IgG4 and IgE are the major immunoglobulins targeting the NC16A domain of BP180 in Bullous pemphigoid: serum levels of these immunoglobulins reflect disease activity

What's new in the pathogeneses and triggering factors of bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal blistering disease induced by autoantibodies to type XVII collagen (COL17, also called BP180) and BP230. Previous studies using patients' samples and animal disease models elucidated the complement-dependent and complement-independent pathways of blister formation, the pathogenic roles of immune cells (T and B cells, macrophages, mast cells, neutrophils, eosinophils), and the pathogenicity of IgE autoantibodies in BP. This review introduces the recent progress on the mechanism behind the epitope-spreading phenomenon in BP, which is considered to be important to understand the chronic and intractable disease course of BP, and the pathogenicity of anti-BP230 autoantibodies, mainly focusing on studies that used active disease models. To clarify the pathogenesis of BP, the mechanism behind the breakdown of immune tolerance to BP antigens should be investigated. Recent studies using various experimental models have revealed important roles for regulatory T cells in the maintenance of self-tolerance to COL17 and BP230 as well as in the suppression of inflammation triggered by the binding of antibodies to COL17. Notably, physical stresses such as trauma, thermal burns, bone fractures, irradiation and ultraviolet exposure, some pathologic conditions such as neurological diseases and hematological malignancies, and the use of dipeptidyl peptidase-IV inhibitors and immune checkpoint inhibitors have been reported as triggering factors for BP. These factors and certain underlying conditions such as genetic background, regulatory T-cell dysfunction or aging might synergistically affect some individuals and eventually induce BP. Further studies on the breakdown of self-tolerance and on the identification of key molecules that are relevant to blister formation and inflammation may expand our understanding of BP's etiology and may lead to the development of novel therapeutic approaches.

IgE autoantibodies in serum and skin of non-bullous and bullous pemphigoid patients

BACKGROUND

Non-bullous pemphigoid (NBP) is a pemphigoid variant which frequently resembles other pruritic skin diseases. In contrast with bullous pemphigoid (BP), blisters are absent. In BP, previous studies showed that IgE autoantibodies may be involved in its pathogenesis. IgE-activated mast cells, basophils and eosinophils may participate in BP by inducing pruritus and possibly blister formation, although the differential role of IgE in NBP compared with BP has not yet been described.

OBJECTIVE

To assess IgE in serum and skin of NBP and BP patients.

METHODS

We examined total IgE and pemphigoid-specific IgE in the serum of 68 NBP and 50 BP patients by enzyme-linked immunosorbent assay (ELISA). Sera of 25 pemphigus patients and 25 elderly patients with pruritus were included as controls. Skin biopsies of 14 NBP and 14 BP patients with the highest IgE titres to NC16A were stained for IgE by immunofluorescence techniques.

RESULTS

Total IgE was elevated in 63% of NBP and 60% of BP patients, and in 20% of pemphigus controls, as well as 60% of elderly controls. IgE ELISAs were more frequently positive in BP than in NBP (NC16A 18% vs. 9%, P = 0.139; BP230 34% vs. 22%, P = 0.149). IgE ELISAs for NC16A and BP230 were positive in 8% and 20% of elderly controls, respectively, while all pemphigus controls were negative. Two of 28 biopsies (7%; one NBP, one BP) showed linear IgE along the basement membrane zone, while in most biopsies (71% NBP; 86% BP) IgE was bound to dermal cells.

CONCLUSION

Since IgE was present in the serum and skin of both NBP and BP patients, this supports IgE-dependent mechanisms common to both diseases, such as pruritus. However, it remains to be elucidated whether IgE contributes to blister formation in BP.

Normal human skin is superior to monkey oesophagus substrate for detection of circulating BP180-NC16A-specific IgG antibodies in bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering skin disease. Two antigens have been identified as targets of circulating autoantibodies (autoAbs) - BP180 and BP230 - with BP180 being a critical transmembrane adhesion protein of basal keratinocytes of the epidermis. The noncollagenous domain 16A (NC16A) of BP180 is the immunodominant epitope in patients with BP, and anti-BP180-NC16A IgG antibodies (Abs) correlate to disease activity. Routine serological testing and follow-up of BP relies on indirect immunofluorescence (IIF) of serum Abs, commonly performed on monkey oesophagus (ME), and/or enzyme-linked immunosorbent assay (ELISA) testing on recombinantly produced fragments of BP180 and BP230 (BP180-NC16A, BP230-C/N).

