Autoantibodies in a subgroup of patients with linear IgA disease react with the NC16A domain of BP1801

Linear IgA bullous dermatosis-a fifty year experience of Warsaw Center of bullous diseases

Linear IgA bullous dermatosis (LABD) is a rare subepidermal blistering disorder characterized by the presence of linear IgA deposits at the basement membrane zone (BMZ) by direct immunofluorescence (DIF). This entity was first described by Chorzelski and Jablonska from Warsaw Center of Bullous Diseases, Poland. The disease affects children and adults, whereby they differ in terms of clinical picture and course. Among polish patients with LABD mucous membrane involvement was exceptional, although, we reported a case presenting severe scarring of esophagus and conjunctivae with circulating IgG and IgA antibodies to LAD-1 antigen. Severe mucosal involvement was also observed in IgA-epidermolysis bullosa acquisita (EBA). Immunologically, LABD is characterized by circulating IgA antibodies directed to several epitopes of antigen BP180: LAD-1, 97kD, NC16A. Other BMZ antigens, like BP230, laminin 332, type VII collagen or p200 may be affected. We as a first published a case of anti-p200kD pemphigoid mediated by IgA. Our immunoelectron microscopic studies showed that the epitopes recognized by LABD sera are ultrastructurally localized in the lamina lucida. The antigenic heterogeneity, low titer of IgA antibodies and the lack of commercially available tests for some antigens (LAD-1, p200kD) makes the diagnosis challenging in many cases. It is under debate whether these cases are the subtypes of LABD or they represent a separate entities (IgA-p200 pemphigoid, IgA-MMP or IgA-EBA). Since, they differ in terms of clinical course, mucosal involvement, coexisting disorders, response to the treatment and prognosis, their differentiation is mandatory. In the literature there are many cases with undetectable circulating IgA antibodies in whom LABD was recognized based on DIF only. To avoid misdiagnosis, more sophisticated methods should be used, like direct immunoeletron microscopy (IEM), which is a time-consuming technique. The alternative for IEM may be: a) analysis of the BMZ serration pattern, b) immunofluorescence mapping of blister, c) direct salt split (patient's) skin, d) fluorescence overlay antigen mapping by laser scanning confocal microscopy. The two latter methods were established by the authors years ago and they allowed precise diagnosis (i.e., differentiation LABD from IgA-EBA), initiation of proper therapy and assessment of prognosis in many cases mediated by IgA.

Improvement of immunological tests for detecting autoantibodies in patients with lamina lucida-type linear IgA bullous dermatosis

BACKGROUND

In the diagnosis of linear IgA bullous dermatosis (LABD), detection of IgA at the epidermal basement membrane zone and circulating IgA autoantibodies are essential. The disease has two subtypes, lamina lucida-type and sublamina densa-type, with 120 kDa LAD-1 and 97 kDa LABD97 as major autoantigens for lamina lucida-type. Normal human epidermal keratinocytes (NHEK) and HaCaT cells are widely used for immunoblotting (IB) in the diagnosis process, but they do not provide high sensitivity and semiquantitative analysis.

OBJECTIVE

To develop a more sensitive and convenient method for detecting IgA antibodies in lamina lucida-type LABD patients.

METHODS

The expressions of LAD-1 and LABD97 in lysates and culture supernatants from Ker-CT, HaCaT, DJM-1, and NHEK were compared. The sensitivity of IBs using concentrated culture supernatants of HaCaT and Ker-CT and ELISAs using several recombinant proteins (RPs) corresponding to BP180 ectodomain were compared using 55 sera from LABD patients.

RESULTS

In culture supernatant, Ker-CT expressed higher amounts of LAD-1 and LABD97. IBs using concentrated culture supernatant of HaCaT and Ker-CT showed 43 % and 46 % positivity to sera from LABD patients, respectively. In ELISAs, the RP of amino acids 490-1421 of BP180 showed the highest positivity (80.0 %) among several proteins. Additionally, this ELISA showed reduced OD values in LABD and related diseases patients' sera at remission.

CONCLUSION

The ELISA using the RP coding amino acids 490-1421 of BP180 is useful for identifying IgA antibodies and monitoring disease activity in lamina lucida-type LABD patients.

Case report: Dupilumab: a promising treatment option for adult linear IgA bullous dermatosis with severe pruritus

Linear IgA bullous dermatosis (LABD) is an acquired autoimmune subepidermal blistering disorder. Diagnosis always relies on skin pathology and direct immunofluorescence (DIF), with typical linear deposits of IgA along the basement membrane zone (BMZ). The typical clinical manifestation is tense bullae arranged like the "string of pearls" companied with severe pruritus. Dapsone is often considered first-line therapy for LABD, and it is necessary to test the HLA-B*1301 gene to prevent the occurrence of dapsone-induced hypersensitivity syndrome (DHS). Here we report a case of LABD resistant to corticosteroid and sulfasalazine, while waiting for HLA-B*1301 gene test results, dupilumab was used to control severe pruritus.

Reactivity against the BP180 ectodomain in patients with bullous pemphigoid, mucous membrane pemphigoid, multiple sclerosis and Parkinson disease

The 16th non-collagenous domain (NC16A) of BP180 is the main antigenic target of autoantibodies in bullous pemphigoid (BP) and mucous membrane pemphigoid (MMP). Commercially available assays detect serum autoantibodies against NC16A in the majority of BP (80%-90%) and in approximately 50% of MMP patients. However, a standardized test system for detecting antibodies against other regions of BP180 is still lacking. Moreover, anti-BP180 autoantibodies have been found in neurological conditions such as multiple sclerosis and Parkinson disease. This study aimed at identifying primary epitopes recognized by BP autoantibodies on the BP180 ectodomain. Serum samples of 51 BP and 30 MMP patients both without anti-NC16A reactivity were included along with 44 multiple sclerosis and 75 Parkinson disease sera. Four overlapping His-tagged proteins covering the entire BP180 ectodomain (BP180(ec)1-4) were cloned, expressed, purified and tested for reactivity by immunoblot. IgG antibodies to BP180(ec)3 were detected in 98% of BP, 77% of MMP and 2% of normal human sera. Only weak reactivity was detected for neurological diseases against BP180(ec)1, BP180(ec)2 and BP180(ec)4, in 3%, 11% and 7% of tested multiple sclerosis sera, respectively. 8% of Parkinson disease sera reacted with BP180(ec)2 and 9% with BP180(ec)4. In conclusion, this study successfully identified epitopes recognized by BP autoantibodies outside the NC16A domain in pemphigoid diseases. These findings contribute to a better understanding of the immune response in BP and MMP with potential implications for a future diagnostic assay for NC16A-negative pemphigoid patients.

