Clinical significance of enzyme-linked immunosorbent assay for the detection of circulating anti-BP180 autoantibodies in patients with bullous pemphigoid

The NC16A domain of the 180-kDa bullous pemphigoid antigen (BP180) is the most immunogenic and, probably, pathogenic region in bullous pemphigoid (BP). In the present study, in order to determine whether serum level of circulating anti-BP180 autoantibodies is a valuable serum marker in BP, the immunoreactivity of sera against the NC16A domain of BP180 was measured using enzyme-linked immunosorbent assay (ELISA) in ten patients with BP. Serum levels of anti-BP180 autoantibodies correlated with the clinical course in BP patients, who received various therapeutic agents. The result suggests that this NC16A-ELISA is a useful method for evaluating the clinical course and efficacy of the therapy in patients with BP.     

Serum levels of IgE anti-BP180 and anti-BP230 autoantibodies in patients with bullous pemphigoid

BACKGROUND: Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the hemidesmosomal proteins, BP180 and BP230. NC16A, a non-collagenous stretch of the BP180 ectodomain is the primary target of pathogenic IgG antibodies. Whereas IgG anti-BP180 autoantibodies play a primary role in the pathogenesis, there is a growing number of data regarding the potential pathogenic roles of IgE class autoantibodies in BP. OBJECTIVES: To examine the levels of IgG and IgE autoantibodies against BP180 and BP230, and to investigate mutual association and clinical relevance. METHODS: Sera obtained from 67BP patients and 36 healthy donors were subjected to ELISA assays to measure serum IgG and IgE levels of anti-BP180 and anti-BP230 antibodies. RESULTS: IgG anti-BP180 antibodies were positive in 63 (94%) of 67BP patients. IgG anti-BP230, IgE anti-BP180, and IgE anti-BP230 antibodies were found in 48 (72%), 20 (30%) and 45 (67%), respectively. IgG anti-BP180 levels were correlated with the affected areas. IgG anti-BP230 antibodies tended to increase in proportion to elongation of disease duration. IgE anti-BP230 levels showed a strong association with local eosinophil accumulation, while the levels were reversely related with the affected areas in BP. CONCLUSIONS: IgE autoantibodies to BP180 and BP230 are detected at high frequencies in BP. IgE anti-BP230 antibodies may have a role in attracting eosinophils to the skin lesions.     

Absence of anti-BP180 antibodies in mothers of infants with bullous pemphigoid

BACKGROUND: It is not clear whether bullous pemphigoid (BP) of infancy is linked to maternal transmission of pathogenic autoantibodies. Objectives To search for anti-BP180 antibodies in the sera of infants with BP and their mothers, using sensitive and specific methods. METHODS: Four infants (<6 months) with BP and their mothers were tested for anti-BP180 antibodies by indirect immunofluorescence, immunoblotting and enzyme-linked immunosorbent assay (ELISA). RESULTS: We found anti-BP180 antibodies in the sera of the four infants with all methods. These antibodies reacted with the extracellular domain NC16A. In the serum of their mothers we found 180 and 160 kDa proteins, each in one case, but indirect immunofluorescence and ELISA were negative, suggesting the absence of anti-BP180 autoantibodies reacting with the extracellular domain NC16A. CONCLUSIONS: BP of infants is not due to maternofetal transmission of pathogenic autoantibodies. Other hypotheses for the pathophysiology of BP are discussed.     

抗BP180NC16A IgG亚型检测方法的建立以及在大疱性类天疱疮中的意义

【摘要】 目的 建立抗BP180NC16A IgG亚型的检测方法,并探讨其在大疱性类天疱疮（BP）中的意义。方法 原核表达GST-NC16A融合蛋白,并采用亲和层析法纯化。优化ELISA关键环节,建立抗BP180NC16A IgG各亚型的ELISA检测方法,并对10例未经治疗的BP、5例妊娠疱疹、1例成人线状IgA大疱性皮病、2例天疱疮患者血清分别进行检测。结果 通过方阵测定法确定GST-NC16A融合蛋白的包被浓度为500 μg/L,包被条件为4 ℃ 12 h,血清稀释倍数为1 ∶ 100,酶标二抗为1 ∶ 2000,孵育条件为37 ℃ 1 h,底物反应条件37 ℃ 20 min。10例大疱性类天疱疮患者10例IgG1阳性,9例IgG2阳性,5例IgG3阳性,9例IgG4阳性。2例寻常型天疱疮、1例成人线状IgA大疱性皮病均阴性。5例妊娠疱疹所有亚型均阳性,以IgG1和IgG3亚型为主。结论 抗BP180NC16A ELISA检测法特异性强、重复性好,是检测BP和妊娠疱疹患者抗BP180NC16A抗体亚型的半定量方法。     

