Demonstration of pemphigus antibodies on the cell surface of murine epidermal cell monolayers and their internalization

The human skin organ culture model as an optimal complementary tool for murine pemphigus models

Pemphigus is a severe autoimmune bullous disease of the skin and/or mucous membranes caused by autoantibodies that mainly target the adhesion proteins desmoglein (Dsg) 3 and/or Dsg1. Clinically, pemphigus is characterized by flaccid blistering, leading to severe water and electrolyte loss. Before the introduction of corticosteroid treatment, the disease turned out to be fatal in many cases. Despite recent therapeutic improvements, treatment of pemphigus patients is centred on prolonged systemic immunosuppression and remains challenging. Current drug development for pemphigus has a strong focus on disease-causing B cells and autoantibodies and, more recently, also on modulating autoantibody-induced tissue pathology and keratinocyte signalling. This drug development requires reliable pre-clinical model systems replicating the pathogenesis of the human disease. Among those are neonatal and adult mouse models based on the transfer of Dsg3, Dsg1/3 or Dsg1-specific autoantibodies. To reduce the number of animal experiments, we recently established a standardized human skin organ culture (HSOC) model for pemphigus. This model reproduces the clinical phenotype of autoantibody-induced tissue pathology in pemphigus vulgaris. For induction of blistering, a recombinant single-chain variable fragment (scFv) targeting both Dsg1 and 3 is injected into pieces of human skin (obtained from plastic surgeries). Further characterization of the HSOC model demonstrated that key morphologic, molecular and immunologic features of pemphigus are being replicated. Thus, the pemphigus HSOC model is an excellent alternative to pemphigus animal model systems that are based on the transfer of (auto)antibodies.

Plasma Exosomal microRNA Profile Reveals miRNA 148a-3p Downregulation in the Mucosal-Dominant Variant of Pemphigus Vulgaris

The mucosal-dominant variant of pemphigus vulgaris (MPV) is an autoimmune disease characterized by oral mucosal blistering and circulating pathogenic IgG antibodies against desmoglein 3 (Dsg3), resulting in life-threatening bullae and erosion formation. Recently, microRNAs (miRNAs) have emerged as promising players in the diagnosis and prognosis of several pathological states. For the first time, we have identified a different expression profile of miRNAs isolated from plasma-derived exosomes (P-EVs) of MPV patients positive for antibodies against Dsg3 (Dsg3-positive) compared to healthy controls. Moreover, a dysregulated miRNA profile was confirmed in MPV tissue biopsies. In particular, a strong downregulation of the miR-148a-3p expression level in P-EVs of MPV patients compared to healthy controls was demonstrated. Bioinformatics prediction analysis identifies metalloproteinase-7 (MMP7) as a potential miR-148a-3p target. An in vitro acantholysis model revealed that the miR-148a-3p expression level was dramatically downregulated after treatment with Dsg3 autoantibodies, with a concomitant increase in MMP7 expression. The increased expression of MMP7 leads to the disruption of intercellular and/or extracellular matrix adhesion in an in vitro cellular model of MPV, with subsequent cell dissociation. Overexpression of miR-148a-3p prevented cell dissociation and regressed MMP7 upregulation. Our findings suggest a pivotal role of P-EV cargo in regulating molecular mechanisms involved in MPV pathogenesis and indicate them as potential MPV therapeutic targets.

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.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Super-Resolution Microscopy Reveals Altered Desmosomal Protein Organization in Tissue from Patients with Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoimmune epidermal blistering disease in which autoantibodies (IgG) are directed against the desmosomal cadherin desmoglein 3 (Dsg3). In order to better understand how PV IgG alters desmosome morphology and function in vivo, PV patient biopsies were analyzed by structured illumination microscopy (SIM), a form of super-resolution fluorescence microscopy. In patient tissue, desmosomal proteins were aberrantly clustered and localized to PV IgG-containing endocytic linear arrays. Patient IgG also colocalized with markers for lipid rafts and endosomes. Additionally, steady-state levels of Dsg3 were decreased and desmosomes were reduced in size in patient tissue. Desmosomes at blister sites were occasionally split, with PV IgG decorating the extracellular faces of split desmosomes. Desmosome splitting was recapitulated in vitro by exposing cultured keratinocytes both to PV IgG and to mechanical stress, demonstrating that splitting at the blister interface in patient tissue is due to compromised desmosomal adhesive function. These findings indicate that Dsg3 clustering and endocytosis are associated with reduced desmosome size and adhesion defects in PV patient tissue. Further, this study reveals that super-resolution optical imaging is powerful approach for studying epidermal adhesion structures in normal and diseased skin.

Desmosomes in acquired disease

Desmosomes are cell-cell junctions that mediate adhesion and couple the intermediate filament cytoskeleton to sites of cell-cell contact. This architectural arrangement integrates adhesion and cytoskeletal elements of adjacent cells. The importance of this robust adhesion system is evident in numerous human diseases, both inherited and acquired, which occur when desmosome function is compromised. This review focuses on autoimmune and infectious diseases that impair desmosome function. In addition, we discuss emerging evidence that desmosomal genes are often misregulated in cancer. The emphasis of our discussion is placed on the way in which human diseases can inform our understanding of basic desmosome biology and in turn, the means by which fundamental advances in the cell biology of desmosomes might lead to new treatments for acquired diseases of the desmosome.

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.

The desmosome

Desmosomes are intercellular junctions that tether intermediate filaments to the plasma membrane. Desmogleins and desmocollins, members of the cadherin superfamily, mediate adhesion at desmosomes. Cytoplasmic components of the desmosome associate with the desmosomal cadherin tails through a series of protein interactions, which serve to recruit intermediate filaments to sites of desmosome assembly. These desmosomal plaque components include plakoglobin and the plakophilins, members of the armadillo gene family. Linkage to the cytoskeleton is mediated by the intermediate filament binding protein, desmoplakin, which associates with both plakoglobin and plakophilins. Although desmosomes are critical for maintaining stable cell-cell adhesion, emerging evidence indicates that they are also dynamic structures that contribute to cellular processes beyond that of cell adhesion. This article outlines the structure and function of the major desmosomal proteins, and explores the contributions of this protein complex to tissue architecture and morphogenesis.

