IgG autoantibodies against desmocollin 3 in pemphigus sera induce loss of keratinocyte adhesion

Data-Driven Image Analysis to Determine Antibody-Induced Dissociation of Cell-Cell Adhesion and Antibody Pathogenicity in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a blistering autoimmune disease that affects the skin and mucous membranes. The precise mechanisms by which PV antibodies induce a complete loss of cohesion of keratinocytes are not fully understood. But it is accepted that the process starts with antibody binding to desmosomal targets which leads to its disassembly and subsequent structural changes to cell-cell adhesions. In vitro immunofluorescence imaging of desmosome molecules has been used to characterize this initial phase, often qualitatively. However, there remains an untapped potential of image analysis in providing us more in-depth knowledge regarding ultrastructural changes after antibody binding. Currently, there is no such effort to establish a quantitative framework from immunofluorescence images in PV pathology. We take on this effort here in a comprehensive study to examine the effects of antibodies on key adhesion molecules and the cytoskeletal network, aiming to establish a correlation of ultrastructural changes in cell-cell adhesion with antibody pathogenicity. Specifically, we introduced a data-driven approach to quantitatively evaluate perturbations in adhesion molecules, including desmoglein 3, E-cadherin, as well as the cytoskeleton, following antibody treatment. We identify distinct immunofluorescence imaging signatures that mark the impact of antibody binding on the remodeling of the adhesion molecules and introduce a pathogenicity score to compare the relative effects of different antibodies. From this analysis, we showed that the biophysical response of keratinocytes to distinct PV associated antibodies is highly specific, allowing for accurate prediction of their pathogenicity. For instance, the high pathogenicity scores of the PVIgG and AK23 antibodies show strong agreement with their reported PV pathology. Our data-driven approach offers a more detailed framework for the action of autoantibodies in pemphigus and has the potential to pave the way for the development of effective novel diagnostic methods and therapeutic strategies.

Quality-controlled characterization of a monoclonal antibody specific to an EC5-domain of human desmoglein 3 for pemphigus research

Background

Pemphigus vulgaris (PV) is a life-threatening autoimmune blistering disease caused mainly by IgG autoantibodies (auto-abs) against the cadherin-type adhesion molecules desmoglein (Dsg) 1 and 3. Pathogenic anti-Dsg3 auto-abs bind to different Dsg3 epitopes, leading, among others, to signalling that is involved in pathogenic events, such as Dsg3 depletion. As central tools in research on PV, a limited number of antibodies such as AK23 are frequently used by the autoimmune bullous disease community.

Methods

Previously, we have introduced a novel Dsg3 EC5-binding antibody termed 2G4 that may potentially serve as a superior tool for numerous PV related analysis. The purpose of this study was to develop a quality-controlled production and verification process that allows I) a continuous quality improvement, and II) a verified and comprehensible overall quality with regard to pathogenic antigen-specific binding in a variety of pemphigus assays for each batch production.

Results

Thus, a workflow based on a standardized operating procedure was established. This includes the verification of purity and in-vitro binding capacity (SDS-page, direct and indirect immunofluorescence) as primary parameters, and size analysis by mass-spectrometry and ex-vivo pathogenicity by monolayer dissociation assay.

Conclusion

We here present an extensive point-by-point quality controlled IgG production protocol, which will serve as a basis for a standardized antibody assessment in PV research.

Desmosomal Hyper-adhesion Affects Direct Inhibition of Desmoglein Interactions in Pemphigus

During differentiation, keratinocytes acquire a strong, hyper-adhesive state, where desmosomal cadherins interact calcium ion independently. Previous data indicate that hyper-adhesion protects keratinocytes from pemphigus vulgaris autoantibody-induced loss of intercellular adhesion, although the underlying mechanism remains to be elucidated. Thus, in this study, we investigated the effect of hyper-adhesion on pemphigus vulgaris autoantibody-induced direct inhibition of desmoglein (DSG) 3 interactions by atomic force microscopy. Hyper-adhesion abolished loss of intercellular adhesion and corresponding morphological changes of all pathogenic antibodies used. Pemphigus autoantibodies putatively targeting several parts of the DSG3 extracellular domain and 2G4, targeting a membrane-proximal domain of DSG3, induced direct inhibition of DSG3 interactions only in non-hyper-adhesive keratinocytes. In contrast, AK23, targeting the N-terminal extracellular domain 1 of DSG3, caused direct inhibition under both adhesive states. However, antibody binding to desmosomal cadherins was not different between the distinct pathogenic antibodies used and was not changed during acquisition of hyper-adhesion. In addition, heterophilic DSC3-DSG3 and DSG2-DSG3 interactions did not cause reduced susceptibility to direct inhibition under hyper-adhesive condition in wild-type keratinocytes. Taken together, the data suggest that hyper-adhesion reduces susceptibility to autoantibody-induced direct inhibition in dependency on autoantibody-targeted extracellular domain but also demonstrate that further mechanisms are required for the protective effect of desmosomal hyper-adhesion in pemphigus vulgaris.

T Regulatory Cell-Associated Tolerance Induction by High-Dose Immunoglobulins in an HLA-Transgenic Mouse Model of Pemphigus

