Cicatricial pemphigoid differs from bullous pemphigoid and pemphigoid gestationis regarding the fine specificity of autoantibodies to the BP180 NC16A domain

Bullous pemphigoid (BP), pemphigoid (herpes) gestationis (PG), cicatricial pemphigoid (CP), and lichen planus pemphigoides (LPP) are autoimmune subepidermal bullous diseases that are characterized by circulating autoantibodies to the transmembrane hemidesmosomal protein BP180/type XVII collagen. Previous studies demonstrated that the majority of patients with BP, PG, and LPP show antibodies to an immunodominant, membrane-proximal non-collagenous domain (NC16A) on the extracellular portion of BP180. By the use of non-overlapping peptides of the NC16A domain, we previously demonstrated that autoantibodies from BP and PG patients mainly react with epitopes clustered within the N-terminus of this immunodominant site of BP180; antibodies from patients with LPP also recognized the C-terminal portion of NC16A. However, some of these results had been obtained indirectly by preadsorption studies. The aim of the present study was to analyze the fine specificity of IgG autoantibodies to NC16A in sera from patients with CP and to compare their reactivity with antibodies from BP, PG, and LPP patients using a series of new overlapping fragments covering the entire NC16A domain. We confirm that BP and PG sera mainly react with N-terminal epitopes of NC16A, whereas sera from patients with LPP also bind to C-terminal portions, of this domain. Interestingly, out of ten patients with CP, the sera of seven reacted with NC16A; within NC16A, these sera bound to both C-terminal fragments and an N-terminal epitope right next to the cell membrane. Our data demonstrate a heterogeneous binding pattern of autoantibodies to BP180 NC16A in patients with CP.     

IgG autoantibodies from a lichen planus pemphigoides patient recognize the NC16A domain of the bullous pemphigoid antigen 180

Lichen planus pemphigoides (LPP) most likely encompasses a heterogeneous group of subepidermal autoimmune blistering disorders occurring in association with lichen planus. We describe the case of a 49-year-old patient with features characteristic of LPP. Direct immunofluorescence microscopy studies demonstrated linear deposits of C3 along the cutaneous basement membrane, while circulating IgG autoantibodies directed against the epidermal side of skin separated by 1 M NaCl were detected. The patient's serum contained IgG autoantibodies immunoblotting a recombinant form of bullous pemphigoid antigen 180 (BP180), but not the COOH-terminus of BP230. By using deletion mutants, it was found that IgG reactivity was restricted to the NC16A domain of BP180, the region harboring the major antigenic sites targeted by IgG autoantibodies from patients with the bullous pemphigoid group of disorders. Our findings provide support to the idea that a subset of patients with LPP have a distinct form of bullous pemphigoid associated with lichen planus.     

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.     

Complementary peptides against the major epitope in the NC16A domain of BP180 show no specificity as vaccines to bullous pemphigoid.

A stretch of 14 amino acids (542-555) (MCW-1) in the NC16A domain of BP180 has been shown to be an immunogenic and pathogenic epitope for bullous pemphigoid (BP). Therefore, it provides an excellent target for treatment through a complementary peptide approach, which has been established in other autoimmune diseases, including experimental autoimmune myasthenia gravis. We examined two synthetic complementary peptides BP3CP5 and BP5CP3 against this region. These peptides were derived, respectively, by reading the antisense RNA of this region of BP180 in 3'-5' and 5'-3' directions. We found evident complementarities in hydropathic scores between MCW-1 and both complementary peptides. However, by enzyme-linked immunosorbent assay (ELISA), the complementary peptides BP3CP5 and BP5CP3 did not bind to either synthetic peptide BPNP or glutathione-S-transferase (GST) fusion proteins BP180NC16a and GST-BP-1050. BPNP, BP180NC16a and GST-BP-1050 cover the MCW-1 region of BP180 and were used as the natural peptides in this study. In addition, neither BP3CP5 nor BP5CP3 blocked the reaction between BPNP and anti-BPNP antibody, nor did they block immunofluorescent staining of the basement membrane zone by BP sera. Pre-incubation with BP3CP5 and BP5CP3 did not block the binding of BP sera to the BP18NC16a fusion protein in immunoblotting. Furthermore, rabbit antisera raised against BP3CP5 and BP5CP3 did not bind BP sera in ELISA. Pre-incubation with these rabbit antisera did not inhibit or reduce the binding of BP sera to the autoanltigen in either imnmunoblotting or immunofluorescence. Thus, we concluded that complementary peptides against this particular epitope in BP180 NC16A domain showed no specificity as vaccines to BP, although this approach should be tried for other epitopes in various autoimmune bullous diseases.     