OBJECTIVES

To determine if NC16A epitopes are well represented on ME substrate.

METHODS

Sera from different BP cohorts were tested by IIF on ME and normal human skin (NHS). To confirm findings, affinity-purified anti-BP180-NC16A/BP230 polyclonal Abs and recombinant anti-BP180-NC16A/BP230 monoclonal antibodies (mAbs) were used.

RESULTS

For sensitive detection of BP180-NC16A-specific IgG Abs, sections of NHS are superior to the widely used ME. Confirmation comes from polyclonal affinity-purified anti-BP180-NC16A/BP230 Abs, and by mAbs cloned from a patient with active BP.

CONCLUSIONS

Use of NHS is preferable over ME in routine IIF testing for BP. These results are of clinical relevance because anti-BP180-NC16A IgG titres are correlated to disease activity and detecting them reliably is important for screening, diagnosis and follow-up of patients with BP.

Eosinophils in Autoimmune Diseases

Eosinophils are multifunctional granulocytes that contribute to initiation and modulation of inflammation. Their role in asthma and parasitic infections has long been recognized. Growing evidence now reveals a role for eosinophils in autoimmune diseases. In this review, we summarize the function of eosinophils in inflammatory bowel diseases, neuromyelitis optica, bullous pemphigoid, autoimmune myocarditis, primary biliary cirrhosis, eosinophilic granulomatosis with polyangiitis, and other autoimmune diseases. Clinical studies, eosinophil-targeted therapies, and experimental models have contributed to our understanding of the regulation and function of eosinophils in these diseases. By examining the role of eosinophils in autoimmune diseases of different organs, we can identify common pathogenic mechanisms. These include degranulation of cytotoxic granule proteins, induction of antibody-dependent cell-mediated cytotoxicity, release of proteases degrading extracellular matrix, immune modulation through cytokines, antigen presentation, and prothrombotic functions. The association of eosinophilic diseases with autoimmune diseases is also examined, showing a possible increase in autoimmune diseases in patients with eosinophilic esophagitis, hypereosinophilic syndrome, and non-allergic asthma. Finally, we summarize key future research needs.

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.

Association between autoimmune pancreatitis and systemic autoimmune diseases

AIM: To investigate the association between autoimmune pancreatitis (AIP) and systemic autoimmune diseases (SAIDs) by measurement of serum immunoglobulin G4 (IgG4).

METHODS: The serum level of IgG4 was measured in 61 patients with SAIDs of different types who had not yet participated in glucocorticosteroid treatment. Patients with an elevated IgG4 level were examined by abdominal ultrasonography (US) and, in some cases, by computer tomography (CT).

RESULTS: Elevated serum IgG4 levels (919 ± 996 mg/L) were detected in 17 (28%) of the 61 SAID patients. 10 patients had Sjögren’s syndrome (SS) (IgG4: 590 ± 232 mg/L), 2 of them in association with Hashimoto’s thyroiditis, and 7 patients (IgG4: 1388 ± 985.5 mg/L) had systemic lupus erythematosus (SLE). The IgG4 level in the SLE patients and that in patients with SS were not significantly different from that in AIP patients (783 ± 522 mg/L). Abdominal US and CT did not reveal any characteristic features of AIP among the SAID patients with an elevated IgG4 level.

CONCLUSION: The serum IgG4 level may be elevated in SAIDs without the presence of AIP. The determination of serum IgG4 does not seem to be suitable for the differentiation between IgG4-related diseases and SAIDs.

