Autoantibodies against the amino-terminal cadherin-like binding domain of pemphigus vulgaris antigen are pathogenic

Pathogenic monoclonal antibody against desmoglein 3 augments desmoglein 3 and p38 MAPK phosphorylation in human squamous carcinoma cell line

Pemphigus vulgaris is an autoimmune blistering disease characterized by cell-cell detachment of epidermal cells. Autoantibody against desmoglein (Dsg) 3, a transmembrane glycoprotein that mediates the association of desmosomes, plays a major role in blistering in pemphigus vulgaris (PV). The mechanisms of autoantibody-induced acantholysis have not been clarified. We previously reported that PV-IgG induces phosphorylation of Dsg3, decreases Dsg3 on the cell surface and forms Dsg3-depleted desmosomes in cultured keratinocytes, and that cell treatment with a potent pathogenic monoclonal antibody against Dsg3 (AK23 mAb) decreases the amount of Dsg3 in cultured keratinocytes. Although the precise mechanisms remain unclear, we have proposed the involvement of intracellular signal transduction resulting from the binding of autoantibodies to Dsg3. In this study, we examined whether AK23 mAb augments phosphorylation of Dsg3 and p38 mitogen-activating protein kinase (MAPK) in a human squamous cell line, DJM-1 cells. AK23 mAb increased serine phosphorylation of Dsg3 and augmented activation levels of p38 MAPK. These results indicate that antibodies bind to Dsg3, but not other antigens, in the IgG fraction and can induce activation of signal transduction.

Desmoglein autoimmunity in the pathogenesis of pemphigus

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

T Helper Type 2-Biased Natural Killer Cell Phenotype in Patients with Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoantibody-mediated bullous disease, but the role of natural killer (NK) cells in its pathogenic process has never been examined in detail. Circulating CD56+ CD3- NK cells as well as CD69+-activated NK cells were increased in PV patients compared with healthy controls and patients with other autoantibody-mediated autoimmune diseases, including immune thrombocytopenic purpura and myasthenia gravis. Gene expression analysis of highly purified NK cells demonstrated an increased expression of IL-10 and decreased expression of IL-12Rbeta2, perforin, and granzyme B ex vivo in PV patients versus healthy controls. The NK cells from PV patients also showed impaired signal transducer and activator of transduction4 phosphorylation upon in vitro IL-12 stimulation. Moreover, NK cells from PV patients exhibited reduced IL-10 production in response to in vitro stimulation with IL-2/IL-12. Finally, IL-5 expression in NK cells was exclusively detected ex vivo in PV patients with active disease, and was lost in subsequent analyses performed during disease remission. Together these findings suggest that NK cells contribute to a T helper type 2-biased immune response in PV patients through impaired IL-12 signaling and an upregulation of IL-10 and IL-5.

Increased serum levels of a proliferation-inducing ligand in patients with bullous pemphigoid

BACKGROUND

B cells have been demonstrated to have critical roles in developing autoimmune bullous diseases. Recently identified tumor necrosis factor-like molecules, B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL) are essential molecules for B cell development, survival, and proliferation. Although the functions of APRIL have not been fully evaluated, recent studies suggest that circulating levels of APRIL are increased in various autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis.

OBJECTIVES

To determine serum APRIL levels in patients with pemphigus vulgaris (PV) and bullous pemphigoid (BP), and compare those with clinical findings and laboratory findings.

PATIENTS/METHODS

Sera from 15 PV patients, 43 BP patients, and 15 normal controls were subjected to ELISA assays to measure serum APRIL, BAFF, Dsg3, and BP180 levels.

RESULTS AND CONCLUSIONS

Circulating APRIL levels were significantly elevated in BP patients but not in PV patients, and correlated with serum BAFF levels. Our study revealed that serum APRIL levels tended to be increased in the quite early stage of disease. In conclusion, circulating APRIL levels may be a useful marker for early activation of autoimmune diathesis, and furthermore, an effective therapeutic target molecule in patients with BP.

IgG reactivity against non-conformational NH-terminal epitopes of the desmoglein 3 ectodomain relates to clinical activity and phenotype of pemphigus vulgaris

Pemphigus vulgaris (PV) is an autoimmune disease caused by immunoglobulin G (IgG) autoantibodies against the desmosomal adhesion molecules, desmoglein (Dsg)3 and Dsg1. The aim of the study was to relate IgG reactivity of 123 PV sera and 40 control sera against NH(2)-terminal non-conformational epitopes of Dsg3 and Dsg1 with disease activity and clinical phenotype by enzyme-linked immunosorbent assay. The results show that (i) the overall reactivity and the titres of IgG reactive with the Dsg3 ectodomain, Dsg3(1-566), significantly correlated with the disease activity of the PV patients; (ii) IgG reactivity against the NH(2)-terminus of Dsg3, Dsg3(1-161), was associated with active PV while there was no direct correlation between the IgG titres and the disease activity; (iii) IgG reactivity against the NH(2)-terminus of Dsg3, Dsg3(1-161), was associated with mucosal and mucocutaneous PV; (iv) IgG titres against a small stretch of the NH(2)-terminus of Dsg3, Dsg3(25-88), were associated with active PV; and (v) IgG in the PV sera detected non-conformational epitopes in addition to the previously identified conformation-dependent epitopes of the Dsg3 and Dsg1 ectodomains.

Antigen mimicry, epitope spreading and the pathogenesis of pemphigus

The molecular and cellular pathogenesis of pemphigus remains unclear. However, the integrity of intraepidermal and dermoepidermal adhesion appears to be of special importance, and the presence of antibodies directed against desmosomal plaque proteins can provoke pemphigus-like pathologies. Antibodies reactive with various tissue antigens have been detected in pemphigus-like skin conditions. Two major factors determining the occurrence of different pemphigus subforms are antigen mimicry and epitope spreading, as these two phenomena underpin antibody generation in response to different antigens. This multiplicity of target antigens and antibody responses may lead to diagnostic problems early in the disease and may also explain the apparent transformation of one disease subform into another as time progresses.