Perp and pemphigus: a disease of desmosome destabilization

In this issue, Nguyen et al. demonstrate a role for Perp in desmosome assembly and trafficking and pemphigus IgG-mediated acantholysis, providing further insights into the complexity of desmosome structure and regulation.

Involvement of the apoptotic mechanism in pemphigus foliaceus autoimmune injury of the skin

Pemphigus foliaceus (PF) is an organ-specific autoimmune skin disease characterized by subcorneal epidermal cell detachment (acantholysis) and pathogenic autoantibodies against desmoglein 1. The mechanism responsible for pemphigus autoantibody-induced epidermal injury is not fully understood. In this study, we used the IgG passive transfer mouse model of PF to investigate the relevance of the apoptotic mechanism in pemphigus pathogenesis. TUNEL-positive epidermal cells and increased oligonucleosomes in the epidermal cytosolic fractions were detected in the diseased mice. Time course study reveals that TUNEL-positive epidermal cells appear before intraepidermal blisters. Moreover, the proapoptotic factor Bax was up-regulated at the earlier time points (2 and 4 h), whereas the antiapoptotic factor Bcl-x(L) was down-regulated at the later time points (6, 8, and 20 h) post-PF IgG injection by Western blot analysis. The active forms of caspase-3 and -6 were detected at the later time period (6, 8, and 20 h). Administration of Ac-DEVD-cmk, a peptide-based caspase-3/7 inhibitor, protected mice from developing intraepidermal blisters and clinical disease induced by PF IgG. The same protective effect was also observed using a broad-spectrum caspase inhibitor, Bok-D-fmk. Collectively, these findings show that biochemical events of apoptosis are provoked in the epidermis of mice injected with PF autoantibodies. Caspase activation may contribute to acantholytic blister formation in PF.

Advances in pemphigus and its endemic pemphigus foliaceus (Fogo Selvagem) phenotype: a paradigm of human autoimmunity

Pemphigus encompasses a group of organ specific, antibody mediated autoimmune diseases of the skin characterized by keratinocyte detachment that leads to the development of blisters and erosions, which can become life-threatening. The pathogenic autoantibodies recognize desmogleins, which are members of the desmosomal cadherin family of cell adhesion molecules. Desmoglein 3 is targeted in pemphigus vulgaris while desmoglein 1 is targeted in pemphigus foliaceus and its endemic form, Fogo Selvagem. This review will briefly define the salient features of pemphigus and the proposed steps in pathogenesis. We will then summarize the most recent advances in three important areas of investigation: (i) epidemiologic, genetic, and immunologic features of Fogo Selvagem, (ii) molecular mechanisms of injury to the epidermis, and (iii) novel therapeutic strategies targeting specific steps in disease pathogenesis. The advances in each of these three seemingly separate areas contribute to the overall understanding of the pemphigus disease model. These recent advancements also underscore the dynamic interplay between the treatment of patients in a clinical setting and basic science research and have led to an integrative understanding of disease pathogenesis and treatment, allowing pemphigus to serve as a paradigm of human autoimmunity.

Pemphigus vulgaris IgG-induced desmoglein-3 endocytosis and desmosomal disassembly are mediated by a clathrin- and dynamin-independent mechanism

Pemphigus vulgaris (PV) is a life-threatening autoimmune disease characterized by oral mucosal erosions and epidermal blistering. The autoantibodies generated target the desmosomal cadherin desmoglein-3 (Dsg3). Previous studies demonstrate that upon PV IgG binding, Dsg3 is internalized and enters an endo-lysosomal pathway where it is degraded. To define the endocytic machinery involved in PV IgG-induced Dsg3 internalization, human keratinocytes were incubated with PV IgG, and various tools were used to perturb distinct endocytic pathways. The PV IgG.Dsg3 complex failed to colocalize with clathrin, and inhibitors of clathrin- and dynamin-dependent pathways had little or no effect on Dsg3 internalization. In contrast, cholesterol binding agents such as filipin and nystatin and the tyrosine kinase inhibitor genistein dramatically inhibited Dsg3 internalization. Furthermore, the Dsg3 cytoplasmic tail specified sensitivity to these inhibitors. Moreover, inhibition of Dsg3 endocytosis with genistein prevented disruption of desmosomes and loss of adhesion in the presence of PV IgG. Altogether, these results suggest that PV IgG-induced Dsg3 internalization is mediated through a clathrin- and dynamin-independent pathway and that Dsg3 endocytosis is tightly coupled to the pathogenic activity of PV IgG.

Anti-desmoglein 3 (Dsg3) Monoclonal Antibodies Deplete Desmosomes of Dsg3 and Differ in Their Dsg3-depleting Activities Related to Pathogenicity

Pemphigus vulgaris (PV) is an autoimmune blistering disease, characterized by the loss of cell-cell adhesion between epidermal keratinocytes and the presence of autoantibody against desmoglein 3 (Dsg3), which provides adhesive integrity to desmosomes between adjacent keratinocytes. We have previously shown that PV-IgG purified from patients depletes desmosomes of Dsg3. However, PV-IgG contains not only antibodies against a variety of different epitopes of Dsg3 but also against other unknown antigens. Therefore, we examined whether the Dsg3-depleting activity of PV-IgG is generated specifically by anti-Dsg3 activity in a human squamous cell carcinoma cell line (DJM-1) and normal human keratinocytes by using four different pathogenic and nonpathogenic monoclonal antibodies against Dsg3. We demonstrate that these monoclonal antibodies deplete cells and desmosomes of Dsg3, as PV-IgG does. Individual monoclonal anti-Dsg3 antibodies display characteristic limits to their Dsg3-depleting activity, which correlates with their pathogenic activities. In combination, these antibodies exert a cumulative or synergistic effect, which may explain the potent Dsg3-depleting capability of PV-IgG, which is polyclonal. Finally, although Dsg3-depletion activity correlated with AK-monoclonal antibody pathogenicity in mouse models, the residual level of Dsg3, when below approximately 50%, does not correlate with the adhesive strength index in the present study. This may suggest that although the Dsg3 depletion is not indicative for adhesive strength, the level of Dsg3 can be used as a read-out of pathogenic changes within the cell and that the Dsg3 depletion from desmosomes plays an important role in skin fragility or susceptibility to blister formation in PV patients.

