The role of intramolecular epitope spreading in the pathogenesis of endemic pemphigus foliaceus (fogo selvagem)

Exploring PLA2R and HLA in membranous nephropathy: A narrative review of pathogenic mechanisms and emerging therapeutic potentials

Membranous Nephropathy (MN), a non-inflammatory autoimmune glomerulopathy, is a prominent cause of nephrotic syndrome, predominantly affecting Caucasian adults. It is characterized by significant thickening of the glomerular basement membrane, a direct result of immune complex deposition. Fundamental to its pathogenesis are the Phospholipase A2 receptor (PLA2R) and Human Leukocyte Antigens (HLA), which play crucial and interconnected roles. Specifically, PLA2R serves as the primary antigen, while HLA molecules facilitate MN-specific immune responses, thereby providing key insights into the disease's etiology. This study critically examines the roles of PLA2R and HLA in MN, with a particular focus on the antigenic epitopes of PLA2R. Given MN's complex nature, personalized therapeutic interventions are essential. Accordingly, targeting immunogenic epitopes has emerged as a transformative approach, aimed at modulating specific immune responses without disrupting overall immune function. Numerous studies and clinical trials have been advancing the application of these epitopes in therapeutic strategies. Nevertheless, challenges such as identifying effective epitopes, enhancing epitope-specific responses, and optimizing therapeutic dosing remain. This narrative review addresses these challenges in depth, offering a comprehensive insight into the pathology and emerging treatment strategies for MN.

Engineering antigen-presenting cells for immunotherapy of autoimmunity

Autoimmune diseases are burdensome conditions that affect a significant fraction of the global population. The hallmark of autoimmune disease is a host's immune system being licensed to attack its tissues based on specific antigens. There are no cures for autoimmune diseases. The current clinical standard for treating autoimmune diseases is the administration of immunosuppressants, which weaken the immune system and reduce auto-inflammatory responses. However, people living with autoimmune diseases are subject to toxicity, fail to mount a sufficient immune response to protect against pathogens, and are more likely to develop infections. Therefore, there is a concerted effort to develop more effective means of targeting immunomodulatory therapies to antigen-presenting cells, which are involved in modulating the immune responses to specific antigens. In this review, we highlight approaches that are currently in development to target antigen-presenting cells and improve therapeutic outcomes in autoimmune diseases.

Anti-Phospholipase A2 Receptor 1 and Anti-Cysteine Rich Antibodies, Domain Recognition and Rituximab Efficacy in Membranous Nephropathy: A Prospective Cohort Study

RATIONALE & OBJECTIVE

Proteinuria and anti-phospholipase A2 receptor 1 (anti-PLA2R1) antibody titers are associated with primary membranous nephropathy (MN) outcomes. We evaluated the association of antibodies against the cysteine-rich (CysR) and C-type lectin 1, 7, and 8 (CTLD1, CTLD7, and CTLD8) domains of PLA2R1 with MN outcomes.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

One-hundred-thirteen consecutive, consenting patients referred to the Nephology Unit of the Azienda-Socio-Sanitaria-Territoriale (ASST) Papa Giovanni XXIII (Bergamo, Italy) with PLA2R1-related, biopsy-proven MN whose persistent nephrotic syndrome (NS) was managed conservatively for>6 months and were monitored with serial evaluations of proteinuria, autoantibodies (by enzyme-linked immunosorbent assay), and clinical outcomes.

EXPOSURE

Rituximab.

OUTCOME

Complete (proteinuria<0.3g/24h) or partial (proteinuria≥0.3g/24h and<3.0g/24h with>50% reduction vs basal) NS remission.

ANALYTICAL APPROACH

Univariable and multivariable Cox regression analyses.

RESULTS

All patients had anti-CysR antibodies; 62 (54.9%) were multidomain recognizers. Anti-PLA2R1 and anti-CysR antibody titers were strongly correlated at baseline (P<0.001, r=0.934), 6 months (P<0.001, r=0.964), and 12 months (P<0.001, r=0.944). During a median follow-up of 37.1 (IQR, 20.3-56.9) months, 71 patients (62.8%) achieved either complete or partial remission of their NS. Lower baseline anti-PLA2R1 (HR, 0.997 [95% CI, 0.996-0.999], P=0.002) and anti-CysR [HR, 0.996 [95% CI, 0.993-0.998], P=0.001) titers were associated with a higher probability of remission, along with female sex, lower proteinuria, and lower serum creatinine levels (P<0.05 for all comparisons). Anti-CTLD antibodies were not associated with outcomes. At 6 and 12 months, compared to baseline, anti-PLA2R1 and anti-CysR antibody titers decreased more in patients progressing to partial or complete remission than in those without remission (P<0.05 for all comparisons).

LIMITATIONS

Observational design.

CONCLUSIONS

In PLA2R1-related MN, anti-PLA2R1 and anti-CysR antibodies similarly predict rituximab efficacy independent of PLA2R1 domain recognition. The choice between these tests should be dictated by feasibility and costs. Evaluating anti-CTLD antibodies appears unnecessary.

PLAIN-LANGUAGE SUMMARY

Primary membranous nephropathy (MN), a leading cause of nephrotic syndrome (NS) in adults, is an autoimmune disease caused by autoantibodies binding to the podocyte antigen phospholipase A2 receptor 1 (PLA2R1). We assessed whether the effects of anti-CD20 cytolytic therapy with the monoclonal antibody rituximab are associated with detection rates and levels of anti-PLA2R1 antibodies and antibodies against PLA2R1 domains such as cysteine-rich (CysR), and C-type lectin 1, 7, and 8 (CTLD1, 7, and 8), in patients with PLA2R1-related MN and persistent NS. The probability of rituximab-induced complete or partial NS remission was associated with baseline anti-PLA2R1 and anti-CysR antibody titers, but not with anti-CTLD1, 7 and 8 antibodies or multidomain recognition. Integrated evaluation of anti-PLA2R1 or anti-CysR antibodies with proteinuria and kidney function may play a role in monitoring the effects of rituximab in patients with PLA2R1-related NS and MN.

