Type XVII Collagen-Specific CD4+ T Cells Induce Bullous Pemphigoid by Producing IL-5

Bullous pemphigoid is an autoimmune subepidermal blistering disease caused by anti-type XVII collagen (COL17) antibodies. Bullous pemphigoid has some immunological features such as eosinophilic infiltration and the deposition of IgE autoantibodies in the skin; however, the mechanism behind such features remains largely unclear. We focused on the autoantigen-specific CD4+ T cells, which are considered to regulate immune response. We established COL17-specific CD4+ T cell lines in vitro. Wild-type mice were immunized with synthesized peptides that include a pathogenic epitope of COL17, and lymphocytes were subjected to a limiting dilution assay. We established 5 T cell lines and examined the pathogenicity by transferring them with COL17-primed B cells into Rag-2-/-/COL17-humanized mice that express human COL17 but not mouse COL17 in the skin. Notably, 3 lines induced bullous pemphigoid-like skin changes associated with subepidermal separation and eosinophilic infiltration histologically and the production of anti-COL17 antibodies. The other 2 lines did not induce such phenotypes. RNA-sequencing analysis revealed that T helper 2 cytokines, particularly IL-5, were highly expressed in the pathogenic T-cell lines. Anti-IL-5 antibody administration significantly reduced the skin changes and attenuated the production of autoantibodies. Thus, the production of IL-5 is critical for COL17-specific CD4+ T cells to induce bullous pemphigoid phenotypes in vivo.

Immune interplay from circulation to local lesion in pemphigus pathogenesis

Pemphigus, a potentially lethal autoimmune skin disease, is mediated by desmoglein-specific antibodies, manifesting cutaneous and mucosal blisters and erosions. The interaction between multiple immune counterparts contributes to the progress of pemphigus. Currently, the emergence of bioinformatic analysis enables investigators to gain a global picture of the pemphigus immune network, based on the exhaustive pedigree annotation of multiple subsets. T helper subsets dominate the landscape as mentioned previously, and innate immune cells have been involved as well. Of particular interests is which phenotype of T cells orchestrates the autoimmune process and chronic inflammation in a certain condition. In this review, the circulatory and peripheral immune cells and cytokine components constituting the immune microenvironment are separately discussed to provide a perspective on pemphigus pathogenesis, with particular reference to insights provided by the bioinformation technique.

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.

Immune cells in pemphigus vulgaris and bullous Pemphigoid: From pathogenic roles to targeting therapies

Pemphigus vulgaris (PV) and bullous pemphigoid (BP) are two major subtypes of autoimmune bullous diseases (AIBD), characterized by blisters and erosions of skin and/or mucous membranes with dysregulated immune activity. Current literature established that T and B cells are the main executors of PV and BP. Emerging evidence revealed that macrophages and related cytokines also contribute to these diseases. While the role of lymphocytes on PV and BP is well established, the definitive functions of macrophages in disease progression are not fully understood. Furthermore, current status of clinical trials targeting immune cells is poorly recapitulated in PV and BP. In this review, we summarized current knowledge in this rapidly advancing field, with emphasis on the individual functions of immune cells and their interactions, as well as ongoing clinical trials targeting immune cells, to provide novel insights in mechanistic understanding and clinical management of PV and BP.

A Novel In Vivo Active Pemphigus Model Targeting Desmoglein1 and Desmoglein3: A Tool Representing All Pemphigus Variants

Background: Pemphigus is a life-threatening blistering autoimmune disease. Several forms, characterized by the presence of autoantibodies against different autoantigens, have been described. In Pemphigus Vulgaris (PV), autoantibodies target the cadherin Desmoglein 3 (DSG3), while in Pemphigus foliaceous (PF) autoantibodies target the cadherin Desmoglein 1 (DSG1). Another variant, mucocutaneous Pemphigus, is characterized by the presence of IgG against both DSG1 and DSG3. Moreover, other forms of Pemphigus characterized by the presence of autoantibodies against other autoantigens have been described. With regard to animal models, one can distinguish between passive models, where pathological IgG are transferred into neonatal mice, and active models, where B cells deriving from animals immunized against a specific autoantigen are transferred into immunodeficient mice that develop the disease. Active models recreate PV and a form of Pemphigus characterized by the presence of IgG against the cadherin Desmocollin 3 (DSC3). Further approaches allow to collect sera or B/T cells from mice immunized against a specific antigen to evaluate the mechanisms underlying the onset of the disease. Objective: To develop and characterize a new active model of Pemphigus where mice express auto antibodies against either DSG1 alone, or DSG1 and DSG3, thereby recapitulating PF and mucocutaneous Pemphigus, respectively. In addition to the existing models, with the active models reported in this work, it will be possible to recapitulate and mimic the main forms of pemphigus in adult mice, thus allowing a better understanding of the disease in the long term, including the benefit/risk ratio of new therapies. Results: The new DSG1 and the DSG1/DSG3 mixed models were developed as proposed. Immunized animals, and subsequently, animals that received splenocytes from the immunized donors produce a high concentration of circulating antibodies against the specific antigens. The severity of the disease was assessed by evaluating the PV score, evidencing that the DSG1/DSG3 mixed model exhibits the most severe symptoms among those analyzed. Alopecia, erosions, and blistering were observed in the skin of DSG1, DSG3 and DSG1/DSG3 models, while lesions in the mucosa were observed only in DSG3 and DSG1/DSG3 animals. The effectiveness of the corticosteroid Methyl-Prednisolone was evaluated in the DSG1 and DSG1/DSG3 models, that showed only partial responsiveness.

