The detection of IgG and IgA autoantibodies to desmocollins 1-3 by enzyme-linked immunosorbent assays using baculovirus-expressed proteins, in atypical pemphigus but not in typical pemphigus

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.

Immune serological diagnosis of pemphigus

Pemphigus is a rare autoimmune blistering disease which manifests with painful erosions and blisters of the skin and mucosa. This disorder is caused by autoantibodies attacking desmosomal proteins, necessary for cell-cell contact stability and epidermal integrity. Desmoglein (Dsg) 1 and Dsg3 are the two major target antigens in pemphigus. Yet, many other target proteins, which have been described over the years, seem to be involved in the loss of epidermal integrity. Clinical examination, combined to serological advances and detection of targeted antigens, permitted to differentiate among several pemphigus subtypes, in which pemphigus vulgaris and pemphigus foliaceus are the most common. Nowadays, serological analysis in pemphigus is a fundamental step of the diagnostic algorithm. This is based on analysis of clinical symptoms, histopathological examination of lesional skin, detection of tissue bound and circulating antibodies by direct and indirect immunofluorescence, and determination of target antigens either by enzyme-linked immunosorbent essay (ELISA) or by western blot analysis. A correct and exhaustive diagnostic algorithm is fundamental to characterize pemphigus subtypes, which lastly permits to adopt a correct treatment approach. Moreover, quality and quantity of circulating antibodies in patient's sera deliver important information regarding clinical course, disease severity and treatment response; thus, relevantly affecting physician's decision. To facilitate this process, "easy-to-perform" diagnostic kits with high sensitivity and specificity are being commercialized. In this review, we focus on available methods and established assays to correctly detect circulating autoantibodies in pemphigus. Moreover, we discuss subtype specific serological peculiarities in the five most relevant subtypes (pemphigus vulgaris, pemphigus foliaceus, pemphigus vegetans, paraneoplastic pemphigus and intercellular IgA dermatosis (also called as IgA pemphigus).

Serological Diagnosis of Autoimmune Bullous Skin Diseases

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

Pathogenic IgG4 autoantibodies from endemic pemphigus foliaceus recognize a desmoglein-1 conformational epitope

Fogo Selvagem (FS), the endemic form of pemphigus foliaceus, is mediated by pathogenic IgG4 autoantibodies against the amino-terminal extracellular cadherin domain of the desmosomal cadherin desmoglein 1 (Dsg1). Here we define the detailed epitopes of these pathogenic antibodies. Proteolytic footprinting showed that IgG4 from 95% of FS donor sera (19/20) recognized a 16-residue peptide (A129LNSMGQDLERPLELR144) from the EC1 domain of Dsg1 that overlaps the binding site for an adhesive-partner desmosomal cadherin molecule. Mutation of Dsg1 residues M133 and Q135 reduced the binding of FS IgG4 autoantibodies to Dsg1 by ∼50%. Molecular modeling identified two nearby EC1 domain residues (Q82 and V83) likely to contribute to the epitope. Mutation of these residues completely abolished the binding of FS IgG4 to Dsg1. Bead aggregation assays showed that native binding interactions between Dsg1 and desmocollin 1 (Dsc1), which underlie desmosome structure, were abolished by Fab fragments of FS IgG4. These results further define the molecular mechanism by which FS IgG4 autoantibodies interfere with desmosome structure and lead to cell-cell detachment, the hallmark of this disease.

Routine detection of serum antidesmocollin autoantibodies is only useful in patients with atypical pemphigus

Autoantibodies against the 3 desmocollin (Dsc; Dsc1-Dsc3) isoforms have been described in different pemphigus variants. Here, we developed state-of-the-art detection systems for serum anti-Dsc1, Dsc2 and Dsc1 IgG and IgA. These assays were applied in 5 different cohorts including pemphigus vulgaris (PV) patients with compatible direct immunofluorescence (IF) microscopy but no reactivity against desmogleins 1 and 3 (n = 24) and sera from patients with autoimmune blistering diseases with positive direct IF microscopy taken at the time of diagnosis (n = 749). We found that detection of anti-Dsc serum reactivity is not helpful in the routine diagnosis of PV, pemphigus foliaceus and paraneoplastic pemphigus but may be valuable in pemphigus vegetans.

