgE (IGHE). This molecule was evaluated in a variety of in vitro assays, demonstrating its ability to inhibit pathogenically relevant neutrophil functions such as migration, adhesion and spreading, and release of reactive oxygen species. Finally, we confirmed that NIF-IGHE-CH4 inhibits blister formation in an ex vivo assay of sAIBD. These results suggest that NIF-IGHE-CH4 is a novel potential anti-inflammatory drug for the treatment of neutrophil-mediated diseases such as sAIBDs. This study promotes the drugs from bugs concept and encourages further research and development focused on turning parasite proteins into useful anti-inflammatory biologics.

Radiosensitive Hematopoietic Cells Determine the Extent of Skin Inflammation in Experimental Epidermolysis Bullosa Acquisita

Animal models have enhanced our understanding of the pathogenesis of autoimmune diseases. For these models, genetically identical, inbred mice have commonly been used. Different inbred mouse strains, however, show a high variability in disease manifestation. Identifying the factors that influence this disease variability could provide unrecognized insights into pathogenesis. We established a novel Ab transfer-induced model of epidermolysis bullosa acquisita (EBA), an autoimmune disease characterized by (muco)-cutaneous blistering caused by anti-type VII collagen (COL7) autoantibodies. Blistering after anti-COL7 IgG (directed against the von Willebrand factor A-like domain 2) transfer showed clear variability among inbred mouse strains, that is, severe cutaneous blistering and inflammation in C57BL/6J and absence of skin lesions in MRL/MpJ mice. The transfer of anti-COL7 IgG into irradiated, EBA-resistant MRL/MpJ mice, rescued by transplantation with bone marrow from EBA-susceptible B6.AK-H2k mice, induced blistering. To the contrary, irradiated EBA-susceptible B6.AK-H2k mice that were rescued using MRL/MpJ bone marrow were devoid of blistering. In vitro, immune complex activation of neutrophils from C57BL/6J or MRL/MpJ mice showed an impaired reactive oxygen species release from the latter, whereas no differences were observed after PMA activation. This finding was paralleled by divergent expression profiles of immune complex-activated neutrophils from either C57BL/6J or MRL/MpJ mice. Collectively, we demonstrate that radiosensitive cells determine the varying extent of skin inflammation and blistering in the end-stage effector phase of EBA.

Activation of Blood Coagulation in Two Prototypic Autoimmune Skin Diseases: A Possible Link with Thrombotic Risk

Coagulation activation has been demonstrated in two prototypic autoimmune skin diseases, chronic autoimmune urticaria and bullous pemphigoid, but only the latter is associated with increased thrombotic risk. Two markers of coagulation activation (prothrombin fragment F1+2 and fibrin fragment D-dimer) were measured by immunoenzymatic methods in plasma samples from 30 patients with active chronic autoimmune urticaria, positive for autologous serum skin test, 30 patients with active bullous pemphigoid and 30 healthy subjects. In skin biopsies, tissue factor expression was evaluated by both immunohistochemistry and in situ hybridization. F1+2 and D-dimer levels were higher in active chronic autoimmune urticaria (276.5±89.8 pmol/L and 5.56±4.40 nmol/L, respectively) than in controls (145.2±38.0 pmol/L and 1.06±0.25 nmol/L; P=0.029 and P=0.011) and were much higher in active bullous pemphigoid (691.7±318.7 pmol/L and 15.24±9.09 nmol/L, respectively) (P<0.0001). Tissue factor positivity was evident in skin biopsies of both disorders with higher intensity in bullous pemphigoid. F1+2 and D-dimer, during remission, were markedly reduced in both disorders. These findings support the involvement of coagulation activation in the pathophysiology of both diseases. The strong systemic activation of coagulation in bullous pemphigoid may contribute to increase the thrombotic risk and provides the rationale for clinical trials on anticoagulant treatments in this disease.

Prevalence of pemphigus and pemphigoid autoantibodies in the general population

BACKGROUND

Mucocutaneous blistering is characteristic of autoimmune bullous dermatoses (AIBD). Blisters are caused by autoantibodies directed against structural components of the skin. Hence, detection of specific autoantibodies has become a hallmark for AIBD diagnosis. Studies on prevalence of AIBD autoantibodies in healthy individuals yielded contradictory results.

METHODS

To clarify this, samples from 7063 blood donors were tested for presence of anti-BP180-NC16A, anti-BP230 and anti-Dsg1/3 IgG by indirect immunofluorescence (IF) microscopy using a biochip.