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 intracellular and extracellular domains of BP180 antigen comprise novel epitopes targeted by pemphigoid gestationis autoantibodies

Pemphigoid gestationis (PG) is an autoimmune sub-epidermal bullous dermatosis of pregnancy associated with circulating autoantibodies targeting the extracellular non-collagenous (NC) 16A domain of bullous pemphigoid (BP) 180 antigen. In order to determine whether BP180 regions other than NC16A are recognized by PG autoantibodies, we have analyzed the reactivity of 15 PG patient sera against several BP180 antigenic sites by sensitive methods such as immunological screening and ELISA. Most PG sera tested (13 of 15) reacted with an epitope (amino acid 508-541) mapped in the NC16A domain. Of note, nine of 15 PG patient sera reacted with at least one additional antigenic site other than NC16A. Specifically, two epitopes in the BP180 extracellular domain and five epitopes in the intracellular one were recognized by three and seven PG sera, respectively. In addition, a representative intracellular epitope was recognized by PG autoantibodies as a portion of BP180 antigen both in denaturating and native conditions. Finally, reactivity against epitopes additional to NC16A was also detected at an early stage of the disease. The identification and characterization of hitherto unrecognized epitopes targeted by PG patient autoantibodies provide novel insights into the pathophysiology of humoral immune response to BP180 in PG.     

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.     

Coexisting lichen planus and bullous pemphigoid or lichen planus pemphigoides?

A patient with lichen planus pemphigoides is reported. Initial pathologic and immunopathologic evaluation was consistent with coexisting bullous pemphigoid and lichen planus. However, further immunologic evaluation suggested that the circulating antibody was not directed toward bullous pemphigoid antigen but another basement membrane zone antigen. This finding indicates a need for immunologic re-evaluation of lichen planus pemphigoides.     

Bullous pemphigoid of childhood: autoantibodies target the same epitopes within the NC16A domain of BP180 as autoantibodies in bullous pemphigoid of adulthood

BACKGROUND: Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease of the elderly that rarely occurs in children. Most adult BP serum samples react with epitopes within the NC16A domain of BP180, a glycoprotein of the cutaneous basement membrane zone. OBJECTIVES: To characterize the autoimmune response in childhood BP using recombinant forms of BP180 and to determine the subclass distribution of autoantibodies and their correlation with disease activity. OBSERVATIONS: Serum samples from 2 infants with BP, aged 4 and 5 months, reacted by immunoblot analysis with 4 epitopes clustered within the N-terminal 45 amino acids of the NC16A domain. The same 4 epitopes have previously been shown to be the target in adult BP. Childhood BP antibodies to BP180 NC16A belonged to IgG1, IgG2, IgG3, and IgG4 immunoglobulin subclasses. IgE reactivity was not detected. Serum levels of antibodies targeting BP180 NC16A paralleled disease activity as detected by enzyme-linked immunosorbent assay. CONCLUSIONS: The fine specificity of autoantibodies to BP180 is the same in BP of childhood and adulthood. Childhood BP is a true variant of BP.     

Therapie des Lichen planus pemphigoides durch Acitretin und pulsweise verabreichtes Kortikosteroid

A patient with lichen planus pemphigoides first developed multiple pruritic papules and subsequently, tense blisters on trunk and extremities. Histopathologic examination of a skin biopsy demonstrated both the typical changes of lichen planus and subepidermal blisters as in bullous pemphigoid. Direct immunofluorescence microscopy revealed both cytoid bodies and linear C3 deposits at the dermal-epidermal junction. By indirect immunofluorescence microscopy on 1 M NaCl-split-skin, circulating autoantibodies labeled the epidermal side of the split. Immunoblot analysis showed binding of the antibodies to the cell-derived soluble 120 kD domain of the 180 kD bullous pemphigoid antigen and to a recombinant form of the immunodominant NC16A region of this protein. When treated with pulsed intravenous corticosteroids, the patient continued to develop new papules and blisters, but when oral acitretin was added, the skin lesions cleared. The immunoblot reactivity of the patient's autoantibodies well reflected disease activity, while the indirect immunofluorescence microscopy titers did not.     