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.

Anti-NC16A IgA from Patients with Linear IgA Bullous Dermatosis Induce Neutrophil-Dependent Subepidermal Blistering in Mice

Linear IgA bullous dermatosis (LABD) is an acquired autoimmune subepidermal blistering skin disease characterized by circulating and tissue-bound IgA autoantibodies that recognize epitopes within the hemidesmosomal protein BP180, including its NC16A domain. Histologically, LABD has long been defined by neutrophil infiltration and dermal-epidermal separation. However, the pathogenic roles of anti-NC16A IgA and neutrophils in LABD, as well as their interactions, have not been thoroughly studied. We show that passive transfer of patient-derived anti-NC16A IgA induce clinical and histologic LABD pathology in humanized NC16A mice that are reconstituted locally or systemically with human neutrophils. The lesional skin of mice exhibits significantly elevated levels of the neutrophil chemoattractants CXCL-1 and CXCL-2. Furthermore, we show significantly increased levels of the neutrophil chemoattractant IL-8 in blister fluids of patients with LABD. This study provides direct evidence that anti-NC16A IgA in patients with LABD are pathogenic and interact with neutrophils to mediate tissue injury and subepidermal blister formation. This study further corroborates the importance of neutrophil-mediated tissue injury in LABD disease physiology and establishes a clinically relevant in vivo model system that can be used to systematically dissect the immunopathogenesis of LABD.

A life for autoimmune blistering diseases: in memoriam Detlef Zillikens

Detlef Zillikens, MD, director and chair of the Department of Dermatology at the University of Lübeck, Lübeck, Germany, died in September 2022, aged only 64. He dedicated his professional life to autoimmune blistering diseases (AIBDs) and built his department into one of the world's leading centers for these diseases. Herein, his professional life and the impact on the field of AIBDs and the research landscape at the University of Lübeck are addressed. With his warm, integrative, open-minded, ever-optimistic attitude, he was a highly reliable colleague, mentor, and friend to many in the field including each of the authors. Combined with his in-depth knowledge of dermatology, interest in many fields of life science, and hard work, Detlef Zillikens initiated the founding of two independent research institutes, the Lübeck Institute of Experimental Dermatology and the Institute and Comprehensive Center for Inflammation Medicine. He was also instrumental in establishing the Center for Research on Inflammation of the Skin, where in a new research building, over 140 scientists pursue research questions related to skin inflammation. By inviting numerous researchers and clinicians to his department and hosting two large international meetings, he brought the field of AIBDs much closer together and inspired multiple national and international research initiatives. His ideas will live on and grow in many of his colleagues and mentees.

Type XVII collagen: Relevance of distinct epitopes, complement-independent effects, and association with neurological disorders in pemphigoid disorders

Pemphigoid diseases (PD) are autoimmune skin blistering diseases characterized by autoantibodies directed against proteins of the cutaneous basement membrane zone (BMZ). One of the major antigens is type XVII collagen (BP180), a transmembrane glycoprotein, which is targeted in four PDs: bullous pemphigoid, mucous membrane pemphigoid, linear IgA dermatosis, and pemphigoid gestationis. To date, different epitopes on BP180 have been described to be recognized by PD disease patients’ autoantibodies. Different BP180 epitopes were associated with distinct clinical phenotypes while the underlying mechanisms are not yet fully understood. So far, the main effects of anti-BP180 reactivity are mediated by Fcγ-receptors on immune cells. More precisely, the autoantibody–antigen interaction leads to activation of complement at the BMZ and infiltration of immune cells into the upper dermis and, by the release of specific enzymes and reactive oxygen species, to the degradation of BP180 and other BMZ components, finally manifesting as blisters and erosions. On the other hand, inflammatory responses independent of Fcγ-receptors have also been reported, including the release of proinflammatory cytokines and internalization and depletion of BP180. Autoantibodies against BP180 can also be found in patients with neurological diseases. The assumption that the clinical expression of PD depends on epitope specificity in addition to target antigens, autoantibody isotypes, and antibody glycosylation is supported by the observation that epitopes of PD patients differ from those of PD patients. The aim of the present review is to describe the fine specificities of anti-BP180 autoantibodies in different PDs and highlight the associated clinical differences. Furthermore, the direct effects after binding of the autoantibodies to their target are summarized.

Evaluation and Comparison of Clinical and iLaboratory Characteristics of Patients With IgA Epidermolysis Bullosa Acquisita, Linear IgA Bullous Dermatosis, and IgG Epidermolysis Bullosa Acquisita

Importance

Immunoglobulin A (IgA) epidermolysis bullosa acquisita (EBA) is an autoimmune skin blistering disease with IgA autoantibodies directed against type VII collagen. There is debate whether it should be considered part of the clinical spectrum of linear IgA bullous dermatosis (LABD) or a separate disease entity.

Objective

This cohort study aimed to define the clinical features and treatment responses of IgA EBA and anti-BP180-driven LABD, and to compare the prevalences of IgA EBA anti-BP180 LABD and classic IgG-mediated EBA in an autoimmune diagnostic laboratory database.

Design, Setting, and Participants

This retrospective cohort study and case series study included demographic, immunopathologic, and serologic data from 300 patients diagnosed with IgA EBA, IgG EBA, or LABD. Furthermore, clinical features and treatment responses of IgA EBA were analyzed in a case series including 4 patients with IgA EBA. All patients from the database of the autoimmune diagnostic laboratory at the Department of Dermatology, University of Lübeck, Germany, who were diagnosed with IgA EBA, LABD, or IgG EBA between October 2010 and July 2019 were included. Four patients diagnosed with IgA EBA between October 2015 and January 2018 are described in detail.

