A novel explanation for acantholysis in pemphigus vulgaris: the basal cell shrinkage hypothesis

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.

Apoptolysis: a less understood concept in the pathogenesis of Pemphigus Vulgaris

Pemphigus Vulgaris (PV) is a severe autoimmune disease characterized by supra-basal blisters in the skin and mucous membranes of a wide range of mammals, including humans. It not only affects the skin but also has severe oral manifestations. It has been stated that auto-antibodies are produced, for unknown reasons, which are directed against desmogleins present on the epithelium and thus leads to acantholysis and intraepithelial blistering. But the exact mechanism is still not completely understood. Here we would like to shed light on a new pathologic mechanism i.e., apoptolysis, which emphasizes that apoptotic enzymes contribute to acantholysis development both in terms of molecular events and chronologic sequence. A possible role of apoptolysis has been discussed in purview of PV.

Chronic exposure to the anti-m3 muscarinic acetylcholine receptor autoantibody in pemphigus vulgaris contributes to disease pathophysiology

Pemphigus vulgaris (PV) is a potentially lethal autoimmune mucocutaneous blistering disease characterized by binding of IgG autoantibodies (AuAbs) to keratinocytes (KCs). In addition to AuAbs against adhesion molecules desmogleins 1 and 3, PV patients also produce an AuAb against the M3 muscarinic acetylcholine (ACh) receptor (M3AR) that plays an important role in regulation of vital functions of KCs upon binding endogenous ACh. This anti-M3AR AuAb is pathogenic because its adsorption eliminates the acantholytic activity of PV IgG; however, the molecular mechanism of its action is unclear. In the present study, we sought to elucidate the mode of immunopharmacologic action of the anti-M3AR AuAb in PV. Short-term exposures of cultured KCs to PV IgG or the muscarinic agonist muscarine both induced changes in the expression of keratins 5 and 10, consistent with the inhibition of proliferation and upregulated differentiation and in keeping with the biological function of M3AR. In contrast, long-term incubations induced a keratin expression pattern consistent with upregulated proliferation and decreased differentiation, in keeping with the hyperproliferative state of KCs in PV. This change could result from desensitization of the M3AR, representing the net antagonist-like effect of the AuAb. Therefore, chronic exposure of KCs to the anti-M3AR AuAb interrupts the physiological regulation of KCs by endogenous ACh, contributing to the onset of acantholysis. Since cholinergic agents have already demonstrated antiacantholytic activity in a mouse model of PV and in PV patients, our results have translational significance and can guide future development of therapies for PV patients employing cholinergic drugs.

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.

Critical appraisal of different triggering pathways for the pathobiology of pemphigus vulgaris-A review

Pemphigus vulgaris is an autoimmune blistering disease with an increased potential for mortality. The epithelium is key in understanding the pathobiology as it is specialized to perform functions like mechanical protection, immunological defense, and proprioception. In order to perform these array of functions, epithelial integrity is important. This integrity is maintained by a host of molecules which orchestrate the ability of the keratinocytes to function as a single unit. Desmoglein 3 antibodies formed in genetically susceptible individuals are known to cause the disruption of the intact oral mucosa leading to the formation of blisters in pemphigus vulgaris patients. However, there are underlying complex triggering pathways leading to the clinical disease. The aim of the review is to congregate and critically appraise the various triggering pathways which contribute toward the pathobiology of pemphigus vulgaris. Articles relevant to the pathobiology of pemphigus vulgaris were identified from various search databases till the year 2020. The pathogenesis of pemphigus vulgaris is complex, and it involves an in-depth understanding of the various predisposing factors, provoking factors, and progression mechanisms. Congregation of the various triggering pathways will open our minds to understand pemphigus vulgaris better and in turn develop a reliable treatment in the near future.

Histopathology of Pemphigus Vulgaris Revisited

ABSTRACT

Pemphigus vulgaris (PV) is a severe, potentially life-threatening autoimmune blistering disease, which is common in India. Although there is abundant literature on clinical and immunologic features, comprehensive studies on its histopathology are lacking. The aim of this study was to describe the histopathologic and immunofluorescence features as well as discuss various diagnostic pitfalls of PV. Histopathologic and immunofluorescence (DIF/IIF) findings were reviewed for 169 biopsies from 2007 to 2017 (11 years). The 169 samples included 152 skin, 16 oral mucosal, and 1 corneal biopsy. Maximum prevalence was noted in the fifth decade (57%) with a slight male preponderance. Vesicles were seen in 149 cases (88%), the level of which was suprabasal in 91(61%) and both suprabasal and intraepidermal in 50 cases (33.5%). Acantholytic cells were present in 142 cases (95%). Acantholytic keratinocytes showed rounded and polygonal acantholysis. 86 (51%) cases showed evidence of regeneration. Adnexal involvement was seen in 92 cases, commonest in the hair follicles. Unusual histologic findings included: intraepidermal bulla, absence of dermal inflammation, free floating hair shafts, multinucleated epithelial cells, eosinophil predominance; all of which are discussed. DIF was performed in 166 cases, of which 163 were positive (98%), and IgG was the commonest immunoreactant (96%). IIF was performed in 11 cases, of which 9 cases were positive for Dsg3. Although the diagnosis of PV rests on combined clinical, histologic, and IF features, histopathology as the sole means is also a powerful tool. It is important to be aware of the diagnostic pitfalls to optimize its utility.

