The anti-desmoglein 1 autoantibodies in pemphigus vulgaris sera are pathogenic

Pemphigus foliaceus: a patient's perspective

A patient’s perspective on pemphigus foliaceus.

B cell tolerance and autoimmunity: Lessons from repertoires

Adaptive immune cell function is regulated by a highly diverse receptor recombined from variable germline-encoded segments that can recognize an almost unlimited array of epitopes. While this diversity enables the recognition of any pathogen, it also poses a risk of self-recognition, leading to autoimmunity. Many layers of regulation are present during both the generation and activation of B cells to prevent this phenomenon, although they are evidently imperfect. In recent years, our ability to analyze immune repertoires at scale has drastically increased, both through advances in sequencing and single-cell analyses. Here, we review the current knowledge on B cell repertoire analyses, focusing on their implication for autoimmunity. These studies demonstrate that a failure of tolerance occurs at multiple independent checkpoints in different autoimmune contexts, particularly during B cell maturation, plasmablast differentiation, and within germinal centers. These failures are marked by distinct repertoire features that may be used to identify disease- or patient-specific therapeutic approaches.

shRNA-Targeting Caspase-3 Inhibits Cell Detachment Induced by Pemphigus Vulgaris Autoantibodies in HaCaT Cells

Pemphigus is an autoimmune disease that affects the skin and mucous membranes, induced by the deposition of pemphigus IgG, which mainly targets desmogleins 1 and 3 (Dsg1 and 3). This autoantibody causes steric interference between Dsg1 and 3 and the loss of cell adhesion, producing acantholysis. This molecule and its cellular effects are clinically reflected as intraepidermal blistering. Pemphigus vulgaris-IgG (PV-IgG) binding involves p38MAPK-signaling-dependent caspase-3 activation. The present work assessed the in vitro effect of PV-IgG on the adherence of HaCaT cells dependent on caspase-3. PV-IgG induced cell detachment and apoptotic changes, as demonstrated by annexin fluorescent assays. The effect of caspase-3 induced by PV-IgG was suppressed in cells pre-treated with caspase-3-shRNA, and normal IgG (N-IgG) as a control had no relevant effects on the aforementioned parameters. The results demonstrated that shRNA reduces caspase-3 expression, as measured via qRT-PCR and via Western blot and immunofluorescence, and increases cell adhesion. In conclusion, shRNA prevented in vitro cell detachment and the late effects of apoptosis induced by PV-IgG on HaCaT cells, furthering our understanding of the molecular role of caspase-3 cell adhesion dependence in pemphigus disease.

Distinct impact of IgG subclass on autoantibody pathogenicity in different IgG4-mediated diseases

IgG4 is the least potent human IgG subclass for the FcγR-mediated antibody effector function. Paradoxically, IgG4 is also the dominant IgG subclass of pathogenic autoantibodies in IgG4-mediated diseases. Here, we show that the IgG subclass and Fc-FcγR interaction have a distinct impact on the pathogenic function of autoantibodies in different IgG4-mediated diseases in mouse models. While IgG4 and its weak Fc-FcγR interaction have an ameliorative role in the pathogenicity of anti-ADAMTS13 autoantibodies isolated from thrombotic thrombocytopenic purpura (TTP) patients, they have an unexpected exacerbating effect on anti-Dsg1 autoantibody pathogenicity in pemphigus foliaceus (PF) models. Strikingly, a non-pathogenic anti-Dsg1 antibody variant optimized for FcγR-mediated effector function can attenuate the skin lesions induced by pathogenic anti-Dsg1 antibodies by promoting the clearance of dead keratinocytes. These studies suggest that IgG effector function contributes to the clearance of autoantibody-Ag complexes, which is harmful in TTP, but beneficial in PF and may provide new therapeutic opportunity.

The Clinical Utility of Soluble Serum Biomarkers in Autoimmune Pancreatitis: A Systematic Review

Autoimmune pancreatitis (AIP) is a rare etiological type of chronic pancreatitis. The clinical and radiological presentation of AIP often resembles that of pancreatic cancer. Identifying non-invasive markers for their early distinction is of utmost importance to avoid unnecessary surgery or a delay in steroid therapy. Thus, this systematic review was conducted to revisit all current evidence on the clinical utility of different serum biomarkers in diagnosing AIP, distinguishing AIP from pancreatic cancer, and predicting disease course, steroid therapy response, and relapse. A systematic review was performed for articles published up to August 2021 by searching electronic databases such as MEDLINE, Web of Science, and EMBASE. Among 5123 identified records, 92 studies were included in the qualitative synthesis. Apart from immunoglobulin (Ig) G4, which was by far the most studied biomarker, we identified autoantibodies against the following: lactoferrin, carboanhydrase II, plasminogen-binding protein, amylase-α2A, cationic (PRSS1) and anionic (PRSS2) trypsinogens, pancreatic secretory trypsin inhibitor (PSTI/SPINK1), and type IV collagen. The identified novel autoantigens were laminin 511, annexin A11, HSP-10, and prohibitin. Other biomarkers included cytokines, decreased complement levels, circulating immune complexes, N-glycan profile changes, aberrant miRNAs expression, decreased IgA and IgM levels, increased IgE levels and/or peripheral eosinophil count, and changes in apolipoprotein isoforms levels. To our knowledge, this is the first systematic review that addresses biomarkers in AIP. Evolving research has recognized numerous biomarkers that could help elucidate the pathophysiological mechanisms of AIP, bringing us closer to AIP diagnosis and its preoperative distinction from pancreatic cancer.