Pemphigus vulgaris (PV) is a potentially lethal autoimmune bullous skin disorder caused by IgG autoantibodies against desmoglein 3 (Dsg3) and Dsg1. During the last three decades, high-dose intravenous immunoglobulins (IVIgs) have been applied as an effective and relatively safe treatment regime in severe, therapy-refractory PV. This prompted us to study T- and B- cell polarization by IVIg in a human-Dsg3-dependent mouse model for PV. Using humanized mice transgenic for HLA-DRB1*04:02, which is a highly prevalent haplotype in PV, we employed IVIg in two different experimental approaches: in prevention and quasi-therapeutic settings. Our data show that intraperitoneally applied IVIg was systemically distributed for up to 42 days or longer. IVIg-treated Dsg3-immunized mice exhibited, in contrast to Dsg3-immunized mice without IVIg, significantly less Dsg3-specific IgG, and showed induction of T regulatory cells in lymphatic tissue. Ex vivo splenocyte analysis upon Dsg3-specific stimulation revealed an initial, temporarily reduced antigen-induced cell proliferation, as well as IFN-γ secretion that became less apparent over the course of time. Marginal-zone B cells were initially reduced in the preventive approach but re-expanded over time. In contrast, in the quasi-therapeutic approach, a robust down-regulation in both spleen and lymph nodes was observed. We found a significant down-regulation of the immature transitional 1 (T1) B cells in IVIg-treated mice in the quasi-therapeutic approach, while T2 and T3, representing a healthy stage of B-cell development, appeared to be up-regulated by IVIg. In summary, in two experimental settings employing an active PV mouse model, we demonstrate distinct alterations of T- and B-cell populations upon IVIg treatment, compatible with a tolerance-associated polarization in lymphatic tissue. Our data suggest that the clinical efficacy of IVIg is at least modulated by distinct alterations of T- and B-cell populations compatible with a tolerance-associated polarization in lymphatic tissue.

Classification and Antigen Molecules of Autoimmune Bullous Diseases

Autoimmune bullous diseases (AIBDs), which are a group of tissue-specific autoimmune diseases of the skin, present with various blistering lesions on the skin and mucous membranes, and show autoantibodies of IgG, IgA and IgM against epidermal cell surfaces and basement membrane zone. To date, AIBDs have been classified into a number of distinct subtypes by clinical and histopathological findings, and immunological characteristics. In addition, various biochemical and molecular biological studies have identified various novel autoantigens in AIBDs, which has resulted in proposals of new subtypes of AIBDs. In this article, we summarized various distinct AIBDs, and proposed the latest and most comprehensive classification of AIBDs with their autoantigen molecules.

Dsg3 epitope-specific signalling in pemphigus

Introduction

Pemphigus is an autoantibody driven disease that impairs the barrier function of the skin and mucosa by disrupting desmosomes and thereby impeding cellular cohesion. It is known that the different clinical phenotypes of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are dependent on the autoantibody profile and target antigens that, amongst others, are primarily desmoglein (Dsg)1 and/or Dsg3 for PV and Dsg1 for PF. However, it was reported that autoantibodiesagainst different epitopes of Dsg1 and Dsg3 can be pathogenic or not. The underlying mechanisms are very complex and involve both direct inhibition of Dsg interactions and downstream signalling. The aim of this study was to find out whether there is target-epitope-specific Dsg3 signalling by comparing the effects of the two pathogenic murine IgGs, 2G4 and AK23.

Methods

Dispase-based dissociation assay, Western Blot analysis, Stimulated emission depletion microscopy, Fura-based Ca2+ flux measurements, Rho/Rac G-Protein-linked immunosorbent assay, Enzyme-linked immunosorbent assay.

Results

The IgGs are directed against the EC5 and EC1 domain of Dsg3, respectively. The data show that 2G4 was less effective in causing loss of cell adhesion, compared to AK23. STED imaging revealed that both autoantibodies had similar effects on keratin retraction and reduction of desmosome number whereas only AK23 induced Dsg3 depletion. Moreover, both antibodies induced phosphorylation of p38MAPK and Akt whereas Src was phosphorylated upon treatment with AK23 only. Interestingly, Src and Akt activation were p38MAPK-dependent. All pathogenic effects were rescued by p38MAPK inhibition and AK23-mediated effects were also ameliorated by Src inhibition.

Discussion

The results give first insights into pemphigus autoantibody-induced Dsg3 epitope-specific signalling which is involved in pathogenic events such as Dsg3 depletion.

Significance of anti-desmocollin autoantibodies in pemphigus

The major autoantigens for pemphigus are desmogleins (Dsgs), cell-cell adhesive structure proteins, one of the desmosomal cadherins. Recent progress in molecular biology has revealed that IgG autoantibodies of classical pemphigus react with Dsg1 or Dsg3. Desmocollins (Dscs) also belong to the cadherin supergene family that provides structure to the desmosomes and play an important role in cell-to-cell adhesion. In addition to the presence of four desmosomal Dsg isoforms, i.e. Dsg1-4, Dsc1, 2 and 3, all of which are derived from different genes, Dsc1 has been previously identified as the target antigen of IgA autoantibodies in the subcorneal pustular dermatosis (SPD)-type of intercellular IgA dermatosis. In addition to the IgA anti-Dsc1 autoantiboides, the presence of IgG anti-Dsc autoantibodies is described in patients of some autoimmune bullous diseases. In particular, the current pemphigus detecting autoantibodies to Dscs has shown a tendency in atypical variants of pemphigus. Therefore, autoantibodies against Dscs alone may cause detachment of cell-cell adhesion in the epidermis in some pemphigus. However, except for the findings of a few in vitro and in vivo studies, there is currently no clear evidence for the pathogenicity of anti-Dsc autoantibodies in pemphigus, whereas significance of anti-Dsg autoantibodies is well established. This article describes the structure and function of the Dscs, and explores the evidence regarding the pathogenic role of anti-Dsc autoantibodies in pemphigus.

IgG against the Membrane-Proximal Portion of the Desmoglein 3 Ectodomain Induces Loss of Keratinocyte Adhesion, a Hallmark in Pemphigus Vulgaris

Pemphigus vulgaris is a severe autoimmune blistering disease characterized by IgG autoantibodies (auto-abs) against the desmosomal adhesion molecules desmoglein (DSG) 3 and DSG1. Underlying mechanisms leading to blister formation upon binding of DSG-specific IgG auto-abs are not fully understood. Numerous studies showed the pathogenicity of IgG auto-ab binding to the aminoterminal region 1 (EC1) of the DSG3 ectodomain. However, auto-abs in pemphigus vulgaris are polyclonal, including IgG against both aminoterminal- and membrane-proximal epitopes of the DSG3 ectodomain. In this study, the pathogenicity of a previously uncharacterized murine monoclonal IgG antibody, 2G4, directed against the membrane-proximal region (EC5) of the DSG3 ectodomain was characterized and tested in various specificity and functionality assays. The results clearly show that 2G4 is capable of inhibiting intercellular keratinocyte adhesion and of inducing cellular DSG3 redistribution by activation of the p38MAPK signal transduction pathway. In this study, we provide evidence that an IgG auto-abs directed against the membrane-proximal region EC5 of DSG3 induces acantholysis, the hallmark in pemphigus vulgaris. These findings challenge the current concept that IgG auto-abs targeting the NH₂-terminal portion of the DSG3 ectodomain are pathogenic only. Our study provides further aspects for a deeper understanding of desmosomal keratinocyte adhesion and improves our insight into the complex auto-ab‒induced blister formation in pemphigus vulgaris.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

