A novel ELISA reveals high frequencies of BP180-specific IgE production in bullous pemphigoid

Molecular diagnosis in autoimmune skin blistering conditions

Blister formation in skin and mucous membranes results from a loss of cell-cell or cell-matrix adhesion and is a common outcome of pathological events in a variety of conditions, including autoimmune and genetic diseases, viral and bacterial infections, or injury by physical and chemical factors. Autoantibodies against structural components maintaining cell-cell and cell-matrix adhesion induce tissue damage in autoimmune blistering diseases. Detection of these autoantibodies either tissue-bound or circulating in serum is essential to diagnose the autoimmune nature of disease. Various immunofluorescence methods as well as molecular immunoassays, including enzyme-linked immunosorbent assay and immunoblotting, belong to the modern diagnostic algorithms for these disorders. There is still a considerable need to increase awareness of the rare autoimmune blistering diseases, which often show a severe, chronic-relapsing course, among physicians and the public. This review article describes the immunopathological features of autoimmune bullous diseases and the molecular immunoassays currently available for their diagnosis and monitoring.

Detection of IgG and IgE reactivity to BP180 using the ISAC® microarray system

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune skin disease in which patient autoantibodies react with BP180 and BP230 proteins. In addition to IgG, IgE has been shown to play a role in the disease.

OBJECTIVES

To evaluate the feasibility of detecting IgE and IgG against the immunodominant BP180 NC16A domain (BP180) using a microarray system.

METHODS

BP180 was immobilized on an experimental version of the ISAC(®) microarray (Exp96). The BP study group and the controls were all tested on the commercial ISAC 103 version and on the Exp96. IgG and IgE were measured in a single run. BP180 IgG and IgE results were compared with those using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

All results obtained using the IgG ELISA on the 31 patients with BP were replicated with the ISAC IgG. Five of eight BP sera tested by ELISA showed similar results with ISAC IgE. Twenty-nine (94%) and 19 (61%) of the 31 patients with BP were IgG and IgE positive to BP180, respectively, whereas four (3%) and six (4%) of 138 normal donors were IgG and IgE positive, respectively. Interestingly, the levels of IgG against BP180 detected using the ISAC system were related to the disease severity. Patients with BP showed a peculiar profile of IgE recognition toward some groups of allergens, which was absent in a group of allergic individuals. A significant, higher prevalence of hen's egg recognition was observed in patients with BP who had specific IgE to BP180.

CONCLUSIONS

The present preliminary study indicates that the ISAC microarray system is suitable for detecting IgG and IgE autoantibodies in patients with BP. Notably, this system allows the assessment of IgE and IgG autoantibodies at the same time, could be employed for the detection of autoantibodies to other autoantigens, and allows profiling for specific IgE to allergens.

Missing the target: characterization of bullous pemphigoid patients who are negative using the BP180 enzyme-linked immunosorbant assay

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by autoantibodies specific for the 180-kd BP antigen-2 (BP180) (also termed "type XVII collagen") protein. The BP180 enzyme-linked immunosorbent assay (ELISA) is specific for the immunodominant NC16A domain of the protein. However, we and others have observed patients whose reactivity to BP180 is exclusive of the NC16A domain (referred to henceforth as non-NC16A BP).

OBJECTIVE

We sought to determine the incidence of non-NC16A BP and identify regions of reactivity within the BP180 protein.

METHODS

Sera from 51 patients who met the clinical and histologic criteria for BP were screened for NC16A reactivity by ELISA. Sera that were negative by ELISA were screened for IgG reactivity to an epidermal extract, recombinant BP180 protein, and subregions of BP180, by immunoblot. Demographic and clinical data were also collected on all patients.

RESULTS

Four sera (7.8%) were negative using the BP180 ELISA but positive for IgG reactivity to the extracellular domain of BP180. Further mapping identified 4 regions outside of NC16A recognized by these sera: amino acid (AA) 1280 to 1315, AA 1080 to 1107, AA 1331 to 1404, and AA 1365 to 1413. One of these sera also had IgE specific for NC16A. One patient had an atypical presentation with lesions limited to the lower aspect of the legs and scarring of the nail beds.

LIMITATIONS

The small total number of patients with non-NC16A BP limits the identification of demographic or clinical correlates.

CONCLUSION

It is significant that 7.8% of sera from patients with new BP react to regions of BP180 exclusively outside of NC16A and, thus, would not be identified using the currently available BP180 ELISA.