BP180/type XVII collagen: its role in acquired and inherited disorders or the dermal-epidermal junction

Abstract BP180 is a member of the collagen protein family and is also referred to as type XVII collagen or BP antigen 2. It is a transmembrane protein constituent of the dermal-epidermal anchoring complex. The long-held hypothesis that BP180 functions as a cell-matrix adhesion molecule has been supported by recent investigations of human disorders of the dermal-epidermal junction in which BP180 is either genetically defective or targeted by the immune system. In generalized atrophic benign epidermolysis bullosa, mutations of BP180 result in an inherited subepidermal blistering disease. In bullous pemphigoid, herpes/ pemphigoid gestationis, cicatricial pemphigoid, lichen planus pemphigoides and linear IgA disease, autoantibodies are directed to different epitopes on the BP180 ectodomain. Recent molecular investigations have provided new insights, not only into the mechanism of autoantibody-mediated subepidermal blistering, but also into the biochemical structure and cell biological functions of BP180 and other components of the dermal-epidermal anchoring complex. These findings have suggested new directions for the development of diagnostic and therapeutic tools for these autoimmune and genetic diseases. Received: 4 September 1998 / Accepted: 27 October 1998     

Cicatricial pemphigoid: IgA and IgG autoantibodies target epitopes on both intra- and extracellular domains of bullous pemphigoid antigen 180

BACKGROUND: Cicatricial pemphigoid (CP) is an autoimmune subepidermal blistering disease where autoantibodies target various components of the dermal-epidermal junction, including the bullous pemphigoid antigen 180 (BP180). OBJECTIVE: We determined the exact specificity of circulating IgG and IgA autoantibodies to BP180 in a large number of CP patients. METHODS: Twenty-six consecutive CP sera were analysed by Western blotting using a panel of cell-derived and recombinant proteins covering the entire BP180 molecule. RESULTS: Circulating autoantibodies were detected in all CP sera. Seven sera reacting with laminin-5 were excluded from further analyses; the remaining 19 sera recognized BP180, including six sera (32%) that showed only IgA reactivity to this protein. With the combined use of the soluble BP180 ectodomain (LAD-1) and recombinant BP180 NC16A, 16 of these 19 CP sera (84%) targeted BP180. IgG reactivity was preferentially found against NC16A, whereas IgA antibodies predominantly recognized LAD-1. Thirty-two per cent of the BP180-reative sera revealed reactivity with the intracellular domain of this protein. CONCLUSIONS: Our findings demonstrate that autoantibodies in CP target epitopes on both extra- and intracellular domains of BP180 and highlight the importance of testing for both IgG and IgA reactivity in these patients' sera.     

Lichen planus pemphigoides: its relationship to bullous pemphigoid

Clinical and immunopathological studies of three patients with lichen planus pemphigoides (LPP) were carried out to investigate the relationship between LPP and bullous pemphigoid (BP) and to determine whether the antigen in LPP is the classical BP antigen. LPP is usually considered to be the coexistence of lichen planus with BP. The bullae in LPP were subepidermal and indistinguishable from BP. Indirect immunofluorescence demonstrated antibody binding to the epidermal surface of 1 M NaCl-split skin and mucosae, as in BP. The tissue distribution of the LPP antigen mirrored the distribution of BP in stratified squamous epithelia but was absent from transitional epithelia (pig bladder). Immunoelectron microscopy, both direct (two cases) and indirect (one case), showed binding to the lamina lucida as with BP antigen. Western blotting of epidermal extracts using the patients' sera showed that instead of reacting with the classical bullous pemphigoid antigen (220 kDa in our series), the antisera reacted with a unique band of 200 kDa in addition to the band of 180 kDa found as a minor antigen in bullous pemphigoid, but more commonly in pemphigoid gestationis. The relationship between these antigens awaits molecular characterization. These findings suggest that the target antigen in LPP may be unique.     

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.     

Immunoreactivity of bullous pemphigoid (BP) autoantibodies against the NC16A and C-terminal domains of the 180 kDa BP antigen (BP180): immunoblot analysis and enzyme-linked immunosorbent assay using BP180 recombinant proteins

The 180 kDa bullous pemphigoid (BP) antigen (BP180) is known to be recognized by sera from patients with BP, herpes gestationis (HG) and cicatricial pemphigoid (CP). A series of previous studies using BP180 recombinant proteins has shown that most sera from patients with BP and HG react with the NC16A domain of BP180, an extracellular non-collagenous region just adjacent to the plasma membrane. In contrast, the C-terminal region of BP180 has been reported to be one of the epitopes of CP. In the present study, we examined the immunoreactivity of 110 BP sera against the NC16A and C-terminal domains of BP180 using immunoblot analysis and enzyme-linked immunosorbent assay (ELISA). Immunoblot analysis revealed that 100 (91%) and 26 (23.5%) of the 110 BP sera recognized the NC16A and C-terminal domains, respectively. The results of the ELISA were correlated with those of immunoblotting. There were no specific or significant clinical features such as severe involvement of mucous membranes and scarring in BP patients whose sera reacted with the C-terminal region. These findings suggest that some BP sera react with the C-terminal region of BP180 without any association with the characteristic clinical features of CP.     