T cell autoimmunity and immune regulation to desmoglein 3, a pemphigus autoantigen

Pemphigus is a life-threatening autoimmune bullous disease mediated by anti-desmoglein IgG autoantibodies. Pemphigus is mainly classified into three subtypes: pemphigus vulgaris, pemphigus foliaceus, and paraneoplastic pemphigus. The pathogenicity of autoantibodies has been extensively studied. Anti-human CD20 antibody therapy targeting B cells emerged as a more effective treatment option compared to conventional therapy for patients with an intractable disease. On the other hand, autoreactive T cells are considered to be involved in the pathogenesis based on the test results of human leukocyte antigen association, autoreactive T cell detection, and cytokine profile analysis. Research on the role of T cells in pemphigus has continued to progress, including that on T follicular helper cells, which initiate molecular mechanisms involved in antibody production in B cells. Autoreactive T cell research in mice has highlighted the crucial roles of cellular autoimmunity and improved the understanding of its pathogenesis, especially in paraneoplastic pemphigus. The mouse research has helped elucidate novel regulatory mechanisms of autoreactive T cells, such as thymic tolerance to desmoglein 3 and the essential roles of regulatory T cells, Langerhans cells, and other molecules in peripheral tissues. This review focuses on the immunological aspects of autoreactive T cells in pemphigus by providing detailed information on various related topics.

In Vitro, Ex Vivo, and In Vivo Models for the Study of Pemphigus

Pemphigus is a life-threatening autoimmune disease. Several phenotypic variants are part of this family of bullous disorders. The disease is mainly mediated by pathogenic autoantibodies, but is also directed against two desmosomal adhesion proteins, desmoglein 1 (DSG1) and 3 (DSG3), which are expressed in the skin and mucosae. By binding to their antigens, autoantibodies induce the separation of keratinocytes, in a process known as acantholysis. The two main Pemphigus variants are Pemphigus vulgaris and foliaceus. Several models of Pemphigus have been described: in vitro, ex vivo and in vivo, passive or active mouse models. Although no model is ideal, different models display specific characteristics that are useful for testing different hypotheses regarding the initiation of Pemphigus, or to evaluate the efficacy of experimental therapies. Different disease models also allow us to evaluate the pathogenicity of specific Pemphigus autoantibodies, or to investigate the role of previously not described autoantigens. The aim of this review is to provide an overview of Pemphigus disease models, with the main focus being on active models and their potential to reproduce different disease subgroups, based on the involvement of different autoantigens.

IgG4 Autoantibodies in Organ-Specific Autoimmunopathies: Reviewing Class Switching, Antibody-Producing Cells, and Specific Immunotherapies

Organ-specific autoimmunity is often characterized by autoantibodies targeting proteins expressed in the affected tissue. A subgroup of autoimmunopathies has recently emerged that is characterized by predominant autoantibodies of the IgG4 subclass (IgG4-autoimmune diseases; IgG4-AID). This group includes pemphigus vulgaris, thrombotic thrombocytopenic purpura, subtypes of autoimmune encephalitis, inflammatory neuropathies, myasthenia gravis and membranous nephropathy. Although the associated autoantibodies target specific antigens in different organs and thus cause diverse syndromes and diseases, they share surprising similarities in genetic predisposition, disease mechanisms, clinical course and response to therapies. IgG4-AID appear to be distinct from another group of rare immune diseases associated with IgG4, which are the IgG4-related diseases (IgG4-RLD), such as IgG4-related which have distinct clinical and serological properties and are not characterized by antigen-specific IgG4. Importantly, IgG4-AID differ significantly from diseases associated with IgG1 autoantibodies targeting the same organ. This may be due to the unique functional characteristics of IgG4 autoantibodies (e.g. anti-inflammatory and functionally monovalent) that affect how the antibodies cause disease, and the differential response to immunotherapies of the IgG4 producing B cells/plasmablasts. These clinical and pathophysiological clues give important insight in the immunopathogenesis of IgG4-AID. Understanding IgG4 immunobiology is a key step towards the development of novel, IgG4 specific treatments. In this review we therefore summarize current knowledge on IgG4 regulation, the relevance of class switching in the context of health and disease, describe the cellular mechanisms involved in IgG4 production and provide an overview of treatment responses in IgG4-AID.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

Anti-Neuronal IgG4 Autoimmune Diseases and IgG4-Related Diseases May Not Be Part of the Same Spectrum: A Comparative Study

Background

IgG4 is associated with two emerging groups of rare diseases: 1) IgG4 autoimmune diseases (IgG4-AID) and 2) IgG4-related diseases (IgG4-RLD). Anti-neuronal IgG4-AID include MuSK myasthenia gravis, LGI1- and Caspr2-encephalitis and autoimmune nodo-/paranodopathies (CNTN1/Caspr1 or NF155 antibodies). IgG4-RLD is a multiorgan disease hallmarked by tissue-destructive fibrotic lesions with lymphocyte and IgG4 plasma cell infiltrates and increased serum IgG4 concentrations. It is unclear whether IgG4-AID and IgG4-RLD share relevant clinical and immunopathological features.

