Neonatal Autoimmune Blistering Disease: A Systematic Review

S2k guidelines on diagnosis and treatment of linear IgA dermatosis initiated by the European Academy of Dermatology and Venereology

INTRODUCTION

Linear IgA dermatosis (LAD) is a rare subepidermal autoimmune bullous disease (AIBD) defined by predominant or exclusive immune deposits of immunoglobulin A at the basement membrane zone of skin or mucous membranes. This disorder is a rare, clinically and immunologically heterogeneous disease occurring both in children and in adults. The aim of this project is to present the main clinical features of LAD, to propose a diagnostic algorithm and provide management guidelines based primarily on experts' opinion because of the lack of large methodologically sound clinical studies.

METHODS

These guidelines were initiated by the European Academy of Dermatology and Venereology (EADV) Task Force Autoimmune Bullous Diseases (AIBD). To achieve a broad consensus for these S2k consensus-based guidelines, a total of 29 experts from different countries, both European and non-European, including dermatologists, paediatric dermatologists and paediatricians were invited. All members of the guidelines committee agreed to develop consensus-based (S2k) guidelines. Prior to a first virtual consensus meeting, each of the invited authors elaborated a section of the present guidelines focusing on a selected topic, based on the relevant literature. All drafts were circulated among members of the writing group, and recommendations were discussed and voted during two hybrid consensus meetings.

RESULTS

The guidelines summarizes evidence-based and expert opinion-based recommendations (S2 level) on the diagnosis and treatment of LAD.

CONCLUSION

These guidelines will support dermatologists to improve their knowledge on the diagnosis and management of LAD.

Autoimmune bullous diseases in pregnancy: an overview of pathogenesis, clinical presentations, diagnostics and available therapies

Autoimmune bullous diseases (AIBDs) are rare organ-specific diseases characterized by the appearance of blisters and erosions on the skin and mucous membranes. These dermatoses are marked by the development of autoantibodies targeting the autoantigens located in intercellular junctions, i.e., between keratinocytes or in the basement membrane area. Therefore, the fundamental division of AIBDs into the pemphigus and pemphigoid groups exists. Although AIBDs are uncommon in the general population, their overall incidence is somewhat higher in women of all ages, for which a pregnant women can be likely affected too. While the pemphigoid gestationis is exclusive bullous dermatosis of pregnancy, the other AIBDs can also start or worsen during this period. The appearance of AIBDs in childbearing women is a particularly sensitive situation requiring exceptional clinicians' caution due to the possibility of pregnancy complications with adverse effects and risks to the mother and the child. Also, there are numerous management difficulties in the period of pregnancy and lactation related to the drugs' choice and safety. This paper aimed to outline the pathophysiologic mechanisms, clinical manifestations, diagnostic approach and therapy of the most commonly recognized AIBDs in pregnancy.

Linear Immunoglobulin A Dermatosis: A Rare Case Illustrating Successful Treatment With Dapsone

This is the case report of a previously healthy four-year-old girl with a history of upper airway infection that was treated with a β-lactam antibiotic. She was seen in the emergency department one month later with vesiculobullous lesions with clear content that were isolated or grouped in rosettes. Direct immunofluorescence showed baseline linear positivity for immunoglobulin A (IgA) (+) and fibrinogen-positive bullous content with absent remaining immunosera expression. The observed results were compatible with linear IgA bullous dermatosis. After confirming the diagnosis and excluding glucose-6-phosphate dehydrogenase (G6PD) deficiency, dapsone was added to the initial treatment with systemic and topical corticosteroids. This case report is a reminder of the importance of a high index of clinical suspicion for this condition to reach a timely diagnosis.

Acral blisters in neonates: Three rare and benign diseases

Exclusive acral involvement in neonatal pemphigus is unusual. Blisters in neonatal bullous pemphigoid, affecting 2%–3% of newborns of mothers with gestational pemphigoid, can be located in the trunk, limbs and acral areas. Unlike neonatal bullous pemphigoid, which can appear up to 5 days after birth, neonatal pemphigus is often revealed at birth. They are benign diseases in newborns. There is no correlation between the disease severity in babies and mothers. Neonatal risk is dominated by the side effects of corticosteroid therapy.

Pustular lesions in the neonate: Focused diagnostic approach based on clinical clues

Pustules in a neonate can be due to various causes. Though the majority of conditions causing pustules in a neonate are benign, it is essential to clearly differentiate these from serious ones. A systematic approach based on detailed history and clinical examination of the neonate along with basic laboratory evaluation narrows down diagnostic possibilities and aids in the correct diagnosis. This review outlines a step-by-step approach so as to avoid clinical dilemmas and unnecessary intervention.

