Epidermolysis Bullosa Acquisita: From Pathophysiology to Novel Therapeutic Options

State-of-the-art diagnosis of autoimmune blistering diseases

Autoimmune blistering disorders (AIBDs) are a heterogeneous group of approximately a dozen entities comprising pemphigus and pemphigoid disorders and dermatitis herpetiformis. The exact diagnosis of AIBDs is critical for both prognosis and treatment and is based on the clinical appearance combined with the detection of tissue-bound and circulating autoantibodies. While blisters and erosions on the skin and/or inspectable mucosal surfaces are typical, lesions may be highly variable with erythematous, urticarial, prurigo-like, or eczematous manifestations. While direct immunofluorescence microscopy (IFM) of a perilesional biopsy is still the diagnostic gold standard, the molecular identification of the major target antigens opened novel therapeutic avenues. At present, most AIBDs can be diagnosed by the detection of autoantigen-specific serum antibodies by enzyme-linked immunosorbent assay (ELISA) or indirect IFM when the clinical picture is known. This is achieved by easily available and highly specific and sensitive assays employing recombinant immunodominant fragments of the major target antigens, i.e., desmoglein 1 (for pemphigus foliaceus), desmoglein 3 (for pemphigus vulgaris), envoplakin (for paraneoplastic pemphigus), BP180/type XVII collagen (for bullous pemphigoid, pemphigoid gestationis, and mucous membrane pemphigoid), laminin 332 (for mucous membrane pemphigoid), laminin β4 (for anti-p200 pemphigoid), type VII collagen (for epidermolysis bullosa acquisita and mucous membrane pemphigoid), and transglutaminase 3 (for dermatitis herpetiformis). Indirect IFM on tissue substrates and in-house ELISA and immunoblot tests are required to detect autoantibodies in some AIBD patients including those with linear IgA disease. Here, a straightforward modern approach to diagnosing AIBDs is presented including diagnostic criteria according to national and international guidelines supplemented by long-term in-house expertise.

Case Report: Biological treatment of epidermolysis bullosa acquisita: report on four cases and literature review

Epidermolysis bullosa acquisita (EBA) is a chronic, recurrent autoimmune subepidermal bullous disease characterized by the presence of autoantibodies targeting type VII collagen -- basement membrane zone antigen. Standard therapy for EBA includes a combination of systemic corticosteroids and dapsone; however, severe cases may require advanced treatment. The current article reports on four EBA cases in which biologics: infliximab, rituximab (Rtx), and intravenous immunoglobulin (IVIG) were applied. All patients fulfilled the clinical and immunological criteria of EBA: they presented tense blisters healing with atrophic scars on the skin on traumatized areas and in mucous membranes. The diagnosis of EBA was established using numerous techniques: direct and indirect immunofluorescence, salt split skin, ELISA, Fluorescence Overlay Antigen Mapping using Laser Scanning Confocal Microscopy. Since all the patients did not achieve long-term remission on standard treatment (prednisone, dapsone) due to ineffectiveness or side effects of drugs, they eventually were treated with biologics leading to extraordinary skin improvement and stopping the disease for 1-3 years. Biologics in all patients were tolerated very well. No side effects were observed during application as well as multi-month follow-up. The presented cases provide a premise that biological drugs can be a valuable component of EBA therapy.

Vesiculobullous Lesions of the Oral Cavity

Several dermatological conditions may manifest in the oral cavity, particularly those that are immune-mediated, and they must be distinguished from the various other types of oral ulcerations. This chapter discusses the clinical features, pathogenesis, differential diagnosis, and diagnostic features, including histology and immunofluorescence findings, as well as management of vesiculobullous diseases. These diseases include pemphigus Vulgaris, benign mucous membrane pemphigoid, bullous pemphigoid, and epidermolysis bullosa acquisita. These diseases have a significant impact on the quality of life, as they can lead to serious complications, depending on the extent of the disease. Therefore, early recognition is crucial, helping to reduce disease-related morbidity, mortality and prevent life-threatening complications.

Autoimmune bullous diseases in pregnancy: an overview of pathogenesis, clinical presentations, diagnostics and available therapies

Autoimmune bullous diseases (AIBDs) are rare organ-specific diseases characterized by the appearance of blisters and erosions on the skin and mucous membranes. These dermatoses are marked by the development of autoantibodies targeting the autoantigens located in intercellular junctions, i.e., between keratinocytes or in the basement membrane area. Therefore, the fundamental division of AIBDs into the pemphigus and pemphigoid groups exists. Although AIBDs are uncommon in the general population, their overall incidence is somewhat higher in women of all ages, for which a pregnant women can be likely affected too. While the pemphigoid gestationis is exclusive bullous dermatosis of pregnancy, the other AIBDs can also start or worsen during this period. The appearance of AIBDs in childbearing women is a particularly sensitive situation requiring exceptional clinicians' caution due to the possibility of pregnancy complications with adverse effects and risks to the mother and the child. Also, there are numerous management difficulties in the period of pregnancy and lactation related to the drugs' choice and safety. This paper aimed to outline the pathophysiologic mechanisms, clinical manifestations, diagnostic approach and therapy of the most commonly recognized AIBDs in pregnancy.