IgG/IgE bullous pemphigoid with CD45 lymphocytic reactivity to dermal blood vessels, nerves and eccrine sweat glands

CONTEXT

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is mediated by autoantibodies. BP primarily affects the elderly and is characterized by the development of urticarial plaques surmounted by subepidermal blisters, and the deposition of immunoglobulins and complement at the basement membrane zone (BMZ) of the skin. BP is immunologically characterized by the development of autoantibodies targeting two structural proteins of the hemidesmosomes, BP180 (collagen XVII) and BP230 (BPAG1).

CASE REPORT

A 63 -year-old Caucasian female patient was evaluated for a 4 day history of several itching, erythematous blisters on her extremities. Biopsies for hematoxylin and eosin (H&E) examination, as well as Periodic acid-Schiff (PAS), immunohistochemistry (IHC) and direct immunofluorescence (DIF) analysis were performed.

RESULTS

H&E demonstrated a subepidermal blister, with partial re-epithelialization of the blister floor. Within the blister lumen, numerous neutrophils were present, with occasional eosinophils and lymphocytes also noted. Within the dermis, a mild, superficial, perivascular and periadnexal infiltrate of lymphocytes, histiocytes and occasional eosinophils was identified, with mild perivascular leukocytoclastic debris. The PAS stain was positive at the BMZ, and around selected blood vessels, nerves and sweat glands. DIF revealed linear deposits of IgG and Complement/C3 and fibrinogen at the BMZ, and around selected dermal nerves, blood vessels and sweat glands. Strong granular deposits of IgE were also observed, colocalizing with monoclonal antibodies to Collagen IV (CIV). By IHC, positive CD45 staining of lymphocytes was seen surrounding selected dermal blood vessels, eccrine sweat glands, and nerves.

CONCLUSION

The patient displayed IgG, IgE, and fibrinogen autoantibodies against the BMZ, as well as around some dermal nerves and sweat glands; their binding in the skin could trigger complement activation. In addition, the role of the dermal CD45 positive lymphocytes warrants further investigation.

Diagnostic accuracy of enzyme-linked immunosorbent assays (ELISA) to detect anti-skin autoantibodies in autoimmune blistering skin diseases: a systematic review and meta-analysis

BACKGROUND

Systematic reviews and meta-analysis are essential tools to accurately and reliably summarize evidence, and can be used as a starting point for developing practice guidelines for the diagnosis and treatment of patients.

AIM

To estimate the diagnostic accuracy of enzyme-linked immunosorbent assays (ELISA) to detect anti-BP180 and anti-desmoglein 3 (Dsg3) autoantibodies in the diagnosis of autoimmune blistering skin diseases.

METHODS

A Medline search of English written articles, published between 1994 and 2011, reporting data on the sensitivity and specificity of diagnostic tests was conducted using the following search terms: "BP180 autoantibodies", "Dsg3 autoantibodies", and "enzyme linked immunosorbent assay". The selected articles have been evaluated according to the quality of the statistical methods used to calculate diagnostic accuracy (definition of cutoff value, use of ROC curves, and selection of control cases). The meta-analysis was performed using a summary ROC (SROC) curve and a random-effect model to independently combine sensitivity and specificity across studies.

RESULTS

The search yielded 69 publications on BP180 autoantibodies and 178 on Dsg3 autoantibodies. A total of 30 studies met the inclusion criteria: 17 provided data on the assays to detect autoantibodies to BP180 in a sample of 583 patients with bullous pemphigoid (BP), while 13 studies provided data on the assays to search for anti-Dsg3 autoantibodies in a sample of 1058 patients with pemphigus vulgaris (PV). The 17 studies on BP180 autoantibodies yielded a pooled sensitivity of 0.87 (95% confidence interval (CI) 0.85 to 0.89) and a pooled specificity of 0.98 (CI, 0.98 to 0.99). The area under the curve (AUC) for the SROC curve was 0.988, and the summary diagnostic odds ratio was 374.91 (CI, 249.97 to 562.30). The 13 studies on Dsg3 autoantibodies which met the inclusion criteria, yielded a pooled sensitivity of 0.97 (CI, 0.95 to 0.98), and a pooled specificity of 0.98 (CI, 0.98 to 0.99). The AUC for the SROC curve was 0.995 and the summary diagnostic odds ratio was 1466.11 (95% CI, 750.36 to 2864.61).

CONCLUSIONS

Results of the meta-analysis demonstrated that ELISA tests for anti-BP180 and anti-Dsg3 autoantibodies have high sensitivity and specificity for BP and PV, respectively, and can be used in daily laboratory practice for the initial diagnosis of autoimmune blistering skin diseases.

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.