Linear Immunoglobulin a Bullous Dermatosis in Children

Linear Immunoglobulin A Bullous Disease (LABD) is a rare dermatosis whose pathomechanisms are not yet completely understood. LABD has different features characterizing adults and children in terms of potential triggers, clinical manifestations, and prognosis. The aim of the present study is to review all neonatal and pediatric cases of LABD and summarize the major characteristics. Childhood LABD is mainly idiopathic with a benign prognosis. Neonatal cases are difficult to differentiate from infectious diseases and usually have a poor prognosis. Drugs are one of the possible triggers that can activate autoimmune responses through antigen mimicry and epitope spreading as well as different stimuli (e.g., infections, inflammatory diseases, trauma). The gold standard for the diagnosis is based on direct immunofluorescence. Prognosis is generally favorable but often depends on the prompt dermatological diagnosis, treatment and follow-up guaranteed by a multidisciplinary team, including pediatricians for this group of age.

A bullous rash

A 3-year-old boy presented with a 5-day history of bullous skin lesions localised mainly in the upper and lower limbs and in the genital region (figure 1). Lesions were not pruritic nor painful and showed a central crust. There was no family history of skin disorders or autoimmune diseases. The child never had fever and his physical examination was otherwise unremarkable.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

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

Neonatal pemphigoid gestationis: An atypical presentation of a rare disease

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by urticarial plaques and/or vesicles and tense bullae. A unique presentation of BP can occur during pregnancy, the postpartum period after delivery, or with the initiation of contraception, in which case it is referred to as pemphigoid gestationis (PG). In rare instances, newborns born to mothers with PG may also present with blisters due to transplacental passage of maternal anti-bullous pemphigoid 180 (BP180) or 230 (BP230) immunoglobulin G (IgG). In this report, we present an unusual case of neonatal PG in an infant born to an asymptomatic mother without a previous diagnosis of PG.

Neonatal Linear IgA Bullous Dermatosis Mediated by Breast Milk-Borne Maternal IgA

Importance

Neonatal linear immunoglobulin A (IgA) bullous dermatosis (LABD) is a rare disease that can be fatal when associated with respiratory failure. All previously reported cases of neonatal LABD have been in newborns with healthy asymptomatic mothers, and the pathogenic IgA was of unknown origin.

Objective

To clarify the origin of IgA associated with LABD in neonates born of healthy asymptomatic mothers.

Design, Setting, and Participants

This case study analyzed the laboratory findings of a single breast-fed newborn male with neonatal LABD admitted to the Keio University Hospital in Tokyo and his healthy asymptomatic mother. The healthy newborn developed life-threatening blisters and erosions of the skin and mucous membranes on day 4 after birth. Blood serum, skin, and maternal breast milk were examined for IgA autoantibodies.

Main Outcomes and Measures

Histopathologic and immunofluorescence analyses of specimens (serum, skin, and breast milk) from the patient and his mother.

Results

Histopathologic evaluation of the newborn's skin revealed subepidermal blisters with neutrophil infiltrates, and immunofluorescence testing showed linear IgA deposition along the basement membrane zone (BMZ), which lead to the diagnosis of neonatal LABD. Indirect immunofluorescence using normal human skin after treatment with 1-mol/L sodium chloride showed the patient to have circulating IgA binding to the dermal side of BMZ. Immunohistochemical staining proved the deposition of secretory IgA in the neonatal skin by demonstrating the presence of J chain-not been seen in other LABD cases-indicating that the autoantibodies producing the blisters were derived from the maternal breast milk. Although no circulating IgA against the skin was detected in mother's sera, the breast milk contained IgA that reacted with the dermal side of the BMZ. No new blister formation was observed after cessation of breastfeeding.

Conclusions and Relevance

The results of this case study suggest a passive transfer of pathogenic IgA to a newborn from an asymptomatic mother via breast milk. In prior reports, no serum from asymptomatic mothers of newborns with LABD had IgA autoantibodies binding to skin components; however, in this case, we found that the maternal breast milk contained IgA autoantibodies associated with neonatal LABD. In neonatal LABD, maternal breast milk should be examined for IgA autoantibodies and breast milk feeding should be discontinued as soon as neonatal LABD is suspected.

How to Deal with Skin Biopsy in an Infant with Blisters?