Main Outcomes and Measures

The clinical course of IgA EBA was observed before and during different treatments.

Results

The database search yielded 21 cases of IgA EBA (12 females [57%]/9 males [43%]), 222 cases of LABD (111 females [51%]/106 males [49]), and 57 cases of IgG EBA (29 females [50%]/28 males [48%]). The median (range) age of each cohort was 64 (4-81) years for IgA EBA, 56 (3-92) years for IgG EBA, and significantly older compared with IgG EBA (P = .002) for those with LAPD (median [range], 70 [1-94] years). The patients with IgA EBA exhibited heterogeneous clinical presentations that significantly differed from those of anti-BP180 LABD. All 4 patients with IgA EBA described in detail were first treated with dapsone, but only 1 responded to this treatment. The others required treatment with high-dose dexamethasone, rituximab, and/or intravenous immunoglobulins to achieve partial clinical remission.

Conclusions and Relevance

Overall, the findings of this cohort study and small case series suggest that IgA EBA may be more common than expected and may require more intensive systemic treatment than LABD, suggesting it should be considered a separate disease entity.

Genetics and Omics Analysis of Autoimmune Skin Blistering Diseases

Autoimmune blistering diseases (AIBDs) of the skin are characterized by autoantibodies against different intra-/extracellular structures within the epidermis and at the basement membrane zone (BMZ). Binding of the antibodies to their target antigen leads to inflammation at the respective binding site and degradation of these structures, resulting in the separation of the affected skin layers. Clinically, blistering, erythema and lesions of the skin and/or mucous membranes can be observed. Based on the localization of the autoantigen, AIBDs can be divided into pemphigus (intra-epidermal blistering diseases) and pemphigoid diseases (sub-epidermal blistering diseases), respectively. Although autoantigens have been extensively characterized, the underlying causes that trigger the diseases are still poorly understood. Besides the environment, genetic factors seem to play an important role in a predisposition to AIBDs. Here, we review currently known genetic and immunological mechanisms that contribute to the pathogenesis of AIBDs. Among the most commonly encountered genetic predispositions for AIBDs are the HLA gene region, and deleterious mutations of key genes for the immune system. Particularly, HLA class II genes such as the HLA-DR and HLA-DQ alleles have been shown to be prevalent in patients. This has prompted further epidemiological studies as well as unbiased Omics approaches on the transcriptome, microbiome, and proteome level to elucidate common and individual genetic risk factors as well as the molecular pathways that lead to the pathogenesis of AIBDs.

Serological Diagnosis of Autoimmune Bullous Skin Diseases

Autoimmune bullous dermatoses (AIBD) encompass a variety of organ-specific autoimmune diseases that manifest with cutaneous and/or mucosal blisters and erosions. They are characterized by autoantibodies targeting structural proteins of the skin, which are responsible for the intercellular contact between epidermal keratinocytes and for adhesion of the basal keratinocytes to the dermis. The autoantibodies disrupt the adhesive functions, leading to splitting and blister formation. In pemphigus diseases, blisters form intraepidermally, whereas in all other disease types they occur subepidermally. Early identification of autoimmune bullous dermatoses is crucial for both treatment and prognosis, particularly as regards tumor-associated disease entities. The diagnosis is based on clinical symptoms, histopathology, direct immunofluorescence to detect antibody/complement deposits, and the determination of circulating autoantibodies. The identification of various target antigens has paved the way for the recent development of numerous specific autoantibody tests. In particular, optimized designer antigens and multiplex test formats for indirect immunofluorescence and ELISA have enhanced and refined the laboratory analysis, enabling highly efficient serodiagnosis and follow-up. This review elaborates on the current standards in the serological diagnostics for autoimmune bullous dermatoses.

Immunological methods for the diagnosis of oral mucosal diseases

Immunological methods, which have been widely used in autoimmune blistering diseases (AIBDs) of the oral mucosa, can also be adopted as auxiliary diagnostic tools in oral lichen planus (OLP) and discoid lupus erythematosus (DLE). AIBDs, characterized by autoantibodies against structural proteins of keratinocytes or the basement membrane zone, clinically present as blisters and erosions of the oral mucosa. When atypical lesions occur, OLP or DLE may be confused with AIBDs. The improvement of diagnostic accuracy is necessary due to the significant differences in treatment and prognosis among these diseases. A variety of immunological methods are used for qualitative and quantitative detection of target antigens and autoantibodies. These methods can evaluate efficacy of treatment, monitor diseases and guide treatment decisions. In this review, we discuss the application of immunofluorescence, biochemical tests, and protein microarrays for AIBDs, OLP and DLE, as well as the differential diagnostic methods using immunological tests.

Linear IgA bullous dermatosis

Aim: to present a clinical case of linear IgA bullous dermatosis.Materials and methods. A 44 years old patient complaining of skin rashes on the trunk and extremities, accompanied by severe itching was examined. We carried out a morphological investigation of biopsy samples derived from the lesion and apparently unaffected skin areas using the method of indirect immunofluorescence.Results. The patient having rashes in the form of multiple vesicles and small bubbles with a tight cover, which had been grouped into figures resembling pearl necklaces, demonstrated the presence of focal subepidermal cracks (subepidermal bubble in one location), as well as a linear deposition of IgA along the epidermal basement membrane. According to the clinical picture and following the histological and immunofluorescent investigation of skin biopsies, the patient was diagnosed with linear IgA bullous dermatosis. Lesion regression was achieved as a result of systemic therapy with prednisolone at a dose of 50 mg per day.Conclusion. The diagnosis of linear IgA bullous dermatosis should be made on the basis of skin biopsy investigation by the method of indirect immunofluorescence. Systemic glucocorticosteroids are seen as an effective approach to the treatment of such patients.