A novel method to investigate pemphigus-induced keratinocyte dysmorphisms through living cell immunofluorescence microscopy

Pemphigus vulgaris (PV) blistering occurs as a result of the disruption of intercellular contacts among keratinocytes, or acantholysis. The hallmark of PV acantholysis in vitro is considered to be the retraction of keratin intermediate filaments (KIF) onto the nucleus, which parallels with loss of cell-cell adhesion and rounding up of keratinocytes. However, the fine morphological changes of keratinocytes as well as the fate of cell adhesion structures cannot be appreciated on immunofluorescence by the simple cytokeratin staining. In this paper, we show that acantholytic dysmorphisms are sharply investigated by using PV IgG as a primary antibody on metabolically quiescent living cells. Indeed, PV IgG recognise a wide spectrum of molecules and enabled us to monitor the main changes occurring in acantholytic keratinocytes, including cell shrinkage with the appearance of prickle-like processes, detachment of keratinocytes from one another and collapse of cytoskeleton-bound proteins along nuclear periphery. This method has wider applications as it could be useful for staining cell periphery of keratinocytes and changes in cell shape. Furthermore, images displayed clear and sharp contours because living cell microscopy allows to avoid antigen distortion due to cell manipulation, which usually precedes the immunolabelling.

How does acantholysis occur in pemphigus vulgaris: a critical review

BACKGROUND

Pemphigus vulgaris is a life-threatening autoimmune blistering disease targeting skin and mucous membranes, characterized by disruption of keratinocytes' adhesion termed acantholysis. Today multiple classes of targets are considered to play a role in the genesis of the acantholysis; of these, the classical pemphigus antigens, desmosomal cadherins (desmoglein 1 and 3) are the best characterized and considered as the most important. Additional antigens include the novel epithelial acetylcholine receptors (alpha9 and pemphaxin). Thus, acantholysis in pemphigus seems to result from a cooperative action of antibodies to different keratinocyte self-antigens, but the mechanisms by which epithelial cleft occurs are not yet clearly understood. In fact, the binding of the autoantibodies to these targets generates a plethora of biological effects due, on one hand, to their direct interference with adhesive function and, on the other, to more complex events involving intracellular pathways that modify proteases activity or calcium metabolism, leading to loss of cell-cell adhesion.

Serum from pemphigus vulgaris reduces desmoglein 3 half-life and perturbs its de novo assembly to desmosomal sites in cultured keratinocytes

Defects of cell-cell adhesion underlie disruption of epithelial integrity observed in patients with pemphigus vulgaris (PV), an autoimmune disease characterized by severe mucosal erosions and skin blisters. Pathogenic PV autoantibodies found in patients' sera target desmoglein 3 (Dsg3), a major component of the desmosome, but how does this phenomenon affect Dsg-dependent adhesion and lead to acantholysis still remains controversial. Here, we show that PV serum determines a reduction of Dsg3 half-life in HaCaT keratinocytes, although the total amount of Dsg3 remains unchanged. Immunofluorescence studies suggest that PV IgG exert their effect prevalently by binding non-desmosomal Dsg3 without causing its massive internalization. Furthermore, PV IgG targeting desmosome-assembled Dsg3 do not induce depletion of Dsg3 from the adhesion sites. Conversely, incorporation of PV IgG-Dsg3 complexes into new forming desmosomes appears perturbed. With our study, the basic biochemical changes of Dsg3 in an in vitro model of PV have been defined.

Desmoglein Endocytosis and Desmosome Disassembly Are Coordinated Responses to Pemphigus Autoantibodies

Desmosomes are adhesive intercellular junctions prominent in the skin and heart. Loss of desmosome function is associated with severe congenital and acquired disorders characterized by tissue fragility. Pemphigus vulgaris (PV) is an autoimmune disorder in which antibodies are directed against the desmosomal adhesion molecule Dsg3, resulting in severe mucosal erosions and epidermal blistering. To define the mechanisms by which Dsg3 autoantibodies disrupt keratinocyte adhesion, the fate of PV IgG and various desmosomal components was monitored in primary human keratinocytes exposed to PV patient IgG. PV IgG initially bound to keratinocyte cell surfaces and colocalized with desmosomal markers. Within 6 h after PV IgG binding to Dsg3, electron microscopy revealed that desmosomes were dramatically disrupted and keratinocyte adhesion was severely compromised. Immunofluorescence analysis indicated that PV IgG and Dsg3 were rapidly internalized from the cell surface in a complex with plakoglobin but not desmoplakin. Dsg3 internalization was associated with retraction of keratin filaments from cell-cell borders. Furthermore, the internalized PV IgG-Dsg3 complex colocalized with markers for both endosomes and lysosomes, suggesting that Dsg3 was targeted for degradation. Consistent with this possibility, biotinylation experiments demonstrated that soluble Dsg3 cell surface pools were rapidly depleted followed by loss of detergent-insoluble Dsg3. These findings demonstrate that Dsg3 endocytosis, keratin filament retraction, and the loss of keratinocyte cell-cell adhesion are coordinated responses to PV IgG.

Mechanisms of blister induction by autoantibodies

Autoimmune diseases are characterized by defined self-antigens, organ specificity, autoreactive T cells and/or autoantibodies that can transfer disease. Autoimmune blistering diseases are organ-specific autoimmune diseases associated with an immune response directed to structural proteins mediating cell-cell and cell-matrix adhesion in the skin. While both autoreactive T and B cells have been detected and characterized in patients with autoimmune blistering diseases, current evidence generally supports a pathogenic role of autoantibodies for blister formation. The immunopathology associated with blisters induced by autoantibodies relies on several mechanisms of action. Autoantibodies from patients with pemphigus diseases can exert a direct effect just by binding to their target mediated by steric hindrance and/or by triggering the transduction of a signal to the cell. In most subepidermal autoimmune blistering conditions, in addition to the binding to their target antigen, autoantibodies need to interact with factors of the innate immune system, including the complement system and inflammatory cells, in order to induce blisters. Generally, decisive progress has been made in the characterization of the mechanisms of blister formation in autoimmune skin diseases. However, various aspects, including the exact contribution of steric hindrance and signal transduction for pemphigus IgG-induced acantholysis or the fine tuning of the inflammatory cascade triggered by autoantibodies in some subepidermal blistering diseases, still need to be addressed. Understanding the mechanisms by which autoantibodies induce blisters should facilitate the development of more specific therapeutic strategies of autoimmune blistering diseases.

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.

