Childhood bullous pemphigoid associated with IgA antibodies against BP180 or BP230 antigens

Linear IgA bullous dermatosis (LABD) comprises a heterogeneous group of subepidermal blistering disorders characterized by in situ bound IgA antibodies in epidermal basement membrane. We report three children presenting clinical and immunopathological features characteristic of LABD. By immunoblotting, the three patients' sera contained IgA antibodies that reacted against the bullous pemphigoid (BP) antigen 180 and or BP230, molecular markers for BP. In addition, IgG antibodies directed against the ectodomain of BP180 were detected by an enzyme-linked immunosorbent assay using a eukaryotic recombinant form of BP180. Consistent with recent studies suggesting that the LABD antigen 1, the predominant autoantigen of LABD, is either a proteolytic product of BP180 or an isoform of the BP180 gene, our findings indicate that a subset of children with features of LABD have a distinct form of BP associated with an IgA response.     

Mapping of epitopes on the BP180 ectodomain targeted by IgA and IgG autoantibodies in patients with the lamina lucida-type of linear IgA disease

Abstract Linear IgA disease (LAD) is an autoimmune subepidermal blistering skin disease characterized by the linear deposition of IgA at the dermoepidermal junction. Serum from patients with LAD most commonly contains autoantibodies that are directed against the hemidesmosomal transmembrane glycoprotein BP180 (type XVII collagen). Various antigenic sites on the extracellular domain of this anchoring filament protein have been shown to be targeted by autoantibodies in different autoimmune bullous skin diseases, including bullous pemphigoid and cicatricial pemphigoid (CP). However, little is known about epitopes on BP180 recognized by autoantibodies in LAD. In this study, we used three recombinant GST fusion proteins, together roughly covering the entire BP180 ectodomain, to characterize the autoimmune response in serum from patients with LAD. Interestingly, we found both IgA and IgG reactivity to all three portions of the BP180 ectodomain. The strongest reactivity was observed with the C-terminal portion of BP180. This is also the major region recognized by autoantibodies in patients with CP. This finding correlates with the observation that there may be significant overlap of the clinical and immunopathological findings in LAD and CP. Received: 21 August 2000 / Revised: 8 November 2000 / Accepted: 13 December 2000     

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.     

IgA autoantibodies in the pemphigoids and linear IgA bullous dermatosis

Please cite this paper as: IgA autoantibodies in the pemphigoids and linear IgA bullous dermatosis. Experimental Dermatology 2010; 19: 648–653. Background: Patients with bullous pemphigoid (BP), mucous membrane pemphigoid (MMP) and pemphigoid gestationis (PG) have IgG antibodies against BP180 and BP230, components of the hemidesmosomes. Patients with linear IgA bullous dermatosis (LABD) have IgA autoantibodies against a 97/120‐kDa protein which is highly homologous to a shedded fragment of the BP180‐ectodomain. Objectives: The aim of our study was to determine the incidence of IgA autoantibodies directed against BP180/BP230 in the pemphigoids and LABD and to determine the antigenic regions that are targeted by IgA autoantibodies. Methods: Utilizing baculovirus‐expressed recombinant BP180 and BP230 proteins, we performed immunoblot analyses for IgA reactivity of sera from patients with BP (n = 30), MMP (n = 10), PG (n = 6), LABD (n = 6) and from control patients with non‐related pruritic dermatoses (n = 8). Results: IgA reactivity against BP180 and/or BP230 was detected in 19/30 of the BP, in 7/10 of the MMP, in 6/6 of the LABD and in 3/6 of the PG sera, respectively, but not in the control group. In all subgroups, the major antigenic site recognized by IgA antibodies was located within the NH₂‐terminus of the BP180‐ectodomain, but only a minority of the sera showed also IgA reactivity against the BP180‐NC16a‐domain. IgA reactivity against the central domain of BP180 was more frequently seen than against its COOH‐terminus. IgA against the COOH‐ and NH₂‐terminus of BP230, respectively, was detected in 6/30 of the BP, 1/10 of the MMP, 1/6 of the LABD and 0/8 control sera. Conclusion: IgA reactivity against BP180 and/or BP230 is a common finding in the pemphigoids.     