Divergent Specificity Development of IgG1 and IgG4 Autoantibodies in Endemic Pemphigus Foliaceus (Fogo Selvagem)

We have shown that although the IgG response in fogo selvagem (FS) is mainly restricted to desmoglein (Dsg) 1, other keratinocyte cadherins are also targeted by FS patients and healthy control subjects living in the endemic region of Limão Verde, Brazil (endemic controls). Evaluating nonpathogenic IgG1 and pathogenic IgG4 subclass responses to desmosomal proteins may reveal important differences between pathogenic and nonpathogenic responses, and how these differences relate to the pathogenic IgG4 response and resultant FS. In this study, we tested by ELISA >100 sera from each FS patient, endemic control, and nonendemic control for IgG1 and IgG4 autoantibodies to keratinocyte cadherins besides Dsg1. IgG1 and IgG4 subclass responses in endemic controls are highly correlated between Dsg1 and other keratinocyte cadherins. This correlation persists in the IgG1 response among FS patients, but diminishes in IgG4 response, suggesting that IgG1 binds highly conserved linear epitopes among cadherins, whereas IgG4 binds mainly specific conformational epitopes on Dsg1. A confirmatory test comparing serum samples of 11 individuals before and after their FS onset substantiated our findings that IgG1 recognizes primarily linear epitopes on Dsg1 both before and after disease onset, whereas IgG4 recognizes primarily linear epitopes before disease onset, but recognizes more conformational epitopes on Dsg1 after the onset of disease. This study may provide a mechanism by which a specificity convergence of the IgG4 response to unique Dsg1 epitopes, most likely conformational pathogenic epitopes, leads to the onset of FS disease.

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.

Clinical and immunological studies of 49 cases of various types of intercellular IgA dermatosis and 13 cases of classical subcorneal pustular dermatosis examined at Kurume University

BACKGROUND

Intercellular IgA dermatosis (IAD) is a subset of autoimmune bullous disease exclusively with IgA antikeratinocyte cell-surface antibodies. The classification and pathogenesis of this condition are still obscure.

OBJECTIVES

To classify IAD and study its pathogenesis.

METHODS

From our cohort of 5402 cases of autoimmune bullous disease, we selected 49 cases of various types of intercellular IgA dermatosis (IAD) and 13 cases of classical subcorneal pustular dermatosis (SPD), for which sera and information were available. We studied these cases clinically and immunologically.

RESULTS

There were 17 SPD-type IAD, 12 intraepidermal neutrophilic IgA dermatosis (IEN)-type IAD, two IgA-pemphigus vegetans, four IgA-pemphigus foliaceus, six IgA-pemphigus vulgaris and eight unclassified IAD cases. There was no sex predominance, and the average age at disease onset was 45·9 years. Clinically, bullous and pustular skin lesions developed on various sites, particularly intertriginous areas. Histopathology showed intraepidermal blisters or pustules at the upper epidermis in the SPD-type and at the midepidermis in the IEN-type. Immunological studies revealed that direct immunofluorescence, indirect immunofluorescence of normal human skin and enzyme-linked immunosorbent assays (ELISAs) of recombinant proteins of desmogleins and desmocollins frequently showed positive results, although no antigens were detected in many cases. All cases of classical SPD, which showed no positive immunological results, were indistinguishable clinically and histopathologically from SPD-type IAD.

CONCLUSIONS

The present study of the largest cohort of cases of IAD showed that the major subtypes are SPD and IEN, and that the combination of indirect immunofluorescence and ELISAs of desmogleins and desmocollins, in addition to direct immunofluorescence, was useful for the diagnosis of IAD and its subtypes.

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.

The expanding spectrum of IgA pemphigus: a case report and review of the literature

IgA pemphigus (IGAP) is a rare, distinct variant of pemphigus, currently classified, depending upon the histological features, immunofluorescence staining pattern and autoantibody profile, into two types: subcorneal pustular dermatosis (SPD) and intraepidermal neutrophilic IgA dermatosis. In a patient with a widespread blistering disease of the skin resembling SPD-type IGAP, we demonstrate the coexistence of IgA reactivity to both epidermal (desmocollins 2 and 3) and basement membrane-associated (BP180) proteins, suggesting the coexistence of atypical IGAP and linear IgA bullous dermatosis, respectively. This case, together with 20 previous reports of atypical IGAP, underscores the limitations of current classification schemes. Therefore, we suggest reclassifying these cases under the general term 'IGAP spectrum'.