IgG4 autoantibodies and autoantigens in the context of IgG4-autoimmune disease and IgG4-related disease

Immunoglobulins are an essential part of the humoral immune response. IgG4 antibodies are the least prevalent subclass and have unique structural and functional properties. In this review, we discuss IgG4 class switch and B cell production. We review the importance of IgG4 antibodies in the context of allergic responses, helminth infections and malignancy. We discuss their anti-inflammatory and tolerogenic effects in allergen-specific immunotherapy, and ability to evade the immune system in parasitic infection and tumour cells. We then focus on the role of IgG4 autoantibodies and autoantigens in IgG4-autoimmune diseases and IgG4-related disease, highlighting important parallels and differences between them. In IgG4-autoimmune diseases, pathogenesis is based on a direct role of IgG4 antibodies binding to self-antigens and disturbing homeostasis. In IgG4-related disease, where affected organs are infiltrated with IgG4-expressing plasma cells, IgG4 antibodies may also directly target a number of self-antigens or be overexpressed as an epiphenomenon of the disease. These antigen-driven processes require critical T and B cell interaction. Lastly, we explore the current gaps in our knowledge and how these may be addressed.

Paraneoplastic pemphigus uncovers distinct clinical and biological phenotypes of western unicentric Castleman disease

Unicentric Castleman disease (UCD) is a lymphoproliferative disease of unknown cause. Paraneoplastic pemphigus (PNP) is a major complication shown to be associated with a poor prognosis, with particular severity in patients with bronchiolitis obliterans (BO). This study describes the clinical and biological characteristics of UCD-PNP patients in a large Western cohort. A total of 148 patients diagnosed with UCD were identified, including 14 patients with a defined PNP. PNP was significantly associated with myasthenia gravis (MG) and FDC sarcoma during follow-up (FDCS). PNP was also significantly associated with reduced survival. These data, together with a multivariate analysis by principal components, led to the identification of UCD-PNP as a group at risk of MG, FDCS and death. PDGFRB sequencing performed on UCD lesions from six patients found the gain-of-function p.N666S variant in two. Interestingly, both patients had hyaline-vascular UCD subtype, were in the UCD-PNP subgroup and had FDCS. Sera from 25 UCD-PNP patients and 6 PNP patients without UCD were tested for PNP-associated autoantibodies. Sera from UCD-PNP patients had a strong reactivity against the N-terminal domain of recombinant periplakin (rPPL, 82%) and showed reactivity against at least two domains of rPPL. These features were not found in patients with UCD alone or in the PNP group without UCD. These data indicate that UCD-PNP patients belong to a subgroup sharing strong clinical and biological identity that might help to decipher the different dynamics of UCD natural history.

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

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

From Insect Bites to a Skin Autoimmune Disease: A Conceivable Pathway to Endemic Pemphigus Foliaceus

In the endemic variants of pemphigus foliaceus (PF), in Brazil and Tunisia, patients generate pathogenic IgG4 anti-desmoglein 1 autoantibodies. Additionally, these patients possess antibodies against salivary proteins from sand flies that react with Dsg1, which may lead to skin disease in susceptible individuals living in endemic areas. This minireview focuses on recent studies highlighting the possible role of salivary proteins from Lutzomyia longipalpis (L. longipalpis) in EPF from Brazil and Phlebotomus papatasi (P. papatasi) in EPF from Tunisia. We will briefly discuss the potential mechanisms of molecular mimicry and epitope spreading in the initiation and development of endemic PF (EPF) in Brazil and Tunisia.

Pemphigus Foliaceus Autoantibodies Induce Redistribution Primarily of Extradesmosomal Desmoglein 1 in the Cell Membrane

The autoimmune dermatosis pemphigus foliaceus (PF) is predominantly caused by IgG autoantibodies against the desmosomal cadherin desmoglein (Dsg) 1. The exact mechanisms that lead to the characteristic epidermal blistering are not yet fully understood. In the present study, we used a variety of biophysical methods to examine the fate of membrane-bound Dsg1 after incubation with PF patients' IgG. Dispase-based dissociation assays confirmed that PF-IgG used for this study reduced intercellular adhesion in a manner dependent on phospholipase C (PLC)/Ca2+ and extracellular signal-regulated kinase (ERK) 1/2 signaling. Atomic force microscopy (AFM) revealed that Dsg1 binding on single molecule level paralleled effects on keratinocyte adhesion under the different conditions. Stimulated emission depletion (STED) super-resolution microscopy was used to investigate the localization of Dsg1 after PF-IgG incubation for 24 h. Under control conditions, Dsg1 was found to be in part co-localized with desmoplakin and thus inside of desmosomes as well as extra-desmosomal along the cell border. Incubation with PF-IgG reduced the extra-desmosomal Dsg1 fraction. In line with this, fluorescence recovery after photobleaching (FRAP) experiments demonstrated a strongly reduced mobility of Dsg1 in the cell membrane after PF-IgG treatment indicating remaining Dsg1 molecules were primarily located inside desmosomes. Mechanistically, experiments confirmed the involvement of PLC/Ca2+ since inhibition of PLC or 1,4,5-trisphosphate (IP3) receptor to reduce cytosolic Ca2+ reverted the effects of PF-IgG on Dsg1 intra-membrane mobility and localization. Taken together, our findings suggest that during the first 24 h PF-IgG induce redistribution predominantly of membrane-bound extradesmosomal Dsg1 in a PLC/Ca2+ dependent manner whereas Dsg1-containing desmosomes remain.