IgG, IgA and IgE autoantibodies against the ectodomain of BP180 in patients with bullous and cicatricial pemphigoid and linear IgA bullous dermatosis

BACKGROUND: Bullous pemphigoid (BP), linear IgA bullous dermatosis (LABD) and cicatricial pemphigoid (CP) are clinically distinct autoimmune bullous skin diseases characterized by autoantibodies against components of the epidermal basement membrane. Like most patients with BP, a significant subgroup of patients with CP has circulating IgG specific for BP180, a transmembraneous protein of hemidesmosomes. Moreover, sera of patients with LABD contain IgA autoantibodies reactive with a 97/120-kDa protein, LABD antigen 1, which is highly homologous to the extracellular portion of BP180. OBJECTIVES: We aimed to determine whether, in these diseases, autoantibody reactivity to BP180 is restricted to distinct immunoglobulin subtypes. METHODS: Utilizing a baculovirus-encoded form of the ectodomain of BP180, sera from patients with BP (n = 10), CP (n = 9), LABD (n = 10) and normal human control sera (n = 10) were analysed by immunoblot for IgG, IgA and IgE reactivity against BP180. RESULTS: All of 10 BP sera displayed IgG, IgA and IgE reactivity with BP180. Six and seven of nine CP sera, respectively, contained IgG and IgA autoantibodies reactive with BP180, but none of nine sera contained BP180-specific IgE. Nine of 10 LABD sera contained IgA, and six of 10 IgG, which was reactive with BP180, but none of 10 sera showed IgE reactivity to BP180. CONCLUSIONS: The presence of IgG and IgA autoantibody responses to BP180 in patients with three clinically distinct autoimmune bullous diseases indicates that an autoimmune response to the same distinct adhesion protein may lead to different clinical manifestations. It is therefore conceivable that variable epitopes of BP180 are targeted by the different autoantibody isotypes, resulting in the distinct clinical pictures.     

Linear IgA disease: the IgA and IgG response to dermal antigens demonstrates a chiefly IgA response to LAD285 and a dermal 180-kDa protein

BACKGROUND: Linear IgA disease (LAD) of adults and children is mediated by IgA antibodies that target proteins of the epithelial adhesion complex. Most studies have concentrated on the epidermal-associated antigens; the dermal antigens remain unresolved. OBJECTIVES: To determine the dermal antigen repertoire of IgA and IgG antibodies in LAD. METHODS: Immunoblotting was carried out on salt-split and urea-extracted dermal skin extracts with IgA antibodies (63 adult and 34 childhood sera) and with IgG antibodies (49 adult and 18 childhood sera). RESULTS: Antigens were identified by IgA (61%), IgG (27%) and by both antibody isotypes (19%). LAD285 and an antigen of 180 kDa were the major dermal antigens identified, and antigens of 230 kDa, collagen VII and a protein under 100 kDa were identified less commonly. IgA autoantibodies from adults bound single antigens more frequently than multiple antigens; from children they bound single and multiple antigens equally. The binding of multiple antigens was, however, more common in children than adults. The IgG response was weaker. The 180-kDa antigen was the main IgG dermal target, and with a single exception, IgG autoantibodies targeted single antigens. CONCLUSIONS: There was an IgA and IgG response to dermal antigens in LAD; however, the dual antibody response was limited. The antibody response to LAD285 and a 180-kDa antigen (probably BP180) suggests that intermolecular epitope spreading of the antigens associated with the extracellular matrix/dermal components of the basement membrane contributes to the immunopathology of the disease. The restricted IgG response suggests that dermal-binding IgG autoantibodies are not pathologically significant.     