In vivo blockade of pemphigus vulgaris acantholysis by inhibition of intracellular signal transduction cascades

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune disease characterized by mucocutaneous intraepithelial blisters and pathogenic autoantibodies against desmoglein 3. The mechanism of blister formation in pemphigus has not been defined; however, in vitro data suggest a role for activation of intracellular signalling cascades.

OBJECTIVES

To investigate the contribution of these signalling pathways to the mechanism of PV IgG-induced acantholysis in vivo.

METHODS

We used the passive transfer mouse model. Mice were injected with IgG fractions of sera from a patient with PV, with or without pretreatment with inhibitors of proteins that mediate intracellular signalling cascades.

RESULTS

Inhibitors of tyrosine kinases, phospholipase C, calmodulin and the serine/threonine kinase protein kinase C prevented PV IgG-induced acantholysis in vivo.

CONCLUSIONS

These observations strongly support the role of intracellular signalling cascades in the molecular mechanism of PV IgG-induced acantholysis.

IgG Binds to Desmoglein 3 in Desmosomes and Causes a Desmosomal Split Without Keratin Retraction in a Pemphigus Mouse Model

Pemphigus vulgaris (PV) is an autoimmune blistering disease caused by IgG autoantibodies against desmoglein 3 (Dsg3). In this study, we characterized the ultrastructural localization of in vivo-bound IgG, Dsg3, and desmoplakin during the process of acantholysis in an active mouse PV model, using post-embedding immunoelectron microscopy. In non-acantholytic areas of keratinocyte contact, IgG labeling was restricted to the extracellular part of desmosomes, and was evenly distributed throughout the entire length of the desmosome. The distribution of in vivo IgG was similar to that of anti-Dsg3 labeling in the control mouse. Within the acantholytic areas, there were abundant split-desmosomes with keratin filaments inserted into the desmosomal attachment plaques. These split-desmosome extracellular regions were also decorated with anti-Dsg3 IgG and were associated with desmoplakin staining in their cytoplasmic attachment plaques. No apparent split-desmosomes, free of IgG-labeling were observed, suggesting that Dsg3 was not depleted from the desmosome before the start of acantholysis in vivo. Desmosome-like structures (without keratin insertion) were found only on the lateral surfaces of basal cells, but not on the apical surfaces at the site of acantholytic splits. These findings indicate that anti-Dsg3 IgG antibodies can directly access Dsg3 present in desmosomes in vivo and cause the subsequent desmosome separation that leads to blister formation in PV.

Antibodies against keratinocyte antigens other than desmogleins 1 and 3 can induce pemphigus vulgaris-like lesions

Pemphigus is an autoimmune disease of skin adhesion associated with autoantibodies against a number of keratinocyte antigens, such as the adhesion molecules desmoglein (Dsg) 1 and 3 and acetylcholine receptors. The notion that anti-Dsg antibodies alone are responsible for blisters in patients with pemphigus vulgaris (PV) stems from the ability of rDsg1 and rDsg3 to absorb antibodies that cause PV-like skin blisters in neonatal mice. Here, we demonstrate that PV IgGs eluted from rDsg1-Ig-His and rDsg3-Ig-His show similar antigenic profiles, including the 38-, 43-, 115-, and 190-kDa keratinocyte proteins and a non-Dsg 3 130-kDa polypeptide present in keratinocytes from Dsg 3 knockout mouse. We injected into Dsg 3-lacking mice the PV IgGs that did not cross-react with the 160-kDa Dsg 1 or its 45-kDa immunoreactive fragment and that showed no reactivity with recombinant Dsg 1. We used both the Dsg3(null) mice with a targeted mutation of the Dsg3 gene and the "balding" Dsg3(bal)/Dsg3(bal) mice that carry a spontaneous null mutation in Dsg3. These PV IgGs caused gross skin blisters with PV-like suprabasal acantholysis and stained perilesional epidermis in a fishnet-like pattern, indicating that the PV phenotype can be induced without anti-Dsg 3 antibody. The anti-Dsg 1 antibody also was not required, as its presence in PV IgG does not alter the PV-like phenotype in skin organ cultures and because pemphigus foliaceus IgGs produce a distinct phenotype in Dsg3(null) mice. Therefore, mucocutaneous lesions in PV patients could be caused by non-Dsg antibodies.

Assembly pathway of desmoglein 3 to desmosomes and its perturbation by pemphigus vulgaris-IgG in cultured keratinocytes, as revealed by time-lapsed labeling immunoelectron microscopy

To determine the assembly pathway of desmoglein 3 (Dsg3) into desmosomes and the subsequent effects of pemphigus vulgaris immunoglobulin G (PV-IgG) on such, we employed a time-lapsed labeling for FITC/Rhodamine (Rod) double-stained immunofluorescence and 5-nm/10-nm gold double-stained immunoelectron microscopy by using PV-IgG, which was confirmed to react specifically Dsg3. Cells from a human squamous cell carcinoma cell line (DJM-1) were first treated briefly with PV-IgG (3 min), then incubated in either anti-human IgG-FITC or 5-nm gold antibody-containing medium (5 min), followed by a 60-minute chase in normal medium without antibodies. The same cells were reincubated with PV-IgG medium for 3 minutes, followed by either anti-human IgG-Rod or 10-nm gold antibodies for 5 minutes. Using this method, FITC and 5-nm gold particles show the fate of Dsg3-PV-IgG complexes during the following 60-minute chase. IgG-Rod or 10-nm gold particles, which are bound during the last 5 minutes of the chase, show Dsg3 molecules newly expressed on the cell surface during the 60-minute-chase period. Initially, Dsg3 formed two types of small clusters on the nondesmosomal plasma membrane, ie, either half-desmosome-like clusters with keratin intermediate filament (KIF) attachment or simple clusters without KIF attachment. The PV-IgG binding to Dsg3 caused the internalization of the simple clusters into endosomes, but not the half-desmosome-like clusters. After the 60-minute-chase period, both types of cell surface Dsg3 clusters were labeled with only 10-nm gold, suggesting that new Dsg3 molecules were being delivered to the cell surface. Desmosomes were labeled with both 5-nm gold and 10-nm gold, whereas the half-desmosome-like clusters were labeled with only 10-nm gold, suggesting that the desmosomes themselves were not split. These results suggest that Dsg3 first forms simple clusters, followed by KIF-attachment, and then becomes integrated into desmosomes, and that PV-IgG-induced internalization of the nondesmosomal simple clusters of Dsg3 may represent the primary effects of PV-IgG on keratinocytes.

