The distribution of pemphigus vulgaris-IgG subclasses and their reactivity with desmoglein 3 and 1 in pemphigus patients and their first-degree relatives

Exploring the depths of IgG4: insights into autoimmunity and novel treatments

IgG4 subclass antibodies represent the rarest subclass of IgG antibodies, comprising only 3-5% of antibodies circulating in the bloodstream. These antibodies possess unique structural features, notably their ability to undergo a process known as fragment-antigen binding (Fab)-arm exchange, wherein they exchange half-molecules with other IgG4 antibodies. Functionally, IgG4 antibodies primarily block and exert immunomodulatory effects, particularly in the context of IgE isotype-mediated hypersensitivity reactions. In the context of disease, IgG4 antibodies are prominently observed in various autoimmune diseases combined under the term IgG4 autoimmune diseases (IgG4-AID). These diseases include myasthenia gravis (MG) with autoantibodies against muscle-specific tyrosine kinase (MuSK), nodo-paranodopathies with autoantibodies against paranodal and nodal proteins, pemphigus vulgaris and foliaceus with antibodies against desmoglein and encephalitis with antibodies against LGI1/CASPR2. Additionally, IgG4 antibodies are a prominent feature in the rare entity of IgG4 related disease (IgG4-RD). Intriguingly, both IgG4-AID and IgG4-RD demonstrate a remarkable responsiveness to anti-CD20-mediated B cell depletion therapy (BCDT), suggesting shared underlying immunopathologies. This review aims to provide a comprehensive exploration of B cells, antibody subclasses, and their general properties before examining the distinctive characteristics of IgG4 subclass antibodies in the context of health, IgG4-AID and IgG4-RD. Furthermore, we will examine potential therapeutic strategies for these conditions, with a special focus on leveraging insights gained from anti-CD20-mediated BCDT. Through this analysis, we aim to enhance our understanding of the pathogenesis of IgG4-mediated diseases and identify promising possibilities for targeted therapeutic intervention.

Faster IgG4 Depletion Kinetics Observed for Anti-Desmoglein 3 Autoantibodies Following Rituximab Treatment in Patients with Pemphigus Vulgaris

Abstract is missing (Short communication)

The Diversity of Serum Anti-DSG3 IgG Subclasses Has a Major Impact on Pemphigus Activity and Is Predictive of Relapses After Treatment With Rituximab

Introduction

We studied the distribution and in vitro pathogenicity of anti-DSG3 IgG subclasses during the course of pemphigus vulgaris (PV).

Methods

We longitudinally studied the distribution of anti-DSG3 IgG subclasses (before versus after treatment) in sera from PV patients, using an addressable-laser bead immunoassay (ALBIA). The in vitro pathogenicity of corresponding sera was tested using keratinocyte dissociation and immunofluorescence assays.

Results

Sixty-five sera were assessed at baseline (33 from patients treated with rituximab and 32 with corticosteroids). Sixty-three percent of these baseline sera contained 2 or more anti-DSG3 IgG subclasses versus 35.7% of sera from patients in complete remission (CR) and 75.0% of sera from patients with persistent disease activity after treatment. IgG4 was the most frequently detected anti-DSG3 IgG subclass, both in patients with disease activity and in those in CR. The presence of three or more anti-DSG3 IgG subclasses was predictive of relapse, in particular when it included IgG3, with a positive predictive value of 62.5% and a negative predictive value of 92%. While anti-DSG3 IgG4 Abs from sera collected before treatment were most often pathogenic, anti-DSG3 IgG4 from sera collected after treatment were pathogenic only after adjusting their titer to the one measured before treatment. The IgG3 fraction containing anti-DSG3 Abs also had an in vitro pathogenic effect. The disappearance of the pathogenic effect of some sera after removal of anti-DSG3 IgG3 suggested an additional effect of this IgG subclass.

Conclusion

The serum levels and number of anti-DSG3 IgG subclasses drive the pathogenic effect of pemphigus sera and may predict the occurrence of relapses.

Utility of IgG4 immunohistochemistry detection in pemphigus diagnosis

Pemphigus includes a group of blistering autoimmune diseases that affect the skin and mucosa, characterized by the formation of epidermal bullous and the presence of antibodies against binding proteins. Pemphigus is classified according to clinical presentation, target molecule, and IgG production as pemphigus vulgaris, foliaceous, IgA-pemphigus, and paraneoplastic pemphigus. Thus, the identification of autoantibodies class and site of deposition is mandatory. The gold standard to identify the immune complex deposition is the direct immunofluorescences technique, performed in fresh tissue; unfortunately, this method is unavailable in the regional hospital at the Mexican provinces. Nevertheless, IgG subclass-4 is the prevalence of immunoglobulin in acantholysis. Therefore, this IgG subclass could be detected using IgG4 immunohistochemistry. Because direct immunofluorescences technique is absent in provinces or patients denied a new biopsy to confirm the diagnosis, this work presented pemphigus vulgaris confirmation using the IgG4 immunohistochemistry technique in patients with clinical lesions suggestive of pemphigus vulgaris and intraepidermal blister manifestation in histopathology.

