Binding of pemphigus vulgaris IgG to antigens in desmosome core domains excludes immune complexes rather than directly splitting desmosomes

Punctate Pattern and Pemphigus: Is There Any Evidence of Punctate Pattern Among Iranian Patients?

AIM

To examine the prevalence of this novel pattern among Iranian patients with pemphigus and peruse the relationship between the presence of a punctate pattern with clinical severity of disease and histopathological findings.

METHODS

One hundred recently diagnosed patients with pemphigus were enrolled. DIF evaluation and routine light microscopy were performed on their biopsy specimens. Disease severity was determined using the Pemphigus Disease Area Index. Serum samples were collected to measure autoantibody titers using enzyme-linked immunosorbent assay.

RESULTS

All the samples evaluated by DIF showed a continuous linear pattern of intercellular IgG deposition, whereas none of them had a punctate pattern. Despite a significant correlation between the Pemphigus Disease Area Index score and autoantibody values, no association between histopathological findings and disease severity has been found.

CONCLUSION

We could not detect any punctate pattern among Iranian patients with pemphigus. The importance of this pattern in the diagnosis of pemphigus might be different among patients with different ethnic and genetic factors.

[Epidemiology, etiology and pathogenesis of oral mucosa bullous lesions]

OBJECTIVE Based on the data available in modern literature, to conduct a study on the epidemiology, etiology and pathogenesis of bullous lesions of the oral mucosa (pemphigus vulgaris, pemphigoid bullosa, lichen ruber planus).

MATERIAL AND METHODS

The article is based on the study of materials of foreign and domestic research databases Pubmed and Elibrary. Used literature data over the past 15 years.

RESULTS

According to domestic and foreign studies, among dermatological diseases, the most frequently detected diseases are: lichen ruber planus, pemphigoid bullosa and pemphigus vulgaris. The initial signs of these diseases are often neglected, both in patients and doctors, which leads to irreversible changes and severe course of the pathological process. In this connection, the number of patients with these lesions of the oral mucosa increases every year in all countries of the world. Bullous lesions of the oral mucosa are inflammatory and destructive diseases characterized mainly by recurrent course, variety of clinical manifestations, resistance to various therapeutic drugs. The specific features of the course of these diseases are explained both by the anatomical and physiological features of the oral mucosa, and by the etiologic and pathogenetic mechanisms of development. Currently, autoimmune processes play a leading role in the genesis of diseases, developing in response to changes in the antigenic structure of epidermal and epithelial cells under the influence of various damaging agents.

CONCLUSION

Thanks to the study, it was found that currently there are no data confirming the presence of microbial contamination of the tissues of the oral mucosa in the pathology under study. Not enough information on the factors of the immune response, in particular, on proinflammatory cytokines in the tissues of the oral mucosa.

[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.

Keratin Retraction and Desmoglein3 Internalization Independently Contribute to Autoantibody-Induced Cell Dissociation in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a potentially lethal autoimmune disease characterized by blister formation of the skin and mucous membranes and is caused by autoantibodies against desmoglein (Dsg) 1 and Dsg3. Dsg1 and Dsg3 are linked to keratin filaments in desmosomes, adhering junctions abundant in tissues exposed to high levels of mechanical stress. The binding of the autoantibodies leads to internalization of Dsg3 and a collapse of the keratin cytoskeleton-yet, the relevance and interdependence of these changes for loss of cell-cell adhesion and blistering is poorly understood. In live-cell imaging studies, loss of the keratin network at the cell periphery was detectable starting after 60 min of incubation with immunoglobulin G fractions of PV patients (PV-IgG). These rapid changes correlated with loss of cell-cell adhesion detected by dispase-based dissociation assays and were followed by a condensation of keratin filaments into thick bundles after several hours. Dsg3 internalization started at 90 min of PV-IgG treatment, thus following the early keratin changes. By inhibiting casein kinase 1 (CK-1), we provoked keratin alterations resembling the effects of PV-IgG. Although CK-1-induced loss of peripheral keratin network correlated with loss of cell cohesion and Dsg3 clustering in the membrane, it was not sufficient to trigger the internalization of Dsg3. However, additional incubation with PV-IgG was effective to promote Dsg3 loss at the membrane, indicating that Dsg3 internalization is independent from keratin alterations. Vice versa, inhibiting Dsg3 internalization did not prevent PV-IgG-induced keratin retraction and only partially rescued cell cohesion. Together, keratin changes appear very early after autoantibody binding and temporally overlap with loss of cell cohesion. These early alterations appear to be distinct from Dsg3 internalization, suggesting a crucial role for initial loss of cell cohesion in PV.