Pemphigus vulgaris antibody identifies pemphaxin. A novel keratinocyte annexin-like molecule binding acetylcholine

Because pemphigus vulgaris (PV) IgGs adsorbed on the rDsg3-Ig-His baculoprotein induced blisters in neonatal mice, it was proposed that anti-desmoglein 3 (Dsg 3) autoantibody causes PV. However, we found that rDsg3-Ig-His absorbs autoantibodies to different antigens, including a non-Dsg 3 keratinocyte protein of 130 kDa. This prompted our search for novel targets of PV autoimmunity. The PV IgG eluted from a 75-kDa keratinocyte protein band both stained epidermis in a pemphigus-like pattern and induced acantholysis in keratinocyte monolayers. Screening of a keratinocyte lambdagt11 cDNA library with this antibody identified clones carrying cDNA inserts encoding a novel molecule exhibiting approximately 40% similarity with annexin-2, named pemphaxin (PX). Recombinant PX (rPX-His) was produced in Escherichia coli M15 cells, and, because annexins can act as cholinergic receptors, its conformation was tested in a cholinergic radioligand binding assay. rPX-His specifically bound [(3)H]acetylcholine, suggesting that PX is one of the keratinocyte cholinergic receptors known to be targeted by disease-causing PV antibodies. Preabsorption of PV sera with rPX-His eliminated acantholytic activity, and eluted antibody immunoprecipitated native PX. This antibody alone did not cause skin blisters in vivo, but its addition to the preabsorbed PV IgG fraction restored acantholytic activity, indicating that acantholysis in PV results from synergistic action of antibodies to different keratinocyte self-antigens, including both acetylcholine receptors and desmosomal cadherins.

In vitro C3 mRNA expression in Pemphigus vulgaris: complement activation is increased by IL-1alpha and TNF-alpha

BACKGROUND

Pemphigus vulgaris (PV) is a potentially life-threatening disease, characterized immunohistologically by IgG deposits and complement activation on the surface of keratinocytes. Complement activation has been implicated in the pathogenesis with C3 deposits in about 90% of patients.

OBJECTIVE

In order to further elucidate the role of complement in PV and to define which cytokines play a role in C3 mRNA expression, we performed an in vitro study in human keratinocytes.

METHODS

Normal human epidermal keratinocytes (NHuK) were incubated with PV serum and C3 mRNA was measured. We previously had shown that IL-1alpha and TNF-alpha are expressed in PV in vivo and in vitro. Since cytokines are able to modulate complement activation, mRNA expression was evaluated in a similar experiment after pretreatment using antibodies against IL-1alpha and TNF-alpha.

RESULTS

Incubation of NHuK with PV sera caused their detachment from the plates after 20-30 minutes with a complete acantholysis within 12 hours. An early C3 mRNA expression was seen after 30 minutes with a peak level after 1 hour. Blocking studies, using antibodies against human IL-1alpha and TNF-alpha in NHuK together with PV-IgG, showed reduction of in vitro induced acantholysis and inhibition of C3 mRNA expression.

CONCLUSION

This study supports the hypothesis that complement C3 is important in PV acantholysis and that complement activation is increased by IL-1alpha and TNF-alpha.

Calcium-independent increases in pericellular plasminogen activator activity in pemphigus vulgaris

Intracellular free calcium ([Ca2+]i), an important second messenger, plays a crucial role in a variety of biochemical reactions leading to cell activation and protein secretion. This study examines the potential role of [Ca2+]i in mediating increases in pericellular plasminogen activator activity of canine keratinocytes observed upon binding of human pemphigus vulgaris IgG (hPV IgG). Using the calcium-sensitive fluorescent probe fura-2 and digital video fluorescence imaging microscopy, [Ca2+]i levels were determined in individual keratinocytes for up to 29 minutes after addition of 0.1-5 mg/ml hPV IgG to monolayers of subconfluent and confluent cultures. Extracellular ATP (a known [Ca2+]i-agonist in canine keratinocytes) and normal human IgG (nh IgG) served as positive and negative controls, respectively. HPV IgG and nh IgG failed to induce significant increases in [Ca2+]i, whereas 500 microM ATP induced a rapid, 3- to 12-fold transient increase above resting levels. Binding of hPV IgG to these keratinocyte cultures was demonstrated by immunofluorescence at the end of selected experiments. ATP stimulation of cultures previously treated with hPV IgG showed normal responsiveness and more than 90% of the cells were still viable at the end of [Ca2+]i imaging, thus demonstrating that failure to respond to hPV IgG was not due to an experimental artifact. Plasminogen activator activity in supernatants of confluent cultures incubated with 0.1-1 mg/ml hPV IgG or nh IgG and harvested at various time intervals was dependent on the IgG dose used and increased steadily over time. Increases in activity were 47-92% higher in cultures treated with hPV IgG than those incubated with the same dose of nh IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunofluorescence and immunoelectron microscopy analyses of a human monoclonal anti-epithelial cell surface antibody that recognizes a 185-kD polypeptide: a component of the paraneoplastic pemphigus antigen complex?

We recently reported the production of a human monoclonal antibody (MoAb) derived from a patient with pemphigus vulgaris (PV) that binds to the keratinocyte membrane and reacts with a 185-kD polypeptide by immunoblot analysis. We have since examined the tissue specificity of that MoAb, F12. By indirect immunofluorescence (IIF), F12 stained both the cell membrane and the basement membrane zone of stratified squamous epithelia. Moreover, MoAb F12 stained other epithelial tissues, such as urinary bladder, small bowel, thymus, and liver, and non-epithelial tissues, such as myocardium. Indirect immunoelectron microscopy (IIEM) analysis showed that MoAb F12 bound to a component common to desmosomal and hemidesmosomal plaques and to zona adherens-type junctions between hepatocytes and bile duct cells. Inhibition experiments were then performed with sera from patients with pemphigus vulgaris, pemphigus foliaceus, paraneoplastic pemphigus, or bullous pemphigoid. Three sera blocked F12 reactivity; two were from paraneoplastic pemphigus patients and the other was from the pemphigus vulgaris patient whose peripheral blood lymphocytes were used to make F12. All these sera recognized a 185-kD band that co-migrated with the polypeptide labeled by MoAb F12 on immunoblots. In addition, the IIF and IIEM staining patterns of MoAb F12 were similar to those observed with sera from two patients with paraneoplastic pemphigus. These observations suggest a relationship between MoAb F12 and the autoimmune response characterizing paraneoplastic pemphigus patients' sera.

