Autoreactive T cells in the immune pathogenesis of pemphigus vulgaris

Type 2 T-Cell Responses against Distinct Epitopes of the Desmoglein 3 Ectodomain in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoimmune blistering disorder of the skin and/or mucous membranes caused by IgG autoantibodies that predominantly target two transmembrane desmosomal cadherins: desmoglein (DSG)1 and DSG3. DSG-specific T cells play a central role in PV pathogenesis because they provide help to autoreactive B cells for autoantibody production. In this study, we characterized DSG3-specific peripheral T cells in a cohort of 52 patients with PV and 41 healthy controls with regard to cytokine profile and epitope specificity. By ELISpot analysis, type 2 T cells reactive with the DSG3 ectodomain were significantly increased in patients with PV compared with those in healthy controls. By dextramer analysis, CD4+ T cells specific for an epitope within the extracellular domain of DSG3, DSG3(206-220), were found at significantly higher frequencies in patients with PV than in HLA-matched healthy controls. T-cell recognition of two distinct DSG3 epitopes, that is, DSG3(206-220) and DSG3(378-392), correlated significantly, suggesting a synergistic effect in B-cell help. Immunization of HLA-DRB1∗04:02-transgenic mice with PV with the same set of DSG3 peptides induced pathogenic DSG3-specific IgG antibodies, which induced loss of keratinocyte adhesion in vitro. Thus, DSG3 peptide-specific T cells are of particular interest as surrogate markers of disease activity and potential therapeutic targets in PV.

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.

A Snapshot of T Cell Subset Cytokines in Pemphigus Vulgaris: A Cross-Sectional Study

Objective: The purpose of this study was to assess the serum levels of cytokines produced by the Th1 (IFN‐γ, IL-12), Th2 (IL‐4), Th17 (IL-6, IL‐17A, IL‐23), and Treg (IL‐10 and TGF-β) pathways in individuals with active pemphigus vulgaris (PV) and to determine whether these levels were correlated with the severity of the disease condition.

Patients and methods: This study was conducted with 90 individuals, of which 50 were PV patients and 40 healthy individuals (age and gender-matched) as controls. Serum samples were collected and tested for cytokine levels by ELISA (enzyme-linked immunosorbent assay). The cytokine levels in the serum of PV patients and healthy controls were compared statistically using the Mann-Whitney test for nonparametric samples. The strength of the association between the variables was evaluated using the Spearman correlation test.

Results: The mean serum levels of IFN- γ (p < 0.001), IL-6 (p < 0.001), IL-10 (p < 0.001), IL-12 (p < 0.05), and IL-17 (p < 0.001) were significantly higher and TGF-β were significantly low in the PV patients than those observed in the control group. The mean concentration of serum IL-4 in patients with PV did not differ from those in the control group.

Conclusions: In active PV, the Th1 and Th17 pathways are involved in the development and progression of the disease, whereas the Th2 pathway is blocked. Both of these pathways play a significant role in the disease. It is possible that the Treg pathway acts as an antagonist to the Th1 and Th17 pathways, which would cause the disease to become more localised. This study lays the foundation for a better understanding of the aetiology of PV and implies that cytokines could be used as potential therapeutic targets and disease activity biomarkers.

Role of Rituximab in the Treatment of Pemphigus Vulgaris: Patient Selection and Acceptability

Anti-CD20 monoclonal antibody rituximab is an approved adjuvant treatment, in combination with oral corticosteroids, for patients with pemphigus vulgaris, a severe and potentially life-threatening autoimmune blistering skin disorder. Updated approaches to the management of pemphigus vulgaris support rituximab as a first-line adjuvant treatment to induce remission early in the course of disease; however, its feasibility in the clinical setting is often reduced by a series of limitations, including high cost of this biological drug, physician and patient concern for the risk of adverse reactions, and uncertainty regarding the optimum dosing and schedule of administration. The standard approved rituximab dosages, which are derived from lymphoma protocols, have been recognized to exceed the effective dose required for inducing B cell depletion, since the B cell burden in pemphigus vulgaris is much lower than in lymphoproliferative disorders. To overcome these limitations, recent research has investigated alternative regimens of rituximab, using lower doses of the drug. Moreover, differences in patient and disease characteristics that are highlighted in the literature strongly suggest that therapy should be tailored individually on a case-by-case basis: personalized treatment schedules may be necessary to optimize response to treatment and tolerability in different subjects, with the possibility of repeated infusions for severe forms and in case of relapse. Finally, low-dose regimens of rituximab were suggested to be favorable during the COVID-19 pandemic by providing a lesser degree of immune cell depletion while retaining a sufficient response. In conclusion, the current literature suggests that lower-dose regimens of rituximab are not only tolerable and cost-effective but may also be associated with a positive response in pemphigus vulgaris, comparable to that achieved with higher doses especially in early disease. Further evidence from rigorous clinical trials will be required to optimize lower-dose regimens of RTX and establish their position within the treatment scenario of pemphigus vulgaris.

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.

