Fab fragments directed against laminin 5 induce subepidermal blisters in neonatal mice

Anti-α6β4 integrin autoantibodies inhibit the binding of laminins to α6β4 integrin in patients with pemphigoid and affect the gastrointestinal tract

BACKGROUND

Anti-α6β4 integrin autoantibodies can be observed in some patients with mucous membrane pemphigoid. We have previously identified anti-α6β4 integrin extracellular domain autoantibodies together with anti-BP180 NC16A antibodies in a patient with DPP-4 inhibitor-induced bullous pemphigoid. However, the significance and impact of anti-α6β4 integrin antibodies are unknown.

OBJECTIVES

To characterize anti-α6β4 integrin extracellular domain autoantibodies in pemphigoid patients, to determine whether these antibodies inhibit laminin-α6β4 integrin binding and to observe their systemic effects.

METHODS

Anti-α6β4 integrin autoantibodies were analysed by staining cells expressing the extracellular region of α6β4 integrin with sera from 20 patients with pemphigoid. The anti-α6β4 integrin autoantibodies were characterized using different transfectants. The binding of laminins to α6β4 integrin was studied using cells expressing the activated conformation of α6β4 integrin and the inhibitory effect of the autoantibodies on the binding of laminins to α6β4 integrin was tested. Trends in antibody titres and clinical symptoms were quantified and analysed.

RESULTS

IgG autoantibodies against the extracellular domain of anti-α6β4 integrin were found in some patients with pemphigoid. Laminin binding to α6β4 integrin was observed in the active conformation of α6β4 integrin, and serum from a patient with a high titre of anti-α6β4 integrin antibodies inhibited the binding of both laminin-511 and laminin-332 to α6β4 integrin. α6β4 integrin is expressed on the basement membrane of both skin and small intestine, and exfoliation was observed in the patient's epidermis and small intestinal epithelium. A reduction in the titre of the anti-α6β4 integrin antibody was associated with improvement in both skin and gastrointestinal symptoms.

CONCLUSIONS

This study demonstrated the presence of anti-α6β4 integrin extracellular domain-specific autoantibodies in some patients with pemphigoid. In addition, these autoantibodies showed inhibitory activity on α6β4 integrin-laminin binding. Anti-α6β4 integrin antibodies can affect the gastrointestinal tract as well as the skin and oral mucosa.

Autoimmunity against laminin 332

Laminin 332 is a heterotrimeric structural protein of the basal membrane zone (BMZ) of the skin and adjacent mucosal tissues. The importance of laminin 332 for the structural integrity of the BMZ is demonstrated by mutations in any of the three genes encoding for its three chains causing variants of junctional epidermolysis bullosa. Autoimmunity against laminin 332 is observed in mucous membrane pemphigoid (MMP) and in the rare patients with orf-induced pemphigoid. MMP is an autoimmune blistering disease with predominant mucosal manifestations and autoantibodies against the BMZ of the skin and orifice-close mucous membranes. The main autoantigens of MMP are type XVII collagen (BP180) and laminin 332 targeted in about 80% and 10-20% of patients, respectively. An increasing number of studies has highlighted the association of anti-laminin 332 MMP and malignancies that can be revealed in about a quarter of these patients. This data has led to the recommendation of current guidelines to assay for anti-laminin 332 reactivity in all MMP patients. The present review focuses on anti-laminin 332 MMP describing clinical features, its pathophysiology, and detection of serum anti-laminin 332 IgG. In addition, the available data about the occurrence of malignancies in anti-laminin 332 MMP, the underlying tumor entities, and its biology are detailed.

[Immunopathogenesis of mucous membrane pemphigoid]

A detailed understanding of the immunopathogenesis of mucous membrane pemphigoid (MMP) is of particular importance in view of the mostly difficult diagnostics and treatment of this blistering autoimmune dermatosis. A still unknown disturbance of the body's own immune tolerance leads to the formation of autoreactive cells. As the disease progresses these produce autoantibodies which are directed against structural proteins in the basement membrane zone (BMZ). After they bind to the target antigen, complement factors are deposited along the BMZ and inflammatory cells invade the underlying tissue and produce the characteristic subepithelial blistering. This inflammatory response is associated with fibrosis and scarring in many affected tissues. Most phases of MMP pathogenesis are poorly understood; however, the last few years have shed more light on this processes. These advances are mostly the result of animal and cell culture models. Typical clinical and immunopathological characteristics of MMP, such as oral, conjunctival and skin lesions, are reflected, for example, in an antibody transfer-induced mouse model for anti-laminin 332 MMP in adult mice. Dapsone, as first-line treatment for MMP patients, significantly reduced the severity of these symptoms, and fibrosis in the skin and mucous membranes was also found histologically, which makes the model well-suited for testing new therapeutic approaches for MMP patients and might be of help for further elucidation of the immunopathogenesis of MMP.