Pemphigus patients with initial negative levels of anti- desmoglein; a subtype with different profile?

BACKGROUND

Pemphigus is a blistering autoimmune disease that is characterized by autoantibodies against desmoglins (Dsg), including anti-Dsg1 and anti-Dsg3. Despite the diagnosis of diseases, the anti-Dsg test by Enzyme-linked immunosorbent assay (ELISA) is negative in a small group of pemphigus patients. The aim of this study was to evaluate the clinical course, clinical symptoms, and response to treatment in pemphigus patients with negative levels of anti-Dsg1 and anti-Dsg3.

METHODS

In this study, the data of pemphigus patients referred to Razi Hospital were retrospectively collected from the medical records from 2016 to 2020. Eight patients, whose initial anti-Dsg1/anti-Dsg3 was negative by the ELISA test, were enrolled and their clinical course, clinical signs, and response to treatment were evaluated.

RESULTS

The mean age of the subjects (8 females) was 38.75±12.09. The most common phenotype of the subjects was pemphigus vulgaris (PV) with mucosal involvement. Additionally, the common site of blister inception was mouth of the patients. The mean prednisolone dose received by the patients at the initiation was 32.5±13.62 mg/day. According to Pemphigus Disease Area Index (PDAI), 6 patients had mild severity, wile 2 cases had moderate severity. Among the patients, 6 subjects received rituximab (RTX). Also, 5 patients experienced remission after 6.2±5.21 months.

CONCLUSION

PV is the most common phenotype of the disease and mucosal involvement is more common in patients with negative anti-Dsg-1/3 results. The severity of the lesions in most of the patients is mild at baseline and most patients seems to respond to RTX therapy and reach remission.

Conceptualization and validation of an innovative direct immunofluorescence technique utilizing fluorescein conjugate against IgG + IgG4 for routinely diagnosing autoimmune bullous dermatoses

Introduction

Autoimmune bullous diseases (ABDs) are potentially life-threatening mucocutaneous illnesses that require diagnosis with direct immunofluorescence (DIF). In this study we compared the diagnostic accuracy of traditional DIF (DIFt; separate immunoglobulin (Ig) G, IgG1, IgG4, IgA, IgM and C3 deposits detection) and modified DIF (DIFm; simultaneous IgG + IgG4 deposits detection instead of separate IgG and IgG4 deposits detection) in routine diagnostics of ABDs.

Material and methods

Eighteen patients with ABDs (7 with pemphigus dermatoses and 11 with subepithelial ABDs) were evaluated with DIFt and DIFm.

Results

The agreement of detectability of IgG immunoreactants was obtained in 16 ABD cases (88.89%), as positive results in both DIFt and DIFm were obtained in 13 cases and negative results in both DIFt and DIFm were obtained in 3 cases. One ABD case (Brunsting-Perry pemphigoid) (5.56%) was negative in DIFm with a positive DIFt result (IgG1 deposits). One ABD case (bullous pemphigoid) (5.56%) had only C3 deposits in DIFt with a positive DIFm reading (IgG + IgG4 deposits). A statistically significant relationship (p = 0.0186) between DIFm and DIFt results was revealed using Fisher’s exact test.

Conclusions

Both DIFt and DIFm are useful methods to detect deposition of IgG immunoreactants, but it seems that the innovative DIFm method slightly increases the detectability of IgG/IgG4 immunoreactants in relation to DIFt. The introduction of DIFm into routine laboratory diagnostics of ABDs seems to be justified, as it enables the abandonment of separate FITC conjugates for IgG and IgG4, which is important for cost-effectiveness.

Longitudinal Pathogenic Properties and N-Glycosylation Profile of Antibodies from Patients with Pemphigus after Corticosteroid Treatment

Pemphigus vulgaris is an autoimmune disease that occurs due to pathogenic autoantibodies that recognize the following epidermal adhesion proteins: desmogleins. Systemic corticosteroids usually decrease the titers of anti-desmoglein autoantibodies and improve patients’ conditions. Since modifications of IgG N-glycosylation have been described in some autoimmune diseases, we hypothesized that changes in the pathogenic activity of pemphigus IgG could be related to changes in their N-glycosylation profile. The purpose of this study was to assess, longitudinally, the pathogenicity of pemphigus serum IgG and their N-glycosylation profile during phases of disease activity and clinical remission. The pathogenic activity of serum IgG was measured in vitro on immortalized keratinocytes, by immunofluorescence and dissociation assays, and IgG N-glycans were analyzed by mass spectrometry. We showed (i) a correlation between pemphigus clinical activity and the pathogenicity of serum IgG at baseline and at month 6, while the persistence of the in vitro pathogenic activity of IgG during its evolution, even in patients in clinical remission, seemed to be predictive of relapse; (ii) that modifications of the N-glycan structure were altered the in vitro pathogenicity of patients’ autoantibodies; (iii) that the pathogenic properties of pemphigus IgG did not appear to be related to the disparity in IgG N-glycans during the course of pemphigus.