Induction of Complement-Fixing Autoantibodies against Type VII Collagen Results in Subepidermal Blistering in Mice

Experimental models reproducing an autoimmune response resulting in skin blistering in immunocompetent animals are lacking. Epidermolysis bullosa acquisita (EBA) is a bullous skin disease caused by autoantibodies to type VII collagen. In this study, we describe an active disease model of EBA by immunizing mice of different strains with murine type VII collagen. All mice developed circulating IgG autoantibodies that recognized type VII collagen and bound to the lamina densa of the dermal-epidermal junction. Importantly, subepidermal blisters developed in 82% of SJL-1, 56% of BALB/c mice, and 45% of Fc gammaRIIb-deficient mice, but not in SKH-1 mice. In susceptible animals, deposits of IgG1, IgG2, and complement C3 were detected at the dermal-epidermal junction. In contrast, in the nondiseased mice, tissue-bound autoantibodies were predominantly of the IgG1 subclass and complement activation was weak or absent. This active disease model reproduces in mice the clinical, histopathological, and immunopathological findings in EBA patients. This robust experimental system should greatly facilitate further studies on the pathogenesis of EBA and the development of novel immunomodulatory therapies for this and other autoimmune diseases.

p38MAPK inhibition prevents disease in pemphigus vulgaris mice

Pemphigus vulgaris (PV) is a life-threatening autoimmune blistering skin disease characterized by detachment of keratinocytes (acantholysis). It has been proposed that PV IgG might trigger signaling and that this process may lead to acantholysis. Indeed, we recently identified a rapid and dose-dependent phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) and heat shock protein (HSP) 27 after binding of PV antibodies to cultured keratinocytes. In human keratinocyte cultures, inhibitors of p38MAPK prevented PV IgG-induced phosphorylation of HSP27 and, more importantly, prevented the early cytoskeletal changes associated with loss of cell-cell adhesion. This study was undertaken to (i) determine whether p38MAPK and HSP25, the murine HSP27 homolog, were similarly phosphorylated in an in vivo model of PV and (ii) investigate the potential therapeutic use of p38MAPK inhibition to block blister formation in an animal model of PV. We now report that p38MAPK inhibitors prevented PV blistering disease in vivo. Targeting the end-organ by inhibiting keratinocyte desmosome signaling may be effective for treating desmosome autoimmune blistering disorders.

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.

Synergistic pathogenic effects of combined mouse monoclonal anti-desmoglein 3 IgG antibodies on pemphigus vulgaris blister formation

Pemphigus vulgaris (PV) is an autoimmune blistering disease caused by anti-desmoglein 3 (Dsg3) IgG antibodies. Previously, we generated an active mouse model for PV by adoptive transfer of splenocytes from immunized or naive Dsg3(-/-) mice. In this study, we isolated 10 anti-Dsg3 IgG mAbs (NAK-series) from PV model mice generated by transfer of naive Dsg3(-/-) splenocytes. We characterized their epitopes using domain-swapped and point-mutated Dsg1/Dsg3 molecules and examined their pathogenic activities in blister formation in three different assays. In a passive transfer model using neonatal mice, eight of 10 NAK mAbs showed pathogenic activity when injected together with half the minimum pathogenic dose of anti-Dsg1 IgG autoantibodies from pemphigus foliaceus (PF) patients. None of the mAbs could induce the PV phenotype when individual hybridoma clones were inoculated by peritoneal injection into adult Rag2(-/-) mice. NAK mAbs displayed a range of potency in an in vitro dissociation assay using primary cultured mouse keratinocytes. Interestingly, when multiple hybridoma clones recognizing different epitopes were inoculated in combination, recipient mice developed the PV phenotype. In vitro dissociation assays confirmed that combined NAK mAbs had synergistic pathogenic effects. These findings indicate that although an individual anti-Dsg3 IgG is not sufficient to cause blistering in adult mice, several together can induce the PV phenotype. These mAbs will provide a valuable tool to investigate the molecular mechanisms of blister formation, mimicking the effects of the polyclonal IgG antibodies found in patients.

T cell control in autoimmune bullous skin disorders

Autoimmune bullous disorders are a group of severe skin diseases characterized clinically by blisters and erosions of skin and/or mucous membranes. A hallmark of these disorders is the presence of IgG and occasionally IgA autoantibodies that target distinct adhesion structures of the epidermis, dermoepidermal basement membrane, and anchoring fibrils of the dermis. This Review focuses on the potential role of autoreactive T cells in the pathogenesis of these disorders. Pemphigus vulgaris (PV) and bullous pemphigoid (BP) are the best-characterized bullous disorders with regard to pathogenesis and T cell involvement. Activation of autoreactive T cells in PV and BP is restricted by distinct HLA class II alleles that are prevalent in individuals with these disorders. Autoreactive T cells are not only present in patients but can also be detected in healthy individuals. Recently, a subset of autoreactive T cells with remarkable regulatory function was identified in healthy individuals and to a much lesser extent in patients with PV, suggesting that the occurrence of autoimmune bullous disorders may be linked to a dysfunction of Tregs.

Healing effect of Pilocarpine gel 4% on skin lesions of pemphigus vulgaris

BACKGROUND

The high rate of morbidity and mortality resulting from long-term use of corticosteroids in pemphigus vulgaris (PV) warrants discovery of a new treatment strategy. Based on a new theory on the pathophysiology of PV, cholinomimetics can block the process of blister formation.

AIMS

This study was conducted to evaluate the clinical effectiveness of Pilocarpine gel in the treatment of skin lesions of PV.

METHODS

In a double-blind, placebo-controlled study, three PV patients with a total of 64 skin lesions were treated by either Pilocarpine or placebo gel. After 15 days of treatment an epithelialization index of the two groups was compared.

