Bullous pemphigoid sera that contain antibodies to BPAg2 also contain antibodies to LABD97 that recognize epitopes distal to the NC16A domain

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.

Deciphering the Contribution of BP230 Autoantibodies in Bullous Pemphigoid

Bullous pemphigoid (BP) is a subepidermal autoimmune blistering disease predominantly affecting elderly patients and carries significant morbidity and mortality. Patients typically suffer from severe itch with eczematous lesions, urticarial plaques, and/or tense blisters. BP is characterized by the presence of circulating autoantibodies against two components of the hemidesmosome, BP180 and BP230. The transmembrane BP180, also known as type XVII collagen or BPAG2, represents the primary pathogenic autoantigen in BP, whereas the intracellular BP230 autoantigen is thought to play a minor role in disease pathogenesis. Although experimental data exist suggesting that anti-BP230 antibodies are secondarily formed following initial tissue damage mediated by antibodies targeting extracellular antigenic regions of BP180, there is emerging evidence that anti-BP230 IgG autoantibodies alone directly contribute to tissue damage. It has been further claimed that a subset of patients has a milder variant of BP driven solely by anti-BP230 autoantibodies. Furthermore, the presence of anti-BP230 autoantibodies might correlate with distinct clinical features. This review summarizes the current understanding of the role of BP230 and anti-BP230 antibodies in BP pathogenesis.

European Guidelines (S3) on diagnosis and management of mucous membrane pemphigoid, initiated by the European Academy of Dermatology and Venereology - Part II

This guideline has been initiated by the task force Autoimmune Blistering Diseases of the European Academy of Dermatology and Venereology, including physicians from all relevant disciplines and patient organizations. It is a S3 consensus-based guideline that systematically reviewed the literature on mucous membrane pemphigoid (MMP) in the MEDLINE and EMBASE databases until June 2019, with no limitations on language. While the first part of this guideline addressed methodology, as well as epidemiology, terminology, aetiology, clinical presentation and outcome measures in MMP, the second part presents the diagnostics and management of MMP. MMP should be suspected in cases with predominant mucosal lesions. Direct immunofluorescence microscopy to detect tissue-bound IgG, IgA and/or complement C3, combined with serological testing for circulating autoantibodies are recommended. In most patients, serum autoantibodies are present only in low levels and in variable proportions, depending on the clinical sites involved. Circulating autoantibodies are determined by indirect IF assays using tissue substrates, or ELISA using different recombinant forms of the target antigens or immunoblotting using different substrates. The major target antigen in MMP is type XVII collagen (BP180), although in 10-25% of patients laminin 332 is recognized. In 25-30% of MMP patients with anti-laminin 332 reactivity, malignancies have been associated. As first-line treatment of mild/moderate MMP, dapsone, methotrexate or tetracyclines and/or topical corticosteroids are recommended. For severe MMP, dapsone and oral or intravenous cyclophosphamide and/or oral corticosteroids are recommended as first-line regimens. Additional recommendations are given, tailored to treatment of single-site MMP such as oral, ocular, laryngeal, oesophageal and genital MMP, as well as the diagnosis of ocular MMP. Treatment recommendations are limited by the complete lack of high-quality randomized controlled trials.

Bullous pemphigoid induced by dipeptidyl peptidase-4 inhibitors. Eight cases with clinical and immunological characterization

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) inhibitors have increasingly been identified as causative agents of bullous pemphigoid. The clinical and immunological characteristics of this pemphigoid variant are still unclear. The objective of our study was to analyze the clinical and immunological features of patients with pemphigoid induced by DPP-4 inhibitors.

METHODS

All patients diagnosed with DPP-4 inhibitor-associated bullous pemphigoid at dermatology departments in three Spanish centers during the period 2013 to 2015 were included. ELISA assays for the NC16A domain of BP180 and BP230 were performed. Immunoblot studies using epidermal/dermal extracts and the C-terminal, NC16A and LAD-1 regions of BP180 were also carried out.

RESULTS

A total of eight patients were identified (5 treated with vildagliptin, 2 with linagliptin, and one with sitagliptin). Of these, four presented the classical inflammatory phenotype of bullous pemphigoid and four a noninflammatory phenotype. The ELISA for BP180 (NC16A domain) was positive in six patients at diagnosis. Most patients reacted to more than one BP180 antigenic site (LAD-1 and/or C-terminal domain) on the immunoblot. Two patients showed no reaction against the NC16A domain of BP180 on either the ELISA or immunoblot but recognized either LAD-1 or both LAD-1 and the C-terminal domain. Only one of the NC16A-negative patients had a noninflammatory subtype of bullous pemphigoid.