Some Good and Some Bad: Sand Fly Salivary Proteins in the Control of Leishmaniasis and in Autoimmunity

Sand flies are hematophagous insects responsible for the transmission of vector-borne diseases to humans. Prominent among these diseases is Leishmaniasis that affects the skin and mucous surfaces and organs such as liver and spleen. Importantly, the function of blood-sucking arthropods goes beyond merely transporting pathogens. The saliva of vectors of disease contains pharmacologically active components that facilitate blood feeding and often pathogen establishment. Transcriptomic and proteomic studies have enumerated the repertoire of sand fly salivary proteins and their potential use for the control of Leishmaniasis, either as biomarkers of vector exposure or as anti-Leishmania vaccines. However, a group of specific sand fly salivary proteins triggers formation of cross-reactive antibodies that bind the ectodomain of human desmoglein 1, a member of the epidermal desmosomal cadherins. These cross-reactive antibodies are associated with skin autoimmune blistering diseases, such as pemphigus, in certain immunogenetically predisposed individuals. In this review, we focus on two different aspects of sand fly salivary proteins in the context of human disease: The good, which refers to salivary proteins functioning as biomarkers of exposure or as anti-Leishmania vaccines, and the bad, which refers to salivary proteins as environmental triggers of autoimmune skin diseases.

Cadherin Signaling in Cancer and Autoimmune Diseases

Cadherins mediate cell–cell adhesion through a dynamic process that is strongly dependent on the cellular context and signaling. Cadherin regulation reflects the interplay between fundamental cellular processes, including morphogenesis, proliferation, programmed cell death, surface organization of receptors, cytoskeletal organization, and cell trafficking. The variety of molecular mechanisms and cellular functions regulated by cadherins suggests that we have only scratched the surface in terms of clarifying the functions mediated by these versatile proteins. Altered cadherins expression is closely connected with tumorigenesis, epithelial–mesenchymal transition (EMT)-dependent fibrosis, and autoimmunity. We review the current understanding of how cadherins contribute to human health and disease, considering the mechanisms of cadherin involvement in diseases progression, as well as the clinical significance of cadherins as therapeutic targets.

Characteristics of Anti-Contactin1 Antibody-Associated Autoimmune Nodopathies With Concomitant Membranous Nephropathy

Background

The concurrence of anti-contactin 1 (CNTN1) antibody-associated chronic inflammatory demyelinating polyneuropathy (CIDP) and membranous nephropathy (MN) has previously been reported in the literature. CIDP with autoantibodies against paranodal proteins are defined as autoimmune nodopathies (AN) in the latest research. In view of the unclear relationship between CIDP and MN, we performed a case study and literature review to investigate the clinical characteristics of anti-CNTN antibody-associated AN with MN.

Methods

We detected antibodies against NF155, NF186, CNTN1, CNTN2, CASPR1 and PLA2R in blood samples of a patient with clinically manifested MN and concomitant peripheral neuropathy via double immunofluorescence staining and conducted a quantitative measurement of anti-PLA2R IgG antibodies via enzyme-linked immunosorbent assay (ELISA). Case reports of anti-CNTN1 antibody-associated AN, anti-CNTN1 antibody-associated AN with MN, and CIDP with MN were retrieved through a literature search for a comparative analysis of clinical characteristics. The cases were grouped according to the chronological order of CIDP and MN onset for the comparison of clinical characteristics.

Results

A 57-year-old man with anti-PLA2R positive MN was admitted to the hospital due to limb numbness, weakness, and proprioceptive sensory disorder. He was diagnosed with anti-CNTN1 antibody-associated AN and recovered well after immunotherapy. Our literature search returned 22 cases of CIDP with MN that occurred before, after, or concurrently with CIDP. Good responses were achieved with early single-agent or combination immunotherapy, but eight out of the 22 patients with CIDP and concomitant MN ultimately developed different motor sequelae. Five patients had anti-CNTN1 antibody-associated AN with MN. Among these patients, males accounted for the majority of cases (male:female=4:1), the mean age at onset was late (60.2 ± 15.7 years, range 43–78 years), and 40% had acute to subacute onset. Clinical manifestations included sensory-motor neuropathy, sensory ataxia caused by proprioceptive impairment, and elevated cerebrospinal fluid protein levels.

Conclusion

The age at onset of CIDP with MN was earlier than that of anti-CNTN1 antibody-associated AN. MN may occur before, after or concurrently with CIDP. The early detection and isotyping of anti-CNTN1 and anti-PLA2R antibodies and the monitoring of isotype switching may be essential for suspected CIDP patients.

Epidemiology of Pemphigus

Pemphigus is an epidemiologically heterogeneous group of autoimmune bullous diseases comprising pemphigus vulgaris (PV), pemphigus foliaceus, paraneoplastic pemphigus, IgA pemphigus, and pemphigus herpetiformis. Recently, our knowledge about the frequency of pemphigus, which is highly variable between different populations, has considerably expanded, and the first non-HLA genes associated with PV have been identified. In addition, a variety of comorbidities, including other autoimmune diseases, hematological malignancies, and psoriasis, have been described in this variant. Here, initial data about the impact of COVID-19 on this fragile patient population are discussed and perspectives for future epidemiological studies are outlined.

Impact of environmental changes on Dermatology

Urbanization, pollution and the modification of natural landscapes are characteristics of modern society, where the change in human relations with the environment and the impact on biodiversity are environmental determinants that affect the health-disease relationship. The skin is an organ that has a strong interface with the environment and, therefore, the prevalence patterns of dermatoses may reflect these environmental changes. In this article, aspects related to deforestation, fires, urbanization, large-scale agriculture, extensive livestock farming, pollution and climatic changes are discussed regarding their influence on the epidemiology of skin diseases. It is important that dermatologists be aware of their social responsibility in order to promote sustainable practices in their community, in addition to identifying the impacts of environmental imbalances on different dermatoses, which is essential for the prevention and treatment of these diseases.