A case of spontaneous autoimmune skin disease in a cynomolgus monkey (Macaca fascicularis)

Pemphigus is an autoimmune blistering disease characterized by lesions on the skin and mucous membranes. To date, no spontaneous cases of this disease have been reported in cynomolgus monkeys. This report describes the histopathological characteristics of spontaneous pemphigus in a cynomolgus monkey. Macroscopically, redness and scaling with pruritus were observed on the skin of the entire body. Histopathologically, the epidermis showed intercellular edema, and eosinophils and mononuclear cells infiltrated the epidermis. There was no obvious acantholysis in the epidermis. The perivascular area showed edema, and eosinophils and mononuclear cells infiltrated the vessels in the dermis. Immunohistochemically, the intercellular area in the epidermis was positive for Immunoglobulin G and Complement component 3. Serologically, anti-desmoglein 1 and desmoglein 3 antibodies in the serum were negative. From these findings, this case was diagnosed as an autoimmune skin disease, suspected to be pemphigus, and concluded as lesions being similar to those in human “pemphigus herpetiformis”.

Anti-Desmocollin Autoantibodies in Autoimmune Blistering Diseases

The presence of anti-desmocollin (Dsc) antibodies is rarely described in autoimmune blistering diseases patients. Moreover, several clinical phenotypes of pemphigus may be associated with these antibodies. In this review we analyze clinicopathological, immunologic and outcome features of anti-Dsc autoimmune blistering diseases patients, to improve their diagnosis and management. We conducted a systematic search of PubMed and Embase (1990-present) for studies reporting cases of autoimmune blistering diseases with anti-Dsc antibodies. We classified the selected patients as patients with exclusively anti-Dsc autoantibodies, and patients with anti-Dsc and other autoantibodies. Of 93 cases with anti-Dsc autoantibodies included, 38 (41%) had exclusively these antibodies. Only 18% of patients presented with the typical clinicopathological phenotype of pemphigus vulgaris or pemphigus foliaceous. Mucosal involvement was seen in approximately half of the patients. Up to 18% of cases were associated with neoplasms. Acantholysis was described in 54% of cases with histopathological information. Treatments and outcomes vary in the different clinical phenotypes. The presence of anti-Dsc antibodies must be suspected mainly in those patients with either atypical pemphigus, in special with clinical pustules, or in cases showing intraepithelial or dermal neutrophilic/eosinophilic infiltrate on histological examination and dual pattern by direct immunofluorescence examination.

Autoantibody-Specific Signalling in Pemphigus

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Human desmocollin 3-specific IgG antibodies are pathogenic in a humanized HLA-class II transgenic mouse model of pemphigus

Pemphigus is a potentially lethal autoimmune bullous skin disorder, which is associated with IgG autoantibodies against desmoglein 3 (Dsg3) and Dsg1. Notably, a subset of pemphigus patients presents with a similar clinical phenotype in the absence of anti-Dsg IgG, suggesting the presence of serum IgG reactive with desmosomal components other than Dsg1 or Dsg3. We and others have previously shown that such patients have serum IgG autoantibodies against desmocollin 3 (Dsc3), a component of desmosomes, that induce loss of keratinocyte adhesion ex vivo. Moreover, Dsc3 hypomorphic mice show a severe blistering phenotype of the mucous membrane which is highly characteristic in pemphigus. These findings prompted us to study induction and regulation of anti-human Dsc3 IgG in humanized mice transgenic for HLA-DRB1*04:02, which is a highly prevalent haplotype in pemphigus. We show that IgG from sera of immunized mice induce acantholysis in a dispase-based keratinocyte dissociation assay via the activation of p38 mitogen-activated protein kinases and epidermal growth factor receptor. Passive IgG transfer from mice immunized with recombinant human Dsc3 into neonates did not induce intraepidermal loss of adhesion presumably due to the lack of homology between human and mouse Dsc3. Ex vivo stimulation of splenocytes from Dsc3-immunized mice with human Dsc3 leads to a significant proliferative interferon-γ and interleukin 4 T cell response, which is restricted by HLA-DR/DQ. These findings suggest that induction of pathogenic anti-Dsc3 IgG is associated with Dsc3-specific T cells that recognize Dsc3 in association with HLA-DRB1*04:02.

Clinicians' pearls and myths in pemphigus

Pemphigus comprises a heterogeneous group of autoimmune blistering diseases, which can affect both skin and mucous membranes, especially oral mucosa. This group of diseases shows usually a chronic-relapsing course. Since pemphigus is a rare disease, the diagnosis is often delayed, because it is based upon the recognition of consistent clinical, histologic, and direct immunofluorescence findings, as well as indirect immunofluorescence, and/or enzyme-linked immunosorbent assay. Usually the patients are treated for multiple other conditions before starting the correct therapy, leading to a critical reduction of the patients' quality of life. This review is a succinct compilation of pearls gathered from clinical experience in pemphigus and the myths that may have influenced everyday practice but have been proven false. This review provided a selection of such dilemmas and controversies, focusing on myths and pearls that can help young dermatologist in the clinic, while also dispelling them.