Mechanisms Causing Acantholysis in Pemphigus-Lessons from Human Skin

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease caused primarily by autoantibodies (PV-IgG) against the desmosomal adhesion proteins desmoglein (Dsg)1 and Dsg3. PV patient lesions are characterized by flaccid blisters and ultrastructurally by defined hallmarks including a reduction in desmosome number and size, formation of split desmosomes, as well as uncoupling of keratin filaments from desmosomes. The pathophysiology underlying the disease is known to involve several intracellular signaling pathways downstream of PV-IgG binding. Here, we summarize our studies in which we used transmission electron microscopy to characterize the roles of signaling pathways in the pathogenic effects of PV-IgG on desmosome ultrastructure in a human ex vivo skin model. Blister scores revealed inhibition of p38MAPK, ERK and PLC/Ca2+ to be protective in human epidermis. In contrast, inhibition of Src and PKC, which were shown to be protective in cell cultures and murine models, was not effective for human skin explants. The ultrastructural analysis revealed that for preventing skin blistering at least desmosome number (as modulated by ERK) or keratin filament insertion (as modulated by PLC/Ca2+) need to be ameliorated. Other pathways such as p38MAPK regulate desmosome number, size, and keratin insertion indicating that they control desmosome assembly and disassembly on different levels. Taken together, studies in human skin delineate target mechanisms for the treatment of pemphigus patients. In addition, ultrastructural analysis supports defining the specific role of a given signaling molecule in desmosome turnover at ultrastructural level.

IgG4-related diseases of the digestive tract

IgG4-related conditions affecting the digestive tract are part of a multi-organ fibro-inflammatory disorder termed IgG4-related disease (IgG4-RD), with autoimmune pancreatitis and IgG4-related cholangitis being the most prominent manifestations. Gastrointestinal symptoms include jaundice, weight loss, abdominal pain, biliary strictures, and pancreatic and hepatic masses that mimic malignant diseases. IgG4-RD manifestations occur less frequently elsewhere in the digestive tract, namely in the oesophagus, retroperitoneum or intestine. Evidence-based European guidelines frame the current state-of-the-art in the diagnosis and management of IgG4-related digestive tract disease. Diagnosis is based on histology (if available), imaging, serology, other organ involvement and response to therapy (HISORt criteria). Few biomarkers beyond serum IgG4 concentrations are reliable. The first-line therapy (glucocorticoids) is swiftly effective but disease flares are common at low doses or after tapering. Second-line therapy might consist of other immunosuppressive drugs such as thiopurines or rituximab. Further trials, for example, of anti-CD19 drugs, are ongoing. Although an association between IgG4-RD and the development of malignancies has been postulated, the true nature of this relationship remains uncertain at this time.

Acrochordons and autoimmunity: Significance of preconceptional counseling

BACKGROUND

Acrochordons are benign hypertrophic lesions of the skin of which the pathophysiology is unclear.

OBJECTIVE

This study aimed to examine the association of acrochordons with autoimmune disorders in patients with a poor obstetric history.

METHODS

This retrospective cohort involved 350 female patients with poor obstetric history who were included in a preconceptional care program to investigate risk factors for obstetric complications. These patients were further investigated for the co-existence of autoimmune disorders (defined by either a diagnosis of autoimmune diseases or autoimmune antibody positivity) and acrochordons.

RESULTS

An autoimmune disorder was present in 55.7% (195/350) of the patients. The rate of acrochordons was significantly higher in patients with autoimmune disorders (n= 195) compared to the control group (n= 155) (8.21% versus 2.58%, respectively) (p= 0.043). When the autoimmune disease positive (n= 58) and autoimmune antibody-positive (n= 137) groups were separately analyzed, acrochordons were found more frequently in the autoimmune disease group (p= 0.004). However, there was no statistically significant co-occurrence of autoimmune antibody positivity and the presence of skin tags (p= 0.135).

CONCLUSION

There may be immune system-related biological mechanisms underlying the pathogenesis of acrochordons. Preconceptional counseling is beneficial for women with poor obstetric history and acrochordons.