Potential effects of shift work on skin autoimmune diseases

Shift work is associated with systemic chronic inflammation, impaired host and tumor defense and dysregulated immune responses to harmless antigens such as allergens or auto-antigens. Thus, shift workers are at higher risk to develop a systemic autoimmune disease and circadian disruption with sleep impairment seem to be the key underlying mechanisms. Presumably, disturbances of the sleep-wake cycle also drive skin-specific autoimmune diseases, but epidemiological and experimental evidence so far is scarce. This review summarizes the effects of shift work, circadian misalignment, poor sleep, and the effect of potential hormonal mediators such as stress mediators or melatonin on skin barrier functions and on innate and adaptive skin immunity. Human studies as well as animal models were considered. We will also address advantages and potential pitfalls in animal models of shift work, and possible confounders that could drive skin autoimmune diseases in shift workers such as adverse lifestyle habits and psychosocial influences. Finally, we will outline feasible countermeasures that may reduce the risk of systemic and skin autoimmunity in shift workers, as well as treatment options and highlight outstanding questions that should be addressed in future studies.

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.

Heat Shock Protein 90 (Hsp90) and Hsp70 as Potential Therapeutic Targets in Autoimmune Skin Diseases

Over a hundred different autoimmune diseases have been described to date, which can affect every organ in the body, including the largest one, the skin. In fact, up to one-fifth of the world's population suffers from chronic, noninfectious inflammatory skin diseases, the development of which is significantly influenced by an autoimmune response. One of the hallmarks of autoimmune diseases is the loss of immune tolerance, which leads to the formation of autoreactive lymphocytes or autoantibodies and, consequently, to chronic inflammation and tissue damage. The treatment of autoimmune skin diseases mainly focuses on immunosuppression (using, e.g., corticosteroids) but almost never leads to the development of permanent mechanisms of immune tolerance. In addition, current therapies and their long-term administration may cause serious adverse effects. Hence, safer and more effective therapies that bring sustained balance between pro- and anti-inflammatory responses are still desired. Both intra- and extracellular heat shock proteins (Hsps), specifically well-characterized inducible Hsp90 and Hsp70 chaperones, have been highlighted as therapeutic targets for autoimmune diseases. This review presents preclinical data on the involvement of Hsp90 and Hsp70 in modulating the immune response, specifically in the context of the treatment of selected autoimmune skin diseases with emphasis on autoimmune bullous skin diseases and psoriasis.

Epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita is a rare autoimmune disease, characterized by the synthesis of anti-collagen VII autoantibodies, the main component of hemidesmosome anchoring fibrils. The antigen-antibody binding elicits a complex inflammatory response, which culminates in the loss of dermo-epidermal adhesion of the skin and/or mucous membranes. Skin fragility with bullae, erosions, and milia in areas of trauma characterizes the mechanobullous form of the disease. In the inflammatory form of epidermolysis bullosa acquisita, urticarial inflammatory plaques with tense bullae, similar to bullous pemphigoid, or mucosal lesions can determine permanent scars and loss of functionality in the ocular, oral, esophageal, and urogenital regions. Due to the similarity of the clinical findings of epidermolysis bullosa acquisita with other diseases of the pemphigoid group and with porphyria cutanea tarda, the diagnosis is currently confirmed mainly based on the clinical correlation with histopathological findings (pauci-inflammatory subepidermal cleavage or with a neutrophilic infiltrate) and the demonstration of the presence of anti-collagen VII IgG in situ by direct immunofluorescence, or circulating anti-collagen VII IgG through indirect immunofluorescence and/or ELISA. There is no specific therapy for epidermolysis bullosa acquisita and the response to treatment is variable, usually with complete remission in children and a worse prognosis in adults with mucosal involvement. Systemic corticosteroids and immunomodulators (colchicine and dapsone) are alternatives for the treatment of mild forms of the disease, while severe forms require the use of corticosteroid therapy associated with immunosuppressants, intravenous immunoglobulin, and rituximab.

Oral Alterations in Heritable Epidermolysis Bullosa: A Clinical Study and Literature Review

Epidermolysis bullosa (EB) is a group of skin disorders with skin fragility characterized by blistering from minimal mechanical trauma with rupture at the dermoepidermal junction. There are four major classical heritable EB types, due to mutations in as many as 20 distinct genes: EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler EB (KEB). This study is aimed at reporting case series on patients (N = 8; males, n = 5 and females, n = 3, age range 12-68 years) affected by EB and performs a review of the literature on this topic. This group of disorders can affect oral soft and hard tissues in various ways, resulting in various effects including enamel hypoplasia, dental caries, microstomia, ankyloglossia, oral blistering, and ulcerations early-onset periodontal disease. From the sample results, it can be concluded that the clinical manifestation of EB patients is highly variable and very different in prognosis. Oral health deeply influences the quality of life of EB patients. Dental management is essential to prevent the aggravation of soft tissue damage and tooth loss and to improve the quality of life through prosthetic and restorative therapies. Dentists should consider the oral alterations of EB subtypes to perform a personalized approach to the patients' needs in a preventive and therapeutic point of view.

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.