150(th) anniversary series: Desmosomes and autoimmune disease, perspective of dynamic desmosome remodeling and its impairments in pemphigus

Desmosomes are the most important intercellular adhering junctions that adhere two adjacent keratinocytes directly with desmosomal cadherins, that is, desmogleins (Dsgs) and desmocollins, forming an epidermal sheet. Recently, two cell-cell adhesion states of desmosomes, that is, "stable hyper-adhesion" and "dynamic weak-adhesion" conditions have been recognized. They are mutually reversible through cell signaling events involving protein kinase C (PKC), Src and epidermal growth factor receptor (EGFR) during Ca(2+)-switching and wound healing. This remodeling is impaired in pemphigus vulgaris (PV, an autoimmune blistering disease), caused by anti-Dsg3 antibodies. The antibody binding to Dsg3 activates PKC, Src and EGFR, linked to generation of dynamic weak-adhesion desmosomes, followed by p38MAPK-mediated endocytosis of Dsg3, resulting in the specific depletion of Dsg3 from desmosomes and acantholysis. A variety of pemphigus outside-in signaling may explain different clinical (non-inflammatory, inflammatory, and necrolytic) types of pemphigus. Pemphigus could be referred to a "desmosome-remodeling disease involving pemphigus IgG-activated outside-in signaling events".

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.

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

Pemphigus is considered an autoimmune bullous skin disorder associated with IgG against the desmosomal components, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). This concept is supported by the in vitro and in vivo pathogenicity of anti-Dsg3/Dsg1 IgG and the mucosal blistering phenotype of mice with a genetic deficiency of Dsg3. Mice deficient for another desmosomal adhesion molecule, desmocollin 3 (Dsc3), show a similar pemphigus phenotype, and we investigated the pathogenicity of Dsc3-reactive IgG autoantibodies that were identified previously in a subset of patients with atypical pemphigus. We here demonstrate that IgG against Dsc3 causes loss of adhesion of epidermal keratinocytes. Specifically, IgG against Dsc3 was purified from Dsc3-reactive pemphigus sera by affinity column chromatography using recombinant human Dsc3. Affinity purified IgG was functionally active and did not only react with recombinant Dsc3 but also with epidermis and cultured human keratinocytes. Moreover, Dsc3-reactive IgG induced loss of adhesion of epidermal keratinocytes in a dispase-based keratinocyte dissociation assay that was reversed on pre-adsorption with human Dsc3 but not Dsg3. These findings demonstrate that IgG autoantibodies against an additional component of the desmosomes, Dsc3, induce loss of keratinocyte adhesion and thus may contribute to blister formation in pemphigus.

A unique case of intra-epidermal neutrophilic dermatosis-type IgA pemphigus presenting with subcorneal pustules

BACKGROUND

While subcorneal pustular dermatosis-type IgA pemphigus shows subcorneal pustules, intra-epidermal neutrophilic dermatosis (IEN)-type IgA pemphigus is characterised by pustule formation throughout the entire epidermis.

OBJECTIVE

We analysed an unusual case of IEN-type IgA pemphigus showing subcorneal pustules.

METHODS

Indirect immunofluorescence, immunoblot analysis, auto-antibody-specific ELISAs, and double-labelling immuno-electron microscopy were performed.

RESULTS

IgA antibodies bound to the surface of keratinocytes distributed throughout the epidermis were detected by indirect immunofluorescence. IgA from the patient's serum failed to react with COS-7 cells expressing desmocollins (Dsc) 1, 2 or 3. IgG or IgA antibodies against desmogleins 1 and 3 were also found to be absent by ELISA. Double-labelling immuno-electron microscopy using an anti-Dsc monoclonal antibody showed localisation in the desmosomes, while IgA from the patient's serum was found in non-desmosomal regions.

CONCLUSION

The patient in the present study most likely suffers from IEN-type IgA pemphigus.