Diagnosis of Autoimmune Blistering Diseases

Autoimmune skin blistering diseases (AIBD) are characterized by autoantibodies that are directed against structural proteins in the skin and adjacent mucous membranes. Some clinical signs are typical for a specific AIBD, however, correct diagnosis requires the detection of tissue-bound or circulating autoantibodies. The gold standard for diagnosis of AIBD is the detection of autoantibodies or complement component 3 by direct immunofluorescence (DIF) microscopy of a perilesional biopsy. Circulating antibodies can be detected via indirect immunofluorescence (IIF) microscopy of different tissue substrates including human skin, monkey esophagus, and more recently, recombinant forms of the different target antigens. Latter are also employed in various commercial ELISA systems and by immunoblotting in in-house assays available in specialized laboratories. ELISA systems are also particularly valuable for monitoring of the disease activity during the disease course which can be helpful for treatment decisions. Exact diagnosis is essential for both treatment and prognosis, since some AIBD are associated with malign tumors such as paraneoplastic pemphigus and anti-laminin 332 mucous membrane pemphigoid. This review presents clinical and immunopathological features of AIBD for the state-of the art diagnosis of these disorders.

Prospective study in bullous pemphigoid: association of high serum anti-BP180 IgG levels with increased mortality and reduced Karnofsky score

BACKGROUND

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the two hemidesmosomal proteins, BP180 (type XVII collagen) and BP230. The multicentre prospective BLISTER (Bullous Pemphigoid Steroids and Tetracyclines) trial randomized 253 patients with BP to compare the benefits and harms between initial treatment with doxycycline or prednisolone.

OBJECTIVES

To analyse distinct autoantibody profiles for the prediction of the disease course in a well-characterized cohort of BP sera.

METHODS

One hundred and forty-three patients of the BLISTER trial consented to participate in this serological study. Sera taken at baseline were analysed by (i) indirect immunofluorescence, (ii) anti-BP180 NC16A (16th noncollagenous domain) and anti-BP230 enzyme-linked immunosorbent assay and (iii) immunoblotting with various substrates. Results were then linked with clinical parameters including age, Karnofsky score, number of blisters, related adverse events and mortality.

RESULTS

Disease activity correlated with immunoglobulin (Ig)G anti-BP180 levels but not with levels of anti-BP230 IgG and anti-BP180 IgE. High levels of both anti-BP180 IgG and anti-BP230 IgG were associated with a low Karnofsky score. The presence of anti-BP230 IgG was more frequent in older patients. Those with higher total IgE serum levels suffered from fewer adverse events. Higher IgG anti-BP180 levels were associated with an increased 1-year mortality rate.

CONCLUSIONS

Analysis of the autoantibody profile is not only of diagnostic relevance but may also be helpful in predicting the course of the disease.

Humoral Epitope Spreading in Autoimmune Bullous Diseases

Autoimmune blistering diseases are characterized by autoantibodies against structural adhesion proteins of the skin and mucous membranes. Extensive characterization of their autoantibody targets has improved understanding of pathogenesis and laid the basis for the study of antigens/epitopes diversification, a process termed epitope spreading (ES). In this review, we have reported and discussed ES phenomena in autoimmune bullous diseases and underlined their functional role in disease pathogenesis. A functional ES has been proposed: (1) in bullous pemphigoid patients and correlates with the initial phase of the disease, (2) in pemphigus vulgaris patients with mucosal involvement during the clinical transition to a mucocutaneous form, (3) in endemic pemphigus foliaceus, underlining its role in disease pathogenesis, and (4) in numerous cases of disease transition associated with an intermolecular diversification of immune response. All these findings could give useful information to better understand autoimmune disease pathogenesis and to design antigen/epitope specific therapeutic approaches.

BP180 Is Critical in the Autoimmunity of Bullous Pemphigoid

Bullous pemphigoid (BP) is by far the most common autoimmune blistering dermatosis that mainly occurs in the elderly. The BP180 is a transmembrane glycoprotein, which is highly immunodominant in BP. The structure and location of BP180 indicate that it is a significant autoantigen and plays a key role in blister formation. Autoantibodies from BP patients react with BP180, which leads to its degradation and this has been regarded as the central event in BP pathogenesis. The consequent blister formation involves the activation of complement-dependent or -independent signals, as well as inflammatory pathways induced by BP180/anti-BP180 autoantibody interaction. As a multi-epitope molecule, BP180 can cause dermal-epidermal separation via combining each epitope with specific immunoglobulin, which also facilitates blister formation. In addition, some inflammatory factors can directly deplete BP180, thereby leading to fragility of the dermal-epidermal junction and blister formation. This review summarizes recent investigations on the role of BP180 in BP pathogenesis to determine the potential targets for the treatment of patients with BP.

Production of Neoepitopes by Dynamic Structural Changes on BP180/Type XVII Collagen

Linear IgA bullous dermatosis is characterized by IgA autoantibodies reactive with LAD-1 and LABD97, truncated forms of BP180 (type XVII collagen), but not with full-length BP180. Toyonaga et al. determined that cleavage within both the C-terminal region and NC16A domain plays a role in exposure of neoepitopes on the 15th collagenous domain of BP180.

C-Terminal Processing of Collagen XVII Induces Neoepitopes for Linear IgA Dermatosis Autoantibodies

Transmembrane collagen XVII (COL17) is a hemidesmosomal component of basal keratinocytes that can be targeted by autoantibodies in autoimmune blistering disorders, including linear IgA dermatosis (LAD). COL17 can be physiologically cleaved within the juxtamembranous extracellular NC16A domain, and LAD autoantibodies preferentially react with the processed ectodomains, indicating that the processing induces neoepitopes. However, the details of how neoepitopes develop have not been elucidated. In this study, we show that C-terminal processing of COL17 also plays a role in inducing neoepitopes for LAD autoantibodies. First, the mAb hC17-ect15 targeting the 15th collagenous domain of COL17 was produced, which showed characteristics similar to LAD autoantibodies. The mAbs preferentially reacted with C-terminally deleted (up to 682 amino acids) recombinant COL17, suggesting that C-terminal processing shows neoepitopes on the 15th collagenous domain. The LAD autoantibodies also react with C-terminal deleted COL17. Therefore, neoepitopes for LAD autoantibodies also develop after C-terminal processing. Finally, the passive transfer of the mAb hC17-ect15 into human COL17-expressing transgenic mice failed to induce blistering disease, suggesting that neoepitope-targeting antibodies are not always pathogenic. In summary, this study shows that C-terminal processing induces dynamic structural changes and neoepitopes for LAD autoantibodies on COL17.