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.

Therapy of autoimmune mouth bullous disease: 2020 review

Most diseases of oral mucosa are either autoimmune in nature or are the results of immunologically mediated events. The diseases with autoimmune pathogenesis are namely pemphigus and pemphigoid; the oral involvement is frequent or regularly observed in these diseases. The treatments with traditional drugs or biologic agents or combinations of these molecules are employed in clinical practice. New therapeutic targets aim to provide new treatment strategies that may go beyond nonspecific immunosuppression.

The pathogenesis of bullous skin diseases

Bullous skin diseases are a group of dermatoses characterized by blisters and bullae in the skin and mucous membranes. The etiology and pathogenesis of bullous skin diseases are not completely clear. The most common are pemphigus and bullous pemphigoid (BP). Autoantibodies play critical roles in their pathogenesis. Abnormalities in the adhesion between keratinocytes in patients with pemphigus leads to acantholysis and formation of intra-epidermal blisters. Anti-desmoglein autoantibodies are present both in the circulation and skin lesions of patients with pemphigus. The deficient adhesion of keratinocytes to the basement membrane in BP patients gives rise to subepidermal blisters. Autoantibodies against the components of hemidesmosome can be detected in BP patients. Many novel therapeutics based on knowledge of the pathogenesis have emerged in recent years.

Immunohistochemistry for Immunoglobulin G4 in the Diagnosis of Pemphigus

Introduction

Pemphigus comprises of a group of autoimmune bullous disorders with intraepithelial lesions involving the skin and mucous membranes. Pemphigus is characterized histologically by an intraepidermal blister and immunopathologically by the finding of in vivo bound immunoglobulin G (IgG) antibodies against desmosomal adhesion proteins on the surface of keratinocytes. Indirect immunofluorescence for IgG is considered as a gold standard method for diagnosis of this group of bullous disorders on the condition that fresh frozen tissue is accessible.

Aim

We designed a new diagnostic method by immunohistochemistry (IHC) for IgG4 on paraffin sections instead of fresh frozen tissue and evaluated sensitivity, specificity, and positive and negative predictive values of this method.

Materials and Methods

We searched our pathologic archive of pemphigus of 35 patients, including 29 cases of pemphigus vulgaris (PV) and 6 patients with pemphigus foliaceus (PF). In all cases, the diagnosis was confirmed by indirect immunofluorescence studies. Thirty-five specimens served as controls, including 31 specimens of safe margins of basal cell carcinoma and 4 specimens of normal skin. Sections with condensed and continuous immunoreactivity localized to the intercellular junctions of keratinocytes were considered as positive.

Results

Sensitivity of IgG4 was estimated to be 72.4% in PV group and 83.3% in PF group. The overall sensitivity and specificity of IgG4 IHC for diagnosis of pemphigus were 74.2% and 82.8%, respectively, in PV and PF groups. Furthermore, positive predictive value and negative predictive value were 81.2% and 76.3%, respectively.

Conclusion

Immunohistochemical labeling for IgG4 on paraffin-embedded tissue provides a sensitive and specific test for diagnosing pemphigus in a situation when fresh frozen tissue is unavailable.

The Usefulness of Indirect Immunofluorescence in Pemphigus and the Natural History of Patients With Initial False-Positive Results: A Retrospective Cohort Study

The specificity and the predictive values of indirect immunofluorescence (IIF) in real-life settings is yet to be firmly established. The natural history of patients with false-positive results has not been sufficiently elucidated. The primary aim of the current study is to evaluate the diagnostic value of IIF analysis on monkey esophagus in pemphigus, utilizing a large cohort arising from the real-life experience of a tertiary referral center. The secondary endpoint was to determine the clinical outcomes of patients with false-positive results. This was a retrospective cohort study including all patients who were tested for the presence of intercellular autoantibodies by IIF on monkey esophagus between 2000 and 2017. Overall, 770 sera from different individuals were tested by IIF microscopy. Of those, 176 patients had been diagnosed with pemphigus vulgaris (PV) and 29 patients with pemphigus foliaceus (PF). The sensitivity of this immunoassay was significantly higher for the diagnosis of PV (87.4%; 95% CI, 81.5-91.9%) as compared to PF (69.0%; 95% CI, 49.2-84.7%; P = 0.018). The specificity for the diagnosis of pemphigus was 93.5% (95% CI, 91.1-95.4%). Patients with false-positive results (n = 37) were followed for a median duration of 5.3 years contributing 280.8 person-years. Thirty patients (81.1%) were eventually diagnosed clinically and immunopathologically with subepidermal autoimmune bullous diseases, whereas the remaining patients (18.9%) were diagnosed clinically and histologically with other inflammatory dermatoses, but none of them developed pemphigus during the follow-up duration. Of note, 7.0% (n = 23) of all patients diagnosed with bullous pemphigoid (BP) in the same period (n = 328) were tested positive for IgG intercellular antibodies. Histopathological review of the biopsy specimens of these patients did not reveal acantholysis. In conclusion, the predictive value of negative test in IIF on monkey esophagus is particularly reliable to exclude a diagnosis of pemphigus. Individuals tested positive for intercellular antibodies without an initial overt pemphigus did not show an increased risk for developing pemphigus subsequently. A sizable fraction of patients with BP showed circulating intercellular autoantibodies by IIF, without a histopathological evidence for acantholysis.