Bioengineered Efficacy Models of Skin Disease: Advances in the Last 10 Years

Models of skin diseases, such as psoriasis and scleroderma, must accurately recapitulate the complex microenvironment of human skin to provide an efficacious platform for investigation of skin diseases. Skin disease research has been shifting from less complex and less relevant 2D (two-dimensional) models to significantly more relevant 3D (three-dimensional) models. Three-dimensional modeling systems are better able to recapitulate the complex cell–cell and cell–matrix interactions that occur in vivo within skin. Three-dimensional human skin equivalents (HSEs) have emerged as an advantageous tool for the study of skin disease in vitro. These 3D HSEs can be highly complex, containing both epidermal and dermal compartments with integrated adnexal structures. The addition of adnexal structures to 3D HSEs has allowed researchers to gain more insight into the complex pathology of various hereditary and acquired skin diseases. One method of constructing 3D HSEs, 3D bioprinting, has emerged as a versatile and useful tool for generating highly complex HSEs. The development of commercially available 3D bioprinters has allowed researchers to create highly reproducible 3D HSEs with precise integration of multiple adnexal structures. While the field of bioengineered models for study of skin disease has made tremendous progress in the last decade, there are still significant efforts necessary to create truly biomimetic skin disease models. In future studies utilizing 3D HSEs, emphasis must be placed on integrating all adnexal structures relevant to the skin disease under investigation. Thorough investigation of the intricate pathology of skin diseases and the development of effective treatments requires use of highly efficacious models of skin diseases.

C5aR2 deficiency ameliorates inflammation in murine epidermolysis bullosa acquisita by regulating FcγRIIb expression on neutrophils

Epidermolysis bullosa acquisita (EBA) is a rare blistering skin disease induced by autoantibodies directed against type VII collagen (COL7). Transfer of antibodies against murine COL7 (mCOL7) into mice mimics the effector phase of EBA and results in a subepidermal blistering phenotype. Activation of the complement system, and especially the C5a/C5aR1 axis driving neutrophil activation, are critical for EBA pathogenesis. However, the role of the alternative C5a receptor, C5aR2, which is commonly thought to be more immunosuppressive, in the pathogenesis of EBA is still elusive. Therefore, we sought to delineate the functional relevance of C5aR2 during the effector phase of EBA. Unexpectedly, C5aR2-deficient (C5ar2^-/-) mice showed an attenuated disease phenotype, suggesting a pathogenic contribution of C5aR2 to disease progression. In vitro, C5ar2^-/- neutrophils exhibited significantly reduced (Ca²⁺)_i flux, reactive oxygen species release, and migratory capacity when activated with immune complexes or exposed to C5a. These functions were completely absent when C5ar1^-/- neutrophils were activated. Moreover, C5aR2 deficiency more than tripled FcγRIIb expression on neutrophils thus lowering the A/I ratio of FcγRs and impeding the sustainment of inflammation. Collectively, we demonstrate here a pro-inflammatory contribution of C5aR2 to the pathogenesis of antibody-induced tissue damage in experimental EBA.

The pathogeneses of pemphigus and pemphigoid diseases

Autoimmune bullous diseases (AIBDs) are skin disorders which are mainly induced by autoantibodies against desmosomal or hemidesmosomal structural proteins. Previous studies using patients' samples and animal disease models identified target antigens and elucidated the mechanisms of blister formation. Pemphigus has been the subject of more active clinical and basic research than any other AIBD. These efforts have revealed the pathogenesis of pemphigus, which in turn has led to optimal diagnostic methods and novel therapies, such as rituximab. In bullous pemphigoid (BP), studies with passive-transfer mouse models using rabbit anti-mouse BP180 antibodies and studies with passive-transfer or active mouse models using autoantigen-humanized mice elucidated the immune reactions to BP180 in vivo. Recently, dipeptidyl peptidase-4 inhibitors have attracted attention as a trigger for BP. For epidermolysis bullosa acquisita (EBA), investigations using mouse models are actively under way and several molecules have been identified as targets for novel therapies. In this review, we give an overview and discussion of the recent progress in our understanding of the pathogenesis of pemphigus, BP, and EBA. Further studies on the breakdown of self-tolerance and on the identification of key molecules that are relevant to blister formation may expand our understanding of the etiology of AIBDs and lead to the development of novel therapeutic strategies.

Dapsone Suppresses Disease in Preclinical Murine Models of Pemphigoid Diseases

Epidermolysis bullosa acquisita and mucous membrane pemphigoid are autoimmune blistering diseases characterized by mucocutaneous blisters elicited by an autoantibody-mediated immune response against specific proteins of the epidermal basement membrane. The antibiotic dapsone is frequently used to treat both diseases, but its therapeutic effectiveness is uncertain, and its mode of action in these diseases is largely unknown. We evaluated the effect of dapsone in antibody transfer mouse models of epidermolysis bullosa acquisita and mucous membrane pemphigoid, which do not allow the drawing of conclusions on clinical treatment regimens but can be instrumental to partially uncover the mode(s) of action of dapsone in these diseases. Dapsone significantly mitigated inflammation in both models, reducing the recruitment of neutrophils into the skin and disrupting their release of leukotriene B4 (LTB4) and ROS in response to immune complexes. LTB4 has been implicated in numerous diseases, but effective LTB4 inhibitors for clinical use are not available. Our findings indicate that the mode of action of dapsone in these models may be based on the inhibition of LTB4 and ROS release from neutrophils. Moreover, they encourage testing the use of dapsone as an effective, albeit nonspecific, inhibitor of LTB4 biosynthesis in other LTB4-driven diseases.

