Detection of autoantibodies against bullous pemphigoid and pemphigus antigens by an enzyme-linked immunosorbent assay using the bacterial recombinant proteins

IgG reactivity to different desmoglein-3 ectodomains in pemphigus vulgaris: novel panels for assessing disease severity

Introduction

Pemphigus vulgaris (PV) is an autoimmune disease characterized by IgG autoantibodies targeting desmoglein-3 (Dsg3), leading to blistering of mucous membranes and skin. Although commercial ELISA kits effectively diagnose PV, correlation with clinical phenotype remains unclear. This study assesses multiple panels for monitoring disease severity and activity by profiling IgG autoantibodies against Dsg3's various extracellular ectodomains.

Method

We designed and expressed different extracellular domains of Dsg3 in HEK293T cell line and developed 15 different ELISA panels, each using a single or multi ectodomains encompassing the entire extracellular region of Dsg3 to detect specific autoantibodies against the particular part of Dsg3.

Results

To validate our approach, we compared our ELISA panel for the full Dsg3 (EC1-5) against a commercial kit using 154 random serum samples from PV patients, demonstrating a strong correlation. For evaluation of IgG autoantibody profiles in our panels, 59 PV patients were included, along with 11 bullous pemphigoid patients, and 49 healthy controls. For all the included subjects, 15 predefined ELISA panels were tested. The IgG autoantibodies against EC1 were detected in 86% of patients with a positive full Dsg3 ectodomain (EC1-5) ELISA, with 26% against EC2, 14% for EC3, 29% for EC4, and 23% for EC5. Among the panels with multiple Dsg3 ectodomains, EC1-3 and EC1-4 were representative of the entire Dsg3 ectodomain in terms of ELISA positivity across all included patients. A significant correlation (P<0.05) was observed between ELISA optical density (OD) and Pemphigus Disease Area Index (PDAI) scores in five panels, EC1, EC2-3, EC2-5, and EC3-4 in addition to the full ectodomain. It suggests an association with disease severity. Interestingly, while the ELISA panel for the entire Dsg3 extracellular ectodomains did not differentiate disease phases, in three of our panels, including EC1, EC3-5, and EC2-5, ANOVA analysis showed a statistically significant difference between the groups of patients in remission, partial remission or persistent lesions, and those with active disease (new cases or relapse). Among these three panels, EC1 was the only one that showed a significant difference in the multiple comparisons analysis; patients in the active phase had higher levels of autoantibodies than those in 'partial remission or persistent lesions' and 'complete remission' groups.

Conclusion

The level of autoantibodies against EC1 was not only correlated with the full ectodomain but also associated with higher disease severity and active disease phase. This study indicates that a detailed autoantibody profile against Dsg3 ectodomains could serve as a marker for PV severity and activity which may potentially enhance early treatment initiation.

Detection of circulating anti-skin antibodies by indirect immunofluorescence and by ELISA: a comparative systematic review and meta-analysis

Background Both enzyme-linked immunosorbent assays (ELISAs) and indirect immunofluorescence (IIF) are available for the diagnosis of autoimmune bullous diseases (AIBD). Many studies have reported on the performance of ELISAs and concluded that ELISAs could replace IIF. This study compares the diagnostic accuracy of ELISA and IIF for the detection of autoantibodies to desmoglein 1 (DSG1), desmoglein 3 (DSG3), bullous pemphigoid antigen 2 (BP180) and bullous pemphigoid antigen 1 (BP230) to support the diagnosis of pemphigus vulgaris (PV), pemphigus foliaceus (PF) and bullous pemphigoid (BP). Methods A literature search was performed in the PubMed database. The meta-analysis was performed using summary values and a bivariate random effect model. Results The five included studies on PV did not demonstrate significant differences between IIF and DSG3-ELISA (sensitivity 82.3% vs. 81.6%, p = 0.9284; specificity 95.6% vs. 93.9%, p = 0.5318; diagnostic odds ratio [DOR] 101.60 vs. 67.760, p = 0.6206). The three included studies on PF did not demonstrate significant differences between IIF and DSG1-ELISA (sensitivity 80.6% vs. 83.1%, p = 0.8501; specificity 97.5% vs. 93.9%, p = 0.3614; DOR 160.72 vs. 75.615, p = 0.5381). The eight included studies on BP showed that BP230-ELISA differed significantly from both IIF on monkey esophagus (MO) and BP180-ELISA with regard to DOR (11.384 vs. 68.349, p = 0.0008; 11.384 vs. 41.699, p = 0.0125, respectively) Conclusions Our meta-analysis shows that ELISA performs as well as IIF for diagnosing PV, PF and BP.

Clinical features and practical diagnosis of bullous pemphigoid

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

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.

