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

Omalizumab in the treatment of bullous pemphigoid: A single-center series of 15 cases

Bullous pemphigoid (BP) is a chronic autoimmune disease affecting the elderly population and characterized by the formation of subepidermal tense bullae. Treatment options include topical steroids, systemic steroids, immunosuppressants, and antimicrobials, and there is emerging evidence of the efficacy of omalizumab. In this study, we aimed to demonstrate omalizumab's efficacy for treating BP, and we also reported treatment-related adverse events. The retrospective cohort study included patients with BP who were followed up in our clinic's bullous diseases department between 2016 and 2023. Patients who received omalizumab were included in the study. Treatment responses of all patients were assessed by BP Disease Area Index activity and damage scores, treatment scale scoring, steroid dose reduction, and the presence/absence of pruritus. Also, total IgE levels of patients before the treatment onset and at the last visit were compared. There were 15 (male/female = 8/7) BP patients receiving omalizumab treatment. Omalizumab therapy allowed steroid dose reduction at a median of 1 month. Omalizumab (25.5 mg, 95% confidence interval 17.2-33.9, P < .001) provided a significant steroid dose reduction at the last visit compared to the beginning of treatment. Omalizumab resulted in a decrease in BP Disease Area Index activity score of 80.8 (95% confidence interval 71.8-89.8, P < .001). Also, omalizumab caused significant decline in IgE levels compared to baseline (1102.5 ± 834.5 vs 834.6 ± 613.6, P = .002). In this study, omalizumab treatment was an effective and safe option in BP patients with high baseline IgE levels who are refractory to or cannot tolerate other immunosuppressive therapies.

High serum total IgE levels correlate with urticarial lesions and IgE deposition in perilesional skin of bullous pemphigoid patients: An observational study

Background In the pathophysiology of bullous pemphigoid, besides IgG, there has been evidence that supports the role of IgE antibodies. However, there have been no studies to evaluate total serum IgE levels or detect IgE deposits in the skin of Vietnamese patients. Aim To analyse the association between IgE levels in the serum and disease severity as well as eosinophils and IgE basement membrane zone (BMZ) deposition in Vietnamese bullous bullous pemphigoid patients. Methods A single-centre observational research on 35 newly diagnosed and untreated bullous bullous pemphigoid patients. Total serum IgE levels were analysed using enzyme-linked immunosorbent assay (ELISA). For controls, we collected sera of 30 pemphigus patients and 30 elderly patients with pruritus. Perilesional skin biopsies underwent direct immunofluorescence (DIF) staining, with biopsies of pemphigus patients as controls. Results Elevated total serum IgE was observed in 60% of bullous pemphigoid patients, the percentage in the pemphigus group and pruritus group was 20% and 40%, respectively. The mean total serum IgE level among the bullous pemphigoid group was higher than that of the pemphigus group (123.3 ± 102.4 IU/mL vs. 64.3 ± 45.1 IU/mL, p = 0.010). Total serum IgE levels of bullous pemphigoid patients correlated with higher eosinophil counts (r = 0.61; p = 0.018) and urticaria/erythema (U/E) Bullous Pemphigoid Disease Area Index (BPDAI) score (r = 0.50; p = 0.035). Among 35 bullous pemphigoid patients, 5 patients showed positive IgE DIF staining, accounting for 14.3%. Higher serum IgE levels correlated with the deposition of IgE in patients' perilesional skin (p = 0.037). Limitations Due to the rarity of bullous pemphigoid, the effect of the COVID-19 pandemic, and self-treatment issues in Vietnam, we could not recruit a larger number of participants. Conclusions Total serum IgE values correlated with urticarial lesions and IgE deposition in perilesional skin of Vietnamese bullous pemphigoid patients. IgE autoantibodies present in the skin of bullous pemphigoid patients support the role of IgE in bullous pemphigoid pathogenesis.

Anti-BP230 IgE autoantibodies in bullous pemphigoid intraindividually correlate with disease activity

BACKGROUND

Bullous pemphigoid (BP), the most common subepidermal autoimmune blistering disease, is classically defined by the presence of IgG autoantibodies directed against the hemidesmosomal proteins BP180 (type XVII collagen) and BP230 and the predominance of skin lesions. Several studies have addressed the role of anti-BP180 IgE in patients and experimental models, while data on anti-BP230 IgE are scarce.

OBJECTIVE

To assess anti-BP230 IgE level by ELISA in BP sera and to correlate it with disease severity and clinical characteristics.

METHODS

BP sera underwent anti-BP230 IgE ELISA and Western blotting against human BP230 fragments.

RESULTS

We demonstrate that 36/154 (23%) of BP sera were positive for anti-BP230 IgE. Anti-BP230 IgE levels had no correlation with clinical phenotype or disease activity per se. Interestingly, anti-BP230 IgE was significantly associated with disease activity within individuals during the course of the disease. Additionally, anti-BP230 IgE and total IgE levels showed a significant correlation. Notably, anti-BP230 IgG correlated interindividually with disease activity. By Western blotting, the C-terminal domain of BP230 fragments (C2; amino acids 2024-2349 and C3; amino acids 2326-2649), provided the best serological assay for anti-BP230 IgE detection.

CONCLUSION

As a complementary tool, IgE immunoblotting is recommended to obtain an optimal serological diagnosis, particularly in patients with severe disease without IgG reactivity by BP180- or BP230-specific ELISA. Although the detection of serum anti-BP230 IgE is not of major diagnostic significance, it may be relevant for therapeutic decisions, e.g., for anti-IgE-directed treatment, which has been successfully used in case series of BP.

[Spontaneous remission of urticaria: does it exist and if so, when?]

BACKGROUND

Urticaria mostly occurs acutely with a very high probability of spontaneous remission. When it persists for more than 6 weeks a chronic urticaria is manifest, which occurs either spontaneously or inducible by specific triggers. The underlying mechanisms are not fully understood but recent research points to defined pathogenetic factors.