IgE recognition of bullous pemphigoid (BP)180 and BP230 in BP patients and elderly individuals with pruritic dermatoses

Bullous pemphigoid (BP) is the most common autoimmune bullous disease of the elderly and is associated with IgG and IgE autoantibodies against the hemidesmosomal proteins, BP180 and BP230. The purpose of this study was to characterize the epitope specificity of IgE against defined regions of BP180 and BP230 in 32 BP patients and 21 elderly patients with pruritic disorders who did not yet fulfill all the criteria of BP by immunoblot (IB), ELISA and indirect immunofluorescence microscopy. Our findings show that IgE from BP sera preferentially targets the COOH-terminus of BP230 (IB: 16/32, ELISA: 12/32) and, to a lesser extent, the BP180-NC16A domain (IB: 11/32, ELISA: 9/32). Noteworthy, a subgroup of elderly patients with pruritic dermatoses also showed IgE recognition of BP180-NC16A (IB: 1/21, ELISA: 4/21) and less frequently of BP230 (IB: 2/21, ELISA: 2/21). Thus, IgE recognition of the BP autoantigens is presumably an early pathogenetic event in BP.

Clinical features and practical diagnosis of bullous pemphigoid

Bullous pemphigoid (BP) represents the most common autoimmune subepidermal blistering disease. BP typically affects the elderly and is associated with significant morbidity. It has usually a chronic course with spontaneous exacerbations. The cutaneous manifestations of BP can be extremely protean. While diagnosis of BP in the bullous stage is straightforward, in the non-bullous stage or in atypical variants of BP signs and symptoms are frequently non-specific with eg, only itchy excoriated, eczematous, papular and/or urticarial lesions that may persist for several weeks or months. Diagnosis of BP critically relies on immunopathologic examinations including direct immunofluorescence microscopy and detection of serum autoantibodies by indirect immunofluorescence microscopy or BP180-ELISA.

Detection of linear IgE deposits in bullous pemphigoid and mucous membrane pemphigoid: a useful clue for diagnosis

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease of the skin associated with IgG autoantibodies to BP180 and BP230, while mucous membrane pemphigoid (MMP) comprises a heterogeneous group of autoimmune blistering diseases characterized by a predominant mucous membrane involvement and scarring tendency associated with an autoantibody response to various autoantigens, including BP180. While the pathogenicity of IgG autoantibodies to BP180 has been demonstrated in BP, the role of IgE autoantibodies in mediating tissue damage in BP and MMP is unclear.

OBJECTIVES

To assess the presence of tissue-bound IgE in patients with BP and MMP, and their correlation with distinct clinical features.

METHODS

In this retrospective study, we assessed the presence of IgE deposits as detected by direct immunofluorescence microscopy of skin biopsy specimens obtained from 44 and 13 patients with a new diagnosis of BP and MMP, respectively. Distinct clinical features at time of diagnosis, such as itch, urticarial papules and plaques and eczematous lesions, were noted.

RESULTS

In 18 of 44 (41%) patients with BP linear deposits of IgE of variable intensity were detectable along the dermoepidermal junction. In 14 (32%) of the cases, IgE deposits were found concomitantly with IgG and C3. In two (5%) patients, diagnosis of BP was based on the isolated detection of IgE together with consistent clinicopathological features. Nine of 13 (69%) patients with MMP also exhibited linear IgE deposits, including one case with isolated linear IgE deposits. Patients with BP with tissue-bound IgE deposits had clinically significant urticarial papules and plaques when compared with patients with BP without IgE deposits.

CONCLUSIONS

Our findings indicate that demonstration of tissue-bound IgE deposits provides an additional useful criterion for diagnosis of BP and MMP in some patients. Prospective studies are needed to better correlate the presence of tissue-bound and circulating IgE autoantibodies and their specificity with distinct clinical features and course of BP and MMP.