Preventive but Not Therapeutic Topical Application of Local Anesthetics Can Inhibit Experimental Epidermolysis Bullosa Acquisita in Mice

Epidermolysis bullosa acquisita (EBA) is an autoimmune blistering disorder characterized and caused by autoantibodies against type VII collagen (COL7). Although it has been noticed that EBA in both patients and mice is associated with an increased scratching, it is not clear whether and how the scratching contributes to disease manifestation. Hence, we here aimed to validate this clinical observation and also to investigate the potential contribution of increased scratching in EBA pathogenesis in mice. Longitudinal assessment of scratching behavior revealed an increased frequency of scratching as early as 12 hours after injection of anti-COL7 IgG into the skin of mice. Subsequently, scratching events became even more frequent in mice. In contrast, mice injected with a control antibody showed an unaltered scratching behavior throughout the observation period. Based on these observations, we hypothesized that mechanical irritation may promote the induction of inflammation in experimental EBA. To challenge this assumption, the local anesthetic dyclonine hydrochloride was topically applied before injection of anti-COL7 IgG. Dyclonine hydrochloride reduced the scratching events and impaired clinical disease manifestation. In therapeutic experimental settings, i.e. administration of the local anesthetic 24 hours after injection of anti-COL7 IgG, dyclonine hydrochloride only inhibited the scratching behavior, but had no significant effect on clinical disease development. In addition, eosinophils were detected in the skin before the injection of anti-COL7 IgG and significantly increased 48 hours after the antibody injection. Collectively, our results suggest that scratching behavior contributes to the initiation phase of disease manifestation in experimental EBA.

Subepithelial autoimmune blistering dermatoses: Clinical features and diagnosis

Subepithelial autoimmune blistering dermatoses are a group of rare skin disorders that are characterized by the disruption of the dermal-epidermal junction through the action of autoantibodies. The third article in this continuing medical education series explores the background, epidemiology, clinical features, and diagnostic criteria of each of the major subepithelial autoimmune blistering dermatoses, including bullous pemphigoid, pemphigoid gestationis, lichen planus pemphigoides, mucous membrane pemphigoid, linear IgA bullous dermatosis, and dermatitis herpetiformis.

Dermatological Manifestations in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) may be associated with extra-intestinal manifestations. Among these, mucocutaneous manifestations are relatively frequent, often difficult to diagnose and treat, and may complicate the course of the underlying disease. In the present review, a summary of the most relevant literature on the dermatologic manifestations occurring in patients with inflammatory bowel diseases has been reviewed. The following dermatological manifestations associated with IBDs have been identified: (i) specific manifestations with the same histological features of the underlying IBD (occurring only in Crohn's disease); (ii) cutaneous disorders associated with IBDs (such as aphthous stomatitis, erythema nodosum, psoriasis, epidermolysis bullosa acquisita); (iii) reactive mucocutaneous manifestations of IBDs (such as pyoderma gangrenosum, Sweet's syndrome, bowel-associated dermatosis-arthritis syndrome, aseptic abscess ulcers, pyodermatitis-pyostomatitis vegetans, etc.); (iv) mucocutaneous conditions secondary to treatment (including injection site reactions, infusion reactions, paradoxical reactions, eczematous and psoriasis-like reactions, cutaneous infections, and cutaneous malignancies); (v) manifestations due to nutritional malabsorption (such as stomatitis, glossitis, angular cheilitis, pellagra, scurvy, purpura, acrodermatitis enteropathica, phrynoderma, seborrheic-type dermatitis, hair and nail abnormalities). An accurate dermatological examination is essential in all IBD patients, especially in candidates to biologic therapies, in whom drug-induced cutaneous reactions may assume marked clinical relevance.

The G Protein-Coupled Receptor (GPR) 15 Counteracts Antibody-Mediated Skin Inflammation

The G protein-coupled receptor 15 (GPR15) has recently been highlighted as an important regulator of T cell trafficking into the gut under physiological and pathophysiological conditions. Additionally, circumstantial evidence has accumulated that GPR15 may also play a role in the regulation of chronic inflammation. However, the (patho)physiological significance of GPR15 has, in general, remained rather enigmatic. In the present study, we have addressed the role of GPR15 in the effector phase of autoantibody-mediated skin inflammation, specifically in the antibody transfer mouse model of bullous pemphigoid-like epidermolysis bullosa acquisita (BP-like EBA). Subjecting Gpr15 ^-/- mice to this model, we have uncovered that GPR15 counteracts skin inflammation. Thus, disease was markedly aggravated in Gpr15 ^-/- mice, which was associated with an increased accumulation of γδ T cells in the dermis. Furthermore, GPR15L, the recently discovered cognate ligand of GPR15, was markedly upregulated in inflamed skin. Collectively, our results highlight GPR15 as counter-regulator of neutrophilic, antibody-mediated cutaneous inflammation. Enhancing the activity of GPR15 may therefore constitute a novel therapeutic principle in the treatment of pemphigoid diseases, such as BP-like EBA.