CONCLUSIONS

Patients with DPP-4 inhibitor-induced BP may present either an inflammatory or a noninflammatory phenotype of BP. IgG response against other BP180 regions different from the NC16A domain, such as LAD-1 and the C-terminal domain, could be pathogenically relevant to the onset of DPP-4 inhibitor-induced 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.

A PTEN-COL17A1 fusion gene and its novel regulatory role in Collagen XVII expression and GBM malignance

Collagen XVII expression has recently been demonstrated to be correlated with the tumor malignance. While Collagen XVII is known to be widely distributed in neurons of the human brain, its precise role in pathogenesis of glioblastoma multiforme (GBM) is unknown. In this study, we identified and characterized a new PTEN-COL17A1 fusion gene in GMB using transcriptome sequencing. Although fusion gene did not result in measurable fusion protein production, its presence is accompanied with high levels of COL17A1 expression, revealed a novel regulatory mechanism of Collagen XVII expression by PTEN-COL17A1 gene fusion. Knocked down Collagen XVII expression in glioma cell lines resulted in decreased tumor invasiveness, along with significant reduction of MMP9 expression, while increased Collagen XVII expression promotes invasive activities of glioma cells and associated with GBM recurrences. Together, our results uncovered a new PTEN-COL17A1 fusion gene and its novel regulatory role in Collagen XVII expression and GBM malignance, and demonstrated that COL17A1 could serve as a useful prognostic biomarker and therapeutic targets for GBM.

IgG antibodies against immunodominant C-terminal epitopes of BP230 do not induce skin blistering in mice

Bullous pemphigoid, the most common autoimmune blistering disease in Western Europe and the USA is characterized by the presence of circulating and tissue-bound autoantibodies against the hemidesmosomal proteins BP230 and BP180/collagen XVII. After binding to their target antigens at the basement membrane of the dermal-epidermal junction these autoantibodies are thought to trigger an inflammatory cascade comprising complement- and granulocyte-dependent reactions that result in tissue damage. Whereas the role of anti-BP180 antibodies has been extensively characterized, few and conflicting data is available on the contribution of anti-BP230 antibodies to bullous pemphigoid pathogenesis. Therefore, we addressed in the present study the role of autoantibodies to BP230 in experimental bullous pemphigoid. Rabbit polyclonal antibodies generated against epitopes of the C-terminal fragment of murine BP230 bound to the basement membrane and activated the complement system ex vivo. Affinity-purified antibodies were subsequently subcutaneously transferred into neonatal and adult BALB/c mice. In vivo, we observed a dose-dependent binding of transferred antibodies in the murine skin; however, there was no complement activation and these mice showed no clinical or histological signs of inflammatory disease, in contrast to mice receiving anti-BP180 antibodies. We further conducted ex vivo experiments and demonstrated that rabbit IgG anti-BP230-specific antibodies, in contrast to antibodies from bullous pemphigoid patients or rabbit IgG anti-BP180 antibodies used as positive controls, did not activate human granulocytes to induce dermal-epidermal separation in skin cryosections. Our present findings demonstrate that antibodies against BP230 are non-pathogenic in experimental models of bullous pemphigoid and suggest that proper activation of the complement and granulocytes represent prerequisites for conferring bullous pemphigoid autoantibodies their tissue destructive potential.

Bullous pemphigoid IgG induces BP180 internalization via a macropinocytic pathway

Bullous pemphigoid (BP) is an autoimmune blistering skin disease induced by pathogenic autoantibodies against a type II transmembrane protein (BP180, collagen type XVII, or BPAG2). In animal models, BP180 autoantibody-antigen interaction appears insufficient to develop blisters, but involvement of complement and neutrophils is required. However, cultured keratinocytes treated with BP-IgG exhibit a reduction in the adhesive strength and a loss of expression of BP180, suggesting that the autoantibodies directly affect epidermal cell-extracellular matrix integrity. In this study, we explored the consequences of two distinct epithelial cells treated with BP-IgG, particularly the fate of BP180. First, we followed the distribution of green fluorescent protein-tagged BP180 in an epithelial cell line, 804G, and normal human epidermal keratinocytes after autoantibody clustering. After BP-IgG treatment, the adhesive strength of the cells to their substrate was decreased, and BP180 was internalized in both cell types, together with the early endosomal antigen-1. By using various endocytosis inhibitors and a fluid-uptake assay, we demonstrated that BP-IgG-induced BP180 internalization is mediated via a macropinocytic pathway. Moreover, a macropinocytosis inhibitor rescued a BP-IgG-induced reduction in the adhesive strength of the cells from their substrate. The results of this study suggest that BP180 internalization induced by BP-IgG plays an important role in the initiation of disease pathogenesis.