Oral Lesions in Autoimmune Bullous Diseases: An Overview of Clinical Characteristics and Diagnostic Algorithm

Autoimmune bullous diseases are a group of chronic inflammatory disorders caused by autoantibodies targeted against structural proteins of the desmosomal and hemidesmosomal plaques in the skin and mucosa, leading to intra-epithelial or subepithelial blistering. The oral mucosa is frequently affected in these diseases, in particular, in mucous membrane pemphigoid, pemphigus vulgaris, and paraneoplastic pemphigus. The clinical symptoms are heterogeneous and may present with erythema, blisters, erosions, and ulcers localized anywhere on the oral mucosa, and lead to severe complaints for the patients including pain, dysphagia, and foetor. Therefore, a quick and proper diagnosis with adequate treatment is needed. Clinical presentations of autoimmune bullous diseases often overlap and diagnosis cannot be made based on clinical features alone. Immunodiagnostic tests are of great importance in differentiating between the different diseases. Direct immunofluorescence microscopy shows depositions of autoantibodies along the epithelial basement membrane zone in mucous membrane pemphigoid subtypes, or depositions on the epithelial cell surface in pemphigus variants. Additional immunoserological tests are useful to discriminate between the different subtypes of pemphigoid, and are essential to differentiate between pemphigus and paraneoplastic pemphigus. This review gives an overview of the clinical characteristics of oral lesions and the diagnostic procedures in autoimmune blistering diseases, and provides a diagnostic algorithm for daily practice.

Systemic and Autoimmune Diseases

This article reviews the clinical features of systemic and autoimmune diseases affecting the perianal region and its surrounding integumentary structures.

Acantholysis may precede elevation of circulating anti-desmoglein 3 antibody levels in pemphigus vulgaris presenting with desquamative gingivitis

Pemphigus vulgaris (PV) is an autoimmune, blistering disease that affects the mucosa and skin. The current theory favors the concept that anti-desmoglein (Dsg) 3 autoimmunity is the only pathogenic event needed to induce acantholysis. However, a few cases of active PV in the oral cavity had no detectable anti-Dsg 3 antibody. The aim of this study was to evaluate the differences in clinical and laboratory findings, whether or not the anti-Dsg 3 antibodies were present. This study was based on a retrospective review of 10 PV cases. The evaluation of the circulating autoantibody titers to Dsg 3 was conducted by using enzyme-linked immunosorbent assay (ELISA). An index value of 20 or more was used as the cutoff for a positive reaction. Only five of the 10 PV cases had a positive Dsg 3 ELISA. There were no differences in clinical, cytological, histopathological, and direct immunofluorescence findings, whether or not the anti-Dsg 3 antibodies were present. Of the five patients with a negative reaction at the time of diagnosis, the Dsg 3 ELISA became positive in the follow-up period in three cases. In the remaining two cases, the Dsg 3 ELISA was consistently negative for 18 months. Dsg 3 ELISA was negative early in some PV cases. Therefore, PV acantholysis may precede the elevation of circulating anti-Dsg 3 antibody levels. The diagnosis of PV should be considered based on comprehensive clinical, histopathological, and immunofluorescent criteria.

[Ultrastructure of epidermocytes in true pemphigus acantholysis]

OBJECTIVE

To investigate the ultrastructure of epidermocytes in skin biopsy specimens, by taking into account an update on the pathomorphogenesis of true pemphigus acantholysis.

MATERIAL AND METHODS

Affected skin biopsy specimens from 4 patients with Pemphigus vulgaris (a mixed mucosal-epidermal variant) and from 1 patient with P. foliaceus at the onset of the disease in the absence of therapy were examined by light microscopy of semifine sections and by transmission electron microscopy.

RESULTS

Skin biopsy specimens from pemphigus patients from the foci with a positive Nikolsky's sign were characterized by acantholysis and dilated intercellular spaces in the basal and spinous layers of the epidermis in combination with desmosomal hypoplasia and destruction. The reduction in the organelles of mitochondrial protein synthesis, which causes a decrease in the cytoplasm of the perikaryon and especially in the processes of a number of tonofilaments involved in the formation of desmosomes engaged our attention when studying the ultrastructure of epidermocytes.

CONCLUSION

A marked reduction in the number and size of desmosomes in P. vulgaris and P. foliaceus starts in the basal layer of the epidermis; however, acanthosis occurs in the suprabasal and spinous layers, respectively. The universal manifestations of pathology of cytoskeletal elements involved in the formation of desmosomes, as well as their underproduction must be considered in the concept of the pathogenesis of true pemphigus acantholysis.

The Genetics of Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune blistering disease caused by auto-antibodies (auto-Abs) directed against epithelial desmosomal components and leading to disruption of cell-cell adhesion. The exact mechanisms underlying the disease pathogenesis remain unknown and treatment is still based on immunosuppressive drugs, such as corticosteroids, which are associated with potentially significant side effects. Ethnic susceptibility, familial occurrence, and autoimmune comorbidity, suggest a genetic component to the pathogenesis of the disease, which, if discovered, could advance our understanding of PV pathogenesis and thereby point to novel therapeutic targets for this life-threatening disorder. In this article, we review the evidence for a genetic basis of PV, summarize the different approaches used to investigate susceptibility traits for the disease and describe past and recent discoveries regarding genes associated with PV, most of which belong to the human leukocyte antigen (HLA) locus with limited data regarding association of non-HLA genes with the disease.

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.

Current concepts of pemphigus with a deep insight into its molecular aspects

Pemphigus vulgaris is an autoimmune bullous disease involving both the skin and mucosal areas, which is characterized by intraepithelial flaccid blisters and erosions. The pathogenesis of this disease is not yet completely established, but novel intuitions into its pathogenesis have recently been published. An unanswered question in its pathophysiology is the mechanism of acantholysis or loss of keratinocyte cell adhesion. Acantholysis seems to result from a communal action of autoantibodies against numerous keratinocyte self-antigens, of which desmogleins 1 and 3, desmocollins and nondesmosome components, such as the mitochondrion, might take part in the disease initiation. Lately, apoptosis was described as a possible underlying mechanism of acantholysis. Likewise, apoptolysis is assumed to be the association between suprabasal acantholytic and cell death pathways. Hence, the present review focuses on the current concepts in the pathogenesis of the pemphigus in a nutshell.