RESULTS

The mean of the epithelialization index in skin lesions that received Pilocarpine was significantly higher than that of the placebo group (40.3 +/- 1.7 vs. 24.4 +/- 3.3, P < 0.001).

CONCLUSIONS

Pilocarpine gel effectively treats PV.

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.

Establishment of the mouse model by rabbit antiserum specific to EC1-2 or EC3-4 epitopes for studying the pathogenesis of pemphigus vulgaris

The research goal was to establish the neonatal mouse model by specific rabbit anti EC1-2 or EC3-4 antiserum for the purpose of studying pemphigus vulgaris (PV) pathogenesis. RNA was extracted from human keratinocytes. The cDNAs was synthesized by reverse transcription. Amplified EC1-2 or EC3-4 genes were inserted into pGEX-4T expression plasmids to constitute the recombinant plasmids, and transformed into E.coli. for the expression of the fusion proteins. The purified fusion proteins were used to immunize New Zealand white rabbits to obtain the specific anti EC1-2 or EC3-4 antisera. IgG fractions from the antisera were purified and passively transferred intradermally into the upper back skin of neonatal BALB/c mice. Histologic, ultrastructural, and immunofluorescence features of PV were evaluated in these mice. PV features were shown in the mice injected with anti EC1-2 antibody, erythema on the flanks and positive Nikolsky sign. The histology showed intraepidermal vesicle formation and acantholytic cells within. Acantholysis, but no clinical symptoms, was seen in the mice treated with the antibody specific to EC3-4. Additionally, skin sections from the abdomen from these neonatal mice were cryo-sectioned for direct-immunofluorescence. FITC-conjugated IgG antibody deposit between the keratinocytes throughout the epidermis. The indirect immunofluorescence with monkey esophagus showed the presence of anti-intracellular antibody with a titer of 1:40. On electronic microscopy, intercellular spaces (ICS) were widened and the desmosomes were split or dissolved. A novel PV mouse model was established by treatment with the specific rabbit antiserum. These data confirmed that both EC1-2 and EC3-4 are pathogenic epitopes in PVA, but EC1-2 is more dominant.

Inhibition of the transcription factor Foxp3 converts desmoglein 3-specific type 1 regulatory T cells into Th2-like cells

Pemphigus vulgaris (PV) is a severe autoimmune bullous skin disorder and is associated with autoantibodies against desmoglein (Dsg)3 that are regulated by Th2 cells. Recently, Dsg3-specific type 1 regulatory T cells (Tr1) were identified that are presumably critical for the maintenance of tolerance against Dsg3 because there is a much lower Dsg3-specific Tr1:Th2 ratio in the PV patients than in healthy individuals. The aim of this study was to down-regulate the transcription factor Foxp3 in Dsg3-specific Tr1 using antisense oligonucleotides because Foxp3 is constitutively expressed by the Dsg3-specific Tr1. Antisense-treated Dsg3-specific Tr1 clones lost expression of Foxp3, glucocorticoid-induced TNFR family-related receptor, and CTLA-4, and started to secrete IL-2, whereas the secretion of IL-5, TGF-beta, and IL-10 remained unchanged. Moreover, antisense treatment induced a proliferative response to Dsg3 of the formerly anergic Tr1 and abrogated their suppressor activity on Dsg3-specific Th2 cell clones. Thus, inhibition of Foxp3 mRNA expression in the Tr1 induced a Th2-like phenotype. In conclusion, Foxp3 expression is inherent to Tr1 function, and modulation of Foxp3 expression in autoaggressive Th2 cells may provide a novel therapeutic approach aimed at restoring tolerance against Dsg3 in PV.

Evidence for the participation of nitric oxide in pemphigus

Pemphigus is an inflammatory autoimmune disorder of the skin. Nitric oxide (NO) is an inflammatory mediator linked to a variety of physiological and pathophysiological phenomena that include skin tumors, psoriasis, urticaria, and atopic dermatitis. Inflammatory cells present in pemphigus lesions are important sources of NO production. We investigated whether NO is involved in pemphigus. A prospective cohort study was conducted at the Dermatology Service of the Hospital Universitário Walter Cantídio of the Federal University of Ceará. All patients seen at the outpatient clinic between August 2000 and July 2001, with a clinically and histologically confirmed diagnosis of pemphigus were included. The median age was 42.5 years (range: 12-69 years) with a male to female ratio of 3:2. Total serum nitrite levels, used as a marker for NO production, were determined by the Griess reaction. Skin biopsies from pemphigus and breast surgery (control) patients were used for the detection of the inducible NO synthase (iNOS) by immunohistochemistry. Twenty-two (22) patients with pemphigus and eight (8) controls who did not differ in demographic characteristics were included. Total serum nitrite levels were significantly higher (>7 micromol/L) in pemphigus patients compared to controls (<6 micromol/L), regardless of the severity of the clinical activity of pemphigus (P < 0.0001). All pemphigus biopsies presented increased immunostaining for iNOS that was not detected in normal skin samples. These data are the first to demonstrate that pemphigus patients display increased serum NO levels that are associated with increased iNOS expression in the affected skin.

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.

Tolerance induction by the blockade of CD40/CD154 interaction in pemphigus vulgaris mouse model

Pemphigus vulgaris (PV) is an autoimmune blistering disease caused by IgG autoantibodies against desmoglein 3 (Dsg3). We have recently developed an active disease mouse model for PV by adoptive transfer of splenocytes from Dsg3(-/-) mice. The purpose of this study was to determine the role of CD40/CD154 interaction in the pathogenic antibody production and development of the disease in PV model mice. When anti-CD154 monoclonal antibody (mAb) was administered to recipient mice prior to adoptive transfer, anti-CD154 mAb almost completely blocked the anti-Dsg3 IgG production and prevented blister formation. The blockade of CD40/CD154 interaction induced tolerance against Dsg3 as the suppression of antibody production was observed through day 70, and it was maintained even after challenge by immunization with recombinant mouse Dsg3 or by adoptive transfer of immunized Dsg3(-/-) splenocytes. Furthermore, the tolerance to Dsg3 was transferable because cotransfer of splenocytes from anti-CD154 mAb-treated mice and naïve Dsg3(-/-) splenocytes significantly suppressed anti-Dsg3 IgG production in recipient mice. In contrast, when anti-CD154 mAb was injected after the mice had developed the PV phenotype, no significant suppression of the production of anti-Dsg3 IgG was observed. These findings indicate that the CD40/CD154 interaction is essential for the induction of pathogenic anti-Dsg3 IgG antibodies and that antigen-specific immune-regulatory cells induced by anti-CD154 mAb would hold a therapeutic option for autoimmune diseases.

