Pemphigus: an unfolding story

Dsg3 epitope-specific signalling in pemphigus

Introduction

Pemphigus is an autoantibody driven disease that impairs the barrier function of the skin and mucosa by disrupting desmosomes and thereby impeding cellular cohesion. It is known that the different clinical phenotypes of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are dependent on the autoantibody profile and target antigens that, amongst others, are primarily desmoglein (Dsg)1 and/or Dsg3 for PV and Dsg1 for PF. However, it was reported that autoantibodiesagainst different epitopes of Dsg1 and Dsg3 can be pathogenic or not. The underlying mechanisms are very complex and involve both direct inhibition of Dsg interactions and downstream signalling. The aim of this study was to find out whether there is target-epitope-specific Dsg3 signalling by comparing the effects of the two pathogenic murine IgGs, 2G4 and AK23.

Methods

Dispase-based dissociation assay, Western Blot analysis, Stimulated emission depletion microscopy, Fura-based Ca2+ flux measurements, Rho/Rac G-Protein-linked immunosorbent assay, Enzyme-linked immunosorbent assay.

Results

The IgGs are directed against the EC5 and EC1 domain of Dsg3, respectively. The data show that 2G4 was less effective in causing loss of cell adhesion, compared to AK23. STED imaging revealed that both autoantibodies had similar effects on keratin retraction and reduction of desmosome number whereas only AK23 induced Dsg3 depletion. Moreover, both antibodies induced phosphorylation of p38MAPK and Akt whereas Src was phosphorylated upon treatment with AK23 only. Interestingly, Src and Akt activation were p38MAPK-dependent. All pathogenic effects were rescued by p38MAPK inhibition and AK23-mediated effects were also ameliorated by Src inhibition.

Discussion

The results give first insights into pemphigus autoantibody-induced Dsg3 epitope-specific signalling which is involved in pathogenic events such as Dsg3 depletion.

Autoantibody-Specific Signalling in Pemphigus

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Successful treatment of pemphigus foliaceus in a Berrichon du Cher ram with methylprednisolone acetate

BACKGROUND

Pemphigus foliaceus is a severe, autoimmune blistering skin disease, which is described in humans and some animal species. In small ruminants pemphigus foliaceus has rarely been described and, to the best of the authors' knowledge, little information is available about successful treatment in sheep.

AIM

This case report describes a Berrichon du Cher ram with the presumed diagnosis of pemphigus foliaceus.

METHODS

The ram was treated with methylprednisolone acetate 40 mg at a dosage of 2.5 mg/kg in one subcuticular injection at four week intervals over a one year period, with regular observation of clinical parameters. Four months after treatment was initiated the haematological parameters showed lymphopenia and leukopenia; some enzyme activities were substantially increased.

RESULTS

The ram's dermatological condition improved to the point of complete healing of the affected skin. The ram was discharged in good condition. No adverse effects, except an elevation of some enzymes associated with liver function, were observed. At postmortem examination moderate fatty liver syndrome was the only abnormality found.

CONCLUSIONS AND CLINICAL IMPORTANCE

This case report demonstrated that long term therapy with methylprednisolone acetate in a sheep with pemphigus foliaceus did not have a negative effect on clinical parameters. Nevertheless, due to the extended statutory withdrawal period resulting from the regular administration of glucocorticoids, such a therapeutic option must be critically assessed in food producing animals.

A reciprocal HLA-Disease Association in Rheumatoid Arthritis and Pemphigus Vulgaris

Human leukocyte antigens (HLA) have been extensively studied as being antigen presenting receptors, but many aspects of their function remain elusive, especially their association with various autoimmune diseases. Here we discuss an illustrative case of the reciprocal relationship between certain HLA-DRB1 alleles and two diseases, rheumatoid arthritis (RA) and pemphigus vulgaris (PV). RA is strongly associated with HLA-DRB1 alleles that encode a five amino acid sequence motif in the 70-74 region of the DR beta chain, called the shared epitope (SE), while PV is associated with the HLA-DRB1*04:02 allele that encodes a different sequence motif in the same region. Interestingly, while HLA-DRB1*04:02 confers susceptibility to PV, this and other alleles that encode the same sequence motif in the 70-74 region of the DR beta chain are protective against RA. Currently, no convincing explanation for this antagonistic effect is present. Here we briefly review the immunology and immunogenetics of both diseases, identify remaining gaps in our understanding of their association with HLA, and propose the possibility that the 70-74 DR beta epitope may contribute to disease risk by mechanisms other than antigen presentation.