Anti-Laminin 332-Type Mucous Membrane Pemphigoid

Anti-laminin (LM) 332-type mucous membrane pemphigoid (MMP) is a rare autoimmune bullous disease and was originally discovered as anti-epiligrin cicatricial pemphigoid. Anti-LM332-type MMP has clinical manifestations similar to those of other types of MMP and can only be distinguished through the detection of circulating autoantibodies against LM332. Our group and others have established a number of immunological methods with varying sensitivity and specificity for detection of anti-LM332 autoantibodies; however, none of the established methods has been widely used for clinical diagnosis. There is currently no unified standard treatment, and it is very difficult to completely cure anti-LM332-type MMP. In addition, an increasing body of evidence suggests that there may be a strong correlation between anti-LM332-type MMP and tumors. In this article, we review the current progression of diagnosis and treatment of anti-LM332-type MMP, as well as the possible correlation between anti-LM332-type MMP and tumors.

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

Mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is a clinically and immunopathologically heterogenous disease with an incidence of about 2/million inhabitants/year in central Europe. Pemphigoid diseases are characterized by autoantibodies against structural proteins of the epidermis and/or surface-close epithelia. MMP has been defined as pemphigoid disease with predominant mucosal lesions. Most frequently, the oral cavity and the conjunctivae are affected. Lesions outside the mouth tend to heal with scarring leading to visual impairment and finally blindness, as well as, more rarely, impairment of breathing and food intake. Autoantibodies target BP180 (collagen type XVII), laminin 332, BP230 (nearly always in conjunction with other antigens), and type VII collagen in about 75%, 10-20%, 10-30%, and <5% of MMP patients, respectively. While the main autoantibody isotype is IgG, additional, and less frequently, exclusive IgA autoantibodies can be detected in the majority of patients. Assaying for anti-laminin 332 reactivity is pivotal, since in about a quarter of patients with anti-laminin 332 MMP, a malignancy, mainly solid cancers, is associated. The pathophysiology of MMP is yet incompletely understood. A recent mouse model of anti-laminin 332 MMP replicating characteristic clinical and immunopathological findings of the human disease may be helpful to close this knowledge gap. Diagnosis is established by the clinical picture with predominant mucosal lesions and visualization of tissue-bound anti-basement membrane zone antibodies by direct immunofluorescence microscopy. In recent S3 guidelines initiated by the European Academy of Dermatology and Venereology, the clinical spectrum and diagnostic strategies are detailed. In addition, treatment regimens for different clinical situations including patients with exclusive oral or ocular involvement are outlined. Future studies are needed to better understand the clinal complexity and associations as well as to establish widely available diagnostic assays and evidence-based therapeutic strategies.

Complement Activation in Autoimmune Bullous Dermatoses: A Comprehensive Review

Autoimmune bullous dermatoses (AIBD) are characterized by circulating autoantibodies that are either directed against epidermal antigens or deposited as immune complexes in the basement membrane zone (BMZ). The complement system (CS) can be activated by autoantibodies, thereby triggering activation of specific complement pathways. Local complement activation induces a pathogenic inflammatory response that eventually results in the formation of a sub- or intraepidermal blister. Deposition of complement components is routinely used as a diagnostic marker for AIBD. Knowledge from different animal models mimicking AIBD and deposition of complement components in human skin biopsies provides more insight into the role of complement in the pathogenesis of the different AIBD. This review outlines the role of the CS in several AIBD including bullous pemphigoid, epidermolysis bullosa acquisita, mucous membrane pemphigoid (MMP), pemphigus, linear IgA-disease, and dermatitis herpetiformis. We also discuss potential therapeutic approaches targeting key complement components, pathways and pathogenic complement-mediated events.