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.

Complete FcRn dependence for intravenous Ig therapy in autoimmune skin blistering diseases

Numerous mechanisms of action have been proposed for intravenous Ig (IVIG). In this study, we used IgG passive transfer murine models of bullous pemphigoid (BP), pemphigus foliaceus (PF), and pemphigus vulgaris (PV) to test the hypothesis that the effect of IVIG in autoantibody-mediated cutaneous bullous diseases is to accelerate the degradation of pathogenic IgG by saturation of the MHC-like Fc receptor neonatal Fc receptor (FcRn). BP, PF, and PV are organ-specific antibody-mediated diseases in which autoantibodies target the hemidesmosomal antigen BP180 and desmosomal antigens Dsg1 and Dsg3, respectively. Antibodies against BP180, Dsg1, and Dsg3, when injected into neonatal mice, induce the BP, PF, and PV disease phenotypes, respectively. We found that FcRn-deficient mice were resistant to experimental BP, PF, and PV. Circulating levels of pathogenic IgG in FcRn-deficient mice were significantly reduced compared with those in WT mice. Administration of high-dose human IgG (HDIG) to WT mice also drastically reduced circulating pathogenic IgG levels and prevented blistering. In FcRn-deficient mice, no additional protective effect with HDIG was realized. These data demonstrate that the therapeutic efficacy of HDIG treatment in the pemphigus and pemphigoid models is dependent on FcRn. Thus, FcRn is a promising therapeutic target for treating such IgG-mediated autoimmune diseases.

Effect of linker segments on the stability of epithelial cadherin domain 2

Epithelial cadherin is a transmembrane protein that is essential in calcium-dependent cell-cell recognition and adhesion. It contains five independently folded globular domains in its extracellular region. Each domain has a seven-strand beta-sheet immunoglobulin fold. Short seven-residue peptide segments connect the globular domains and provide oxygens to chelate calcium ions at the interface between the domains (Nagar et al., Nature 1995;380:360-364). Recently, stability studies of ECAD2 (Prasad et al., Biochemistry 2004;43:8055-8066) were undertaken with the motivation that Domain 2 is a representative domain for this family of proteins. The definition of a domain boundary is somewhat arbitrary; hence, it was important to examine the effect of the adjoining linker regions that connect Domain 2 to the adjacent domains. Present studies employ temperature-denaturation and proteolytic susceptibility to provide insight into the impact of these linkers on Domain 2. The significant findings of our present study are threefold. First, the linker segments destabilize the core domain in the absence of calcium. Second, the destabilization due to addition of the linker segments can be partially reversed by the addition of calcium. Third, sodium chloride stabilizes all constructs. This result implies that electrostatic repulsion is a contributor to destabilization of the core domain by addition of the linkers. Thus, the context of Domain 2 within the whole molecule affects its thermodynamic characteristics.

Pemphigus foliaceus IgG causes dissociation of desmoglein 1-containing junctions without blocking desmoglein 1 transinteraction

Autoantibodies against the epidermal desmosomal cadherins desmoglein 1 (Dsg1) and Dsg3 have been shown to cause severe to lethal skin blistering clinically defined as pemphigus foliaceus (PF) and pemphigus vulgaris (PV). It is unknown whether antibody-induced dissociation of keratinocytes is caused by direct inhibition of Dsg1 transinteraction or by secondary cellular responses. Here we show in an in vitro system that IgGs purified from PF patient sera caused cellular dissociation of cultured human keratinocytes as well as significant release of Dsg1-coated microbeads attached to Dsg-containing sites on the keratinocyte cellular surface. However, cell dissociation and bead release induced by PF-IgGs was not caused by direct steric hindrance of Dsg1 transinteraction, as demonstrated by single molecule atomic force measurements and by laser trapping of surface-bound Dsg1-coated microbeads. Rather, our experiments strongly indicate that PF-IgG-mediated dissociation events must involve autoantibody-triggered cellular signaling pathways, resulting in destabilization of Dsg1-based adhesive sites and desmosomes.

Inflammatory dermatoses of the vulva

Inflammatory, non-neoplastic epidermal alterations of the vulva can be correctly diagnosed using classification schemes applied to skin elsewhere on the body. A wide range of inflammatory disorders may occur on the vulva, and they may have a similar clinical presentation to HPV lesions. However, HPV is incurable and often is treated surgically. Accordingly, as inflammatory dermatoses commonly occur on the vulva and are often curable with topical therapy, an awareness of these entities and an ability to distinguish them from HPV are imperative.

Altered expression of CLC, DSG3, EMP3, S100A2, and SLPI in corneal epithelium from keratoconus patients

PURPOSE

This investigation was designed to determine whether the five genes, CLC, DSG3, EMP3, S100A2 and SLPI, are differentially expressed in keratoconus, as indicated from another study.

METHODS

Gene expression was monitored using quantitative real-time PCR on 14 keratoconus samples and 16 controls, and normalized to GAPDH and B2M. The DSG3, S100A2, and SLPI proteins were quantified by Western blotting, and the cellular localization was determined by immunohistochemistry. One of the genes, CLC, was reduced in gene expression and its four exons were sequenced.