Skin Barrier and Autoimmunity-Mechanisms and Novel Therapeutic Approaches for Autoimmune Blistering Diseases of the Skin

One of the most important functions of the skin besides regulating internal body temperature includes formation of the barrier between the organism and the external environment, hence protecting against pathogen invasion, chemical and physical assaults and unregulated loss of water and solutes. Disruption of the protective barrier is observed clinically in blisters and erosions of the skin that form in autoimmune blistering diseases where the body produces autoantibodies against structural proteins of the epidermis or the epidermal-dermal junction. Although there is no cure for autoimmune skin blistering diseases, immune suppressive therapies currently available offer opportunities for disease management. In cases where no treatment is sought, these disorders can lead to life threatening complications and current research efforts have focused on developing therapies that target autoantibodies which contribute to disease symptoms. This review will outline the involvement of the skin barrier in main skin-specific autoimmune blistering diseases by describing the mechanisms underpinning skin autoimmunity and review current progress in development of novel therapeutic approaches targeting the underlying causes of autoimmune skin blistering diseases.

Humoral Epitope Spreading in Autoimmune Bullous Diseases

Autoimmune blistering diseases are characterized by autoantibodies against structural adhesion proteins of the skin and mucous membranes. Extensive characterization of their autoantibody targets has improved understanding of pathogenesis and laid the basis for the study of antigens/epitopes diversification, a process termed epitope spreading (ES). In this review, we have reported and discussed ES phenomena in autoimmune bullous diseases and underlined their functional role in disease pathogenesis. A functional ES has been proposed: (1) in bullous pemphigoid patients and correlates with the initial phase of the disease, (2) in pemphigus vulgaris patients with mucosal involvement during the clinical transition to a mucocutaneous form, (3) in endemic pemphigus foliaceus, underlining its role in disease pathogenesis, and (4) in numerous cases of disease transition associated with an intermolecular diversification of immune response. All these findings could give useful information to better understand autoimmune disease pathogenesis and to design antigen/epitope specific therapeutic approaches.

Sparking Fire Under the Skin? Answers From the Association of Complement Genes With Pemphigus Foliaceus

Skin blisters of pemphigus foliaceus (PF) present concomitant deposition of autoantibodies and components of the complement system (CS), whose gene polymorphisms are associated with susceptibility to different autoimmune diseases. To investigate these in PF, we evaluated 992 single-nucleotide polymorphisms (SNPs) of 44 CS genes, genotyped through microarray hybridization in 229 PF patients and 194 controls. After excluding SNPs with minor allele frequency <1%, out of Hardy-Weinberg equilibrium in controls or in strong linkage disequilibrium (r2 ≥ 0.8), 201 SNPs remained for logistic regression. Polymorphisms of 11 genes were associated with PF. MASP1 encodes a crucial serine protease of the lectin pathway (rs13094773: OR = 0.5, p = 0.0316; rs850309: OR = 0.23, p = 0.03; rs3864098: OR = 1.53, p = 0.0383; rs698104: OR = 1.52, p = 0.0424; rs72549154: OR = 0.55, p = 0.0453). C9 (rs187875: OR = 1.46, p = 0.0189; rs700218: OR = 0.12, p = 0.0471) and C8A (rs11206934: OR = 4.02, p = 0.0323) encode proteins of the membrane attack complex (MAC) and C5AR1 (rs10404456: OR = 1.43, p = 0.0155), a potent anaphylatoxin-receptor. Two encode complement regulators: MAC-blocking CD59 (rs1047581: OR = 0.62, p = 0.0152) and alternative pathway-blocking CFH (rs34388368: OR = 2.57, p = 0.0195). One encodes opsonin: C3 (rs4807895: OR = 2.52, p = 0.0239), whereas four encode receptors for C3 fragments: CR1 (haplotype with rs6656401: OR = 1.37, p = 0.0382), CR2 (rs2182911: OR = 0.23, p = 0.0263), ITGAM (CR3, rs12928810: OR = 0.66, p = 0.0435), and ITGAX (CR4, rs11574637: OR = 0.63, p = 0.0056). Associations reinforced former findings, regarding differential gene expression, serum levels, C3, and MAC deposition on lesions. Deregulation of previously barely noticed processes, e.g., the lectin and alternative pathways and opsonization-mediated phagocytosis, also modulate PF susceptibility. The results open new crucial avenues for understanding disease etiology and may improve PF treatment through additional therapeutic targets.

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

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

Accuracy of molecular diagnostics in pemphigus and bullous pemphigoid: comparison of commercial and modified mosaic indirect immunofluorescence tests as well as enzyme-linked immunosorbent assays

Introduction

Pemphigus and bullous pemphigoid (BP) are identified by autoantibodies (abs) against desmoglein 1, 3 (DSG1/3) and BP180/BP230, respectively. A novel mosaic to indirect immunofluorescence (IIF) using purified BP180 recombinant proteins spotted on slide and transfected cells expressing BP230, DSG1, DSG3 is available. The commercial (IgG detection) and modified (IgG4 detection) mosaic for indirect immunofluorescence (IIFc – IIF commercial, IIFm – IIF modified) and IgG ELISAs were evaluated in pemphigus and bullous pemphigoid (BP) molecular diagnostics.