Vesicular pemphigoid in a 16-year-old boy

We describe a case of a 16-year-old African-American boy with bullous pemphigoid (BP), an acquired autoimmune blistering disease that is rarely seen in children. The patient's lesions, however, were distinctly herpetiform, complicating initial diagnosis and therapy. A diagnosis of BP was made by direct and indirect immunofluorescence. Immunoblotting and enzyme-linked immunosorbent assay analysis confirmed the presence of autoantibodies directed against the BP180 antigen. The autoantibodies reacted with the same epitopes within the immunodominant BP180 NC16A domain that have previously been shown to be the target of autoantibodies in BP. This case describes an uncommon disease in the pediatric population and should be included in the differential diagnosis in young patients with an unusual generalized vesicular eruption.     

Epitopes targeted by bullous pemphigoid T lymphocytes and autoantibodies map to the same sites on the bullous pemphigoid 180 ectodomain

Bullous pemphigoid is a blistering skin disease characterized by autoantibodies directed against the NC16A domain of bullous pemphigoid 180 (collagen XVII), a transmembrane protein of epidermal basal cells. Passive transfer studies in mice have shown that antibodies that bind to this immunodominant region of bullous pemphigoid 180 are capable of inducing a skin disease that closely mimics bullous pemphigoid, supporting the hypothesis that epitopes within NC16A are involved in the pathogenesis of bullous pemphigoid. In this study, we examined the autoimmune T cell response in bullous pemphigoid patients. T cells from eight of 12 bullous pemphigoid patients, all of whom had circulating anti-bullous pemphigoid 180 autoantibodies, showed a specific proliferative response to recombinant forms of NC16A. T cell lines and clones developed from four of these patients recognize the same NC16A peptides as those targeted by autoantibodies from the corresponding individuals. These NC16A-responding T lymphocytes express alpha/beta T cell receptors and CD4 memory T cell surface markers and exhibited a Th1/Th2 mixed cytokine profile that may support the production of antibodies. This new information will aid in defining the key steps involved in the development of the autoimmune response in bullous pemphigoid.     

Lichen planus pemphigoides: case report and results of immunofluorescence and immunoelectron microscopic study

A Japanese woman with lichen planus pemphigoides is reported. Immunologic characteristics of lichen planus pemphigoides antigen in the patient were investigated by indirect immunofluorescence and compared with those of bullous pemphigoid antigen or epidermolysis bullosa acquisita antigen. Ultrastructural localization of lichen planus pemphigoides antigen was studied with the use of immunoelectron microscopic techniques. Lichen planus pemphigoides antigen showed localization similar to that of bullous pemphigoid antigen but different from that of epidermolysis bullosa acquisita antigen. The antigenic stability of lichen planus pemphigoides antigen was different from that of bullous pemphigoid antigen or epidermolysis bullosa acquisita antigen. Thus this study demonstrates that lichen planus pemphigoides antigen is different from bullous pemphigoid antigen.     

Case of subepidermal autoimmune bullous disease with psoriasis vulgaris reacting to both BP180 C‐terminal domain and laminin gamma‐1

A number of cases of psoriasis vulgaris developing bullous skin lesions have been diagnosed as either bullous pemphigoid with antibodies to the 180‐kDa bullous pemphigoid antigen (BP180) non‐collagenous 16a (NC16a) domain or anti‐laminin‐γ1 (p200) pemphigoid. We report a case of subepidermal bullous disease with psoriasis vulgaris, showing antibodies to both BP180 C‐terminal domain and laminin‐γ1. A 64‐year‐old Japanese man with psoriasis vulgaris developed exudative erythemas and tense bullae on the whole body but he did not have mucosal involvement. The blistering lesion showed subepidermal blisters histopathologically. In indirect immunofluorescence of 1 mol/L NaCl‐split skin, immunoglobulin (Ig)G antibodies reacted with both the epidermal and dermal side. Immunoblotting showed positive IgG with recombinant protein of BP180 C‐terminal domain and 200‐kDa laminin‐γ1 in normal human dermal extract.     

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.