The Diagnosis and Blistering Mechanisms of Mucous Membrane Pemphigoid

Mucous membrane pemphigoid (MMP) is a mucous membrane-dominated autoimmune subepithelial blistering disease that is caused by autoantibodies against various autoantigens in basement membrane zone (BMZ) proteins, including collagen XVII (COL17). Clinicians face diagnostic problems in detecting circulating antibodies and targeted antigens in MMP. The diagnostic difficulties are mainly attributed to the low titers of MMP autoantibodies in sera and to heterogeneous autoantigens. Additionally, no unanimous diagnostic criteria have been drawn for MMP, which can result in delayed diagnoses or misdiagnoses. This review aims to integrate and present currently available data to clarify diagnostic strategies and to present diagnostic criteria for MMP. The ultimate blistering mechanism in MMP has not been elucidated, and such mechanism is especially obscure in COL17-type MMP. In bullous pemphigoid (BP), which is the most common autoimmune subepidermal blistering disease, some patients show oral lesion as well as predominant skin lesions. However, there is no fundamental explanation for the onset of oral lesions in BP. This article summarizes innovative research perspectives on the pathogenesis of oral lesions in pemphigoid. Finally, we propose a potential pathogenesis for COL17-type MMP.

Molecular diagnosis of anti-laminin 332 (epiligrin) mucous membrane pemphigoid

BACKGROUND

Mucous membrane pemphigoid is a group of chronic subepithelial autoimmune blistering diseases that mainly affect mucous membranes. Laminin 332-specific autoantibodies are present in approximately 1/3 of the patients, being associated with an increased risk of malignancy. Because of the severe complications, an early recognition of the disease allowing a timely therapy is essential. The gold standard methods for detection of laminin 332-specific autoantibodies, including the immunoprecipitation and immunoblotting are non-quantitative, laborious and restricted to a few specialized laboratories worldwide. In addition, the use of radioimmunoassays, although highly sensitive and specific, are laborious, expensive and tightly regulated. Therefore, there is a stringent need for a quantitative immunoassay for the routine detection of laminin 332-specific autoantibodies more broadly available to diagnostic laboratories. The aim of this study was to compare different antigenic substrates, including native, recombinant laminin 332 and laminin 332-rich keratinocyte extracellular matrix, for development of an ELISA to detect autoantibodies in mucous membrane pemphigoid.

RESULTS

Using a relatively large number of sera from MMP patients with well-characterized autoantibody reactivity we show the suitability of ELISA systems using laminin 332 preparations as adjunct diagnostic tools in MMP. While glycosylation of laminin 332 does not appear to influence its recognition by MMP autoantibodies, ELISA systems using both purified, native and recombinant laminin 332 demonstrated a high sensitivity and good correlation with the detection of autoantibodies by immunoblotting. ELISA systems using different laminin 332 preparations represent a feasible and more accessible alternative for a broad range of laboratories.

CONCLUSIONS

Our findings qualify the use of immunoassays with the laminin 332-rich preparations as an ancillary diagnostic tool in mucous membrane pemphigoid.

Structural proteins of the dermal-epidermal junction targeted by autoantibodies in pemphigoid diseases

The dermal-epidermal junction consists of a network of several interacting structural proteins that strengthen adhesion and mediate signalling events. This structural network consists of hemidesmosomal-anchoring filament complexes connecting the basal keratinocytes to the basement membrane. The anchoring filaments in turn interact with the anchoring fibrils to attach the basement membrane to the underlying dermis. Several of these structural proteins are recognized by autoantibodies in pemphigoid diseases, a heterogeneous group of clinically and immunopathologically diverse entities. Targeted proteins include the two intracellular plakins, plectin isoform 1a and BP230 (also called bullous pemphigoid antigen (BPAG) 1 isoform e (BPAG1e)). Plectin 1a and BP230 are connected to the intermediate filaments and to the cell surface receptor α6β4 integrin, which in turn is connected to laminin 332, a component of the anchoring filaments. Further essential adhesion proteins are BP180, a transmembrane protein, laminin γ1 and type VII collagen. Latter protein is the major constituent of the anchoring fibrils. Mutations in the corresponding genes of these adhesion molecules lead to inherited epidermolysis bullosa emphasizing the importance of these proteins for the integrity of the dermal-epidermal junction. This review will provide an overview on the structure and function of the proteins situated in the dermal-epidermal junction targeted by autoantibodies.