Serum Detection of Anti-thyroid Peroxidase and Anti-thyroglobulin Antibodies in Chinese Patients With Pemphigus Vulgaris and Pemphigus Foliaceus and Literature Review

Background

Pemphigus is a rare but life-threatening autoimmune skin disease characterized by blistering on skin and/or mucous membranes. The physiological process of blister formation involves IgG antibodies against the desmogleins (Dsgs) and desmocollins (Dscs). Additional autoAbs have also been suggested to mediate the disease heterogeneity, such as anti-thyroid peroxidase (anti-TPO) and antithyroglobulin (anti-Tg) antibodies, the essential culprits of the immune system in autoimmune thyroid diseases.

Purpose

To investigate the levels and antibody positivity of anti-TPO and anti-Tg antibodies in pemphigus patients.

Methods

Antibody positivity and levels of anti-TPO and anti-Tg antibodies in pemphigus patients as compared to healthy controls were examined. A meta-analysis was conducted by reviewing six similar studies.

Results

98 Chinese pemphigus patients and 65 healthy controls were enrolled in the study. Our meta-analysis revealed a significant correlation between increased presence of positive anti-TPO and anti-Tg antibodies and pemphigus, particularly for pemphigus vulgaris (PV). Such correlation was also observed in our own hospitalized PV patients, but not in pemphigus foliaceus (PF) patients. In addition, the status of anti-TPO and anti-Tg antibodies were also compared between females and males within PV patients, PF patients or controls, as well as compared for females or males between pemphigus patients and controls. In the analysis of T cell counts, we found abnormal low CD3 + T cell counts (< 690 n/µl) were only detected in patients whose thyroid antibody levels were less than 20 IU/ml.

Conclusion

Pemphigus patients showed higher levels and antibody positivity of anti-TPO and anti-Tg antibodies than healthy controls. Further investigations are needed to identify the pathogenic functions of these antibodies in pemphigus, as well as to identify the potential shared susceptibility genes.

Autoreactive T cells in pemphigus: perpetrator and target

Pemphigus vulgaris (PV) is an autoimmune blistering disease, in which autoantibodies against epidermal cadherins, such as desmoglein (Dsg)1 and Dsg3, lead to the development of blisters and erosions on the skin and mucous membranes. Autoreactive CD4+ T cells are essential for the induction and perpetuation of the disease by interaction with B cells producing autoantibodies. PV has a strong genetic association with certain human leucocyte antigen (HLA) alleles with HLA-DRB1*04:02 and LA-DQB1*05:03 being the most prevalent in patients. Recently, genome-wide association studies have provided a new approach to identify single nucleotide polymorphisms, alongside the known association with HLA alleles. Loss of tolerance against Dsgs and other autoantigens is a critical event in the pathogenesis of PV. Epitope spreading contributes to the progression of PV, leading to an extension of the Dsg-specific autoimmune response to other molecular epitopes of autoantigens, such as desmocollins or muscarinic receptors. Alterations in CD4+CD25+ FoxP3+ regulatory T cells are thought to contribute to the development of PV representing a suitable target for therapeutic interventions. Several CD4+ T-cell subsets and cytokines are involved in the pathogenesis of PV, while Th2 cells are the extensively studied population. Recently, other T cell subsets like T follicular helper cells and Th17 have gained attention as new potential players in PV pathogenesis. The involvement of local autoantibody production in the lesional skin of PV patients in tertiary lymphoid organs is currently discussed but not yet clarified. In this study, we reviewed the current knowledge about the development, characteristics and function of autoreactive T cells in pemphigus and present current new T cell-targeted therapeutic approaches.

The involvement of ADAM10 in acantholysis in mucocutaneous pemphigus vulgaris depends on the autoantibody profile of each patient

BACKGROUND

Acantholysis in pemphigus vulgaris (PV) may be triggered by desmoglein (Dsg) and non-Dsg autoantibodies. The autoantibody profile of each patient results in distinct intracellular signalling patterns.

OBJECTIVES

Based on our previous findings, we aimed to elucidate whether PV acantholysis in a mouse model may be mediated by activation of a disintegrin and metalloproteinase 10 (ADAM10).

METHODS

We used three PV-IgG fractions from different patients containing high or low levels of anti-Dsg1 and anti-Dsg3 antibodies, and the presence or not of anti-desmocollin (Dsc) antibodies, using a passive transfer mouse model of PV.

RESULTS

Although all of the PV-IgG fractions produced suprabasal acantholysis, only those containing anti-Dsg1/3, but not anti-Dsc2/3 antibodies, induced ADAM10 activation in a Src-dependent way, and an increase in the epidermal growth factor (EGF) receptor ligands EGF and betacellulin (BTC). In contrast, the presence of anti-Dsc2/3 antibodies, in addition to anti-Dsg1/3, triggered earlier and ADAM10-independent epidermal detachment, with no increase in EGF and BTC, which was associated with an earlier and more intense acantholysis.

CONCLUSIONS

All PV-IgG fractions produced suprabasal acantholysis, but our results reveal that depending on the levels of anti-Dsg antibodies or the presence of non-Dsg antibodies, such as anti-Dsc, more severe cell-cell epidermal detachment will occur at different times, and in an ADAM10-dependent manner or not. Acantholysis in these different groups of patients with PV may be a consequence of the activation of specific intracellular mechanisms downstream of Autoantibodies binding to Dsg or non-Dsg proteins, and therefore more specific therapeutic approaches in PV should be used. What's already known about this topic? Suprabasal acantholysis in pemphigus vulgaris (PV) may be triggered by both desmoglein (Dsg) and non-Dsg autoantibodies. The autoantibody profile of each patient is associated with a distinct intracellular signalling pattern. What does this study add? In patients with PV with anti-Dsg3 and anti-Dsg1, but not anti-desmocollin (Dsc)3 antibodies, ADAM10 activation is induced in an Src-dependent way, together with an increase in the epidermal growth factor receptor (EGFR) ligands EGF and betacellulin. The presence of anti-Dsc3 antibodies triggers an earlier and ADAM10-independent acantholysis, without increasing EGFR ligands, and is associated with more severe epidermal detachment. Lower levels of anti-Dsc3 antibodies are associated with less severe acantholysis. What is the translational message? In some patients with PV, the severity and the timing for cell-cell detachment seem to depend on the level of anti-Dsg1/3 antibodies, although other as yet uncharacterized antibodies may also participate. These patients with PV would exhibit inhibition of acantholysis by Src, ADAM10, EGF and EGFR inhibitors. In other patients, the presence of non-Dsg antibodies, such as anti-Dsc2/3, would produce an earlier and more severe ADAM10-independent suprabasal acantholysis.