The flavonoid luteolin inhibits Fcγ-dependent respiratory burst in granulocytes, but not skin blistering in a new model of pemphigoid in adult mice

Bullous pemphigoid is an autoimmune blistering skin disease associated with autoantibodies against the dermal-epidermal junction. Passive transfer of antibodies against BP180/collagen (C) XVII, a major hemidesmosomal pemphigoid antigen, into neonatal mice results in dermal-epidermal separation upon applying gentle pressure to their skin, but not in spontaneous skin blistering. In addition, this neonatal mouse model precludes treatment and observation of diseased animals beyond 2-3 days. Therefore, in the present study we have developed a new disease model in mice reproducing the spontaneous blistering and the chronic course characteristic of the human condition. Adult mice were pre-immunized with rabbit IgG followed by injection of BP180/CXVII rabbit IgG. Mice pre-immunized against rabbit IgG and injected 6 times every second day with the BP180/CXVII-specific antibodies (n = 35) developed spontaneous sustained blistering of the skin, while mice pre-immunized and then treated with normal rabbit IgG (n = 5) did not. Blistering was associated with IgG and complement C3 deposits at the epidermal basement membrane and recruitment of inflammatory cells, and was partly dependent on Ly-6G-positive cells. We further used this new experimental model to investigate the therapeutic potential of luteolin, a plant flavonoid with potent anti-inflammatory and anti-oxidative properties and good safety profile, in experimental BP. Luteolin inhibited the Fcγ-dependent respiratory burst in immune complex-stimulated granulocytes and the autoantibody-induced dermal-epidermal separation in skin cryosections, but was not effective in suppressing the skin blistering in vivo. These studies establish a robust animal model that will be a useful tool for dissecting the mechanisms of blister formation and will facilitate the development of more effective therapeutic strategies for managing pemphigoid diseases.

Bullous pemphigoid: from the clinic to the bench

Bullous pemphigoid (BP) constitutes the most frequent autoimmune subepidermal blistering disease. It is associated with autoantibodies directed against the BP antigens 180 (BP180, BPAG2) and BP230 (BPAG1-e). The pathogenicity of anti-BP180 antibodies has been convincingly demonstrated in animal models. The clinical features of BP are extremely polymorphous. The diagnosis of BP critically relies on immunopathologic findings. The recent development of novel enzyme-linked immunosorbent assays has allowed the detection of circulating autoantibodies with relatively high sensitivity and specificity. Although potent topical steroids have emerged in the past decade as first-line treatment of BP, management of the disease may be challenging.

Sequential intramolecular epitope spreading of humoral responses to human BPAG2 in a transgenic model

Bullous pemphigoid (BP) is a subepidermal autoimmune disease characterized by a humoral response to an epidermal basement membrane (BM) component, BP antigen 2 (BPAG2). BP patients have IgG autoantibodies against an immunodominant BPAG2 extracellular domain termed NC16A as well as additional epitopes located both in the intracellular and extracellular domains (ICD and ECD, respectively) of this autoantigen. To study the evolution of humoral responses to BPAG2, sequential serum samples obtained from C57BL/6Ncr mice grafted with otherwise syngeneic skin from transgenic mice expressing human BPAG2 (hBPAG2) in epidermal BM were studied for IgG reactivity to seven ECD and ICD hBPAG2 epitopes. All grafted mice developed specific IgG against hBPAG2 ECD and ICD epitopes. In seven of eight mice, anti-hBPAG2 IgG was initially directed against ECD epitopes; in six mice, humoral responses subsequently targeted additional ECD and ICD BPAG2 epitopes. In contrast to IgG specific for ECD epitopes, IgG against ICD epitopes was present at lower levels, detectable for shorter periods, and non-complement fixing. Interestingly, the appearance of IgG directed against ICD epitopes correlated with the development of graft loss in this experimental model. These studies provide a comprehensive and prospective characterization of the evolution of humoral immune responses to hBPAG2 in vivo.