Aim

To compare diagnostic accuracy of commercial (IgG detection) and modified (IgG4 detection) mosaic IIF assay and to examine the diagnostic value of ELISAs in relation to mosaic IIF in routine laboratory diagnostics of pemphigus and BP.

Material and methods

Sera from 37 BP and 19 pemphigus patients were studied. Associations between tests were assessed using Fisher’s exact test.

Results

There are associations between the positive/negative samples detected by IIFc with desmoglein1 (DSG1)/desmoglein3 (DSG3)/BP230 transfected cells and ELISAs and no association between anti-BP180 IgG detection by IIFc and ELISA. IIFm with DSG1 and DSG3 showed both 100% sensitivity and 100% and 78% specificity, respectively, and 100% and 83% positive predictive value in relation to IIFc. IIFm with BP230 had 87% specificity, 55% sensitivity, whereas IIFm with BP180 had a 100% sensitivity and 13% specificity in relation to IIFc.

Conclusions

The IIFc with DSG1/DSG3/BP230 transfected cells, excluding BP180 spots, is an alternative method to ELISA in pemphigus/BP diagnostics. IgG4 antibodies, both pathogenically and diagnostically important, are inconsistently detectable with IIFm.

Rituximab therapy in pemphigus and other autoantibody-mediated diseases

Rituximab, a monoclonal antibody targeting the B cell marker CD20, was initially approved in 1997 by the United States Food and Drug Administration (FDA) for the treatment of non-Hodgkin lymphoma. Since that time, rituximab has been FDA-approved for rheumatoid arthritis and vasculitides, such as granulomatosis with polyangiitis and microscopic polyangiitis. Additionally, rituximab has been used off-label in the treatment of numerous other autoimmune diseases, with notable success in pemphigus, an autoantibody-mediated skin blistering disease. The efficacy of rituximab therapy in pemphigus has spurred interest in its potential to treat other autoantibody-mediated diseases. This review summarizes the efficacy of rituximab in pemphigus and examines its off-label use in other select autoantibody-mediated diseases.

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.

Mucosal pemphigus vulgaris anti-Dsg3 IgG is pathogenic to the oral mucosa of humanized Dsg3 mice

There are two major clinical subsets of pemphigus vulgaris (PV), mucosal PV (mPV) and mucocutaneous PV (mcPV). The mPV subset exhibits anti-human desmoglein (Dsg) 3 autoantibodies that fail to recognize murine Dsg3; thus, passive transfer experiments of mPV IgG into WT mice have been unsuccessful at inducing disease. We therefore generated a fully humanized Dsg3 (hDSG3) murine model utilizing a human Dsg3 transgenic animal crossed to the murine Dsg3 knockout line. Expression of hDsg3 in the mucosa rescues the murine Dsg3 knockout phenotype. Well characterized mPV sera bind mucosal epithelia from the hDsg3 mice, but not mucosal tissues from WT mice by as detected by indirect immunofluorescence. The majority of mPV sera preferentially recognize hDsg3 compared to mDsg3 by immunoprecipitation as well. Passive transfer of mPV IgG into adult hDsg3 mice, but not WT mice, induces suprabasilar acantholysis in mucosal tissues, thus confirming pathogenicity of mPV anti-hDsg3 IgG in vivo. Human anti-hDsg3 antibodies are detected in perilesional mucosa as well as in sera of recipient mice by immunofluorescence. These findings suggest that the Dsg3 epitopes targeted by pathogenic mPV IgG are human specific. This hDsg3 mouse model will be invaluable in studying the clinical transition from mPV to mcPV.

Desmosomal adhesion in vivo

Desmosomes are intercellular junctions that provide strong adhesion or hyper-adhesion in tissues. Here, we discuss the molecular and structural basis of this with particular reference to the desmosomal cadherins (DCs), their isoforms and evolution. We also assess the role of DCs as regulators of epithelial differentiation. New data on the role of desmosomes in development and human disease, especially wound healing and pemphigus, are briefly discussed, and the importance of regulation of the adhesiveness of desmosomes in tissue dynamics is considered.

Hyper-adhesion: a unique property of desmosomes

Hyper-adhesion is a unique, strongly adhesive form of desmosomal adhesion that functions to maintain tissue integrity. In this short review, we define hyper-adhesion, summarise the evidence for it in culture and in vivo, discuss its role in development, wound healing, and skin disease, and speculate about its molecular and cellular basis.

Enrichment of total serum IgG4 in patients with pemphigus

BACKGROUND

Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are potentially fatal blistering diseases caused by autoantibodies targeting desmoglein (Dsg) adhesion proteins. Previous studies have shown an IgG4 > IgG1 predominance of anti-Dsg antibodies in pemphigus; however, no studies have examined total serum IgG4 levels in pemphigus. IgG4 is induced by chronic antigen stimulation, which could occur with persistent skin blistering and potentially elevate the total serum IgG4 relative to other IgG subclasses in patients with pemphigus.