Development of concepts of etiology, pathogenesis and treatment of pemphigus vulgaris based on the hypothesis of atavistic origin of the disease

Atavistically dependent expression of pemphigus vulgaris 'immune' antigen (PVIA) on the human epidermocyte surface is hypothetically the key factor of autoimmune aggression onset in pemphigus patients. Normal epidermocytes can express PVIA in response to a putative factor of 'sheding' as well as to certain biologic, chemical and physical effects. Taking into account the fact that the antibodies against 'shedding' factor carry out the function of anti-idiotypic ones, they can be used as blocking antibodies in treatment of pemphigus vulgaris.

Ultrastructural localization of pemphigus vulgaris and pemphigus foliaceus antigens in cultured human squamous carcinoma cells

The ultrastructural localization of the pemphigus vulgaris (PV) and pemphigus foliaceus (PF) antigens in cultured human squamous carcinoma cells was observed using immunogold electron microscopy. Both the PV and PF autoantibodies bound only to the extracellular portion of the desmosomal structures. After incubation at 37 degrees C, the PV antigen-antibody complexes were observed within the cultured cells. PV and PF antigen expression was markedly reduced when the cells were cultured in medium with a low Ca2+ concentration.

Ultrastructural study of clinically uninvolved skin of patients with pemphigus vulgaris

We investigated skin biopsies from pemphigus vulgaris (PV) patients by light, fluorescent and electron microscopy in order to study the ultrastructural appearances of epidermis at the pre-acantholytic stage. The biopsies were obtained from uninvolved forearm skin in 10 patients with PV in the acute stage of the disease, from perilesional skin of the same patients as well as from the forearm skin of 10 healthy subjects. Light microscopy showed no pathological changes in clinically uninvolved skin of pemphigus patients. Direct immunofluorescence confirmed the presence of IgG auto-antibodies fixed in intercellular space of the spinous-cell layer of uninvolved skin. Electron microscopy of the uninvolved skin biopsies revealed the following changes: disintegration of desmosomes of spinous cells with their replacement by finger-shaped protrusions of cytoplasm; clarification of the nuclear matrix; widening of the perinuclear slit; an increased number of secondary lysosomes in cells; oedema and swelling of mitochondria with destruction of their cristae. The cells retained their polygonal shape and the intercellular distance did not increase. We conclude that at the pre-acantholytic stage the breakage and dissolution of desmosomes precedes the increase in the intercellular space.

Oral pemphigus vulgaris in young adults

Three patients, aged 31, 26, and 22 years, had pemphigus vulgaris. A delay in diagnosis and appropriate treatment occurred because the initial presentation was confined to the oral mucosa.

Monovalent Fab' immunoglobulin fragments from endemic pemphigus foliaceus autoantibodies reproduce the human disease in neonatal Balb/c mice

Fogo selvagem (FS) is an autoimmune disease caused by IgG autoantibodies to desmoglein I (DG-I), a desmosomal glycoprotein. We have previously shown that the autoantibodies in these patients are pathogenic and restricted mainly to the IgG4 subclass. The purpose of this study was to determine if the Fc domain or the valence of FS autoantibodies were relevant in the induction of epidermal disease in neonatal mice. IgG4 was prepared from sera of FS patients by anion exchange chromatography, and digested with pepsin to yield F(ab')2 fragments. Monovalent FS Fab' were made by reduction and alkylation of FS F(ab')2. Intact FS IgG4, FS F(ab')2, and FS Fab' fragments were injected into neonatal mice. Intact FS IgG4 and both FS IgG fragments were pathogenic. The disease in the animals was dose dependent, and on the molar basis, FS Fab' fragments were more potent and efficient in producing disease than whole FS IgG. These results suggest: (a) simple binding of FS autoantibodies to DG-I may trigger keratinocyte detachment and epidermal disease; (b) DG-I may represent a keratinocyte cell adhesion molecule; and (c) complement activation and surface cross-linking may not be relevant in keratinocyte detachment.

Pemphigus antibodies and shedding snake serum enhance susceptibility of epidermal keratinocytes in natural cytotoxic reactions

In order to clarify the role of natural cytotoxicity (NC) in the damage of epidermal keratinocytes (EK) in pemphigus vulgaris (PV) we used the direct 51Cr-release assay in studying the cytotoxic activity of large grandular lymphocytes (LGL), obtained from 34 acute PV patients and 19 healthy donors against EK of PV patients, donors, intact newborn BALB/c mice and mice with experimental PV, shedding and non-shedding grass snakes. We also investigated the effect of pemphigus antibodies and shedding snake serum protein (SSSP) upon EK sensitivity to cytotoxic effects of NC effectors. In other experiments, studied were the amount of serine proteinase secreted by donor LGL in the presence of membrane antigen of antibody- or SSSP-transformed EK, and direct effect of pemphigus antibodies and SSSP upon the release of radioactive label and endoproteinases from EK. It was found that EK, which had interacted with pemphigus antibodies or SSSP, became a sensitive target for NC effectors. Membrane antigen of antibody- and SSSP-transformed human, murine and snake EK induces the secretion of endproteinases by NC effector cells. The conclusion was made that the effect of both pemphigus antibodies and SSSP on EK resulted in the emergences of a new antigen on EK cellular membrane which is recognized by NC effectors and plays the role of the ligand in receptor/ligand interaction between LGL and their targets.

Stimulating effect of pemphigus antibodies upon interleukin inhibitor production by normal human epidermocytes

The present study deals with the effect of pemphigus antibodies upon immunoregulatory activity of normal human keratinocytes. In vitro experiments were carried out to determine the effect of epidermal keratinocyte culture supernatants (EKCS) upon the ability of peripheral blood mononuclear cells from healthy subjects to give lymphoproliferative response to lectins, and to induce production of interleukin I and interleukin 2 activity, and exogenous interleukin 2 absorption. It was found that EKCS, obtained in response to epidermal keratinocyte cultivation in the presence of I mg/ml pemphigus antibodies, inhibit both interleukin cascade reactions and mitogen-induced lymphoproliferative response. It is supposed that the interleukin production deficiency in pemphigus may emerge as a result of suppressive effect made by autoantibodies on epidermal keratinocytes.