The Genetics of Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune blistering disease caused by auto-antibodies (auto-Abs) directed against epithelial desmosomal components and leading to disruption of cell-cell adhesion. The exact mechanisms underlying the disease pathogenesis remain unknown and treatment is still based on immunosuppressive drugs, such as corticosteroids, which are associated with potentially significant side effects. Ethnic susceptibility, familial occurrence, and autoimmune comorbidity, suggest a genetic component to the pathogenesis of the disease, which, if discovered, could advance our understanding of PV pathogenesis and thereby point to novel therapeutic targets for this life-threatening disorder. In this article, we review the evidence for a genetic basis of PV, summarize the different approaches used to investigate susceptibility traits for the disease and describe past and recent discoveries regarding genes associated with PV, most of which belong to the human leukocyte antigen (HLA) locus with limited data regarding association of non-HLA genes with the disease.

Monopathogenic vs multipathogenic explanations of pemphigus pathophysiology

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

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.

IgG4 autoantibodies against muscle-specific kinase undergo Fab-arm exchange in myasthenia gravis patients

Autoimmunity mediated by IgG4 subclass autoantibodies is an expanding field of research. Due to their structural characteristics a key feature of IgG4 antibodies is the ability to exchange Fab-arms with other, unrelated, IgG4 molecules, making the IgG4 molecule potentially monovalent for the specific antigen. However, whether those disease-associated antigen-specific IgG4 are mono- or divalent for their antigens is unknown. Myasthenia gravis (MG) with antibodies to muscle specific kinase (MuSK-MG) is a well-recognized disease in which the predominant pathogenic IgG4 antibody binds to extracellular epitopes on MuSK at the neuromuscular junction; this inhibits a pathway that clusters the acetylcholine (neurotransmitter) receptors and leads to failure of neuromuscular transmission. In vitro Fab-arm exchange-inducing conditions were applied to MuSK antibodies in sera, purified IgG4 and IgG1-3 sub-fractions. Solid-phase cross-linking assays were established to determine the extent of pre-existing and inducible Fab-arm exchange. Functional effects of the resulting populations of IgG4 antibodies were determined by measuring inhibition of agrin-induced AChR clustering in C2C12 cells. To confirm the results, κ/κ, λ/λ and hybrid κ/λ IgG4s were isolated and tested for MuSK antibodies. At least fifty percent of patients had IgG4, but not IgG1-3, MuSK antibodies that could undergo Fab-arm exchange in vitro under reducing conditions. Also MuSK antibodies were found in vivo that were divalent (monospecific for MuSK). Fab-arm exchange with normal human IgG4 did not prevent the inhibitory effect of serum derived MuSK antibodies on AChR clustering in C2C12 mouse myotubes. The results suggest that a considerable proportion of MuSK IgG4 could already be Fab-arm exchanged in vivo. This was confirmed by isolating endogenous IgG4 MuSK antibodies containing both κ and λ light chains, i.e. hybrid IgG4 molecules. These new findings demonstrate that Fab-arm exchanged antibodies are pathogenic.