Critical Role of the Neonatal Fc Receptor (FcRn) in the Pathogenic Action of Antimitochondrial Autoantibodies Synergizing with Anti-desmoglein Autoantibodies in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a life-long, potentially fatal IgG autoantibody-mediated blistering disease targeting mucocutaneous keratinocytes (KCs). PV patients develop pathogenic anti-desmoglein (Dsg) 3 ± 1 and antimitochondrial antibodies (AMA), but it remained unknown whether and how AMA enter KCs and why other cell types are not affected in PV. Therefore, we sought to elucidate mechanisms of cell entry, trafficking, and pathogenic action of AMA in PV. We found that PVIgGs associated with neonatal Fc receptor (FcRn) on the cell membrane, and the PVIgG-FcRn complexes entered KCs and reached mitochondria where they dissociated. The liberated AMA altered mitochondrial membrane potential, respiration, and ATP production and induced cytochrome c release, although the lack or inactivation of FcRn abolished the ability of PVIgG to reach and damage mitochondria and to cause detachment of KCs. The assays of mitochondrial functions and keratinocyte adhesion demonstrated that although the pathobiological effects of AMA on KCs are reversible, they become irreversible, leading to epidermal blistering (acantholysis), when AMA synergize with anti-Dsg antibodies. Thus, it appears that AMA enter a keratinocyte in a complex with FcRn, become liberated from the endosome in the cytosol, and are trafficked to the mitochondria, wherein they trigger pro-apoptotic events leading to shrinkage of basal KCs uniquely expressing FcRn in epidermis. During recovery, KCs extend their cytoplasmic aprons toward neighboring cells, but anti-Dsg antibodies prevent assembly of nascent desmosomes due to steric hindrance, thus rendering acantholysis irreversible. In conclusion, FcRn is a common acceptor protein for internalization of AMA and, perhaps, for PV autoantibodies to other intracellular antigens, and PV is a novel disease paradigm for investigating and elucidating the role of FcRn in this autoimmune disease and possibly other autoimmune diseases.

Large-Scale Electron Microscopy Maps of Patient Skin and Mucosa Provide Insight into Pathogenesis of Blistering Diseases

Large-scale electron microscopy ("nanotomy") allows straight forward ultrastructural examination of tissue, cells, organelles, and macromolecules in a single data set. Such data set equals thousands of conventional electron microscopy images and is freely accessible (www.nanotomy.org). The software allows zooming in and out of the image from total overview to nanometer scale resolution in a 'Google Earth' approach. We studied the life-threatening human autoimmune blistering disease pemphigus, using nanotomy. The pathomechanism of cell-cell separation (acantholysis) that underlies the blistering is poorly understood. Ultrastructural examination of pemphigus tissue revealed previously unreported findings: (i) the presence of double-membrane structures between cells in all pemphigus types; (ii) the absence of desmosomes around spontaneous blisters in pemphigus foliaceus (PF); (iii) lower level blistering in PF when force induced; and (iv) intercellular widening at non-acantholytic cell layers. Thus, nanotomy delivers open-source electron microscopic maps of patient tissue, which can be analyzed for additional anomalies from any computer by experts from different fields.

Is Grover's disease an autoimmune dermatosis?

Grover's disease (GD) is a transient or persistent, monomorphous, papulovesicular, asymptomatic or pruritic eruption classified as non-familial acantholytic disorder. Contribution of autoimmune mechanisms to GD pathogenesis remains controversial. The purpose of this study was to investigate antibody-mediated autoimmunity in 11 patients with GD, 4 of which were positive for IgA and/or IgG antikeratinocyte antibodies by indirect immunofluorescence. We used the most sensitive proteomic technique for an unbiased analysis of IgA- and IgG-autoantibody reactivities. Multiplex analysis of autoantibody responses revealed autoreactivity of all 11 GD patients with cellular proteins involved in the signal transduction events regulating cell development, activation, growth, death, adhesion and motility. Semiquantitative fluorescence analysis of cultured keratinocytes pretreated with sera from each patient demonstrated decreased intensity of staining for desmoglein 1 and/or 3 and PCNA, whereas 4 of 10 GD sera induced BAD expression, indicating that binding of autoantibodies to keratinocytes alters expression/function of their adhesion molecules and activates apoptosis. We also tested the ability of GD sera to induce visible alterations of keratinocyte shape and motility in vitro but found no specific changes. Thus, our results demonstrated that humoral autoimmunity in GD can be mediated by both IgA and IgG autoantibodies. At this point, however, it is impossible to conclude whether these autoantibodies cause or are caused by the disease. Antidesmoglein antibodies may be triggered by exposure to immune system of sequestered antigens due to disintegration of desmosomes during primary acantholysis. Clarifying aetiology of GD will help improve treatment, which currently is symptomatic and of marginal effectiveness.

Pemphigus vulgaris autoimmune globulin induces Src-dependent tyrosine-phosphorylation of plakophilin 3 and its detachment from desmoglein 3

The cell adhesion molecule plakophilin 3 (Pkp3) plays an essential role in the maintenance of skin integrity and is targeted in certain autoimmune conditions. In one example, we have shown that Pkp3 is instrumental in mediating the discohesive effects of sera from patients with pemphigus vulgaris (PV), a life-threatening autoimmune disease that targets intercellular adhesion in the epidermis. In the present study, we determine the effect of PV autoimmune globulin (PV IgG) on Pkp3 in an in-vitro model of PV. We demonstrate that Pkp3 becomes tyrosine phosphorylated as early as 30 min upon binding of PV IgG to keratinocyte surface and eventually detaches from its binding partner desmoglein 3 (Dsg3). In parallel, Pkp3 is depleted from the membrane (Triton X-soluble) fraction and accumulates in the cytoplasm within 240 min of incubation with PV IgG. Inhibition of Pkp3 phosphorylation by a Src inhibitor attenuates the discohesive effects of PV IgG. Taken together, the data demonstrate that activation of Src-kinase signalling is crucial for PV acantholysis and acts, at least in part, via phosphorylation of the adaptor protein Pkp3.

