Insights Into the Pathogenesis of Bullous Pemphigoid: The Role of Complement-Independent Mechanisms

Targeting antibody-mediated complement-independent mechanism in bullous pemphigoid with diacerein

BACKGROUND

Bullous pemphigoid (BP) is an antibody-mediated blistering disease predominantly affecting the elderly. The pathogenesis involves both complement-dependent and complement-independent mechanisms. The therapeutic potential of targeting complement-independent mechanism has not yet been determined. The mainstay of treatment, corticosteroid, has many side effects, indicating the needs of better treatments.

OBJECTIVE

We tempted to establish an in vitro model of BP which resembles complement-independent mechanism and to examine the therapeutic potential of a novel anti-inflammatory agent, diacerein.

METHODS

Cultured HaCaT cells were treated with purified antibodies from BP patients, with or without diacerein to measure the cell interface presence of BP180, protein kinase C, and the production of proinflammatory cytokines. An open-label, randomized, phase 2 trial was conducted to compare topical diacerein and clobetasol ointments in patients with mild-to-moderate BP (NCT03286582).

RESULTS

The reduced presentation of BP180 at cell interface after treating with BP autoantibodies was noticed in immunofluorescence and western blotting studies. The phenomenon was restored by diacerein. Diacerein also reduced the autoantibody-induced increase of pro-inflammatory cytokines. Reciprocal changes of BP180 and protein kinase C at the cell interface were found after treating with BP autoantibodies. This phenomenon was also reversed by diacerein in a dose-dependent manner. The phase 2 trial showed that topical diacerein reduced the clinical symptoms which were comparable to those of topical clobetasol.

CONCLUSION

Diacerein inhibited BP autoantibody-induced reduction of BP180 and production of proinflammatory cytokines in vitro and showed therapeutic potential in patients with BP. It is a novel drug worthy of further investigations.

Bullous pemphigoid induced by IgG targeting type XVII collagen non-NC16A/NC15A extracellular domains is driven by Fc gamma receptor- and complement-mediated effector mechanisms and is ameliorated by neonatal Fc receptor blockade

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by autoantibodies targeting type XVII collagen (Col17) with the noncollagenous 16A (NC16A) ectodomain representing the immunodominant site. The role of additional extracellular targets of Col17 outside NC16A has not been unequivocally demonstrated. In this study, we showed that Col17 ectodomain-reactive patient sera depleted in NC16A IgG induced dermal-epidermal separation in a cryosection model indicating the pathogenic potential of anti-Col17 non-NC16A extracellular IgG. Moreover, injection of IgG targeting the murine Col17 NC14-1 domains (downstream of NC15A, the murine homologue of human NC16A) into C57BL/6J mice resulted in erythematous skin lesions and erosions. Clinical findings were accompanied by IgG/C3 deposits along the basement membrane and subepidermal blistering with inflammatory infiltrates. Disease development was significantly reduced in either Fc-gamma receptor (FcγR)- or complement-5a receptor-1 (C5aR1)-deficient mice. Inhibition of the neonatal FcR (FcRn), an atypical FcγR regulating IgG homeostasis, with the murine Fc fragment IgG2c-ABDEG, a derivative of efgartigimod, reduced anti-NC14-1 IgG levels, resulting in ameliorated skin inflammation compared with isotype-treated controls. These data demonstrate that the pathogenic effects of IgG targeting the Col17 domain outside human NC16A/murine NC15A are partly attributable to antibody-mediated FcγR- and C5aR1 effector mechanisms while pharmacological inhibition of the FcRn represents a promising treatment for BP. The mouse model of BP will be instrumental in further investigating the role of Col17 non-NC16A/NC15A extracellular epitopes and validating new therapies for this disease. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The Syk Inhibitor Entospletinib Abolishes Dermal-Epidermal Separation in a Fully Human Ex Vivo Model of Bullous Pemphigoid