Idiopathic linear IgA bullous dermatosis: prognostic factors based on a case series of 72 adults

BACKGROUND

Linear IgA bullous dermatosis (LABD) is a clinically and immunologically heterogeneous, subepidermal, autoimmune bullous disease (AIBD), for which the long-term evolution is poorly described.

OBJECTIVES

To investigate the clinical and immunological characteristics, follow-up and prognostic factors of adult idiopathic LABD.

METHODS

This retrospective study, conducted in our AIBD referral centre, included adults, diagnosed between 1995 and 2012, with idiopathic LABD, defined as pure or predominant IgA deposits by direct immunofluorescence. Clinical, histological and immunological findings were collected from charts. Standard histology was systematically reviewed, and indirect immunofluorescence (IIF) on salt-split skin (SSS) and immunoblots (IBs) on amniotic membrane extracts using anti-IgA secondary antibodies were performed, when biopsies and sera obtained at diagnosis were available. Prognostic factors for complete remission (CR) were identified using univariate and multivariate analyses.

RESULTS

Of the 72 patients included (median age 54 years), 60% had mucous membrane (MM) involvement. IgA IIF on SSS was positive for 21 of 35 patients tested; 15 had epidermal and dermal labellings. Immunoelectron microscopy performed on the biopsies of 31 patients labelled lamina lucida (LL) (26%), lamina densa (23%), anchoring-fibril zone (AFz) (19%) and LL+AFz (23%). Of the 34 IgA IBs, 22 were positive, mostly for LAD-1/LABD97 (44%) and full-length BP180 (33%). The median follow-up was 39 months. Overall, 24 patients (36%) achieved sustained CR, 19 (29%) relapsed and 35% had chronic disease. CR was significantly associated with age > 70 years or no MM involvement. No prognostic immunological factor was identified.

CONCLUSIONS

Patients with LABD who are < 70 years old and have MM involvement are at risk for chronic evolution.

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.

Serum autoantibodies against the dermal-epidermal junction in patients with chronic pruritic disorders, elderly individuals and blood donors prospectively recruited

BACKGROUND

Bullous pemphigoid (BP) is a subepidermal blistering autoimmune disease characterized by autoantibodies against two structural proteins of the epidermal basal membrane zone (BMZ), BP180 (type XVII collagen) and BP230. Patients are usually old and suffer from severe pruritus. Advanced age and severe pruritus have been hypothesized as potential risk factors for the development of autoantibodies in BP.

OBJECTIVES

To prospectively determine anti-BMZ antibodies in sera from patients with advanced age and/or pruritus compared with regular blood donors.

METHODS

Sera from (i) patients with chronic pruritic skin disorders (PSD, n = 78; mean age 62 years), (ii) patients with noninflammatory skin disease aged ≥ 70 years (n = 93; mean age 78 years), and (iii) blood donors (n = 50; mean age 41 years) were included. A large panel of validated test systems used for routine diagnosis were employed comprising indirect immunofluorescence (IF) microscopy on monkey oesophagus and human salt-split skin, BP180 NC16A- and BP230-specific enzyme-linked immunosorbent assay (ELISA) systems, and immunoblotting with various substrates, including LAD-1 (the soluble ectodomain of BP180), BP180, BP230, laminin 332, p200 antigen, laminin γ1 and type VII collagen.

RESULTS

No statistically significant difference was seen between the three study groups. The same result was obtained when data for IF microscopy, ELISA and immunoblotting were analysed separately.

CONCLUSIONS

Neither advanced age nor chronic pruritus have been verified as risk factors for autoantibodies against the epidermal BMZ.

Context-Dependent Regulation of Collagen XVII Ectodomain Shedding in Skin

Pemphigoid is a common autoimmune blistering disorder in which autoantibodies target transmembrane collagen XVII (COL17), a component of hemidesmosomes in basal keratinocytes. The ectodomain of COL17 can be cleaved from the cell surface within the juxtamembranous extracellular NC16A domain, and, interestingly, certain autoantibodies of pemphigoid patients preferentially react with the shed ectodomain. These findings suggest that COL17 ectodomain shedding generates neoepitopes on the shed form; however, the regulatory mechanism of the shedding in in vivo skin and the pathogenicity of the neoepitope-targeting antibodies still are uncertain. To address these issues, we produced rabbit antibodies specifically reacting with N-terminal cleavage sites of the shed COL17 ectodomain. The antibodies showed that certain amounts of the human COL17 ectodomain are cleaved physiologically at Gln(525) in in vivo skin. In contrast, migrating human keratinocytes cleave COL17 at Leu(524) but not at Gln(525). The passive transfer of antibodies reacting with an N-terminal cleavage site of the mouse COL17 ectodomain into neonatal wild-type mice failed to induce blister formation, even though the antibodies bound to the dermal-epidermal junctions, indicating that cleavage site-specific antibodies have reduced or absent pathogenicity for blister formation. This study shows the ectodomain shedding of COL17 to be a physiological event in in vivo human skin that probably generates nonpathologic epitopes on the cleavage sites.

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

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

Major cleavage-dependent epitopes for linear IgA bullous dermatosis are formed at the boundary between the non-collagenous 16A and collagenous 15 domains of BP180

BACKGROUND

The autoantigen for the major type of linear IgA bullous dermatosis (LAD, lamina lucida type) is the shed ectodomain of BP180. However, it is unknown why most LAD sera react with the shed ectodomain but not with the intact BP180/type XVII collagen.

OBJECTIVE

The aim of this study was to characterize the unique cleavage-dependent epitope(s) in the shed ectodomain.

METHODS

We used a monoclonal antibody (MAb-1337) and six LAD sera, which reacted preferentially with the shed ectodomain of BP180. The location and characteristics of the epitopes for these antibodies were analyzed mainly by immunoblotting using chimeric bovine-human BP180 mammalian recombinant proteins and variously truncated bacterial recombinant proteins.

RESULTS

LAD sera and MAb-1337 reacted with the plasmin-digested products of full-length BP180. Four of the six LAD sera reacted to a bacterial recombinant protein consisting of the human non-collagenous 16th A (NC16A) and the collagenous 15th (C15) domains, while these sera were negative or only faintly reactive with the NC16A and C15 recombinants. The epitope for MAb-1337 was localized to the COOH-terminal 21 amino acid region within the NC16A domain.