IgG Fc N-Glycosylation Translates MHCII Haplotype into Autoimmune Skin Disease

The major histocompatibility complex haplotype represents the most prevalent genetic risk factor for the development of autoimmune diseases. However, the mechanisms by which major histocompatibility complex-associated genetic susceptibility translates into autoimmune disease are not fully understood. Epidermolysis bullosa acquisita is an autoimmune skin-blistering disease driven by autoantibodies to type VII collagen. Here, we investigated autoantigen-specific plasma cells, CD4⁺ T cells, and IgG fraction crystallizable glycosylation in murine epidermolysis bullosa acquisita in congenic mouse strains with the disease-permitting H2s or disease-nonpermitting H2b major histocompatibility complex II haplotypes. Mice with an H2s haplotype showed increased numbers of autoreactive CD4⁺ T cells and elevated IL-21 and IFN-γ production, associated with a higher frequency of IgG autoantibodies with an agalactosylated, proinflammatory N-glycan moiety. Mechanistically, we show that the altered antibody glycosylation leads to increased ROS release from neutrophils, the main drivers of autoimmune inflammation in this model. These results indicate that major histocompatibility complex II-associated susceptibility to autoimmune diseases acuminates in a proinflammatory IgG fraction crystallizable N-glycosylation pattern and provide a mechanistic link to increased ROS release by neutrophils.

Epidermolysis Bullosa Acquisita: A Case Report

Patient: Male, 79-year-old

Final Diagnosis: Epidermal bullosa acquisita (differential: anti-epiligrin variants of pemphigoid)

Symptoms: Multiple blisters on hands and feet

Medication: Dapsone

Clinical Procedure: Direct immunofluorescence (DIF) • hematoxylin and eosin (H&E) punch biopsies

Specialty: Dermatology

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.

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.

Resolution in bullous pemphigoid

Pemphigoid diseases are a group of autoimmune blistering skin diseases defined by an immune response against certain components of the dermal-epidermal adhesion complex. They are prototypical, autoantibody-driven, organ-specific diseases with the emergence of inflammatory skin lesions dependent on the recruitment of immune cells, particularly granulocytes, into the skin. During an acute flare of disease, inflammatory skin lesions typically progressing from erythema through urticarial plaques to subepidermal blisters erosions erupt and, finally, completely resolve, thus illustrating that resolution of inflammation is continuously executed in pemphigoid disease patients and can be directly monitored on the skin. Despite these superb conditions for examining resolution in pemphigoid diseases as paradigm diseases for antibody-induced tissue inflammation, the mechanisms of resolution in pemphigoid are underinvestigated and still largely elusive. In the last decade, mouse models for pemphigoid diseases were developed, which have been instrumental to identify several key pathways for the initiation of inflammation in these diseases. More recently, also protective pathways, specifically IL-10 and C5aR2 signalling on the molecular level and Tregs on the cellular level, counteracting skin inflammation have been highlighted and may contribute to the continuous execution of resolution in pemphigoid diseases. The upstream orchestrators of this process are currently under investigation. Pemphigoid disease patients, particularly bullous pemphigoid patients, who are predominantly above 75 years of age, often succumb to the side effects of the immunosuppressive therapeutics nowadays still required to suppress the disease. Pemphigoid disease patients may therefore represent a group of patients benefiting most substantially from the introduction of non-immunosuppressive, proresolving therapeutics into the treatment regimens for their disease.

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.

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.

Proteases in Pemphigoid Diseases

Pemphigoid diseases are a subgroup of autoimmune skin diseases characterized by widespread tense blisters. Standard of care typically involves immunosuppressive treatments, which may be insufficient and are often associated with significant adverse events. As such, a deeper understanding of the pathomechanism(s) of pemphigoid diseases is necessary in order to identify improved therapeutic approaches. A major initiator of pemphigoid diseases is the accumulation of autoantibodies against proteins at the dermal-epidermal junction (DEJ), followed by protease activation at the lesion. The contribution of proteases to pemphigoid disease pathogenesis has been investigated using a combination of in vitro and in vivo models. These studies suggest proteolytic degradation of anchoring proteins proximal to the DEJ is crucial for dermal-epidermal separation and blister formation. In addition, proteases can also augment inflammation, expose autoantigenic cryptic epitopes, and/or provoke autoantigen spreading, which are all important in pemphigoid disease pathology. The present review summarizes and critically evaluates the current understanding with respect to the role of proteases in pemphigoid diseases.