QUESTION AND AIM

Whether spontaneous remission is possible in urticaria is summarized descriptively in this review, and suggestions are given for the "step down" of urticaria treatment after remission. The mechanisms including autoallergic, immunoglobulin E (IgE)-dependent type I reactions and autoimmune, activating IgG-dependent type IIb reactions are presented. These are discussed in the context of spontaneous remission and the possibilities of induced remission.

Association between bullous pemphigoid and atopic dermatitis: a population-based case-control study in Taiwan

Although bullous pemphigoid (BP) and atopic dermatitis (AD) share pathogenic mechanisms, their relationship remains controversial. Therefore, we conducted a population-based case-control study to investigate the association between BP and AD in Taiwan. Based on the Taiwan National Health Insurance Research Database, 9344 patients with BP and 18,688 age- and sex-matched controls were enrolled between 2000 and 2013. Furthermore, the study included 7,196 BP patients and 14,392 controls, matched for age, sex, and propensity score of comorbidities, with a case to controls ratio of 1:2. Logistic regression analysis was performed to examine the association between AD and BP. In the age- and sex-matched cohorts, AD (odds ratio [OR], 1.71; 95% confidence interval [CI], 1.50-1.95) was independently associated with BP. In the age, sex, and comorbidities-matched cohorts, AD (OR 1.76, 95% CI 1.55-2.00) remained a significant risk factor for BP. Other significant risk factors included psoriasis, hypertension, diabetes mellitus, chronic kidney disease, chronic obstructive pulmonary disease, neuropsychiatric diseases, and autoimmune connective tissue disease. Limitations of this study include the lack of information on disease severity and phenotypes of BP and misclassification of diseases as potential sources of bias. In conclusion, AD increased the risk of developing BP by 76%, and this association was independent of many BP comorbidities. Further studies are warranted to investigate the clinical and pathophysiological relevance of factors contributing to BP and AD.

Research progress of omalizumab in the treatment of bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune blistering disease associated with anti-BP180 and anti-BP230 antibodies. The pathogenic action mechanism of immunoglobulin E (IgE) antibodies in BP has been studied since the 1970s, and IgE antibodies have gradually been confirmed as being important in BP; therefore, anti-IgE therapy may be a new option for the treatment of BP. Omalizumab, as an IgE monoclonal antibody, has been increasingly used clinically to treat BP in recent years. Here, we collected 35 papers investigating omalizumab for BP treatment in a total of 83 patients, and the vast majority of patients showed varying degrees of improvement after treatment, except for a small number of patients with poor clinical outcomes. The patients were then divided into three groups according to dosing frequency and number of doses. Statistical analysis indicated that dosing frequency had little effect on clinical efficacy. While the groups with different numbers of doses were evaluated, the results concluded that clinical efficacy was affected by the number of doses, but there was no positive correlation between the number of doses and clinical efficacy.

Rituximab, Omalizumab, and Dupilumab Treatment Outcomes in Bullous Pemphigoid: A Systematic Review

Background

Bullous pemphigoid (BP) is the most common autoimmune subepidermal bullous disease of the skin. First-line treatment of systemic corticosteroids may cause serious adverse events. Rituximab, omalizumab, and dupilumab should be explored as alternative treatment options to improve outcomes.

Objective

To systematically review the rituximab, omalizumab, and dupilumab treatment outcomes in bullous pemphigoid.

Methods

A PubMed, Embase, Web of Science, and Cochrane library search were conducted on March 10, 2022. A total of 75 studies were included using Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

Results

Use of rituximab (n=122), omalizumab (n=53) and dupilumab (n=36) were reported in 211 patients with BP. Rituximab led to complete remission in 70.5% (n=86/122) and partial remission in 23.8% (n=29/122) of patients within 5.7 months, with a recurrence rate of 20.5% (n=25/122). 9.0% (n=11/122) of patients died and infection (6.6%, n=8/122) was the most common adverse event. Omalizumab led to complete remission in 67.9% (n=36/53) and partial remission in 20.8% (n=11/53) of patients within 6.6 months, with a recurrence rate of 5.7% (n=3/53). 1.9% (n=1/53) of patients died and thrombocytopenia (1.9%, n=1/53) was observed as the most common adverse event. Dupilumab led to complete remission in 66.7% (n=24/36) and partial remission in 19.4% (n=7/36) of patients within 4.5 months of treatment without any reported adverse events, with a recurrence rate of 5.6% (n=2/36).

Conclusions

Rituximab, omalizumab, and dupilumab have similar clinical benefits for BP patients. However, rituximab resulted in higher recurrence rates, adverse events, and mortality rates.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022316454.

Rapid Disease Control in First-Line Therapy-Resistant Mucous Membrane Pemphigoid and Bullous Pemphigoid with Omalizumab as Add-On Therapy: A Case Series Of 13 Patients

The role of IgE autoantibodies has been demonstrated in the pathogenesis of bullous pemphigoid for many years. Recently, omalizumab (OMZ), a humanized monoclonal anti-IgE antibody that depletes total serum IgE, has been used off-label in a few case series of bullous pemphigoids demonstrating a rapid efficacy and allowing significant improvements or complete remission as add-on therapy in first-line treatment-resistant patients. Herein, we report the largest retrospective study to evaluate OMZ effectiveness in patients with subepidermal autoimmune blistering diseases. Our series included 13 patients from a single center with bullous pemphigoid or mucous membrane pemphigoid, of whom 7 had mucous membrane involvement. OMZ was added to the unchanged immunosuppressive therapies. Detailed clinical and immunological data during the first year were collected, notably for specific anti-BP180-NC16A IgE and IgG, and the median total follow-up was 30 months (range: 3-81). Our series demonstrated that OMZ induced a significant improvement in pruritus, urticarial score, and daily blister count on day 15, allowing disease control to be achieved in a 1-month median time and complete remission (CR) in a 3-month median time in 85% of these patients previously in therapeutic impasse. At the end of the follow-up, 31% of patients achieved CR on minimal therapy after OMZ weaning without relapses, and 54% achieved CR on OMZ continuation with a minimal dose of concomitant treatment. Two patients experienced therapeutic failure (15%). At baseline, clinical variables reflecting activity were significantly positively correlated with eosinophil blood count, total IgE serum level, specific anti-BP180 IgE and IgG. While baseline anti-BP180 IgG and specific anti-BP180 IgE were significantly positively correlated, only the two patients who experienced a therapeutic failure with OMZ did not fit with this correlation, demonstrating elevated levels of anti-BP180 IgG with no measurable BP180-specific IgE. Follow-up of immunological variables demonstrated a rapid decrease of eosinophilia towards normalization, whereas a slower decline towards negativation was observed over 1 year for anti-BP180 IgG and anti BP180 IgE in patients who responded to OMZ. This case series demonstrated that OMZ is a rapidly effective biologic therapy for refractory bullous pemphigoid and mucous membrane pemphigoid, permitting rapid disease control and reduction of concomitant therapeutics.