Experimental Laminin 332 Mucous Membrane Pemphigoid Critically Involves C5aR1 and Reflects Clinical and Immunopathological Characteristics of the Human Disease

Mucous membrane pemphigoid is an autoantibody-mediated disease predominantly affecting the oral cavity, pharynx, and conjunctiva. Conjunctival lesions may lead to impaired vision and, finally, blindness. About 25% of mucous membrane pemphigoid patients generate autoantibodies against the α3 chain of laminin 332 (LAMα3), a structural protein of epidermal/epithelial basement membranes. Here, we established a mouse model by the passive transfer of rabbit IgG against the murine homologs of two immunodominant fragments in adult C57BL/6 mice (mLAMα3). After repeated subcutaneous injections of anti-mLAMα3 IgG erosions and crusts occurred predominantly around the snout, eyes, and on ears. Conjunctival and oral/pharyngeal lesions with subepithelial splitting were found in 80% and 100% of mice, respectively. In contrast, disease development was abrogated in FcRγ chain-deficient mice and markedly reduced in C5aR1-deficient mice. Furthermore, wild-type mice injected with anti-mLAMα3 F(ab')2 were completely protected. Our findings suggest a crucial codominant role of FcRγ and complement activation of the anti-mLAMα3 IgG-induced mouse model of mucous membrane pemphigoid. This model will help further discover the pathomechanisms of this devastating disease. Furthermore, it may be of use to explore the effect of urgently needed more specific anti-inflammatory mediators on mucosal and skin lesions in autoantibody-mediated diseases.

Autoimmunity against laminins

Laminins are ubiquitous constituents of the basement membranes with major architectural and functional role as supported by the fact that absence or mutations of laminins lead to either lethal or severely impairing phenotypes. Besides genetic defects, laminins are involved in a wide range of human diseases including cancer, infections, and inflammatory diseases, as well as autoimmune disorders. A growing body of evidence implicates several laminin chains as autoantigens in blistering skin diseases, collagenoses, vasculitis, or post-infectious autoimmunity. The current paper reviews the existing knowledge on autoimmunity against laminins referring to both experimental and clinical data, and on therapeutic implications of anti-laminin antibodies. Further investigation of relevant laminin epitopes in pathogenic autoimmunity would facilitate the development of appropriate diagnostic tools for thorough characterization of patients' antibody specificities and should decisively contribute to designing more specific therapeutic interventions.

Autoimmune bullous diseases with skin and eye involvement: Cicatricial pemphigoid, pemphigus vulgaris, and pemphigus paraneoplastica

Autoimmune blistering diseases are a heterogeneous group of disorders that mostly affect the skin and mucous membranes. Occasionally, other organ systems may be involved, depending on the unique pathophysiology of each disease. Cicatricial pemphigoid, pemphigus vulgaris, and paraneoplastic pemphigus are distinct entities, but all have the potential to have cutaneous and ocular involvement. Awareness and early recognition of ocular involvement in these diseases is important given the increased risk for vision loss and blindness with delay in management. Several skin diseases may be associated with involvement of the external eye. The most common autoimmune diseases are cicatricial pemphigoid, pemphigus vulgaris, and paraneoplastic pemphigus.

Pemphigoid diseases

Pemphigoid diseases are a group of well defined autoimmune disorders that are characterised by autoantibodies against structural proteins of the dermal-epidermal junction and, clinically, by tense blisters and erosions on skin or mucous membranes close to the skin surface. The most common of these diseases is bullous pemphigoid, which mainly affects older people and the reported incidence of which in Europe has more than doubled in the past decade. Prognosis and treatments vary substantially between the different disorders and, since clinical criteria are usually not sufficient, direct immunofluorescence microscopy of a perilesional biopsy specimen or serological tests are needed for exact diagnosis. In eight pemphigoid diseases the target antigens have been identified molecularly, which has allowed the development of standard diagnostic assays for detection of serum autoantibodies-some of which are commercially available. In this Seminar we discuss the clinical range, diagnostic criteria, diagnostic assay systems, and treatment options for this group of diseases.

Laminin 332 deposition is diminished in irradiated skin in an animal model of combined radiation and wound skin injury