Usefulness of Enzyme-linked Immunosorbent Assay Using Recombinant BP180 and BP230 for Serodiagnosis and Monitoring Disease Activity of Bullous Pemphigoid

Background

Bullous pemphigoid (BP) is an autoimmune subepidermal bullous disease associated with autoantibodies against BP180 and BP230. Enzyme-linked immunosorbent assay (ELISA) is a sensitive tool for the detection of immunoglobulin G (IgG) anti-BP180 and anti-BP230 autoantibodies.

Objective

The aim of this study was to evaluate the usefulness of ELISA for diagnosing and monitoring the disease activity of BP.

Methods

We evaluated serum IgG levels of anti-BP180 and anti-BP230 autoantibodies in 47 BP patients, 16 epidermolysis bullosa aquisita patients, and 15 healthy volunteers using ELISA. Through retrospective review of the medical records, the clinical characteristics of BP including disease activity, duration, pruritus severity and peripheral blood eosinophil counts were assessed.

Results

The sensitivity of BP180 ELISA was 97.9%, BP230 ELISA 72.3%, and a combination of the two was 100%. The specificity of BP180 ELISA was 90.3%, BP230 ELISA 100%, and a combination of the two was 90.3%. BP180 ELISA scores showed strong associations with disease activity, pruritus severity, peripheral blood eosinophil counts, and disease duration, whereas BP230 ELISA scores did not.

Conclusion

BP180 and BP230 ELISAs are highly sensitive methods for the diagnosis of BP, and BP180 ELISA, in particular, is a sensitive tool for monitoring the disease activity of BP.     

大疱性类天疱疮和妊娠疱疹患者血清抗BP180 NC16A抗体的纯化和鉴定

目的 探讨大疱性类天疱疮（BP）和妊娠疱疹（HG）患者血清抗BPl80 NC16A 抗体的纯化和鉴定方法。方法 原核表达系统pGEX-2TBP180NC16A表达GST/NC16A融合蛋白,将融合蛋白与谷胱甘肽琼脂糖凝聚微珠进行共价偶联。微珠亲和层析法纯化BP和HG患者血清中抗BP180 NC16A抗体,并用ELISA、免疫荧光、及Western印迹进行鉴定。结果 原核表达系统pGEX-2TBP180NC16A表达37 000 GST/NC16A融合蛋白,微珠亲和层析法纯化后得单一抗BP180 NC16A抗体。经ELISA方法定量后确定其含量为2.4 mg/ml;该抗体能与人皮肤基底膜带结合,证明抗体活性;免疫印迹可见单一片段,显示抗体纯度。结论 微珠亲和层析法纯化的BP和HG患者血清中抗BP180 NC16A自身抗体活性高、特异性强。     

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.     

Place of human amniotic membrane immunoblotting in the diagnosis of autoimmune bullous dermatoses