Pemphigus-A Disease of Desmosome Dysfunction Caused by Multiple Mechanisms

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

Mechanisms Causing Loss of Keratinocyte Cohesion in Pemphigus

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

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.

150th Anniversary Series: Desmosomes and the Hallmarks of Cancer

Desmosomes represent adhesive, spot-like intercellular junctions that in association with intermediate filaments mechanically link neighboring cells and stabilize tissue architecture. In addition to this structural function, desmosomes also act as signaling platforms involved in the regulation of cell proliferation, differentiation, migration, morphogenesis, and apoptosis. Thus, deregulation of desmosomal proteins has to be considered to contribute to tumorigenesis. Proteolytic fragmentation and downregulation of desmosomal cadherins and plaque proteins by transcriptional or epigenetic mechanisms were observed in different cancer entities suggesting a tumor-suppressive role. However, discrepant data in the literature indicate that context-dependent differences based on alternative intracellular, signal transduction lead to altered outcome. Here, modulation of Wnt/β-catenin signaling by plakoglobin or desmoplakin and of epidermal growth factor receptor signaling appears to be of special relevance. This review summarizes current evidence on how desmosomal proteins participate in carcinogenesis, and depicts the molecular mechanisms involved.

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.

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".

IgG antibodies in patients with pemphigus vulgaris before and after diagnosing with immunofluorescence

Pemphigus is defined as a group of chronic self-immune vesicular diseases histologically recognized by inter-epidermic vesicles resulting from acantholysis. The aim of this study was to evaluate the precipitant and circulative IgG antibodies in patients with pemphigus vulgaris before and after treating with immunofluorescence. Sixty-two patients (34 females and 28 males) with clinically and pathologically confirmed P.V. were studied prospectively over a one year period of time during which direct and indirect immunofluorescent tests were performed before and after treatment. They had mild or moderate forms of disease. All patients received prednisolon 1-2 mg/kg/day and Azathioprine 2-3 mg/kg/day or methylpredisolon (1 g day(-1) for 4 days) and cyclophosphamide (500 mg/first day) pulse therapy due to general condition. Thirty- four females and 28 males enrolled, the mean age were 39.5 years (SD = 12.7). Before treatment, 10 and 52 cases were positive for skin depositing + or ++) and circulatory IgG (1/20 -1/60), respectively. Two to 3 month later, 37 were IgG positive with titers 1/20 to 1/160. The correlation between circulatory IgG before and after treatment was weakly positive (p = 0.05, r = 0.415). In the present study, treatment methods used for patients suffering from pemphigus vulgaris were not successful in significantly decreasing the circulative autoantibodies levels.

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.

Signaling dependent and independent mechanisms in pemphigus vulgaris blister formation

Pemphigus vulgaris (PV) is an autoimmune epidermal blistering disease caused by autoantibodies directed against the desmosomal cadherin desmoglein-3 (Dsg3). Significant advances in our understanding of pemphigus pathomechanisms have been derived from the generation of pathogenic monoclonal Dsg3 antibodies. However, conflicting models for pemphigus pathogenicity have arisen from studies using either polyclonal PV patient IgG or monoclonal Dsg3 antibodies. In the present study, the pathogenic mechanisms of polyclonal PV IgG and monoclonal Dsg3 antibodies were directly compared. Polyclonal PV IgG cause extensive clustering and endocytosis of keratinocyte cell surface Dsg3, whereas pathogenic mouse monoclonal antibodies compromise cell-cell adhesion strength without causing these alterations in Dsg3 trafficking. Furthermore, tyrosine kinase or p38 MAPK inhibition prevents loss of keratinocyte adhesion in response to polyclonal PV IgG. In contrast, disruption of adhesion by pathogenic monoclonal antibodies is not prevented by these inhibitors either in vitro or in human skin explants. Our results reveal that the pathogenic activity of polyclonal PV IgG can be attributed to p38 MAPK-dependent clustering and endocytosis of Dsg3, whereas pathogenic monoclonal Dsg3 antibodies can function independently of this pathway. These findings have important implications for understanding pemphigus pathophysiology, and for the design of pemphigus model systems and therapeutic interventions.