Bullous pemphigoid (BP) is an autoantibody-mediated blistering skin disease characterized by local inflammation and dermal-epidermal separation, with no approved targeted therapy. The Syk tyrosine kinase is critical for various functions of the immune response. Second-generation Syk inhibitors such as entospletinib are currently being tested for hematological malignancies. Our aim was to test the effect of entospletinib in a fully human model system of BP. Incubating BP serum-treated human frozen skin sections with normal human granulocytes and fresh plasma triggered dermal-epidermal separation that was dependent on complement, NADPH oxidase, and protease activity. Entospletinib dramatically reduced dermal-epidermal separation with a half-maximal inhibitory concentration of ≈16 nM. Entospletinib also reduced ROS production, granule release, and spreading of human granulocytes plated on immobilized immune complexes consisting either of a generic antigen-antibody pair or of recombinant collagen type XVII (BPAg2) and BP serum components (supposedly autoantibodies). However, entospletinib did not affect the chemotactic migration of human granulocytes or their responses to nonphysiological stimulation by phorbol esters. Entospletinib had no effect on the survival of granulocytes either. Taken together, entospletinib abrogates dermal-epidermal separation, likely through inhibition of granulocyte responsiveness to deposited immune complexes. Entospletinib or other Syk inhibitors may provide therapeutic benefits in BP.

Anti-Idiotypic mRNA Vaccine to Treat Autoimmune Disorders

The 80+ existing autoimmune disorders (ADs) affect billions with little prevention or treatment options, except for temporary symptomatic management, leading to enormous human suffering and a monumental financial burden. The autoantibodies formed in most ADs have been identified, allowing the development of novel anti-idiotypic antibodies to mute the autoantibodies using vaccines. Nucleoside vaccines have been successfully tested as antigen-specific immunotherapies (ASI), with mRNA technology offering multi-epitope targeting to mute multiple autoantibodies. This paper proposes using mRNA technology to produce anti-idiotypic antibodies with broad effectiveness in preventing and treating them. This paper delves into the state-of-the-art mRNA design strategies used to develop novel ASIs by selecting appropriate T cell and B cell epitopes to generate anti-idiotypic antibodies. The low cost and fast development of mRNA vaccines make this technology the most affordable for the global control of ADs.

Risk factors predisposing relapse of bullous pemphigoid at initial diagnosis: A retrospective cohort study of 205 patients

BACKGROUND

Previous studies have revealed the factors associated with the relapse of bullous pemphigoid (BP). This study aims to assess the characteristics of BP patients at the time of initial diagnosis and a potential association with subsequent relapse occurrences.

METHODS

A retrospective cohort study was conducted on 205 BP patients from January 2009 to May 2022 at the Peking Union Medical College Hospital in Beijing, China. The median follow-up duration was 2.7 years. We conducted univariate and multivariate analyses on various clinical indicators (e.g., lesional involvements and medical history) and laboratory test results.

RESULTS

Among the 205 patients, 118 (57.6 %) relapsed during the follow-up period. Univariate analysis revealed several factors associated with relapse, which were greater age [Hazard Ratio (HR)1.018, 95 % confidence interval (CI) 1.004-1.032] (p = 0.010), a past medical history of thyroid diseases [HR 3.674, 95 % CI 1.472-9.167] (p = 0.005), hematological disease complications [HR 4.123, 95 % CI 1.301-13.061] (p = 0.016), negative C3 deposition in direct immunofluorescence [HR 0.574, 95 % CI 0.374-0.883] (p = 0.011) and prealbumin level less than 200 mg/L[HR 0.580, 95 % CI 0.351-0.957] (p = 0.033). Multivariate analysis demonstrated that patients with negative C3 deposition in direct immunofluorescence [HR 0.524, 95 % CI 0.296-0.927] (p = 0.026) and prealbumin levels below 200 mg/L [HR 0.541, 95 % CI 0.301-0.974] (p = 0.041) were associated with further relapses of BP.