CONCLUSION

The results in this study indicate that the major epitopes for LAD sera are formed or exposed by a cleavage-induced conformational change, but not by a post-translational modification that occurs only in the shed ectodomain, and are located at the boundary between the NC16A and C15 domains.

Update on the pathogenesis of bullous pemphigoid: an autoantibody-mediated blistering disease targeting collagen XVII

Bullous pemphigoid (BP) is a common autoimmune blistering skin disorder that tends to affect the elderly. Autoantibodies (autoAbs) from BP patients react with two hemidesmosomal components: transmembrane collagen XVII (BP180 or BPAG2) and plakin family protein BP230 (BPAG1). Of these, collagen XVII (COL17) is thought to be a major autoantigen. The binding of autoAbs to COL17 following the activation of complements and inflammatory pathways eventually leads to the degradation of COL17, and this has been regarded as the main pathogenesis of BP. However, recent investigations have suggested other pathways, including a complement-independent pathway and a pathway involving IgE-autoAbs. BP-autoAbs can directly deplete COL17, leading to fragility of the dermal-epidermal junction. In addition, IgE-autoAbs to COL17 may be involved in the formation of itchy urticarial erythema associated with eosinophilic infiltration. This article summarizes the update on pathogenesis of BP, with a special focus on blister formation by autoAbs to COL17.

Diagnosis and classification of autoimmune blistering diseases

Blistering skin diseases are a group of autoimmune disorders that are characterized by autoantibodies against structural proteins of the epidermis or the dermal-epidermal junction and clinically by blisters and erosions on skin and/or mucous membranes. Since clinical criteria and histopathological characteristics are not sufficient for diagnosis, direct immunofluorescence microscopy of a biopsy specimen or serological tests are needed for exact diagnosis. The differentiation between the various disorders became more important since prognosis as well as different treatment options are nowadays available for the various diseases. Moreover, some bullous diseases may indicate the presence of an underlying malignancy. The detection of serum autoantibodies have been shown to correlate with disease activity and thus may be helpful in deciding treatment options for these patients.

Pemphigoid diseases

Pemphigoid diseases are a group of well defined autoimmune disorders that are characterised by autoantibodies against structural proteins of the dermal-epidermal junction and, clinically, by tense blisters and erosions on skin or mucous membranes close to the skin surface. The most common of these diseases is bullous pemphigoid, which mainly affects older people and the reported incidence of which in Europe has more than doubled in the past decade. Prognosis and treatments vary substantially between the different disorders and, since clinical criteria are usually not sufficient, direct immunofluorescence microscopy of a perilesional biopsy specimen or serological tests are needed for exact diagnosis. In eight pemphigoid diseases the target antigens have been identified molecularly, which has allowed the development of standard diagnostic assays for detection of serum autoantibodies-some of which are commercially available. In this Seminar we discuss the clinical range, diagnostic criteria, diagnostic assay systems, and treatment options for this group of diseases.

Linear IgA disease: clinical presentation, diagnosis, and pathogenesis

Linear IgA disease is one of the rarer subepidermal blistering diseases. Linear IgA disease is a chronic, acquired, autoimmune blistering disease that is characterized by subepidermal blistering and linear deposition of IgA basement membrane antibodies. The disease affects both children and adults and, although there are some differences in their clinical presentations, there is considerable overlap with shared immunopathology and immunogenetics.

Linear immunoglobulin A bullous dermatosis

Linear immunoglobulin A (IgA) bullous dermatosis, also known as linear IgA disease, is an autoimmune mucocutaneous disorder characterized by subepithelial bullae, with IgA autoantibodies directed against several different antigens in the basement membrane zone. Its immunopathologic characteristic resides in the presence of a continuous linear IgA deposit along the basement membrane zone, which is clearly visible on direct immunofluorescence. This disorder shows different clinical features and distribution when adult-onset of linear IgA disease is compared with childhood-onset. Diagnosis is achieved via clinical, histopathologic, and immunopathologic examinations. Two common therapies are dapsone and sulfapyridine, which reduce the inflammatory response and achieve disease remission in a variable period of time.

Linear IgA disease: clinical presentation, diagnosis, and pathogenesis

Linear IgA disease is one of the rarer subepidermal blistering diseases. Linear IgA disease is a chronic, acquired, autoimmune blistering disease that is characterized by subepidermal blistering and linear deposition of IgA basement membrane antibodies. The disease affects both children and adults and, although there are some differences in their clinical presentations, there is considerable overlap with shared immunopathology and immunogenetics.

The diagnosis and treatment of autoimmune blistering skin diseases

BACKGROUND

Autoimmune blistering skin diseases are a heterogeneous group of disorders associated with autoantibodies that are directed against desmosomal structural proteins (in pemphigus diseases) or hemidesmosomal ones (in pemphigoid diseases and epidermolysis bullosa acquisita), or else against epidermal/ tissue transglutaminases (in dermatitis herpetiformis). Knowledge of the clinical presentation of these disorders and of the relevant diagnostic procedures is important not just for dermatologists, but also for general practitioners, ophthalmologists, ENT specialists, dentists, gynecologists, and pediatricians.

METHODS

The literature on the subject was selectively reviewed. There are no existing guidelines available in Germany.

RESULTS

The recently developed sensitive and specific assays for circulating autoantibodies in these diseases now enable a serological diagnosis in about 90% of cases. The incidence of autoimmune blistering skin diseases in Germany has doubled in the last 10 years, to a current figure of about 25 new cases per million persons per year, because of improved diagnostic techniques as well as the aging of the population. Accurate and specific diagnosis is the prerequisite for reliable prognostication and appropriate treatment. For severe and intractable cases, more effective treatments have recently become available, including immunoadsorption, high-dose intravenous immunoglobulin, the anti-CD20 antibody rituximab, and combinations of the above.

CONCLUSION

The diagnostic assessment of autoimmune blistering skin diseases can be expected to improve in the near future as new serological testing systems are developed that employ recombinant forms of the target antigens. The treatments currently in use still need to be validated by prospective, controlled trials.