Biologics in autoimmune bullous diseases: Current scenario

Autoimmune bullous diseases can be intraepidermal (pemphigus group of disorders) or subepidermal (pemphigoid group of disorders). The treatment of these disorders chiefly comprises corticosteroids and immunosuppressant adjuvants like azathioprine and mycophenolate mofetil. Autoantibodies are the main mediators of these diseases. Rituximab, a chimeric anti-CD20 monoclonal antibody targeting B-cells, has emerged as an excellent treatment option for refractory pemphigus vulgaris in the last decade. Since then, many new biologics have been proposed/explored for managing autoimmune bullous diseases. These hold potential for greater efficacy and lesser adverse effects than conventional immunosuppressants. In this review, we discuss the role of various biologics in the treatment of autoimmune bullous diseases, followed by a brief discussion on the drawbacks to their use and new developments in this area.

Decreased Serum Levels of Interleukin-4 and Interleukin-21 in New Pemphigus Vulgaris Patients, but Not Chronic Patients With Inactive Disease Compared to Healthy Controls

Background

Pemphigus is a rare group of autoimmune blistering diseases with unknown etiology and unclear pathogenesis. Pemphigus vulgaris (PV) is the most common subtype, and is characterized by ulcerations or flaccid blisters on mucous membranes and on the skin. It is accepted that cytokines have a critical role in the pathogenesis of PV, while their exact roles remain to be elucidated.

Objectives

This study assessed serum levels of interleukin (IL)-4 and IL-21 in different phases of the disease in comparison with healthy controls.

Methods

In a case-control cohort design, serum levels of IL-4 and IL-21 were determined by ELISA in three groups: patients with newly diagnosed PV, patients with chronic, inactive PV (PV in remission), and healthy controls.

Results

The study included 88 individuals (58 women and 30 men), including 26 with newly diagnosed PV, 33 with PV in remission, and 29 healthy controls. A significant difference was found among the groups for IL-21 (P = .044), but not for IL-4 (P = .374). Serum levels of IL-4 and IL-21 in newly diagnosed patients were significantly lower than in healthy controls (P = .005 for both), but these cytokine levels in patients with PV in remission were not different from those of controls (P = .343 and P = .221, respectively). Also, no differences in cytokine levels were detected between the newly diagnosed patients and patients with PV in remission. Regardless of disease phase, we detected significantly lower levels of IL-21 in patients than controls (P = .027), but no differences for IL-4 (P = .374).

Conclusions

IL-4 and IL-21 are involved in PV pathogenesis and disease severity. More studies are required to clarify the role of IL-4 and IL-21 in immunopathogenesis and immune response during PV.

Application of photodynamic therapy in immune-related diseases

Photodynamic therapy (PDT) is a therapeutic modality that utilizes photodamage caused by photosensitizers and oxygen after exposure to a specific wavelength of light. Owing to its low toxicity, high selectivity, and minimally invasive properties, PDT has been widely applied to treat various malignant tumors, premalignant lesions, and infectious diseases. Moreover, there is growing evidence of its immunomodulatory effects and potential for the treatment of immune-related diseases. This review mainly focuses on the effect of PDT on immunity and its application in immune-related diseases.

Patients with pemphigus are at an increased risk of developing rheumatoid arthritis: a large-scale cohort study

Data regarding the association between pemphigus and rheumatoid arthritis (RA) is inconclusive and yet to be firmly established. In the current study, we aimed to evaluate the risk of developing RA during the course of pemphigus. A large-scale population-based longitudinal cohort study was conducted to evaluate the hazard ratio (HR) of RA among 1985 patients with pemphigus relative to 9874 age-, sex-, and ethnicity-matched control subjects. A multivariate Cox regression model was utilized. The incidence of RA was 1.07 (95% CI, 0.62-1.72) and 0.36 (95% CI, 0.24-0.52) per 1000 person-years among patients with pemphigus and controls, respectively. The lifetime prevalence of RA was 2.3% (95% CI, 1.7-3.1%) among cases and 1.8% (95% CI, 1.5-2.0%) among controls. Patients with pemphigus were more than twice as likely to develop RA as compared to control subjects (adjusted HR, 2.54; 95% confidence interval [CI], 1.31-4.92). The increased risk was robust to a sensitivity analysis that included only cases managed by pemphigus-related systemic medications (adjusted HR, 2.56; 95% CI, 1.30-5.05). In conclusion, pemphigus is associated with an increased risk of RA. Physicians treating patients with pemphigus should be aware of this possible association. Further research is required to better understand the mechanism underlying this association.

Immune-Mediated Dermatoses in Patients with Haematological Malignancies: A Comprehensive Review

Haematological malignancies induce important alterations of the immune system, which account for the high frequency of autoimmune complications observed in patients. Cutaneous immune-mediated diseases associated with haematological malignancies encompass a heterogeneous group of dermatoses, including, among others, neutrophilic and eosinophilic dermatoses, autoantibody-mediated skin diseases, vasculitis and granulomatous dermatoses. Some of these diseases, such as paraneoplastic pemphigus, are associated with an increased risk of death; others, such as eosinophilic dermatoses of haematological malignancies, run a benign clinical course but portend a significant negative impairment on a patient’s quality of life. In rare cases, the skin eruption reflects immunological alterations associated with an unfavourable prognosis of the associated haematological disorder. Therapeutic management of immune-mediated skin diseases in patients with haematological malignancies is often challenging. Systemic corticosteroids and immunosuppressive drugs are considered frontline therapies but may considerably augment the risk of serious infections. Indeed, developing a specific targeted therapeutic approach is of crucial importance for this particularly fragile patient population. This review provides an up-to-date overview on the immune-mediated skin diseases most frequently encountered by patients with onco-haematological disorders, discussing new pathogenic advances and therapeutic options on the horizon.