Plasmin plays a role in the in vitro generation of the linear IgA dermatosis antigen LADB97

Collagen XVII (BP180) and its shed ectodomain represent major autoantigens in dermatoses of the pemphigoid group. The 120 kDa ectodomain is constitutively shed from the cell surface by disintegrin-metalloproteinases (ADAMs). Part of it is further processed to a 97 kDa fragment (LABD97), an autoantigen in linear IgA dermatosis (LAD), but the responsible proteinases remain elusive. In this study, we identified the 120 and the 97 kDa ectodomain in blister fluids of bullous pemphigoid patients using new mAbs. As blister fluids contain significant plasmin-like serine protease activity, HaCaT keratinocytes or purified 120 kDa ectodomain were incubated with several human serine proteases. In vitro, only plasmin generated a stable 97 kDa fragment that was also targeted by LAD sera. Characterization of the plasmin-derived 97 kDa fragment with domain-specific collagen XVII antibodies, heparin binding and N-glycosylation studies indicates that the N-terminus is located approximately at AA 515 and the C-terminus N-terminally from AA 1,421. Interestingly, plasmin-derived LABD97 was also generated in the presence of ADAM inhibitors and remained stable over more than 12 hours incubation at 37 degrees C, indicating that this disease relevant collagen XVII fragment can also arise in an ADAM-independent manner through direct action by plasmin.

Enzyme-linked immunosorbent assay using multimers of the 16th non-collagenous domain of the BP180 antigen for sensitive and specific detection of pemphigoid autoantibodies

Bullous pemphigoid (BP) and pemphigoid gestationis (PG) are acquired autoimmune subepidermal blistering diseases characterized by autoantibodies against the hemidesmosomal proteins BP180/type XVII collagen and BP230. In the vast majority of BP and PG patients, these autoantibodies bind to epitopes clustered within the 16th non-collagenous domain of BP180. An ELISA system for the detection of these autoantibodies was developed and evaluated using 16th non-collagenous domain (NC16A) tetramers instead of monomers. In contrast to antigens fused to large proteins used in the past for the detection of autoantibodies against type XVII collagen, tetrameric antigen fragments bearing a small hexahistidine tag allow for high expression levels without the need to cleave off the fusion partner. Using tetrameric BP180 NC16A, positive reactions were found in 106 (89.8%) of 118 randomly selected BP sera and in all of 20 (100%) randomly selected PG sera, whereas only 2.2% of a large cohort of control subjects were positive in this assay, including patients with rheumatoid arthritis (two of 107), progressive systemic sclerosis (two of 50), systemic lupus erythematosus (one of 72), and healthy blood donors (10 of 494). Thus, the sensitivity and specificity of the new anti-tetrameric NC16A ELISA were 89.9% and 97.8% respectively. Levels of circulating autoantibodies against BP180 paralleled disease activity in the pemphigoid patients. In conclusion, the use of tetrameric NC16A in ELISA results in a sensitive and specific tool for diagnosis and monitoring of BP and PG.

Vesicular pemphigoid with circulating autoantibodies against 230-kDa and 180-kDa proteins, and additional autoantibodies against 97-kDa and 45-kDa proteins

The vesicular variant of bullous pemphigoid is a clinical entity in which the principal type of lesions are multiple small tense vesicles in a symmetric distribution, instead of the classical large, more randomly distributed large bullae. We describe a 62-year-old female who developed a vesicular variant of bullous pemphigoid, with intensely pruritic vesiculopapular eruptions and erythematous irregularly outlined patches confluent on the face, neck, trunk, extremities and oral mucosa. Direct immunofluorescence revealed a linear deposition of IgG and C3 at the basement membrane zone of the skin, and indirect immunofluorescence detected circulating IgG autoantibodies reacting with antigens located on the epidermal side of skin split with 1 M NaCl. Indirect immunogold electron microscopy revealed IgG deposition at the underneath membrane of the basal cells and in the lamina lucida. In addition to the 230-kDa and 180-kDa bullous pemphigoid antigen, immunoblot analysis also demonstrated the presence of IgG antibodies reactive with 97-kDa and 45-kDa protein. Treatment with systemic corticosteroid, minocycline and antihistamines plus topical steroid resulted in moderate improvement. A few vesicles, however, continued to appear intermittently during the past year of treatment.