FcR-independent effects of IgE and IgG autoantibodies in bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by IgE and IgG class autoantibodies specific for 180-kDa BP Ag 2 (BP180), a protein involved in cell-substrate attachment. Although some direct effects of BP IgG have been observed on keratinocytes, no study to date has examined direct effects of BP IgE. In this study, we use primary cultures of human keratinocytes to demonstrate Ag-specific binding and internalization of BP IgE. Moreover, when BP IgE and BP IgG were compared, both isotypes stimulated FcR- independent production of IL-6 and IL-8, cytokines critical for BP pathology, and elicited changes in culture confluence and viability. We then used a human skin organ culture model to test the direct effects of these Abs on the skin, whereas excluding the immune inflammatory processes that are triggered by these Abs. In these experiments, physiologic concentrations of BP IgE and BP IgG exerted similar effects on human skin by stimulating IL-6 and IL-8 production and decreasing the number of hemidesmosomes localized at the basement membrane zone. We propose that the Ab-mediated loss of hemidesmosomes could weaken attachment of basal keratinocytes to the basement membrane zone of affected skin, thereby contributing to blister formation. In this article, we identify a novel role for IgE class autoantibodies in BP mediated through an interaction with BP180 on the keratinocyte surface. In addition, we provide evidence for an FcR-independent mechanism for both IgE and IgG class autoantibodies that could contribute to BP pathogenesis.

Development of an ELISA for sensitive and specific detection of IgA autoantibodies against BP180 in pemphigoid diseases

BACKGROUND

Pemphigoids are rare diseases associated with IgG, IgE and IgA autoantibodies against collagen XVII/BP180. An entity of the pemphigoid group is the lamina lucida-type of linear IgA disease (IgA pemphigoid) characterized by IgA autoantibodies against BP180. While for the detection of IgG and IgE autoantibodies specific to collagen XVII several ELISA systems have been established, no quantitative immunoassay has been yet developed for IgA autoantibodies. Therefore, the aim of the present study was to develop an ELISA to detect IgA autoantibodies against collagen XVII in the sera of patients with pemphigoids.

METHODS

We expressed a soluble recombinant form of the collagen XVII ectodomain in mammalian cells. Reactivity of IgA autoantibodies from patients with IgA pemphigoid was assessed by immunofluorescence microscopy and immunoblot analysis. ELISA test conditions were determined by chessboard titration experiments. The sensitivity, specificity and the cut-off were determined by receiver-operating characteristics analysis.

RESULTS

The optimized assay was carried out using sera from patients with IgA pemphigoid (n = 30) and healthy donors (n=105). By receiver operating characteristics (ROC) analysis, an area under the curve of 0.993 was calculated, indicating an excellent discriminatory capacity. Thus, a sensitivity and specificity of 83.3% and 100%, respectively, was determined for a cut-off point of 0.48. As additional control groups, sera from patients with bullous pemphigoid (n=31) and dermatitis herpetiformis (n = 50), a disease associated with IgA autoantibodies against epidermal transglutaminase, were tested. In 26% of bullous pemphigoid patients, IgA autoantibodies recognized the ectodomain of collagen XVII. One of 50 (2%) of dermatitis herpetiformis patients sera slightly topped the cut-off value.

CONCLUSIONS

We developed the first ELISA for the specific and sensitive detection of serum IgA autoantibodies specific to collagen XVII in patients with pemphigoids. This immunoassay should prove a useful tool for clinical and translational research and should essentially improve the diagnosis and disease monitoring of patients with IgA pemphigoid. Moreover, our findings strongly suggest that IgA pemphigoid and IgG bullous pemphigoid represent two ends of the clinical spectrum of an immunological loss of tolerance against components of hemidesmosomes, which is mediated by both IgG and IgA autoantibodies.

A novel ELISA reveals high frequencies of BP180-specific IgE production in bullous pemphigoid

Bullous pemphigoid (BP) is a humoral autoimmune disease directed predominantly against the non-collagenous NC16A domain of the BP180 hemidesmosomal protein. Our laboratory has recently shown, using a mouse xenograft model, that passive transfer of IgE autoantibodies from BP sera induces a skin phenotype that recapitulates the early phases of the disease. Herein, we describe the development of a highly specific and sensitive ELISA to detect circulating IgE autoantibodies that recognize BP180-NC16A. Using this assay, we detected NC16A-specific IgE-class autoantibodies in 77% of BP sera. This frequency, which is significantly higher than reported previously, is comparable to that of anti-NC16A IgG autoantibody production. In 3 BP patients monitored over time, the circulating NC16A-specific levels of both IgE and IgG were associated with clinical disease activity; however, patient sera did not always contain high levels of both isotypes. In conclusion, our ELISA provides a highly sensitive and specific tool for the detection of BP180-specific IgE in patient sera. Furthermore, we report that the majority of BP sera contain both IgE and IgG class autoantibodies specific for NC16A and suggest that screening for both isotypes of autoantibodies may provide a better diagnostic value than IgG alone.