Pemphigus

Pemphigus consists of a group of rare and severe autoimmune blistering diseases mediated by pathogenic autoantibodies mainly directed against two desmosomal adhesion proteins, desmoglein (Dsg)1 and Dsg3 (also known as DG1 and DG3), which are present in the skin and surface-close mucosae. The binding of autoantibodies to Dsg proteins induces a separation of neighbouring keratinocytes, in a process known as acantholysis. The two main pemphigus variants are pemphigus vulgaris, which often originates with painful oral erosions, and pemphigus foliaceus, which is characterised by exclusive skin lesions. Pemphigus is diagnosed on the basis of either IgG or complement component 3 deposits (or both) at the keratinocyte cell membrane, detected by direct immunofluorescence microscopy of a perilesional biopsy, with serum anti-Dsg1 or anti-Dsg3 antibodies (or both) detected by ELISA. Corticosteroids are the therapeutic mainstay, which have recently been complemented by the anti-CD20 antibody rituximab in moderate and severe disease. Rituximab induces complete remission off therapy in 90% of patients, despite rapid tapering of corticosteroids, thus allowing for a major corticosteroid-sparing effect and a halved number of adverse events related to corticosteroids.

Identification of a Novel Non-desmoglein Autoantigen in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoimmune bullous disease of the skin and mucous membranes characterized by the presence of circulating and tissue-bound autoantibodies against keratinocyte cell surface antigens, specifically desmoglein (Dsg) 1 and 3. The pathogenic role of anti-Dsg antibodies is well-established, while the mechanism of blister formation is only partly defined. We have applied a previously developed method for the efficient immortalization of IgG+ memory B cells to identify novel target antigens in PV. A human monoclonal antibody reactive with a hitherto unreported non-Dsg antigen was isolated. Immunoprecipitation and immunoblotting studies with keratinocyte extracts indicated α-catenin as the putative antigen, then confirmed by immunoblotting on the recombinant protein. Four of ten PV sera reacted with recombinant α-catenin. Although the isolated human monoclonal antibody was per se unable to dissociate keratinocyte monolayers and also to synergize with a pathogenic antibody in vitro, further studies are warranted to assess its possible in vivo contribution in the multifactorial pathogenesis and heterogeneous manifestations of PV disease.

Development of a Desmocollin-3 Active Mouse Model Recapitulating Human Atypical Pemphigus

Pemphigus vulgaris (PV) is a life-threatening mucocutaneous autoimmune blistering disease. It is often associated with autoantibodies to the desmosomal adhesion proteins Desmoglein 3 (DSG3) and Desmoglein 1 (DSG1). Recently, auto-antigens, such as desmocollins and others have been described in PV and in atypical pemphigus forms such as Pemphigus Herpetiformis (PH), Pemphigus Vegetans (PVeg), and Paraneoplastic Pemphigus (PP). Desmocollins belong to a cadherin subfamily that provides structure to the desmosomes and play an important role in cell-to-cell adhesion. In order to verify the pathogenic activity of anti-Desmocollin 3 (DSC3) antibodies, we developed an active disease model of pemphigus expressing anti-DSC3 autoantibodies or anti-DSC3 and anti-DSG3 antibodies. This approach included the adoptive transfer of DSC3 and/or DSG3 lymphocytes to Rag2^-/- immunodeficient mice that express DSC3 and DSG3. Our results show that the presence of anti-DSC3 auto-antibodies is sufficient to determine the appearance of a pathological phenotype relatable to pemphigus, but with features not completely super-imposable to those observed in the DSG3 active model, suggesting that the DSC3 active model might mimic the atypical pemphigus. Moreover, the presence of both anti-DSC3 and anti-DSG3 antibodies determines a more severe phenotype and a slower response to prednisolone. In conclusion, we have developed an adult DSC3 pemphigus mouse model that differs from the DSG3 model and supports the concept that antigens other than desmogleins may be responsible for different phenotypes in human pemphigus.

ST18 Enhances PV-IgG-Induced Loss of Keratinocyte Cohesion in Parallel to Increased ERK Activation

Pemphigus is an autoimmune blistering disease targeting the desmosomal proteins desmoglein (Dsg) 1 and Dsg3. Recently, a genetic variant of the Suppression of tumorigenicity 18 (ST18) promoter was reported to cause ST18 up-regulation, associated with pemphigus vulgaris (PV)-IgG-mediated increase in cytokine secretion and more prominent loss of keratinocyte cohesion. Here we tested the effects of PV-IgG and the pathogenic pemphigus mouse anti-Dsg3 antibody AK23 on cytokine secretion and ERK activity in human keratinocytes dependent on ST18 expression. Without ST18 overexpression, both PV-IgG and AK23 induced loss of keratinocyte cohesion which was accompanied by prominent fragmentation of Dsg3 immunostaining along cell borders. In contrast, release of pro-inflammatory cytokines such as IL-1α, IL-6, TNFα, and IFN-γ was not altered significantly in both HaCaT and primary NHEK cells. These experiments indicate that cytokine expression is not strictly required for loss of keratinocyte cohesion. Upon ST18 overexpression, fragmentation of cell monolayers increased significantly in response to autoantibody incubation. Furthermore, production of IL-1α and IL-6 was enhanced in some experiments but not in others whereas release of TNF-α dropped significantly upon PV-IgG application in both EV- and ST18-transfected HaCaT cells. Additionally, in NHEK, application of PV-IgG but not of AK23 significantly increased ERK activity. In contrast, ST18 overexpression in HaCaT cells augmented ERK activation in response to both c-IgG and AK23 but not PV-IgG. Because inhibition of ERK by U0126 abolished PV-IgG- and AK23-induced loss of cell cohesion in ST18-expressing cells, we conclude that autoantibody-induced ERK activation was relevant in this scenario. In summary, similar to the situation in PV patients carrying ST18 polymorphism, overexpression of ST18 enhanced keratinocyte susceptibility to autoantibody-induced loss of cell adhesion, which may be caused in part by enhanced ERK signaling.