Autoreactive T cells in pemphigus: perpetrator and target

Pemphigus vulgaris (PV) is an autoimmune blistering disease, in which autoantibodies against epidermal cadherins, such as desmoglein (Dsg)1 and Dsg3, lead to the development of blisters and erosions on the skin and mucous membranes. Autoreactive CD4+ T cells are essential for the induction and perpetuation of the disease by interaction with B cells producing autoantibodies. PV has a strong genetic association with certain human leucocyte antigen (HLA) alleles with HLA-DRB1*04:02 and LA-DQB1*05:03 being the most prevalent in patients. Recently, genome-wide association studies have provided a new approach to identify single nucleotide polymorphisms, alongside the known association with HLA alleles. Loss of tolerance against Dsgs and other autoantigens is a critical event in the pathogenesis of PV. Epitope spreading contributes to the progression of PV, leading to an extension of the Dsg-specific autoimmune response to other molecular epitopes of autoantigens, such as desmocollins or muscarinic receptors. Alterations in CD4+CD25+ FoxP3+ regulatory T cells are thought to contribute to the development of PV representing a suitable target for therapeutic interventions. Several CD4+ T-cell subsets and cytokines are involved in the pathogenesis of PV, while Th2 cells are the extensively studied population. Recently, other T cell subsets like T follicular helper cells and Th17 have gained attention as new potential players in PV pathogenesis. The involvement of local autoantibody production in the lesional skin of PV patients in tertiary lymphoid organs is currently discussed but not yet clarified. In this study, we reviewed the current knowledge about the development, characteristics and function of autoreactive T cells in pemphigus and present current new T cell-targeted therapeutic approaches.

From bench to bedside: evolving therapeutic targets in autoimmune blistering disease

Autoimmune blistering diseases comprise a group of heterogenous conditions characterized by the loss of tolerance and subsequent development of autoantibodies targeting epidermal and subepidermal adhesion proteins. Blisters and erosions form on the skin and mucous membranes leading to significant morbidity and mortality. Traditional therapies rely on systemic immunosuppression. Advancements in our understanding of the pathophysiology of pemphigus and pemphigoid have led to the development of molecules which target specific pathways involved in induction and perpetuation of disease. In this review, we outline the novel therapeutic strategies including B-cell depletion, T-regulatory cell repletion, cell signalling inhibitors and small molecular inhibitors, inhibitory monoclonal antibodies, as well as complement inhibition. We additionally review their current level of clinical evidence. We lastly review therapeutics targets gleaned from the experimental epidermolysis bullosa acquisita mouse model. These emerging treatments offer an exciting progression from basic science discoveries that have the potential to transform the treatment paradigm in autoimmune blistering diseases.

Pemphigus vulgaris

Pemphigus vulgaris is a chronic autoimmune bullous dermatosis that results from the production of autoantibodies against desmogleins 1 and 3. It is the most frequent and most severe form of pemphigus, occurring universally, usually between 40 and 60 years of age. It usually begins with blisters and erosions on the oral mucosa, followed by lesions on other mucous membranes and flaccid blisters on the skin, which can be disseminated. There is a clinical variant, pemphigus vegetans, which is characterized by the presence of vegetating lesions in the large folds of the skin. Clinical suspicion can be confirmed by cytological examination, histopathological examination, and direct and indirect immunofluorescence tests. The treatment is performed with systemic corticosteroids, and immunosuppressive drugs may be associated, among them azathioprine and mycophenolate mofetil. More severe cases may benefit from corticosteroids in the form of intravenous pulse therapy, and recent studies have shown a beneficial effect of rituximab, an anti-CD20 immunobiological drug. It is a chronic disease with mortality around 10%, and septicemia is the main cause of death. Patients need long-term and multidisciplinary follow-up.

Targeted Therapies for Autoimmune Bullous Diseases: Current Status

Autoimmune bullous skin disorders are rare but meaningful chronic inflammatory diseases, many of which had a poor or devastating prognosis prior to the advent of immunosuppressive drugs such as systemic corticosteroids, which down-regulate the immune pathogenesis in these disorders. Glucocorticoids and adjuvant immunosuppressive drugs have been of major benefit for the fast control of most of these disorders, but their long-term use is limited by major side effects such as blood cytopenia, osteoporosis, diabetes mellitus, hypertension, and gastrointestinal ulcers. In recent years, major efforts were made to identify key elements in the pathogenesis of autoimmune bullous disorders, leading to the identification of their autoantigens, which are mainly located in desmosomes (pemphigus) and the basement membrane zone (pemphigoids). In the majority of cases, immunoglobulin G, and to a lesser extent, immunoglobulin A autoantibodies directed against distinct cutaneous adhesion molecules are directly responsible for the loss of cell-cell and cell-basement membrane adhesion, which is clinically related to the formation of blisters and/or erosions of the skin and mucous membranes. We describe and discuss novel therapeutic strategies that directly interfere with the production and regulation of pathogenic autoantibodies (rituximab), their catabolism (intravenous immunoglobulins), and their presence in the circulation and extravascular tissues such as the skin (immunoadsorption), leading to a significant amelioration of disease. Moreover, we show that these novel therapies have pleiotropic effects on various proinflammatory cells and cytokines. Recent studies in bullous pemphigoid suggest that targeting of immunoglobulin E autoantibodies (omalizumab) may be also beneficial. In summary, the introduction of targeted therapies in pemphigus and pemphigoid holds major promise because of the high efficacy and fewer side effects compared with conventional global immunosuppressive therapy.