Background Fine analysis of antiskin autoantibodies can contribute to the differential diagnosis of autoimmune bullous dermatoses. Objectives To develop a high‐performance immunoblotting method using human amniotic membrane as the antigen source, and to compare it with current laboratory methods. Methods Sera from 113 patients were tested by immunoblotting (IB), rat and monkey oesophagus and salt‐split skin indirect immunofluorescence (IIF), and enzyme‐linked immunosorbent assay (ELISA) quantification of anti‐BP180‐NC16a and anti‐BP230, or antidesmoglein (Dsg) 1 and 3 antibodies. There were 56 cases of bullous pemphigoid (BP), 22 cases of mucous membrane pemphigoid (MMP), eight cases of epidermolysis bullosa acquisita (EBA), two cases of bullous systemic lupus erythematosus (BSLE), 17 cases of pemphigus vulgaris (PV), and four cases each of pemphigus foliaceus (PF) and paraneoplastic pemphigus (PNP). Results In BP, the three methods had similar sensitivity (84–89%) for both anti‐BP180‐NC16a and anti‐BP230 antibody detection. In MMP, autoantibodies (mainly directed against BP180 or laminin 332 subunits) were detected in 77% of patients by IB, compared with only 9% by IIF on rat and monkey oesophagus and 36% on salt‐split skin, and 14% by anti‐BP180‐NC16a and anti‐BP230 ELISA. In patients with pemphigus, ELISA had 92% sensitivity for anti‐Dsg1 and 3, but IB and rat bladder IIF were necessary to confirm PNP by revealing specific and rare patterns (antidesmoplakin I/II, antienvoplakin and antiperiplakin antibodies). IB also revealed anticollagen VII antibodies in 60% of patients with EBA and BSLE, and antibodies to BP180, BP230 and Dsg3 in a few patients who were negative using the other two techniques. Conclusion Amniotic membrane immunoblotting is an interesting diagnostic tool for bullous diseases, as the entire panel of autoantibodies can be detected with a single extract. This method improves the identification of complex and heterogeneous autoimmune processes in conjunction with IIF and ELISA, and is particularly useful for MMP characterization.     

大疱性类天疱疮疾病严重程度与BP180抗体水平关系的研究

目的 研究大疱性类天疱疮患者临床疾病严重程度和BP180抗体滴度之间的关系.方法 用BP180NC16a-ELISA分别测定大疱性类天疱疮患者治疗前,病情缓解、糖皮质激素开始减量时和糖皮质激素减量至相当于泼尼松0.5 mg·kg^-1·d^-1时,体内BP180抗体滴度,观察其与患者病情严重程度的一致性.结果 在治疗前,19例大疱性类天疱疮患者的BP180 ELISA平均A值为0.520(0.832～0.372);在病情得到控制、糖皮质激素准备减量时,其BP180 ELISA平均A值为0.405(O.723～0.204);在病情缓解、糖皮质激素减至相当于泼尼松0.5 mg·kg^-1·d^-1时,其BP180 ELISA平均A值为0.215(0.412～0.093).结论 BP180抗体的滴度与大疱性类天疱疮患者疾病严重程度相关,是一种评估疾病病情的有用手段,也可对治疗的有效性作出评价.     

Immunoglobulin E and bullous pemphigoid

Clinical features and histological findings in bullous pemphigoid (BP) suggest a Th2-oriented inflammatory reaction, especially in the early stages of the disease. Elevated total serum IgE levels, blood eosinophilia, and elevated serum levels of different soluble inflammatory Th2 response mediators have been described in large cohorts of patients with classic clear-cut BP manifestations. Direct immunofluorescence, indirect immunofluorescence, and anti-BP230 and anti-BP180 IgE ELISA testing show self-reactive IgE autoantibodies in a consistent number of BP patients. Both IgE autoantibodies and a Th2-oriented immune response may play a role in the initial phases of BP and atypical cases of BP, such as severe erythematous and urticarial forms of BP, as well as blister formation. Two recently reported experimental murine models employing IgE autoantibodies against BP180 have been reported and the successful treatment of bullous pemphigoid with the anti-IgE antibody, omalizumab, supports the roles played by IgE autoantibodies in BP pathogenesis.     

Mapping the binding sites of anti-BP180 immunoglobulin E autoantibodies in bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the hemidesmosomal protein BP180 (BPAg2, type XVII collagen). NC16A, a non-collagenous stretch of the BP180 ectodomain, is the primary target of pathogenic immunoglobulin (Ig)G autoantibodies and IgE class autoantibodies. This study further characterized the IgE-reactive regions of BP180. Of the ten sera from untreated BP patients, eight contained IgE reactive with the entire BP180 ectodomain. The IgE in four of these eight sera reacted with NC16A, whereas in the remaining four sera IgE immunoreactivity was restricted to sites downstream of NC16A. In contrast, IgG reactivity to NC16A was detected in nine of the ten BP sera, and in the remaining serum, IgG, as well as IgE, reacted exclusively with non-NC16A sites on the BP180 ectodomain. Fine mapping of the antigenic sites within NC16A revealed very similar reactivity patterns for IgE and IgG, with NC16A subregion-2 being the major site recognized by both isotypes. Eight of the untreated BP patients were tested for histamine release from their basophils in response to NC16A. Antigen-specific histamine release was observed only in those patients with detectable circulating IgE directed against NC16A (three of eight). Future studies will investigate the pathogenic relevance of anti-BP180 IgE.     