Tannic Acid Induces in vitro Acantholysis of Keratinocytes via IL-1α and TNF-α

The mechanism of acantholysis in pemphigus vulgaris (PV) is an intriguing argument since several chemical mediators are implicated. We previously reported a central role for IL-1α and TNF-α, both able to regulate complement activation and plasminogen activators. Very little is known about what triggers the disease (drugs, viruses or food). In this study, we evaluate the molecular role of tannins in acantholysis. By HPLC chromatography we measured tannic acid (TA) and gallic acid (GA) in blister fluid of 4 groups of patients divided according to their dietary habits, including a regular diet, a diet rich in tannins, a diet free of tannins, and a group of pemphigus patients. Blister fluid was obtained from patients using a suction blister apparatus. We show that people with a diet rich in tannins have increased tannin metabolites (TA and GA) in the skin in respect to controls (tannin-rich diet: GA = 194.52±2.39 nmol/ml; TA = 348.28±1.4 nmol/ml versus tannin-Mediterranean diet: GA = 15.28±1.63 nmol/ml; TA = 22.81±1.68 nmol/ml). PV patients showed similar values to the Mediterranean diet population (PV patients: GA = 95.8±1.97 nmol/ml; TA = 199.09±4.15 nmol/ml versus Mediterranean diet: GA = 83.53±2.35 nmol/ml; TA = 195.1±2.50 nmol/ml). In an in vitro acantholysis system using TA and PV-IgG we show that TA 0.1 mM in NHEK culture is able to induce acantholysis. This effect was able to amplify the acantholytic action of PV-IgG in vitro. A blocking study using anti IL-1α and anti TNF-α antibodies showed a reduction in TA-induced acantholysis. Taken together, these results suggest that a diet rich in tannins could be a trigger in genetically predisposed patients. If these data are confirmed, a complementary diet poor in tannins may be useful in patients affected by PV.

Pathogenicity and Epitope Characteristics Do Not Differ in IgG Subclass-Switched Anti-Desmoglein 3 IgG1 and IgG4 Autoantibodies in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is characterized by IgG1 and IgG4 autoantibodies to desmoglein (Dsg) 3, causing suprabasal blistering of skin and mucous membranes. IgG4 is the dominant autoantibody subclass in PV and correlates with disease activity, whereas IgG1 can be associated with remittent disease. It is unknown if switching the same variable region between IgG4 and IgG1 directly impacts pathogenicity. Here, we tested whether three pathogenic PV monoclonal antibodies (mAbs) from three different patients demonstrate differences in antigen affinity, epitope specificity, or pathogenicity when expressed as IgG1 or IgG4. F706 anti-Dsg3 IgG4 and F779 anti-Dsg3 IgG1, previously isolated as heterohybridomas, and Px43, a monovalent anti-Dsg3/Dsg1 IgG antibody isolated by phage display, were subcloned to obtain paired sets of IgG1 and IgG4 mAbs. Using ELISA and cell surface staining assays, F706 and F779 demonstrated similar antigen binding affinities of IgG1 and IgG4, whereas Px43 showed 3- to 8-fold higher affinity of IgG4 versus IgG1 by ELISA, but identical binding affinities to human skin, perhaps due to targeting of a quaternary epitope best displayed in tissues. All 3 mAb pairs targeted the same extracellular cadherin (EC) domain on Dsg3, caused Dsg3 internalization in primary human keratinocytes, and caused suprabasal blisters in human skin at comparable doses. We conclude that switching IgG1 and IgG4 subclasses of pathogenic PV mAbs does not directly affect their antigen binding or pathogenic properties.

Identification of a Functional Risk Variant for Pemphigus Vulgaris in the ST18 Gene

Pemphigus vulgaris (PV) is a life-threatening autoimmune mucocutaneous blistering disease caused by disruption of intercellular adhesion due to auto-antibodies directed against epithelial components. Treatment is limited to immunosuppressive agents, which are associated with serious adverse effects. The propensity to develop the disease is in part genetically determined. We therefore reasoned that the delineation of PV genetic basis may point to novel therapeutic strategies. Using a genome-wide association approach, we recently found that genetic variants in the vicinity of the ST18 gene confer a significant risk for the disease. Here, using targeted deep sequencing, we identified a PV-associated variant residing within the ST18 promoter region (p<0.0002; odds ratio = 2.03). This variant was found to drive increased gene transcription in a p53/p63-dependent manner, which may explain the fact that ST18 is up-regulated in the skin of PV patients. We then discovered that when overexpressed, ST18 stimulates PV serum-induced secretion of key inflammatory molecules and contributes to PV serum-induced disruption of keratinocyte cell-cell adhesion, two processes previously implicated in the pathogenesis of PV. Thus, the present findings indicate that ST18 may play a direct role in PV and consequently represents a potential target for the treatment of this disease.

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.

Pemphigus vulgaris is characterized by low IgG reactivities to specific self-antigens along with high IgG reactivity to desmoglein 3

Pemphigus vulgaris (PV) is an autoimmune skin disease, which has been characterized by IgG autoantibodies to desmoglein 3. Here we studied the antibody signatures of PV patients compared with healthy subjects and with patients with two other autoimmune diseases with skin manifestations (systemic lupus erythematosus and scleroderma), using an antigen microarray and informatics analysis. We now report a previously unobserved phenomenon--patients with PV, compared with the healthy subjects and the two other diseases, show a significant decrease in IgG autoantibodies to a specific set of self-antigens. This novel finding demonstrates that an autoimmune disease may be associated with a loss of specific, healthy IgG autoantibodies and not only with a gain of specific, pathogenic IgG autoantibodies.