Subepidermal blistering induced by human autoantibodies to BP180 requires innate immune players in a humanized bullous pemphigoid mouse model

Bullous pemphigoid (BP) is a cutaneous autoimmune inflammatory disease associated with subepidermal blistering and autoantibodies against BP180, a transmembrane collagen and major component of the hemidesmosome. Numerous inflammatory cells infiltrate the upper dermis in BP. IgG autoantibodies in BP fix complement and target multiple BP180 epitopes that are highly clustered within a non-collagen linker domain, termed NC16A. Anti-BP180 antibodies induce BP in mice. In this study, we generated a humanized mouse strain, in which the murine BP180NC14A is replaced with the homologous human BP180NC16A epitope cluster region. We show that the humanized NC16A (NC16A+/+) mice injected with anti-BP180NC16A autoantibodies develop BP-like subepidermal blisters. The F(ab')(2) fragments of pathogenic IgG fail to activate the complement cascade and are no longer pathogenic. The NC16A+/+ mice pretreated with mast cell activation blocker or depleted of complement or neutrophils become resistant to BP. These findings suggest that the humoral response in BP critically depends on innate immune system players.

Serum levels of IgE anti-BP180 and anti-BP230 autoantibodies in patients with bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the hemidesmosomal proteins, BP180 and BP230. NC16A, a non-collagenous stretch of the BP180 ectodomain is the primary target of pathogenic IgG antibodies. Whereas IgG anti-BP180 autoantibodies play a primary role in the pathogenesis, there is a growing number of data regarding the potential pathogenic roles of IgE class autoantibodies in BP.

OBJECTIVES

To examine the levels of IgG and IgE autoantibodies against BP180 and BP230, and to investigate mutual association and clinical relevance.

METHODS

Sera obtained from 67BP patients and 36 healthy donors were subjected to ELISA assays to measure serum IgG and IgE levels of anti-BP180 and anti-BP230 antibodies.

RESULTS

IgG anti-BP180 antibodies were positive in 63 (94%) of 67BP patients. IgG anti-BP230, IgE anti-BP180, and IgE anti-BP230 antibodies were found in 48 (72%), 20 (30%) and 45 (67%), respectively. IgG anti-BP180 levels were correlated with the affected areas. IgG anti-BP230 antibodies tended to increase in proportion to elongation of disease duration. IgE anti-BP230 levels showed a strong association with local eosinophil accumulation, while the levels were reversely related with the affected areas in BP.

CONCLUSIONS

IgE autoantibodies to BP180 and BP230 are detected at high frequencies in BP. IgE anti-BP230 antibodies may have a role in attracting eosinophils to the skin lesions.

Experimental models for the autoimmune and inflammatory blistering disease, Bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal skin blistering disease characterized immunohistologically by dermal-epidermal junction (DEJ) separation, an inflammatory cell infiltrate in the upper dermis, and autoantibodies targeted toward the hemidesmosomal proteins BP230 and BP180. Development of an IgG passive transfer mouse model of BP that reproduces these key features of human BP has demonstrated that subepidermal blistering is initiated by anti-BP180 antibodies and mediated by complement activation, mast cell degranulation, neutrophil infiltration, and proteinase secretion. This model is not compatible with study of human pathogenic antibodies, as the human and murine antigenic epitopes are not cross-reactive. The development of two novel humanized mouse models for the first time has enabled study of disease mechanisms caused by BP autoantibodies, and presents an ideal in vivo system to test novel therapeutic strategies for disease management.

Significance of IgG4 in the diagnosis of mucous membrane pemphigoid

OBJECTIVE

To determine the diagnostic value and frequency of tissue deposition of IgG4 in comparison to polyclonal IgG, IgA, IgM, and C3.