The imbalance of gut microbiota and its correlation with plasma inflammatory cytokines in pemphigus vulgaris patients

Pemphigus vulgaris (PV) is an autoimmune disease characterized by the production of IgG autoantibodies owing to an imbalance in the Th1/Th2 and Th17/Tregs cell pathways. The role of gut microbiota in the development of immune system and autoimmune diseases has been unraveled in the last two decades. However, data pertaining to gut microbiota of PV patients is largely lacking. We aimed to compare the gut microbiota of PV patients and healthy controls and assessed potential correlation with circulating cytokines of Th1/Th2/Th17 cell. Faecal bacterial diversity was analysed in 18 PV patients and 14 age‐ and gender‐matched healthy individuals using hypervariable tag sequencing of the V3‐V4 region of the 16S rRNA gene. Plasma levels of 20 inflammatory cytokines were assessed using the Luminex screening system. As a result, we identified 10 differentially abundant taxa between patients and controls. At the genera level, Lachnospiracea_incertae_sedis and Coprococcus decreased, while Granulicatella, Flavonifractor enriched in PV. Plasma levels of C5a, interleukin (IL)‐2R, IL‐6, IL‐8, IL‐7, IL‐1β, IL17A, IL‐5 and IL‐21 were significantly increased in PV Flavonifractor exhibited a positive correlation with C5a, IL‐6, IL‐8, IL‐7, IL‐1β, IL17A and IL‐21. Lachnospiracea_incertae_sedis and Coprococcus showed a negative correlation with IL‐17A. Our results are consistent with the hypothesis that PV patients have gut microbial dysbiosis which might contribute to the immune disorder and the development of PV.

Pemphigus: Current and Future Therapeutic Strategies

Pemphigus encompasses a heterogeneous group of autoimmune blistering diseases, which affect both mucous membranes and the skin. The disease usually runs a chronic-relapsing course, with a potentially devastating impact on the patients' quality of life. Pemphigus pathogenesis is related to IgG autoantibodies targeting various adhesion molecules in the epidermis, including desmoglein (Dsg) 1 and 3, major components of desmosomes. The pathogenic relevance of such autoantibodies has been largely demonstrated experimentally. IgG autoantibody binding to Dsg results in loss of epidermal keratinocyte adhesion, a phenomenon referred to as acantholysis. This in turn causes intra-epidermal blistering and the clinical appearance of flaccid blisters and erosions at involved sites. Since the advent of glucocorticoids, the overall prognosis of pemphigus has largely improved. However, mortality persists elevated, since long-term use of high dose corticosteroids and adjuvant steroid-sparing immunosuppressants portend a high risk of serious adverse events, especially infections. Recently, rituximab, a chimeric anti CD20 monoclonal antibody which induces B-cell depletion, has been shown to improve patients' survival, as early rituximab use results in higher disease remission rates, long term clinical response and faster prednisone tapering compared to conventional immunosuppressive therapies, leading to its approval as a first line therapy in pemphigus. Other anti B-cell therapies targeting B-cell receptor or downstream molecules are currently tried in clinical studies. More intriguingly, a preliminary study in a preclinical mouse model of pemphigus has shown promise regarding future therapeutic application of Chimeric Autoantibody Receptor T-cells engineered using Dsg domains to selectively target autoreactive B-cells. Conversely, previous studies from our group have demonstrated that B-cell depletion in pemphigus resulted in secondary impairment of T-cell function; this may account for the observed long-term remission following B-cell recovery in rituximab treated patients. Likewise, our data support the critical role of Dsg-specific T-cell clones in orchestrating the inflammatory response and B-cell activation in pemphigus. Monitoring autoreactive T-cells in patients may indeed provide further information on the role of these cells, and would be the starting point for designating therapies aimed at restoring the lost immune tolerance against Dsg. The present review focuses on current advances, unmet challenges and future perspectives of pemphigus management.

Consensus on the treatment of autoimmune bullous dermatoses: pemphigus vulgaris and pemphigus foliaceus - Brazilian Society of Dermatology

Pemphigus are intraepidermal autoimmune bullous dermatoses that occur with lesions on the skin and / or mucous membranes. The most frequent types are pemphigus vulgaris and pemphigus foliaceus (classic and endemic). This consensus aims to present a complete and updated review of the treatment of these two more frequent forms of pemphigus, based on the literature and the personal experience of the authors. In moderate and severe cases of pemphigus vulgaris and foliaceus, systemic corticosteroid therapy (prednisone or prednisolone) is the treatment of choice. Adjuvant drugs, usually immunosuppressive drugs (azathioprine, mycophenolate mofetil, methotrexate, cyclophosphamide) may be prescribed as corticosteroid sparers in refractory cases or with contraindications to corticosteroids to minimize side effects. In severe and nonresponsive cases, corticosteroids in the form of intravenous pulse therapy, immunoglobulin and plasmapheresis / immunoadsorption can be administered. Immunobiological drugs, particularly rituximab, appear as a promising alternative. For milder cases, smaller doses of oral corticosteroid, dapsone and topical corticosteroids are options. At the end flowcharts are presented as suggestions for a therapeutic approach for patients with pemphigus vulgaris and pemphigus foliaceus.