RESULTS

The five genes were all differentially expressed in keratoconus (P < 0.04) and so were at least three of the encoded proteins (P = 0.009). DSG3 was expressed in association with the cell membrane of the basal and suprabasal epithelial cells, and S100A2 was expressed in the nucleus and cytoplasm, often as intracellular granules. Two SNPs (rs374185 and rs384138) were observed in the CLC gene, each with an allele frequency of 68%. No other mutations were detected.

CONCLUSIONS

The five genes, and three of the encoded proteins, were shown differentially expressed between a group of keratoconus patients and a reference group using different techniques. These alterations, in combination with earlier findings, strongly demonstrate the genes to be involved in the corneal disease. We suggest the unambiguously expressed DSG3 protein to be used as a marker for keratoconus.

Ex vivo analysis of desmoglein 1-responsive T-helper (Th) 1 and Th2 cells in patients with pemphigus foliaceus and healthy individuals

Pemphigus foliaceus (PF) is a severe autoimmune bullous disorder, characterized by autoantibodies (autoAb) against desmoglein 1 (Dsg1). As T cells may be critical in the pathology of PF, the aim of the present study was to identify and characterize autoaggressive T-helper cells reactive to Dsg1 in PF patients and healthy individuals. Eight patients with the clinical diagnosis of PF and six HLA class II-matched healthy individuals were examined. By magnetic cell-sorting (MACS) cytokine-secretion assay, Dsg1-responsive T-helper (Th) 1 and Th2 cells were isolated and cloned by limiting dilution. The generated T-cell clones (TCC) were characterized regarding proliferative response, TCR Vbeta-chain usage, and cytokine profile upon in vitro stimulation with Dsg1. Both Dsg1-reactive Th1 and Th2 cells were detected in PF patients and controls at similar frequencies. A total of 15 Th1 and Th2 clones were isolated from patients and 27 TCC from healthy controls. Analysis of TCR Vbeta-chain usage of autoreactive T cells from both groups revealed no predominance of a specific Vbeta chain. Noteworthy, the isolated TCC showed a polarized Th1- or Th2-like phenotype upon in vitro culture and stable expression of Th1 or Th2 cytokines during long-term in vitro culture. In summary, our data demonstrate that T-cell autoreactivity against Dsg1 is not restricted to patients with PF. Moreover, both Th1 and Th2 cells were present in patients and healthy donors, suggesting that the loss of B-cell tolerance against Dsg1 in PF is not exclusively determined by the presence of autoaggressive T cells.

Pemphigus

Pemphigus is a rare autoimmune disease that results in blistering of the skin and oral cavity. It is caused by autoantibodies directed against cell-surface antigens on keratinocytes, which when targeted lose their cellular adhesion properties and separate from one another to form blisters within the epidermis. Differences in the particular antigens targeted by the antibodies and in the distribution of these antigens in the different regions of the body and in the separate layers of the epidermis result in different clinical manifestations of the disease. The disease is diagnosed based on its clinical manifestations (flaccid blisters and erosions on skin and oral mucosa), histology (epidermal acantholysis), and immunological abnormalities (circulating and tissue-fixed antibodies against keratinocyte surface antigens). Pemphigus, which if left untreated is almost always fatal, is generally managed with topical, oral, or intralesional corticosteroids. Other options include plasmapheresis and intravenous immunoglobulin (IVIg), coupled with cytotoxic drugs. Immunosupressants, anti-inflammatory drugs, and antibiotics are used as adjuvants, but apart from IVIg, these therapy options are non-specific and more research is needed to develop treatments with improved side-effect profiles.

Role of intramolecular epitope spreading in pemphigus vulgaris

Pemphigus vulgaris (PV) is an acquired immunobullous disorder. At the early stage of the disease (mucosal PV), patients display only autoimmunity to desmoglein (Dsg) 3 and develop mucosal blisters; while at the later stage of the disease (mucocutaneous PV), patients exhibit non-cross-reactive autoimmunity to both Dsg3 and Dsg1 and acquire cutaneous as well as mucosal blisters. At these two disease stages, Dsg3 autoantibodies exhibit different tissue-binding patterns and pathogenic activities, suggesting that they may recognize distinct epitopes. To test this hypothesis and to investigate the mechanism underlying the disease transition, we studied Dsg3 autoantibody epitopes from mucosal PV patients and patients exhibiting disease transition to mucocutaneous PV. We demonstrated that autoantibodies from the majority of mucosal PV patients target epitopes at the COOH-terminal portion of the Dsg3 ectodomain. Interestingly, only autoantibodies against the Dsg3 NH2-terminal epitope(s) are able to bind human skin. Moreover, we discovered that the intramolecular epitope spreading from Dsg3(87-566) to Dsg3(1-88) is a critical step that precedes the intermolecular epitope spreading from Dsg3 to Dsg1. During disease transition, this mechanism dictates the development of Dsg3 autoantibodies that recognize human skin and lead to expression of cutaneous PV lesions.

Genetic and functional characterization of human pemphigus vulgaris monoclonal autoantibodies isolated by phage display

Pemphigus is a life-threatening blistering disorder of the skin and mucous membranes caused by pathogenic autoantibodies to desmosomal adhesion proteins desmoglein 3 (Dsg3) and Dsg1. Mechanisms of antibody pathogenicity are difficult to characterize using polyclonal patient sera. Using antibody phage display, we have isolated repertoires of human anti-Dsg mAbs as single-chain variable-region fragments (scFvs) from a patient with active mucocutaneous pemphigus vulgaris. ScFv mAbs demonstrated binding to Dsg3 or Dsg1 alone, or both Dsg3 and Dsg1. Inhibition ELISA showed that the epitopes defined by these scFvs are blocked by autoantibodies from multiple pemphigus patients. Injection of scFvs into neonatal mice identified 2 pathogenic scFvs that caused blisters histologically similar to those observed in pemphigus patients. Similarly, these 2 scFvs, but not others, induced cell sheet dissociation of cultured human keratinocytes, indicating that both pathogenic and nonpathogenic antibodies were isolated. Genetic analysis of these mAbs showed restricted patterns of heavy and light chain gene usage, which were distinct for scFvs with different desmoglein-binding specificities. Detailed characterization of these pemphigus mAbs should lead to a better understanding of the immunopathogenesis of disease and to more specifically targeted therapeutic approaches.