Evaluation of a BP180-NC16a enzyme-linked immunosorbent assay in the initial diagnosis of bullous pemphigoid

BACKGROUND: Bullous pemphigoid (BP) is the most common subepidermal immunobullous disease, characterized by circulating IgG autoantibodies targeting BP180 and BP230 hemidesmosomal proteins. Several immunological studies have demonstrated that the membrane proximal noncollagenous domain NC16a of BP180 is the immunodominant region targeted by BP autoantibodies. Recently, a commercial BP180 NC16a-specific enzyme-linked immunosorbent assay (ELISA) has become available for detecting pathogenic anti-BP180 autoantibodies in BP sera. However, it remains unclear whether the diagnostic potential of the ELISA is equivalent to that of the 'gold-standard' diagnostic technique of immunofluorescence (IF). OBJECTIVES: To examine the usefulness of a commercially available BP180-NC16a ELISA in the initial serodiagnosis of BP. METHODS: Sera from a large cohort of patients with BP (n = 102) and control subjects (age- and sex-matched normal volunteers, n = 60; pemphigus foliaceus, n = 18; pemphigus vulgaris, n = 16) were assayed by BP180-NC16a ELISA. All BP sera were obtained at presentation before initiation of systemic immunosuppressive therapy. The values of IgG antibody levels measured by ELISA were compared with those measured by indirect IF on salt-split skin. Results Receiver operating characteristic analysis was used to calculate the cut-off value for the ELISA in the diagnosis of BP which maximizes both sensitivity and specificity, and to estimate the diagnostic accuracy of the ELISA as represented by the area under the curve (AUC = 0.965). A cut-off value of 9 was associated with a sensitivity of 89% (91 of 102 BP sera showed a positive result) and a specificity of 98%. Fifty-eight of 60 normal controls and all the pemphigus sera showed a negative result. There was a correlation between the mean ELISA values and indirect IF titres (Spearman rank correlation 0.286; P = 0.004). CONCLUSIONS: Our results suggest that the BP180-NC16a ELISA is a useful tool for the detection of pathogenic anti-BP180 IgG autoantibodies at the initial disease stage of BP. Because it is not only highly sensitive and specific, but is also easy to perform, is objective, and semiquantitative, the ELISA may provide valuable information for the accurate and reliable serodiagnosis of BP.     

Autoantibodies to bullous pemphigoid antigen 180 induce dermal-epidermal separation in cryosections of human skin

Bullous pemphigoid is a subepidermal autoimmune blistering disease associated with autoantibodies to the hemidesmosomal bullous pemphigoid antigens 180 and 230. Most sera from bullous pemphigoid patients recognize epitopes within the N-terminal NC16A portion of the bullous pemphigoid 180 ectodomain. Using cryosections of human skin, patients' sera were shown to generate dermal-epidermal separation when coincubated with leukocytes and complement from healthy volunteers; however, the specificity of pathogenic autoantibodies in bullous pemphigoid patients has not yet been elucidated. In this study, by the use of a modified version of the cryosection model, we show that sera from all of 13 bullous pemphigoid patients and from two rabbits, immunized against bullous pemphigoid 180 NC16A, induced dermal-epidermal separation. This finding was confirmed with the use of IgG purified from patients' sera, whereas sera and purified IgG from healthy controls were not pathogenic. The induction of subepidermal splits in this experimental model was shown to be dependent on the presence of neutrophils, but not complement. Interestingly, patients' autoantibodies affinity purified against a recombinant form of bullous pemphigoid 180 NC16A retained their blister-inducing capacity, whereas patients' IgG depleted of reactivity to NC16A lost this ability. F(ab')2 fragments of antibodies specific to NC16A, lacking the Fc portion, did not induce splits. In addition, patients' autoantibodies purified against a recombinant fragment of the C-terminus of bullous pemphigoid 180 as well as rabbit antibodies to the intracellular portion of bullous pemphigoid 180 and to bullous pemphigoid 230 did not cause dermal-epidermal separation. Our in vitro results support the idea that autoantibodies to bullous pemphigoid 180 from patients with bullous pemphigoid are of pathogenic relevance.     