Methods

We collected and analyzed clinical, serological, and histopathological data in 50 patients with anti-neuronal IgG4-AID and 19 patients with IgG4-RLD.

Results

A significantly higher proportion of IgG4-RLD patients had serum IgG4 elevation when compared to IgG4-AID patients (52.63% vs. 16%, p = .004). Moreover, those IgG4-AID patients with elevated IgG4 did not meet the diagnostic criteria of IgG4-RLD, and their autoantibody titers did not correlate with their serum IgG4 concentrations. In addition, patients with IgG4-RLD were negative for anti-neuronal/neuromuscular autoantibodies and among these patients, men showed a significantly higher propensity for IgG4 elevation, when compared to women (p = .005). Last, a kidney biopsy from a patient with autoimmune paranodopathy due to CNTN1/Caspr1-complex IgG4 autoantibodies and concomitant nephrotic syndrome did not show fibrosis or IgG4+ plasma cells, which are diagnostic hallmarks of IgG4-RLD.

Conclusion

Our observations suggest that anti-neuronal IgG4-AID and IgG4-RLD are most likely distinct disease entities.

The pathogeneses of pemphigus and pemphigoid diseases

Autoimmune bullous diseases (AIBDs) are skin disorders which are mainly induced by autoantibodies against desmosomal or hemidesmosomal structural proteins. Previous studies using patients' samples and animal disease models identified target antigens and elucidated the mechanisms of blister formation. Pemphigus has been the subject of more active clinical and basic research than any other AIBD. These efforts have revealed the pathogenesis of pemphigus, which in turn has led to optimal diagnostic methods and novel therapies, such as rituximab. In bullous pemphigoid (BP), studies with passive-transfer mouse models using rabbit anti-mouse BP180 antibodies and studies with passive-transfer or active mouse models using autoantigen-humanized mice elucidated the immune reactions to BP180 in vivo. Recently, dipeptidyl peptidase-4 inhibitors have attracted attention as a trigger for BP. For epidermolysis bullosa acquisita (EBA), investigations using mouse models are actively under way and several molecules have been identified as targets for novel therapies. In this review, we give an overview and discussion of the recent progress in our understanding of the pathogenesis of pemphigus, BP, and EBA. Further studies on the breakdown of self-tolerance and on the identification of key molecules that are relevant to blister formation may expand our understanding of the etiology of AIBDs and lead to the development of novel therapeutic strategies.

mTOR pathway regulates the differentiation of peripheral blood Th2/Treg cell subsets in patients with pemphigus vulgaris

Pemphigus vulgaris (PV) is a chronic and potentially life-threatening autoimmune blistering disease. Aberrant mTOR pathway activity is involved in many autoimmune diseases. This study investigated the correlation of mTOR pathway (PI3K/AKT/mTOR/p70S6K) activity with the loss of balance in T helper 2/regulatory T (Th2/Treg) cells in the peripheral blood of PV patients. CD4+ T cells were isolated from 15 PV patients and 15 healthy controls (HCs), the ratios of Th2/CD4+ T cells and Treg/CD4+ T cells, the activity of the mTOR pathway (PI3K/AKT/mTOR/p70S6K), the transcription factors and cytokines of Th2 and Treg cells were detected. Primary CD4+ T cells from PV patients were cultured under Th2- or Treg-polarizing conditions with or without rapamycin in vitro. We found that PV patients showed significantly elevated serum IL-4 when compared with HCs, and serum IL-4 level was positively correlated with the titer of anti-Dsg1/3 antibody and disease severity, while the serum TGF-β level was negatively correlated with the titer of anti-Dsg3 antibody and disease severity. Meanwhile, PV patients showed increased Th2/CD4+ T cell ratio; decreased Treg/CD4+ T cell ratio; elevated mRNA of PI3K, AKT, mTOR and protein of PI3K (P85), AKT, p-AKT (Ser473), mTOR, p-mTOR (Ser2448), p-p70S6K (Thr389), GATA3; reduced protein of forkhead box protein 3. Rapamycin inhibited Th2 cell differentiation and promoted Treg cell differentiation in vitro. These data suggest a close association between mTOR pathway activation and the loss of balance in Th2/Treg cells in peripheral blood of PV patients. Inhibiting mTORC1 can help restore the Th2/Treg balance.

Common Denominators in the Immunobiology of IgG4 Autoimmune Diseases: What Do Glomerulonephritis, Pemphigus Vulgaris, Myasthenia Gravis, Thrombotic Thrombocytopenic Purpura and Autoimmune Encephalitis Have in Common?