Strategies to Improve Outcomes of Bullous Pemphigoid: A Comprehensive Review of Clinical Presentations, Diagnosis, and Patients' Assessment

Bullous pemphigoid (BP) is the most frequent autoimmune bullous disease mainly affecting elderlies. Diagnosis usually results from clinical features, histological examination, and the quantification of circulating typical autoantibodies, due to its higher incidence in elderly patients, bullous pemphigoid treatment and management still represents a challenge due to the higher frequency of several comorbidities in this group of patients, which may also be linked to a reduced tolerance to BP treatments. Hence, an early diagnosis and a prompt correct treatment are mandatory to reach better clinical outcomes and improve as much as possible BP outcomes. Herein, we carried out a comprehensive literature review about the known clinical presentations, diagnosis, assessment and monitoring procedures used in daily clinical practice in patients with BP, to better define strategies to improve as much as possible BP clinical outcomes.

State-of-the-art review of human autoimmune blistering diseases (AIBD)

Autoimmune blistering diseases (AIBDs) are a heterogenous group of skin conditions, broadly classified into two categories depending on the location of blister formation: intraepidermal blistering in the pemphigus group and subepidermal blistering in the pemphigoid group. Although AIBDs occur in both humans and animals, the arsenal of data for human AIBDs far exceeds those of their animal counterpart. Therefore, the main purpose of this review is to highlight existing knowledge, and recent advances in the diagnosis and management of AIBDs in humans - to serve as a road map for veterinary dermatologists. AREAS COVERED: Recent findings include complement-independent pathways in the pathogenesis of bullous pemphigoid, as well as the role of desmoglein and desmocollin autoantibodies in inducing acantholysis. Systemic glucocorticoids are the mainstay of treatment for AIBDs in humans, yet their long-term use is associated with severe adverse effects and complications, thereby limiting their use. Therefore, researchers have been exploring new and safer alternative therapeutic options for human AIBDs such as anti-CD20 monoclonal antibodies (Rituximab), Bruton's tyrosine kinase inhibitors (BTKi) and neonatal Fc receptor (FcRn) blockers. EXPERT OPINION: Randomised controlled trial (RCT) level evidence show that Rituximab and short-course GC regimes are more effective and safer than traditional GC treatment for human AIBDs. FcRn blockers such as SYNT001 have shown positive results in preliminary phase 2 clinical trials for treatment of human pemphigus; further trials are required. Rilzabrutinib (PRN1008), an orally administered BTKi, has recently completed phase 2 trials in pemphigus and is in a phase 3 RCT in humans.

Non-Bullous Pemphigoid: A Single-Center Retrospective Study

INTRODUCTION

Bullous pemphigoid (BP) is an autoimmune disease that typically presents with blisters, but sometimes early lesions may be eczematous, maculopapular, or urticarial. The aim of the present study was to highlight possible differences between typical bullous and non-bullous pemphigoid (NBP) and compare results with the literature. Material &amp; methods: Patients receiving a diagnosis of BP between January 2000 and December 2019 were analyzed. Patients who developed a blister after 3 months from the onset of pruritus were considered as NBP. Demographic features, clinical findings at diagnosis and at 2-year follow-up, histological features, auto-antibodies titers, comorbidities and their treatment were retrieved. Categorical variables were evaluated for normal distribution using a histogram and a Q-Q plot. The χ2 and Fisher's exact tests were used to compare categorical variables between the groups. Continuous variables were compared between the groups using analysis of variance and the independent-samples t test. For multivariate analysis, logistic regression was performed.

RESULTS

A total of 532 patients received a diagnosis of BP. A total of 122 patients were enrolled in the study; 63 were females, and the mean age at the diagnosis was 77.2 years (±11.9 SD). 98 were affected by BP and 24 were categorized as NBP. Mean time to diagnosis was 2.9 months (±5.8 SD) for BP and 30.4 months (±59.8 SD) for NBP (p = 0.0001). Skin manifestations in NBP patients were, in order of frequency: urticarial, papular or nodular, eczematous, and excoriations. Pruritus intensity was high but similar in the two groups (Numerical Rating Scale - NRS, 9.3 vs. 8.9). Seven out of 24 NBP patients (29%) never developed blisters; the other patients developed blisters after a mean follow-up time of 24.9 months (±54.9 SD). NBP patients had a more frequent history of myocardial infarction than BP patients (37.5 vs. 10.2%; p < 0.003). More NBP patients were taking diuretics than BP patients (66.7 vs. 49%; p = 0.03). NBP patients had a worse response to pruritus compared to BP patients at 2 years (NRS 3.7 vs. 11; p 0.001).

CONCLUSIONS

NBP patients have a delayed diagnosis and may be at an increased risk of cardiovascular disease, especially myocardial infarction. Severely and persistently itchy skin disorders in aged patients should be investigated for BP diagnosis.