OBJECTIVES

The primary aim of the study was to quantitate total and Dsg-specific IgG subclasses in patients with pemphigus.

METHODS

IgG subclasses and Dsg-specific IgG1 and IgG4 were quantitated in patients with PV and PF, and in sera from age-matched controls using a subclass enzyme-linked immunosorbent assay. The effectiveness of IgG4 depletion in blocking IgG pathogenicity in PV was determined using a keratinocyte dissociation assay.

RESULTS

Dsg-specific antibodies comprised a median of 7·1% and 4·2% of total IgG4 in patients with PV and PF, respectively, with eightfold and fourfold enrichment in IgG4 vs. IgG1. Total serum IgG4, but not other IgG subclasses, was enriched in patients with PV and PF compared with age-matched controls (P = 0·004 and P = 0·005, respectively). IgG4 depletion of PV sera reduced pathogenicity in a keratinocyte dissociation assay and showed that affinity-purified IgG4 is more pathogenic than other serum IgG fractions.

CONCLUSIONS

Dsg-specific autoantibodies are significantly enriched in IgG4, which may explain the enrichment of total serum IgG4 in some patients with pemphigus. By preferentially targeting autoimmune rather than beneficial immune antibodies, IgG4-targeted therapies may offer safer treatment options for pemphigus.

IgG autoantibody response against keratinocyte cadherins in endemic pemphigus foliaceus (fogo selvagem)

It is well established that autoantibodies against desmoglein 3 and desmoglein 1 (Dsg1) are relevant in the pathogenesis of pemphigus vulgaris and pemphigus foliaceus, including its endemic form fogo selvagem (FS). Isolated reports have shown that in certain patients with these diseases, autoantibodies against other desmosomal cadherins and E-cadherin may also be present. The goal of this investigation was to determine whether FS patients and normal individuals living in endemic areas possess autoantibodies against other desmosomal cadherins and E-cadherin. By testing a large number of FS and endemic control sera by ELISA, we found a consistent and specific autoantibody response against Dsg1 and other keratinocyte cadherins in these individuals, which is quite different from healthy individuals from the United States (US controls). Overall, the highest correlations among the autoantibody responses tested were in the endemic controls, followed by FS patients, and lowest in the US controls. These findings suggest that multiple, perhaps cross-reactive, keratinocyte cadherins are recognized by FS patients and endemic controls.

Cutting Edge: Brazilian pemphigus foliaceus anti-desmoglein 1 autoantibodies cross-react with sand fly salivary LJM11 antigen

The environmental factors that contribute to the development of autoimmune diseases are largely unknown. Endemic pemphigus foliaceus in humans, known as Fogo Selvagem (FS) in Brazil, is mediated by pathogenic IgG4 autoantibodies against desmoglein 1 (Dsg1). Clusters of FS overlap with those of leishmaniasis, a disease transmitted by sand fly (Lutzomyia longipalpis) bites. In this study, we show that salivary Ags from the sand fly, and specifically the LJM11 salivary protein, are recognized by FS Abs. Anti-Dsg1 monoclonal autoantibodies derived from FS patients also cross-react with LJM11. Mice immunized with LJM11 generate anti-Dsg1 Abs. Thus, insect bites may deliver salivary Ags that initiate a cross-reactive IgG4 Ab response in genetically susceptible individuals and lead to subsequent FS. Our findings establish a clear relationship between an environmental, noninfectious Ag and the development of potentially pathogenic autoantibodies in an autoimmune disease.

Pemphigus pathogenesis: problems and prospects

Provides the survey of most prospective trends of research of the pathogenesis of the true acantholytic pemphigus. Cites key results of studies of factors of genetic predisposition to the development of this bullous dermatosis. Highlights problems of studies of the role of antiself antibodies and self-antigens in pemphigus pathogenesis. Represents the apoptolyse theory, explaining mechanisms of the loss of link between keratinocytes. Discusses issues of the cellular regulation of autoimmune reactions at acantholytic pemphigus.

Desmoglein as a target in skin disease and beyond

Much of the original research on desmosomes and their biochemical components was through analysis of skin and mucous membranes. The identification of desmogleins 1 and 3, desmosomal adhesion glycoproteins, as targets in pemphigus, a fatal autoimmune blistering disease of the skin and mucous membranes, provided the first link between desmosomes, desmogleins, and human diseases. The clinical and histological similarities of staphylococcal scalded skin syndrome or bullous impetigo and pemphigus foliaceus led us to identify desmoglein 1 as the proteolytic target of staphylococcal exfoliative toxins. Genetic analysis of striate palmoplantar keratoderma and hypotrichosis identified their responsible genes as desmogleins 1 and 4, respectively. More recently, these fundamental findings in cutaneous biology were extended beyond the skin. Desmoglein 2, which is expressed earliest among the four isoforms of desmoglein in development and found in all desmosome-bearing epithelial cells, was found to be mutated in arrythmogenic right ventricular cardiomyopathy and has also been identified as a receptor for a subset of adenoviruses that cause respiratory and urinary tract infections. The story of desmoglein research illuminates how dermatological research, originally focused on one skin disease, pemphigus, has contributed to understanding the biology and pathophysiology of many seemingly unrelated tissues and diseases.