Cell-cell connectivity: desmosomes and disease

Cell-cell connectivity is an absolute requirement for the correct functioning of cells, tissues and entire organisms. At the level of the individual cell, direct cell-cell adherence and communication is mediated by the intercellular junction complexes: desmosomes, adherens, tight and gap junctions. A broad spectrum of inherited, infectious and auto-immune diseases can affect the proper function of intercellular junctions and result in either diseases affecting specific individual tissues or widespread syndromic conditions. A particularly diverse group of diseases result from direct or indirect disruption of desmosomes--a consequence of their importance in tissue integrity, their extensive distribution, complex structure, and the wide variety of functions their components accomplish. As a consequence, disruption of desmosomal assembly, structure or integrity disrupts not only their intercellular adhesive function but also their functions in cell communication and regulation, leading to such diverse pathologies as cardiomyopathy, epidermal and mucosal blistering, palmoplantar keratoderma, woolly hair, keratosis, epidermolysis bullosa, ectodermal dysplasia and alopecia. Here, as well as describing the importance of the other intercellular junctions, we focus primarily on the desmosome, its structure and its role in disease. We will examine the various pathologies that result from impairment of desmosome function and thereby demonstrate the importance of desmosomes to tissues and to the organism as a whole.

An adult passive transfer mouse model to study desmoglein 3 signaling in pemphigus vulgaris

Evidence has accumulated that changes in intracellular signaling downstream of desmoglein 3 (Dsg3) may play a significant role in epithelial blistering in the autoimmune disease pemphigus vulgaris (PV). Currently, most studies on PV involve passive transfer of pathogenic antibodies into neonatal mice which have not finalized epidermal morphogenesis, and do not permit analysis of mature hair follicles (HFs) and stem cell niches. To investigate Dsg3 antibody-induced signaling in the adult epidermis at defined stages of the HF cycle, we here developed a model with passive transfer of the monospecific pathogenic Dsg3 antibody AK23 into adult 8-week-old C57Bl/6J mice. Validated using histopathological and molecular methods, we found that this model faithfully recapitulates major features described in PV patients and PV models. Two hours after AK23 transfer we observed widening of intercellular spaces between desmosomes and EGFR activation, followed by increased Myc expression and epidermal hyperproliferation, desmosomal Dsg3 depletion and predominant blistering in HFs and oral mucosa. These data confirm that the adult passive transfer mouse model is ideally suited for detailed studies of Dsg3 antibody-mediated signaling in adult skin, providing the basis for investigations on novel keratinocyte-specific therapeutic strategies.

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.

Pathogenic relevance of IgG and IgM antibodies against desmoglein 3 in blister formation in pemphigus vulgaris

Pemphigus vulgaris is an autoimmune disease caused by IgG antibodies against desmoglein 3 (Dsg3). Previously, we isolated a pathogenic mAb against Dsg3, AK23 IgG, which induces a pemphigus vulgaris-like phenotype characterized by blister formation. In the present study, we generated a transgenic mouse expressing AK23 IgM to examine B-cell tolerance and the pathogenic role of IgM. Autoreactive transgenic B cells were found in the spleen and lymph nodes, whereas anti-Dsg3 AK23 IgM was detected in the cardiovascular circulation. The transgenic mice did not develop an obvious pemphigus vulgaris phenotype, however, even though an excess of AK23 IgM was passively transferred to neonatal mice. Similarly, when hybridoma cells producing AK23 IgM were inoculated into adult mice, no blistering was observed. Immunoelectron microscopy revealed IgM binding at the edges of desmosomes or interdesmosomal cell membranes, but not in the desmosome core, where AK23 IgG binding has been frequently detected. Furthermore, in an in vitro dissociation assay using cultured keratinocytes, AK23 IgG and AK23 IgM F(ab')(2) fragments, but not AK23 IgM, induced fragmentation of epidermal sheets. Together, these observations indicate that antibodies must gain access to Dsg3 integrated within desmosomes to induce the loss of keratinocyte cell-cell adhesion. These findings provide an important framework for improved understanding of B-cell tolerance and the pathophysiology of blister formation in pemphigus.