Skin exposure to ionizing radiation affects the normal wound healing process and greatly impacts the prognosis of affected individuals. We investigated the effect of ionizing radiation on wound healing in a rat model of combined radiation and wound skin injury. Using a soft X-ray beam, a single dose of ionizing radiation (10-40 Gy) was delivered to the skin without significant exposure to internal organs. At 1 h postirradiation, two skin wounds were made on the back of each rat. Control and experimental animals were euthanized at 3, 7, 14, 21 and 30 days postirradiation. The wound areas were measured, and tissue samples were evaluated for laminin 332 and matrix metalloproteinase (MMP) 2 expression. Our results clearly demonstrate that radiation exposure significantly delayed wound healing in a dose-related manner. Evaluation of irradiated and wounded skin showed decreased deposition of laminin 332 protein in the epidermal basement membrane together with an elevated expression of all three laminin 332 genes within 3 days postirradiation. The elevated laminin 332 gene expression was paralleled by an elevated gene and protein expression of MMP2, suggesting that the reduced amount of laminin 332 in irradiated skin is due to an imbalance between laminin 332 secretion and its accelerated processing by elevated tissue metalloproteinases. Western blot analysis of cultured rat keratinocytes showed decreased laminin 332 deposition by irradiated cells, and incubation of irradiated keratinocytes with MMP inhibitor significantly increased the amount of deposited laminin 332. Furthermore, irradiated keratinocytes exhibited a longer time to close an artificial wound, and this delay was partially corrected by seeding keratinocytes on laminin 332-coated plates. These data strongly suggest that laminin 332 deposition is inhibited by ionizing radiation and, in combination with slower keratinocyte migration, can contribute to the delayed wound healing of irradiated skin.

Pathogenesis of mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is the clinical phenotype of a group of autoimmune blistering diseases characterized by autoantibodies directed against different structural proteins in epidermal basement membranes. The clinical course and prognosis of MMP are affected by the specific autoantigen targeted, the titer and bioactivity profile of corresponding autoantibodies, and the specific mucosal sites of disease activity. Irreversible scarring and loss of function must be prevented by early diagnosis and appropriate interventions.

Clinical and immunological heterogeneity of canine subepidermal blistering dermatoses with anti-laminin-332 (laminin-5) auto-antibodies

Laminin-332 (laminin-5) is a basement membrane heterotrimeric protein composed of alpha-3, beta-3 and gamma-2 laminin chains. Laminin-332 polypeptides are targeted by auto-antibodies in human patients with mucous membrane (cicatricial) pemphigoid or, more rarely, subepidermal vesicular diseases that resemble epidermolysis bullosa acquisita (EBA) or bullous pemphigoid (BP). The objectives of this report were to characterize the clinical, histopathological and immunological characteristics of nine dogs with auto-antibodies targeting laminin-332. Immunological investigations consisted of direct immunofluorescence (IF), indirect IF with intact and salt-split canine gingival, and salt-split normal or laminin-332-deficient human skin, immunoblotting with purified human laminin-332 and immunoblotting with recombinant NC1 domain of human collagen VII. All dogs exhibited varying degrees of skin blistering and ulceration associated with microscopic subepidermal vesiculation with or without inflammatory cells. Indirect IF established that circulating IgG auto-antibodies bound the dermal side of salt-split canine lip and human skin. In five dogs, IgG variably recognized the basement membrane of laminin-332-deficient human skin (three dogs negative, two dogs positive). In all nine dogs, IgG auto-antibodies detected purified human laminin-332 by immunoblotting. In two dogs, additional targeting of collagen VII-NC1 was present. These observations establish laminin-332 as a novel basement membrane antigen in dogs with autoimmune blistering diseases with variable clinical phenotypes. The names 'acquired junctional epidermolysis bullosa', 'anti-laminin-332 mucous membrane pemphigoid (MMP)' and 'mixed auto-immune subepidermal blistering dermatosis' are proposed for dogs with clinical signs reminiscent of EBA, MMP or BP respectively.

Histopathology of anti-laminin 5 mucous membrane pemphigoid

BACKGROUND

Anti-laminin 5 mucous membrane pemphigoid (MMP) is an autoimmune blistering disease characterized by autoantibodies against the major basement membrane component laminin 5 (laminin 332, epiligrin).

OBJECTIVE AND METHODS

We reviewed 17 biopsy specimens from 9 patients with anti-laminin 5 MMP in an attempt to define typical histopathologic features of the disease.

RESULTS

Fifteen specimens showed subepidermal blister formation, while two biopsy specimens revealed an epithelial ulcer. In 11 biopsies a sparse to moderate inflammatory infiltrate composed of lymphocytes and neutrophils with some eosinophils was observed. Four biopsies showed a dense infiltrate dominated by neutrophils in two cases and by eosinophils in one case. The remaining biopsy revealed a dense lymphoplasmacellular infiltrate without granulocytes. Scarring of the upper dermis was present only in 5 specimens. Immunohistochemical analysis localized type IV collagen to the dermal side of the blister, suggesting that split formation occurred within the lamina lucida of the cutaneous basement membrane.

LIMITATIONS

The number of patients studied was relatively small.