Pemphigus vulgaris autoantibody profiling by proteomic technique

Pemphigus vulgaris (PV) is a mucocutaneous blistering disease characterized by IgG autoantibodies against the stratified squamous epithelium. Current understanding of PV pathophysiology does not explain the mechanism of acantholysis in patients lacking desmoglein antibodies, which justifies a search for novel targets of pemphigus autoimmunity. We tested 264 pemphigus and 138 normal control sera on the multiplexed protein array platform containing 701 human genes encompassing many known keratinocyte cell-surface molecules and members of protein families targeted by organ-non-specific PV antibodies. The top 10 antigens recognized by the majority of test patients’ sera were proteins encoded by the DSC1, DSC3, ATP2C1, PKP3, CHRM3, COL21A1, ANXA8L1, CD88 and CHRNE genes. The most common combinations of target antigens included at least one of the adhesion molecules DSC1, DSC3 or PKP3 and/or the acetylcholine receptor CHRM3 or CHRNE with or without the MHC class II antigen DRA. To identify the PV antibodies most specific to the disease process, we sorted the data based on the ratio of patient to control frequencies of antigen recognition. The frequency of antigen recognition by patients that exceeded that of control by 10 and more times were the molecules encoded by the CD33, GP1BA, CHRND, SLC36A4, CD1B, CD32, CDH8, CDH9, PMP22 and HLA-E genes as well as mitochondrial proteins encoded by the NDUFS1, CYB5B, SOD2, PDHA1 and FH genes. The highest specificity to PV showed combinations of autoantibodies to the calcium pump encoded by ATP2C1 with C5a receptor plus DSC1 or DSC3 or HLA-DRA. The results identified new targets of pemphigus autoimmunity. Novel autoantibody signatures may help explain individual variations in disease severity and treatment response, and serve as sensitive and specific biomarkers for new diagnostic assays in PV patients.

Immunohistochemistry for Immunoglobulin G4 on Paraffin Sections for the Diagnosis of Pemphigus

Context.—Pemphigus is a group of autoimmune vesiculobullous diseases characterized by immunoglobulin G (IgG) antibodies directed against desmosomal adhesion proteins, with IgG4 being the predominant subclass in active diseases. Direct immunofluorescence for IgG performed on fresh-frozen tissue plays a crucial role in diagnosing pemphigus. However, the diagnosis might be hindered when frozen tissue is not available.

Objective.—To evaluate the usefulness of immunohistochemistry for IgG4 performed on paraffin sections as a diagnostic test for pemphigus.

Design.—Eighteen immunofluorescence-proven pemphigus cases (12 pemphigus vulgaris, 6 pemphigus foliaceus) were studied. Four normal skin specimens and 32 nonpemphigus vesiculobullous disease specimens served as controls. Paraffin sections of all cases were examined immunohistochemically for IgG4 expression. Positivity was defined as distinct, condensed, continuous immunoreactivity localized to the intercellular junctions of keratinocytes.

Results.—The immunostains were independently evaluated in a masked manner by 3 pathologists, with a 100% interobserver agreement. Nine of 12 pemphigus vulgaris cases (sensitivity 75.0%), and 4 of 6 pemphigus foliaceus cases (sensitivity 66.7%), were positive for IgG4 immunostain. The overall sensitivity was 72.2%. One control specimen (bullous pemphigoid) showed IgG4 positivity (specificity 97.2%). In specimens demonstrating acantholysis, 8 of 10 pemphigus vulgaris cases (sensitivity 80.0%) and 4 of 4 pemphigus foliaceus cases (sensitivity 100.0%) were positive for IgG4. The overall sensitivity for specimens with acantholytic lesions was 85.7%.

Conclusion.—Immunohistochemistry for IgG4 provides a reasonably sensitive and highly specific test for diagnosing pemphigus, especially when frozen tissue is not available, and active acantholytic lesions are examined.

Enrichment of total serum IgG4 in patients with pemphigus

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Specific immunoglobulin isotypes correlate with disease activity, morphology, duration and HLA association in Pemphigus vulgaris

The molecular basis of disease heterogeneity in autoimmune conditions such as Pemphigus vulgaris is poorly understood. Although desmoglein 3 (Dsg3) has been well established as a primary target of immunoglobulin (Ig) autoantibodies in PV, there remain several questions regarding the overall distribution of anti-Dsg3 Ig subtypes among patient subsets and considerable controversy regarding whether an isotype switch can be observed between phases of disease activity. To systematically address the outstanding questions related to Ig-isotype specificity in PV, we analyzed IgA, IgM, IgG1, 2, 3 and 4 anti-Dsg3 levels by ELISA in 202 serum samples obtained from 92 patients with distinct clinical profiles based on a set of defined variable (activity, morphology, age, duration) and constant (HLA-type, gender, age of onset) clinical parameters, and 47 serum samples from HLA-matched and -unmatched controls. Our findings provide support for earlier studies identifying IgG4 and IgG1 as the predominant antibodies in PV with significantly higher levels in active than remittent patients. We do not see evidence for an isotype switch between phases of disease activity and remission, and both IgG4 and IgG1 subtypes remain elevated in remittent patients relative to controls. We do, however, find IgG4 to be the sole subtype that further distinguishes PV patient subgroups based on different disease morphologies, disease duration, and HLA-types. These data provide further insight into the immune mechanisms responsible for phenotypic expression of disease, and contribute to the broader effort to establish comprehensive immunoprofiles underlying disease heterogeneity to facilitate increasingly specific and individualized therapeutic interventions.