CONCLUSIONS

Negative C3 deposition in direct immunofluorescence and a prealbumin level below 200 mg/L at initial diagnosis served as predictive markers for future relapses of BP. Systemic evaluation of BP patients at initial diagnosis could be essential in helping prevent recurrences and achieve more effective disease management.

Advancing Treatment in Bullous Pemphigoid: A Comprehensive Review of Novel Therapeutic Targets and Approaches

Bullous pemphigoid is one of the most common autoimmune bullous diseases occurring primarily in the elderly. Pathogenic autoantibodies against BP180 and BP230 at the dermal-epidermal junction cause subepidermal blisters, erosions, and intense pruritus, all of which adversely affect the patients' quality of life and may increase their morbidity and mortality. Current systemic treatment options for bullous pemphigoid are limited to corticosteroids and immunosuppressants, which can have substantial side effects on these vulnerable patients that even exceed their therapeutic benefits. Therefore, more precisely, targeting therapies to the pathogenic cells and molecules in bullous pemphigoid is an urgent issue. In this review, we describe the pathophysiology of bullous pemphigoid, focusing on autoantibodies, complements, eosinophils, neutrophils, proteases, and the T helper 2 and 17 axes since they are crucial in promoting proinflammatory environments. We also highlight the emerging therapeutic targets for bullous pemphigoid and their latest discoveries in clinical trials or experimental studies. Further well-designed studies are required to establish the efficacy and safety of these prospective therapeutic options.

From Molecular Insights to Clinical Perspectives in Drug-Associated Bullous Pemphigoid

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is characterized by the presence of autoantibodies targeting BP180 and BP230 in the basement membrane zone. This leads to the activation of complement-dependent and independent pathways, resulting in proteolytic cleavage at the dermoepidermal junction and an eosinophilic inflammatory response. While numerous drugs have been associated with BP in the literature, causality and pathogenic mechanisms remain elusive in most cases. Dipeptidyl peptidase 4 inhibitors (DPP4i), in particular, are the most frequently reported drugs related to BP and, therefore, have been extensively investigated. They can potentially trigger BP through the impaired proteolytic degradation of BP180, combined with immune dysregulation. DPP4i-associated BP can be categorized into true drug-induced BP and drug-triggered BP, with the latter resembling classic BP. Antineoplastic immunotherapy is increasingly associated with BP, with both B and T cells involved. Other drugs, including biologics, diuretics and cardiovascular and neuropsychiatric agents, present weaker evidence and poorly understood pathogenic mechanisms. Further research is needed due to the growing incidence of BP and the increasing identification of new potential triggers.

Pemphigus and pemphigoids: Clinical presentation, diagnosis and therapy

Pemphigus and pemphigoid are two potentially life-threatening groups of autoimmune diseases, characterized by autoantibodies targeting structural components of desmosomes or hemidesmosomes, respectively. Affected patients typically show itchy/painful plaques or blistering skin lesions and/or impairing mucosal blistering and erosions, which may strongly impact their quality of life. Since the milestone work of Walter Lever in 1953, who differentiated these two groups of diseases by histopathological analysis of the level of antibody-mediated skin cleavage, enormous progresses occurred. Achievements made in laboratory diagnostics now allow to identify antigen specific structural proteins of the skin that are targeted by pathogenic autoantibodies. These progresses were accompanied by an increased understanding of the pathogenesis of these diseases thanks to the establishment of animal models reproducing disease and on studies on skin and blood of affected individuals, which have been leading to novel and disease-specific treatments. Yet, given their phenotypical overlap with more common dermatological diseases, correct diagnosis and appropriate treatment are often delayed, in some cases leading to irreversible sequelae, including organ dysfunction (i.e., loss of vision in mucous membrane pemphigoid). Here, we provide a concise overview of the clinical appearance, diagnosis and therapeutic management of pemphigus and pemphigoid diseases.