Emerging role of immune cell network in autoimmune skin disorders: An update on pemphigus, vitiligo and psoriasis

Autoimmune skin diseases are a group of disorders that arise due to a deregulated immune system resulting in skin tissue destruction. In the majority of these conditions, either autoreactive immune cells or the autoantibodies are generated against self-antigens of the skin. Although the etiology of these diseases remains elusive, biochemical, genetic, and environmental factors such as infectious agents, toxins damage the skin tissue leading to self-antigen generation, autoantibody attack and finally results in autoimmunity of skin. Immune dysregulation, which involves predominantly T helper 1/17 (Th1/Th17) polarization and the inability of regulatory T cells to regress immune response, is implicated in autoimmune skin diseases. The emerging roles of immune cells, cytokines, and chemokines in the pathogenesis of common autoimmune skin diseases like pemphigus, vitiligo, and psoriasis are discussed in this review. The main focus is on the interplay between immune cell network including the innate and adaptive immune system, regulatory cells, immune checkpoints and recently identified tissue-resident memory cells (TRMs) in disease pathogenesis and relapse. We also attempt to highlight on the immune mechanisms common to these diseases which can be targeted for designing novel therapeutics.

Pemphigus group: overview, epidemiology, mortality, and comorbidities

Pemphigus forms a group of rare autoimmune bullous diseases that affect the skin and mucous membranes. This group has a chronic course leading to high morbidity and mortality. It is characterized by the production of pathogenic autoantibodies directed against different proteins of the desmosome, leading histologically to intraepidermal cleavage, and clinically to vesicles and erosions on the epithelium of the mucous membranes and/or the skin. The diagnosis of the subtype of pemphigus is based on clinical features, the level of histologic cleavage, and the identification of the antigens recognized by circulating autoantibodies by immunoserological analyses. The epidemiological features of pemphigus vary considerably in different regions of the world. Observational studies examining comorbidities and associations among patients with pemphigus are scarce and sometimes inconclusive. The prognosis, mortality, and clinical outcomes in pemphigus have undergone dramatic change throughout the years. This review provides a brief overview about the different subtypes of pemphigus: pemphigus vulgaris, pemphigus foliaceus, paraneoplastic pemphigus, pemphigus herpetiformis, and IgA pemphigus. In addition, it summarizes the most recent understanding of the epidemiology, mortality data, and comorbidities of this group of organ-specific autoimmune diseases.

Autoimmune bullous diseases during pregnancy: insight into pathogenetic mechanisms and clinical features

Pemphigoid gestationis (PG), also known as herpes gestationis, is the prototypic pregnancy-associated autoimmune bullous disease (AIBD), but also the other AIBDs, notably pemphigus vulgaris, may begin or exacerbate during pregnancy. Although the increase in concentration of T and B regulatory cells makes pregnancy a state of increased immunologic tolerance toward the semiallogeneic fetal antigens, a prevalent T helper (Th) 2 profile, that is reported to be associated with pregnancy, may cause exacerbation of pemphigus and AIBDs in general during this period. Active disease may lead to stillbirth, spontaneous abortion, preterm pregnancy, low birthweight, and neonatal pemphigus. PG is a rare AIBD usually starting during the third trimester of pregnancy and healing in the postpartum. It is due to the formation of autoantibodies directed against different epitopes of bullous pemphigoid (BP) 180 as a consequence of the aberrant expression of BP180 in the placental tissue of genetically predisposed women. PG is characterized by vesicles with herpetiform distribution, blisters and urticarial elements typically involving the periumbilical area and the distal portion of the upper limbs. Diagnosis is based on: 1) physical examination; 2) histopathological pattern consisting of a dermal inflammatory infiltrate rich in eosinophils; 3) direct immunofluorescence test demonstrating linear deposits of complement fraction 3 and immunoglobulin G along the basement membrane zone; 4) detection of circulating autoantibodies by means of indirect immunofluorescence or enzyme linked immunosorbent assay. Here, we provide an updated overview on the pathophysiologic mechanisms of pregnancy-associated or pregnancy-exacerbated AIBDs, focusing also on peculiar clinical features of these disorders.

Sporadic pemphigus foliaceus and class II human leucocyte antigen allele associations in the white British and Indo-Asian populations in the UK

BACKGROUND

Pemphigus foliaceus (PF) has both genetic and environmental susceptibility factors. Current data on human leucocyte antigen (HLA) in patients with sporadic PF are limited.

AIM

To better define the distribution of HLA alleles in patients with PF in the UK.

METHODS

We recruited 36 patients [26 of white British (WB) descent, 10 of Indo-Asian (IA) descent] with PF who were living in the UK and 159 ethnically matched normal controls, and analysed their class II HLA DRB1 and DQB1 allele distribution.

RESULTS

There was an increased frequency of DRB1*1404 in association with DQB1*0503 in IA patients with PF. The DRB1*04 allele group as a whole had an increased frequency (P < 0.001) in the WB patient group compared with controls. The alleles contributing to this significance were DRB1*0401 (P = 0.03) and DRB1*0404 (P < 0.01).