Approach to the patient with autoimmune mucocutaneous blistering diseases

Autoimmune mucocutaneous blistering diseases (AMBD) are a rare group of dermatoses that can be potentially fatal. There are many subtypes and their clinical presentation can vary from being localized to general involvement. It is crucial that a diagnosis be made as early as possible and appropriate treatments are implemented. This article will discuss the diagnosis and available treatments of the major AMBDs. There are very few case-controlled studies regarding the treatments of these diseases. Most of the treatments used for these diseases are based on anecdotal reports. Hence, a synopsis of the conventional treatments and some brief recommendations will also be discussed. A brief discussion regarding "rescue" therapies that have been used for those patients with more recalcitrant cases of AMBD will also be presented.

Analysis of the reactivity of indirect immunofluorescence in patients with pemphigus foliaceus and pemphigus vulgaris using rat bladder epithelium as a substrate

OBJECTIVES

To evaluate the reactivity of indirect immunofluorescence using rat bladder epithelium as a substrate in patients with pemphigus foliaceus and pemphigus vulgaris from the Department of Dermatology, University of São Paulo Medical School, Brazil.

METHODS

Thirty-two patients (8 male and 24 female) from the Department of Dermatology, University of São Paulo Medical School, were selected. Three had mucosal pemphigus vulgaris, 20 had mucocutaneous pemphigus vulgaris, and 9 had pemphigus foliaceus. Patients' sera were tested by indirect immunofluorescence performed on human foreskin and rat bladder epithelium and by ELISA assays utilizing baculovirus-expressed recombinant desmoglein 3 and desmoglein 1.

RESULTS

No patients with mucosal pemphigus vulgaris, 5 of 20 patients with mucocutaneous pemphigus vulgaris (25%) and 4 of 9 patients with pemphigus foliaceus (44%) had positive indirect immunofluorescence using rat bladder epithelium as a substrate.

CONCLUSION

Indirect immunofluorescence using rat bladder epithelium as a substrate is recommended whenever a diagnosis of paraneoplastic pemphigus is considered. The identification of a subset of pemphigus foliaceus and pemphigus vulgaris patients that recognizes desmoplakins by this laboratory tool is critical to avoid the misdiagnosis of paraneoplastic pemphigus.

Multicenter prospective study of the humoral autoimmune response in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune bullous disease, associated with autoantibodies directed against the hemidesmosomal components BP180 and BP230. In this study for the first time different laboratories have analyzed the autoantibody profile in the same group of 49 prospectively recruited BP patients. The results show that: 1) disease severity and activity correlated with levels of IgG against the BP180-NC16A domain, but also against a COOH-terminal epitope of BP180, 2) distinct epitopes of the BP180 ectodomain other than BP180-NC16A were recognized by 96% of the BP sera; and 3) the combined use of BP180 and BP230 ELISA led to the detection of IgG autoantibodies in all the BP sera. These results demonstrate the usefulness of the combined ELISAs based on various BP180 and BP230 fragments in establishing the diagnosis of BP and support the concept that BP180 is the major autoantigen of BP.

Protein kinase C isoenzymes differentially regulate the differentiation-dependent expression of adhesion molecules in human epidermal keratinocytes

Epidermal expression of adhesion molecules such as desmogleins (Dsg) and cadherins is strongly affected by the differentiation status of keratinocytes. We have previously shown that certain protein kinase C (PKC) isoforms differentially alter the growth and differentiation of human epidermal HaCaT keratinocytes. In this paper, using recombinant overexpression and RNA interference, we define the specific roles of the different PKC isoenzymes in modulation of expression of adhesion molecules in HaCaT keratinocytes. The level of Dsg1, a marker of differentiating keratinocytes, was antagonistically regulated by two Ca-independent 'novel' nPKC isoforms; i.e. it increased by the differentiation-promoting nPKCdelta and decreased by the growth-promoting nPKCepsilon. The expression of Dsg3 (highly expressed in proliferating epidermal layers) was conversely regulated by these isoenzymes, and was also inhibited by the differentiation inducer Ca-dependent 'conventional' cPKCalpha. Finally, the expression of P-cadherin (a marker of proliferating keratinocytes) was regulated by all of the examined PKCs, also in an antagonistic manner (inhibited by cPKCalpha/nPKCdelta and stimulated by cPKCbeta/nPKCepsilon). Collectively, the presented results strongly argue for the marked, differential, and in some instances antagonistic roles of individual Ca-dependent and Ca-independent PKC isoforms in the regulation of expression of adhesion molecules of desmosomes and adherent junctions in human epidermal keratinocytes.