Histopathological characterisation of trunk-dominant canine pemphigus foliaceus, and comparison with classic facial and insecticide-triggered forms

BACKGROUND

While the clinical features were described recently, the histopathological characterisation of trunk-dominant canine pemphigus foliaceus (PF) is lacking, and whether it differs from classic facial or insecticide-triggered PF is unknown.

HYPOTHESIS/OBJECTIVES

This study describes the histopathological findings of trunk-dominant PF, and compares the results to classic facial and insecticide-triggered PF.

ANIMALS

Skin biopsies from 103 dogs with clinically characterised trunk-dominant (n = 33), classic facial (n = 26) and insecticide-triggered PF (n = 44) were included.

MATERIALS AND METHODS

Histological sections, randomised and blinded, were scored for over 50 morphological parameters of pustules, epidermis, dermis, adnexa and crusts. Intact pustule area and width were measured by digital microscopy.

RESULTS

In trunk-dominant PF, 77 intact pustules were predominantly subcorneal (0.0019-1.940 mm2 area, 0.0470-4.2532 mm wide), and contained from one to over 100 acantholytic keratinocytes. Pustules had boat acantholytic cells, corneocytes, perinuclear eosinophilic rings, neutrophil rosettes, acantholytic cell necrosis, rafts, cling-ons and/or eosinophils. Peripustular epidermal spongiosis, necrosis and lymphocyte exocytosis occurred, as did follicular pustules. Mixed dermal inflammation often contained eosinophils. Trunk-dominant PF did not differ from the other PF groups except for few parameters, such as having fewer rafts (p = 0.003). Additional autoimmune inflammatory patterns occurred in all PF groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Trunk-dominant PF and other canine PF variants are histologically similar, which indicates shared pathomechanisms. The identification of common boat acantholytic cells and corneocyte separation has implications for the mechanisms of acantholysis. The diversity of histopathological and polyautoimmunity features support complicated immune mechanisms. Finally, results indicate that diagnostic biopsies cannot differentiate between these PF variants in dogs.

Pemphigus- und Pemphigoid-Erkrankungen: Klinik, Diagnostik und Therapie: Pemphigus and pemphigoids: Clinical presentation, diagnosis and therapy

Pemphigus und Pemphigoid sind seltene Autoimmunkrankheiten der Haut mit potenziell lebensbedrohlichem Verlauf. Autoantikörper gegen epidermale und junktionale Strukturproteine (Desmosomen sowie Hemidesmosomen) führen bei Betroffenen typischerweise zu juckenden, schmerzhaften Plaques oder Blasen an der Haut und/oder Blasenbildung und Erosionen der Schleimhäute mit möglicher Einschränkung der Lebensqualität. Seit der bahnbrechenden Arbeit von Walter Lever im Jahr 1953, dem es gelang, mittels histopathologischer Untersuchung diese beiden Krankheitsgruppen anhand des Musters der Antikörper‐vermittelten Blasenbildung zu differenzieren, wurden enorme Fortschritte im Verständnis der Erkrankungen erzielt. Die Errungenschaften in der Labordiagnostik ermöglichten die Identifikation von Zielstrukturen zur präzisen Unterscheidung verschiedener Varianten der bullösen Autoimmunerkrankungen. Diese Fortschritte gingen dank der Entwicklung von Tiermodellen mit einem besseren Verständnis der Pathogenese einher. Außerdem haben Studien an Haut und Blut betroffener Patienten zu neuen und krankheitsspezifischen Behandlungen geführt. Aufgrund ihrer Seltenheit und der klinischen Ähnlichkeit mit anderen dermatologischen Erkrankungen verzögern sich die korrekte Diagnosestellung und die Einleitung einer entsprechenden Therapie häufig, was in einigen Fällen zu irreversiblen Folgeerscheinungen, einschließlich Funktionsstörungen von Organen (zum Beispiel Verlust des Sehvermögens beim Schleimhautpemphigoid) führt. Wir geben hier einen Überblick über das klinische Erscheinungsbild, den Diagnosealgorithmus und das therapeutische Management von Pemphigus‐ und Pemphigoid‐Erkrankungen.