Neural nitric oxide synthase participates in pemphigus vulgaris acantholysis through upregulation of Rous sarcoma, mammalian target of rapamycin and focal adhesion kinase

Pemphigus vulgaris (PV) is an autoimmune blistering skin disease characterized by suprabasal acantholysis produced as a consequence of desmoglein (Dsg) and non-Dsg autoantibodies binding to several targeting molecules localized on the membrane of keratinocytes. Nitric oxide (NO) may exert a pathogenic function in several immunological processes. We have previously demonstrated that neural nitric oxide synthase (nNOS) plays part in PV acantholysis. Also, our group has described a relevant role for HER [human epidermal growth factor receptor (EGFR) related] isoforms and several kinases such as Src (Rous sarcoma), mammalian target of rapamycin (mTOR) and focal adhesion kinase (FAK), as well as caspases in PV development. Using a passive transfer mouse model of PV, we aimed to investigate the relationship between the increase in nNOS and EGFR, Src, mTOR and FAK kinase upregulation observed in PV lesions. Our results revealed a new function for nNOS, which contributes to EGFR-mediated PV acantholysis through the upregulation of Src, mTOR and FAK. In addition, we found that nNOS participates actively in PV at least in part by increasing caspase-9 and caspase-3 activities. These findings underline the important issue that in PV acantholysis, caspase activation is a nNOS-linked process downstream of Src, mTOR and FAK kinase upregulation.

Desmosomal adhesion and pemphigus vulgaris: the first half of the story

Pemphigus vulgaris (PV) is a paradigm of autoimmune disease affecting intercellular adhesion. The mechanisms that lead to cell-cell detachment (acantholysis) have crucial therapeutic implications and are currently undergoing major scrutiny. The first part of this review focuses on the classical view of the pathogenesis of PV, which is dominated by the cell adhesion molecules of the desmosome, namely desmogleins (Dsgs). Cloning of the DSG3 gene, generation DSG3 knock-out mice and isolation of monoclonal anti-Dsg3 IgG have aided to clarify the pathogenic mechanisms of PV, which are in part dependent on the fate of desmosomal molecules. These include perturbation of the desmosomal network at the transcriptional, translational, and interaction level, kinase activation, proteinase-mediated degradation, and hyper-adhesion. By the use of PV models, translational research has in turn helped shed light into the basic structure, function, and dynamics of assembly of desmosomal cadherins. The combined efforts of basic and applied research has resulted in tremendous advance into the understanding of epidermal adhesion and helped debunk old myths on the supposedly unique role of desmogleins in the mechanisms of cell-cell detachment in PV.

Population-specific association between a polymorphic variant in ST18, encoding a pro-apoptotic molecule, and pemphigus vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune blistering disease caused by anti-epithelial antibodies, leading to disruption of cell-cell adhesion. Although the disease is exceedingly rare worldwide, it is known to be relatively prevalent in Jewish populations. The low prevalence of the disease represents a significant obstacle to a genome-wide approach to the mapping of susceptibility genes. We reasoned that the study of a genetically homogeneous cohort characterized by a high prevalence of PV may help exposing associated signals while reducing spurious results due to population sub-structure. We performed a genome-wide association study using 300K single-nucleotide polymorphisms (SNPs) in a case-control study of 100 PV patients of Jewish descent and 397 matched control individuals, followed by replication of significantly associated SNPs in three additional cohorts of Jewish, Egyptian, and German origin. In addition to the major histocompatibility complex locus, a genomic segment on 8q11.23 that spans the ST18 gene was also found to be significantly associated with PV. This association was confirmed in the Jewish and Egyptian replication sets but not in the German sample, suggesting that ST18-associated variants may predispose to PV in a population-specific manner. ST18 regulates apoptosis and inflammation, two processes of direct relevance to the pathogenesis of PV. Further supporting the relevance of ST18 to PV, we found this gene to be overexpressed in the skin of PV patients as compared with healthy individuals.

Urban legends: pemphigus vulgaris

Pemphigus vulgaris (PV) is the most common type of pemphigus. PV pathogenesis is still debated, and treatment remains challenging. We investigated five controversial topics: (1) What are the target antigens in PV? (2) Do desmogleins adequately address PV pathophysiology? (3) How does acantholysis occur in PV? (4) Is PV still a lethal disease? (5) What is the role of rituximab (RTX) in PV treatment? Results from extensive literature searches suggested the following: (1) Target antigens of PV include a variety of molecules and receptors that are not physically compartmentalized within the epidermis. (2) PV is caused by a variety of autoantibodies to keratinocyte self-antigens, which concur to cause blistering by acting synergistically. (3) The concept of apoptolysis distinguishes the unique mechanism of autoantibody-induced keratinocyte damage in PV from other known forms of cell death. (4) PV remains potentially life-threatening largely because of treatment side effects, but it is uncertain which therapies carry the highest likelihood of lethal risk. (5) RTX is a very promising treatment option in patients with widespread recalcitrant or life-threatening PV. RTX's cost is an issue, its long-term side effects are still unknown, and randomized controlled trials are needed to establish the optimal dosing regimen.