IgA basement membrane zone autoantibodies in bullous pemphigoid detect epidermal antigens of 270–280 kDa, 230 kDa, and 180 kDa molecular weight by immunoblotting

Bullous pemphigoid (BP) is an acquired subepidermal blistering disease characterized by circulating IgG autoantibodies binding to the 230 and 180 kDa hemidesmosomal proteins. Associated basement membrane zone (BMZ) autoantibodies of the IgA class have been reported in few BP patients. The incidence and clinical relevance of these IgA antibodies, as well as their target antigens are unknown. Sera of 26 patients with BP were analysed for circulating IgG- and IgA-anti-BMZ autoantibodies by indirect immunofluorescence on salt-split human skin. All of the patients had circulating IgG autoantibodies and, in addition, nine (35%) also had circulating anti-BMZ IgA antibodies, that bound to the epidermal side of salt-split skin. By immunoblotting, IgA antibodies in seven of nine sera recognized either the 180 kDa, the 230 kDa, or both BP antigens. Moreover, IgA anti-BMZ antibodies in seven sera also detected an epidermal protein of 270-280 kDa. IgA antibodies did not identify specific bands on immunoblots of dermal extracts. There was no clinical difference between BP patients with or without circulating anti-BMZ-IgA.     

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

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

The localization of the binding site of circulating IgA antibodies in linear IgA disease of adults, chronic bullous disease ofchildhood and childhood cicatricial pemphigoid

Biopsies from suction blisters raised in three normal volunteers were used as substrate in the indirect immunofluorescence technique to determine the binding site of circulating IgA antibodies in serum from three patients with adult linear IgA disease (LAD), nine with chronic bullous disease of childhood (CBDC), three with childhood cicatricial pemphigoid (CCP), and four with bullous pemphigoid (BP). Direct immunofluorescence was done using suction blisters raised in two patients with LAD and one with CCP. The circulating IgA antibodies in LAD and CBDC bound mainly to the roof of the blister but also to the base, and in CCP they bound only to the base of the blister. The circulating IgG antibodies in BP bound to the roof and base of the blister. These results demonstrate that the antigens in the various linear IgA dermatoses are heterogenous and are localized at different sites. The LAD and CBDC antigens are present in the lamina lucida, and the antigen in CCP is associated with the basal lamina.     

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.     

Lichen planus pemphigoides with circulating autoantibodies against 200 and 180 kDa epidermal antigens

We describe a case of lichen planus pemphigoides with circulating autoantibodies against 200 and 180 kDa epidermal antigens. A 24-year-old man presented pruritic erythematous patches with occasional central blister formation on the face, neck, and trunk and erythematous hyperkeratotic patches on the elbows and feet for 10 months. Histopathological findings of the neck and plantar lesions were consistent with lichen planus. Direct immunofluorescence studies from both lesions showed a linear deposition of IgG and C3 and cytoid bodies along the basement membrane zone. Indirect immunofluorescence studies demonstrated circulating IgG antibodies deposited on the epidermal side of salt-split skin. Immunoblot analysis using epidermal extract showed that the patient's serum reacted with 180 kDa bullous pemphigoid antigen (BPAG2) and a 200 kDa antigen. The cutaneous lesions almost cleared with a low dose of prednisolone and acitretin.     

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.     

Concomitant Occurrence of Circulating IgA Anti-intercellular and Anti-basement Membrane Zone Antibodies in Autoimmune Blistering Diseases: Immunofluorescence and Immunoblot Studies