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.

A single conformational transglutaminase 2 epitope contributed by three domains is critical for celiac antibody binding and effects

The multifunctional, protein cross-linking transglutaminase 2 (TG2) is the main autoantigen in celiac disease, an autoimmune disorder with defined etiology. Glutamine-rich gliadin peptides from ingested cereals, after their deamidation by TG2, induce T-lymphocyte activation accompanied by autoantibody production against TG2 in 1-2% of the population. The pathogenic role and exact binding properties of these antibodies to TG2 are still unclear. Here we show that antibodies from different celiac patients target the same conformational TG2 epitope formed by spatially close amino acids of adjacent domains. Glu153 and 154 on the first alpha-helix of the core domain and Arg19 on first alpha-helix of the N-terminal domain determine the celiac epitope that is accessible both in the closed and open conformation of TG2 and dependent on the relative position of these helices. Met659 on the C-terminal domain also can cooperate in antibody binding. This composite epitope is disease-specific, recognized by antibodies derived from celiac tissues and associated with biological effects when passively transferred from celiac mothers into their newborns. These findings suggest that celiac antibodies are produced in a surface-specific way for which certain homology of the central glutamic acid residues of the TG2 epitope with deamidated gliadin peptides could be a structural basis. Monoclonal mouse antibodies with partially overlapping epitope specificity released celiac antibodies from patient tissues and antagonized their harmful effects in cell culture experiments. Such antibodies or similar specific competitors will be useful in further functional studies and in exploring whether interference with celiac antibody actions leads to therapeutic benefits.

Diagnosis and clinical features of pemphigus vulgaris

Autoimmune bullous diseases are associated with autoimmunity against structural components that maintain cell-cell and cell-matrix adhesion in the skin and mucous membranes. They include those where the skin blisters at the basement membrane zone and those where the skin blisters within the epidermis (pemphigus vulgaris, pemphigus foliaceus, and other subtypes of pemphigus). The variants of pemphigus are determined according to the level of intraepidermal split formation. There are 5 main variants of pemphigus: pemphigus vulgaris, pemphigus foliaceus, pemphigus erythematosus, drug-induced pemphigus, and paraneoplastic pemphigus. This review focuses only on pemphigus vulgaris.

Controversial role of antibodies against linear epitopes of desmoglein 3 in pemphigus vulgaris, as revealed by semiquantitative living cell immunofluorescence microscopy and in-cell ELISA

A novel explanation of pemphigus vulgaris (PV) pathogenesis suggests that serum autoantibodies may affect desmoglein 3 (Dsg3)-mediated adhesion by triggering depletion of Dsg3 from desmosomes. Furthermore, abrogation of Dsg3 from the cell seems to depend on anti-Dsg3 pemphigus IgG. In this study we sought to gain more insights into the role of PV IgG recognizing non-conformational epitopes of Dsg3 (anti-Dsg3-L IgG) by semi-quantitative living cell immunofluorescence (LCIF) microscopy, in-cell ELISA and morphometric analysis of acantholysis. Our data demonstrate that PV serum and PV IgG can induce acantholysis and reduce the total amount of Dsg3 in cultured keratinocytes, whereas anti-Dsg3-L IgG fail to do so when administered at concentrations comparable to those present in pathogenic PV sera. However, the Dsg3-depleting activity of such polyclonal anti-Dsg3 IgG was acquired when used at 1 microg/ml. Interestingly, both PV sera and IgG, including anti-Dsg3-L IgG, caused early depletion of surface Dsg3 while slightly affecting the total cell content of Dsg3 until late acantholysis. This raises a possibility that depletion of Dsg3 from cell membrane and reduction of the total cellular levels of Dsg3 represent distinct phenomena in PV acantholysis. Taken together, our data demonstrate that anti-Dsg3 PV IgG against linear epitopes of Dsg3 can induce acantholytic changes of keratinocytes in a dose- and time-dependent manner. Specifically, both morphological and biochemical changes suggestive of acantholysis are seen only at high IgG concentrations. We conclude that anti-Dsg3L IgG play a minor role in experimental PV under physiologic conditions.

B cell immunotherapy in autoimmunity--2010 update

B cells play important roles in normal immunity and human disease. While much has been learned from elegant studies utilizing genetically modified mice or with immunotherapy in normal and in autoimmune mice, we are merely at the start of learning about the mechanism(s) by which B cells contribute to human autoimmune disease. Here, I will review the most recent insights obtained with immunomodulatory therapies in human disease highlighting the clinical and immunological lessons we have learned with B cell depleting (e.g., rituximab) and immunomodulatory (e.g., BAFF/BLys neutralization through belimumab) therapies.