Autoimmunity to desmocollin 3 in pemphigus vulgaris

Pemphigus vulgaris is a blistering disease associated with autoantibodies to the desmosomal adhesion protein, desmoglein 3. Genetic deficiency of desmoglein 3 in mice mimics autoimmunity to desmoglein 3 in pemphigus vulgaris, with mucosal-dominant blistering in the suprabasal layer of the epidermis. Mice with an epidermal-specific deletion of desmocollin 3, the other major desmosomal cadherin isoform expressed in the basal epidermis, develop suprabasal blisters in skin that are histologically identical to those observed in pemphigus vulgaris, suggesting that desmocollin 3 might be a target of autoantibodies in some pemphigus vulgaris patients. We now demonstrate that desmocollin 3 is an autoantigen in pemphigus vulgaris, illustrated in a patient with mucosal-dominant blistering. Six of 38 pemphigus vulgaris and one of 85 normal serum samples immunoprecipitate desmocollin 3 (P = 0.003). Incubation of patient IgG with human keratinocytes causes loss of intercellular adhesion, and adsorption with recombinant desmocollin 3 specifically prevents this pathogenic effect. Additionally, anti-desmocollin 3 sera cause loss of keratinocyte cell surface desmocollin 3, but not desmoglein 3 by immunofluorescence, indicating distinct cellular pathogenic effects in anti-desmocollin and anti-desmoglein pemphigus, despite their identical clinical presentations. These data demonstrate that desmocollin 3 is a pathogenic autoantigen in pemphigus vulgaris and suggest that pemphigus vulgaris is a histological reaction pattern that may result from autoimmunity to desmoglein 3, desmocollin 3, or both desmosomal cadherins.

Desmocollin 3-mediated binding is crucial for keratinocyte cohesion and is impaired in pemphigus

Desmocollin (Dsc) 1-3 and desmoglein (Dsg) 1-4, transmembrane proteins of the cadherin family, form the adhesive core of desmosomes. Here we provide evidence that Dsc3 homo- and heterophilic trans-interaction is crucial for epidermal integrity. Single molecule atomic force microscopy (AFM) revealed homophilic trans-interaction of Dsc3. Dsc3 displayed heterophilic interaction with Dsg1 but not with Dsg3. A monoclonal antibody targeted against the extracellular domain reduced homophilic and heterophilic binding as measured by AFM, caused intraepidermal blistering in a model of human skin, and a loss of intercellular adhesion in cultured keratinocytes. Because autoantibodies against Dsg1 are associated with skin blistering in pemphigus, we characterized the role of Dsc3 binding for pemphigus pathogenesis. In contrast to AFM experiments, laser tweezer trapping revealed that pemphigus autoantibodies reduced binding of Dsc3-coated beads to the keratinocyte cell surface. These data indicate that loss of heterophilic Dsc3/Dsg1 binding may contribute to pemphigus skin blistering.

A perspective of pemphigus from bedside and laboratory-bench

Pemphigus represents a distinct organ-specific acquired autoimmune disease characterized by intra-epidermal blistering, which is induced by autoantibodies against desmosomal cadherins, desmoglein 1 (Dsg1), and Dsg3. Pemphigus is currently divided into three distinct varieties, i.e., pemphigus vulgaris (PV), pemphigus foliaceus (PF) and other variants of pemphigus (mostly associated with inflammation), depending on clinical features, the level of separation in the epidermis, and immunologic characteristics of auto-antigens. Blistering pathomechanisms differ for each of the types of pemphigus. Pemphigus, which results from autoantibodies against desmogleins and possibly to other proteins, binds to the cell surface antigens. This binding may cause steric hindrance to homophilic adhesion of desmogleins, and may, in turn, lead to internalization of desmogleins and inhibition of desmogleins' integration into desmosomes, resulting in the formation of Dsg3-depleted desmosomes in PV or Dsg1-depleted desmosomes in PF. Furthermore, PV-IgG activates an "outside-in" signaling pathway to induce disassembly of desmosomal components from the inside of the cells by phosphorylation of proteins, including Dsg3. On the other hand, Pemphigus-IgG-augmented signaling pathways may be linked to the secretion of cytokines such as in case of pemphigus herpetiformis and chemokines that initiate or activate inflammation. In this article, the classification of pemphigus and the characteristic pathomechanisms for acantholysis will be reviewed, with particular emphasis on the molecular and biochemical cell biology of these diseases.