The pathophysiology of bullous pemphigoid

Bullous pemphigoid (BP) is a blistering skin disease characterized by an autoimmune response to 2 hemidesmosomal proteins within the dermal-epidermal junction, designated BP180 and BP230. While BP230 localizes intracellularly and associates with the hemidesmosomal plaque, BP180 is a transmembrane glycoprotein with an extracellular domain. Most BP patients have autoantibodies binding to an immunodominant region of BP180, the noncollagenous 16A domain (NC16A), which is located extracellularly close to the transmembrane domain of the protein. Autoreactive T and B cell responses to BP180 have been found in patients with BP. Passive transfer of antibodies to the murine BP180 ectodomain triggers a blistering skin disease in mice that closely mimics human BP. Lesion formation in this animal model depends upon complement activation, mast cell degranulation and accumulation of neutrophils and eosinophils. Patients' autoantibodies to BP180 induce dermal-epidermal separation in cryosections of human skin when co-incubated with leukocytes. The loss of cell-matrix adhesion is mediated by proteinases released by granulocytes. The increased knowledge of the pathophysiology of BP should facilitate the development of novel therapeutic strategies for this disease.

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.

Experimental bullous pemphigoid generated in mice with an antigenic epitope of the human hemidesmosomal protein BP230

Bullous pemphigoid (BP) is an IgG-mediated autoimmune blistering disease that targets the hemidesmosomal proteins BP230 and BP180. To investigate the pathogenic role of anti-BP230 antibodies, rabbit polyclonal antibodies were generated against an antigenic sequence of the human BP230 antigen (BPAG 1, 2479-2499), which shows 67% homology in the human and the mouse BP230. Purified IgG from the rabbit anti-serum was transferred subcutaneously into the dorsal skin of neonatal isogeneic CBA/Ca (CBA) mice in a dose of 5 mg (n=7) or 1.2 mg IgG/50 microl (n=16). After 24 h, 1 of the mice injected with 5 mg IgG exhibited blisters, but the dorsal skin of all 7 of them was erythematous, and gentle friction produced a fine persistent wrinkling of the epidermis in 4 mice. The mice injected with 1.2 mg IgG developed less severe symptoms. Immunohistological examinations revealed linear rabbit IgG and mouse C3 depositions along the basement membrane of the perilesional skin and subepidermal blister formation. An intradermal inflammatory reaction (granulocyte infiltration) was also detected. None of these symptoms was seen in mice injected with IgG from a control rabbit anti-serum. These findings demonstrate that antibodies against BP230 can elicit the clinical and immunopathological features of BP in neonatal mice, suggesting that anti-BP230 antibodies may possibly play a pathogenic role in this disease.

Development of an ELISA for the detection of autoantibodies to BP230

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies against the transmembrane hemidesmosomal protein BP180/collagen type XVII and the intracellular plaque protein BP230. The aim of the present study was to develop an ELISA system for the detection of circulating autoantibodies to BP230. We generated five overlapping cDNA constructs covering the entire length of BP230 and expressed them in baculovirus-infected Sf21 insect cells. ELISA reactivity against BP230 was found in 63% of 56 BP patients' sera; the specificity of the ELISA was 93%. Epitope mapping studies showed that the fragment representing the C-terminal portion of BP230 was by far the most frequent target within the molecule. This ELISA provides a useful tool for the detection of autoantibodies to BP230 in BP and other diseases associated with an autoimmune response to this protein.

Production of the bullous pemphigoid antigen 230 (BP230) by Saccharomyces cerevisiae and Pichia pastoris

BP230 is a cytoskeletal linker protein of 2649 amino acids originally identified as the target autoantigen in bullous pemphigoid, a potentially devastating autoimmune skin blistering disorder. To better define its function, we sought to generate recombinant forms of BP230 in both Saccharomyces cerevisiae and Pichia pastoris after cloning its entire cDNA. By immunoblot analysis, full-length BP230 was not found in extracts of P. pastoris, whereas minor amounts of degraded BP230 were detected in extracts of S. cerevisiae. In contrast, both S. cerevisiae and P. pastoris were able to produce the 770-amino acid COOH-terminal domain of BP230. Furthermore, the production level of the recombinant BP230 tail in S. cerevisiae was significantly higher than that observed in P. pastoris and that of endogenous BP230 in cultured human keratinocytes. Finally, 12 of 17 (71%) BP sera recognized the recombinant BP230 protein in yeast extracts. Our results indicate that S. cerevisiae occasionally constitutes a better tool for recombinant protein production than P. pastoris. Although both its large size and poor solubility limit production of BP230, the developed yeast system provides cellular fractions enriched in BP230 recombinant proteins that constitute useful tools for the diagnosis of bullous pemphigoid.

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.