Identification of a primary antigenic target of epitope spreading in endemic pemphigus foliaceus

Epitope spreading is an important mechanism for the development of autoantibodies (autoAbs) in autoimmune diseases. The study of epitope spreading in human autoimmune diseases is limited due to the major challenge of identifying the initial/primary target epitopes on autoantigens in autoimmune diseases. We have been studying the development of autoAbs in an endemic human autoimmune disease, Brazilian pemphigus foliaceus (or Fogo Selvagem (FS)). Our previous findings demonstrated that patients before (i.e. preclinical) and at the onset of FS have antibody (Ab) responses against other keratinocyte adhesion molecules in addition to the main target autoantigen of FS, desmoglein 1 (Dsg1), and anti-Dsg1 monoclonal Abs (mAbs) cross-reacted with an environmental antigen LJM11, a sand fly saliva protein. Since sand fly is prevalent in FS endemic regions, individuals in these regions could develop Abs against LJM11. The anti-LJM11 Abs could recognize different epitopes on LJM11, including an epitope that shares the structure similarity with an epitope on Dsg1 autoantigen. Thus, Ab response against this epitope on LJM11 could be the initial autoAb response detected in individuals in FS endemic regions, including those who eventually developed FS. Accordingly, this LJM11 and Dsg1 cross-reactive epitope on Dsg1 could be the primary target of the autoimmune response in FS. This investigation aimed to determine whether the autoAb responses against keratinocyte adhesion molecules are linked and originate from the immune response to LJM11. The anti-Dsg1 mAbs from preclinical FS and FS individuals were employed to determine their specificity or cross-reactivity to LJM11 and keratinocyte adhesion molecules. The cross-reactive epitopes on autoantigens were mapped. Our results indicate that all tested mAbs cross-reacted with LJM11 and keratinocyte adhesion molecules, and we identified an epitope on these keratinocyte adhesion molecules which is mimicked by LJM11. Thus, the cross-reactivity could be the mechanism by which the immune response against an environmental antigen triggers the initial autoAb responses. Epitope spreading leads to the pathogenic autoAb development and ensuing FS among genetically susceptible individuals.

B-cell targeted therapies in pemphigus

Pemphigus is a rare autoimmune disease of the skin, characterized by autoantibodies targeting adhesion proteins of the epidermis, in particular desmoglein 3 and desmoglein 1, that cause the loss of cell-cell adhesion and the formation of intraepidermal blisters. Given that these autoantibodies are both necessary and sufficient for pemphigus to occur, the goal of pemphigus therapy is the elimination of autoreactive B-cells responsible for autoantibody production. Rituximab, an anti-CD20 monoclonal antibody, was the first targeted B-cell therapy approved for use in pemphigus and is now considered the frontline therapy for new onset disease. One limitation of this treatment is that it targets both autoreactive and non -autoreactive B-cells, which accounts for the increased risk of serious infections in treated patients. In addition, most rituximab-treated patients experience disease relapse, highlighting the need of new therapeutic options. This review provides a concise overview of rituximab use in pemphigus and discusses new B-cell and antibody-directed therapies undergoing investigation in clinical studies.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

A Lutzomyia longipalpis Salivary Protein Induces Cross-Reactive Antibodies to Pemphigus Autoantigen Desmoglein 1

Fogo selvagem (FS) is a blistering skin disease caused by pathogenic IgG4 autoantibodies to desmoglein 1 (DSG1). Preclinical FS and leishmaniasis are endemic to certain regions of Brazil and exhibit nonpathogenic anti-DSG1 antibodies. Recurring bites from Lutzomyia longipalpis, the sand fly vector of leishmaniasis, immunize individuals with L. longipalpis salivary antigens LJM17 and LJM11. We measured the antibody responses to LJM17, LJM11, and DSG1 in normal settlers and patients with FS from an endemic focus of FS and nonendemic control populations. We also immunized mice with these antigens and assessed the IgG response. Healthy individuals and patients with FS from endemic areas had significantly higher values of IgG4 anti-LJM17 antibodies than nonendemic controls (P < 0.001 for both). The levels of IgG anti-DSG1 and IgG4 anti-LJM17 and anti-LJM11 antibodies correlated positively in normal settlers and patients with FS. Mice immunized with recombinant LJM17 produced IgG1 antibodies (human IgG4 homolog) that strongly cross-reacted with recombinant DSG1; these IgG1 antibodies were inhibited by LJM17, LJM11, and DSG1 in a dose-dependent manner. However, they did not bind human or mouse epidermis by indirect immunofluorescence. Lastly, we identified short-sequence homologies of surface-exposed residues within the human DSG1 ectodomain and LJM17. Inoculation by LJM17 from L. longipalpis-elicited DSG1-cross-reactive IgG4 antibodies may lead to FS in genetically predisposed individuals.

Pemphigus

Pemphigus consists of a group of rare and severe autoimmune blistering diseases mediated by pathogenic autoantibodies mainly directed against two desmosomal adhesion proteins, desmoglein (Dsg)1 and Dsg3 (also known as DG1 and DG3), which are present in the skin and surface-close mucosae. The binding of autoantibodies to Dsg proteins induces a separation of neighbouring keratinocytes, in a process known as acantholysis. The two main pemphigus variants are pemphigus vulgaris, which often originates with painful oral erosions, and pemphigus foliaceus, which is characterised by exclusive skin lesions. Pemphigus is diagnosed on the basis of either IgG or complement component 3 deposits (or both) at the keratinocyte cell membrane, detected by direct immunofluorescence microscopy of a perilesional biopsy, with serum anti-Dsg1 or anti-Dsg3 antibodies (or both) detected by ELISA. Corticosteroids are the therapeutic mainstay, which have recently been complemented by the anti-CD20 antibody rituximab in moderate and severe disease. Rituximab induces complete remission off therapy in 90% of patients, despite rapid tapering of corticosteroids, thus allowing for a major corticosteroid-sparing effect and a halved number of adverse events related to corticosteroids.