Serum levels of autoantibodies to BP180 correlate with disease activity in patients with bullous pemphigoid

OBJECTIVE: To investigate the possible correlation of levels of circulating anti-BP180 autoantibodies with disease activity in bullous pemphigoid (BP). DESIGN: Diagnostic study. SETTING: Regional referral center at a university dermatology department. PATIENTS: Fifteen patients with typical clinical, histologic, and immunofluorescence findings of BP who had not received prior systemic treatment. INTERVENTIONS: Initially, 6 consecutive patients with BP were treated with oral doxycycline and niacinamide. Subsequently, 9 consecutive patients with BP received a combination of oral dapsone and prednisolone. MAIN OUTCOME MEASURES: Disease activity, serum levels of autoantibodies to BP180, and titers of antibasement membrane zone autoantibodies were assayed before initiation of treatment and 4 and 8 weeks later. Reactivity to BP180 was analyzed by enzyme-linked immunosorbent assay using a recombinant form of BP180 NC16A. Titers of anti-basement membrane zone autoantibodies were assayed by indirect immunofluorescence on 1-mol/L sodium chloride-split human skin. RESULTS: In both treatment groups, disease activity correlated with serum levels of autoantibodies to BP180 NC16A (P = .004 [dapsone-prednisolone] and .007 [doxycycline-niacinamide]). No correlation was seen between disease activity and indirect immunofluorescence reactivity (P = .18 and .16, respectively). In patients receiving dapsone plus prednisolone, the dose of corticosteroids necessary to suppress new blister formation correlated with anti-BP180 reactivity (P = .002). CONCLUSIONS: In contrast to indirect immunofluorescence reactivity that reflects reactivity to both BP 180 and BP230, serum levels of autoantibodies to BP180 correlate with disease activity in BP. Assaying reactivity to BP180 should be a helpful guide for the therapeutic management of patients with this disease. Our results underline the pathogenic relevance of autoantibodies to human BP180.     

Autoantibodies to basement membrane proteins BP180 and BP230 are commonly detected in normal subjects by immunoblotting

Autoantibodies to basement membrane proteins BP180 and BP230 are characteristic of bullous pemphigoid and other subepidermal immunobullous disorders. These antibodies are, however, reported in other pruritic dermatoses, non-bullous disorders and non-cutaneous disease. Few studies have assessed basement membrane antibodies in normal subjects; antibody prevalence in this population is not clear. This study aims to examine basement membrane zone antibodies in normal middle-aged to elderly subjects. Sera from 61 healthy subjects (majority age 50–70 years) were assessed by immunoblot, indirect immunofluorescence and enzyme-linked immunosorbent assay. Ninety-one bullous pemphigoid patients acted as positive controls. Antigenic target, antibody class and titre were examined; sera binding BP180 were assessed for reactivity to the non-collagenous 16A (NC16A) domain. Thirty-six normal subjects (59%) had antibodies to either BP180 or BP230 on immunoblot analysis. BP180 was the commonest target antigen, detected in 35 subjects; binding to the immunodominant NC16A domain was not detected. Immunofluorescence was positive in three subjects. Of the bullous pemphigoid sera, 88% were positive on immunoblot or immunofluorescence; a higher frequency had antibodies against BP230. In conclusion, significant numbers of normal healthy subjects have circulating autoantibodies to basement membrane proteins, chiefly BP180 detectable by immunoblot, but these do not bind the NC16A domain.     