Bullous pemphigoid autoantibodies

<abstract> <p>Autoimmune blistering skin disorders are rare. According to direct immunofluorescence studies, three categories are described: pemphigus group, pemphigoid group and dermatitis herpetiformis. Among these diseases, bullous pemphigoid is the most common. Patients with typical bullous pemphigoid disease are usually elderly and have many comorbidities. Considering that topical and systemic corticosteroids are the first choice therapy, these patients also have increased morbidity and risk of death. The main characteristic of bullous pemphigoid as an acquired autoimmune blistering disease is the formation of autoantibodies against hemidesmosomal antigens BP180 and BP230. Although IgG autoantibodies predominate within the plasma and skin of BP patients, some features of the disease cannot be explained solely by IgG-mediated mechanisms. Epitope spreading phenomena, immunoglobulin class switch and the relevance of IgM and IgE autoantibodies are discussed in this article.</p> </abstract>

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.

Basement membrane zone IgE deposition is associated with bullous pemphigoid disease severity and treatment results

BACKGROUND

A subset of patients with bullous pemphigoid (BP) show deposition of IgE in the basement membrane zone (BMZ), yet the relationship between BMZ IgE and the clinical presentation of BP remains unclear.

OBJECTIVES

To investigate the relationship between IgE deposition, IgE levels in serum, and disease severity in patients with BP.

METHODS

We investigated IgE autoantibodies in 53 patients with BP by direct immunofluorescence (DIF), indirect immunofluorescence and enzyme-linked immunosorbent assay.

RESULTS

Of 53 patients with BP, 23 (43%) had IgE deposition, 10 (19%) of whom were IgE+ and 13 (25%) IgE± according to DIF analyses. Erosion/blister (E/B) Bullous Pemphigoid Disease Area Index (BPDAI) scores were significantly higher in IgE+ patients than in IgE- patients (n = 15), while no significant differences were found for urticaria/erythema BPDAI scores. IgE+ and IgE± patients took longer to reduce their E/B BPDAI score by 75% after systemic corticosteroid treatment. BP180-IgE levels were significantly higher among IgE+ patients than IgE± or IgE- patients (n = 10). Total IgE levels in the serum and blood eosinophil counts did not differ between IgE+, IgE± and IgE- patients. A significant correlation was detected between BP180-IgG and BP180-IgE, but not between BPDAI scores and any of BP180-IgG, BP180-IgE or blood eosinophil count.

CONCLUSIONS

IgE deposition in the BMZ is associated with higher E/B BPDAI scores and longer treatment periods. We conclude that IgE binding in the BMZ may contribute to BP pathogenesis by promoting blister formation. What's already known about this topic? BP180-IgE autoantibodies have an important role in the pathogenesis of bullous pemphigoid (BP). A subset of patients with BP display deposition of IgE within the basement membrane zone (BMZ) of skin tissue. What does this study add? Patients with in vivo IgE deposition in the BMZ displayed higher erosion/blister Bullous Pemphigoid Disease Area Index (BPDAI) scores, while urticaria/erythema BPDAI scores were not significantly different. Patients with in vivo IgE deposition in the BMZ took longer to reduce their erosion/blister BPDAI score by 75% after systemic corticosteroid treatment. BP180-specific IgE levels in serum were higher among patients with linear IgE deposition in the BMZ than in those with granular or no IgE deposition.

The Intersection of IgE Autoantibodies and Eosinophilia in the Pathogenesis of Bullous Pemphigoid

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by autoantibodies targeting cellular adhesion molecules. While IgE autoantibodies are occasionally reported in other autoimmune blistering diseases, BP is unique in that most BP patients develop an IgE autoantibody response. It is not known why BP patients develop self-reactive IgE and the precise role of IgE in BP pathogenesis is not fully understood. However, clinical evidence suggests an association between elevated IgE antibodies and eosinophilia in BP patients. Since eosinophils are multipotent effector cells, capable cytotoxicity and immune modulation, the putative interaction between IgE and eosinophils is a primary focus in current studies aimed at understanding the key components of disease pathogenesis. In this review, we provide an overview of BP pathogenesis, highlighting clinical and experimental evidence supporting central roles for IgE and eosinophils as independent mediators of disease and via their interaction. Additionally, therapeutics targeting IgE, the Th2 axis, or eosinophils are also discussed.

Effects of Omalizumab on FcεRI and IgE Expression in Lesional Skin of Bullous Pemphigoid

Recent studies suggest an important role of immunoglobulin E (IgE) as an alternative pathogenic pathway in the development of bullous pemphigoid (BP), as the most frequent subepidermal blistering disease of the skin Use of IgE targeted therapies, such as omalizumab, has been shown promising in recent studies. The aim of this study was to assess the effect of omalizumab on FcεRI and IgE expression on circulating basophils and on lesional intradermal cells in BP to generate insight into the immunological effects of omalizumab in BP. We report two cases of BP patients treated with omalizumab. Efficacy of treatment was assessed clinically 4 months after initiation of the therapy. Lesional and non-lesional skin biopsies where taken before and 4 weeks after initiation of omalizumab therapy. In addition, FcεRI expression on circulating cells and IgE levels in serum and in the skin samples, as well as anti-BP180 and anti-BP230 in serum and eosinophils and basophils counts in blood were assessed before and during treatment. Both patients showed a marked improvement after 4 months, with no adverse effects. Down-regulation of FcεRI, IgE in lesional skin and on circulating basophils were observed in parallel with clinical improvement. The current case study supports the role of omalizumab in the treatment of a subset of BP patients. Our observations suggest that omalizumab represents a valuable therapeutic option in the management of BP patients. Its efficacy might be related to reduction in FcεRI+ and IgE+ basophils and intradermal cells.