RESULTS

Cumulative prevalence of these autoantibodies was 0.9 % (CI: 0.7-1.1 %), with anti-BP180-NC16A IgG being most prevalent. Validation of IF findings using ELISA confirmed presence of autoantibodies in 7/15 (anti-Dsg1), 6/7 (anti-Dsg3), 35/37 (anti-BP180-NC16A) and 2/3 (anti-BP230) cases. Moreover, in 16 samples, anti-BP180-NC16A autoantibody concentrations exceeded the cut-off for the diagnosis of bullous pemphigoid. Interestingly, these anti-BP180-NC16A autoantibodies from healthy individuals formed immune complexes with recombinant antigen and dose-dependently activated neutrophils in vitro. However, fine-epitope mapping within NC16A showed a different binding pattern of anti-BP180-NC16A autoantibodies from healthy individuals compared to bullous pemphigoid patients, while IgG subclasses were identical.

CONCLUSIONS

Collectively, we here report a low prevalence of AIBD autoantibodies in a large cohort of healthy individuals. Furthermore, functional analysis shows differences between autoantibodies from healthy donors and AIBD patients.

Conditional depletion of mast cells has no impact on the severity of experimental epidermolysis bullosa acquisita

The role of mast cells (MCs) in autoimmunity is the matter of an intensive scientific debate. Based on observations in different MC-deficient mouse strains, MCs are considered as fundamental players in autoimmune diseases. However, most recent data suggest that the outcome of such diseases is strongly affected by the individual mouse strain used. By the use of two c-Kit mutant MC-deficient mouse strains and one c-Kit-independent strain, we here investigated the role of MCs in a systemic Ab transfer model of epidermolysis bullosa acquisita, a subepidermal autoimmune blistering skin disease characterized by autoantibodies against type VII collagen. While C57BL/6J-Kit(W-sh/W-sh) mice developed an unexpected increased blistering phenotype, no significant differences to WT controls were seen in WBB6F1 -Kit(W/W-v) or the novel Mcpt5-Cre iDTR animals. Interestingly, in a local Ab transfer model, which induces a localized disease, we showed that application of high concentrations of anti-COL7 (where COL7 is type VII collagen) Abs induced MC activation and MC-dependent edema formation that did, however, not contribute to blister induction. Our results indicate that in the autoimmune disorder epidermolysis bullosa acquisita MCs do not contribute to the immune-mediated tissue injury. Modern c-Kit mutant-independent MC-deficient mouse strains will help to further redefine the role of MCs in autoimmunity.

Autoantibodies to Multiple Epitopes on the Non-Collagenous-1 Domain of Type VII Collagen Induce Blisters

Epidermolysis bullosa acquisita (EBA) is an autoimmune blistering disease of the skin and mucous membranes, characterized by autoantibodies against type VII collagen (COL7), a major component of anchoring fibrils. Different clinical EBA phenotypes are described, including mechanobullous and inflammatory variants. Most EBA patients' sera react with epitopes located within the non-collagenous 1 (NC1) domain of human COL7. However, it has remained unclear whether antibody binding to these different epitopes is pathogenically relevant. To address this issue, we generated recombinant proteins covering the entire NC1 domain. IgG reactivity with these proteins was analyzed in sera of 69 EBA patients. Most recognized clusters of epitopes throughout the NC1 domain. No correlation was detected between antibody specificity and clinical phenotype. To study the pathogenicity of antibodies specific to different NC1 subdomains, rabbit antibodies were generated. All these antibodies caused dermal-epidermal separation ex vivo. Antibodies against two of these subdomains were injected into mice carrying null mutations of mouse COL7 and the human COL7 transgene and induced subepidermal blisters. We here document that autoantibodies to COL7, independent of the targeted epitopes, induce blisters both ex vivo and in vivo. In addition, using COL7-humanized mice, we provide in vivo evidence of pathogenicity of autoantibodies binding to human COL7.

New strategies with anti-IgE in allergic diseases

IgE has long been known as a therapeutic target for allergic disease, but the difficulty has been in selecting agents that don't trigger cross linkage of IgE when bound to its high affinity receptor (FceR1) on mast cells and basophils. By "designing" a monoclonal antibody (mAb) which targets that part of IgE that binds to that binds to the a-chain of FceR1, the allergic cascade can be effectively interrupted and diseases such as asthma greatly improved, providing a substantial part of their phenotype engages IgE. Clinical trials and real life studies confirm this. Beyond asthma, a whole range of other diseases dependent upon IgE initiation and triggering are being identified. These diseases are now being explored as being amenable to anti-IgE therapy some of which are comorbidities of asthma and others not. The advent of an even more potent anti-IgE mAb - QGE031 - is creating further opportunities for anti-IgE therapy to improve the lives of so many people with IgE-related diseases.