Binding modes of IgG from pemphigus autoimmune sera onto guinea pig keratinocytes and the fate of bound IgGs

Pemphigus is an intraepidermal autoimmune blistering disease of humans caused by circulating IgGs. We have investigated the binding mode and the fate of bound antibodies from Pemphigus sera (P-IgG) on guinea pig keratinocytes in suspension in order to find clues to the loss of cell adhesion in vivo (acantholysis). Flow cytometry, following indirect immunofluorescent labeling of the keratinocytes, and dead cells' staining with ethidium bromide, demonstrated the specific surface binding of P-IgG onto living keratinocytes only. This was shown with several Pemphigus sera or purified P-IgG. This technique, used with various Pemphigus sera, showed that the specific binding is increased when the serum titer is higher, and "Km" values for P-IgG were roughly and inversely correlated to the titers. Upon saturation the same average number of Pemphigus IgG sites per cell were found for the sera of different patients. Analysis of the specific binding of [125I]-P-IgG onto Percoll-separated (living) keratinocytes showed the existence of two classes of sites: 2 x 10(6) sites/cell high-affinity sites (Kd = 1.5 x 10(-6) M total IgG) and 25 x 10(6) sites/cell low-affinity sites (Kd = 6 x 10(-5) M total IgG). Cell sorting and flow cytometry of individual cells allowed us to correlate the light-scattering signal, the RNA content, the size and morphology, and the P-IgG binding to the cells. The results indicated that P-IgG binding is homogeneous within the living keratinocytes and increases with cell size (cell maturity). Cell-sorter analysis of cells with membrane-bound P-IgG, coupled to direct determination of P-IgG released in the medium, revealed the fate of bound P-IgG: 40-60% of the P-IgGs were released in the medium within 30 minutes at 37 degrees C. This was accompanied and followed by a much slower, metabolic energy-dependent, internalization process of the membrane-bound P-IgG. The internalization has been confirmed by electron microscopy of bound P-IgG labeled with protein A-gold. Internalized IgGs were seen in the cells in coated membranous vesicles and other endocytic compartments. Similar behavior was also observed with two other membrane ligands: i.e., concanavalin A and multispecific rabbit "antisurface" antibodies.

In vivo binding site of pemphigus vulgaris antibodies and their fate during acantholysis

Ultrastructural localization of pemphigus vulgaris antigen-antibody complexes and their fate during acantholysis were studied in epidermal sheets obtained from the area surrounding the bullae and in acantholytic cells in blister fluid. The distribution of pemphigus vulgaris antibodies already bound to the keratinocytes in early acantholytic lesions was detected with ferritin-conjugated goat antihuman IgG. Ferritin particles were observed on the surface of keratinocytes with particular affinity for desmosomal structures. The acantholytic cells in the blister fluid bound only a small number of ferritin particles on their surface. During incubation at 37 degrees C, pemphigus vulgaris antigen-antibody complexes on the surface of separated desmosomes were internalized and recognized in cytoplasmic vesicles. Endocytosis of separated desmosomes also was observed in vivo when freshly obtained epidermal sheets were immediately processed for routine electron microscopic study. These findings suggest that pemphigus vulgaris antibodies are densely located on desmosomes and that the antigen-antibody complexes, together with other serum proteins on the keratinocyte surface, are internalized by a process of endocytosis.

Autoreactive cytotoxic T lymphocytes in pemphigus and pemphigoid

In order to know whether effector cells are capable of recognizing the epidermal targets in pemphigus vulgaris (PV) and bullous pemphigoid (BP), non-adherent cells (NAC) of peripheral blood from 27 primary PV, 19 BP patients and 12 healthy volunteers were used in cytotoxic tests. Autologous, allogenic and murine epidermal keratinocytes as well as autologous and allogenic fibroblasts were employed as targets. Total esterase activity of serine proteinases was measured in supernatants of samples and the results obtained were compared with the data received in 51Cr-release assay. These two techniques yielded similar results. The effector cells of PV and BP patients were found to lyse the epidermal target cells without presensitization in vitro. Epidermal cells from involved and uninvolved skin of PV patients, as well as from perilesional skin of BP patients, were highly sensitive to cytotoxic effect on the part of effector cells. The NAC activity in BP was higher than in PV. On the one hand, the obtained data suggest that PV and BP patients develop autoreactive cytotoxic T lymphocytes, sensitized to pemphigus and pemphigoid antigens, respectively, and on the other hand that epidermocytes in pemphigus and pemphigoid patients turned to be more fragile compared to normal human epidermal keratinocytes. It was supposed that cell-mediated cytotoxic reactions are probably related to enhanced proteolytic activity in the site of bullous eruption.

Interleukin cascade reaction inhibition by supernatants of the cultures of antibody-transformed human basal keratinocytes

We investigated the ability of normal human basal keratinocytes, treated with antibodies against basal keratinocytes, to produce an effect upon the activity of allogenic peripheral blood mononuclear cells. We determined the influence of basal keratinocyte culture supernatants (BKCS) upon the mononuclear cell ability for proliferation in the response to PHA and Con A, for IL 1 and IL 2 production as well as for absorption of exogenous IL 2. It was found that BKCS inhibit the lectin-dependent transformation of mononuclears and interleukin cascade reactions. The conclusion was made about the capacity of antibody-transformed basal keratinocytes for down regulation of immune-response as well as about the role of antibodies in feedback interactions between interleukin-induced antibody synthesis and interleukin production.

Pemphigus

The term pemphigus refers to a group of autoimmune intraepidermal blistering diseases of the skin and mucous membranes. Several clinical variants of pemphigus are recognized. The major histologic feature of all variants is acantholysis, the disruption of normal cell-to-cell adhesion, which leads to intraepidermal blister formation. Most patients with pemphigus demonstrate IgG autoantibodies directed against an antigen located on the surface of keratinocytes. Although the stimulus for autoantibody production is unknown, several mechanisms have been proposed to explain the pathogenesis of acantholysis. One popular model proposes that pemphigus antibodies induce acantholysis through local stimulation of the plasminogen-plasmin system. Another model proposes that pemphigus antibodies fix complement and thereby alter cell membrane integrity to produce acantholysis. Prior to the availability of corticosteroids, pemphigus vulgaris was commonly fatal. Treatment with glucocorticosteroids has drastically improved the prognosis. Immunosuppressive agents and plasmapheresis have been used successfully in some patients with severe disease.