IgG4 autoimmune diseases (IgG4-AID) are an emerging group of autoimmune diseases that are caused by pathogenic autoantibodies of the IgG4 subclass. It has only recently been appreciated, that members of this group share relevant immunobiological and therapeutic aspects even though different antigens, tissues and organs are affected: glomerulonephritis (kidney), pemphigus vulgaris (skin), thrombotic thrombocytopenic purpura (hematologic system) muscle-specific kinase (MuSK) in myasthenia gravis (peripheral nervous system) and autoimmune encephalitis (central nervous system) to give some examples. In all these diseases, patients’ IgG4 subclass autoantibodies block protein-protein interactions instead of causing complement mediated tissue injury, patients respond favorably to rituximab and share a genetic predisposition: at least five HLA class II genes have been reported in individual studies to be associated with several different IgG4-AID. This suggests a role for the HLA class II region and specifically the DRβ1 chain for aberrant priming of autoreactive T-cells toward a chronic immune response skewed toward the production of IgG4 subclass autoantibodies. The aim of this review is to provide an update on findings arguing for a common pathogenic mechanism in IgG4-AID in general and to provide hypotheses about the role of distinct HLA haplotypes, T-cells and cytokines in IgG4-AID.

Immunophenotyping in pemphigus reveals a TH17/TFH17 cell-dominated immune response promoting desmoglein1/3-specific autoantibody production

BACKGROUND

T_H2 cells were thought to be a pivotal factor for initiation of the autoimmune blistering disease pemphigus. However, the role of other T-cell subsets in pemphigus pathogenesis remained unclear.

OBJECTIVE

We aimed to characterize the exact phenotype of T cells responsible for the development of pemphigus.

METHODS

Whole transcriptome shotgun sequencing was performed to determine differential gene expression in pemphigus lesions and skin of healthy individuals. The cutaneous cytokine signature was further evaluated by real-time quantitative PCR. In peripheral blood, the distribution of T_H cell and folliclular helper (T_FH) cell subsets was analyzed by flow cytometry. Finally, the capacity of T_H and T_FH cell subsets to induce desmoglein (Dsg)-specific autoantibodies by memory B cells was evaluated in coculture experiments.

RESULTS

Transcriptome analysis of skin samples identified an IL-17A-dominated immune signature in patients with pemphigus, and Kyoto Encyclopedia of Genes and Genomes pathway analysis confirmed the dominance of the IL-17A signaling pathway. Increased expression of IL17A and associated cytokines was also detected by real-time quantitative PCR comparing lesional with perilesional or healthy skin. Interestingly, utilization of flow cytometry showed that patients with active pemphigus had elevated levels of circulating IL-17⁺_, T_H17, T_FH17, and T_FH17.1 cells. Notably, levels of T_H17 and T_FH17 cells correlated with levels of Dsg-specific CD19⁺CD27⁺ memory B cells, and patients with acute pemphigus showed higher levels of Dsg3-autoreactive T_FH17 cells. Coculture experiments revealed T_FH17 cells as primarily responsible for inducing Dsg-specific autoantibody production by B cells.

CONCLUSION

Our findings show that T_FH17 cells are critically involved in the pathogenesis of pemphigus and offer novel targets for therapeutic intervention.

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.

Targeting inducible costimulator expressed on CXCR5+PD-1+ TH cells suppresses the progression of pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune bullous disease mediated by autoantibodies against desmoglein 3 (DSG3). Inducible costimulator (ICOS) is a costimulatory receptor expressed on T cells and influences the activity of T follicular helper (T_FH) cells in various autoimmune diseases, but the roles of ICOS and T_FH cells in PV remain unclear.

OBJECTIVE

We examined the immunological characteristics, antigen specificity, and pathogenicity of CD4⁺ T-cell subpopulations, as well as the therapeutic effect of anti-ICOS blocking antibodies in PV.

METHODS

A mouse model of PV was established by adoptive transfer of immune cells from the skin-draining lymph nodes or spleens of DSG3-expressing skin-grafted Dsg3^-/- mice into Rag1^-/- mice. The T_FH cells and CD4⁺ T cells in PBMCs from PV patients were examined by flow cytometry.

RESULTS

Among CD4⁺ T cells from the mouse model, ICOS-positive T_FH cells were associated with B-cell differentiation and were required for disease induction. Using an MHC class II tetramer, DSG3-specific ICOS⁺ T_FH cells were found to be associated with anti-DSG3 antibody production and expanded in the absence of B cells. In human PV, the frequency of ICOS⁺CXCR5⁺PD-1⁺ memory CD4⁺ T cells correlated with the autoantibody level. Treatment with anti-ICOS blocking antibodies targeting ICOS⁺ T_FH cells decreased the anti-DSG3 antibody level and delayed disease progression in vivo.

CONCLUSIONS

Mouse Dsg3-specific ICOS⁺ T_FH cells and human ICOS⁺CXCR5⁺PD-1⁺ T_H cells are associated with the anti-DSG3 antibody response in PV. ICOS expressed on CXCR5⁺PD-1⁺ T_H cells may be a therapeutic target for PV.