Synergy among non-desmoglein antibodies contributes to the immunopathology of desmoglein antibody-negative pemphigus vulgaris

Pemphigus vulgaris (PV) is a potentially lethal mucocutaneous blistering disease characterized by IgG autoantibodies (AuAbs) binding to epidermal keratinocytes and inducing this devastating disease. Here, we observed that non-desmoglein (Dsg) AuAbs in the sera of patients with Dsg1/3 AuAb-negative acute PV are pathogenic, because IgGs from these individuals induced skin blistering in neonatal mice caused by suprabasal acantholysis. Serum levels of AuAbs to desmocollin 3 (Dsc3), M3 muscarinic acetylcholine receptor (M3AR), and secretory pathway Ca2+/Mn2+-ATPase isoform 1 (SPCA1) correlated with the disease stage of PV. Moreover, AuAb absorption on recombinant Dsc3, M3AR, or SPCA1 both prevented skin blistering in the passive transfer of AuAbs model of PV in BALB/c mice and significantly decreased the extent of acantholysis in a neonatal mouse skin explant model. Although acantholytic activities of each of these immunoaffinity-purified AuAbs could not induce a PV-like phenotype, their mixture produced a synergistic effect manifested by a positive Nikolskiy sign in the skin of neonatal mice. The downstream signaling of all pathogenic non-Dsg AuAbs involved p38 mitogen-activated protein kinase (MAPK)-mediated phosphorylation and elevation of cytochrome c release and caspase 9 activity. Anti-Dsc3 and anti-SPCA1 AuAbs also activated SRC proto-oncogene, nonreceptor tyrosine kinase (SRC). Of note, although a constellation of non-Dsg AuAbs apparently disrupted epidermal integrity, elimination of a single pathogenic AuAb could prevent keratinocyte detachment and blistering. Therefore, anti-Dsg1/3 AuAb-free PV can be a model for elucidating the roles of non-Dsg antigen-specific AuAbs in the physiological regulation of keratinocyte cell-cell adhesion and blister development.

Immunoadsorption of Desmoglein-3-Specific IgG Abolishes the Blister-Inducing Capacity of Pemphigus Vulgaris IgG in Neonatal Mice

Pemphigus vulgaris (PV) is a potentially life-threatening autoimmune blistering disease which is associated with autoantibodies directed against two desmosomal proteins, desmoglein (Dsg) 3 and 1. Treatment of PV is rather challenging and relies on the long-term use of systemic corticosteroids and additional immunosuppressants. More recently, autoantibody-depleting therapies such as rituximab, high-dose intravenous immunoglobulins, and immunoadsorption were shown to be valuable treatment options in PV. Specific removal of pathogenic autoantibodies would further increase efficacy and usability of immunoadsorption. Here, we tested the capacity of our recently developed prototypic Dsg1- and Dsg3-specific adsorbers to remove circulating pathogenic autoantibodies from three different PV patients. The pathogenic potential of the Dsg3/1-depleted IgG fractions and the anti-Dsg3-specific IgG was explored in two different in vitro assays based on cultured human keratinocytes, the desmosome degradation assay and the dispase-based dissociation assay. In addition, the neonatal mouse model of PV was used. In both in vitro assays, no difference between the pathogenic effect of total PV IgG and anti-Dsg3-specific IgG was seen, while Dsg3/1-depleted and control IgG were not pathogenic. For the samples of all 3 PV patients, depletion of anti-Dsg3/1 IgG resulted in a complete loss of pathogenicity when injected into neonatal mice. In contrast, injection of anti-Dsg3-specific IgG, eluted from the column, induced gross blistering in the mice. Our data clearly show that anti-Dsg3-specific IgG alone is pathogenic in vitro and in vivo, whereas Dsg3/1-depletion results in a complete loss of pathogenicity. Furthermore, our data suggest that Dsg-specific adsorption may be a suitable therapeutic modality to efficiently reduce pathogenic autoantibodies in patients with severe PV.

Pemphigus-A Disease of Desmosome Dysfunction Caused by Multiple Mechanisms

Pemphigus is a severe autoimmune-blistering disease of the skin and mucous membranes caused by autoantibodies reducing desmosomal adhesion between epithelial cells. Autoantibodies against the desmosomal cadherins desmogleins (Dsgs) 1 and 3 as well as desmocollin 3 were shown to be pathogenic, whereas the role of other antibodies is unclear. Dsg3 interactions can be directly reduced by specific autoantibodies. Autoantibodies also alter the activity of signaling pathways, some of which regulate cell cohesion under baseline conditions and alter the turnover of desmosomal components. These pathways include Ca²⁺, p38MAPK, PKC, Src, EGFR/Erk, and several others. In this review, we delineate the mechanisms relevant for pemphigus pathogenesis based on the histology and the ultrastructure of patients’ lesions. We then dissect the mechanisms which can explain the ultrastructural hallmarks detectable in pemphigus patient skin. Finally, we reevaluate the concept that the spectrum of mechanisms, which induce desmosome dysfunction upon binding of pemphigus autoantibodies, finally defines the clinical phenotype.

Monopathogenic vs multipathogenic explanations of pemphigus pathophysiology

This viewpoint highlights major, partly controversial concepts about the pathogenesis of pemphigus. The monopathogenic theory explains intra-epidermal blistering through the "desmoglein (Dsg) compensation" hypothesis, according to which an antibody-dependent disabling of Dsg 1- and/or Dsg 3-mediated cell-cell attachments of keratinocytes (KCs) is sufficient to disrupt epidermal integrity and cause blistering. The multipathogenic theory explains intra-epidermal blistering through the "multiple hit" hypothesis stating that a simultaneous and synchronized inactivation of the physiological mechanisms regulating and/or mediating intercellular adhesion of KCs is necessary to disrupt epidermal integrity. The major premise for a multipathogenic theory is that a single type of autoantibody induces only reversible changes, so that affected KCs can recover due to a self-repair. The damage, however, becomes irreversible when the salvage pathway and/or other cell functions are altered by a partnering autoantibody and/or other pathogenic factors. Future studies are needed to (i) corroborate these findings, (ii) characterize in detail patient populations with non-Dsg-specific autoantibodies, and (iii) determine the extent of the contribution of non-Dsg antibodies in disease pathophysiology.