An autoantibody in pemphigus serum, specific for the 59 kD keratin, selectively binds the surface of keratinocytes: evidence for an extracellular keratin domain

We have identified a novel IgG antikeratin autoantibody in the serum of a Brazilian pemphigus foliaceus patient (Cascas-42). This antibody is specific for the 59 kD acidic murine keratin and its 56.5 kD human counterpart (Moll's catalogue #10), and is distinct from the pemphigus antibody system. Antikeratin autoantibodies present in the Cascas-42 serum were purified by affinity chromatography with a 59 kD murine keratin-agarose column (IAP-Cascas-42 antibodies). The specificity of the IAP-Cascas-42 antibodies was tested by indirect immunofluorescence and immunoelectron microscopy against epidermal cryosections, trypsin-dissociated keratinocytes, and epidermal cell cultures. The serum was also tested with extracts from unlabeled and surface 125I-labeled keratinocytes (Iodo-Gen method) by immunoblot analysis of one- and two-dimensional polyacrylamide gel electrophoresis. The IAP-Cascas-42 antibodies bind the intercellular spaces of murine epidermis, and the cell surfaces of viable, dissociated murine keratinocytes, as well as murine epidermal cells in culture by immunofluorescence and immunoelectron microscopy. These autoantibodies did not stain cytoplasmic keratins and did not react with parallel human epidermal substrates. The Cascas-42 serum identified the 59 kD murine acidic keratin and its 56.5 kD human counterpart in epidermal extracts by two-dimensional polyacrylamide gel electrophoresis and immunoblot analysis. In addition, surface radioiodination of viable murine keratinocytes selectively labeled the 59 kD keratin suggesting that a domain of this molecule is exposed on the cell surface. The 125I-labeled 59 kD keratin was also recognized by the Cascas-42 serum by immunoblotting and autoradiography. These studies suggest that in murine epidermis, the 59 kD keratin is a transmembrane protein with an extracellular domain recognized by the IAP-Cascas-42 antibodies.

Effects of colchicine and cytochalasin B on distribution of concanavalin A receptors in isolated and cultured guinea pig epidermal cells

Regulation of the distribution of concanavalin A (Con A)/receptor complexes by the cytoskeletal contracture system was studied in guinea pig epidermal cells in suspension and culture using the fluorescence double staining method. After treatment with 100 micrograms/ml of Con A at 37 degrees C for 30 min lectin/receptor complexes were endocytosed by the less-differentiated cells in suspension and by the adherent cells in 1- and 3-day cultures that represent a growing cell fraction. The same treatment resulted in diffuse surface distribution of the complexes in the well-differentiated cells in suspension. Colchicine (10(-5) and 10(-6) M) inhibited internalization of the complexes with resultant diffuse distribution in 60% of the adherent cells in culture. Cytochalasin B (5 and 10 micrograms/ml) not only inhibited endocytosis but promoted formation of surface patchy clumps of the complexes in suspended, less-differentiated cells and cultured adherent cells. The distribution profile was not influenced by these drug treatments in the well-differentiated cells. SDS polyacrylamide gel electrophoresis and autoradiography of 125I-labelled epidermal membranes revealed several Con A-reactive polypeptides common to the cells at various differentiation steps. The progressive decrease in endocytosis and mobility of Con A/receptor complexes was suggested to occur with differentiation. In the germinative cells the distribution of lectin/receptor complexes seemed to be regulated by microfilaments and microtubules.

Effects of pemphigus antibody on the regeneration of cell-cell contact in keratinocyte cultures grown in low to normal Ca++ concentration

Pemphigus is an autoimmune blistering disease of epidermal cells in which autoantibodies to the surface develop. The present study was performed to determine whether the binding of pemphigus antibodies to the surface of keratinocytes can inhibit the regeneration of cell-cell contact induced by altering from low to normal Ca++ concentration medium. Human keratinocytes (a cell line of squamous cell carcinoma, DJM-1 cell) were grown in low Ca++ medium for 4 days, then the cells were incubated in normal Ca++ medium containing 10% pemphigus (4 patients with pemphigus vulgaris and 4 patients with pemphigus foliaceus) or normal serum (treated at 56 degrees C, for 30 min) for various incubation periods (2, 6, 12, 24 h). The cells were fixed and stained with antikeratin antibody by the indirect immunofluorescence method so that the detachment of cell-cell contact was able to be clearly visualized by observing the cytoskeletal arrays of keratin filaments. The cells grown in normal Ca++ medium showed detachments of cell-cell contact 24-36 h after addition of any one of the pemphigus sera used in this study. The cells grown in low Ca++ medium formed no cell-cell contacts and expressed no pemphigus antigens. However, re-formation of cell-cell contacts and reexpression of the antigens were confirmed by immunofluorescence microscopy 30 min after the addition of Ca++ to the medium. The addition of any pemphigus vulgaris and foliaceus sera with Ca++ did not inhibit the regeneration of cell-cell contact and exerted no effects on the contact during the subsequent 12 h. However, after 24 h, these cells again lost the contact. These results indicate that pemphigus antibody and antigen reaction on the cell surface did not directly inhibit the Ca++-induced re-formation of cell-cell contact.

Human pemphigus autoantibodies are pathogenic to squamous epithelium

In 1957, Witbesky et al. put forward several criteria that ideally should be fulfilled in order to prove the pathogenic role of an autoantibody in a putative autoimmune disease. There can now be very little doubt of the autoimmune nature of this disease and of the primary role of autoantibodies in its pathogenesis. The evidence that supports the concept that pemphigus autoantibodies are of primary pathogenic importance in the disease is as follows: IgG class autoantibodies can be found both circulating in the serum and bound to the epithelial cell surfaces in and around lesions in patients with pemphigus. These autoantibodies, purified from the serum of pemphigus patients, can induce acantholytic lesions typical of pemphigus both in experimental animals (neonatal mice) and in human and murine epidermal cell cultures. These autoantibodies react with a specific antigen of the epidermal cell. This purified antigen has been used to immunize rabbits and the resulting antibodies are capable of inducing pemphigus-like lesions in neonatal mice.