Pemphigus autoimmunity: hypotheses and realities

The goal of contemporary research in pemphigus vulgaris and pemphigus foliaceus is to achieve and maintain clinical remission without corticosteroids. Recent advances of knowledge on pemphigus autoimmunity scrutinize old dogmas, resolve controversies, and open novel perspectives for treatment. Elucidation of intimate mechanisms of keratinocyte detachment and death in pemphigus has challenged the monopathogenic explanation of disease immunopathology. Over 50 organ-specific and non-organ-specific antigens can be targeted by pemphigus autoimmunity, including desmosomal cadherins and other adhesion molecules, PERP cholinergic and other cell membrane (CM) receptors, and mitochondrial proteins. The initial insult is sustained by the autoantibodies to the cell membrane receptor antigens triggering the intracellular signaling by Src, epidermal growth factor receptor kinase, protein kinases A and C, phospholipase C, mTOR, p38 MAPK, JNK, other tyrosine kinases, and calmodulin that cause basal cell shrinkage and ripping desmosomes off the CM. Autoantibodies synergize with effectors of apoptotic and oncotic pathways, serine proteases, and inflammatory cytokines to overcome the natural resistance and activate the cell death program in keratinocytes. The process of keratinocyte shrinkage/detachment and death via apoptosis/oncosis has been termed apoptolysis to emphasize that it is triggered by the same signal effectors and mediated by the same cell death enzymes. The natural course of pemphigus has improved due to a substantial progress in developing of the steroid-sparing therapies combining the immunosuppressive and direct anti-acantholytic effects. Further elucidation of the molecular mechanisms mediating immune dysregulation and apoptolysis in pemphigus should improve our understanding of disease pathogenesis and facilitate development of steroid-free treatment of patients.

The pathogenic role of autoantibodies in pemphigus vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune bullous disease involving both the skin and mucosal areas, and characterized by intraepithelial flaccid blisters and erosions. The pathogenesis of this disease is not yet completely understood, but novel insights into desmoglein biology and autoantibody pathogenesis have recently been published. Acantholysis in PV seems to result from a collective action of autoantibodies against various keratinocyte self antigens, of which desmogleins 1 and 3 are the most important. Additional antigens including desmocollins and nondesmosome components, such as the mitochondrion, might take part in disease activation. Recently, apoptosis was reported as a possible underlying mechanism of acantholysis. Furthermore, apoptolysis is believed to be the link between suprabasal acantholytic and cell-death pathways. We review the possible hypotheses of the pathogenesis of PV: the desmoglein compensation theory, the antibody-induced apoptosis theory, the basal-cell shrinkage hypothesis and the newly published apoptolysis theory.

Actin reorganization contributes to loss of cell adhesion in pemphigus vulgaris

In the human autoimmune blistering skin disease pemphigus vulgaris autoantibodies (PV-IgG), which are mainly directed against keratinocyte cell adhesion molecules desmoglein (Dsg) 3 and Dsg1, cause keratinocyte cell dissociation (acantholysis). Recent studies reported that loss of keratinocyte cell adhesion was accompanied by profound alterations of the actin cytoskeleton. Nevertheless, the relevance of actin reorganization in this process is unclear at present. In this study, we provide evidence for an important role of actin reorganization in pemphigus pathogenesis. In parallel to loss of cell adhesion and fragmentation of Dsg3 staining along cell borders, PV-IgG treatment resulted in striking changes in actin cytoskeleton organization. Moreover, in experiments using fluorescence recovery after photobleaching (FRAP), PV-IgG were detected to interfere with actin dynamics. Therefore, we investigated whether pharmacological manipulation of actin polymerization modulates pathogenic effects of PV-IgG. Pharmacological stabilization of actin filaments via jasplakinolide significantly blocked cell dissociation and Dsg3 fragmentation, whereas cytochalasin D-induced actin depolymerization strongly enhanced pathogenic effects of PV-IgG. To substantiate these findings, we studied whether the protective effects of Rho GTPases, which are potent regulators of the actin cytoskeleton and were shown to be involved in pemphigus pathogenesis, were dependent on modulation of actin dynamics. Cytotoxic necrotizing factor-1 (CNF-1)-mediated activation of Rho-GTPases enhanced the cortical junction-associated actin belt and blunted PV-IgG-induced cell dissociation. However, when actin polymerization was blocked under these conditions via addition of latrunculin B, the protective effects of CNF-1 were abrogated. Taken together, these experiments indicate that reorganization of cortical actin filaments is a critical step in PV-IgG-induced keratinocyte dissociation.

Experimental human cell and tissue models of pemphigus

Pemphigus is a chronic mucocutaneous autoimmune bullous disease that is characterized by loss of cell-cell contact in skin and/or mucous membranes. Past research has successfully identified desmosomes as immunological targets and has demonstrated that acantholysis is initiated through direct binding of IgG. The exact mechanisms of acantholysis, however, are still missing. Experimental model systems have contributed considerably to today's knowledge and are still a favourite tool of research. In this paper we will describe to what extent human cell and tissue models represent the in vivo situation, for example, organ cultures of human skin, keratinocyte cultures, and human skin grafted on mice and, furthermore, how suitable they are to study the pathogenesis of pemphigus. Organ cultures closely mimic the architecture of the epidermis but are less suitable to answer posed biochemical questions. Cultured keratinocyte monolayers are convenient in this respect, but their desmosomal make-up in terms of adhesion molecules does not exactly reflect the in vivo situation. Reconstituted skin is a relatively new model that approaches organ culture. In models of human skin grafted on mice, acantholysis can be studied in actual human skin but now with all the advantages of an animal model.