Autoimmunity and immunological tolerance in autoimmune bullous diseases

Autoimmune diseases are devastating conditions in which the immune system is directed against the host, leading to life-threatening destruction of organs. Although autoantigens are ill-defined in most autoimmune diseases, this is not the case in the skin. Autoimmune bullous diseases have been extensively studied with detailed characterization of autoantigens, the epitopes that are targeted, and the mechanisms of action that mediate autoimmune tissue destruction. Pemphigus is an autoimmune bullous disease caused by circulating IgG that targets two desmosomal proteins, desmoglein 1 and 3, which are crucial for cell-cell adhesion of keratinocytes. Binding of auto-antibodies to desmogleins impairs keratinocyte adhesion, leading to severe blistering disease. Mouse models that recapitulate the human disease have been instrumental in elucidating the detailed pathophysiology. Taking advantage of the fact that desmogleins are specifically targeted in pemphigus, studying humoral and cellular autoimmunity against these autoantigens provides us with an opportunity to understand not only the effector mechanisms of B and T cells in mediating pathology but also how autoreactive lymphocytes are regulated during development in the thymus and post-development in the periphery. This review introduces pemphigus and its subtypes as prototypic autoimmune diseases from which recent basic and translational developments should provide insight into how autoimmunity develops.

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.

Role of Regulatory Immune Cells and Molecules in Autoimmune Bullous Dermatoses

Autoimmune bullous dermatoses (AIBD) include a series of typical organ-specific autoimmune diseases characterized by extensive mucocutaneous blisters. It is generally accepted to be caused by pathological autoantibodies that directly target specific adhesion components of the skin or the adjacent mucous membranes. Both innate and adaptive immune systems are critically involved in the misguided immune response against self-antigens. Recent studies have indicated that the dysfunction of regulatory T cells, regulatory B cells, and complement regulatory proteins that play essential roles in maintaining a healthy immune environment is also closely related to immune disorders in AIBD. It is important to summarize these studies, elucidate the changes in these regulatory immune cells and molecules for the pathogenesis of AIBD, and reveal the mechanisms by which they lose their ability to regulate immune disorders. In this review, we highlight the role of regulatory immune cells and molecules in the pathogenesis of pemphigus vulgaris and bullous pemphigoid, the two most representative forms of AIBD, and indicate issues that should be addressed in future investigations.

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.

Emerging treatment options for the management of pemphigus vulgaris

Pemphigus vulgaris (PV) is a life-threatening disease belonging to the pemphigus group of autoimmune intra-epidermal bullous diseases of the skin and mucosae. The therapeutic management of PV remains challenging and, in some cases, conventional therapy is not adequate to induce clinical remission. The cornerstone of PV treatment remains systemic corticosteroids. Although very effective, long-term corticosteroid administration is characterized by substantial adverse effects. Corticosteroid-sparing adjuvant therapies have been employed in the treatment of PV, aiming to reduce the necessary cumulative dose of corticosteroids. Specifically, immunosuppressive agents such as azathioprine and mycophenolate mofetil are widely used in PV. More recently, high-dose intravenous immunoglobulins, immunoadsorption, and rituximab have been established as additional successful therapeutic options. This review covers both conventional and emerging therapies in PV. In addition, it sheds light on potential future treatment strategies for this disease.

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.

Analysis of Serum Cytokine Profile in Pemphigus

BACKGROUND

Pemphigus is a group of autoimmune blistering diseases affecting skin and mucous membranes. While pemphigus is an autoantibody mediated disease, the role of T cells and cytokines in the pathogenesis is being increasingly recognized.

OBJECTIVE

This study was conducted to observe alterations in the serum cytokine levels of patients with pemphigus vulgaris (PV), pemphigus foliaceous (PF), paraneoplastic pemphigus (PNP) and compare with bullous pemphigoid (BP) and healthy subjects.

METHODS

A total of 75 subjects (28 PV, 13 PF, 7 PNP, 7 BP, and 20 healthy controls) were included, all patients in active disease state. Serum levels of interferon (IFN)-γ, interleukin (IL)-4, IL-6, IL-17A, IL-10, tumor necrosis factor (TNF)-α, and IL-8 were measured by enzyme-linked immunosorbent assay.

RESULTS

The median concentration of IFN-γ was lower in PV and BP patients compared to control (0.77, 0.34 and 1.63 pg/ml, respectively). IL-6 and IL-10 was significantly higher in PNP patients compared to control (4.92 and 0.24 pg/ml for IL-6, 0.86 and <0.12 pg/ml for IL-10, respectively). IL-8 was increased significantly in PV and PNP patients compared with control (11.85, 31.5 and 8.31 pg/ml, respectively). For IL-4, IL-17A and TNF-α, no significant difference was observed between the five groups.

CONCLUSION

The decreased level of IFN-γ in PV may imply suppressed Th1 response in the active disease stage. A Th2 predominant response is suggested in the active stage of PNP, with elevated serum levels of IL-6 and IL-10. Increased level of proinflammatory cytokine IL-8 is observed in the sera of PV and PNP patients.