The onset of blisters in a neonate or an infant is often a source of great concern for both parents and physicians. A blistering rash can reveal a wide range of diseases with various backgrounds (infectious, genetic, autoimmune, drug-related, traumatic, etc.), so the challenge for the dermatologist and the pediatrician is to quickly determine the etiology, between benign causes and life-threatening disorders, for a better management of the patient. Clinical presentation can provide orientation for the diagnosis, but skin biopsy is often necessary in determining the cause of blister formations. In this article, we will provide information on the skin biopsy technique and discuss the clinical orientation in the case of a neonate or infant with a blistering eruption, with a focus on the histology for each etiology.

Clinicians' pearls and myths in pemphigus

Pemphigus comprises a heterogeneous group of autoimmune blistering diseases, which can affect both skin and mucous membranes, especially oral mucosa. This group of diseases shows usually a chronic-relapsing course. Since pemphigus is a rare disease, the diagnosis is often delayed, because it is based upon the recognition of consistent clinical, histologic, and direct immunofluorescence findings, as well as indirect immunofluorescence, and/or enzyme-linked immunosorbent assay. Usually the patients are treated for multiple other conditions before starting the correct therapy, leading to a critical reduction of the patients' quality of life. This review is a succinct compilation of pearls gathered from clinical experience in pemphigus and the myths that may have influenced everyday practice but have been proven false. This review provided a selection of such dilemmas and controversies, focusing on myths and pearls that can help young dermatologist in the clinic, while also dispelling them.

Treatment of Autoimmune Bullous Diseases During Pregnancy and Lactation: A Review Focusing on Pemphigus and Pemphigoid Gestationis

Pregnancy may induce the onset or exacerbation of autoimmune bullous diseases such as pemphigus or pemphigoid gestationis. A shift toward T helper (Th) 2 immune response and the influence of hormonal changes have been evoked as possible triggering factors. Therapeutic management of this setting of patients may represent a challenge, mainly due to safety concerns of some immunosuppressive drugs during pregnancy and lactation. In this narrative review, we provided a comprehensive overview of the therapeutic management of autoimmune bullous diseases in pregnant and breastfeeding women, focusing on pemphigus and pemphigoid gestationis.

Neonatal Autoimmune Subepidermal IgG/IgA Blistering Disease With Severe Laryngeal and Esophageal Involvement: A Report of a Case and Review of the Literature

Neonatal autoimmune subepidermal blistering disease is rare. Mucosal involvement is more common in neonatal linear immunoglobulin A (IgA) bullous dermatosis. We describe a neonate with subepidermal cutaneous blistering disease with severe laryngeal and esophageal involvement leading to acute respiratory distress. Histopathology demonstrated a subepidermal blister with neutrophils and eosinophils at the dermal base. Collagen IV was detected at the dermal floor, and direct immunofluorescence showed linear IgG, IgA, and C3 deposits at the basement membrane zone. The patient demonstrated markedly increased serum levels of anti-BP180 NC16A and anti-BP230 IgG antibodies (Abs) but failed to show anti-LAD-1 IgA Abs. His healthy mother showed serum anti-LAD-1 IgA Abs but did not show anti-BP180 and anti-BP230 Abs. The neonate responded promptly to systemic corticosteroid therapy. A review of the literature detected 11 cases of neonatal subepidermal blistering disease with linear IgA deposits. Nine of these cases demonstrated coexisting linear IgG deposits, often with C3. Respiratory compromise was present in most of the cases. Neutrophils and eosinophils were commonly present in the inflammatory cell infiltrates. Besides our case, 2 cases of neonatal IgG/IgA subepidermal blistering disease with esophageal involvement were previously described. IgA Abs were present in the sera of both cases. Anti-LAD-1 IgA Abs were detected in the mother's serum of our case alone, but IgA Abs do not cross the placenta. Our case was consistent with neonatal IgG/IgA pemphigoid. Neonatal IgG/IgA subepidermal blistering disease may be associated with severe laryngeal and esophageal involvement leading to respiratory compromise. Expedited diagnosis and prompt treatment are warranted.

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.

Benefits and Risks of IgG Transplacental Transfer

Maternal passage of immunoglobulin G (IgG) is an important passive mechanism for protecting the infant while the neonatal immune system is still immature and ineffective. IgG is the only antibody class capable of crossing the histological layers of the placenta by attaching to the neonatal Fc receptor expressed at the level of syncytiotrophoblasts, and it offers protection against neonatal infectious pathogens. In pregnant women with autoimmune or alloimmune disorders, or in those requiring certain types of biological therapy, transplacental passage of abnormal antibodies may cause fetal or neonatal harm. In this review, we will discuss the physiological mechanisms and benefits of transplacental transfer of maternal antibodies as well as pathological maternal situations where this system is hijacked, potentially leading to adverse neonatal outcomes.