Differential structural properties and expression patterns suggest functional significance for multiple mouse desmoglein 1 isoforms

The four isoforms of desmosomal cadherin desmogleins (Dsg1-4) are expressed in epithelial tissues in a differentiation-specific manner. Extensive sequencing of the human genome has revealed only one copy of the Dsg1 gene. However, we recently cloned two novel additional mouse Dsg1 genes, Dsg1-beta and -gamma, which flank the original Dsg1-alpha on chromosome 18. Sequence conservation between the Dsg1 isoforms diverged significantly at exon 11, particularly in the region that encodes for the extracellular anchoring (EA) domains. Computational analysis revealed very low hydrophilic potential of the Dsg1-gamma EA compared with the corresponding sequences of Dsg1-alpha and -beta, suggesting that the Dsg1-gamma EA domain may have a stronger affinity to the cell membrane. We generated antibodies using synthetic peptides or recombinant proteins localized within the EA domains. These antibodies were tested for their specificity and were then used to demonstrate expression of Dsg1 isoforms in various tissues. In the epidermis, all Dsg1 isoforms were differentially expressed in the differentiating cell layers. In the hair follicle, all Dsg1 isoforms were present throughout the entire process of its development and cycling but the expression of Dsg1 isoforms is subject to significant hair cycle-dependent changes. Dsg1-beta and -gamma, but not Dsg1-alpha, were detected in the sebaceous gland epithelium and the stratified epithelium of the stomach. Finally, Dsg1-alpha and Dsg1-beta, but not Dsg1-gamma, are proteolytically cleaved by exfoliative toxin A. These results suggest that the developmental complexity of mouse tissues, including skin and hair, may play a significant role in the evolutionary driving force to maintain multiple Dsg1 genes in mouse.

In vitro keratinocyte dissociation assay for evaluation of the pathogenicity of anti-desmoglein 3 IgG autoantibodies in pemphigus vulgaris

Patients with pemphigus vulgaris (PV) have circulating anti-desmoglein (Dsg) 3 immunoglobulin G (IgG) autoantibodies that induce blister formation. We developed an in vitro quantitative assay to evaluate the pathogenic strength of anti-Dsg3 IgG autoantibodies in blister formation. To obtain intercellular adhesion mediated dominantly by Dsg3, we used primary cultured normal human keratinocytes expressing low level of Dsg2 in the presence of exfoliative toxin A that specifically digests Dsg1. After incubation with various antibodies, monolayers released by dispase were subjected to mechanical stress by pipetting, and the number of cell fragments were counted. When anti-Dsg3 monoclonal antibodies (mAb) obtained from pemphigus model mice were tested, pathogenic AK23 mAb yielded significantly higher number of cell fragments than AK7 or AK20 non-pathogenic mAb. Dissociation scores, defined with AK23 mAb as the positive control, were significantly higher with active stage PV sera (n=10, 77.4+/-21.4) than controls (n=11, 16.0+/-9.6; p=0.003). When pair sera obtained from 6 PV patients in active stage and in remission were compared, the dissociation scores reflected well the disease activity as those in active stage were four to 17 times higher than those in remission. When sera from different patients showing similar ELISA scores but different clinical severity were tested (n=6), the dissociation scores with sera from severe disease activity were significantly higher than those with sera in remission. These findings indicate that this dissociation assay will provide a simple and objective biological method to measure the pathogenic strength of pemphigus autoantibodies.

Genetic factors in pemphigus

Epidemiological studies performed in different ethnic populations and family studies, notably based on a partial phenotype of the autoimmune process, indicate that genetic factors are involved in the occurrence of pemphigus. However, the precise heritability remains uncertain in the absence of twin concordance rate studies. Among the different strategies available to identify genetic factors participating in autoimmune disease susceptibility, only population studies based on case-control design have been performed in pemphigus. These studies consistently showed that MHC locus, in particular HLA class II alleles, are associated with pemphigus vulgaris and pemphigus foliaceus. Other genes of the MHC locus may also participate in disease susceptibility as shown by studies using microsatellite markers across different regions of the MHC. It is likely that other non-MHC genes are involved in the pathogenesis of pemphigus. In particular, involvement of a polymorphic variant of desmoglein 1 gene was shown to be associated with pemphigus foliaceus and to interact in an epistatic manner with MHC class II genes to contribute to the autoimmune process. Other candidate genes to which a role can be assigned in the disease pathogenesis should be considered to design case-control or family-based association studies. Genome scan studies which require a large number of multiplex families to reach statistical power, should also be considered in the endemic form of pemphigus foliaceus because of the high number of familial cases.

Number II Pemphigus vulgaris

Pemphigus is a group of potentially life-threatening autoimmune diseases characterized by cutaneous and/or mucosal blistering. Pemphigus vulgaris (PV), the most common variant, is characterized by circulating IgG antibodies directed against desmoglein 3 (Dsg3), with about half the patients also having Dsg1 autoantibodies. There is a fairly strong genetic background to pemphigus with linkage to HLA class II alleles and ethnic groups such as Ashkenazi Jews and those of Mediterranean and Indian origin, are especially liable. Oral lesions are initially vesiculobullous but readily rupture, new bullae developing as the older ones rupture and ulcerate. Biopsy of perilesional tissue, with histological and immunostaining examination are essential to the diagnosis. Serum autoantibodies to either Dsg1 or Dsg3 are best detected using both normal human skin and monkey oesophagus or by enzyme-linked immunosorbent assay. Before the introduction of corticosteroids, PV was typically fatal mainly from dehydration or secondary systemic infections. Current treatment is largely based on systemic immunosuppression using corticosteroids, with azathioprine or other adjuvants or alternatives but newer therapies with potentially fewer adverse effects, also appear promising.