CONCLUSION

This is the largest HLA association study in sporadic PF from the UK to date. There appears to be a difference in PF susceptibility alleles between WB and IA patients, highlighting the importance of racial variation in genetic susceptibility to disease development.

Non-Desmoglein Antibodies in Patients With Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a potentially life-threatening mucocutaneous autoimmune blistering disease. Patients develop non-healing erosions and blisters due to cell–cell detachment of keratinocytes (acantholysis), with subsequent suprabasal intraepidermal splitting. Identified almost 30 years ago, desmoglein-3 (Dsg3), a Ca²⁺-dependent cell adhesion molecule belonging to the cadherin family, has been considered the “primary” autoantigen in PV. Proteomic studies have identified numerous autoantibodies in patients with PV that have known roles in the physiology and cell adhesion of keratinocytes. Antibodies to these autoantibodies include desmocollins 1 and 3, several muscarinic and nicotinic acetylcholine receptor subtypes, mitochondrial proteins, human leukocyte antigen molecules, thyroid peroxidase, and hSPCA1—the Ca²⁺/Mn²⁺-ATPase encoded by ATP2C1, which is mutated in Hailey–Hailey disease. Several studies have identified direct pathogenic roles of these proteins, or synergistic roles when combined with Dsg3. We review the role of these direct and indirect mechanisms of non-desmoglein autoantibodies in the pathogenesis of PV.

Regulatory effects of Nr4a2 on Th2 cells from patients with pemphigus vulgaris

Pemphigus vulgaris is an autoimmune blistering disease characterized by a loss of epidermal cell-cell adhesion caused by anti-desmoglein (Dsg) autoantibodies. The pathogenesis of PV remains unclear. However, abnormal frequency and function of Th2 cells are believed to contribute to PV. We investigated Nr4a2, a transcription factor, which has been found to regulate T cell differentiation, for its association with Th2 cell differentiation and functions in PV. We found significantly decreased mRNA and protein levels of Nr4a2 in CD4+ T cells from patients with PV, compared with healthy control subjects. In addition, mRNA and protein levels of Nr4a2 in CD4+ T cells were inversely correlated with serum levels of IL-4 and IL-13 in patients with PV. Overexpression of Nr4a2 in CD4+ T cells from patients with PV significantly reduced the mRNA levels of GATA3, IL-4, and IL-13, while Nr4a2 siRNA treatment showed the reverse effects on the expression of these Th2-related cytokines and transcription factors. The data suggest that the altered level of Nr4a2 in CD4+ T cells is associated with the development of PV. Nr4a2 may contribute to the pathogenesis of PV by negatively regulating Th2 activity and secretion of Th2-related cytokines.

Monopathogenic vs multipathogenic explanations of pemphigus pathophysiology

This viewpoint highlights major, partly controversial concepts about the pathogenesis of pemphigus. The monopathogenic theory explains intra-epidermal blistering through the "desmoglein (Dsg) compensation" hypothesis, according to which an antibody-dependent disabling of Dsg 1- and/or Dsg 3-mediated cell-cell attachments of keratinocytes (KCs) is sufficient to disrupt epidermal integrity and cause blistering. The multipathogenic theory explains intra-epidermal blistering through the "multiple hit" hypothesis stating that a simultaneous and synchronized inactivation of the physiological mechanisms regulating and/or mediating intercellular adhesion of KCs is necessary to disrupt epidermal integrity. The major premise for a multipathogenic theory is that a single type of autoantibody induces only reversible changes, so that affected KCs can recover due to a self-repair. The damage, however, becomes irreversible when the salvage pathway and/or other cell functions are altered by a partnering autoantibody and/or other pathogenic factors. Future studies are needed to (i) corroborate these findings, (ii) characterize in detail patient populations with non-Dsg-specific autoantibodies, and (iii) determine the extent of the contribution of non-Dsg antibodies in disease pathophysiology.

Pemphigus trigger factors: special focus on pemphigus vulgaris and pemphigus foliaceus

Pemphigus is a general term for a rare group of autoimmune diseases which result in the formation of blisters on the skin and oral cavity. Although there is no way to prevent autoimmune diseases, some factors may trigger pemphigus initiation in susceptible individuals or be exacerbated in affected patients. Recognition of these triggers, based on the latest studies and experiences is essential and should be updated every few years. In this study, several triggers, including different drugs and treatments, diseases, vaccines, genetic factors, nutrients, micronutrients, pregnancy, stress, and various other triggers have been discussed. Some possible triggers, such as blood antigens and the effect of seasons have also been discussed briefly. Moreover, some protective factors against pemphigus have been reviewed. Considering the molecular mechanism of pemphigus and immune response alteration during this disease, some possible triggers have been suggested and discussed. Although those triggers may be a real threat, more studies are needed to support these hypotheses.

Application of autologous hematopoietic stem cell transplantation for pemphigus

BACKGROUND

Pemphigus is a rare and fatal autoimmune disease for which the treatment options are limited. This study aimed to evaluate the efficacy of autologous peripheral hematopoietic stem cell transplantation (APHSCT) for pemphigus.