Autoimmunity to desmocollin 3 in pemphigus vulgaris

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

The Thomsen-Friedenreich antigen-binding lectin jacalin interacts with desmoglein-1 and abrogates the pathogenicity of pemphigus foliaceus autoantibodies in vivo

Pemphigus foliaceus (PF) is an autoimmune skin blistering disease mediated by pathogenic autoantibodies against the desmosomal core glycoprotein desmoglein-1 (Dsg1). This study demonstrated that the O-glycan-specific plant lectin jacalin binds Dsg1 and inhibits the interaction of Dsg1/PF IgG. N-glycosylation is not involved in the interaction of Dsg1/jacalin or Dsg1/PF IgG. Subcutaneous injection of jacalin into neonatal mice drastically reduced PF IgG deposition at the epidermal cell surface and blocked PF IgG-induced skin blisters, both clinically and histologically. Interestingly, another plant lectin, peanut agglutinin, which shares the same carbohydrate specificity toward the O-linked carbohydrate structure known as Thomsen-Friedenreich antigen (TF antigen, Galβ1-3GalNAcα-O-Ser/Thr), also bound Dsg1 and blocked the skin blistering. In contrast, the plant lectin vicia villosa-B4 (VVL-B4), which shares the carbohydrate specificity toward the O-linked monosaccharide known as Thomsen-nouveau antigen (GalNAc-α1-O-Ser/Thr), did not bind Dsg1 and did not show a protective effect against the disease induced by the autoantibodies. Collectively, these results suggest that the binding of jacalin to O-linked TF carbohydrate motifs on Dsg1 impairs the Dsg1/PF autoantibody interactions and abrogates its pathogenicity in vivo. TF-specific binding ligands may have a potential therapeutic value for PF.

Desmosomes in vivo

The structure, function, and regulation of desmosomal adhesion in vivo are discussed. Most desmosomes in tissues exhibit calcium-independent adhesion, which is strongly adhesive or “hyperadhesive”. This is fundamental to tissue strength. Almost all studies in culture are done on weakly adhesive, calcium-dependent desmosomes, although hyperadhesion can be readily obtained in confluent cell culture. Calcium dependence is a default condition in vivo, found in wounds and embryonic development. Hyperadhesion appears to be associated with an ordered arrangement of the extracellular domains of the desmosomal cadherins, which gives rise to the intercellular midline identified in ultrastructural studies. This in turn probably depends on molecular order in the desmosomal plaque. Protein kinase C downregulates hyperadhesion and there is preliminary evidence that it may also be regulated by tyrosine kinases. Downregulation of desmosomes in vivo may occur by internalisation of whole desmosomes rather than disassembly. Hyperadhesion has implications for diseases such as pemphigus.

Immunogenetics of pemphigus: An update

Pemphigus are rare but informative models of organ-specific autoimmune diseases, resulting from the interplay of environmental, genetic and stochastic factors. There are many arguments to consider that pemphigus have a genetic basis involving, as many other autoimmune diseases, several different genes with additive or synergistic effects. So far, the unique strategy used to identify the contributive loci has been direct analysis of candidate genes through conventional case-control association studies. The major histocompatibility complex in particular the class II locus was demonstrated to be associated with pemphigus with a high rate of replicability. The progresses in the understanding of pemphigus physiopathology and the development of new molecular tools offer new perspectives to unveiled the genetic basis of this group of autoimmune blistering diseases, as shown by recent studies of candidate genes expressed at different levels of the autoimmune process.

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

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

E-cadherin is an additional immunological target for pemphigus autoantibodies

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

Isolation of pathogenic monoclonal anti-desmoglein 1 human antibodies by phage display of pemphigus foliaceus autoantibodies

Pemphigus foliaceus (PF) is a blistering disease caused by autoantibodies to desmoglein 1 (Dsg1) that cause loss of epidermal cell adhesion. To better understand PF pathophysiology, we used phage display to isolate anti-Dsg1 mAbs as single-chain variable fragments (scFvs) from a PF patient. Initial panning of the library isolated only non-pathogenic scFvs. We then used these scFvs to block non-pathogenic epitopes and were able to isolate two unique scFvs, each of which caused typical PF blisters in mice or human epidermis models, showing that a single mAb can disrupt Dsg1 function to cause disease. Both pathogenic scFvs bound conformational epitopes in the N terminus of Dsg1. Other PF sera showed a major antibody response against the same or nearby epitopes defined by these pathogenic scFvs. Finally, we showed restriction of the heavy-chain gene usage of all anti-Dsg1 clones to only five genes, which determined their immunological properties despite promiscuous light-chain gene usage. These mAbs will be useful for studying Dsg1 function and mechanisms of blister formation in PF and for developing targeted therapies and tools to monitor disease activity.