Early Detection and Successful Management of Oral Pemphigus Vulgaris: A Case Report

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune disease characterized by acantholysis in the epithelium. PV is often difficult to diagnose in the early stages, since the oral lesions are relatively nonspecific. We report on a case with a favorable outcome due to early diagnosis and effective treatment of oral lesions.

METHODS

A 53-year-old Japanese woman presented with a month-long history of painful gingiva. PV was diagnosed using clinical, histopathological, and direct immunofluorescence criteria 1 month after the first visit. Evaluation of the circulating autoantibody titers to desmoglein (Dsg)1 and Dsg3 was conducted by enzyme-linked immunosorbent assay (ELISA). Occlusive steroid therapy (OST) using a topical corticosteroid (0.1% triamcinolone acetonide) was provided for 8 weeks. After OST was completed, a buccal frenectomy was performed to eliminate localized toothbrushing trauma.

RESULTS

There were no adverse effects on wound healing after the procedure. No oral PV lesions were detectable at the 9-month reevaluation, and the patient remains in complete remission. The Dsg1 ELISA was negative while the Dsg3 ELISA was indeterminate at the first visit. The Dsg1 ELISA was also negative at reevaluation, but Dsg3 ELISA reactivity had increased 9 months after completion of treatment.

CONCLUSION

Large scale clinical trials will be required to validate the clinical benefits of the OST treatment regimen, and further research is necessary to determine the importance of ELISA antibody examination in long-term management of oral PV.

Epitope definition by proteomic similarity analysis: identification of the linear determinant of the anti-Dsg3 MAb 5H10

BACKGROUND: Walking along disease-associated protein sequences in the search for specific segments able to induce cellular immune response may direct clinical research towards effective peptide-based vaccines. To this aim, we are studying the targets of the immune response in autoimmune diseases by applying the principle of non-self-discrimination as a driving concept in the identification of the autoimmunogenic peptide sequences. METHODS: Computer-assisted proteomic analysis of the autoantigen protein sequence and dot-blot/NMR immunoassays are applied to the prediction and subsequent validation of the epitopic sequences. RESULTS: Using the experimental model Pemphigus vulgaris/desmoglein 3, we have identified the antigenic linear determinant recognized by MAb 5H10, a monoclonal antibody raised against the extracellular domain of human desmoglein-3. The computer-assisted search for the Dsg3 epitope was conducted by analyzing the similarity level to the mouse proteome of the human desmoglein protein sequence. Dot-blot immunoassay analyses mapped the epitope within the sequence Dsg349-60 REWVKFAKPCRE, which shows low similarity to the mouse proteome. NMR spectroscopy analyses confirmed the specificity of MAb 5H10 for the predicted epitope. CONCLUSIONS: This report promotes the concept that low level of sequence similarity to the host's proteome may modulate peptide epitopicity.

Management of autoimmune bullous diseases: Pharmacology and therapeutics

Bullous diseases are associated with high morbidity and mortality. They result from autoimmune response to one or more components of the basement membrane or desmosomes. Management consists of treating the immunologic basis of the disease, treating the inflammatory process involved in lesion formation, and providing supportive care both locally and systemically. Therapeutic agents are chosen based on their known pharmacologic properties and evidence of effectiveness derived from observations and studies. Learning objectives At the completion of this learning activity, participants should be able to understand the pharmacology of drugs used in the treatment of bullous diseases, the principles of therapy for various such diseases, and a practical approach to the management of these diseases.

Desmosomes and disease: pemphigus and bullous impetigo

Desmosomal cadherins are the pathophysiologic targets of autoimmune or toxin-mediated disruption in the human diseases pemphigus and bullous impetigo (including its generalized form, called staphylococcal scalded skin syndrome). Experiments exploiting the production of both pathogenic and nonpathogenic antidesmoglein antibodies in pemphigus patients' sera have afforded data that make an invaluable contribution towards identifying the functional domains of the desmogleins involved in intercellular adhesion. Conformational epitopes of antidesmoglein autoantibodies in pemphigus patients' sera and the specific cleavage site of desmoglein 1 by exfoliative toxin have been identified, implicating the N-terminal extracellular domains of the desmogleins as critical regions for controlling intercellular adhesion. Furthermore, the development of active autoimmune mouse models for pemphigus allows in vivo characterization of the disease and its pathogenesis. These studies offer new insight into the potential mechanisms of acantholysis in pemphigus and staphylococcal-associated blistering disease, with implications for the role of desmogleins in desmosomal structure and function.

Conformational epitope mapping of antibodies against desmoglein 3 in experimental murine pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris (PV) is a blistering skin disease caused by IgG autoantibodies against desmoglein 3 (Dsg3). We have recently developed an active disease mouse model for PV by adoptive transfer of splenocytes from immunized or naive Dsg3-/- mice into Rag2-/- recipient mice.

OBJECTIVE

In this study, we characterized the conformational epitopes of anti-Dsg3 IgG antibodies and their pathogenic activities in the PV model mice.

METHODS

The binding regions of anti-Dsg3 IgG antibodies were assessed by competition ELISAs with domain-swapped mouse Dsg1/Dsg3 molecules in PV model mice receiving immunized (n = 53) or naive (n = 56) splenocytes. To compare the pathogenic activity of antibodies against N-terminal versus C-terminal extracellular domains, Dsg3-/- mice were immunized with the residues 1-162 or the residues 403-565 of mouse Dsg3, and the splenocytes were adoptively transferred into Rag2-/- mice.

RESULTS

The middle to C-terminal extracellular domains of Dsg3 (residues 195-565) showed >50% competition in 51/53 (96.2%) and 45/56 (80.4%) while the N-terminal domain (residues 1-162) showed >50% competition only in 3/53 (5.7%) and 8/56 (14.3%) in mice receiving immunized and naive splenocytes, respectively. The mice receiving Dsg3-/- splenocytes immunized with the residues 403-565 developed the PV phenotype as early as and as severely as the mice receiving splenocytes immunized with the residues 1-162.