Bullous pemphigoid: physiopathology, clinical features and management

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

Enzyme-linked immunosorbent assay using bacterial recombinant proteins of human BP230 as a diagnostic tool for bullous pemphigoid

BACKGROUND

By immunoblot analyses of normal human epidermal extracts, the 230kDa bullous pemphigoid antigen (BP230) is recognized by most bullous pemphigoid (BP) sera. We produced different recombinant glutathione-S-transferase-fusion proteins, which roughly presented N-terminal domain, central rod domain and C-terminal domain of human BP230.

OBJECTIVE

In the present study, we developed an enzyme-linked immunosorbent assay (ELISA) using the recombinant proteins for detection of anti-BP230 IgG antibodies and assessed the usefulness of this assay in conjunction with an anti-BP180 ELISA to establish the diagnosis of BP.

METHODS

Using the bacterial recombinant proteins of N-terminal and C-terminal domains, we developed an ELISA. A receiver-operating-characteristic (ROC) analysis was performed to determine a cut-off value for the BP230 ELISA.

RESULTS

By this BP230 ELISA, 173 (72.4%) of 239 BP sera were positive, while only one (1.1%) of 94 sera from pemphigus vulgaris and pemphigus foliaceus patients was positive and all the 109 normal control sera were negative. Thus, the sensitivity and specificity of the BP230 ELISA were 72.4 and 99.5%, respectively. Interestingly, while 54 (84.4%) of 64 BP sera in active stage and 113 (64.6%) of 175 BP sera in remission were positive in BP180 ELISA, 37 (57.8%) of 64 BP sera in active stage and 136 (77.7%) of 175 BP sera in remission were positive in BP230 ELISA. These results indicate that the titer of anti-BP230 antibodies is not related with disease activity in some BP cases. Most significantly, by combining the results of BP230 ELISA and BP180 ELISA, 232 (97.1%) of 239 BP sera were positive.

CONCLUSION

The combination of BP230 ELISA and BP180 ELISA is the highly sensitive method for the diagnosis of BP.

Characterization of the anti-BP180 autoantibody reactivity profile and epitope mapping in bullous pemphigoid patients

Bullous pemphigoid is a subepidermal bullous disease of skin and mucosae associated with autoantibodies to BP180. To characterize the humoral response to BP180, we generated a random BP180 epitope library displayed on lambda bacteriophage. After validation of the library by epitope mapping of three BP180-specific monoclonal antibodies, 15 novel or known BP180 epitopes were identified using 10 bullous pemphigoid serum samples. Fifty-seven bullous pemphigoid and 81 control sera were then assayed against the selected epitopes. Thirty-one out of 57 (54%) bullous pemphigoid sera reacted with at least an additional antigenic site other than the NC16A, within the extracellular (37%) and intracellular (28%) domains of BP180. In addition, the reactivity with extracellular epitopes of BP180 contained within the residue stretches 508-541 and 1331-1404 appeared to be related to the presence of both skin and mucosal involvement. Finally, a preliminary analysis of the epitope pattern in the disease course indicated that bullous pemphigoid patients exhibit a specific reactivity pattern, and that binding to intracellular epitopes of BP180, in addition to NC16A, may be detectable at an early clinical stage. Our findings provide novel insights into the pathophysiology of bullous pemphigoid and show the potential of the utilized approach as a tool for a rapid diagnosis of bullous pemphigoid patients and their management.

Pemphigoid gestationis with predominant involvement of oral mucous membranes and IgA autoantibodies targeting the C-terminus of BP180

Pemphigoid gestationis (PG) is an autoimmune pregnancy-associated subepidermal blistering disease. It usually affects skin and, rarely, mucous membranes. In the vast majority of patients with PG, the autoimmune response is directed to the membrane-proximal NC16A domain of the 180-kd bullous pemphigoid (BP) antigen (BP180) and is mediated by IgG1 and IgG3 autoantibodies. We report the case of a patient with PG associated with extensive lesions on oral mucous membranes. Immunoblotting studies demonstrated the presence of circulating IgA autoantibodies in the patient's serum that were exclusively directed to a 49 amino acid stretch on the C-terminal portion of the BP180 ectodomain located 800 amino acids downstream from NC16A. This C-terminal stretch of BP180 has previously been demonstrated to localize to the lamina lucida/lamina densa interface and to be recognized by IgG and IgA antibodies in a subgroup of patients with cicatricial pemphigoid as well as by IgG autoantibodies in some BP sera. Our patient's lesions healed without scarring within 6 weeks after delivery of a healthy child. The findings in this patient extend the clinical and immunopathologic spectrum of PG.