Urban legends: pemphigus vulgaris

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

The cochlear CRF signaling systems and their mechanisms of action in modulating cochlear sensitivity and protection against trauma

A key requirement for encoding the auditory environment is the ability to dynamically alter cochlear sensitivity. However, merely attaining a steady state of maximal sensitivity is not a viable solution since the sensory cells and ganglion cells of the cochlea are prone to damage following exposure to loud sound. Most often, such damage is via initial metabolic insult that can lead to cellular death. Thus, establishing the highest sensitivity must be balanced with protection against cellular metabolic damage that can lead to loss of hair cells and ganglion cells, resulting in loss of frequency representation. While feedback mechanisms are known to exist in the cochlea that alter sensitivity, they respond only after stimulus encoding, allowing potentially damaging sounds to impact the inner ear at times coincident with increased sensitivity. Thus, questions remain concerning the endogenous signaling systems involved in dynamic modulation of cochlear sensitivity and protection against metabolic stress. Understanding endogenous signaling systems involved in cochlear protection may lead to new strategies and therapies for prevention of cochlear damage and consequent hearing loss. We have recently discovered a novel cochlear signaling system that is molecularly equivalent to the classic hypothalamic-pituitary-adrenal (HPA) axis. This cochlear HPA-equivalent system functions to balance auditory sensitivity and susceptibility to noise-induced hearing loss, and also protects against cellular metabolic insults resulting from exposures to ototoxic drugs. We review the anatomy, physiology, and cellular signaling of this system, and compare it to similar signaling in other organs/tissues of the body.

The pathogenic role of autoantibodies in pemphigus vulgaris

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

Captopril modulates acetylcholinesterase in human keratinocytes

Human keratinocytes synthesize and secrete non-neuronal acetylcholine, which acts as a local cell signaling molecule, regulating functions like proliferation, cell adhesion, motility, desmosomal cell contact, and glandular activity. The keratinocyte acetylcholine axis is composed of the enzymes mediating acetylcholine synthesis (acetyltransferase) and degradation (acetylcholinesterase), and two classes of acetylcholine receptors. In this study we investigated the effect of captopril, an ACE-inhibitor, on acetylcholinesterase and acetylcholine secretion in human keratinocytes. We analyzed the level of acetylcholinesterase in HaCat and NHEK cells by RT-PCR and Western blotting analysis. In addition, the effect of captopril on AChE activity was evaluated. We found that captopril induces a strong AChE up-regulation leading to ACh degradation and reduced secretion. Our results suggest that acantholysis induced by ACE-inhibitors might be linked to altered level of Ach.

Autoimmune blistering diseases in children

Autoimmune blistering disorders comprise a series of conditions in which autoantibodies target components of the skin and mucous membranes, leading to blister and bullae formation. Most conditions in the spectrum of autoimmune blistering disorders are uncommonly seen in the pediatric population, even the most common ones, such as chronic bullous disease of childhood and dermatitis herpetiformis; however, they often come into the differential diagnosis of other more common pediatric entities. In addition, prompt recognition and treatment avoids unnecessary morbidity and improves ultimate outcome.

Pemphigus herpetiformis: analysis of the autoantibody profile during the disease course with changes in the clinical phenotype

BACKGROUND

Pemphigus herpetiformis (PH) is a rare dapsone-responsive variant of pemphigus, characterized by annular and vesiculopustular cutaneous lesions. Most PH serum samples contain autoantibodies against desmoglein (Dsg)1, but not Dsg3, and the presence of the latter is almost invariably associated with mucosal involvement, as predicted based on the 'Dsg compensation theory'.