Targeted Therapies for Autoimmune Bullous Diseases: Current Status

Autoimmune bullous skin disorders are rare but meaningful chronic inflammatory diseases, many of which had a poor or devastating prognosis prior to the advent of immunosuppressive drugs such as systemic corticosteroids, which down-regulate the immune pathogenesis in these disorders. Glucocorticoids and adjuvant immunosuppressive drugs have been of major benefit for the fast control of most of these disorders, but their long-term use is limited by major side effects such as blood cytopenia, osteoporosis, diabetes mellitus, hypertension, and gastrointestinal ulcers. In recent years, major efforts were made to identify key elements in the pathogenesis of autoimmune bullous disorders, leading to the identification of their autoantigens, which are mainly located in desmosomes (pemphigus) and the basement membrane zone (pemphigoids). In the majority of cases, immunoglobulin G, and to a lesser extent, immunoglobulin A autoantibodies directed against distinct cutaneous adhesion molecules are directly responsible for the loss of cell-cell and cell-basement membrane adhesion, which is clinically related to the formation of blisters and/or erosions of the skin and mucous membranes. We describe and discuss novel therapeutic strategies that directly interfere with the production and regulation of pathogenic autoantibodies (rituximab), their catabolism (intravenous immunoglobulins), and their presence in the circulation and extravascular tissues such as the skin (immunoadsorption), leading to a significant amelioration of disease. Moreover, we show that these novel therapies have pleiotropic effects on various proinflammatory cells and cytokines. Recent studies in bullous pemphigoid suggest that targeting of immunoglobulin E autoantibodies (omalizumab) may be also beneficial. In summary, the introduction of targeted therapies in pemphigus and pemphigoid holds major promise because of the high efficacy and fewer side effects compared with conventional global immunosuppressive therapy.

New Insights Into the Pathogenesis of Bullous Pemphigoid: 2019 Update

There are several lines of evidence indicating that the physiopathological bases of bullous pemphigoid (BP), the most common subepidermal autoimmune bullous disease, are hallmarked by the production of autoantibodies directed against the hemidesmosomal anchoring proteins BP180 and BP230. In contrast to the robustness of the latter assumption, the multifaceted complexity of upstream and downstream mechanisms implied in the pathogenesis of BP remains an area of intense speculation. So far, an imbalance between T regulatory cells and autoreactive T helper (Th) cells has been regarded as the main pathogenic factor triggering the autoimmune response in BP patients. However, the contributory role of signaling pathways fostering the B cell stimulation, such as Toll-like receptor activation, as well as that of ancillary inflammatory mechanisms responsible for blister formation, such as Th17 axis stimulation and the activation of the coagulation cascade, are still a matter of debate. In the same way, the pathomechanisms implied in the loss of dermal-epidermal adhesion secondary to autoantibodies binding are not fully understood. Herein, we review in detail the current concepts and controversies on the complex pathogenesis of BP, shedding light on the most recent theories emerging from the literature.

Bullous pemphigoid

Bullous pemphigoid is the most frequent autoimmune bullous disease and mainly affects elderly individuals. Increase in incidence rates in the past decades has been attributed to population aging, drug-induced cases and improvement in the diagnosis of the nonbullous presentations of the disease. A dysregulated T cell immune response and synthesis of IgG and IgE autoantibodies against hemidesmosomal proteins (BP180 and BP230) lead to neutrophil chemotaxis and degradation of the basement membrane zone. Bullous pemphigoid classically manifests with tense blisters over urticarial plaques on the trunk and extremities accompanied by intense pruritus. Mucosal involvement is rarely reported. Diagnosis relies on (1) the histopathological evaluation demonstrating eosinophilic spongiosis or a subepidermal detachment with eosinophils; (2) the detection of IgG and/or C3 deposition at the basement membrane zone using direct or indirect immunofluorescence assays; and (3) quantification of circulating autoantibodies against BP180 and/or BP230 using ELISA. Bullous pemphigoid is often associated with multiple comorbidities in elderly individuals, especially neurological disorders and increased thrombotic risk, reaching a 1-year mortality rate of 23%. Treatment has to be tailored according to the patient's clinical conditions and disease severity. High potency topical steroids and systemic steroids are the current mainstay of therapy. Recent randomized controlled studies have demonstrated the benefit and safety of adjuvant treatment with doxycycline, dapsone and immunosuppressants aiming a reduction in the cumulative steroid dose and mortality.

IgE blockade in autoimmunity: Omalizumab induced remission of bullous pemphigoid

Bullous pemphigoid (BP) is a blistering dermopathy and a prototypic antibody-mediated autoimmune disease. Detection of IgG autoantibodies against hemidesmosomal proteins BP180 and/or BP230 are diagnostic and levels can correlate with disease activity. Therapies include corticosteroids and oral immunosuppressants, while intravenous immunoglobulin and rituximab are reserved for treatment resistant cases. Here we describe a patient with severe BP which was refractory to standard first line therapy, intravenous immunoglobulin and rituximab induced depletion of peripheral B cells. Use of the monoclonal anti-IgE antibody omalizumab resulted in rapid resolution of blistering despite ongoing high levels of anti-skin IgG antibodies. To our knowledge this is the first case of BP responsive to omalizumab after failure of rituximab to be reported. This case adds to emerging data on omalizumab as a novel BP treatment as well as providing new evidence of an independent role for autoreactive IgE-mediated inflammation in the formation of BP skin lesions.

Detection of IgE autoantibodies in mucous membrane pemphigoid and their association with disease severity

BACKGROUND

Mucous membrane pemphigoid (MMP) is an autoimmune disease characterized by scarring lesions at mucosal sites. Although the pathogenic role of specific IgG and/or IgA has been already demonstrated and the detection of these immunoglobulins is a criterion in the diagnosis of MMP, little is known about IgE role in this disease. Therefore, the main purpose of this study was to assess the presence of circulating and tissue bound IgE in patients with MMP and their possible correlations with clinical presentation and disease course.

METHODS

We conducted a retrospective study on 29 patients affected by MMP, recruited from a single center. Direct and indirect immunofluorescence studies were assessed to analyze the presence of specific IgE directed against the basal membrane zone. For each patient, fluorescence data were compared to clinical features.

RESULTS

Linear deposits of C3, IgG and IgA were present in 86.2%, 62% and 37.9% of cases respectively, while IgE linear deposits were detected in 17 out of 29 patients (58.6%) including one case with isolated IgE positivity. Circulating IgE and IgA anti-BMZ were present in 7 (24.1%) and 5 (17.2%) patients, respectively. Both the presence of circulating IgA and of tissue bound IgE deposits correlated with disease activity index (P<0.014).