Role of BP180NC16a-enzyme-linked immunosorbent assay (ELISA) in the diagnosis of bullous pemphigoid in China

Background Autoantibodies of bullous pemphigoid (BP) patients react with two components of the hemidesmosome of stratified epithelia: the BP antigen 230 (BP230) and the BP antigen 180 (BP180). Recently, strong evidence has been provided that autoantibodies to BP180 play a key role in subepidermal blister formation in BP patients, and NC16A contains an important antigen determinant of BP. Objective To study the role of BP180NC16a enzyme‐linked immunosorbent assay (BP180NC16a‐ELISA) in the diagnosis of BP in China. Methods Sera from BP patients (n = 42) and control subjects (normal controls, n = 24; pemphigus patients, n = 18) were measured by BP180NC16a‐ELISA. All BP sera were obtained at presentation from patients who had not received previous systemic treatment. The values of immunoglobulin G (IgG) antibody levels measured by ELISA were compared with those measured by indirect immunofluorescence (IIF) (gold standard for the diagnosis of BP) on salt‐split skin. Results Using BP180NC16a‐ELISA, 41 of the 42 BP sera were positive, whereas only one of the serum samples from 24 normal controls was positive and all the pemphigus sera showed a negative result. Thus, the sensitivity and specificity of BP180NC16a‐ELISA were both 97.62%. There was no correlation between the mean ELISA values and IIF titers. The ELISA and IIF results were further compared and analyzed using a 2 × 2 contingency table, which showed that they were not significantly different. Conclusions It is suggested that BP180NC16a‐ELISA is a useful tool for the diagnosis of BP.     

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.     

Development of a novel ELISA system for detection of anti-BP180 IgG and characterization of autoantibody profile in bullous pemphigoid patients

BACKGROUND: The NC16A immunodominant region of the bullous pemphigoid (BP) antigen BP180 has been used to develop several enzyme-linked immunosorbent assays (ELISAs) as diagnostic tools for BP autoantibody detection. OBJECTIVES: Because BP180 autoantibody reactivity is not restricted to NC16A, we have investigated the possibility of developing an ELISA based on selected epitopes additional to this immunodominant region. METHODS: Initially 78 BP sera were tested using an NC16A ELISA and IgG reactivity was detected in 64 BP sera (82%). The 14 NC16A-negative BP sera were then analysed by immunological screening against seven BP180-specific epitopes. Recombinant phages displaying BP180 epitopes were grown as plaques, blotted onto a nitrocellulose filter and incubated with BP sera. RESULTS: Three and five NC16A-negative BP sera reacted with epitopes AA 1080-1107 and AA 1331-1404 of the BP180 ectodomain, respectively. Thus, a novel ELISA with GST-1080 and GST-1331 (GST-1080/1331) was developed: 32 of 78 BP sera (41%) proved positive by this assay. The combined use of ELISAs with GST-NC16A and GST-1080/1331 detected IgG reactivity in 72 of 78 BP sera, increasing the sensitivity from 82% to 92%. In addition, autoreactivity against the three extracellular epitopes appeared to be related to the presence of both skin and mucosal involvement as assessed by Fisher's exact probability test. CONCLUSIONS: Our findings further characterize the autoimmune response in BP by identifying a subgroup of NC16A-negative patients who react with different BP180 extracellular epitopes. The developed ELISA system appears more sensitive than the ELISA based on NC16A alone and also informative about the epitope profile of BP patients.     

The majority of bullous pemphigoid and herpes gestationis serum samples react with the NC16a domain of the 180-kDa bullous pemphigoid antigen

A series of previous studies have indicated that the NC16a domain of the 180-kDa bullous pemphigoid antigen (BP180) is the most immunogenic and probably pathogenic region in both bullous pemphigoid and herpes gestationis. To confirm these previous results by a large-scale study, we examined serum from 154 bullous pemphigoid and 43 herpes gestationis patients using an immunoblot technique with the BP180 NC16a domain fusion protein, which had been prepared using cDNA obtained from a human keratinocyte cDNA library by polymerase chain reaction amplification. This fusion protein was recognized by 90% of bullous pemphigoid and 79% of herpes gestationis serum samples, but not by any other disease or normal control serum samples. These results indicate that this system is very sensitive and specific for the detection of anti-BP180 antibodies and should be useful for the diagnosis of various subepidermal bullous diseases. Received: 17 October 1995     

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.