METHODS

We describe a patient with features characteristic of PH with histologically eosinophilic spongiosis who repeatedly tested positive for anti-Dsg3 but not anti-Dsg1 autoantibodies by ELISA. To investigate whether the peculiar clinical phenotype was due to a distinct immunological profile, the patient's serum was tested by ELISA and immunoblotting using recombinant forms of Dsg3.

RESULTS

Serum samples were found to have low and high reactivity against the EC1 and the EC4 domains of Dsg3, respectively, whereas the autoantibodies belonged predominantly to the IgG1 and IgG4 subclasses. The overall immunological profile was typical of pemphigus vulgaris. The patient finally developed isolated oral erosions 22 months after initial presentation, without significant changes in the autoantibody profile and of the targeted antigenic sites.

CONCLUSIONS

Our patient presented features characteristic of PH. Although circulating anti-Dsg3 antibodies were present, the patient had only cutaneous involvement for a long period. Our findings indicate that the proposed Dsg compensation theory cannot always explain the clinical phenotype, changes in which may occur without apparent modification of the autoantibody profile and antibody specificity. Hence, additional factors, such as Fcgamma-dependent neutrophil activation, may critically affect the clinical presentation of pemphigus.

Significance of autoimmunity to non-desmoglein targets in pemphigus

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

Vesicular and Bullous Disorders: Pemphigus

Pemphigus is a chronic, autoimmune disease involving the skin and Malpighian mucous membranes. Pemphigus leads to progressive blistering and subsequent erosions. This article describes the etiology and treatment of pemphigus.

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

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

Pemphigus and associated environmental factors: a case?control study

BACKGROUND

Recent reports have revealed the relatively high incidence of pemphigus in Iran. Occupational exposure and personal habits have been suggested to play a role in the aetiopathogenesis of this life-threatening disease.

AIM

In order to analyse the association of environmental factors with pemphigus, we conducted a case-control study to evaluate the possible role of smoking, pesticide exposure and hormonal factors in Iran.

METHODS

This study was conducted in Iran using a structured questionnaire. Questions included information on patients' smoking habits, occupational exposure to pesticides, use of oral contraception (OC) and number of pregnancies.

RESULTS

We enrolled 210 patients with pemphigus and 205 control subjects. Fewer of patients with pemphigus (17.1%) reported a current or past history of smoking, which was statistically different from the control group (27.3% smokers). The duration of smoking and the number of cigarettes smoked daily was also significantly lower in patients. Although OC use was significantly higher in women with pemphigus, the mean number of pregnancies was not different between the two groups. Occupational exposure to pesticides was significantly higher in patients with pemphigus (14.8%) than in controls (5.4%); patients with pemphigus were exposed to pesticides three times more often than were healthy subjects.

CONCLUSION

As a positive history of smoking was lower in patients with pemphigus compared with healthy subjects, it seems that smoking is a protective factor in pemphigus. This should encourage further investigations, searching for novel therapies. If pesticides and OC are confirmed as triggering factors, their cessation might reduce the need for pharmacological therapy.

Improved protocol for treatment of pemphigus vulgaris with protein A immunoadsorption

BACKGROUND

Pemphigus vulgaris is a life-threatening autoimmune blistering skin disease, usually treated with high-dose corticosteroids in combination with other immunosuppressants. However, this regimen may prove inadequate in severe cases and can cause dangerous side-effects. We have recently reported protein A immunoadsorption (PAIA) to be an effective adjuvant treatment for induction of remission in severe pemphigus. However, in a significant number of cases, the disease rapidly recurred once PAIA and immunosuppressive medication were tapered.

AIMS

The aim of the present study was to develop a PAIA-based therapeutic regimen that would result in a more prolonged remission of pemphigus.