Skin Barrier and Autoimmunity-Mechanisms and Novel Therapeutic Approaches for Autoimmune Blistering Diseases of the Skin

One of the most important functions of the skin besides regulating internal body temperature includes formation of the barrier between the organism and the external environment, hence protecting against pathogen invasion, chemical and physical assaults and unregulated loss of water and solutes. Disruption of the protective barrier is observed clinically in blisters and erosions of the skin that form in autoimmune blistering diseases where the body produces autoantibodies against structural proteins of the epidermis or the epidermal-dermal junction. Although there is no cure for autoimmune skin blistering diseases, immune suppressive therapies currently available offer opportunities for disease management. In cases where no treatment is sought, these disorders can lead to life threatening complications and current research efforts have focused on developing therapies that target autoantibodies which contribute to disease symptoms. This review will outline the involvement of the skin barrier in main skin-specific autoimmune blistering diseases by describing the mechanisms underpinning skin autoimmunity and review current progress in development of novel therapeutic approaches targeting the underlying causes of autoimmune skin 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]

Epidermolysis bullosa acquisita (EBA) is a rare acquired subepidermal bullous autoimmune dermatosis, associated with autoantibodies against collagen type VII, the most important component of dermal anchoring fibrils. Blister induction occurs after binding of autoantibodies to collagen type VII, leading to complement activation, recruitment of neutrophils and secretion of proteases. Clinically, the disease is mostly characterized by tense blisters on trauma-exposed body areas which heal with scarring (mechanobullous form of EBA). The second most frequent subtype of EBA is inflammatory EBA, a bullous pemphigoid-like disease associated with pruritus. Involvement of mucous membranes and/or lesions in the head and neck area additionally point to the diagnosis of EBA. The mechanobullous type of EBA and EBA with intensive mucous membrane lesions display a chronic course and are often extremely resistant to therapy. Topical and systemic glucocorticoids, dapsone, colchicine, classical immunosuppressants, anti-CD20 antibodies, immunoadsorption or intravenous immunoglobulins have been reported as treatments.

Drug Discovery for Pemphigoid Diseases

Pemphigoid diseases (PDs) are a group of autoimmune bullous diseases characterized and caused by autoantibodies targeting structural proteins of the skin and mucous membranes. Chronic inflammation, subepidermal blistering, and often scaring are the clinical characteristics of PDs. Itching and, in severe cases, disabilities resulting from scaring (i.e., blindness, esophageal strictures) are the leading subjective symptoms. Treatment of PDs, which is based on nonspecific immunosuppression, is challenging because of frequent relapses, lack of efficacy, and numerous adverse events. In addition, the incidence of PDs is increasing. Given the high morbidity, limited therapeutic options, and increasing incidence, there is a growing urgency for drug discovery to help treat this condition. The recent development of PD model systems has added to the understanding of PD pathogenesis and, based on these insights, new clinical trials will soon be launched. The (auto-)antibody transfer PD models allow for investigations into autoantibody-mediated tissue pathology, while immunization-induced PD models more closely resemble the clinical situation. The latter duplicate all aspects of the human disease and are useful for investigating PD pathogenesis and testing therapeutic interventions. This article describes antibody transfer and immunization-induced PD mouse models currently employed for translational PD research. © 2019 by John Wiley & Sons, Inc.

Biomarkers related to bullous pemphigoid activity and outcome

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease of the skin. Investigation of the BP-associated pathophysiological processes during the last decades showed that the generation of autoantibodies directed against the hemidesmosome proteins BP180 and BP230, a hallmark of the BP-associated autoimmune response, leads to the recruitment of inflammatory immune cells at the dermal-epidermal junction, and subsequently to the release of a large amount of inflammatory molecules involved in blister formation. Analysis in transversal and longitudinal studies of autoantibodies and inflammatory molecules production both at the time of diagnosis and under treatment was mainly performed within the serum but also in the blister fluid. Some autoimmune or inflammatory molecules expression was related to the presence of clinical signs, while others were mere bystanders. In this review, we focused on the autoimmune and inflammatory molecules that have been identified as potential biomarkers of BP development and outcome.

[Immunoadsorption in dermatology]

Autoimmmune bullous diseases are mediated by pathogenetically relevant autoantibodies against components of the epidermis and/or superficial mucous membranes (in pemphigus) and structural proteins of the dermal-epidermal junction (in pemphigoid diseases). Using immunoadsorption (IA), an already well-established procedure in cardiac and rheumatic disorders, antibodies can be removed from the plasma. At present, most data on the adjuvant use of IA in dermatology are derived from patients with severe and/or refractory pemphigus vulgaris or pemphigus foliaceus and also from patients with pemphigoid diseases. Additionally, in the last few years different protocols for IA in patients with severe atopic dermatitis and elevated total serum IgE levels have been published. While panimmunoglobulin adsorbers are mainly used in dermatology, an IgE-specific adsorber has been used in some patients with atopic dermatitis and in the future, antigen-specific adsorbers are to be expected that will enable the specific reduction of autoantibodies.

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.