CONCLUSIONS

Histopathology of anti-laminin 5 MMP is characterized by subepidermal blistering and a sparse to moderate superficial lymphohistiocytic infiltrate with neutrophils and/or eosinophils. Both infiltrate density and composition may vary, making anti-laminin 5 MMP indistinguishable from other autoimmune subepidermal blistering diseases by histopathology alone. Scarring is present only in a minority of cases and is not a sensitive clue to the diagnosis of anti-laminin 5 MMP.

A widening perspective regarding the relationship between anti-epiligrin cicatricial pemphigoid and cancer

Anti-epiligrin cicatricial pemphigoid (AECP) is a chronic, autoimmune, subepidermal blistering disease characterized by circulating anti-basement membrane autoantibodies to laminin 5. Recent studies have shown that patients with this form of cicatricial pemphigoid have an increased relative risk for malignant solid tumors. The mechanism underlying this association of AECP and cancer is unknown, but there is accumulating evidence that laminin 5 plays a central role. In this article we report a patient with AECP and co-associated cutaneous T cell lymphoma and summarize all to date reported cases of AECP associated with malignancies. In addition we provide a review of the biology of laminin 5 and its potential role in cancer development.

Laminin-5-deficient human keratinocytes: defective adhesion results in a saltatory and inefficient mode of migration

Laminin-5 is a major adhesion protein of the skin basement membrane and crucially involved in integrin-mediated cell substrate attachment of keratinocytes, which is important for hemidesmosomal anchorage as well as for keratinocyte migration during epidermal wound healing. To investigate its role in keratinocyte migration, we analyzed laminin-5-deficient cells of patients with a lethal variant of junctional epidermolysis bullosa. Normal migrating keratinocytes adopted monopolar morphology with a distinct front lamella and employed a continuous mode of translocation. In contrast, laminin-5-deficient cells assumed a stretched bipolar shape with two lamella regions and migrated in a discontinuous, saltatory manner characterized by significantly decreased directional persistence and reduced migration velocity. The distinct morphology as well as the migratory phenotype apparently resulted from a defect in the formation of cell substrate adhesions that were completely missing in the cell body and less stable in the lamella regions. Accordingly in normal keratinocytes, a bipolar shape and a saltatory migration mode were inducible by blocking laminin-5-mediated substrate adhesion. Our findings clearly point to an essential role of laminin-5 in forming dynamic cell substrate adhesion during migration of epidermal keratinocytes and provide an explanation for the cellular mechanisms that underlie the lethal form of junctional epidermolysis bullosa.

Mechanisms of blister induction by autoantibodies

Autoimmune diseases are characterized by defined self-antigens, organ specificity, autoreactive T cells and/or autoantibodies that can transfer disease. Autoimmune blistering diseases are organ-specific autoimmune diseases associated with an immune response directed to structural proteins mediating cell-cell and cell-matrix adhesion in the skin. While both autoreactive T and B cells have been detected and characterized in patients with autoimmune blistering diseases, current evidence generally supports a pathogenic role of autoantibodies for blister formation. The immunopathology associated with blisters induced by autoantibodies relies on several mechanisms of action. Autoantibodies from patients with pemphigus diseases can exert a direct effect just by binding to their target mediated by steric hindrance and/or by triggering the transduction of a signal to the cell. In most subepidermal autoimmune blistering conditions, in addition to the binding to their target antigen, autoantibodies need to interact with factors of the innate immune system, including the complement system and inflammatory cells, in order to induce blisters. Generally, decisive progress has been made in the characterization of the mechanisms of blister formation in autoimmune skin diseases. However, various aspects, including the exact contribution of steric hindrance and signal transduction for pemphigus IgG-induced acantholysis or the fine tuning of the inflammatory cascade triggered by autoantibodies in some subepidermal blistering diseases, still need to be addressed. Understanding the mechanisms by which autoantibodies induce blisters should facilitate the development of more specific therapeutic strategies of autoimmune blistering diseases.

Number III Mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is a sub-epithelial vesiculobullous disorder. It is now quite evident that a number of sub-epithelial vesiculobullous disorders may produce similar clinical pictures, and also that a range of variants of MMP exist, with antibodies directed against various hemidesmosomal components or components of the epithelial basement membrane. The term immune-mediated sub-epithelial blistering diseases (IMSEBD) has therefore been used. Immunological differences may account for the significant differences in their clinical presentation and responses to therapy, but unfortunately data on this are few. The diagnosis and management of IMSEBD on clinical grounds alone is impossible and a full history, general, and oral examination, and biopsy with immunostaining are now invariably required, sometimes supplemented with other investigations. No single treatment regimen reliably controls all these disorders, and it is not known if the specific subsets of MMP will respond to different drugs. Currently, apart from improving oral hygiene, immunomodulatory-especially immunosuppressive-therapy is typically used to control oral lesions. The present paper reviews pemphigoid, describing the present understanding of this fascinating clinical phenotype, summarising the increasing number of subsets with sometimes-different natural histories and immunological features, and outlining current clinical practice.