Neonatal Pemphigus Vulgaris: A Case Report

: Pemphigus vulgaris (PV) is an autoimmune blistering disorder of the skin and mucous membranes. The transplacental passage of maternal immunoglobulin G (IgG) autoantibodies to desmoglein-3 (a transmembrane glycoprotein component in the skin) from the mother’s blood to the fetus can cause transient PV in the neonatal period. The duration of PV is short in the neonatal period, and the disease is improved with no prolonged sequelae. The similarity of skin lesions in PV to other skin conditions, such as infectious diseases caused by bacterial, viral, and fungal pathogens, or inherited bullous disorders, such as epidermolysis bullosa and incontinentia pigmenti, leads to misdiagnosis, inappropriate hospital admission, and poor antimicrobial treatment of patients. On the other hand, the maternal history of PV, besides laboratory examination, confirms the exact diagnosis. In this case report, we present a male term neonate with multiple pustules and blisters on the skin, developed within the first hours of life. The patient was admitted to the neonatal ward of our hospital for a sepsis workup and antibiotic treatment. Regarding the positive maternal history of PV in the second trimester of pregnancy and neonatal examinations skin biopsy confirmed the diagnosis of this disease.

A case of neonatal pemphigus vulgaris with co-existing BP180 autoantibodies

A male neonate was born with blisters on the trunk to a 37-year-old primigravid woman with a past medical history of recurrent, painful, topical steroid-responsive oral blisters. The diagnosis of neonatal pemphigus was made after the neonate and mother were found to have elevated desmoglein 3 (Dsg3) antibodies in conjunction with histopathologic features of pemphigus vulgaris. Interestingly, both neonate and mother also had elevated levels of BP180 antibodies, classically seen in bullous pemphigoid. This case is unique in that it portrays neonatal pemphigus, an already rare condition, complicated by the presence of BP180 antibodies.

Bullous Diseases in Children: A Review of Clinical Features and Treatment Options

Bullous diseases are uncommon in children; however, as they have the potential to affect quality of life, occasionally have long-term side effects in the setting of scarring processes, and carry a rare risk of underlying malignancy [e.g., with paraneoplastic pemphigus (PNP)], knowledge of their clinical presentation and treatment options is essential. Given the rarity of these conditions, our current state of knowledge is largely derived from case reports and case series, with a paucity of evidence-based recommendations. In this review, we discuss the clinical presentation of and treatment options for linear immunoglobulin A disease, dermatitis herpetiformis, pemphigus vulgaris, pemphigus foliaceus, PNP, bullous pemphigoid, mucus membrane pemphigoid, epidermolysis bullosa acquisita, and inherited epidermolysis bullosa. In general, when these conditions, except for PNP, occur in childhood, they have a better prognosis than when they occur in adults. Clinical, histopathological, and immunologic features frequently overlap, but distinct differences have also been reported, most commonly in clinical presentation. Treatment is often similar to that in adults, although specific considerations are necessary for a pediatric population.

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.

Management of autoimmune blistering diseases in pregnancy and the neonate

The management of autoimmune blistering diseases (AIBD) is therapeutically challenging, particularly in patients who plan to conceive, or are pregnant or breastfeeding. Not only is a patient's immune system altered by pregnancy-associated hormonal changes, but several medications used for AIBD treatment are not recommended for use in pregnancy or lactation. The data acquired regarding the safety and efficacy of these therapeutic interventions are gathered from studies or case reports from other diseases, as the treatment modalities are similar and randomized controlled trials are typically not performed in the setting of pregnancy. Although some medications for AIBD treatment are considered unsafe for use in pregnancy, many effective and tolerable therapies are able to provide benefit to these patients. In fact, most first-line agents may be used in pregnancy, to a given extent. This article discusses the medications used to treat AIBD prior to conception, during pregnancy, and while breastfeeding, as well as highlights those that are contraindicated. The preferred approach to management in these patients is also discussed. Additionally, we present the available information regarding neonates of mothers with a diagnosis of AIBD, including the likelihood, identification, and management of neonatal blistering and the effects from medication exposure in utero.

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.

In utero development of epidermolysis bullosa acquisita

We report the case of an infant born with perioral vesicles that rapidly spread to involve his mouth and the majority of his body. Histopathology, immunofluorescence, and enzyme-linked immunohistochemistry assays confirmed a diagnosis of epidermolysis bullosa acquisita (EBA). His mother had no history of EBA, and serum indirect immunofluorescence was negative. The patient improved rapidly with local wound care and oral dapsone.

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

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

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.

Pemphigus

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