A highly sensitive and simple assay for the detection of circulating autoantibodies against full-length bullous pemphigoid antigen 180

Bullous pemphigoid antigen 180 (BP180) is the target of autoantibodies in various subepidermal blistering diseases. The most common one is bullous pemphigoid (BP). The pathological importance of anti-BP180 antibodies has been demonstrated in a passive transfer mouse model. However, sensitive assays for routinely detecting circulating antibodies directed against both intra- and extracellular domains of BP180 are only available in specialized laboratories. In addition, most current assays use prokaryotic recombinant fragments of BP180 that lack conformation-dependent epitopes. A simple and very sensitive immunofluorescence (IF) assay based on eukaryotic cells is described here. Sf21 insect cells were transfected with full-length (FL) BP180. As revealed by FACS and confocal laser scanning microscopy the protein was expressed as type II transmembrane protein as in human keratinocytes. By testing serial dilutions of BP180-specific mouse monoclonal antibodies, the eukaryotic IF assay was demonstrated to be more sensitive compared to conventional assays including (1) indirect IF microscopy of human salt-split skin, (2) Western blotting (WB) of the keratinocyte-derived BP180 ectodomain, (3) WB of recombinant BP180 NC16A, and (4) WB of FL-BP180 extracted from Sf21 insect cells. When applied to sera from patients with BP (n = 65), pemphigoid gestationis (n = 16), and cicatricial pemphigoid (n = 7), the novel assay revealed that 58 (89%), 13 (81%), and 6 (84%), respectively, were positive. In contrast, all control sera (pemphigus, n = 20; epidermolysis bullosa acquisita, n = 5; anti-laminin 5 cicatricial pemphigoid, n = 5; systemic lupus erythematosus, n = 5; atopic dermatitis, n = 7; contact dermatitis, n = 3; normal human sera, n = 30) were negative indicating that the assay is highly specific. In addition, reactivity of the assay was conserved to a large extent when the cells had been stored at -20 degrees C for 3 months. Thus, this assay meets the demands of a simple and effective diagnostic tool for detecting circulating antibodies against FL-BP180 and may also be used in laboratories without access to molecular biological technology.

Bullous pemphigoid sera react specifically with various domains of BP230, most frequently with C-terminal domain, by immunoblot analyses using bacterial recombinant proteins covering the entire molecule

By immunoblot analyses of normal human epidermal extracts, the 230 kDa bullous pemphigoid antigen (BP230) is recognized by most bullous pemphigoid sera. By polymerase chain reaction using keratinocyte cDNA library as a template, we successfully amplified 3 cDNAs of about 3 kb, which covered whole human BP230 molecule. By inserting the cDNAs into bacterial expression vector pGEX, we prepared 3 different recombinant glutathione-S-transferase-fusion proteins, which roughly presented N-terminal domain, central rod domain and C-terminal domain of BP230. By immunoblotting using these 3 recombinant proteins, we demonstrated that the majority of bullous pemphigoid sera reacted clearly with multiple recombinant proteins of BP230, most frequently with C-terminal domain. We also examined sera of pemphigus vulgaris, pemphigus foliaceus and herpetiform pemphigus that showed BP230-like protein band by immunoblotting of epidermal extracts, as well as paraneoplastic pemphigus, for reactivity with the 3 recombinant proteins. In the study, we found that only very few of these non-bullous pemphigoid sera reacted with some of the recombinant proteins. These results indicate that the BP230 is specifically reacted by bullous pemphigoid sera, and that the immunoblotting using the BP230 recombinant proteins should be a useful tool for the diagnosis of bullous pemphigoid.

Linear IgA bullous dermatosis induced by atorvastatin

Linear IgA bullous dermatosis (LABD) is an autoimmune blistering skin disease characterized by circulating IgA antibodies binding the basement membrane zone. In most cases the origin is not clear, but in a minority of cases LABD is drug induced. We describe a patient in whom linear IgA disease developed shortly after beginning therapy with atorvastatin. In Western blotting analysis we detected IgA and IgG class antibodies targeting a 97-kd protein. To our knowledge this is the first reported case of atorvastatin-induced LABD.