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.

Pathogenic activity of circulating anti-desmoglein-3 autoantibodies isolated from pemphigus vulgaris patients

INTRODUCTION

There are scarce data on immunochemical properties of pemphigus antibodies detected in clinical remission in pemphigus vulgaris (PV) patients. The aim of the study was to compare biological activity of anti-Dsg3 autoantibodies purified from the sera of PV patients in active stage and in clinical remission.

MATERIAL AND METHODS

The effect of purified antibodies on expression of procaspase-3, Bax, Bcl-2, uPAR, IL-1β, IL-6, and TNF-α mRNAs in the HaCaT keratinocytes was evaluated by Western blot and RT-PCR method.

RESULTS

Incubation of HaCaT cells with anti-Dsg-3 autoantibodies caused their binding to cell membranes surfaces. Anti-Dsg3 autoantibodies isolated from the patients in active stage and clinical remission showed proapoptotic effect, caused enhanced expression of analyzed proinflammatory cytokines' mRNAs and uPAR mRNA.

CONCLUSIONS

Our data revealed similar pathogenic activity of anti Dsg-3 autoantibodies isolated from active and clinical remission PV patients.

Urban legends: pemphigus vulgaris

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

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.

Diagnosis and clinical features of pemphigus vulgaris

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

Constructing immunoprofiles to deconstruct disease complexity in pemphigus

The complex etiology of multifactorial diseases such as pemphigus vulgaris complicates mechanistic investigations and confounds current therapeutic approaches. Two major sources contribute to the overall complexity of disease. Biological complexity involves the disruption of multiple immune pathways that underlie autoimmune destruction in the skin. Overlaying this altered immunobiology is clinical complexity that is manifest as heterogeneous presentations of disease. Merging cumulative data on immune dysfunction with the detailed clinical information can be expected to allow the deconstruction of the processes that lead to specific disease presentations. Our group has undertaken comprehensive analyses in stratified patient populations to assign T cell, cytokine, and autoantibody immunoprofiles linked to defined constant and variable clinical parameters. We propose the concept of a "disease array" that is based on a matrix of supporting biological and clinical information that can be used to guide the development of next-generational tools that enhance our ability to diagnose, prognose, and individually treat disease.

Autoimmune oral mucosal diseases: clinical, etiologic, diagnostic, and treatment considerations

This article discusses the classic autoimmune diseases: pemphigus vulgaris, mucosal pemphigoid, and oral lichen planus. These are generally considered of autoimmune origin or, at a minimum, immune system mediated. Cause, diagnosis, and treatment are discussed. As management of these diseases progresses, continued advances in molecular pathogenesis will allow insight into which strategies can be employed in interfering with the complex cascade of events leading to mucosal impairment and clinical morbidity.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Advances in pemphigus and its endemic pemphigus foliaceus (Fogo Selvagem) phenotype: a paradigm of human autoimmunity

Pemphigus encompasses a group of organ specific, antibody mediated autoimmune diseases of the skin characterized by keratinocyte detachment that leads to the development of blisters and erosions, which can become life-threatening. The pathogenic autoantibodies recognize desmogleins, which are members of the desmosomal cadherin family of cell adhesion molecules. Desmoglein 3 is targeted in pemphigus vulgaris while desmoglein 1 is targeted in pemphigus foliaceus and its endemic form, Fogo Selvagem. This review will briefly define the salient features of pemphigus and the proposed steps in pathogenesis. We will then summarize the most recent advances in three important areas of investigation: (i) epidemiologic, genetic, and immunologic features of Fogo Selvagem, (ii) molecular mechanisms of injury to the epidermis, and (iii) novel therapeutic strategies targeting specific steps in disease pathogenesis. The advances in each of these three seemingly separate areas contribute to the overall understanding of the pemphigus disease model. These recent advancements also underscore the dynamic interplay between the treatment of patients in a clinical setting and basic science research and have led to an integrative understanding of disease pathogenesis and treatment, allowing pemphigus to serve as a paradigm of human autoimmunity.