STUDY DESIGN

Oral mucosal biopsies of 82 patients clinically suspected to have mucous membrane pemphigoid (MMP) were analyzed by direct immunofluorescence (IF) using polyclonal anti-human IgG, IgM, IgA, fibrin, complement C3, and anti-human IgG4 subclass monoclonal antibodies.

RESULTS

Based on clinical, hematoxylin and eosin (H & E), and direct IF studies, 34 cases were diagnosed as MMP. The most common antibody deposited was IgG (90%), followed by C3 (82%), and IgG4 (71%). In more than half the cases of MMP, IgG4 deposition was seen in combination with IgG and or C3. Strikingly, IgG4 was the sole antibody detected in 2 cases (6%).

CONCLUSION

Our results suggest that the use of monoclonal IgG4 is important in the diagnosis of MMP. We suggest adding monoclonal IgG4 to the routine panel of antibodies used in studies of cases suspected to have MMP to avoid false-negatives.

The relevance of the IgG subclass of autoantibodies for blister induction in autoimmune bullous skin diseases

Autoimmune bullous skin diseases are characterized by autoantibodies and T cells specific to structural proteins maintaining cell-cell and cell-matrix adhesion in the skin. Existing clinical and experimental evidence generally supports a pathogenic role of autoantibodies for blister formation. These autoantibodies belong to several IgG subclasses, which associate with different functional properties and may thus determine the pathogenic potential of IgG antibodies. In pemphigus diseases, binding of IgG to keratinocytes is sufficient to cause intraepidermal blisters without engaging innate immune effectors and IgG4 autoantibodies seem to mainly mediate acantholysis. In contrast, in most subepidermal autoimmune blistering diseases, complement activation and recruitment and activation of leukocytes by autoantibodies are required for blister induction. In these conditions, tissue damage is thought to be mainly mediated by IgG1, but not IgG4 autoantibodies. This review summarizes the current knowledge on the pathogenic relevance of the IgG subclass of autoantibodies for blister formation. Characterization of the pathogenically relevant subclass(es) of autoantibodies not only provides mechanistic insights, but should greatly facilitate the development of improved therapeutic modalities of autoimmune blistering diseases.

Bullous pemphigoid: physiopathology, clinical features and management

There has been a considerable progress in the understanding of the physiopathology of BP during the past 2 decades. The insights into the humoral and cellular immune response against BP180 and BP230 have increased significantly. Nevertheless, the factors underlying the initiation of the disease leading to a disruption of self-tolerance remain unclear. Clinically, the disease shows protean presentations, and diagnostic delay is common. A practical, relevant, and unresolved question is how to identify patients suffering from BP at an early stage of the disease, when direct immunofluorescence microscopy findings still may be negative. The characterization of markers allowing the differentiation of BP from other pruritic eruptions occurring in the elderly population would be extremely helpful in daily practice. Finally, despite the knowledge that potent topical steroids are efficient in controlling the disease, management of BP sometimes remains difficult and requires systemic therapies. It is hoped that a better knowledge of the regulation of the autoimmune response in BP also will facilitate the design of novel immunomodulatory therapeutic approaches devoid of the severe side effects of current immunosuppressive treatments.

Role of FcRs in animal model of autoimmune bullous pemphigoid

Bullous pemphigoid (BP) is a bullous dermatosis associated with autoantibodies directed against the hemidesmosomal Ags BP180 and BP230. Lesional skin is characterized by detachment of the epidermis from the dermis with an intense inflammatory cell infiltrate in the upper dermis. In experimental BP, subepidermal blistering is triggered by rabbit anti-murine BP180 (mBP180) IgG and depends upon complement activation, mast cell degranulation, and neutrophil infiltration. In this study, we determined the role of Fc gammaRs on neutrophils in experimental BP. Mice deficient in Fc gammaRIII (Fc gammaRIII-/-) and those deficient in both Fc gammaRI and Fc gammaRIII (Fc gammaRI&III-/-) but not in Fc gammaRII (Fc gammaRII-/-) were resistant to BP. Pathogenic IgG activated wild-type neutrophils, but not Fc gammaRIII-deficient neutrophils, to secrete proteolytic enzymes. The function of anti-mBP180 IgG depended entirely on its Fc domain; F(ab')2 of IgG had no pathogenic activities. In wild-type mice injected with pathogenic IgG, an Fc gammaR blocker abolished the BP phenotype and inhibited activation of wild-type neutrophils stimulated by pathogenic IgG. Results from this study establish that Fc gammaRIII plays a critical role in the activation of infiltrating neutrophils and the subsequent blistering in experimental BP.