Mechanisms Causing Loss of Keratinocyte Cohesion in Pemphigus

The autoimmune blistering skin disease pemphigus is caused by IgG autoantibodies against desmosomal cadherins, but the precise mechanisms are in part a matter of controversial discussions. This review focuses on the currently existing models of the disease and highlights the relevance of desmoglein-specific versus nondesmoglein autoantibodies, the contribution of nonautoantibody factors, and the mechanisms leading to cell dissociation and blister formation in response to autoantibody binding. As the review brings together the majority of laboratories currently working on pemphigus pathogenesis, it aims to serve as a solid basis for further investigations for the entire field.

Mechanisms of Autoantibody-Induced Pathology

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

Pemphigus

Pemphigus is a group of IgG-mediated autoimmune diseases of stratified squamous epithelia, such as the skin and oral mucosa, in which acantholysis (the loss of cell adhesion) causes blisters and erosions. Pemphigus has three major subtypes: pemphigus vulgaris, pemphigus foliaceus and paraneoplastic pemphigus. IgG autoantibodies are characteristically raised against desmoglein 1 and desmoglein 3, which are cell-cell adhesion molecules found in desmosomes. The sites of blister formation can be physiologically explained by the anti-desmoglein autoantibody profile and tissue-specific expression pattern of desmoglein isoforms. The pathophysiological roles of T cells and B cells have been characterized in mouse models of pemphigus and patients, revealing insights into the mechanisms of autoimmunity. Diagnosis is based on clinical manifestations and confirmed with histological and immunochemical testing. The current first-line treatment is systemic corticosteroids and adjuvant therapies, including immunosuppressive agents, intravenous immunoglobulin and plasmapheresis. Rituximab, a monoclonal antibody against CD20⁺ B cells, is a promising therapeutic option that may soon become first-line therapy. Pemphigus is one of the best-characterized human autoimmune diseases and provides an ideal paradigm for both basic and clinical research, especially towards the development of antigen-specific immune suppression treatments for autoimmune diseases.

Atypical Clinical and Serological Manifestation of Pemphigus Vegetans: A Case Report and Review of the Literature

Pemphigus vegetans (PVeg) is a rare variant of pemphigus vulgaris characterized by pustules and/or papillomatous vegetations, preferentially affecting intertriginous and periorificial areas. Exceptional manifestations may be misdiagnosed resulting in delayed diagnosis and treatment. Diagnosis is confirmed by immunofluorescence and detection of anti-desmoglein (Dsg) 3 and/or anti-Dsg1 antibodies. We herein report an unusual manifestation of PVeg. At the time of first presentation, lesions were restricted to the right ring finger's tip. Although mucous membranes were initially not affected, high levels of anti-Dsg3 antibodies were detected while anti-Dsg1 and anti-desmocollin (Dsc) 1, 2, and 3 antibodies were absent. To compare our immunological findings with previous reports, all accessible Anglophone literature published since December 1988 was evaluated. We identified 52 patients suffering from PVeg, 7 of these showed anti-Dsg3 antibodies without any mucous membrane involvement. Notably, the detection of anti-Dsg1 and anti-Dsg3 antibodies does not necessarily correlate with the involvement of skin and/or mucous membranes. This might be due to more specific and complex antibody constellations in nonclassical or atypical pemphigus.

Rituximab therapy in pemphigus and other autoantibody-mediated diseases

Rituximab, a monoclonal antibody targeting the B cell marker CD20, was initially approved in 1997 by the United States Food and Drug Administration (FDA) for the treatment of non-Hodgkin lymphoma. Since that time, rituximab has been FDA-approved for rheumatoid arthritis and vasculitides, such as granulomatosis with polyangiitis and microscopic polyangiitis. Additionally, rituximab has been used off-label in the treatment of numerous other autoimmune diseases, with notable success in pemphigus, an autoantibody-mediated skin blistering disease. The efficacy of rituximab therapy in pemphigus has spurred interest in its potential to treat other autoantibody-mediated diseases. This review summarizes the efficacy of rituximab in pemphigus and examines its off-label use in other select autoantibody-mediated diseases.

Pathophysiology of the Desmo-Adhesome

Advances in our understanding of desmosomal diseases have provided a clear demonstration of the key role played by desmosomes in tissue and organ physiology, highlighting the importance of their dynamic and finely regulated structure. In this context, non-desmosomal regulatory molecules have acquired increasing relevance in the study of this organelle resulting in extending the desmosomal interactome, named the "desmo-adhesome." Spatiotemporal changes in the expression and regulation of the desmo-adhesome underlie a number of genetic, infectious, autoimmune, and malignant conditions. The aim of the present article was to examine the structural and functional relationship of the desmosome, by providing a comprehensive, yet focused overview of the constituents targeted in human disease. The inclusion of the novel regulatory network in the desmo-adhesome pathophysiology opens new avenues to a deeper understanding of desmosomal diseases, potentially unveiling pathogenic mechanisms waiting to be explored. J. Cell. Physiol. 232: 496-505, 2017. © 2016 Wiley Periodicals, Inc.