CONCLUSIONS

Our results demonstrated the presence of IgE autoantibodies in MMP, particularly in more severe cases. Thus, IgE detection may represent an additional useful diagnostic tool in this disease.

Recent advances in the understanding and treatment of pemphigus and pemphigoid

Pemphigus and pemphigoid are characterized as autoimmune blistering diseases in which immunoglobulin G autoantibodies cause blisters and erosions of the skin or mucosa or both. Recently, understanding of the pathophysiology of pemphigus and pemphigoid has been furthered by genetic analyses, characterization of autoantibodies and autoreactive B cells, and elucidation of cell–cell adhesion between keratinocytes. For the management of pemphigus and pemphigoid, the administration of systemic corticosteroids still represents the standard treatment strategy; however, evidence of the efficacy of therapies not involving corticosteroids, such as those employing anti-CD20 antibodies, is increasing. The goal should be to develop antigen-specific immune suppression-based treatments.

Eosinophils Mediate Tissue Injury in the Autoimmune Skin Disease Bullous Pemphigoid

Eosinophils are typically associated with unique inflammatory settings, including allergic inflammation and helminth infections. However, new information suggests that eosinophils contribute more broadly to inflammatory responses and participate in local immune regulation and the tissue remodeling/repair events linked with a variety of diseases. Eosinophilic infiltration has long been a histologic hallmark of bullous pemphigoid (BP), a subepidermal autoimmune blistering disease characterized by autoantibodies directed against basement membrane protein BP180. However, the exact role of eosinophils in disease pathogenesis remains largely unknown. We show here that eosinophils are necessary for IgE autoantibody-mediated BP blister formation in a humanized IgE receptor mouse model of BP. Disease severity is IgE dose dependent and correlates with the degree of eosinophil infiltration in the skin. Furthermore, IgE autoantibodies fail to induce BP in eosinophil-deficient mice, confirming that eosinophils are required for IgE-mediated tissue injury. Thus, eosinophils provide the cellular link between IgE autoantibodies and skin blistering in this murine model of BP. These findings suggest a role for eosinophils in autoimmune disease and have important implications for the treatment of BP and other antibody-mediated inflammatory and autoimmune diseases.

Immunoglobulin E-Mediated Autoimmunity

The study of autoimmunity mediated by immunoglobulin E (IgE) autoantibodies, which may be termed autoallergy, is in its infancy. It is now recognized that systemic lupus erythematosus, bullous pemphigoid (BP), and chronic urticaria, both spontaneous and inducible, are most likely to be mediated, at least in part, by IgE autoantibodies. The situation in other conditions, such as autoimmune uveitis, rheumatoid arthritis, hyperthyroid Graves’ disease, autoimmune pancreatitis, and even asthma, is far less clear but evidence for autoallergy is accumulating. To be certain of an autoallergic mechanism, it is necessary to identify both IgE autoantibodies and their targets as has been done with the transmembrane protein BP180 and the intracellular protein BP230 in BP and IL-24 in chronic spontaneous urticaria. Also, IgE-targeted therapies, such as anti-IgE, must have been shown to be of benefit to patients as has been done with both of these conditions. This comprehensive review of the literature on IgE-mediated autoallergy focuses on three related questions. What do we know about the prevalence of IgE autoantibodies and their targets in different diseases? What do we know about the relevance of IgE autoantibodies in different diseases? What do we know about the cellular and molecular effects of IgE autoantibodies? In addition to providing answers to these questions, based on a broad review of the literature, we outline the current gaps of knowledge in our understanding of IgE autoantibodies and describe approaches to address them.

BP180 Is Critical in the Autoimmunity of Bullous Pemphigoid

Bullous pemphigoid (BP) is by far the most common autoimmune blistering dermatosis that mainly occurs in the elderly. The BP180 is a transmembrane glycoprotein, which is highly immunodominant in BP. The structure and location of BP180 indicate that it is a significant autoantigen and plays a key role in blister formation. Autoantibodies from BP patients react with BP180, which leads to its degradation and this has been regarded as the central event in BP pathogenesis. The consequent blister formation involves the activation of complement-dependent or -independent signals, as well as inflammatory pathways induced by BP180/anti-BP180 autoantibody interaction. As a multi-epitope molecule, BP180 can cause dermal-epidermal separation via combining each epitope with specific immunoglobulin, which also facilitates blister formation. In addition, some inflammatory factors can directly deplete BP180, thereby leading to fragility of the dermal-epidermal junction and blister formation. This review summarizes recent investigations on the role of BP180 in BP pathogenesis to determine the potential targets for the treatment of patients with BP.

IgE autoreactivity in bullous pemphigoid: eosinophils and mast cells as major targets of pathogenic immune reactants

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune disease characterized by tense blisters that are usually preceded by urticarial eruptions. Affected patients exhibit IgG and/or IgE autoantibodies against BP180 and/or BP230. Their relative importance in disease pathogenesis has not been fully elucidated.

OBJECTIVES

The aim of this study was to provide a better characterization of the circulating and tissue-resident IgE in patients with BP at the serological, structural and functional levels.

METHODS

Sera (n = 19) and skin (n = 33) from patients with BP were analysed via enzyme-linked immunosorbent assay (ELISA) and immunofluorescence, respectively.

RESULTS

The results obtained show that many patients with BP exhibit elevated IgE levels in the serum and in the skin. In the skin, it is very rarely and only sparsely found along the basement membrane zone, but is prominently present on mast cells and eosinophils. At least a portion of these IgE antibodies are BP-specific, as evidenced by serum ELISA and by the colocalization of BP180 and FcεRI-bound IgE on mast cells and/or eosinophils. An important role of these immune reactants can be inferred from our additional finding that cross-linking of IgE, derived from BP sera, on FcεRI-expressing rat basophils with BP180 results in robust degranulation of these cells.

CONCLUSIONS

We propose the existence of a disease pathway alternative to IgG and complement that may well be responsible for some of the clinical features of this autoimmune disease.