Patients with bullous pemphigoid and linear IgA disease show a dual IgA and IgG autoimmune response to BP180

Bullous pemphigoid (BP) and linear IgA disease (LAD) are autoimmune subepidermal blistering skin diseases associated with autoantibodies against the transmembrane hemidesmosomal protein BP180/type XVII collagen. It has been demonstrated previously that BP is characterized predominantly by IgG autoantibodies, while autoantibodies in LAD mainly belong to the IgA isotype. The aim of the present study was to investigate the hypothesis that there is a significant overlap in the autoantibody isotype profiles associated with these two diseases. Several new recombinant forms of BP180 were generated in the baculovirus expression system, including the full-length protein. IgG autoantibodies to BP 180 were detectable in 39 of 40 (98%) of BP sera; interestingly, 88% of BP sera also contained IgA anti-BP180 autoantibodies. Similarly, anti-BP180 reactivity in LAD sera (n=22) was also attributed to both an IgA (68%) and an IgG (76%) autoantibody response. IgA and IgG autoantibodies to the intracellular portion of BP180 were found in 14% and 28% of BP sera, respectively, and in 8% of LAD sera (same percentage for both isotypes). Our findings clearly demonstrate that both BP and LAD patients have a dual IgA and IgG autoimmune response to BP180 which is directed not only to the ectodomain, but also to the intracellular portion of this protein.

Hemizygosity for a glycine substitution in collagen XVII: unfolding and degradation of the ectodomain

Defects of collagen XVII, a keratinocyte adhesion protein, are associated with epidermal detachment in junctional epidermolysis bullosa. Although some missense mutations in the collagen XVII gene COL17A1 have been described, the molecular mechanisms leading to disease have remained elusive in these cases. Here we assessed the biologic consequences of a missense mutation by studying the folding and stability of wild-type and mutated recombinant collagen XVII domains. The mutation occurred in a junctional epidermolysis bullosa patient who was compound heterozygous for the novel glycine substitution mutation G633D and the novel nonsense mutation R145X. Collagen XVII mRNA was significantly reduced, indicating nonsense-mediated mRNA degradation and hemizygosity of the patient for the G633D substitution. As glycine residues within the collagen triple helices are important for stable conformation, the thermal stability of the wild-type and mutated eukaryotic recombinant Col15 domain of collagen XVII was assessed. The stability of the mutated fragment was clearly reduced. The midpoint of the helix-to-coil transition, Tm, was 5 degrees C lower than that of wild-type rCol15, indicating abnormal triple-helix folding and susceptibility to proteolysis. Consistently, immunoassays demonstrated reduced amounts of the full-length collagen XVII and absence of the soluble ectodomain in keratinocyte cultures, and lack of the ectodomain from the junctional epidermolysis bullosa skin. These observations show that the glycine substitution G633D in collagen XVII causes abnormal folding and susceptibility to degradation, and thus perturbs the physiologic adhesive functions of collagen XVII in the skin.

The 120-kDa soluble ectodomain of type XVII collagen is recognized by autoantibodies in patients with pemphigoid and linear IgA dermatosis

BACKGROUND

Type XVII collagen promotes adhesion of basal keratinocytes to epidermal basement membrane, and is the target of disease in patients with certain inherited or acquired blistering diseases. Two forms of type XVII collagen are produced by cultured human keratinocytes: a 180-kDa full-length, transmembrane protein, and a recently identified 120-kDa soluble fragment that corresponds to its collagenous ectodomain.

OBJECTIVES

We aimed to determine the incidence and pattern of reactivity of autoantibodies against the 180- and 120-kDa forms of type XVII collagen in sera from 40 patients with bullous pemphigoid (BP), pemphigoid gestationis or cicatricial pemphigoid (CP), as well as six patients with linear IgA dermatosis (LAD).

METHODS

Various immunochemical techniques were used.

RESULTS

These studies found that the 120-kDa fragment of type XVII collagen was bound by circulating autoantibodies in 13 of 38 patients with BP or CP and all six patients with LAD. While many pemphigoid sera had specific reactivity against one but not both forms of this protein, autoantibodies from patients with LAD bound only the soluble ectodomain.

CONCLUSIONS

These findings are consistent with the presence of both neoepitopes and cross-reactive epitopes on the ectodomain of type XVII collagen. The finding that sera from patients with LAD showed specific reactivity to epidermal basement membrane suggests that such neoepitopes are present in human skin and that their targeting by autoantibodies may contribute to disease pathogenesis.

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

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune blistering disease associated with autoantibodies against the hemidesmosomal glycoprotein BP180. The noncollagenous (NC)16A domain of BP180 has recently been shown to harbor major antigenic sites recognized by BP sera.