Loss of flotillin expression results in weakened desmosomal adhesion and Pemphigus vulgaris-like localisation of desmoglein-3 in human keratinocytes

Desmosomes are adhesion plaques that mediate cell-cell adhesion in many tissues, including the epidermis, and generate mechanical resistance to tissues. The extracellular domains of desmosomal cadherin proteins, desmogleins and desmocollins, are required for the interaction with cadherins of the neighbouring cells, whereas their cytoplasmic tails associate with cytoplasmic proteins which mediate connection to intermediate filaments. Disruption of desmosomal adhesion by mutations, autoantibodies or bacterial toxins results in severe human disorders of e.g. the skin and the heart. Despite the vital role of desmosomes in various tissues, the details of their molecular assembly are not clear. We here show that the two members of the flotillin protein family directly interact with the cytoplasmic tails of desmogleins. Depletion of flotillins in human keratinocytes results in weakened desmosomal adhesion and reduced expression of desmoglein-3, most likely due to a reduction in the desmosomal pool due to increased turnover. In the absence of flotillins, desmoglein-3 shows an altered localisation pattern in the cell-cell junctions of keratinocytes, which is highly similar to the localisation observed upon treatment with pemphigus vulgaris autoantibodies. Thus, our data show that flotillins, which have previously been connected to the classical cadherins, are also of importance for the desmosomal cell adhesion.

Mechanisms of Disease: Pemphigus and Bullous Pemphigoid

Pemphigus and bullous pemphigoid are autoantibody-mediated blistering skin diseases. In pemphigus, keratinocytes in epidermis and mucous membranes lose cell-cell adhesion, and in pemphigoid, the basal keratinocytes lose adhesion to the basement membrane. Pemphigus lesions are mediated directly by the autoantibodies, whereas the autoantibodies in pemphigoid fix complement and mediate inflammation. In both diseases, the autoantigens have been cloned and characterized; pemphigus antigens are desmogleins (cell adhesion molecules in desmosomes), and pemphigoid antigens are found in hemidesmosomes (which mediate adhesion to the basement membrane). This knowledge has enabled diagnostic testing for these diseases by enzyme-linked immunosorbent assays and dissection of various pathophysiological mechanisms, including direct inhibition of cell adhesion, antibody-induced internalization of antigen, and cell signaling. Understanding these mechanisms of disease has led to rational targeted therapeutic strategies.

A Case of Pemphigus Herpetiformis with Only Immunoglobulin G Anti-Desmocollin 3 Antibodies

Pemphigus represents a group of autoimmune blistering diseases caused by autoantibodies against desmogleins (Dsgs), a class of desmosomal cadherins. Recently, several pemphigus patients only with desmocollin (Dsc) 3-specific antibodies have been reported. Here, we report a case of pemphigus herpetiformis (PH), where only anti-Dsc3-specific antibodies but not anti-Dsg antibodies were detected. A 76-year-old woman presented with a 3-year history of blister formation. Physical examination revealed pruritic erythemas with vesicles on the trunk and legs, but no lesions of the oral mucosa. A skin biopsy specimen revealed intraepidermal blister containing neutrophils, eosinophils, and lymphocytes. Direct immunofluorescence (IF) showed immunoglobulin G (IgG) and complement 3 (C3) depositions on the keratinocyte cell surfaces. Indirect IF showed IgG anti-keratinocyte cell surface antibodies. These findings hinted at a diagnosis of pemphigus. However, repeated enzyme-linked immunosorbent assays (ELISAs) for both anti-Dsg1 and 3 antibodies proved to be negative. Immunoblotting of normal human epidermal extracts revealed Dsc antibodies, and recently established ELISAs using human Dsc1-Dsc3 recombinantly expressed in mammalian cells detected anti-Dsc3 antibodies. Based on these clinical, histopathological, and immunological findings, the patient was diagnosed as PH with only anti-Dsc3 antibodies. Treatment with corticosteroid prednisolone and steroid-sparing agent dapsone accomplished complete clinical remission of the patient.

Childhood Pemphigus Foliaceus with Exclusive Immunoglobulin G Autoantibodies to Desmocollins

Pemphigus refers to a group of potentially fatal blistering skin diseases that are often due to the deleterious effects of autoantibodies directed against desmosomal antigens. Although desmogleins have been mainly implicated as autoantigens in pemphigus, a steadily growing body of evidence suggests that other desmosomal proteins may be causally involved as well. Antibodies directed against desmocollin-3 have been shown to play a direct role in the pathogenesis of several types of pemphigus. Here we describe the case of a child with localized pemphigus foliaceus and immunoglobulin G (IgG) reactivity exclusively directed to desmocollins. The present report suggests that autoantibodies against nondesmoglein antigens may play a role in the pathogenesis of superficial pemphigus, in addition to pemphigus vulgaris, paraneoplastic pemphigus, and IgA pemphigus.

Anti-desmocollin autoantibodies in nonclassical pemphigus

BACKGROUND

Despite the established pathogenic role of anti-desmoglein (Dsg) antibodies in classical pemphigus, the significance of autoantibodies to another desmosomal cadherin, desmocollin (Dsc) is at present unknown. No consistent immunoassay for immunoglobulin (Ig) G autoantibodies to Dscs has been developed.

OBJECTIVES

The aim of this study was to develop reliable assays to detect anti-Dsc autoantibodies.

METHODS

We expressed soluble recombinant proteins (RPs) of human Dsc1-3 in mammalian cells and examined sera of various types of pemphigus, including 79 paraneoplastic pemphigus (PNP) sera, by novel enzyme-linked immunosorbent assays (ELISAs) using the RPs. We also performed ELISAs of Dsc baculoproteins and used the complementary DNA (cDNA) transfection method, and compared the results with those of mammalian ELISAs.

RESULTS

Through mammalian ELISAs, IgG autoantibodies to Dsc1, Dsc2 and Dsc3 were detected in 16.5%, 36.7% and 59.5% of PNP sera, respectively, and considerable numbers of pemphigus herpetiformis (PH) and pemphigus vegetans (PVeg) sera reacted strongly with Dsc1 and Dsc3. Mammalian ELISAs were highly specific and more sensitive than baculoprotein ELISAs or the cDNA transfection method. Several Dsc-positive sera, particularly PH sera, showed no reactivity with Dsgs. The reactivity of PNP serum and PVeg serum with Dscs was not abolished by pre-absorption with Dsg RPs.

CONCLUSIONS

The results of these novel ELISAs indicated that IgG anti-Dsc autoantibodies were frequently detected and potentially pathogenic in nonclassical pemphigus.