METHODS

We conducted APHSCT for 12 pemphigus patients (seven males and five females, mean age 23.8 years) with life-threatening complications or who responded poorly to conventional therapy. Peripheral blood stem cells were mobilized with cyclophosphamide, granulocyte colony-stimulating factor, and rituximab, and purified autologous CD34⁺ stem cells were infused. Overall survival rate, progression-free survival, and adverse events were recorded.

RESULTS

With a mean follow-up period of 80.3 months, overall survival and complete clinical remission rates were 92% (11/12) and 75% (9/12), respectively. Adverse effects included pyrexia, allergy, infection, and elevation of enzymes. Only one patient died of severe sepsis and multiple organ failure 2 months after APHSCT.

CONCLUSION

Overall APHSCT is a promising therapeutic option for pemphigus.

Pemphigus vulgaris and pemphigus foliaceus determined by CD86 and CTLA4 polymorphisms

Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are rare autoimmune blistering diseases with presumed T-cell-dependent pathology. Activation of naïve T cells is dependent on antigen recognition, subsequent signaling through the T-cell receptor complex (signal 1), and various other interactions of T cells with antigen presenting cells that may be collectively designated as signal 2, which is unconditionally required for T-cell activation both in response to infection and to autoantigens. Among the best described interactions contributing to signal 2 are those mediated by B7 family molecules, such as CD80 and CD86 with their ligands; CD28, providing activation signals; and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), conferring inhibition. Single nucleotide polymorphisms (SNPs) within genes encoding those molecules may alter the signaling process. It is not known whether functional genetic polymorphisms within genes encoding the aforementioned proteins may increase risk for developing PV and PF and, if so, whether they might serve as biomarkers for susceptibility to these diseases. To address those questions, we examined functional single nucleotide polymorphisms within CD86 (rs1129055) and CTLA4 (rs733618 and rs5742909) genes in 61 pemphigus patients and 486 healthy controls. We found statistically significant differences in allele and genotype frequencies between PV patients and controls for rs1129055, as well as for rs5742909 among PV and PF patients. Namely, the rs1129055 A allele was significantly more common in PV patients compared with controls (35.4% versus 25.7%, respectively; P = .040), whereas the rs5742909 T allele was significantly more common in PF compared with PV patients (19.2% versus 5.2%, respectively; P = .035). The frequency of the rs5742909 T allele did not, however, differ significantly in PF or in PV compared with controls (10.5%; P = .187 and P = .100, respectively). We report a novel association of SNPs within CD86 and CTLA4 genes with pemphigus. The CD86 rs1129055 A allele appears to confer susceptibility to PV but not to PF. © 2016 Elsevier Inc. All rights reserved.

[Pemphigus. Model disease for targeted therapy]

BACKGROUND

Pemphigus is a severe bullous autoimmune dermatosis that represents a clinical challenge despite high-dose immunosuppressive therapy due to the therapy-related comorbidities and the lack of long-term control of disease activity.

OBJECTIVES

Which targeted therapies are currently used in pemphigus and which innovative therapeutic strategies are in clinical development?

MATERIALS AND METHODS

A review of the literature in PubMed was performed under consideration of the current guideline for the treatment of pemphigus as well as of our own results. Discussion of basic findings and results of targeted therapies in autoantibody-mediated autoimmune disorders were taken into account.

RESULTS

Immunapheresis and high-dose intravenous immunoglobulins with the aim of reducing circulating autoantibodies have been successfully used in the treatment of pemphigus. Depletion of autoreactive B-lymphocytes provides the rationale for the use of the monoclonal anti-CD20 antibody rituximab which demonstrated long-term clinical remission of pemphigus in clinical trials. Current developments include the investigation of humanised B-cell depleting antibodies in other B-cell driven autoimmune disorders as well as the identification of new cellular and molecular target structures that are essential in the humoral autoimmune cascade and exert important immune regulatory functions, respectively.

CONCLUSIONS

The well-characterised basic pathogenesis of pemphigus results in targeted therapies. Currently, therapies aiming at rapid reduction of circulating autoantibodies and the depletion of autoreactive B-cells are in clinical use. More cellular and molecular target structures are being investigated in other autoantibody-driven autoimmune disorders and they provide promising candidates for innovative pathogenesis-related therapeutic strategies in pemphigus in the future.

Increased Frequency of T Follicular Helper Cells and Elevated Interleukin-27 Plasma Levels in Patients with Pemphigus

Pemphigus is an autoimmune disease in which IgG auto-antibodies (auto-ab) against the desmosomal cadherins desmoglein (Dsg) 3 and Dsg1 cause loss of epidermal keratinocyte adhesion. Aim of this study was to investigate cytokines derived from antigen-presenting cells (APC) and their relation to CD4⁺ T cell subpopulations and to the auto-ab response in pemphigus. In this regard, patients with pemphigus were compared to patients with myasthenia gravis (MG), an unrelated auto-ab–mediated autoimmune disease, and healthy controls. In pemphigus and MG, the plasma concentrations of the APC-derived immunomodulatory cytokine IL-27 were highly increased. Strikingly, IL-27 strongly correlated with Dsg-specific IgG auto-ab titers. T helper (Th) 17 cells were augmented in both pemphigus and MG patients while T follicular helper (Tfh) cells, which are essential in providing B cell help, were increased only in pemphigus along with increasing plasma concentrations of IL-21, a cytokine produced by Th17 and Tfh cells. Moreover, we could detect Dsg3-specific autoreactive T cells producing IL-21 upon ex vivo stimulation with Dsg3. These findings suggest that IL-27 and IL-21-producing T cells, are involved in the pathogenesis of pemphigus. The further characterization of IL-21-producing T cells and of the role of IL-27 will lead to a more defined understanding of the auto-ab response in pemphigus.