Single-Cell Analysis Suggests that Ongoing Affinity Maturation Drives the Emergence of Pemphigus Vulgaris Autoimmune Disease

Pemphigus vulgaris (PV) is an autoimmune disease characterized by blistering sores on skin and mucosal membranes, caused by autoantibodies primarily targeting the cellular adhesion protein, desmoglein-3 (Dsg3). To better understand how Dsg3-specific autoantibodies develop and cause disease in humans, we performed a cross-sectional study of PV patients before and after treatment to track relevant cellular responses underlying disease pathogenesis, and we provide an in-depth analysis of two patients by generating a panel of mAbs from single Dsg3-specific memory B cells (MBCs). Additionally, we analyzed a paired sample from one patient collected 15-months prior to disease diagnosis. We find that Dsg3-specific MBCs have an activated phenotype and show signs of ongoing affinity maturation and clonal selection. Monoclonal antibodies (mAbs) with pathogenic activity primarily target epitopes in the extracellular domains EC1 and EC2 of Dsg3, though they can also bind to the EC4 domain. Combining antibodies targeting different epitopes synergistically enhances in vitro pathogenicity.

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.

Fogo selvagem: endemic pemphigus foliaceus

Fogo selvagem or endemic pemphigus foliaceus is an autoimmune acantholytic anti-cadherin bullous disease that primarily affects seborrheic areas, which might disseminate. Brazil has the world's largest number of patients, mainly in the Central-West region, but the disease has also been reported in other South American countries. It affects young people and adults who have been exposed to rural areas, with occurrence of familial cases. Anti-desmoglein-1 autoantibodies are directed against desmosomal structures, with loss of adhesion of the upper layers of the epidermis, causing superficial blisters. The etiology is multifactorial and includes genetic, immune, and environmental factors, highlighting hematophagous insect bites; drug-related factors are occasionally involved. Flaccid blisters readily rupture to yield erosive-crusty lesions that sometimes resemble seborrheic dermatitis, actinic keratosis, and chronic cutaneous lupus erythematosus. The clinical presentation varies from localized to disseminated lesions. Clinical suspicion should be confirmed with histopathological and immunofluorescence tests, among others. The progression is usually chronic, and therapy varies according to clinical presentation, but generally requires systemic corticosteroid therapy associated with adjuvant immunosuppressive treatment to decrease the adverse effects of corticosteroids. Once the disease is under control, many patients remain stable on low-dose medication, and a significant proportion achieve remission.

[Membranous nephropathy: Pathophysiology and natural history]

Membranous nephropathy is a major cause of nephrotic syndrome in adults, with various etiologies and outcomes. One third of patients enter spontaneous remission with blockade of the renin-angiotensin system, one third develop a persistent nephrotic syndrome, while another third of patients develop end-stage kidney disease and 40% of them relapse after kidney transplantation. Treatment of membranous nephropathy remains controversial. Immunosuppressive therapy is only recommended in case of renal function deterioration or persistent nephrotic syndrome after 6months of renin-angiotensin system blockade. Therefore, delayed immunosuppressive treatments may lead to significant and potentially irreversible complications. For long, no biological markers could predict clinical outcome and guide therapy. The discovery of autoantibodies to the phospholipase A2 receptor (PLA2R1) in 2009, and to the thrombospondin type 1 domain containing 7A (THSD7A) in 2014 in respectively 70 and 5% of patients with membranous nephropathy were major breakthroughs. The passive infusion of human anti-THSD7A antibodies in mouse induces proteinuria and membranous nephropathy. The identification of these antigens has allowed developing diagnostic and prognostic tests. High anti-PLA2R1 titers at time of diagnosis predict a poor renal outcome. Anti-PLA2R1 antibodies can bind at least three different domains of PLA2R1. Epitope spreading with binding of two or three of these antigenic domains is associated with active membranous nephropathy and poor renal survival. These new tools could help us to monitor disease severity and to predict renal prognosis for a better selection of patients that should benefit of early immunosuppressive therapy.

Pathogenic IgG4 autoantibodies from endemic pemphigus foliaceus recognize a desmoglein-1 conformational epitope

Fogo Selvagem (FS), the endemic form of pemphigus foliaceus, is mediated by pathogenic IgG4 autoantibodies against the amino-terminal extracellular cadherin domain of the desmosomal cadherin desmoglein 1 (Dsg1). Here we define the detailed epitopes of these pathogenic antibodies. Proteolytic footprinting showed that IgG4 from 95% of FS donor sera (19/20) recognized a 16-residue peptide (A129LNSMGQDLERPLELR144) from the EC1 domain of Dsg1 that overlaps the binding site for an adhesive-partner desmosomal cadherin molecule. Mutation of Dsg1 residues M133 and Q135 reduced the binding of FS IgG4 autoantibodies to Dsg1 by ∼50%. Molecular modeling identified two nearby EC1 domain residues (Q82 and V83) likely to contribute to the epitope. Mutation of these residues completely abolished the binding of FS IgG4 to Dsg1. Bead aggregation assays showed that native binding interactions between Dsg1 and desmocollin 1 (Dsc1), which underlie desmosome structure, were abolished by Fab fragments of FS IgG4. These results further define the molecular mechanism by which FS IgG4 autoantibodies interfere with desmosome structure and lead to cell-cell detachment, the hallmark of this disease.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Humoral Epitope Spreading in Autoimmune Bullous Diseases

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

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

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

A New Classification System for IgG4 Autoantibodies

IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus "blocking" their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein-protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky's postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.