Eosinophils as putative therapeutic targets in bullous pemphigoid

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering skin disease and is characterized by the presence of autoantibodies directed against the hemidesmosomal proteins BP180 and BP230 that can be detected in the skin and serum of BP patients. Histologically, the dermal infiltration of eosinophils is obvious. The objective of this review was to present evidence that eosinophils play a key role in the pathogenesis of BP. Eosinophils, together with cytokines and chemokines regulating their production, recruitment and activation, are abundantly present in lesional skin, in blisters and in peripheral blood of patients with BP. Recently, using a cryosection model, eosinophils were demonstrated to induce dermal-epidermal separation in the presence of BP antibodies. Thus, eosinophils and their products, as well as mediators regulating their function, present promising targets for the treatment of BP.

IgE autoantibodies and their association with the disease activity and phenotype in bullous pemphigoid: a systematic review

Bullous pemphigoid (BP) is the most common autoimmune skin disease of blistering character. The underlying pathophysiological mechanism involves an immune attack, usually by IgG class autoantibodies, on the autoantigen BP 180/BPAg2, which is a type XVII collagen (COL17) protein acting as the adhesion molecule between the epidermis and the basement membrane of the dermis. About 40 years ago, following consistent findings of elevated total serum IgE levels in BP patients, it was hypothesized that IgE may be involved in the pathophysiology of BP. Our objective was to determine whether there is strong evidence for an association between IgE class autoantibodies and the clinical severity or phenotype of BP. Three databases were searched for relevant studies and appropriate exclusion and inclusion criteria were applied. Data was extracted and assessed in relation to the study questions concerning the clinical significance of IgE autoantibodies in BP. Nine studies found that anti-BP180 autoantibodies of IgE class are associated with increased severity of BP, whereas two studies did not find such an association. The number of studies which found an association between higher IgE autoantibody levels and the erythematous urticarial phenotype of BP (5) was equal in number to the studies which found no such association (5). In conclusion, higher serum IgE autoantibody levels are associated with more severe clinical manifestations of BP. There is insufficient evidence to support higher IgE autoantibody levels being associated with specific clinical phenotypes of BP.

Detection of IgE autoantibodies to BP180 and BP230 and their relationship to clinical features in bullous pemphigoid

BACKGROUND

IgE autoantibodies are considered to be involved in the pathogenesis of bullous pemphigoid (BP), particularly inflammatory and erythematous phenotypes.

OBJECTIVES

To develop reliable enzyme-linked immunosorbent assays (ELISAs) for the detection of IgE autoantibodies to both BP180 and BP230 in BP sera, and to compare the ELISA results with clinical features.

METHODS

We used commercially available IgG ELISAs to develop IgE ELISAs for both BP180 and BP230. To determine the influence of excess amounts of IgG autoantibodies, all normal and BP sera were tested before and after IgG adsorption. The results of the IgE ELISAs were statistically compared with various ELISAs and various clinical parameters, including our own severity scores and BP phenotypes.

RESULTS

IgG adsorption generally showed no changes in sensitivity and specificity for IgE ELISAs, although slight cross-reactivity of anti-IgE secondary antibody to IgG and interference of excess amounts of IgG autoantibodies to IgE reactivity were suggested. IgE autoantibodies to BP180 were found in 21 of 36 BP sera and IgE autoantibodies to BP230 were found in 18 of 36 BP sera. The results of IgG and IgE ELISAs for both BP180 and BP230 were well correlated. IgG and IgE anti-BP180 antibodies correlated with disease activity but IgG and IgE anti-BP230 autoantibodies did not. IgE anti-BP230 autoantibodies correlated with nodular phenotype but not erythematous phenotype.

CONCLUSIONS

The results of this study indicated that IgE autoantibodies to both BP180 and BP230 are frequently detected in BP sera. IgE anti-BP180 autoantibodies seemed to be pathogenic, while an association between IgE autoantibodies and inflammatory BP phenotype was not indicated.

Diagnostic value of immunohistochemistry on formalin-fixed, paraffin-embedded skin biopsy specimens for bullous pemphigoid

BACKGROUND

Direct immunofluorescence microscopy (DIF) studies constitute the gold standard for diagnosis of bullous pemphigoid (BP) but depend on the availability of specialized laboratories and often on an additional skin biopsy specimen.

OBJECTIVES

To assess the value of immunohistochemical analyses (IHCA) in the diagnosis of BP using formalin-fixed, paraffin-embedded skin biopsy specimens as an alternative to DIF; and to study the correlation between the results of IHCA and the presence of histological subepidermal blister formation and of circulating autoantibodies by indirect immunofluorescence studies using split skin or by enzyme-linked immunosorbent assays.

METHODS

We included all patients newly diagnosed with BP evaluated between 2008 and 2010. There were 51 consecutive skin biopsy specimens obtained from 38 patients with BP with positive DIF.

RESULTS

By IHCA, deposits of immunoreactants were found in 45% of all tested cases. Deposits of C3d, IgG, IgM, IgE and IgA were found in 37%, 23%, 2%, 0% and 0% of cases, respectively. Deposits of C3d and/or IgG were found in 79% of the 24 cases with a blister and in 83% of the 12 cases with subepidermal blistering and positive immunoserological analyses, respectively.

CONCLUSIONS

In contrast to previous studies, our findings in an unselected patient cohort indicate that IHCA are not sufficiently sensitive to replace DIF studies for confirming the diagnosis of BP. IHCA sensitivity significantly increases in the presence of histological blistering and/or of circulating autoantibodies. IHCA represents a potential rescue diagnostic technique only if specialized laboratories and/or a second biopsy specimen for DIF are unavailable.