Dupilumab effectively and rapidly treats bullous pemphigoid by inhibiting the activities of multiple cell types

Background

Bullous pemphigoid (BP) is an autoimmune skin-blistering disease. Systemic corticosteroids remain the first line treatment for moderate-to-severe BP with the potential for severe adverse events. Dupilumab has emerged as an alternative option for BP patients.

Objective

We evaluated the efficiency and safety of dupilumab on BP treatment and explored a mode of drug action in depth.

Methods and results

A multicenter retrospective cohort included 20 BP patients who received dupilumab with or without systemic corticosteroid in dupilumab group, and 20 matched BP patients who received corticosteroid alone in conventional group. Serum samples were collected from 20 patients (10 from dupilumab group and 10 from conventional group) at baseline and week 4. Compared to systemic corticosteroid alone, dupilumab with or without systemic corticosteroid was similarly efficacious in clinical remission at week4 (complete remission plus partial remission: 100%) and week24 (complete remission plus partial remission:100%), but allowing significant decreases in the cumulative doses of corticosteroids with reducing the incidence of adverse events. However, dupilumab did not decrease BP180 antibody despite an obvious clinical improvement. Comparative plasma proteomic analysis performed before and after treatment in 3 BP patients from dupilumab group revealed that drug use was associated with 30 differentially expressed proteins, including 26 down-regulated and 4 up-regulated proteins. The former consisted of immune related proteins involved in T/B cell interactions (inducible T-cell co-stimulator ligand, ICOSL) and in the activation of eosinophils (PRG2), mast cells (S100A12), and complement (CR2). TARC and ICOSL levels correlated with BP severity in patients who received either dupilumab or conventional treatment.

Conclusion

Dupilumab has similar efficacy in treating BP as conventional drugs, by inhibiting the activities of many types of immune cells and complement, and regulating the interactions between T and B cells.

The efficacy and safety of dupilumab combined with methylprednisolone in the treatment of bullous pemphigoid in China

We access the safety and efficacy of methylprednisolone combined with dupilumab in treating the bullous pemphigoid. 27 patients were enrolled, of which 9 received dupilumab in addition to methylprednisolone (dupilumab group, D group), while the other 18 patients were administered methylprednisolone alone (traditional group, T group). The median time to stop the formation of the new blister was 5.5 days (3.5-11.75 days) and 10 days (9-15 days) in the D group and the T group, respectively (p = 0.032). Additionally, the median time of complete healing reached was 21 days (16.25-31 days) and 29 days (25-50 days) in the D group and the T group, separately (p = 0.042). The median amount of cumulative methylprednisolone at the time of disease control was 240 mg (140-580 mg) and 460 mg (400-840 mg) in the D group and the T group, respectively (p = 0.031). The total amount of the methylprednisolone used at the time of complete healing reached was 792 mg (597-1,488.5 mg) in the D group while that was 1,370 mg (1,000-2,570 mg) in the T group (p = 0.028). No adverse event associated with dupilumab was recorded. Methylprednisolone in combination with dupilumab appeared superior to methylprednisolone alone in control of disease progression and the methylprednisolone-sparing effect.

Adaptive and innate immune pathogenesis of bullous pemphigoid: A review

Bullous pemphigoid (BP) is an autoimmune blistering disease that primarily affects elderly individuals. The presentation of BP is heterogeneous, typically manifesting as microscopic subepidermal separation with a mixed inflammatory infiltrate. The mechanism of pemphigoid development is unclear. B cells play a major role in pathogenic autoantibody production, and T cells, type II inflammatory cytokines, eosinophils, mast cells, neutrophils, and keratinocytes are also implicated in the pathogenesis of BP. Here, we review the roles of and crosstalk between innate and adaptive immune cells in BP.