Pemphigus

Pemphigus is a group of IgG-mediated autoimmune diseases of stratified squamous epithelia, such as the skin and oral mucosa, in which acantholysis (the loss of cell adhesion) causes blisters and erosions. Pemphigus has three major subtypes: pemphigus vulgaris, pemphigus foliaceus and paraneoplastic pemphigus. IgG autoantibodies are characteristically raised against desmoglein 1 and desmoglein 3, which are cell-cell adhesion molecules found in desmosomes. The sites of blister formation can be physiologically explained by the anti-desmoglein autoantibody profile and tissue-specific expression pattern of desmoglein isoforms. The pathophysiological roles of T cells and B cells have been characterized in mouse models of pemphigus and patients, revealing insights into the mechanisms of autoimmunity. Diagnosis is based on clinical manifestations and confirmed with histological and immunochemical testing. The current first-line treatment is systemic corticosteroids and adjuvant therapies, including immunosuppressive agents, intravenous immunoglobulin and plasmapheresis. Rituximab, a monoclonal antibody against CD20⁺ B cells, is a promising therapeutic option that may soon become first-line therapy. Pemphigus is one of the best-characterized human autoimmune diseases and provides an ideal paradigm for both basic and clinical research, especially towards the development of antigen-specific immune suppression treatments for autoimmune diseases.

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.

The dual nature of interleukin-10 in pemphigus vulgaris

The immunomodulatory cytokine interleukin-10 (IL-10) plays beneficial but also potentially detrimental roles in inflammation, infection, and autoimmunity. Recent studies suggest a regulatory role for IL-10-expressing B cells in the autoimmune blistering disease pemphigus vulgaris. Here we review the studies on IL-10 in pemphigus vulgaris and discuss the potential pathophysiological significance of these findings in comparison to prior studies of IL-10 in other human conditions. A better understanding of the complex roles of IL-10 in immune regulation may improve our understanding of pemphigus pathogenesis and treatment.

Overexpression of interleukin-23 and interleukin-17 in the lesion of pemphigus vulgaris: a preliminary study

IL-23/IL-17 axis has been identified as major factor involved in the pathogenesis of several autoimmune diseases; yet its pathogenetic role in pemphigus vulgaris (PV) remains controversial. The aim of this research was to investigate the potential role of IL-23/IL-17 axis in the immunopathogenesis of PV, and correlation between IL-23+ cells and IL-17+ cells was also evaluated. For this purpose, ten patients with PV, three patients with pemphigus foliaceus (PF), and six healthy individuals were allocated to this research. The lesional skin biopsy specimens were obtained before treatment. Then immunofluorescence staining was performed to analyze the expression of IL-23 and IL-17 in the PV/PF patients and the healthy individuals. The results showed that the numbers of IL-23+ and IL-17+ cells were significantly higher in PV lesions, compared to PF lesions and normal control skins, respectively (all P < 0.05). Moreover, the correlation between IL-23+ cells and IL-17+ cells was significant (r = 0.7546; P < 0.05). Taken together, our results provided evidence that the IL-23/IL-17 axis may play a crucial role in the immunopathogenesis of PV and may serve as novel therapeutic target for PV.

Autoimmune reactivity against precursor form of desmoglein 1 in healthy Tunisians in the area of endemic pemphigus foliaceus

BACKGROUND

Desmoglein 1 (Dsg1), the pemphigus foliaceus (PF) antigen, is produced as a precursor (preDsg1) and is transported to the cell surface as the mature form (matDsg1). Recent studies show that B cells from North American individuals without pemphigus can potentially produce anti-preDsg1 IgG antibodies, but ELISA screening of large numbers of normal people in North America and Japan hardly ever shows circulating antibodies against preDsg1 or matDsg1. In contrast, in Tunisia, where PF is endemic, anti-Dsg1 IgGs are frequently detected in healthy individuals.

OBJECTIVE

To characterize these anti-Dsg1 antibodies from normal individuals in Tunisia.

METHODS

Sera from 16 healthy individuals and 9 PF patients in the endemic PF area in Tunisia, and sera from Japanese non-endemic PF patients were analyzed by immunoprecipitation-immunoblotting using recombinant proteins of preDsg1, matDsg1, and domain-swapped Dsg1/Dsg2 molecules.

RESULTS

Sera from normal Tunisian individuals reacted to preDsg1 alone (8/16) or more strongly to preDsg1 than to matDsg1 (7/16), while those from all Tunisian PF patients and Japanese non-endemic PF patients reacted similarly to preDsg1 and matDsg1, or preferentially to matDsg1. The epitopes recognized by anti-Dsg1 IgGs from normal Tunisian individuals were more frequently found in the C-terminal extracellular domains (EC3 to EC5), while those in Tunisian endemic PF patients were more widely distributed throughout the extracellular domains, suggesting IgGs against EC1 and EC2 developed during disease progression.

CONCLUSIONS

These findings indicate that IgG autoantibodies against Dsg1 are mostly raised against preDsg1 and/or C-terminal domains of Dsg1 in healthy Tunisians in the endemic area of PF.