METHODS

Nine patients with pemphigus vulgaris were treated with a modified protocol characterized by a combination of PAIA with a higher initial dose of systemic methylprednisolone (2 mg/kg). In addition, azathioprine or mycophenolate mofetil was administered as a steroid-sparing agent.

RESULTS

In all nine patients treated with this regimen, we observed a sharp decline of circulating autoantibody levels and dramatic improvement of cutaneous and mucosal lesions within 4 weeks of therapy. The patients remained free of clinical disease for up to 26 months after PAIA treatment was discontinued.

CONCLUSION

The improved treatment protocol appears to combine highly effective induction of clinical remission in severe or treatment-resistant pemphigus with a prolonged subsequent symptom-free interval.

Functional Characterization of the Epidermal Cholinergic System In Vitro

The aim of this study was to analyze the influence of cholinergic and anticholinergic drugs on epidermal physiology using organotypic cocultures (OTCs). Blocking of all acetylcholine receptors (AChRs) by combined treatment with mecamylamine and atropine or treatment with strychnine (blocking alpha9nAChR) for 7-14 days resulted in a complete inhibition of epidermal differentiation and proliferation. Blockage of nicotinic (n)AChR with mecamylamine led to a less pronounced delay in epidermal differentiation and proliferation than blockage of muscarinic (m)AChR with atropine, evidenced by reduced epithelial thickness and expression of terminal differentiation markers like cytokeratin 2e or filaggrin. In OTCs treated with atropine, mecamylamine, or strychnine, we could demonstrate intracellular lipid accumulation in the lower epidermal layers, indicating a severely disturbed epidermal barrier. In addition, we observed prominent acantholysis in the basal and lower suprabasal layers in mecamylamine-, atropine-, and strychnine-treated cultures, accompanied by a decreased expression of cell adhesion proteins. This globally reduced cell adhesion led to cell death via intrinsic activation of apoptosis. In contrast, stimulation of nAChR and mAChR with cholinergic drugs resulted in a significantly thickened epithelium, accompanied by an improved epithelial maturation. In summary, we show that epidermal AChR are crucially involved in the regulation of epidermal homeostasis.

Proteomic definition of a desmoglein linear determinant common to Pemphigus vulgaris and Pemphigus foliaceous

Background

A number of autoimmune diseases have been clinically and pathologically characterized. In contrast, target antigens have been identified only in a few cases and, in these few cases, the knowledge of the exact epitopic antigenic sequence is still lacking. Thus the major objective of current work in the autoimmunity field is the identification of the epitopic sequences that are related to autoimmune reactions. Our labs propose that autoantigen peptide epitopes able to evoke humoral (auto)immune response are defined by the sequence similarity to the host proteome. The underlying scientific rationale is that antigen peptides acquire immunoreactivity in the context of their proteomic similarity level. Sequences uniquely owned by a protein will have high potential to evoke an immune reaction, whereas motifs with high proteomic redundancy should be immunogenically silenced by the tolerance phenomenon. The relationship between sequence redundancy and peptide immunoreactivity has been successfully validated in a number of experimental models. Here the hypothesis has been applied to pemphigus diseases and the corresponding desmoglein autoantigens.

Methods

Desmoglein 3 sequence similarity analysis to the human proteome followed by dot-blot/NMR immunoassays were carried out to identify and validate possible epitopic sequences.

Results

Computational analysis led to identifying a linear immunodominant desmoglein-3 epitope highly reactive with the sera from Pemphigus vulgaris as well as Pemphigus foliaceous. The epitopic peptide corresponded to the amino acid REWVKFAKPCRE sequence, was located in the extreme N-terminal region (residues 49 to 60), and had low redundancy to the human proteome. Sequence alignment showed that human desmoglein 1 and 3 share the REW-KFAK–RE sequence as a common motif with 75% residue identity.