Development of an ELISA for sensitive and specific detection of IgA autoantibodies against BP180 in pemphigoid diseases

BACKGROUND

Pemphigoids are rare diseases associated with IgG, IgE and IgA autoantibodies against collagen XVII/BP180. An entity of the pemphigoid group is the lamina lucida-type of linear IgA disease (IgA pemphigoid) characterized by IgA autoantibodies against BP180. While for the detection of IgG and IgE autoantibodies specific to collagen XVII several ELISA systems have been established, no quantitative immunoassay has been yet developed for IgA autoantibodies. Therefore, the aim of the present study was to develop an ELISA to detect IgA autoantibodies against collagen XVII in the sera of patients with pemphigoids.

METHODS

We expressed a soluble recombinant form of the collagen XVII ectodomain in mammalian cells. Reactivity of IgA autoantibodies from patients with IgA pemphigoid was assessed by immunofluorescence microscopy and immunoblot analysis. ELISA test conditions were determined by chessboard titration experiments. The sensitivity, specificity and the cut-off were determined by receiver-operating characteristics analysis.

RESULTS

The optimized assay was carried out using sera from patients with IgA pemphigoid (n = 30) and healthy donors (n=105). By receiver operating characteristics (ROC) analysis, an area under the curve of 0.993 was calculated, indicating an excellent discriminatory capacity. Thus, a sensitivity and specificity of 83.3% and 100%, respectively, was determined for a cut-off point of 0.48. As additional control groups, sera from patients with bullous pemphigoid (n=31) and dermatitis herpetiformis (n = 50), a disease associated with IgA autoantibodies against epidermal transglutaminase, were tested. In 26% of bullous pemphigoid patients, IgA autoantibodies recognized the ectodomain of collagen XVII. One of 50 (2%) of dermatitis herpetiformis patients sera slightly topped the cut-off value.

CONCLUSIONS

We developed the first ELISA for the specific and sensitive detection of serum IgA autoantibodies specific to collagen XVII in patients with pemphigoids. This immunoassay should prove a useful tool for clinical and translational research and should essentially improve the diagnosis and disease monitoring of patients with IgA pemphigoid. Moreover, our findings strongly suggest that IgA pemphigoid and IgG bullous pemphigoid represent two ends of the clinical spectrum of an immunological loss of tolerance against components of hemidesmosomes, which is mediated by both IgG and IgA autoantibodies.

A Case of Chronic Bullous Disease of Childhood That Was Reactive to the Antigen of 120 kDa (LAD-1)

Chronic bullous disease of childhood (CBDC) is an autoimmune blistering disease that is characterized by Immunoglobulin A (IgA) deposits at the basement membrane zone. IgA autoantibodies (aAbs) from the serum of patients with CBDC react with antigens of 97 kDa (LABD97) and 120 kDa (LAD-1), and both of which are fragments of the extracellular domain of bullous pemphigoid 180 (BP180, type XVII collagen). The CBDC sera reacts with the immunodominant NC16a domain of BP180, which is the major region recognized by IgG aAbs in patients with bullous pemphigoid. A five-year-old boy presented with multiple pruritic tense blisters on the umbilical and inguinal areas for six weeks. The direct immunofluorescence of the perilesional area demonstrated linear deposits of IgA at the basement membrane zone. Using immunoblotting and an enzyme linked immunosorbent assay (ELISA), we identified the IgA aAbs reactive to antigens with a molecular weight of 120 kDa (LAD-1), which is a fragment of the extracellular domain of BP180.

Ectodomain shedding generates Neoepitopes on collagen XVII, the major autoantigen for bullous pemphigoid

As a type II transmembrane protein in basal keratinocytes, collagen XVII provides stable adhesion between epidermis and dermis in the skin. Its ectodomain can be shed from the cell surface, and autoantibodies in certain blistering diseases preferentially recognize the shed form. Major epitopes of collagen XVII are clustered within the juxtamembranous noncollagenous 16th A domain, and ectodomain shedding occurs within this region, suggesting that cleavage generates neoepitopes. However, the candidate cleavage sites have been controversial, and the mechanism of neoepitope generation is unclear. In this study, we investigated cleavage sites in the noncollagenous 16th A domain to understand the generation of neoepitopes and their pathological role. Polyclonal Abs recognizing the stretch Leu(524)-Gly(532) preferentially reacted with the shed ectodomain, but not with the full-length form, indicating that a neoepitope was localized at this site. The neoepitope-specific Ab fixed complement and induced granulocyte-dependent dermal-epidermal separation in cryosections of normal human skin. The physiological cleavage sites were identified using mass spectrometry. N termini were found at Asp(514), Leu(524), Glu(525), and Gly(526), among which Asp(514) and Glu(525) were blocked by acetylation and pyroglutaminate. In silico prediction of B cell epitopes indicated that the antigenicity of the Leu(524)-Gly(532) region increased substantially after shedding, regardless of the cleavage sites. Correspondingly, neoepitopes were found in the skin and blister fluids of patients with bullous pemphigoid, and bullous pemphigoid sera reacted with the peptide Leu(524)-Gly(532). Taken together, these data demonstrate that physiological shedding of collagen XVII generates neoepitopes, which may serve as a target of blister-inducing autoantibodies.

IgA autoantibodies in the pemphigoids and linear IgA bullous dermatosis

BACKGROUND

Patients with bullous pemphigoid (BP), mucous membrane pemphigoid (MMP) and pemphigoid gestationis (PG) have IgG antibodies against BP180 and BP230, components of the hemidesmosomes. Patients with linear IgA bullous dermatosis (LABD) have IgA autoantibodies against a 97/120-kDa protein which is highly homologous to a shedded fragment of the BP180-ectodomain.

OBJECTIVES

The aim of our study was to determine the incidence of IgA autoantibodies directed against BP180/BP230 in the pemphigoids and LABD and to determine the antigenic regions that are targeted by IgA autoantibodies.

METHODS

Utilizing baculovirus-expressed recombinant BP180 and BP230 proteins, we performed immunoblot analyses for IgA reactivity of sera from patients with BP (n = 30), MMP (n = 10), PG (n = 6), LABD (n = 6) and from control patients with non-related pruritic dermatoses (n = 8).