Antimitochondrial autoantibodies in pemphigus vulgaris: a missing link in disease pathophysiology

A loss of epidermal cohesion in pemphigus vulgaris (PV) results from autoantibody action on keratinocytes (KCs) activating the signaling kinases and executioner caspases that damage KCs, causing their shrinkage, detachment from neighboring cells, and rounding up (apoptolysis). In this study, we found that PV antibody binding leads to activation of epidermal growth factor receptor kinase, Src, p38 MAPK, and JNK in KCs with time pattern variations from patient to patient. Both extrinsic and intrinsic apoptotic pathways were also activated. Although Fas ligand neutralizing antibody could inhibit the former pathway, the mechanism of activation of the latter remained unknown. PV antibodies increased cytochrome c release, suggesting damage to mitochondria. The immunoblotting experiments revealed penetration of PVIgG into the subcellular mitochondrial fraction. The antimitochondrial antibodies from different PV patients recognized distinct combinations of antigens with apparent molecular sizes of 25, 30, 35, 57, 60, and 100 kDa. Antimitochondrial antibodies were pathogenic because their absorption abolished the ability of PVIgG to cause keratinocyte detachment both in vitro and in vivo. The downstream signaling of antimitochondrial antibodies involved JNK and late p38 MAPK activation, whereas the signaling of anti-desmoglein 3 (Dsg3) antibody involved JNK and biphasic p38 MAPK activation. Using KCs grown from Dsg3(-/-) mice, we determined that Dsg3 did not serve as a surrogate antigen allowing antimitochondrial antibodies to enter KCs. The PVIgG-induced activation of epidermal growth factor receptor and Src was affected neither in Dsg3(-/-) KCs nor due to absorption of antimitochondrial antibodies. These results demonstrated that apoptolysis in PV is a complex process initiated by at least three classes of autoantibodies directed against desmosomal, mitochondrial, and other keratinocyte self-antigens. These autoantibodies synergize with the proapoptotic serum and tissue factors to trigger both extrinsic and intrinsic pathways of cell death and break the epidermal cohesion, leading to blisters. Further elucidation of the primary signaling events downstream of PV autoantigens will be crucial for the development of a more successful therapy for PV patients.

Significance of autoimmunity to non-desmoglein targets in pemphigus

The pathogenesis of pemphigus vulgaris (PV) is a highly controversial, "hot" topic that has received considerable enrichment in recent years by both clinical and basic researchers. On the one hand, the classical view of desmogleins (Dsg) as main targets of this autoimmune disease is supported by the characterization of pathogenic anti-Dsg3 antibodies from both patients and animal models. On the other hand, fundamental doubt has been raised towards this monopathogenic view by several independent factors: (1) pemphigus lesions can be induced in Dsg3-knockout (KO) mice; (2) pemphigus sera contain multiple autoantibodies against different adhesion molecules and also cholinergic receptors; (3) experimental inhibition of PV IgG induced acantholysis can be obtained by interference with different signaling cascades regulating both calcium homeostasis and apoptosis; and (4) cholinergic agonists exhibit anti-acantholytic activity both in vitro and in vivo. The field is open for controlled clinical trials and further basic research to unfold the true story of the pemphigus enigma and provide the basis for a better treatment of pemphigus patients.

Apoptolysis: a novel mechanism of skin blistering in pemphigus vulgaris linking the apoptotic pathways to basal cell shrinkage and suprabasal acantholysis

Understanding the acantholytic pathways leading to blistering in pemphigus vulgaris (PV) is a key to development of novel treatments. A novel paradigm of keratinocyte damage in PV, termed apoptolysis, links the suprabasal acantholytic and cell death pathways to basal cell shrinkage rendering a 'tombstone' appearance to PV lesions. In contrast to apoptolysis, the classic keratinocyte apoptosis mediating toxic epidermal necrolysis causes death and subsequent sloughing of the entire epidermis. Apoptolysis includes five consecutive steps. (1) Binding of autoantibodies to PV antigens. (2) Activation of EGF receptor, Src, mTOR, p38 MAPK and other signalling elements downstream of ligated antigens, elevation of intracellular calcium and launching of the cell death cascades. (3) Basal cell shrinkage due to: (i) collapse and retraction of the tonofilaments cleaved by executioner caspases; and (ii) dissociation of interdesmosomal adhesion complexes caused by phosphorylation of adhesion molecules. (4) Massive cleavage of cellular proteins by activated cell death enzymes leading to cell collapse, and tearing off desmosomes from the cell membrane stimulating secondary autoantibody production. (5) Rounding up and death of acantholytic cells. Thus, the structural damage (acantholysis) and death (apoptosis) of keratinocytes are mediated by the same cell death enzymes. Appreciation of the unifying concept of apoptolysis have several important implications: (i) linking together a number of seemingly unrelated events surrounding acantholysis; (ii) opening new avenues of investigation into the pathomechanism of pemphigus; and (iii) creating new approaches to the treatment of pemphigus based on blocking the signalling pathways and enzymatic processes that lead to blistering.

An imbalance in Akt/mTOR is involved in the apoptotic and acantholytic processes in a mouse model of pemphigus vulgaris

Pemphigus vulgaris (PV) is an autoimmune blistering disease characterized by the presence of IgG autoantibodies against Dsg3. Our aim was to investigate the molecular events implicated in the development and localization of apoptosis and acantholysis in PV. We used a passive transfer mouse model together with immunohistochemical (IHC) techniques and the TUNEL assay, with quantification analysis in the basal layer of the epidermis. The activated signalling molecules analysed and apoptotic cells detected showed an identical localization. Herein, we found for the first time in vivo an increased expression of activated HER receptor isoforms in the basal layer in PV lesions. Besides, we observed the almost total lack of activated Akt compared with a higher level of activated mTOR within the basal cells of the epidermis. Our observations strongly support that the restriction of acantholysis to the basal layer may be due, at least in part, to the selective and increased presence of activated HER receptor isoforms in these cells. After phosphorylation of HER receptor isoforms, intracellular signalling pathways are activated in the basal layer. In addition, the imbalance in Akt/mTOR that takes place in the basal cells may provide intracellular signals necessary for the development of apoptosis and acantholysis.

Serum of patients with oral pemphigus vulgaris impairs keratinocyte wound repair in vitro: a time-lapse study on the efficacy of methylprednisolone and pyridostigmine bromide

OBJECTIVES

Pemphigus vulgaris (PV) is an autoimmune blistering disease affecting primarily oral mucosa and skin. Among the drugs used for the therapy of pemphigus, both methylprednisolone (MP) and pyridostigmine bromide (PBr) can prevent acantholysis in vitro. However, their putative therapeutic properties in regenerating PV-like lesions and promoting the healing process still remain to be demonstrated. To address this issue, here we have developed a model for studying the process of epithelial cleft regeneration in PV by artificially wounding keratinocyte monolayers.