Autoimmune Subepidermal Bullous Diseases of the Skin and Mucosae: Clinical Features, Diagnosis, and Management

Autoimmune subepidermal blistering diseases of the skin and mucosae constitute a large group of sometimes devastating diseases, encompassing bullous pemphigoid, gestational pemphigoid, mucous membrane pemphigoid, epidermolysis bullosa acquisita, and anti-p200 pemphigoid. Their clinical presentation is polymorphic. These autoimmune blistering diseases are associated with autoantibodies that target distinct components of the basement membrane zone of stratified epithelia. These autoantigens represent structural proteins important for maintenance of dermo-epidermal integrity. Bullous pemphigoid (BP) is the most common subepidermal autoimmune blistering disease of the skin and mucosae. Although the disease typically presents with a generalized blistering eruption associated with itch, atypical variants with either localized bullous lesions or "non-bullous" presentations are observed in approximately 20% of patients. A peculiar form of BP typically associated with pregnancy is pemphigoid gestationis. In anti-p200 pemphigoid, patients present with tense blisters on erythematosus or normal skin resembling BP, with a predilection for acral surfaces. These patients have antibodies targeting the 200-kDa basement membrane protein. Epidermolysis bullosa is a rare autoimmune blistering disease associated with autoantibodies against type VII collagen that can have several phenotypes including a classical form mimicking dystrophic epidermolysis bullosa, an inflammatory presentation mimicking BP, or mucous membrane pemphigoid-like lesions. Mucous membrane pemphigoid (MMP) is the term agreed upon by international consensus for an autoimmune blistering disorder, which affects one or more mucous membrane and may involve the skin. The condition involves a number of different autoantigens in the basement membrane zone. It may result in severe complications from scarring, such as blindness and strictures. Diagnosis of these diseases relies on direct immunofluorescence microscopy studies and immunoserological assays. Management of affected patients is often challenging. We will here review the clinical and immunopathological features as well as the pathophysiology of this group of organ-specific autoimmune diseases. Finally, we will discuss the diagnostic approach and the principles of management in clinical practice.

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.

Regulatory T-cell deficiency leads to pathogenic bullous pemphigoid antigen 230 autoantibody and autoimmune bullous disease

BACKGROUND

Autoimmune bullous diseases/dermatoses (AIBDs) are severe autoantibody-mediated skin diseases. The pathogenic relevance of autoreactive CD4⁺ T cells for the induction of autoantibody production remains to be fully evaluated. Scurfy mice lack functional regulatory T (Treg) cells, experience spontaneous activation of autoreactive CD4⁺ T cells, and display severe erosive skin lesions suggestive of AIBDs.

OBJECTIVE

We sought to determine whether AIBDs develop in Treg cell-deficient scurfy mice.

METHODS

Histology, indirect immunofluorescence (IF) microscopy, direct IF, and ELISA were used to prove the presence of AIBDs in scurfy mice. Monoclonal autoantibodies from sera of scurfy mice were screened by using indirect IF on murine skin, and immunoprecipitation and mass spectrometry were used for target antigen identification, followed by confirmation in modified human embryonic kidney cells and murine keratinocytes. Pathogenicity was determined by injecting the autoantibody into neonatal mice and transferring scurfy CD4⁺ T cells into nu/nu mice.

RESULTS

Autoantibodies against different known autoantigens of AIBDs spontaneously develop in scurfy mice. Histology reveals subepidermal blisters, and direct IF of skin of scurfy mice shows a predominant linear staining pattern. The mAb 20B12 shows a linear staining pattern in indirect IF, recognizes the murine hemidesmosomal protein bullous pemphigoid antigen 230 (BP230) as the target antigen, and cross-reacts with human BP230. Purified mAb 20B12 induces subepidermal blisters in neonatal mice. Transfer of scurfy CD4⁺ T cells is sufficient to induce antibodies with reactivity to AIBD autoantigens and subepidermal blisters in the skin of recipient T cell-deficient nu/nu mice.

CONCLUSION

We show that the absence of Treg cells leads to AIBDs by pathogenic autoantibodies targeting BP230.

The critical role of C5a as an initiator of neutrophil-mediated autoimmune inflammation of the joint and skin

The deposition of IgG autoantibodies in peripheral tissues and the subsequent activation of the complement system, which leads to the accumulation of the anaphylatoxin C5a in these tissues, is a common hallmark of diverse autoimmune diseases, including rheumatoid arthritis (RA) and pemphigoid diseases (PDs). C5a is a potent chemoattractant for granulocytes and mice deficient in its precursor C5 or its receptor C5aR1 are resistant to granulocyte recruitment and, consequently, to tissue inflammation in several models of autoimmune diseases. However, the mechanism whereby C5a/C5aR regulates granulocyte recruitment in these diseases has remained elusive. Mechanistic studies over the past five years into the role of C5a/C5aR1 in the K/BxN serum arthritis mouse model have provided novel insights into the mechanisms C5a/C5aR1 engages to initiate granulocyte recruitment into the joint. It is now established that the critical actions of C5a/C5aR1 do not proceed in the joint itself, but on the luminal endothelial surface of the joint vasculature, where C5a/C5aR1 mediate the arrest of neutrophils on the endothelium by activating β₂ integrin. Then, C5a/C5aR1 induces the release of leukotriene B₄ (LTB₄) from the arrested neutrophils. The latter, subsequently, initiates by autocrine/paracrine actions via its receptor BLT1 the egress of neutrophils from the blood vessel lumen into the interstitial. Compelling evidence suggests that this C5a/C5aR1-LTB₄/BLT1 axis driving granulocyte recruitment in arthritis may represent a more generalizable biological principle critically regulating effector cell recruitment in other IgG autoantibody-induced diseases, such as in pemphigoid diseases. Thus, dual inhibition of C5a and LTB₄, as implemented in nature by the lipocalin coversin in the soft-tick Ornithodoros moubata, may constitute a most effective therapeutic principle for the treatment of IgG autoantibody-driven 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.