Granulocyte-derived elastase and gelatinase B are required for dermal-epidermal separation induced by autoantibodies from patients with epidermolysis bullosa acquisita and bullous pemphigoid

Epidermolysis bullosa acquisita (EBA) and bullous pemphigoid (BP) are two clinically and immunologically distinct autoimmune subepidermal blistering skin diseases associated with IgG autoantibodies against the dermal-epidermal junction. BP antibodies are directed against the hemidesmosomal antigens BP180 and BP230, and those in patients with EBA target type VII collagen, a major component of anchoring fibrils. While the pathogenetic mechanisms of subepidermal blistering in BP have been previously studied using a passive transfer mouse model, the effector pathways of blister formation in EBA are largely unknown. Autoantibodies to type VII collagen and BP180 have recently been shown to induce leucocyte-mediated subepidermal cleavage in cryosections of human skin. The aim of the present study was to identify human leucocyte protease(s) instrumental in dermal-epidermal separation induced by autoantibodies to type VII collagen and BP180. When incubated with cryosections of human skin pretreated with IgG from patients with EBA or BP but not from patients with anti-laminin 5 mucous membrane pemphigoid or healthy controls, granulocytes were recruited to the dermal-epidermal junction and induced subepidermal splits. A combination of broad-range protease inhibitors as well as inhibitors of serine and matrix metalloproteases completely abolished dermal-epidermal separation induced by EBA or BP autoantibodies. When characterizing the proteases involved more specifically, selective inhibition of human leucocyte elastase or gelatinase B/MMP-9 was also found to result in suppression of blistering. These findings strongly suggest that elastase and gelatinase B are essential for granulocyte-mediated proteolysis resulting in dermal-epidermal separation in EBA and BP patients' skin.

Comparative analysis of methods for detection of anti-laminin 5 autoantibodies in patients with anti-epiligrin cicatricial pemphigoid

BACKGROUND

Anti-epiligrin cicatricial pemphigoid (AECP) is a subepidermal blistering disease characterized by circulating anti-basement membrane autoantibodies to laminin 5.

OBJECTIVE

To evaluate the relative sensitivity of immunoblotting and immunoprecipitation techniques for the detection of anti-laminin 5 antibodies, comparative studies using reference laminin 5 antiserum as well as sera from patients with AECP, other immunobullous diseases, and normal volunteers were performed.

METHODS

Equivalent amounts of protein from five different substrates were studied by immunoblotting; immunoprecipitation experiments examined biosynthetically radiolabeled human keratinocyte (HK) extracts. Results HK extracellular matrix (ECM) was the most sensitive substrate for detection of antibodies to laminin 5; extracts of HKs, A-431 cells and HaCat cells represented alternative test substrates (though the later required higher amounts of protein input). Sera from patients with AECP immunoblotted laminin 5 in HK ECM at end titers exceeding those identified in indirect immunofluorescence microscopy studies of 1 M NaCl split skin. Immunoprecipitation studies found that a 10,000-fold dilution of reference laminin 5 antiserum retained the ability to identify laminin 5. Maximal dilutions of sera from AECP patients retaining the ability to immunoprecipitate laminin 5 ranged from 500 to 5,000.

CONCLUSION

Immunoprecipitation was the most sensitive technique for detection of anti-laminin 5 antibodies, while immunoblotting of HK ECM or HK extracts represented practical alternatives.

Usefulness of immunoblotting using purified laminin 5 in the diagnosis of anti-laminin 5 cicatricial pemphigoid

BACKGROUND

Anti-laminin 5 cicatricial pemphigoid (CP) is a mucosal-dominant subepithelial blistering disease characterized by IgG anti-basement membrane zone autoantibodies, that bind to dermal side of 1 M NaCl split skin and immunoprecipitate laminin 5. Laminin 5 is an epidermis-specific extracellular matrix consisting of alpha3, beta3 and gamma2 subunits. Recent studies have suggested that autoantibodies of anti-laminin 5 CP recognize the G domains of alpha3 subunit.