IgE-mediated mechanisms in bullous pemphigoid and other autoimmune bullous diseases

Autoimmune bullous diseases (AIBDs) are characterized by autoantibodies against structural proteins of the dermal-epidermal junction (in pemphigoid diseases) and the epidermal/ epithelial desmosomes (in pemphigus diseases). By far, the most common AIBD is bullous pemphigoid, which is immunopathologically characterized by autoantibodies against BP180 (type XVII collagen) and BP230. IgG and, to a lesser extent, IgA autoantibodies are the major autoantibody isotypes in these disorders. IgE autoantibodies are increasingly reported in particular in bullous pemphigoid. The development of specific and sensitive anti-BP180 IgE ELISA systems, the report of two experimental murine models employing IgE autoantibodies against BP180, and the successful treatment of bullous pemphigoid with the anti-IgE antibody omalizumab have raised interest in the role of IgE autoantibodies and the modulation of their production in AIBDs. Here, the relevance of IgE autoantibodies in the diagnosis, pathophysiology, and treatment decisions of AIBDs, with a focus on bullous pemphigoid, is reviewed.

IgE autoantibodies in bullous pemphigoid: supporting role, or leading player?

Bullous pemphigoid (BP) is a common autoimmune blistering skin disease in which two hemidesmosomal components--the transmembrane collagen XVII (BP180 or BPAG2) and the plakin family protein BP230 (BPAG1)--are targeted by autoimmunity. Of these, collagen XVII (COL17) is thought to be a major autoantigen, and vital roles of IgG autoantibodies in blister formation have been elucidated. However, BP shows distinct features, including pruritic urticarial erythema and eosinophilic infiltration, which may be independent of IgG-mediated autoimmunity. Recently, it has been revealed that sera from certain patients with BP contain IgE autoantibodies to COL17 and that IgE autoantibodies bind to peri-lesional dermal-epidermal junctions. Mouse models have demonstrated that IgE antibodies to COL17 induce erythema and eosinophilic infiltration in skin. In addition, the successful treatment of severe BP with omalizumab, a humanized monoclonal antibody targeting IgE, has been reported. These findings suggest that both IgG and IgE autoantibodies to COL17 may be involved in the BP pathogenesis. This article summarizes IgE-mediated autoimmunity to COL17 in BP.

In vivo analysis of IgE autoantibodies in bullous pemphigoid: a study of 100 cases

BACKGROUND

Bullous pemphigoid (BP) is an acquired autoimmune blistering disease characterized by subepidermal blister formation, in vivo linear deposition of immunoglobulin G (IgG) and complements at the dermal-epidermal junction (DEJ). The circulating IgG autoantibodies are directed against two epidermal hemidesmosomal glycoproteins: BP180, also known as type XVII collagen (COL17), and BP230. In addition, recent studies have shown that IgE autoantibodies may be involved in the pathogenesis of BP, although in vivo IgE deposition in lesional skin has not been fully characterized in large numbers of BP patients.

OBJECTIVE

This study investigated the incidence of in vivo deposition of IgE autoantibodies at the DEJ in lesional skin from a large number of BP patients.

METHODS

Peri-lesional skin samples from 100 patients who met the clinical and histopathological criteria for BP were investigated by direct immunofluorescence for the deposition of autoantibodies and complement. Patients' sera were also investigated by enzyme-linked immunosorbent assay and indirect immunofluorescence.

RESULTS

18% of BP patients were found to show IgE deposition at the DEJ. Disease severity, clinical course and outcome did not differ between IgE-positive and IgE-negative patients. In 3 IgE-positive cases, IgG was undetectable in vivo, and these cases showed atypical manifestations.

CONCLUSION

The results of in vivo IgE deposition may not be useful in predicting the disease course of BP, although predominant IgE deposition could alter the pattern of clinical manifestations.

Update on the pathogenesis of bullous pemphigoid: an autoantibody-mediated blistering disease targeting collagen XVII

Bullous pemphigoid (BP) is a common autoimmune blistering skin disorder that tends to affect the elderly. Autoantibodies (autoAbs) from BP patients react with two hemidesmosomal components: transmembrane collagen XVII (BP180 or BPAG2) and plakin family protein BP230 (BPAG1). Of these, collagen XVII (COL17) is thought to be a major autoantigen. The binding of autoAbs to COL17 following the activation of complements and inflammatory pathways eventually leads to the degradation of COL17, and this has been regarded as the main pathogenesis of BP. However, recent investigations have suggested other pathways, including a complement-independent pathway and a pathway involving IgE-autoAbs. BP-autoAbs can directly deplete COL17, leading to fragility of the dermal-epidermal junction. In addition, IgE-autoAbs to COL17 may be involved in the formation of itchy urticarial erythema associated with eosinophilic infiltration. This article summarizes the update on pathogenesis of BP, with a special focus on blister formation by autoAbs to COL17.

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.

Functional characterization of an IgE-class monoclonal antibody specific for the bullous pemphigoid autoantigen, BP180

BP180 (collagen XVII) is the target antigen in several autoimmune diseases including bullous pemphigoid (BP). Both IgE and IgG class autoantibodies have been shown to be pathogenic in BP; however, studies designed to elucidate the patho-mechanisms mediated specifically by the IgE-class autoantibodies are limited by the low levels (ng/mL) of IgE in human sera. In this report, we developed mouse IgE class monoclonal antibodies (MAbs) against the immunodominant NC16A domain of the human BP180 protein and characterized two of the resultant MAbs, designated 395A5 and 395D2. Epitope mapping studies revealed that both MAbs target segment 2 of NC16A, as was described for IgE and IgG class BP autoantibodies. Also similar to BP IgE, MAb 395A5 showed indirect immunofluorescence labeling of the basement membrane zone (BMZ) of human skin, stimulated histamine release from mast cells when triggered with NC16A, and induced keratinocyte production of IL-8. The 395D2 MAb was also able to trigger antigen-specific histamine release from mast cells; however, in contrast to BP IgE and 395A5, 395D2 did not label the cutaneous BMZ, nor did it induce IL-8 production in keratinocytes. In summary, these studies underscore the importance of functionally characterizing MAbs generated for use in human disease models. The 395A5 IgE class murine MAb was shown to share several key functional properties with the pathogenically active IgE produced by BP patients. We therefore expect that this MAb will prove to be a useful tool for dissecting the mechanisms used by BP180-NC16A-specific IgE antibodies in the induction of BP skin lesions.