Mucocutaneous pemphigus vulgaris carrying high-titre antidesmoglein 1 antibodies with skin lesions resembling pemphigus erythematosus

Patients with pemphigus vulgaris (PV) who have both antidesmoglein (Dsg)1 and anti-Dsg3 antibodies usually develop flaccid blisters on skin and mucous membranes. We report a case of PV with crusting skin lesions resembling pemphigus erythematosus, the localized variant of pemphigus foliaceus (PF). Notably, the patient had high titres of anti-Dsg1 IgG, as assessed by ELISA. We then established an in vitro model of pemphigus, and found that patient's serum was able to induce suprabasilar acantholysis in mouse skin culture. However, epidermal splitting also occurred within the granular layer, suggesting that the pathogenic potential of such a high-titre anti-Dsg1 serum was intermediate between PV and PF. Thus, the levels of anti-Dsg1 antibodies could play a role in determining the clinical phenotype of pemphigus.

The IgM anti-desmoglein 1 response distinguishes Brazilian pemphigus foliaceus (fogo selvagem) from other forms of pemphigus

Fogo selvagem (FS) and pemphigus foliaceus (PF) possess pathogenic IgG anti-desmoglein 1-(Dsg1) autoantibodies. Although PF occurs sporadically, FS is endemic in Limao Verde (LV), Brazil (3.4% prevalence). IgM anti-Dsg1 were detected in 58% FS LV patients (n=31), 19% of FS patients from Hospital-Campo Grande (n=57), 19% from Hospital-Goiania (n=42), 12% from Hospital-Sao Paulo (n=56), 10% of PF patients from United States (n=20), and 0% of PF patients from Japan (n=20). Pemphigus vulgaris (n=40, USA and Japan), bullous pemphigoid (n=40, USA), and healthy donors (n=55, USA) showed negligible percentages of positive sera. High percentages of positive IgM anti-Dsg1 were found in healthy donors from four rural Amerindian populations (42% of 243) as compared with urban donors (14% of 81; P<0.001). More than 50% of healthy donors from LV (n=99, age 5-20 years) possess IgM anti-Dsg1 across ages, whereas IgG-anti-Dsg1 was detected in 2.9% (age 5-10 years), 7.3% (age 11-15 years), and 29% of donors above age 16. IgM anti-Dsg1 epitopes are Ca2+ and carbohydrate-independent. We propose that IgM anti-Dsg1 are common in FS patients in their native environment and uncommon in other pemphigus phenotypes and in FS patients who migrate to urban hospitals. Recurrent environmental antigenic exposure may lead to IgM and IgG responses that trigger FS. JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article please go to http://network.nature.com/group/jidclub.

Dissecting the anti-desmoglein autoreactive B cell repertoire in pemphigus vulgaris patients

Pemphigus vulgaris (PV) encompasses two clinical phenotypes, one producing mucosal blisters and the other mucosal and skin lesions (mcPV). The mucosal blister-producing PV variant is characterized by autoantibodies against desmoglein (Dsg)3, whereas mucosal and skin lesion-producing PV is characterized by autoantibodies to Dsg3 and Dsg1. The present study was aimed at disclosing the diversity and clonality of the anti-Dsg3 response, as well as whether anti-Dsg3 B cells are Ag selected. Human-mouse heterohybridomas were generated by fusion of EBV-transformed or freshly isolated PBLs from six PV patients with mouse myeloma cells. A total of 73 anti-Dsg hybridomas (47 IgM and 26 IgG) were isolated. Over 90% are specific for both Dsg1 and Dsg3 indicating extensive cross-reactivity between these responses. V(H) gene segment use by IgM hybridomas is diverse, but is restricted among IgG hybridomas, where the majority uses one of two V(H) genes. V(L) gene segment use was diverse even among IgG hybridomas suggesting that the V(L) is less critical to defining desmoglein specificity. Additionally, the IgG hybridomas were extensively mutated and the distribution and nature of the mutations suggested that they had been Ag selected. We conclude that the potentially pathogenic IgG anti-Dsg response is restricted in V(H) use, is somatically mutated, and is Ag selected.

Pemphigus vulgaris presenting in a radiation portal

We report a case of mucocutaneous pemphigus vulgaris in a patient with squamous cell carcinoma of the lung. The cutaneous involvement was limited to the skin within his therapeutic radiation portal. The diagnosis of pemphigus vulgaris was confirmed by histopathology and immunologic studies. Direct immunofluorescence demonstrated IgG and C3 in the intercellular spaces and indirect immunofluorescence was positive on monkey esophagus at a titer of 1:160. Enzyme-linked immunosorbent assay of the patient's serum detected autoantibodies only to desmoglein (Dsg)3, with no reactivity to Dsg1. Immunomapping of perilesional skin from the irradiated field illustrated decreased Dsg1 expression compared with a control sample from an area that was not exposed to radiation. This case provides support for the Dsg compensation hypothesis and may also suggest a mechanism by which irradiation may induce skin lesions.