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

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

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

BACKGROUND

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease of the skin associated with IgG autoantibodies to BP180 and BP230, while mucous membrane pemphigoid (MMP) comprises a heterogeneous group of autoimmune blistering diseases characterized by a predominant mucous membrane involvement and scarring tendency associated with an autoantibody response to various autoantigens, including BP180. While the pathogenicity of IgG autoantibodies to BP180 has been demonstrated in BP, the role of IgE autoantibodies in mediating tissue damage in BP and MMP is unclear.

OBJECTIVES

To assess the presence of tissue-bound IgE in patients with BP and MMP, and their correlation with distinct clinical features.

METHODS

In this retrospective study, we assessed the presence of IgE deposits as detected by direct immunofluorescence microscopy of skin biopsy specimens obtained from 44 and 13 patients with a new diagnosis of BP and MMP, respectively. Distinct clinical features at time of diagnosis, such as itch, urticarial papules and plaques and eczematous lesions, were noted.

RESULTS

In 18 of 44 (41%) patients with BP linear deposits of IgE of variable intensity were detectable along the dermoepidermal junction. In 14 (32%) of the cases, IgE deposits were found concomitantly with IgG and C3. In two (5%) patients, diagnosis of BP was based on the isolated detection of IgE together with consistent clinicopathological features. Nine of 13 (69%) patients with MMP also exhibited linear IgE deposits, including one case with isolated linear IgE deposits. Patients with BP with tissue-bound IgE deposits had clinically significant urticarial papules and plaques when compared with patients with BP without IgE deposits.

CONCLUSIONS

Our findings indicate that demonstration of tissue-bound IgE deposits provides an additional useful criterion for diagnosis of BP and MMP in some patients. Prospective studies are needed to better correlate the presence of tissue-bound and circulating IgE autoantibodies and their specificity with distinct clinical features and course of BP and MMP.

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.

FcR-independent effects of IgE and IgG autoantibodies in bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by IgE and IgG class autoantibodies specific for 180-kDa BP Ag 2 (BP180), a protein involved in cell-substrate attachment. Although some direct effects of BP IgG have been observed on keratinocytes, no study to date has examined direct effects of BP IgE. In this study, we use primary cultures of human keratinocytes to demonstrate Ag-specific binding and internalization of BP IgE. Moreover, when BP IgE and BP IgG were compared, both isotypes stimulated FcR- independent production of IL-6 and IL-8, cytokines critical for BP pathology, and elicited changes in culture confluence and viability. We then used a human skin organ culture model to test the direct effects of these Abs on the skin, whereas excluding the immune inflammatory processes that are triggered by these Abs. In these experiments, physiologic concentrations of BP IgE and BP IgG exerted similar effects on human skin by stimulating IL-6 and IL-8 production and decreasing the number of hemidesmosomes localized at the basement membrane zone. We propose that the Ab-mediated loss of hemidesmosomes could weaken attachment of basal keratinocytes to the basement membrane zone of affected skin, thereby contributing to blister formation. In this article, we identify a novel role for IgE class autoantibodies in BP mediated through an interaction with BP180 on the keratinocyte surface. In addition, we provide evidence for an FcR-independent mechanism for both IgE and IgG class autoantibodies that could contribute to BP pathogenesis.

Development of an ELISA for sensitive and specific detection of IgA autoantibodies against BP180 in pemphigoid diseases

BACKGROUND

Pemphigoids are rare diseases associated with IgG, IgE and IgA autoantibodies against collagen XVII/BP180. An entity of the pemphigoid group is the lamina lucida-type of linear IgA disease (IgA pemphigoid) characterized by IgA autoantibodies against BP180. While for the detection of IgG and IgE autoantibodies specific to collagen XVII several ELISA systems have been established, no quantitative immunoassay has been yet developed for IgA autoantibodies. Therefore, the aim of the present study was to develop an ELISA to detect IgA autoantibodies against collagen XVII in the sera of patients with pemphigoids.

METHODS

We expressed a soluble recombinant form of the collagen XVII ectodomain in mammalian cells. Reactivity of IgA autoantibodies from patients with IgA pemphigoid was assessed by immunofluorescence microscopy and immunoblot analysis. ELISA test conditions were determined by chessboard titration experiments. The sensitivity, specificity and the cut-off were determined by receiver-operating characteristics analysis.