E-cadherin is an additional immunological target for pemphigus autoantibodies

Pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are autoimmune blistering diseases characterized by autoantibodies against desmoglein (Dsg)1 and Dsg3, respectively. The role of classical cadherins as immunological targets of pemphigus autoantibodies is unknown. In this study, we tested the reactivity of sera from patients with PF, Fogo Selvagem (FS), and PV by immunoprecipitation coupled with immunoblotting (IP-IB) and ELISA techniques using a baculovirus-expressed ectodomain of E-cadherin. By IP-IB, anti-E-cadherin reactivity was detected in all tested sera of PF (n=13) and FS (n=15) patients, and in 79% of mucocutaneous-type PV patients (n=33), but in none of the mucosal-type PV patients (n=7). By ELISA, anti-E-cadherin IgG was detected in most pemphigus sera that produced strong E-cadherin bands by IP-IB. The immunoreactivity of PF/FS sera with E-cadherin was also demonstrated by IP-IB using human epidermal extracts. However, immunofluorescence staining of A431DE cells (E-cadherin positive, Dsg1 negative) with pemphigus sera showed negative results. Immunoadsorption and competitive ELISA analysis suggest that most of the anti-E-cadherin antibodies cross-react with Dsg1, whereas others may represent independent antibodies that do not cross-react with Dsg1. The functional relevance of these anti-E-cadherin IgG autoantibodies detected in these pemphigus sera remains to be defined.

Acquired palmoplantar keratoderma and immunobullous disease associated with antibodies to desmocollin 3

We present a case of immunobullous disease with an impressive acquired palmoplantar keratoderma (PPK) and unique antigenicity. The palms of the patient showed hyperkeratotic ridges with a tripe pattern that decreased with the amelioration of the immunobullous condition. The histopathology of perilesional skin (blister) demonstrated eosinophilic spongiosis and suprabasal blistering as in pemphigus vulgaris. In palmar skin, acantholysis, intraepidermal pustules, papillomatosis and marked hyperkeratosis were observed. Direct and indirect immunofluorescence displayed intraepidermal intercellular IgG staining as well as linear IgG staining along the epidermal basement membrane zone. Immunochemical assays revealed IgG antibodies to the desmosomal protein desmocollin 3 and to the hemidesmosomal proteins BP230 and LAD-1. Affinity-purified antidesmocollin 3 serum IgG bound to monkey oesophagus in the typical pemphigus pattern. Desmocollins are transmembrane proteins of the desmosome. Desmosome diseases may cause hereditary PPK. In our patient with acquired PPK, we hypothesize that the antibodies to desmocollin 3 were, apart from their role in eliciting the pemphigus-like blistering disease, also implicated in the pathogenesis of the PPK.

Cutaneous type pemphigus vulgaris: a rare clinical phenotype of pemphigus

Pemphigus is an autoimmune blistering disease of the skin, mucous membranes, or both. There are two main categories of pemphigus: pemphigus foliaceus (PF) and pemphigus vulgaris (PV). PV is further subdivided into mucosal dominant and mucocutaneous types, according to the extent of cutaneous lesions. These classes of pemphigus have distinct histopathologic and serologic findings, with most cases falling into these subtypes. We report 4 cases that clinically showed blisters and erosions in the skin only, without mucosal involvement. Histologic examination of cutaneous lesions demonstrated suprabasilar acantholysis, a typical finding for PV. These patients had predominant anti-desmoglein 1 (Dsg1) IgG autoantibodies as well as anti-Dsg3 IgG autoantibodies, as determined by enzyme-linked immunosorbent assay. The desmoglein compensation theory posits that this rare phenotype can be produced by pathogenically weak anti-Dsg3 IgG in the presence of potent anti-Dsg1 IgG autoantibodies. Thus, cutaneous type PV without apparent mucosal involvement is observed as a rare clinical and histologic expression of pemphigus. This expression can be a transient phenotype that may develop from, or evolve into, other subtypes of pemphigus.

Pénfigo

Pemphigus is an infrequent, organ-specific, autoimmune bullous disease, which affects the skin, mucous membranes and appendages. Histopathologically, it is characterized by acantholysis. Pemphigus has classically been divided into two major groups, pemphigus vulgaris and pemphigus foliaceus, with their respective clinical variants pemphigus vegetans and pemphigus erythematosus. In recent years, new variants of pemphigus have been described: paraneoplastic pemphigus, IgA pemphigus and pemphigus herpetiformis. This article reviews the epidemiology, etiopathogenesis, clinical symptoms, diagnosis, treatment and prognosis of pemphigus. Advances in molecular biology techniques have made it possible to more precisely identify the different antigens against which antibodies are directed, and to fine-tune ELISA diagnostic techniques. Treating pemphigus vulgaris and foliaceus with general steroids has modified their prognosis; it is estimated that mortality in recent decades is less than 10 %. Managing the clinical complications that appear during the evolution of the pemphigus has contributed to reducing morbidity and mortality.