Immunoreactivity against intracellular domains of desmogleins in pemphigus

In pemphigus vulgaris (PV) and pemphigus foliaceus (PF), most of the autoantibodies are directed against the extracellular domains of desmoglein 1 (Dsg1) or Dsg3, and those antibodies are proved to play a pathogenic role in blister formation in the skin and mucous membranes. However, some pemphigus sera have been reported to react with the intracellular domains of these antigens. In the present study, we examined the reactivity of the sera from various types of pemphigus with recombinant proteins of extracellular and intracellular domains of human Dsg1 and Dsg3 by immunoblot analysis. We produced the entire extracellular domain of Dsg1 or Dsg3 fused with mouse IgG2a by baculovirus expression. We prepared the intracellular domain of Dsg1 or Dsg3 fused with glutathione-S-transferase by bacterial expression. All of the 31 PV sera reacted with the extracellular domain of Dsg3 and four reacted with the intracellular domain. Six out of 19 PF sera reacted with the extracellular domain of Dsg1 and five reacted with the intracellular domain. In addition, some sera of Brazilian PF patients or cases with mixed features of PV and PF also reacted with the intracellular domains of Dsg1 or Dsg3. Although the frequency was low, some sera did react with the intracellular domain of Dsgs.

IgG autoantibodies from bullous pemphigoid patients recognize multiple antigenic reactive sites located predominantly within the B and C subdomains of the COOH-terminus of BP230

Bullous pemphigoid is a subepidermal bullous disorder characterized by an autoantibody response against the bullous pemphigoid antigen 230 (BP230) and the bullous pemphigoid antigen 180 (BP180), a cytoplasmic component and a transmembrane component, respectively, of hemidesmosomes. Although immunodominant sequences within the extracellular domain of BP180 have been identified, characterization of the antigenic sites on BP230 is still incomplete. To identify autoantibody-reactive sites on BP230 and to examine whether the targeted regions are contained within functionally important domains, recombinant fragments encompassing almost the entire BP230 were used to assess the reactivity of 25 bullous pemphigoid sera by immunoblotting. Our results demonstrate that (i) the region bearing the B and C subdomains of the COOH-terminus of BP230 contains immunodominant sequences recognized by the majority of bullous pemphigoid sera; (ii) additional autoantibody- reactive sites are present over extended regions of the NH2-terminal half of BP230 without evidence for antigenic cross-reactivity between the NH2- and COOH-termini of BP230; and, finally, (iii) autoantibodies reacting with the BP230 tail predominantly belong to the IgG4 and IgG1 subclasses, suggesting that both autoreactive TH2 and autoreactive TH1 cells regulate the autoantibody response to immunodominant sequences of BP230. As the COOH- terminus of BP230 mediates the attachment of keratin intermediate filaments to the hemidesmosomal plaque, whereas its NH2-terminus contains sequences important for its interaction with other constituents of hemidesmosomes, autoantibodies to BP230 might precipitate subepidermal blister formation and perpetuate the disease not only by eliciting an inflammatory reaction but also by interfering with the function of BP230 and thus the stability of hemidesmosomes.

A highly sensitive enzyme-linked immunosorbent assay for the detection of circulating anti-BP180 autoantibodies in patients with bullous pemphigoid

The BP180 antigen, a component of the epidermal anchoring complex, has been identified as one of the major antigenic targets of autoantibodies associated with the blistering skin disease, bullous pemphigoid. Our research group has recently demonstrated that reactivity of bullous pemphigoid autoantibodies to the BP180 ectodomain is almost entirely restricted to a set of four antigenic sites clustered within the membrane-proximal noncollagenous stretch (NC16A). Using a passive transfer mouse model, antibodies to the corresponding noncollagenous region of murine BP180 were shown to trigger an inflammatory subepidermal blistering disease that closely mimics bullous pemphigoid. We now report the development of an enzyme-linked immunoabsorbent assay system that is extremely sensitive in detecting disease-specific autoantibodies in the sera of bullous pemphigoid patients. The target antigen in this assay is a recombinant form of the BP180 NC16A domain that contains all four of the well-defined bullous pemphigoid-associated antigenic sites. Of 50 randomly selected bullous pemphigoid sera tested, 47 (94%) were positive in this assay, whereas no specific reactivity was detected in any of the 107 controls. Interestingly, all three of the bullous pemphigoid sera that were negative in this assay had been obtained from patients who were already undergoing treatment. The NC16A enzyme-linked immunosorbent assay is more sensitive than any of the standard techniques for detecting circulating bullous pemphigoid autoantibodies, including other enzyme-linked immunosorbent assays, immunoblotting, and indirect immunofluorescence. Finally, the NC16A enzyme-linked immunosorbent assay provides immunologic information that cannot be obtained from direct immunofluorescence studies of skin biopsies, and that may well be relevant in the diagnosis and treatment of bullous pemphigoid.