IgG4 as the predominant IgG subclass in pemphigoides gestationis

BACKGROUND

Pemphigoides gestationis (PG) is a blistering disorder of pregnancy caused by antibodies against basement membrane proteins. They are directed against the 180 kD bullous pemphigoid antigen (BPAg2), towards the epitopes within the NC 16A domain. There are many similarities between pemphigoid gestationis and bullous pemphigoid (BP), but the literature so far indicated different immunofluorescence results in regards with C3 and IgG, and IgG subclasses (IgG4 vs. IgG1).

METHODS

We evaluated staining patterns and IgG subclasses, as well as C5b-9 membrane attack complex (MAC) in 10 pregnant patients with PG, using sandwich double antibody immunofluorescence (SDAI) and direct immunofluorescence (DIF).

RESULTS

All ten specimens stained with C3 by DIF, but only five had trace amount of IgG reactants by this method. By SDAI, 100% were positive for the IgG4 and C5b-9 MAC, 70% for IgG2, 50% for IgG1, and 40% for IgG3.

CONCLUSION

IgG4 was the predominant IgG subtype identified. This finding has not been reported for PG, but it mimics results reported for BP. One explanation is prolonged disease course, as well as blocking of antigenic domains by IgG4. Understanding this completely will help develop therapies and prevention strategies for immunobullous and other autoimmune diseases, and perhaps aid in an exact classification.

Elevated expression of CD23 on peripheral blood B lymphocytes from patients with bullous pemphigoid: correlation with increased serum IgE

BACKGROUND

Increased serum IgE levels are occasionally found in patients with severe bullous pemphigoid (BP). CD23, a low affinity Fc receptor for IgE, is mainly expressed on mature B lymphocytes. Studies have suggested that serum levels of soluble CD23 (sCD23) correlate with serum IgE levels and disease severity in BP.

OBJECTIVE

The purpose of our study is to examine whether the expression of CD23 is elevated in BP and whether this expression correlates with serum IgE levels and disease severity.

METHODS

We measured CD23 expression on B cells from patients with active BP, pemphigus vulgaris, pemphigus foliaceus, and atopic dermatitis (AD), as well as healthy control subjects, using a flow cytometer. Serum levels of IgE and sCD23 were also measured.

RESULTS

The expression of CD23 was significantly higher in BP patients compared with healthy control subjects (P < 0.05), whereas the levels were normal in the other bullous diseases. CD23 expression tended to be higher in severe BP compared with moderate BP, and the levels in severe BP were comparable to the levels in AD. Furthermore, CD23 expression correlated positively with serum IgE levels (P < 0.002), and the IgE levels were significantly higher in severe BP than in moderate BP (P < 0.01 ). CD23 expression in BP did not correlate with sCD23 levels.

CONCLUSIONS

These results suggest that the up-regulated surface CD23 on B cells may be involved in IgE synthesis and inflammatory events in BP.

Isotype determination of circulating autoantibodies in canine autoimmune subepidermal blistering dermatoses

The three most common canine autoimmune blistering skin diseases (AISBD), bullous pemphigoid (BP), mucous membrane pemphigoid (MMP) and epidermolysis bullosa acquisita (EBA) have recently been separated based on clinical, histological and immunological grounds. The objectives of this study were to determine the isotype profiles of circulating autoantibodies in these dermatoses. Serum was collected from 5 dogs with BP, 15 with MMP and 11 with EBA. All sera were tested using an indirect immunofluorescence method using salt-split canine gingiva as substrate. Anti-basement membrane IgG autoantibodies were detected in all patients. Among the IgG autoantibodies, IgG1 and IgG4 were encountered most frequently, while IgG2 and IgG3 were uncovered in some dogs. IgE autoantibodies were detected more often than IgA or IgM autoantibodies in any of the three entities. The predominance of IgG1, IgG4 and IgE autoantibody isotypes in dogs with AISBD is very similar to the situation found in humans with the homologous diseases.