Conclusion

This study 1) validates sequence redundancy to autoproteome as a main factor in shaping desmoglein peptide immunogenicity; 2) offers a molecular mechanicistic basis in analyzing the commonality of autoimmune responses exhibited by the two forms of pemphigus; 3) indicates possible peptide-immunotherapeutical approaches for pemphigus diseases.

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.

Cholinergic control of epidermal cohesion

The non-neuronal cholinergic system of human epidermis includes the keratinocyte (KC) acetylcholine (ACh) axis composed of the enzymes mediating ACh synthesis and degradation, and two classes of ACh receptors, the nicotinic and muscarinic ACh receptors, mediating biological effects of the cutaneous cytotransmitter ACh. Regulation of KC cell-cell and cell-matrix adhesion is one of the important biological functions of cutaneous ACh. The downstream targets of ACh effects mediated by distinct ACh receptor subtypes include both the intercellular adhesion molecules, such as classical and desmosomal cadherins, and integrins mediating KC adhesion to a substrate. The signaling pathways include activation or inhibition of kinase cascades resulting in either up- or down-regulation of the expression of cell adhesion molecules or changes in their phosphorylation status, or both. The components of the KC ACh axis are involved in cutaneous blistering in patients with autoimmune pemphigus, junctional and dystrophic forms of epidermolysis bullosa, thermal burns, and mustard-induced vesication. Recent progress with the development of antiacantholytic therapies of patients with pemphigus using cholinomimetics indicates that cholinergic drugs may be a promising approach for other cutaneous blistering disorders.

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.

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.

Increased activity of plasma and tissue kallikreins, plasma kininase II and salivary kallikrein in pemphigus foliaceus (fogo selvagem)

BACKGROUND

Pemphigus foliaceus (PF) is an autoimmune blistering disease of unknown aetiology, which is endemic in Brazil. Although the pathogenesis of PF is still unknown, proteins of the contact system have been implicated.

OBJECTIVES

As the components of the kinin system may interact with those of the contact system, in this study we evaluated the plasma levels of high-molecular-weight kininogen (HK) and low-molecular-weight kininogen (LK), and the activity of plasma kallikrein, tissue kallikrein and kininase II in plasma of patients with PF presenting with Nikolsky's sign. As kidneys and salivary glands are relevant sources of tissue kallikrein for plasma, we also evaluated urinary/salivary kallikrein and urinary kininase II activities.

METHODS

Fifteen patients and 15 age- and sex-matched controls were studied. Kininogen levels were determined by enzyme-linked immunosorbent assay, and the activities of kallikreins and kininase II were determined using selective chromogenic substrates.

RESULTS

Compared with controls, plasma HK levels were decreased (P = 0.031), whereas the activities of plasma kallikrein, tissue kallikrein and kininase II in plasma, and the activity of salivary kallikrein, were increased in patients (P < 0.001 for each comparison). Plasma levels of LK and the activities of urinary kallikrein and urinary kininase II were not significantly different from controls.

CONCLUSIONS

Diminished levels of HK associated with increased activities of plasma kallikrein and kininase II indicate that the kinin system is activated at the systemic level in PF. As active plasma kallikreins may act on some proteins of the contact system, it is possible that the enzyme may contribute to blister formation. The further observation of an increased tissue kallikrein activity at the systemic and saliva levels may be interpreted as a systemic reflex of skin inflammation. Whether the activation of the kinin system is a cause or a consequence of blister formation needs further clarification.

Pemphigus

Pemphigus is an umbrella term for more than 10 different epidermal disease types and subtypes currently classified under this name. Characteristic for pemphigus are the presence of autoantibodies against epidermal cell adhesion structures (desmosomes), leading to a breakdown of cutaneous and mucosal barriers. The two most important disease types for dentists are pemphigus vulgaris and paraneoplastic pemphigus because they almost invariably present with oral manifestations. This article highlights current knowledge on the pathophysiology, the clinical signs, and the practical clinical diagnostic approach to these two serious disorders and treatment.