RESULTS

IgA reactivity against BP180 and/or BP230 was detected in 19/30 of the BP, in 7/10 of the MMP, in 6/6 of the LABD and in 3/6 of the PG sera, respectively, but not in the control group. In all subgroups, the major antigenic site recognized by IgA antibodies was located within the NH(2)-terminus of the BP180-ectodomain, but only a minority of the sera showed also IgA reactivity against the BP180-NC16a-domain. IgA reactivity against the central domain of BP180 was more frequently seen than against its COOH-terminus. IgA against the COOH- and NH(2)-terminus of BP230, respectively, was detected in 6/30 of the BP, 1/10 of the MMP, 1/6 of the LABD and 0/8 control sera.

CONCLUSION

IgA reactivity against BP180 and/or BP230 is a common finding in the pemphigoids.

Plasmin plays a role in the in vitro generation of the linear IgA dermatosis antigen LADB97

Collagen XVII (BP180) and its shed ectodomain represent major autoantigens in dermatoses of the pemphigoid group. The 120 kDa ectodomain is constitutively shed from the cell surface by disintegrin-metalloproteinases (ADAMs). Part of it is further processed to a 97 kDa fragment (LABD97), an autoantigen in linear IgA dermatosis (LAD), but the responsible proteinases remain elusive. In this study, we identified the 120 and the 97 kDa ectodomain in blister fluids of bullous pemphigoid patients using new mAbs. As blister fluids contain significant plasmin-like serine protease activity, HaCaT keratinocytes or purified 120 kDa ectodomain were incubated with several human serine proteases. In vitro, only plasmin generated a stable 97 kDa fragment that was also targeted by LAD sera. Characterization of the plasmin-derived 97 kDa fragment with domain-specific collagen XVII antibodies, heparin binding and N-glycosylation studies indicates that the N-terminus is located approximately at AA 515 and the C-terminus N-terminally from AA 1,421. Interestingly, plasmin-derived LABD97 was also generated in the presence of ADAM inhibitors and remained stable over more than 12 hours incubation at 37 degrees C, indicating that this disease relevant collagen XVII fragment can also arise in an ADAM-independent manner through direct action by plasmin.

A case of linear IgA disease in a child with IgA and IgG circulating antibodies directed to BPAg2

A 7-year-old Caucasian girl had multiple bullae on the trunk, upper and lower limbs (Fig. 1a,b) for 10 days. The lesions were large, tense, and asymptomatic, and mucosae were not involved. Laboratory findings were all normal. Histopathology revealed a subepidermal blister containing numerous neutrophils, eosinophils, and fibrin. Direct immunofluorescence of perilesional skin disclosed linear deposition of IgA and slight linear deposits of IgM at the basement membrane zone (Fig. 2). Indirect immunofluorescence on monkey esophagus and on human salt-split skin was negative. Immunoblot assay (IB), performed with an epidermal extract, revealed IgA and IgG antibodies directed to BPAg2 antigen (Fig. 3), while it was negative when performed on dermal extract. Enzyme-linked immunosorbent serologic assay using a commercial kit (MBL, Naka-Ku Nagoya, Japan) with the noncollagenous domain (NC16A) of the BPAg2 antigen was negative for both IgA and IgG. A diagnosis of linear IgA disease (LAD) was made and a treatment with dapsone (50 mg/day) and prednisolone (30 mg/day) was initiated. One month later, lesions had cleared.

What's new in blistering disorders?

From the characterization of new animal models for the study of disease pathogenesis, to the demonstration of new therapeutic modalities, many developments have revolutionized the field of autoimmune bullous diseases in the past several years. This review highlights many of the significant advances that have taken place in the diagnosis, pathogenesis, and treatment options for pemphigus, pemphigoid, epidermolysis bullosa acquisita, and immunoglobulin (Ig) A-mediated bullous disorders.

Generation and characterization of monoclonal antibodies against the intracellular domain of hemidesmosomal type XVII collagen

Type XVII collagen, also referred to as bullous pemphigoid antigen 2 (BPAG2) or bullous pemphigoid antigen 180 (BP180), is a transmembrane protein of the hemidesmosomal complexes of keratinocytes. Type XVII collagen has an unusual type II orientation with its N-terminus intracellularly located and with a large extracellular domain that spans lamina lucida of the dermal-epidermal junction. Type XVII collagen is an autoantigen in patients with pemphigoid diseases and its gene is mutated in patients with junctional epidermolysis bullosa. In the present work, we generated new monoclonal antibodies (MAbs) against the intracellular domain of type XVII collagen. We further characterized reactivity and fine specificity of an MAb (clone V58) from this panel of antibodies. The epitope recognized by the mAb V58 was mapped to a stretch of type XVII collagen corresponding to residues 234-398 of its sequence. Possible applications of this new MAb include antigen mapping in patients with hereditary epidermolysis bullosa and immunoaffinity purification of cell-derived type XVII collagen.

Immunoadsorption against two distinct epitopes on human type XVII collagen abolishes dermal-epidermal separation induced in vitro by autoantibodies from pemphigoid gestationis patients

Pemphigoid gestationis (PG) is a subepidermal autoimmune blistering disease characterized by self-reactive T and B cells specific for the transmembrane hemidesmosomal protein type XVII collagen/BP180. Major T and B cell epitopes are located within the immunodominant 16th non-collagenous domain A (NC16A) of type XVII collagen. The aim of the present study was to map the pathogenically relevant epitopes targeted by blister-inducing patients' autoantibodies. For this purpose, we used an in vitro model of autoantibody-induced leukocyte-dependent dermal-epidermal separation. Pre-adsorption against a recombinant form of the NC16A region abolished the blister-inducing potential of autoantibodies from all PG patients. Using overlapping synthetic peptides, we demonstrated that PG autoantibodies bind to two defined epitopes within the NC16A region (aa 500-514 and aa 511-523). Importantly, pre-adsorption using an affinity matrix containing these epitopes completely abolished dermal-epidermal separation induced by PG autoantibodies. This study identifies the epitopes relevant for blister induction in PG and should facilitate the development of an antigen-specific immunoadsorption therapy for this disease.