Phospholipase A2 Receptor 1 Epitope Spreading at Baseline Predicts Reduced Likelihood of Remission of Membranous Nephropathy

The phospholipase A2 receptor (PLA2R1) is the major autoantigen in primary membranous nephropathy. Several PLA2R1 epitopes have been characterized, and a retrospective study identified PLA2R1 epitope spreading as a potential indicator of poor prognosis. Here, we analyzed the predictive value of anti-PLA2R1 antibody (PLA2R1-Ab) titers and epitope spreading in a prospective cohort of 58 patients positive for PLA2R1-Ab randomly allocated to rituximab (n=29) or antiproteinuric therapy alone (n=29). At baseline, the epitope profile (CysR, CysRC1, CysRC7, or CysRC1C7) did not correlate with age, sex, time from diagnosis, proteinuria, or serum albumin, but epitope spreading strongly correlated with PLA2R1-Ab titer (P<0.001). Ten (58.8%) of the 17 patients who had epitope spreading at baseline and were treated with rituximab showed reversal of epitope spreading at month 6. In adjusted analysis, epitope spreading at baseline was associated with a decreased remission rate at month 6 (odds ratio, 0.16; 95% confidence interval, 0.04 to 0.72; P=0.02) and last follow-up (median, 23 months; odds ratio, 0.14; 95% confidence interval, 0.03 to 0.64; P=0.01), independently from age, sex, baseline PLA2R1-Ab level, and treatment group. We propose that epitope spreading at baseline be considered in the decision for early therapeutic intervention in patients with primary membranous nephropathy.

Crosstalk between Signaling Pathways in Pemphigus: A Role for Endoplasmic Reticulum Stress in p38 Mitogen-Activated Protein Kinase Activation?

Pemphigus consists of a group of chronic blistering skin diseases mediated by autoantibodies (autoAbs). The dogma that pemphigus is caused by keratinocyte dissociation (acantholysis) as a distinctive and direct consequence of the presence of autoAb targeting two main proteins of the desmosome—desmoglein (DSG) 1 and/or DSG3—has been put to the test. Several outside-in signaling events elicited by pemphigus autoAb in keratinocytes have been described, among which stands out p38 mitogen-activated protein kinase (p38 MAPK) engagement and its apoptotic effect on keratinocytes. The role of apoptosis in the disease is, however, debatable, to an extent that it may not be a determinant event for the occurrence of acantholysis. Also, it has been verified that compromised DSG trans-interaction does not lead to keratinocyte dissociation when p38 MAPK is inhibited. These examples of conflicting results have been followed by recent work revealing an important role for endoplasmic reticulum (ER) stress in pemphigus’ pathogenesis. ER stress is known to activate the p38 MAPK pathway, and vice versa. However, this relationship has not yet been studied in the context of activated signaling pathways in pemphigus. Therefore, by reviewing and hypothetically connecting the role(s) of ER stress and p38 MAPK pathway in pemphigus, we highlight the importance of elucidating the crosstalk between all activated signaling pathways, which may in turn contribute for a better understanding of the role of apoptosis in the disease and a better management of this life-threatening condition.

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

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

Importance of serological tests in diagnosis of autoimmune blistering diseases

Autoimmune blistering diseases are organ-specific autoimmune diseases characterized by autoantibodies against structural proteins that maintain cell-cell (pemphigus diseases) and cell-matrix adhesions (pemphigoid diseases) in the skin and mucous membranes. Over the last few decades, identification of autoantigens and extensive characterization of autoantibodies have improved understanding of the pathogenesis of these diseases. In addition, the development of new sensitive and specific immunoassays enabled accurate diagnosis and proper evaluation of disease activity in autoimmune blistering diseases. In this review, we describe practical updates for molecular diagnostic tests for autoimmune blistering diseases and the basis for interpreting the results of the assays.

Update on fogo selvagem, an endemic form of pemphigus foliaceus

Pemphigus are organ-specific autoimmune diseases, where autoantibodies (mainly immunoglobulin [Ig]G) directed against epidermal targets (glycoproteins of the desmosomal core) are detected. Endemic pemphigus foliaceus or fogo selvagem (FS) is one of the variants of pemphigus foliaceus pemphigus foliaceus that shares the same clinical and immunopathological features of the classic non-endemic pemphigus foliaceus form, including pathogenic IgG (mainly IgG4) autoantibodies directed against the ectodomain of desmoglein 1 (Dsg1), that lead to acantholysis. Pathogenesis of FS is complex, involving genetic, environmental and immunological factors. Human leukocyte antigen (HLA)-DRB1 alleles DRB1*0404, *1402, *1406 or *0102 have been previously identified as risk factors for FS (relative risk, >14). Individuals exposed to hematophagous insects are more susceptible to develop the disease. Non-pathogenic anti-Dsg1 antibodies of the IgG1 subclass, directed against the extracellular 5 domain of Dsg1, are detected in patients in the preclinical stage of the disease, and also in healthy controls living in endemic areas. In counterpart, patients with FS show pathogenic anti-Dsg1 IgG4 autoantibodies that bind the pathogenic extracellular 1 and 2 domains of Dsg1, emphasizing the intramolecular epitope-spreading hypothesis. A possible explanation for the development of the autoimmune process would be antigenic mimicry, initiated by environmental stimuli in those genetically predisposed individuals. Characterization of the pathogenesis of FS will allow the development of specific therapeutic targets, and the elucidation of other autoimmune processes.

Non-infectious environmental antigens as a trigger for the initiation of an autoimmune skin disease

Pemphigus represents a group of organ specific autoimmune blistering disorders of the skin mediated by pathogenic autoantibodies with well-defined antigenic targets. While most of these diseases are sporadic, endemic forms of disease do exist. The endemic form of pemphigus foliaceus (also known as fogo selvagem, FS) exhibits epidemiological features that suggest exposure to hematophagous insect bites are a possible precipitating factor of this autoimmune disease, and provides a unique opportunity to study how environmental factors contribute to autoimmune disease development. FS patients and healthy individuals from endemic regions show an autoreactive IgM response that starts in early childhood and becomes restricted to IgG4 autoantibodies in FS patients. In searching for triggering environmental antigens, we have found that IgG4 and IgE autoantibodies from FS patients cross-react with a salivary antigen from sand flies. The presence of these cross-reactive antibodies and antibody genetic analysis confirming that these antibodies evolve from the same naïve B cells provides compelling evidence that this non-infectious environmental antigen could be the initial target of the autoantibody response in FS. Consequently, FS serves as an ideal model to study the impact of environmental antigens in the development of autoimmune disease.