Recently, cases with circulating IgA anti-intercellular antibodies have been described. The objective of this study was to present immunofluorescence and immunoblot findings in three cases of bullous diseases with concomitant circulating IgA anti-intercellular and anti-basement membrane zone antibodies. Direct immunofluorescence, indirect immunofluorescence on intact and 1M NaCl-split skin, immunoblotting of epidermal extracts from dispase- and EDTA-separated (two different procedures) human skin, and immunoblotting of the bovine desmosome preparation were performed. All three cases had IgA anti-intercellular and anti-basement membrane zone antibodies. However, immunoblot results were divergent. Case 1 had antibodies against the 150 kD pemphigus foliaceus antigen (IgG), the 170 kD protein (IgG and IgA), and the 97 kD antigen (IgG and IgA). Case 2 had IgG antibodies reactive with the 230 kD and the 170 kD bullous pemphigoid antigens, while case 3 had IgA antibodies against the 97 kD antigen only. The results of immunofluorescence and immunoblot studies in our patients widen the spectrum of laboratory features in blistering skin diseases mediated, at least in part, by antibodies of the IgA class.     

Characterization of the antibody response in oesophageal cicatricial pemphigoid

Cicatricial pemphigoid (CP) is a subepidermal, autoimmune bullous dermatosis. It is classified as a clinical subset of bullous pemphigoid (BP). However, it differs from BP in some significant ways: (i) in CP mucosal involvement with clinical scarring is prominent; (ii) there is a prominent IgA class antibody response alone or in addition to the IgG class antibody response; and (iii) there is a heterogeneous antibody response in CP, whereas in BP the majority of the antibodies are directed against a 180-kDa hemidesmosomal protein, bullous pemphigoid antigen 2 (BPAg2). Oesophageal involvement in CP is a rare, but often devastating manifestation. In this study we examined the humoral autoimmune response in oesophageal CP, in an attempt to characterize the autoantibody reactivity profile. We used direct and indirect immunofluorescence and Western immunoblotting using normal human skin and oesophagus substrates. We studied patient sera over time in order to search for evidence of epitope spreading in these patients. All patients had positive direct immunofluorescence of perilesional oesophageal epithelium. All patients had positive circulating antibasement membrane zone autoantibody titres. There was a significant IgA class in addition to an IgG class autoantibody response. IgA and IgG antibodies demonstrated significant reactivity with BPAg2 and the 97 kDa linear IgA disease antigen on Western immunoblot suggesting intraprotein epitope spreading. There was no evidence of interprotein epitope spreading over time. Our findings suggest that there is a heterogeneous antibody response in oesophageal CP with the predominant antigen being BPAg2.     

False-negative results in immunoblot assay of serum IgA antibodies reactive with the 180-kDa bullous pemphigoid antigen: the importance of primary incubation temperature

BACKGROUND: Different subepidermal autoimmune blistering skin disorders are characterized by linear deposition of IgA, sometimes accompanied by linear IgG, along the epidermal basement membrane zone. Identification of the targeted autoantigen is usually attempted by immunoblotting. Although immunoblotting works well for human IgG, the method is less successful for IgA and often no or only faint signals are obtained. OBJECTIVES: To improve the method of immunoblotting for diagnosis of IgA-mediated bullous dermatoses. METHODS: Eleven sera, selected from patients with linear deposition of IgA along the epidermal basement membrane zone in vivo, were tested by immunoblotting for antigen specificity using different primary incubation temperatures. RESULTS: No reliable information regarding IgA antigen specificity was obtained when the primary incubation was undertaken at room temperature. In 10 of 11 sera, IgA bound to the 180-kDa bullous pemphigoid antigen (BP180) when the primary incubation temperature was increased to 37 degrees C. CONCLUSIONS: Primary incubation at room temperature may result in false-negative results in the IgA-BP180 immunoblot assay.     

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.     

Vancomycin-induced linear IgA disease with autoantibodies to BP180 and LAD285

Linear IgA disease (LAD) is an acquired autoimmune subepidermal bullous disease characterized by the linear deposition of IgA at the basement membrane zone. A minority of cases are induced by drugs, of which the most frequently implicated is vancomycin. The target antigens in idiopathic LAD are heterogeneous, but have not previously been reported in vancomycin-induced LAD. We report three cases, and in two of these we investigated the target antigens. In both we identified IgA antibodies to LAD285 and IgA and IgG antibodies (dual response) to BP180.     