Whole-Genome Expression Profiling in Skin Reveals SYK As a Key Regulator of Inflammation in Experimental Epidermolysis Bullosa Acquisita

Because of the morbidity and limited therapeutic options of autoimmune diseases, there is a high, and thus far, unmet medical need for development of novel treatments. Pemphigoid diseases, such as epidermolysis bullosa acquisita (EBA), are prototypical autoimmune diseases that are caused by autoantibodies targeting structural proteins of the skin, leading to inflammation, mediated by myeloid cells. To identify novel treatment targets, we performed cutaneous genome-wide mRNA expression profiling in 190 outbred mice after EBA induction. Comparison of genome-wide mRNA expression profiles in diseased and healthy mice, and construction of a co-expression network identified Sykb (spleen tyrosine kinase, SYK) as a major hub gene. Aligned, pharmacological SYK inhibition protected mice from experimental EBA. Using lineage-specific SYK-deficient mice, we identified SYK expression on myeloid cells to be required to induce EBA. Within the predicted co-expression network, interactions of Sykb with several partners (e.g., Tlr13, Jdp2, and Nfkbid) were validated by curated databases. Additionally, novel gene interaction partners of SYK were experimentally validated. Collectively, our results identify SYK expression in myeloid cells as a requirement to promote inflammation in autoantibody-driven pathologies. This should encourage exploitation of SYK and SYK-regulated genes as potential therapeutic targets for EBA and potentially other autoantibody-mediated diseases.

Epidermal aspects of type VII collagen: Implications for dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita

Type VII collagen (COL7), a major component of anchoring fibrils in the epidermal basement membrane zone, has been characterized as a defective protein in dystrophic epidermolysis bullosa and as an autoantigen in epidermolysis bullosa acquisita. Although COL7 is produced and secreted by both epidermal keratinocytes and dermal fibroblasts, the role of COL7 with regard to the epidermis is rarely discussed. This review focuses on COL7 physiology and pathology as it pertains to epidermal keratinocytes. We summarize the current knowledge of COL7 production and trafficking, its involvement in keratinocyte dynamics, and epidermal carcinogenesis in COL7 deficiency and propose possible solutions to unsolved issues in this field.

Regulatory T Cells Suppress Inflammation and Blistering in Pemphigoid Diseases

Regulatory T cells (Tregs) are well known for their modulatory functions in adaptive immunity. Through regulation of T cell functions, Tregs have also been demonstrated to indirectly curb myeloid cell-driven inflammation. However, direct effects of Tregs on myeloid cell functions are insufficiently characterized, especially in the context of myeloid cell-mediated diseases, such as pemphigoid diseases (PDs). PDs are caused by autoantibodies targeting structural proteins of the skin. Autoantibody binding triggers myeloid cell activation through specific activation of Fc gamma receptors, leading to skin inflammation and subepidermal blistering. Here, we used mouse models to address the potential contribution of Tregs to PD pathogenesis in vivo. Depletion of Tregs induced excessive inflammation and blistering both clinically and histologically in two different PD mouse models. Of note, in the skin of Treg-depleted mice with PD, we detected increased expression of different cytokines, including Th2-specific IL-4, IL-10, and IL-13 as well as pro-inflammatory Th1 cytokine IFN-γ and the T cell chemoattractant CXCL-9. We next aimed to determine whether Tregs alter the migratory behavior of myeloid cells, dampen immune complex (IC)-induced myeloid cell activation, or both. In vitro experiments demonstrated that co-incubation of IC-activated myeloid cells with Tregs had no impact on the release of reactive oxygen species (ROS) but downregulated β2 integrin expression. Hence, Tregs mitigate PD by altering the migratory capabilities of myeloid cells rather than their release of ROS. Modulating cytokine expression by administering an excess of IL-10 or blocking IFN-γ may be used in clinical translation of these findings.

Nanoparticles prepared from porcine cells support the healing of cutaneous inflammation in mice and wound re-epithelialization in human skin

Previous reports have demonstrated that cell-derived nanoparticles (CDNPs) composed of bovine or porcine protein complexes exerted therapeutic effects against viral infections and cancer in mice and humans. Based on these observations, we asked whether CDNPs would improve inflammatory skin disorders. To address this, we utilized two distinct mouse models of cutaneous inflammation: the autoimmune skin-blistering disease epidermolysis bullosa acquisita (EBA) as an example of an autoantibody-induced cutaneous inflammation, and Leishmania major (L. major) infection as an example of a pathogen-induced cutaneous inflammation. In both models, we observed that CDNPs increased mRNA expression of the Th2 cytokine IL-4. Clinically, CDNPs decreased inflammation due to EBA and increased L. major-specific IgG1 levels without major effects on infected skin lesions. In addition, CDNPs supported the growth of keratinocytes in human skin cultures. In vitro studies revealed that CDNPs were taken up predominantly by macrophages, leading to a shift towards the expression of anti-inflammatory cytokine genes. Altogether, our data demonstrate that treatment with porcine CDNPs may be a new therapeutic option for the control of autoimmune-mediated inflammatory skin disorders.