Possible enhancement of BP180 autoantibody production by herpes zoster

Bullous pemphigoid (BP) is an autoimmune blistering disease caused by autoantibodies against type XVII collagen/BP180 (BP180). Although the mechanisms of autoantibody production remain to be elucidated, herpes virus infections have been identified as a possible triggering factor for pemphigus. We report a case of herpes zoster (HZ) having anti-BP180 serum antibodies. The patient developed sudden-onset, tense blisters and edematous erythema on the right anterior chest, shoulder and upper back. Histopathology showed remarkable degeneration of keratinocytes, acantholysis and blister formation with ballooning cells, indicating herpes virus infection. A polymerase chain reaction analysis of varicella zoster virus (VZV) was positive in crusts and effusions from the skin lesions, confirming the definitive diagnosis of HZ. Notably, we found that the patient had anti-BP180 serum antibodies in association with the occurrence of HZ. After successful treatment with valacyclovir hydrochloride for 7 days, the serum levels of anti-BP180 antibodies decreased in accordance with the improvement of skin lesions. These findings suggest that the production of anti-BP180 antibodies could be triggered by the reactivation of VZV.

Overlapping IgG4 Responses to Self- and Environmental Antigens in Endemic Pemphigus Foliaceus

The etiology of human autoimmune diseases in general remains largely unknown, although the genetic and environmental interplay may be relevant. This applies to the autoimmune diseases of the skin such as the pemphigus phenotypes and others. In this group, there is an endemic form of pemphigus foliaceus (also known as fogo selvagem [FS]) in which the pathogenic IgG4 autoantibody response to the self-antigen desmoglein 1 (Dsg1) cross-reacts with the LJM11 sand fly salivary gland Ag. In this investigation, we dissected the IgG4 autoantibody repertoires used by FS patients in response to endogenous self-Dsg1 and exogenous LJM11 sand fly Ag. Based on analyses of the genetic clonal signatures of these Abs, our results indicate that there is a significant overlap between these two responses, as all identified IgG4 mAbs cross-react to both Dsg1 and LJM11 Ags. Germline H- and L-chain V gene Abs generated according to mutated cross-reactive mAbs preserved their reactivity to both Ags. Our findings suggest that both Dsg1 autoantigen and LJM11 environmental Ag could be the initial antigenic stimulants for the IgG4 autoimmune responses in FS. These results support our hypothesis that LJM11 Ag plays a substantial role in triggering the IgG4 autoantibody development in FS and provide new insights on how noninfectious environmental Ag(s) may drive the generation of autoantibodies in IgG4-related autoimmune diseases.

Epitope Spreading of Autoantibody Response to PLA2R Associates with Poor Prognosis in Membranous Nephropathy

The phospholipase A2 receptor (PLA2R1) is the major autoantigen in idiopathic membranous nephropathy. However, the value of anti-PLA2R1 antibody titers in predicting patient outcomes is unknown. Here, we screened serum samples from 50 patients positive for PLA2R1 for immunoreactivity against a series of PLA2R1 deletion mutants covering the extracellular domains. We identified reactive epitopes in the cysteine-rich (CysR), C-type lectin domain 1 (CTLD1), and C-type lectin domain 7 (CTLD7) domains and confirmed the reactivity with soluble forms of each domain. We then used ELISAs to stratify 69 patients positive for PLA2R1 by serum reactivity to one or more of these domains: CysR (n=23), CysRC1 (n=14), and CysRC1C7 (n=32). Median ELISA titers measured using the full-length PLA2R1 antigens were not statistically different between subgroups. Patients with anti-CysR-restricted activity were younger (P=0.008), had less nephrotic range proteinuria (P=0.02), and exhibited a higher rate of spontaneous remission (P=0.03) and lower rates of renal failure progression (P=0.002) and ESRD (P=0.01) during follow-up. Overall, 31 of 69 patients had poor renal prognosis (urinary protein/creatinine ratio >4 g/g or eGFR<45 ml/min per 1.73 m(2) at end of follow-up). High anti-PLA2R1 activity and epitope spreading beyond the CysR epitope were independent risk factors of poor renal prognosis in multivariable Cox regression analysis. Epitope spreading during follow-up associated with disease worsening (n=3), whereas reverse spreading from a CysRC1C7 profile back to a CysR profile associated with favorable outcome (n=1). We conclude that analysis of the PLA2R1 epitope profile and spreading is a powerful tool for monitoring disease severity and stratifying patients by renal prognosis.

Allelic and copy-number variations of FcγRs affect granulocyte function and susceptibility for autoimmune blistering diseases

Low-affinity Fcγ receptors (FcγR) bridge innate and adaptive immune responses. In many autoimmune diseases, these receptors act as key mediators of the pathogenic effects of autoantibodies. Genes encoding FcγR exhibit frequent variations in sequence and gene copy number that influence their functional properties. FcγR variations also affect the susceptibility to systemic autoimmunity, e.g. systemic lupus erythematosus and rheumatoid arthritis. This raises the question whether FcγR variations are also associated with organ-specific autoimmunity, particularly autoantibody-mediated diseases, such as subepidermal autoimmune blistering diseases (AIBD). A multitude of evidence suggests a pathogenic role of neutrophil granulocyte interaction with autoantibodies via FcγR. In a two-stage study, we analyzed whether the FcγR genotype affects neutrophil function and mRNA expression, and consequently, bullous pemphigoid (BP) disease risk. We compared this to findings in pemphigus vulgaris/foliaceus (PV/PF), two Fc-independent AIBDs. Our results indicate that both allele and copy number variation of FcγR genes affect FcγR mRNA expression and reactive oxygen species (ROS) release by granulocytes. Susceptibility of BP was associated with FcγR genotypes that led to a decreased ROS release by neutrophils, indicating an unexpected protective role for these cells. BP and PV/PF differed substantially regarding the FcγR genotype association patterns, pointing towards different disease etiologies.