HLA-E*0103X is associated with susceptibility to Pemphigus vulgaris

Non-classical human leucocyte antigen-E (HLA-E) mediates natural killer and CD8+ T-cell activity, suggesting a role in the regulation of autoimmunity. HLA-E*0103X/*0103X has been associated with Behcet's disease and HLA-E *0101/*0103X with childhood onset diabetes. We investigated HLA-E allele status in 52 Caucasian and Ashkenazi Jewish Pemphigus vulgaris (PV) patients and 51 healthy controls by restriction fragment length polymorphism-polymerase chain reaction and amplification refractory mutation system. Associations were determined via chi-square test, Fisher's exact test and logistical regression analysis. HLA-E outcomes included presumed homozygous *0101/*0101 or *0103X/*0103X genotype status or *0101/*0103X heterozygous status. PV did not significantly associate with either *0101/*0101 or *0101/*0103X genotypes. HLA-E*0103X/*0103X (presumed homozygote) is significantly increased in patients with PV versus controls (P = 0.0146, OR = 3.730, 95%CI = 1.241-11.213). Our data provide the first evidence that HLA-E*0103X is a marker for genetic risk in PV.

Cytokine gene polymorphisms in Tunisian endemic pemphigus foliaceus: a possible role of il-4 variants

Polymorphism in the genes of TH2 cytokines and/or theirs receptors can influence serum cytokine levels in and the switch to the pathologic IgG4 auto-antibodies. In order to underline the role of these genes in the aethiopathogenesis of Pemphigus Foliaceus, we conduct a familial and a case control studies including 80 Tunisian patients, 147 related subjects and 160 matched healthy controls. We investigated, by PCR-RFLP technique, seven nucleotide polymorphisms: rs2243250 in promoter region of IL4 gene, rs47877948, rs3024530 and rs30246223 in the IL4R gene, rs1881457and rs205412 SNPs in IL13 gene and rs535036 in IL13RA2 gene. After Bonferroni adjustment, T allele and the TT genotype of IL4-590 were significantly increased in the PF patients group compared to healthy controls. This association was confirmed by the family study. Interestingly, the serum IL-4 levels were significantly increased in patients with the TT genotype compared to CT or CC genotypes. Interestingly, the IL4/IL13:T-A-C haplotype exhibited a significant effect on PF susceptibility. In addition, a significant gene-gene interaction between the IL4/IL4R (TACA) significantly increases in PF patients as compared to controls. These findings assess the role of the IL4/IL4R axis in the aethiopathogenesis of Tunisian endemic PF by the induction of a high transcriptional activity which could enhance the T-cell balance and inducing immunoglobulin isotype switching.

Evidence for pathogenicity of autoreactive T cells in autoimmune bullous diseases shown by animal disease models

Autoimmune bullous diseases (AIBDs) are characterized by blisters and erosions on the skin and/or mucous membranes, which are caused by autoantibodies directed to structural proteins of the epidermis and the epidermal basement membrane zone. This Viewpoint Essay discusses the contribution by autoreactive T cells to the pathogenesis of bullous pemphigoid, pemphigus and epidermolysis bullosa acquisita, with an emphasis on studies using active animal mouse models for these diseases. Previous studies have demonstrated that cytokines produced by autoreactive T cells, the interaction between antigen-specific T cells and B cells and the function of regulatory T cells are likely related to the pathogenesis of AIBDs. In interpreting the experimental results, the limitations of those animal models should be considered. Further understanding of the pathogenicity of autoreactive CD4(+) T cells may lead to disease-specific treatments.

Cytokine networks in Pemphigus vulgaris: An integrated viewpoint

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease where tolerance to the desmosomal protein desmoglein 3 (Dsg3), and perhaps additional epidermal targets, is lost, leading to the production of autoantibodies directed against cellular adhesion molecules. As auto-reactive T cells are involved in the induction and maintenance of antibody production, it has been hypothesized that cytokines play a crucial role in disease pathogenesis. Qualitative and quantitative alterations in cytokine profiles have been previously reported; however, despite recent advancements, the characterization of the disease supporting cytokine network in PV has yet to be fully elucidated. It is overwhelmingly suggested that PV is a TH2-mediated disease, confirmed by the majority of studies demonstrating an increase in TH2-type cytokines. Recently, a focus has been placed on the contribution of the newly discovered TH17 subset to autoimmune states, and current evidence suggests that this inflammatory pathway may play a role in PV as well. Anti-cytokine medications are on the forefront as potential therapeutic options, and the growing number of reports of clinical benefit serves to confirm the major contribution of various inflammatory mediators in the development of disease phenotype. This work aimed to comprehend the complexity of cytokine and T cell involvement in pemphigus, taking account of known information and emphasizing the areas where additional research would be of great benefit, particularly in pharmacological development and expansion of the pemphigus therapeutic armamentarium.

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.