OBJECTIVE

We examined the reactivity of anti-laminin 5 CP by immunoblotting using purified laminin 5 and recombinant proteins of alpha3 subunit.

METHOD

We first examined the reactivity of anti-laminin 5 CP by immunoblotting using purified laminin 5. To further investigate the epitopes in the G domains of alpha3 subunit, we produced recombinant proteins of G1-2, G1-3, G2-3, G3-5 domains, that covered entire G domain, and examined the reactivity of anti-laminin 5 CP sera with these recombinant proteins by immunoblotting.

RESULTS

By immunoblotting using purified laminin 5, 7 of 21 anti-laminin 5 CP sera reacted with alpha3 subunit, while 8 sera reacted with beta3 subunit and one serum reacted with gamma2 subunit. Two sera reacted with both alpha3 and beta3 subunits, while seven sera did not show positive reactivity. This result indicates that the reactivity of anti-laminin 5 CP sera is much more heterogeneous, although the previous studies suggested that most sera reacted with alpha3 subunit. However, in the studies using recombinant proteins of G domains of alpha3 subunit, none of the CP sera, including the sera reactive with alpha3 subunit in purified laminin 5, reacted with any recombinant proteins. The reason for this negative reactivity with the recombinant proteins is not clear.

CONCLUSION

The immunoblotting using purified laminin 5 should be useful technique for the diagnosis of anti-laminin 5 CP, although the sensitivity was less than conventional immunoprecipitation analysis.

Anti-epiligrin cicatricial pemphigoid: clinical findings, immunopathogenesis, and significant associations

We report the clinical and immunopathologic findings in a cohort of 35 patients with anti-epiligrin cicatricial pemphigoid (AECP). These patients have a mucosal predominant subepithelial blistering disease that is clinically indistinguishable from other forms of cicatricial pemphigoid. The mucosal surfaces of the mouth and eye are most commonly involved. The skin is also involved in most patients, but usually this is less severe than mucosal involvement. AECP is characterized by the binding of circulating IgG autoantibodies to the dermal side of 1M NaCl split human skin on indirect immunofluorescence microscopy. These IgG antibasement membrane autoantibodies target laminin 5, a heterotrimeric protein consisting of alpha3, beta3, and gamma2 subunits. IgG autoantibodies predominantly target the G domain within the alpha subunit. The presence of circulating IgG autoantibodies are specific for the diagnosis of AECP and are not seen in patients with other autoimmune blistering diseases or normal volunteers. Furthermore, we expand on data previously reported on the finding of an increased relative risk for solid cancer in patients with AECP, especially in the first year after blister onset. The majority of cancers documented in a cohort of 35 patients assembled over 12 years of study were adenocarcinomas that were at an advanced stage at their time of detection. This circumstance is thought to account for a high incidence of mortality among AECP patients who develop an associated cancer. AECP patients also demonstrate a significant risk for mortality as a consequence of treatment with systemic immunosuppressives. The current longitudinal study suggests that only a minority of AECP patients go into remission.

IgG autoantibodies in patients with anti-epiligrin cicatricial pemphigoid recognize the G domain of the laminin 5 alpha-subunit

Anti-epiligrin cicatricial pemphigoid (AECP) is a mucosal-predominant, subepithelial blistering disease characterized by IgG anti-basement membrane autoantibodies to laminin 5 (alpha3beta3gamma2). This and prior studies found that autoantibodies from most patients recognize the alpha-subunit of this laminin isoform. Accordingly, sera from 10 representative patients were tested against prokaryotic recombinants of this polypeptide in epitope mapping studies. cDNAs spanning the full length of the alpha-subunit were generated by PCR, directionally cloned into the pGEX-4T-3 vector, and expressed as glutathione-S-transferase fusion proteins of appropriate size and immunoreactivity. Sera from 9 of 10 AECP patients immunoblotted fusion proteins corresponding to subdomains G2, G3, G4, and G5 at the carboxyl terminus of the laminin 5 alpha-subunit. Serum from 1 patient (and that from normal volunteers) showed no reactivity to any fusion proteins; no sera bound recombinant glutathione-S-transferase alone. Immunoadsorption of patient sera with fusion proteins corresponding to the G domain substantially reduced basement membrane autoantibody titers. IgG from patients with this form of cicatricial pemphigoid recognize the portion of laminin 5 thought to play a key role in promoting keratinocyte adhesion to epidermal basement membrane.