CONCLUSIONS

In PV model mice the antibodies were dominantly raised against the middle to C-terminal extracellular domains of mouse Dsg3 where amino acid sequences are less conserved among desmoglein isoforms and that those antibodies may also be involved in the blister formation.

T cell recognition of desmoglein 3 peptides in patients with pemphigus vulgaris and healthy individuals

Pemphigus vulgaris is a severe autoimmune disease caused by autoantibodies against the cutaneous adhesion molecule, desmoglein 3 (Dsg3). The aim of this study was to characterize the specificity of autoreactive Th cells, which presumably regulate Dsg3-specific autoantibody production. Ninety-seven Th1 and Th2 clones isolated from 16 pemphigus patients and 12 HLA-matched healthy donors recognized the Dsg3 peptides, DG3(78-94), DG3(96-112), DG3(189-205), DG3(205-221), and DG3(250-266). Peptide DG3(96-112), and to a lesser extent DG3(250-266), was recognized by the majority of T cells from patients and healthy donors in association with HLA-DRB1*0402 and DQB1*0503 which were prevalent in the pemphigus patients and Dsg3-responsive healthy donors. Analyzing the Vbeta-chain of the TCR of the DG3(96-112)-specific T cells showed no restricted TCR usage. Peptides DG3(342-358) and DG3(376-392) were exclusively recognized by T cell clones (n=13) from patients while DG3(483-499) was only recognized by T cell clones (n=3) from a healthy donor. All Dsg3 peptides contained conserved amino acids at relative positions 1, 4, and 6; amino acids with a positive charge at position 4 presumably represent anchor motifs for DRB1*0402. These findings demonstrate that T cell recognition of distinct Dsg3 peptides is restricted by distinct HLA class II molecules and is independent from the development of pemphigus vulgaris.

Thermodynamic Stability of Domain 2 of Epithelial Cadherin

Cadherin is a cell adhesion molecule that participates in ordered calcium-dependent self-association interactions both between molecules on the same cell surface (cis-interactions) and on neighboring cell surfaces (trans-interactions). Cadherin is a transmembrane protein that has 3-7 independently folded beta-barrel extracellular domains. Both types of self-association interactions are mediated through the most N-terminal domain (Domain 1). Although the structural nature of the trans-interactions is clear, the nature of the cis-interactions is ambiguous despite several high-resolution structural studies. From earlier studies, it is understood that for the trans-interactions to happen, cis-interactions are mandatory. Hence, our first steps are to study the energetic driving forces for the cis-interactions. We have simplified the approach by first examining participating extracellular domains individually. We report here our initial experiments into the stability of Domain 2 of E-cadherin (ECAD2). ECAD2 appears monomeric, according to results from mass spectrometry and sedimentation equilibrium studies. We report denaturation data from differential scanning calorimetric experiments, and temperature and denaturant-induced unfolding experiments monitored by circular dichroism. These studies give a unified picture of the energetics of ECAD2-folding and stability, for which DeltaG degrees is 6.6 kcal/mol, T(m) is 54 degrees C, DeltaH(m) is 90 kcal/mol, and DeltaC(p) is 1300 cal/Kmol. These parameters are independent of calcium up to 5 mM, indicating that ECAD2 does not bind calcium at physiological calcium levels.

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.

Pemphigus vulgaris autoantibodies induce apoptosis in HaCaT keratinocytes

Pemphigus vulgaris (PV) is an autoimmune disease characterized by binding of IgG autoantibodies to epidermal keratinocyte desmosomes. IgG autoantibodies obtained from a patient with mucocutaneous PV reacted with plakoglobin (Plkg) in addition to desmoglein-3 (Dsg3) and Dsg1. Immunofluorescence analysis confirmed that IgG autoantibodies, unlike antibodies from a healthy volunteer, caused disruption of cell-cell contacts in HaCaT keratinocytes. Moreover, apoptosis was enhanced in cells treated with autoantibodies compared to those treated with normal antibodies. The apoptotic process induced by IgG autoantibodies was characterized by caspase-3 activation, Bcl-2 depletion and Bax expression. The present report demonstrates that PV IgG autoantibodies promote apoptosis in HaCaT keratinocytes.

New approaches to the treatment of pemphigus

In pemphigus vulgaris, treatment with systemic glucocorticosteroids is life saving; it may, however, cause severe side effects, including death. A patient with pemphigus vulgaris and myasthenia gravis was treated for approximately five years with the cholinomimetic Mestinon (pyridostigmine bromide), Imuran (azathioprine), and a topical corticosteroid gel before the need to introduce systemic glucocorticosteroids. Because activation of keratinocyte acetylcholine receptors also has been shown to abolish pemphigus IgG-induced acantholysis in cultured keratinocyte monolayers, a clinical trial of Mestinon was initiated in patients with active pemphigus vulgaris, pemphigus foliaceus, and paraneoplastic autoimmune multiorgan syndrome (also known as paraneoplastic pemphigus). First results indicate that nonsteroidal treatment of pemphigus is possible. Mestinon may be used to slow down progression of the disease and to treat mild cases with chronic lesions on limited areas. Stimulation of the keratinocyte- acetylcholine axis may lead to a therapeutic effect through any of the following mechanisms: (1) stimulating keratinocyte cell-to-cell attachment; (2) accelerating reepithelialization; and (3) competing with the disease-causing pemphigus antibodies, preventing them from attachment to keratinocytes. Glucocorticosteroids and various types of steroid-sparing drugs used to treat pemphigus exhibit cholinergic side effects, including effects on expression and function of keratinocyte adhesion molecules, that are very similar to those produced by the cholinomimetic drugs. Further elucidation of the mechanisms underlying therapeutic efficacy of antiacantholytics may shed light on the immunopharmacological mechanisms of pemphigus antibody-induced acantholysis.