MATERIALS AND METHODS

The experimental model was established by scratching confluent monolayers to simulate the epithelial cleft; then, wound regeneration in the presence of submaximal concentrations of PV sera was studied by time-lapse microscopy, with or without the addition of MP and PBr in the culture medium.

RESULTS

Pemphigus vulgaris serum inhibited epithelial cleft repair of wounded monolayers. Indeed, in the presence of 10% (v/v) PV serum, keratinocytes reached only 2% confluence within 72 h vs an almost complete healing of controls. When administered together with PV sera, MP significantly (P < 0.01) enhanced wound fill by 30% after 72 h. PV-associated wound repair was significantly (P < 0.05) ameliorated by PBr by 24 h and keratinocytes reached 20% confluence after 72 h. Interestingly, neither MP nor PBr could accelerate wound healing when compared with untreated control monolayers.

CONCLUSIONS

In PV, MP and PBr exert their curative effects in part by enhancing the regeneration properties of keratinocytes. Indeed, our data suggest that both drugs can specifically counterbalance the detrimental effects of PV serum on keratinocyte wound healing. These findings provide an explanation for the efficacy of MP and PBr in the treatment of PV lesions in human skin and oral mucosa.

The desmosome and pemphigus

Desmosomes are patch-like intercellular adhering junctions ("maculae adherentes"), which, in concert with the related adherens junctions, provide the mechanical strength to intercellular adhesion. Therefore, it is not surprising that desmosomes are abundant in tissues subjected to significant mechanical stress such as stratified epithelia and myocardium. Desmosomal adhesion is based on the Ca(2+)-dependent, homo- and heterophilic transinteraction of cadherin-type adhesion molecules. Desmosomal cadherins are anchored to the intermediate filament cytoskeleton by adaptor proteins of the armadillo and plakin families. Desmosomes are dynamic structures subjected to regulation and are therefore targets of signalling pathways, which control their molecular composition and adhesive properties. Moreover, evidence is emerging that desmosomal components themselves take part in outside-in signalling under physiologic and pathologic conditions. Disturbed desmosomal adhesion contributes to the pathogenesis of a number of diseases such as pemphigus, which is caused by autoantibodies against desmosomal cadherins. Beside pemphigus, desmosome-associated diseases are caused by other mechanisms such as genetic defects or bacterial toxins. Because most of these diseases affect the skin, desmosomes are interesting not only for cell biologists who are inspired by their complex structure and molecular composition, but also for clinical physicians who are confronted with patients suffering from severe blistering skin diseases such as pemphigus. To develop disease-specific therapeutic approaches, more insights into the molecular composition and regulation of desmosomes are required.

Differential coupling of M1 muscarinic and alpha7 nicotinic receptors to inhibition of pemphigus acantholysis

The mechanisms mediating and regulating assembly and disassembly of intercellular junctions is a subject of intensive research. The IgG autoantibodies produced in patients with the immunoblistering skin disease pemphigus vulgaris (PV) can induce keratinocyte (KC) dyshesion (acantholysis) via mechanisms that involve signaling kinases targeting intercellular adhesion molecules, thus providing a useful model to study the physiologic regulation of KC cohesion. Previous studies showed that activation of Src and protein kinase C are the earliest events in the PV IgG-induced intracellular phosphorylation cascades and that cholinergic agonists are effective for treating patients with pemphigus. In this study, we sought to elucidate the molecular mechanisms allowing cholinergic agonists to inhibit PV IgG-induced acantholysis and phosphorylation of KC adhesion molecules. The extent of acantholysis in KC monolayers correlated closely with the degree of PV IgG-induced phosphorylation of p120- and beta-catenins, with classic isoforms of protein kinase C mediating serine phosphorylation of beta-catenin and Src-tyrosine phosphorylation of p120-catenin. The M(1) muscarinic agonist pilocarpine blocked phosphorylation of both catenins, which could be abolised by the M(1) antagonist MT7. The alpha7 nicotinic agonist AR-R17779 inhibited phosphorylation of P120-cateinin. The alpha7 antagonist methyllycaconitine abolished the effect of AR-R17779. Okadaic acid abrogated protective effects of agonists on phosphorylation of beta-catenin, and pervanadate, on that of p120-catenin. Stimulation of KCs with pilocarpine significantly (p < 0.05) elevated both serine/threonine and tyrosine phosphatase activities in KCs. AR-R17779 both stimulated tyrosine phosphatase and decreased PV IgG-induced Src activity. Methyllycaconitine released Src activity in intact KCs and caused acantholysis. Thus, downstream signaling from M(1) abolished PV IgG-dependent catenin phosphorylation due to activation of both serine/threonine and tyrosine phosphatases, whereas alpha7 action involved both activation of tyrosine phosphatase and inhibition of Src. These findings identified novel paradigm of regulation of signaling kinases associated with cholinergic receptors and provided mechanistic explanation of therapeutic activity of cholinomimetics in PV patients.

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.