Pemphigus Vulgaris IgG and Methylprednisolone Exhibit Reciprocal Effects on Keratinocytes

Pemphigus vulgaris (PV) is a life-threatening autoimmune disease of skin adhesion associated with IgG autoantibodies against keratinocytes (KC). Treatment of PV with systemic corticosteroids is life-saving, but the mechanism of the therapeutic action has not been fully understood. We have developed an animal model that demonstrates that methylprednisolone (MP) can block PV IgG-induced acantholysis, decreasing the extent of keratinocyte detachment in the epidermis of 3-5-day-old nude mice from 77.5 +/- 0.6 to 24.1 +/- 1.5% (p < 0.05). We hypothesized that in addition to immunosuppression, MP may exhibit direct anti-acantholytic effects in epidermis, and we compared the effects of PV IgG and MP on KC. The use of DNA microarray showed that PV IgG down-regulated and MP up-regulated expression of the genes encoding keratinocyte adhesion molecules, antigen-processing proteins, regulators of cell cycle and apoptosis, differentiation markers, Na+,K+-ATPase, protein kinases and phosphatases, and serine proteases and their inhibitors. Overall, PV IgG decreased transcription of 198 genes and increased transcription of 31 genes. MP decreased transcription of 14 genes and increased transcription of 818 genes. Specific effects of PV IgG and MP on keratinocyte adhesion molecules were further investigated by Western blot and immunofluorescence assays. By immunoblotting, MP increased the protein levels of E-cadherin and desmogleins 1 and 3 by 300, 180, and 40%, respectively. Specific staining of KC for E-cadherin and desmogleins 1 and 3 increased by 235, 228, and 148%, respectively. In addition, PV IgG increased the level of phosphorylation of E-cadherin by 42%, beta-catenin by 37%, gamma-catenin by 136%, and desmoglein 3 by 300%, whereas pretreatment with 0.25 mm MP abolished phosphorylation of these adhesion molecules. These results suggested that therapeutic effects of MP in PV include both the up-regulated synthesis and post-translational modification of the keratinocyte adhesion molecules.

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.

Keratinocyte acetylcholine receptors regulate cell adhesion

We investigated the mechanism mediating cholinergic control of cell-to-cell adhesion of human epidermal keratinocytes (KC) by non-neuronal acetylcholine produced by KC themselves. We first measured cholinergic effects on the expression of desmoglein (Dsg) 1 and 3 in KC using the semi-quantitative immunofluorescence and Western blot assays. Monolayers of KC were treated overnight with 0.25 mM of the cholinergic agonist carbachol (CCh) or the acetylcholinesterase inhibitor pyridostigmine bromide (PBr). Both CCh and PBr increased the relative amounts of Dsg 1 and Dsg 3. To determine the role for cholinergic receptor-mediated phosphorylation of Dsg molecules in assembly/disassembly of keratinocyte desmosomes, we tested the effects of a cholinergic antagonist on keratinocyte adhesion and Dsg phosphorylation status in DJM-1 cell line. Atropine (Atr), 0.02 mM, induced rapid detachment of cells from each other (acantholysis), and also increased phosphorylation of Dsg 3 by 33%. The Atr-dependent phosphorylation of Dsg 3 was inhibited in the presence of 0.5 mM CCh. Thus, keratinocyte cholinergic receptors regulate desmosomal adhesion of KC by altering the level of expression of both Dsg 1 and Dsg 3 and the phosphorylation status of Dsg 3.

Desmosomal cadherins

New evidence from blocking desmosomal adhesion with anti-adhesion peptides reveals a role for desmosomes in cell positioning in morphogenesis. Desmosomal adhesion is necessary for the stability of adherens junctions in epithelial cell sheets. Knockout and mis-expression of desmosomal cadherins in mice suggests that they may function directly or indirectly in regulating epidermal differentiation. Protein kinase C signalling and tyrosine phosphorylation appear to regulate desmosomal adhesion. There are new insights into the role of desmosomal cadherins in autoimmune, infectious and genetic disease.