Oral mucosal disease: Pemphigus

Pemphigus defines a group of rare mucocutaneous autoimmune diseases of which pemphigus vulgaris (PV) is the most common. The aetiology and pathogenesis of PV are not completely clear, but there is a fairly strong genetic background: ethnic groups such as Ashkenazi Jews and people of Mediterranean and Indian origin are particularly susceptible and there is a link to HLA class II alleles. The initiating event in PV is not clear, but circulating IgG autoantibodies develop, directed particularly against the intercellular cadherin desmoglein 3 (Dsg3) in desmosomes of stratified squamous epithelium. Oral lesions often herald the disease and are initially vesiculobullous, but they rupture readily to leave ulcers. Involvement of other mucosa and skin is almost inevitable and PV is potentially life threatening. The diagnosis is confirmed by biopsy with histological examination and immunostaining. Management is largely by systemic immunosuppression with corticosteroids, usually azathioprine or other agents, but newer treatments with potentially fewer adverse effects look promising.

A perspective of pemphigus from bedside and laboratory-bench

Pemphigus represents a distinct organ-specific acquired autoimmune disease characterized by intra-epidermal blistering, which is induced by autoantibodies against desmosomal cadherins, desmoglein 1 (Dsg1), and Dsg3. Pemphigus is currently divided into three distinct varieties, i.e., pemphigus vulgaris (PV), pemphigus foliaceus (PF) and other variants of pemphigus (mostly associated with inflammation), depending on clinical features, the level of separation in the epidermis, and immunologic characteristics of auto-antigens. Blistering pathomechanisms differ for each of the types of pemphigus. Pemphigus, which results from autoantibodies against desmogleins and possibly to other proteins, binds to the cell surface antigens. This binding may cause steric hindrance to homophilic adhesion of desmogleins, and may, in turn, lead to internalization of desmogleins and inhibition of desmogleins' integration into desmosomes, resulting in the formation of Dsg3-depleted desmosomes in PV or Dsg1-depleted desmosomes in PF. Furthermore, PV-IgG activates an "outside-in" signaling pathway to induce disassembly of desmosomal components from the inside of the cells by phosphorylation of proteins, including Dsg3. On the other hand, Pemphigus-IgG-augmented signaling pathways may be linked to the secretion of cytokines such as in case of pemphigus herpetiformis and chemokines that initiate or activate inflammation. In this article, the classification of pemphigus and the characteristic pathomechanisms for acantholysis will be reviewed, with particular emphasis on the molecular and biochemical cell biology of these diseases.

What's new in blistering disorders?

From the characterization of new animal models for the study of disease pathogenesis, to the demonstration of new therapeutic modalities, many developments have revolutionized the field of autoimmune bullous diseases in the past several years. This review highlights many of the significant advances that have taken place in the diagnosis, pathogenesis, and treatment options for pemphigus, pemphigoid, epidermolysis bullosa acquisita, and immunoglobulin (Ig) A-mediated bullous disorders.

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

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

Circulating pemphigus autoantibodies in healthy relatives of pemphigus patients: coincidental phenomenon with a risk of disease development?

Pemphigus is a severe autoimmune disease characterized by circulating and bound in vivo pemphigus autoantibodies. It was revealed that the autoantibodies occur in healthy first-degree relatives of pemphigus patients; however, their significance is not fully elucidated. Thus, the aim of the study was to assess the frequency of circulating IgG pemphigus autoantibodies in the healthy relatives of pemphigus patients and of their ability to bind in vivo in the epidermis. We also analyzed IgG subclasses distribution, both in the serum-positive relatives and in the patients. Our study included 67 healthy relatives, 50 healthy normal controls and 33 patients (25 at an active stage of the disease, 8 in clinical remission). To detect circulating pemphigus antibodies we applied indirect immunofluorescence and anti-desmoglein ELISA. Monoclonal anti-human IgG1, IgG2, IgG3, IgG4 antibodies were used to assess subclass distribution. The frequency of circulating pemphigus autoantibodies in the relatives, detected by IIF (30/67) was statistically higher (P < 0.001) than in the control group (0/50). ELISA revealed anti-desmoglein 1 and/or 3 antibodies in 13 out of 67 relatives. Direct immunofluorescence performed in 25 out of 32 seropositive relatives did not show intercellular bound in vivo IgG and/or C3 in the epidermis in any cases. Circulating IgG2 subclass was observed in 60% of the examined relatives and IgG4 was detected in 23.3% of them. In the patients at an active stage of pemphigus IgG4 and IgG1 were the dominant subclasses (96 and 76% relatively) while in clinical remission antibodies predominantly belonged to the IgG2 (75%) and IgG4 (37.5%) subclass. The obtained results confirmed polyclonal production of pemphigus autoantibodies and their different distributions dependent on the disease activity. Statistical analysis showed that the frequency of IgG1 and IgG4 subclasses was significantly higher in the patients at an active stage of the disease when compared to the patients in clinical remission (P < 0.001) or with seropositive healthy relatives (P < 0.001). The relevance of the presence of IgG4 autoantibodies in the healthy relatives' sera requires further studies that focus on their potential pathogenicity.