Pemphigus IgG causes skin splitting in the presence of both desmoglein 1 and desmoglein 3

According to the desmoglein (Dsg) compensation concept, different epidermal cleavage planes observed in pemphigus vulgaris and pemphigus foliaceus have been proposed to be caused by different autoantibody profiles against the desmosomal proteins Dsg 1 and Dsg 3. According to this model, Dsg 1 autoantibodies would only lead to epidermal splitting in those epidermal layers in which no Dsg 3 is present to compensate for the functional loss of Dsg 1. We provide evidence that both pemphigus foliaceus-IgG containing Dsg 1- but not Dsg 3-specific antibodies and pemphigus vulgaris-IgG with antibodies to Dsg 1 and Dsg 3 were equally effective in causing epidermal splitting in human skin and keratinocyte dissociation in vitro. These effects were present where keratinocytes expressed both Dsg 1 and Dsg 3, demonstrating that Dsg 3 does not compensate for Dsg 1 inactivation. Rather, the cleavage plane in intact human skin caused by pemphigus autoantibodies was similar to the plane of keratinocyte dissociation in response to toxin B-mediated inactivation of Rho GTPases. Because we recently demonstrated that pemphigus-IgG causes epidermal splitting by inhibition of Rho A, we propose that Rho GTPase inactivation contributes to the mechanisms accounting for the cleavage plane in pemphigus skin splitting.

Desmoglein Versus Non-desmoglein Signaling in Pemphigus Acantholysis

Although it is accepted that pemphigus antibody binding to keratinocytes (KCs) evokes an array of intracellular biochemical events resulting in cell detachment and death, the triggering events remain obscure. It has been postulated that the binding of pemphigus vulgaris IgG (PVIgG) to KCs induces "desmosomal" signaling. Because in contrast to integrins and classical cadherins, desmoglein (Dsg) molecules are not known to elicit intracellular signaling, and because PV patients also produce non-Dsg autoantibodies, we investigated the roles of both Dsg and non-desmoglein PV antigens. The time course studies of KCs treated with PVIgG demonstrated that the activity of Src peaked at 30 min, EGF receptor kinase (EGFRK) at 60 min, and p38 MAPK at 240 min. The Src inhibitor PP2 decreased EGFRK and p38 activities by approximately 45 and 30%, respectively, indicating that in addition to Src, PVIgG evokes other triggering events. The shrinkage of KCs (cell volume reduction) became significant at 120 min, keratin aggregation at 240 min, and an increase of TUNEL positivity at 360 min. Pretreatment of KCs with PP2 blocked PVIgG-dependent cell shrinkage and keratin aggregation by approximately 50% and TUNEL positivity by approximately 25%. The p38 MAPK inhibitor PD169316 inhibited these effects by approximately 15, 20, and 70%, respectively. Transfection of KCs with small interfering RNAs that silenced expression of Dsg1 and/or Dsg3 proteins, blocked approximately 50% of p38 MAPK activity but did not significantly alter the PVIgG-dependent rise in Src and EGFRK activities. These results indicate that activation of p38 MAPK is a late signaling step associated with collapse of the cytoskeleton and disassembly of desmosomes caused by upstream events involving Src and EGFRK. Therefore, the early acantholytic events are triggered by non-Dsg antibodies.

Apoptotic mechanism in pemphigus autoimmunoglobulins-induced acantholysis--possible involvement of the EGF receptor

Pemphigus is an autoimmune cutaneous disease characterized by circulating autoantibodies that cause blistering and erosions on skin and mucous membranes. Circulating autoantibodies bind to epidermal cell membrane and cause cell-cell detachment (acantholysis), leading to epidermal tissue damage and cell death. The principal target of pemphigus vulgaris autoantibodies (PV-IgG) is desmosomal cadherin desmoglein 3 (Dsg3), a constituent of desmosomes, mediating cell-cell adhesion. Several hypotheses for the mechanisms of acantholysis induction by PV-IgG exist, but the actual mechanism is not clear as yet. We have previously reported on apoptosis induction in PV-IgG-mediated epidermal tissue and cell damage as a possible mechanism of acantholysis and cell death (Wang et al. 2004, Apoptosis, 9:131-143). In this study we investigated the involvement of the EGFR and intracellular signal transduction pathways in the PV-IgG-induced apoptosis. We show here that PV-IgG induced activation/autophosphorylation of EGFR in cultured keratinocytes in vitro. The specific tyrosine kinase inhibitor AG1478 abrogated EGFR autophosphorylation, cell death, FasL appearance and acantholysis, all induced by PV-IgG, in parallel, confirming the involvement of EGFR in this Fas apoptotic cascade. Activation of EGFR was followed by phosphorylation of its downstream substrates, MAP kinase ERK and transcription factor c-Jun, and internalization of EGFR. Pharmacological inactivation of the EGFR and ERK kinase activities, by use of specific inhibitors AG1478 and PD98059 respectively, blocked PV-IgG-induced phosphorylation of EGFR, ERK and c-Jun and cellular apoptosis, measured by flow cytometry and caspase 3 activity. Prolonged activation of EGFR by PV-IgG led to dramatic internalization of this receptor, possibly reducing the ability of the cell to perform survival signals. This suggests that activation of EGFR, followed by its internalization, is pivotal for intracellular apoptotic signal transduction via ERK/c-Jun pathways, leading to acantholysis. Our experimental data indicate that the EGFR is instrumental in transducing apoptotic/acantholytic signals in keratinocytes cultures in response to PV-IgG treatment. The acantholytic effect caused by PV-IgG binding to cell surface receptors begins with and depends on cell surface receptor (EGFR) activation of intracellular signaling pathways (ERK pathway) and apoptosis induction (FasR pathway), which later lead to major cell-cell separation (acantholysis) and cell death.

Desmoglein autoimmunity in the pathogenesis of pemphigus

The most characteristic feature of pemphigus is a loss of cohesion between keratinocytes, resulting in formation of blisters and erosions on the mucosal membranes and the skin. Identification of circulating antibodies which bind to desmogleins (Dsg), transmembrane proteins involved in assembly of the desmosomes, led to the immediate realization that these antibodies may be pathogenic by interfering with desmosomal function. Despite extensive experimental evidence documenting the presence of the anti-Dsg response, its pathogenic relevance is still debated. At the current stage of the knowledge it seems likely that anti-Dsg imunoglobulins may play a role in pemphigus via interference with cellular Dsg trafficking and by activation of specific signalling pathways rather than by simple interference with desmosomal adhesion.