OBJECTIVE

The purpose of this study was to characterize the subclass distribution and fine specificities of autoantibodies to BP180 NC16A present in the circulation of patients with BP before, and during the course of, therapy for this disease.

METHODS

Eighteen BP sera were analyzed by immunoblotting and enzyme-linked immunosorbent assay for the presence of IgG1, IgG2, IgG3, IgG4, and IgE reactive with various sites on the BP180 NC16A domain. The sera were collected before treatment was started and at 4- and 8-week time points after initiation of treatment.

RESULTS

We identified IgG4 and IgE as the major immunoglobulins that preferentially react with two distinct epitopes (MCW-1 and MCW-2) within BP180 NC16A. Levels of these autoantibodies correlated with disease activity in BP. During the course of disease, no change was observed with regard to the immunoglobulin subclass predominantly reacting with BP180 NC16A or the specific epitopes within this domain.

CONCLUSION

Our data demonstrate that remission of BP is paralleled by a decrease of serum levels of IgE and the different IgG subclasses reactive with BP180 NC16A.

The shed ectodomain of collagen XVII/BP180 is targeted by autoantibodies in different blistering skin diseases

Collagen XVII/BP180, an epidermal adhesion molecule, exists as a full-length transmembrane protein and as a soluble 120-kd ectodomain that is shed from the keratinocyte surface by furin-mediated proteolysis. Despite a number of studies on autoantibody targets in blistering skin diseases, it has remained unclear whether the physiologically shed ectodomain of collagen XVII plays a role as an autoantigen. Here we isolated the authentic, soluble form of human collagen XVII and showed that it is an autoantigen recognized by IgG and IgA autoantibodies in different blistering skin diseases and is, in some cases, the preferential target. The ectodomain was isolated from the epidermis, keratinocyte media, amniotic fluid, and pemphigoid blister fluid, and autoantibodies affinity-purified with this ectodomain bound to the proximal surface of the epidermis in normal skin but not in collagen XVII-deficient skin. The antibody reactivity was not dependent on the native conformation or the N-glycosylation of the soluble ectodomain, but was abolished by collagenase treatment. Sera of 81 patients with a clinically active blistering skin disease were reacted with full-length collagen XVII, the authentic soluble ectodomain, and recombinant fragments. In bullous and cicatricial pemphigoid, IgG reactive with full-length collagen XVII also recognized the soluble ectodomain. In linear IgA dermatosis and chronic bullous dermatosis of childhood, IgA targeted the soluble ectodomain more efficiently than the full-length protein. The use of recombinant fragments demonstrated that epitopes were present in several noncollagenous and collagenous subdomains of the molecule, and that a significant portion of the sera targeted Col15 domain, a hitherto unrecognized epitope region.

Autoantibodies in a subgroup of patients with linear IgA disease react with the NC16A domain of BP1801

Linear IgA disease is an autoimmune subepidermal blistering disease characterized by IgA deposits at the cutaneous basement membrane zone. IgA antibodies from linear IgA disease sera react with antigens of 97 kDa (LABD97) and 120 kDa (LAD-1), both of which appear to be fragments of the extracellular domain of bullous pemphigoid 180 (type XVII collagen). The aim of this study was to determine whether linear IgA disease sera react with the immunodominant region of BP180 (NC16A domain), which is a major target of IgG autoantibodies produced by patients with bullous pemphigoid. Indeed, 11 of 50 linear IgA disease sera were found to contain IgA autoantibodies that recognized a recombinant form of NC16A by immunoblotting. The same sera also reacted with NC16A by enzyme-linked immunosorbent assay. An epitope mapping analysis uncovered four linear IgA disease-associated epitopes located within the 45 amino acid N-terminal stretch of NC16A, all of which were previously identified as antigenic sites targeted by bullous pemphigoid autoantibodies. Eight of the linear IgA disease sera that were reactive with NC16A also recognized LAD-1 secreted by the SCC-25 cell line, and five sera recognized BP180 extracted from keratinocytes. Linear IgA disease sera depleted of reactivity to NC16A by immunoadsorption continued to react with both the LAD-1 antigen and BP180 by immunoblotting and with the basement membrane zone by indirect immunofluorescence microscopy. Our results demonstrate that IgA autoantibodies from a subset of linear IgA disease patients react with the same sites on BP180 that are targeted by IgG autoantibodies in bullous pemphigoid.