Prevalence of pemphigus and pemphigoid autoantibodies in the general population

BACKGROUND

Mucocutaneous blistering is characteristic of autoimmune bullous dermatoses (AIBD). Blisters are caused by autoantibodies directed against structural components of the skin. Hence, detection of specific autoantibodies has become a hallmark for AIBD diagnosis. Studies on prevalence of AIBD autoantibodies in healthy individuals yielded contradictory results.

METHODS

To clarify this, samples from 7063 blood donors were tested for presence of anti-BP180-NC16A, anti-BP230 and anti-Dsg1/3 IgG by indirect immunofluorescence (IF) microscopy using a biochip.

RESULTS

Cumulative prevalence of these autoantibodies was 0.9 % (CI: 0.7-1.1 %), with anti-BP180-NC16A IgG being most prevalent. Validation of IF findings using ELISA confirmed presence of autoantibodies in 7/15 (anti-Dsg1), 6/7 (anti-Dsg3), 35/37 (anti-BP180-NC16A) and 2/3 (anti-BP230) cases. Moreover, in 16 samples, anti-BP180-NC16A autoantibody concentrations exceeded the cut-off for the diagnosis of bullous pemphigoid. Interestingly, these anti-BP180-NC16A autoantibodies from healthy individuals formed immune complexes with recombinant antigen and dose-dependently activated neutrophils in vitro. However, fine-epitope mapping within NC16A showed a different binding pattern of anti-BP180-NC16A autoantibodies from healthy individuals compared to bullous pemphigoid patients, while IgG subclasses were identical.

CONCLUSIONS

Collectively, we here report a low prevalence of AIBD autoantibodies in a large cohort of healthy individuals. Furthermore, functional analysis shows differences between autoantibodies from healthy donors and AIBD patients.

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

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

B cell epitope spreading: mechanisms and contribution to autoimmune diseases

While a variety of factors act to trigger or initiate autoimmune diseases, the process of epitope spreading is an important contributor in their development. Epitope spreading is a diversification of the epitopes recognized by the immune system. This process happens to both T and B cells, with this review focusing on B cells. Such spreading can progress among multiple epitopes on a single antigen, or from one antigenic molecule to another. Systemic lupus erythematosus, multiple sclerosis, pemphigus, bullous pemphigoid and other autoimmune diseases, are all influenced by intermolecular and intramolecular B cell epitope spreading. Endocytic processing, antigen presentation, and somatic hypermutation act as molecular mechanisms that assist in driving epitope spreading and broadening the immune response in autoimmune diseases. The purpose of this review is to summarize our current understanding of B cell epitope spreading with regard to autoimmunity, how it contributes during the progression of various autoimmune diseases, and treatment options available.

Mycophenolate Mofetil as an Adjuvant Therapy for Classic and Endemic Pemphigus Foliaceus

Pemphigus foliaceus is an autoimmune cutaneous disease with subcorneal acantholysis and pathogenic IgG4 autoantibodies directed against desmoglein 1. We present our experience with mycophenolate mofetil (MMF) in the treatment of one case of endemic pemphigus foliaceus (fogo selvagem) and two cases of the classic form. All patients had severe, refractory disease and developed marked adverse effects due to long-term corticosteroid therapy. MMF proved to be an effective corticosteroid-sparing agent at doses varying from 35 to 45 mg/kg/d. It was well tolerated, and we found no significant adverse effects from this drug.

E-cadherin autoantibody profile in patients with pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease. The main targets of autoantibodies are the desmosomal proteins desmoglein (Dsg)3 and Dsg1. Anti-E-cadherin antibody is the second most frequent antibody found in pemphigus foliaceus (fogo selvagem), but the frequency in PV is unknown.

OBJECTIVES

To determine the anti-E-cadherin antibody profile in the two major subtypes of PV: mucosal PV (mPV) and mucocutaneous PV (mcPV).

METHODS

Sera from 80 patients with PV and 80 controls were tested. Patients with PV were subdivided into mPV (n = 18) and mcPV (n = 62). Samples were tested by E-cadherin, Dsg1 and Dsg3 enzyme-linked immunosorbent assays (ELISAs), and immunoprecipitation coupled with Western blotting (IP-WB).

RESULTS

Both mPV and mcPV sera have antibodies against E-cadherin as demonstrated by ELISA and IP-WB. Both subtypes of PV have low levels of anti-E-cadherin antibodies, but significantly higher levels than healthy controls by ELISA (P < 0·0001). No difference exists in antibody levels between subgroups (P = 0·82). By IP-WB, 78% of mcPV sera reacted to E-cadherin, vs. 33% of mPV sera tested. Correlation analysis suggests a moderate correlation between anti-E-cadherin antibodies and Dsg1 antibodies (average r = 0·61), but no correlation with Dsg3 antibodies (average r = 0·19). Patients with mPV can have lower levels of Dsg1 antibodies compared with controls by ELISA (P < 0·0001). A few mPV sera also reacted to Dsg1 protein by IP-WB (17%).

CONCLUSIONS

Anti-E-cadherin antibodies are present in both major subtypes of PV. A moderate correlation exists between E-cadherin and Dsg1 antibodies. Patients with mPV can have low levels of both E-cadherin and Dsg1 antibodies.