RESULTS

The optimized assay was carried out using sera from patients with IgA pemphigoid (n = 30) and healthy donors (n=105). By receiver operating characteristics (ROC) analysis, an area under the curve of 0.993 was calculated, indicating an excellent discriminatory capacity. Thus, a sensitivity and specificity of 83.3% and 100%, respectively, was determined for a cut-off point of 0.48. As additional control groups, sera from patients with bullous pemphigoid (n=31) and dermatitis herpetiformis (n = 50), a disease associated with IgA autoantibodies against epidermal transglutaminase, were tested. In 26% of bullous pemphigoid patients, IgA autoantibodies recognized the ectodomain of collagen XVII. One of 50 (2%) of dermatitis herpetiformis patients sera slightly topped the cut-off value.

CONCLUSIONS

We developed the first ELISA for the specific and sensitive detection of serum IgA autoantibodies specific to collagen XVII in patients with pemphigoids. This immunoassay should prove a useful tool for clinical and translational research and should essentially improve the diagnosis and disease monitoring of patients with IgA pemphigoid. Moreover, our findings strongly suggest that IgA pemphigoid and IgG bullous pemphigoid represent two ends of the clinical spectrum of an immunological loss of tolerance against components of hemidesmosomes, which is mediated by both IgG and IgA autoantibodies.

Understanding the genetic regulation of IgE production

Immunoglobulin E (IgE) is a key mediator of anti-parasitic and anti-tumour immunity. However it is also a critical component of atopic and autoimmune diseases, and elevated serum IgE levels are a common indicator of immune dysregulation. In this review we survey the literature on genetic associations of elevated IgE in humans and mice. We find that defects in a limited number of pathways explain the majority of gene associations with IgE. Commonly, elevated IgE is associated with defects in Th bias and B cell class switching, severe T cell tolerance defects and defects in immunity at the host-environment interface. These genetic data demonstrate the mechanisms of control over IgE production and the manner in which they can be circumvented.

Pregnant women have increased incidence of IgE autoantibodies reactive with the skin and placental antigen BP180 (type XVII collagen)

BP180 (type XVII collagen) is a transmembrane protein expressed in a variety of cell types. It is also the target of autoantibodies in cutaneous autoimmune disease including bullous pemphigoid and pemphigoid gestationis, a disease unique to pregnancy. The purpose of this study was to determine the prevalence and specificity of cutaneous autoantibodies in a cohort of pregnant women. De-identified sera were collected from pregnant women (n=299) and from non-pregnant controls (n=134). Sera were analyzed by ELISA for the presence of IgG and IgE autoantibodies directed against several cutaneous autoantigens. IgE antibodies against the NC16A domain of BP180 were detected in 7.7% of pregnant women, compared to 2.2% of healthy controls (p=0.01). No increase in total or cutaneous autoantigen specific IgG was seen. Total serum IgE was within the normal range. Full-length BP180 was detected by western immunoblot in epidermal, keratinocyte, placental and cytotrophoblast (CTB) cell lysates. Furthermore, flow cytometry and indirect immunofluorescence confirmed the expression of BP180 on the surface of cultured CTBs. Finally, it was demonstrated that IgE antibodies in the pregnancy sera labeled not only cultured CTBs, but also the placental amnion and cutaneous basement membrane zone using indirect immunofluorescence. We conclude that some pregnant women develop antibodies specific for BP180, and that these autoantibodies are capable of binding both CTB and the placental amnion, potentially affecting placental function.

Antigenic properties of the coat of Cucumber mosaic virus using monoclonal antibodies

The coat protein (CP) of Cucumber mosaic virus (CMV) was characterized by antigen-capture-ELISA using a panel of monoclonal antibodies (mAbs) which were produced against Pepo-CMV-CP. Comparative analysis of three mAbs with four different strains by competitive ELISA revealed that the binding affinity of the mAb decreased about 10-fold with both MY17- and Y-CMV than with Pepo-CMV. The CP of these three strains showed high homology (approximately 98%) following comparison in the GenBank database. CMV has a negatively charged loop structure, the betaH-betaI loop, although the amino acid at position 193 is not conserved. In addition, an amino acid residue identified within the variable region spanning amino acids 191-198, specifically at position 194, showed significant changes in Threonine, Alanine, Alanine, and Lysine of the Pepo-, MY17-, Y-, and M2-CMV strains, respectively. Evidence from competitive ELISA and GenBank database amino acid residues, when taken together, provide strong support suggesting that the dominant epitope site of CMV-CP-specific mAbs is the betaH-betaI loop 191-198. The four mAbs were chosen because they represent distinct, overlapping epitopes within the group-specific determinant located on the CMV-CP and because they all recognize linear epitopes. Knowledge of specific immunoglobulin genes for a common epitope may lead to insight on pathogen-host co-evolution and may help prevent virus infection in plants.