Characterization of desmoglein-3 epitope region peptides as synthetic antigens: analysis of their in vitro T cell stimulating efficacy, cytotoxicity, stability, and their conformational features

Desmoglein-3 (Dsg3) adhesion protein is the main target of autoantibodies and autoreactive T cells in Pemphigus vulgaris (PV) autoimmune skin disorder. Several mapping studies of Dsg3 T cell epitope regions were performed, and based on those data, we designed and synthesized four peptide series corresponding to Dsg3 T cell epitope regions. Each peptide series consists of a 17mer full-length peptide (Dsg3/189-205, Dsg3/206-222, Dsg3/342-358, and Dsg3/761-777) and its N-terminally truncated derivatives, resulting in 15 peptides altogether. The peptides were prepared on solid phase and were chemically characterized. In order to establish a structure-activity relationship, the solution conformation of the synthetic peptides has been investigated using electronic circular dichroism spectroscopy. The in vitro T cell stimulating efficacy of the peptides has been determined on peripheral blood mononuclear cells isolated from whole blood of PV patients and also from healthy donors. After 20 h of stimulation, the interferon (IFN)-γ content of the supernatants was measured by enzyme-linked immunosorbent assay. In the in vitro conditions, peptides were stable and non-cytotoxic. The in vitro IFN-γ production profile of healthy donors and PV patients, induced by peptides as synthetic antigens, was markedly different. The most unambiguous differences were observed after stimulation with 17mer peptide Dsg3/342-358, and three truncated derivatives from two other peptide series, namely, peptides Dsg3/192-205, Dsg3/763-777, and Dsg3/764-777. Comparative analysis of in vitro activity and the capability of oligopeptides to form ordered or unordered secondary structure showed that peptides bearing high solvent sensibility and backbone flexibility were the most capable to distinguish between healthy and PV donors.

Pathogenic IgG antibodies against desmoglein 3 in pemphigus vulgaris are regulated by HLA-DRB1*04:02-restricted T cells

Pemphigus vulgaris (PV) is considered as a model for an autoantibody-mediated organ-specific autoimmune disorder. IgG autoantibodies directed against the desmosomal cadherin desmoglein 3 (Dsg3), the major autoantigen in PV, cause loss of epidermal keratinocyte adhesion, resulting in blisters and erosions of the skin and mucous membranes. The association of human autoimmune diseases with distinct HLA alleles is a well-known phenomenon, such as the association with HLA-DRB1*04:02 in PV. However, direct evidence that HLA-DRB1*04:02-restricted autoreactive CD4(+) T cells recognizing immunodominant epitopes of Dsg3 initiate the production of Dsg3-reactive IgG autoantibodies is still missing. In this study, we show in a humanized HLA-DRB1*04:02-transgenic mouse model that HLA-DRB1*04:02-restricted T cell recognition of human Dsg3 epitopes leads to the induction of pathogenic IgG Abs that induce loss of epidermal adhesion, a hallmark in the immune pathogenesis of PV. Activation of Dsg3-reactive CD4(+) T cells by distinct human Dsg3 peptides that bind to HLA-DRβ1*04:02 is tightly regulated by the HLA-DRB1*04:02 allele and leads, via CD40-CD40L-dependent T cell-B cell interaction, to the production of IgG Abs that recognize both N- and COOH-terminal epitopes of the human Dsg3 ectodomain. These findings demonstrate key cellular and humoral immune events in the autoimmune cascade of PV in a humanized HLA-transgenic mouse model. We show that CD4(+) T cells recognizing immunodominant Dsg3 epitopes in the context of the PV-associated HLA-DRB1*04:02 induce the secretion of Dsg3-specific IgG in vivo. Finally, these results identify Dsg3-reactive CD4(+) T cells as potential therapeutic targets in the future.

Serum leptin levels in pemphigus: a case control study

BACKGROUND

Pemphigus is an autoimmune blistering disease mediated by autoantibodies directed against keratinocyte adhesion molecules. Leptin, an adipocyte-derived hormone, plays a role in immune responses and promotes autoimmunity.

OBJECTIVES

This study was conducted to determine whether serum leptin levels are altered in pemphigus patients and whether there is any correlation between leptin levels and the severity of disease.

METHODS

This study included 47 newly diagnosed patients with pemphigus and 43 age- and sex-matched healthy controls. Clinical characteristics and pemphigus area and activity score (PAAS) were assessed. Serum leptin levels (ng/mL) were measured by a commercial enzyme-linked immunosorbent assay (ELISA).

RESULTS

Patients did not differ significantly in serum leptin levels from healthy controls (median (range): 10.8 (0.1-110) ng/mL versus 12 (0.5-69.9) ng/mL and P = 0.53). There was no significant association between serum leptin concentrations and severity of disease measured by PAAS (r s = 0.06, P = 0.70).

CONCLUSION

The results suggest that pemphigus does not have a direct influence on serum leptin levels and the pathogenesis of pemphigus seems to be not dependent on the connection with adipose tissue.