Pemphigus autoimmunity: hypotheses and realities

The goal of contemporary research in pemphigus vulgaris and pemphigus foliaceus is to achieve and maintain clinical remission without corticosteroids. Recent advances of knowledge on pemphigus autoimmunity scrutinize old dogmas, resolve controversies, and open novel perspectives for treatment. Elucidation of intimate mechanisms of keratinocyte detachment and death in pemphigus has challenged the monopathogenic explanation of disease immunopathology. Over 50 organ-specific and non-organ-specific antigens can be targeted by pemphigus autoimmunity, including desmosomal cadherins and other adhesion molecules, PERP cholinergic and other cell membrane (CM) receptors, and mitochondrial proteins. The initial insult is sustained by the autoantibodies to the cell membrane receptor antigens triggering the intracellular signaling by Src, epidermal growth factor receptor kinase, protein kinases A and C, phospholipase C, mTOR, p38 MAPK, JNK, other tyrosine kinases, and calmodulin that cause basal cell shrinkage and ripping desmosomes off the CM. Autoantibodies synergize with effectors of apoptotic and oncotic pathways, serine proteases, and inflammatory cytokines to overcome the natural resistance and activate the cell death program in keratinocytes. The process of keratinocyte shrinkage/detachment and death via apoptosis/oncosis has been termed apoptolysis to emphasize that it is triggered by the same signal effectors and mediated by the same cell death enzymes. The natural course of pemphigus has improved due to a substantial progress in developing of the steroid-sparing therapies combining the immunosuppressive and direct anti-acantholytic effects. Further elucidation of the molecular mechanisms mediating immune dysregulation and apoptolysis in pemphigus should improve our understanding of disease pathogenesis and facilitate development of steroid-free treatment of patients.

The genetics of pemphigus

Pemphigus vulgaris (PV) is an autoimmune blistering disorder with a complex etiology involving an interplay of genetic as well as environmental factors, most of which remain unknown. Despite the identification of several human leukocyte antigen (HLA) alleles as risk factors for disease, no other non-HLA genes have clearly been implicated in disease susceptibility. Newer candidate gene and whole-genome approaches are needed to illuminate the full palate of genetic risk elements in PV. Based on this information, genetic-based tools can be expected to provide a scientific rationale for future clinical decision-making by physicians and facilitate an era of personalized medicine.

Desmoglein 3-specific CD4+ T cells induce pemphigus vulgaris and interface dermatitis in mice

Pemphigus vulgaris (PV) is a severe autoimmune disease involving blistering of the skin and mucous membranes. It is caused by autoantibodies against desmoglein 3 (Dsg3), an adhesion molecule critical for maintaining epithelial integrity in the skin, oral mucosa, and esophagus. Knowing the antigen targeted by the autoantibodies renders PV a valuable model of autoimmunity. Recently, a role for Dsg3-specific CD4+ T helper cells in autoantibody production was demonstrated in a mouse model of PV, but whether these cells exert cytotoxicity in the tissues is unclear. Here, we analyzed 3 Dsg3-specific TCRs using transgenic mice and retrovirus induction. Dsg3-specific transgenic (Dsg3H1) T cells underwent deletion in the presence of Dsg3 in vivo. Dsg3H1 T cells that developed in the absence of Dsg3 elicited a severe pemphigus-like phenotype when cotransferred into immunodeficient mice with B cells from Dsg3-/- mice. Strikingly, in addition to humoral responses, T cell infiltration of Dsg3-expressing tissues led to interface dermatitis, a distinct form of T cell-mediated autoimmunity that causes keratinocyte apoptosis and is seen in various inflammatory/autoimmune skin diseases, including paraneoplastic pemphigus. The use of retrovirally generated Dsg3-specific T cells revealed that interface dermatitis occurred in an IFN-γ- and TCR avidity-dependent manner. This model of autoimmunity demonstrates that T cells specific for a physiological skin-associated autoantigen are capable of inducing interface dermatitis and should provide a valuable tool for further exploring the immunopathophysiology of T cell-mediated skin diseases.

Antigen-independent development of Foxp3+ regulatory T cells suppressing autoantibody production in experimental pemphigus vulgaris

The CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) play suppressive roles in various types of autoimmunity. It has been reported that Tregs develop in the thymus after high-affinity interaction of their TCR with self-peptide/MHC ligands mostly utilizing TCR-transgenic system. In this study, we examined whether the specific antigen is involved in the development of polyclonal Tregs in pemphigus vulgaris (PV), an autoimmune blistering disease caused by anti-desmoglein 3 (Dsg3) IgG antibodies, as a model system. Adoptive transfer of splenocytes of Dsg3(-)(/-) mice immunized with recombinant mouse Dsg3 to Rag2(-)(/-) recipient mice expressing Dsg3 resulted in the stable production of anti-Dsg3 IgG and the development of PV phenotypes. We show here that Tregs control anti-Dsg3 antibody production in PV model mice: the adoptive transfer of Tregs and the depletion of endogenous Tregs suppressed and augmented, respectively, the anti-Dsg3 antibody production. To examine whether the endogenous expression of Dsg3 is involved in the generation of these PV-relevant Tregs, we compared the potential of wild-type Tregs with that of Tregs from Dsg3(-)(/-) mice. Polyclonal Tregs from Dsg3(-)(/-) mice were more potent than that of wild-type mice, in both adoptive transfer and Treg-depletion experiments, while suppressive activities against IgG production against an irrelevant antigen were similar between Tregs from wild-type and Dsg3(-)(/-) mice. Our observation implies that Tregs capable of suppressing T(h) cells that drive autoantibody production can develop in the absence of the target antigen.