Drug-induced bullous pemphigoid with dermal fluorescence on salt-split skin

The immunological features of drug-induced bullous pemphigoid appear to be similar to those of idiopathic bullous pemphigoid (BP), with presence of circulating and tissue-bound antibodies showing anti-basement membrane zone specificity. We describe a 28-year-old woman who developed a widespread blistering eruption with marked involvement of the mucous membranes shortly after commencing treatment with oral flucloxacillin. The eruption gradually cleared following drug withdrawal and treatment with oral corticosteroids. Indirect immunofluorescence showed circulating IgG anti-basement membrane zone (BMZ) antibody and C3 which bound to the dermal aspect of salt-split skin, and direct immunofluorescence (IMF) of perilesional skin showed a linear band of C3 at the BMZ. Western immunoblotting of the patient's serum showed positive reactivity with a 180 kDa antigen in epidermal extracts and no reactivity with dermal extracts. The dermal-binding pattern on indirect IMF with salt-split skin only occurs in a minority of patients with BP and has not been described previously in a drug-induced case.     

Cicatricial pemphigoid with circulating autoantibodies to beta4 integrin, bullous pemphigoid 180 and bullous pemphigoid 230

Cicatricial pemphigoid is a heterogeneous group of autoimmune subepidermal blistering diseases associated most commonly with autoantibodies to bullous pemphigoid (BP)180 and less frequently with those to laminin 5 or type VII collagen. In addition, a few cases have been described with autoantibodies to the beta4 subunit of alpha6beta4 integrin. We describe a patient with extensive disease of ocular, oral, pharyngeal, laryngeal and genital mucous membranes that healed with scarring of conjunctivae. IgG autoantibodies bound to the dermal-epidermal junction on direct immunofluorescence (IF) microscopy and to the epidermal side of 1 mol L(-1) NaCl-split skin on indirect IF microscopy. Our patient's circulating IgG recognized a 205-kDa protein in extracts of 293T cells transfected with the beta4 subunit of alpha6beta4 integrin and in the cell extract of DJM-1 cells. Our patient's IgG and IgA autoantibodies also reacted with full-length BP180 derived from epidermal extracts and the ectodomain of BP180 (LAD-1) derived from culture supernatant of keratinocytes. In addition, a weak IgG reaction with BP230 was noted. The disease rapidly responded to dexamethasone-cyclophosphamide pulse therapy, and immunoblot reactivity to both beta4 integrin and BP180 decreased according to disease activity.     

Identification of the target antigen in chronic bullous disease of childhood and linear IgA disease of adults

Disease-associated autoantibodies to basement membrane proteins have been used to characterize structural components of the epidermal basement membrane such as bullous pemphigoid (BP) antigen and epidermolysis bullosa acquisita (EBA) antigen (type VII collagen). The autoimmune bullous diseases characterized by IgA autoantibodies to the basement membrane zone (BMZ), i.e. linear IgA disease of adults (LAD) and chronic bullous disease of childhood (CBDC) may have circulating antibodies. Previous studies of tissue distribution and ultrastructural binding have suggested that the LAD and CBDC antigens are similar, if not identical, and differ from the target antigens of the other bullous diseases. We present the molecular characterization of the LAD/CBDC antigens by Western blotting of a large series of antisera. Seven of 33 sera (21%) were positive on immunoblotting and bound to the same antigen which has a molecular weight (MW) of 285 kDa. Using both defined polyclonal antisera to BP and LH 7.2 monoclonal antibody to type VII collagen (carboxy terminal) we have shown that the LAD and CBDC antisera both bind to an identical molecular weight protein which clearly differs from both the BP and EBA (type VII collagen) antigens. Although detectable in dermal tissue extracts like EBA, the MW of 285 kDa is heavier than type VII collagen (250 kDa, in our system, using non-collagenous standards). This study confirms the identity of LAD and CBDC antigens to be the same and to differ from previously described basement membrane proteins.