High level of thymus and activation-regulated chemokine in blister fluid and sera of patients with bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by eosinophilia and high serum IgE levels. The accumulated evidence suggests that various cytokines are involved in the lesional skin of patients with BP. Recently, thymus and activation-regulated chemokine (TARC/CCL17), a CC chemokine, was identified as a selective chemoattractant for CC chemokine receptor 4 (CCR4)-expressing cells.

OBJECTIVE

In this study, we examined the involvement of TARC in patients with BP.

METHODS

We determined the fluid and serum TARC levels in patients with BP by enzyme-linked immunosorbent assay and compared the serum TARC levels with the eosinophil numbers in peripheral blood. We also compared the serum TARC levels in five patients with BP before and after they were treated. Moreover, we examined TARC, CCR4 and CXC chemokine receptor 3 (CXCR3) expression in the lesional skin of patients with BP by immunohistochemical procedures. Furthermore, we measured CCR4 positivity in CD4+ CD45RO+ cells of peripheral blood mononuclear cells (PBMCs) in patients with BP and healthy control subjects.

RESULTS

The fluid TARC levels in patients with BP were significantly higher than those in blisters from burn patients or suction blisters of healthy control subjects. The serum TARC levels in patients with BP were also significantly higher than those in pemphigus vulgaris (PV) patients and healthy control subjects, and decreased after the treatment. The serum TARC levels in patients with BP significantly correlated with the eosinophil numbers in peripheral blood (r = 0.72, P < 0.002). Immunohistochemistry showed a strong reactivity of TARC in the epidermal keratinocytes (KCs) of BP. Moreover, both CCR4 and CXCR3 were expressed on the dermal infiltrating CD4+ T cells mainly beneath the bullae of patients with BP. Fluorescence-activated cell sorting analysis showed a higher percentage of CCR4 positivity in CD4+ CD45RO+ cells of PBMCs in patients with BP than that in healthy control subjects, while there was no significant difference of CXCR3 positivity in CD4+ CD45RO+ cells of PBMCs between patients with BP and healthy control subjects.

CONCLUSIONS

These findings strongly suggest that TARC may be one of the important chemokines that are involved in the pathogenesis of BP.

Autoantibodies to the extracellular and intracellular domain of bullous pemphigoid 180, the putative key autoantigen in bullous pemphigoid, belong predominantly to the IgG1 and IgG4 subclasses

BACKGROUND

Autoantibodies to the extracellular domain (ECD) of bullous pemphigoid (BP) antigen 180 (BP180) are thought to play a crucial part in the pathophysiology of BP.

OBJECTIVES

As the various IgG subclasses have different biological properties, we have sought to assess the relative isotype distribution of IgG to BP180 and their reactivity against the ECD and intracellular domain (ICD) of BP180.

METHODS

The reactivity of 27 sera from patients with BP was assayed by immunoblotting against recombinant proteins covering the ECD and ICD of BP180.

RESULTS

Twenty-seven (100%) and 21 (77%) of 27 BP sera, respectively, contained IgG1 and IgG4 autoantibodies binding to the ECD of BP180. Fourteen (82%) and six (35%) of the 17 BP sera that were reactive with the ICD of BP180 had autoantibodies of the IgG1 and IgG4 subclass, respectively. The profile of the isotype restriction appeared to be similar when the response to the ECD vs. that to the ICD was compared. IgG2 and IgG3 reactivity with BP180 was found less frequently. Patients with BP of longer duration showed a tendency to have, in addition to IgG1, an IgG4 response.

CONCLUSIONS

Consistent with prior evidence indicating that subepidermal blister formation in BP is dependent upon complement activation, the frequent finding of complement-fixing IgG1 autoantibodies to both the ECD and ICD of BP180 might have pathogenic relevance in BP. These findings provide new insights relevant for our understanding of the immune response to BP180, the putative key autoantigen in BP.