Diminished expression of the extracellular domain of bullous pemphigoid antigen 2 (BPAG2) in the epidermal basement membrane of patients with generalized atrophic benign epidermolysis bullosa

Abstract Generalized atrophic benign epidermolysis bullosa (GABEB) is a nonlethal form of junctional epidermolysis bullosa characterized by generalized skin and mucosal blisters that heal with atrophy; other features include alopecia, nail dystrophy, large melanocytic nevi, and autosomal recessive inheritance. The specific aim of this study was to identify an abnormality in epidermal basement membrane adhesion molecules in well characterized GABEB patients that would explain why these subjects' epidermis separates from their epidermal basement membrane. Cryostat sections of nonlesional skin from 8 GABEB patients in 5 different families as well as skin from normal volunteers (controls) were studied by indirect iminunofluorescence microscopy using rabbit antiserum directed against a BPAG1 fusion protein or monoclonal antibodies directed against the extracellular domain of BPAG2 (HD18 and 233), epiligrin (P1E1), laminin 5 (GB3), types IV and VII collagen, or integrin subunits α2, α3, β, α6, or β4. In these studies, monoclonal antibodies HD18 and 233 showed no reactivity and diminished reactivity, respectively, to the epidermal BM of all GABEB patients. Interestingly, in one patient, the absent or diminished reactivities of monoclonal anti-BPAG2 antibodies were limited to well demarcated portions of an otherwise intact epidermal basement membrane. Moreover, BPAG1, epiligrin, laminin 5, types IV and VII collagen, and all integrin subunits under study were expressed in the same manner in both GABEB and normal human skin. These findings identify an abnormality in the extracellular domain of BPAG2 in the skin of GABEB patients. BPAG2 (type XVII collagen) is a transmembrane, hemidesmo-some-associated molecule whose extracellular domain resides at the exact level where blisters develop in the skin of patients with GABEB. Impairment of this adhesion molecule may play a key role in the pathogenesis of this inherited subepidermal bullous disease.     

Compound heterozygosity for novel splice site mutations in the BPAG2/COL17A1 gene underlies generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa, GABEB (OMIM# 226650), is a nonlethal variant of epidermolysis bullosa with autosomal recessive inheritance pattern. The pathogenesis of this disorder can be caused by mutations affecting two different gene/protein systems. Most of the mutations have been identified in the BPAG2/COL17A1 gene encoding a hemidesmosomal transmembrane protein, the 180 kDa bullous pemphigoid antigen (BP180), also known as type XVII collagen. The minority of the mutations are localized in the LAMB3 gene encoding the beta3 polypeptide of laminin 5. In In this study we describe a GABEB patient who showed absent expression of BP180 in the cultured keratinocytes as well as in the skin. The patient was a compound heterozygote for two different splice site mutations, 3053-1G-->C and 3871+1G-->C, affecting the extra-cellular domain of the protein. These mutations resulted in multiple aberrant splice variants, three of them causing premature termination codons for translation. This case, dealing with out-of-frame splice site mutations in BPAG2/COL17A1, attests to the molecular heterogeneity of GABEB.     

A novel homozygous point mutation in the COL17A1 gene in a Chinese family with generalized atrophic benign epidermolysis bullosa

We describe a Chinese family with generalized atrophic benign epidermolysis bullosa (GABEB), a non-lethal variant of junctional epidermolysis bullosa. The proband was an offspring of consanguineous parents, had generalized blisters since birth and developed severe alopecia during early childhood. Ultrastructural examination of the proband's skin revealed fissures in the lamina lucida. Immunofluorescence assays using a monoclonal antibody recognizing the extracellular domain of the 180 kDa bullous pemphigoid antigen (BPAG2) showed loss of fluorescent signal in the basal membrane zone of the skin. DNA sequencing revealed a homozygous C-to-G transversion at nucleotide position 899 in exon 11 of the COL17A1 gene, which encodes BPAG2. This mutation results in serine to cysteine at position 265, which is located in a highly conserved region of the intracellular domain of BPAG2. We showed that the proband's father was heterozygous for this mutation. In addition, we found a novel polymorphic substitution of C-to-G at nucleotide position 798 in exon 10 of the COL17A1 gene, which results in an I233M change in BPAG2 and is a common polymorphic allele in a limited Chinese population.     

Internalization of the 180 kDa bullous pemphigoid antigen as immune complexes in basal keratinocytes: an important early event in blister formation in bullous pemphigoid

We have previously shown that the 180 kDa bullous pemphigoid antigen (BPAG2) is distributed on the lateral-apical (as a pool) and ventral (as hemidesmosomes) cell membranes of monolayer cultured keratinocytes and that addition of IgG purified from bullous pemphigoid (BP) patients (BP-IgG) causes the internalization of immune complexes of BPAG2 and BP-IgG from the lateral-apical cell membrane. This internalization of BPAG2 is believed to inhibit the Ca²⁺ induced reformation of hemidesmosomes on the ventral cell membrane, possibly by inhibiting the supply of the antigen from the lateral-apical to the ventral membranes to form hemidesmosomes. The purpose of this paper is to examine, by using biopsy specimens from BP patients (12 cases), whether or not this internalization of BPAG2 is generated in situ . The fates of BPAG2, 230 kDa BPA (BPAG1) and bound BP-IgG were traced by immunofluorescence microscopy using monoclonal antibodies to BPAG1, BPAG2 and human IgG. In more than half of the lesional and perilesional biopsy specimens, internalization of BPAG2 into the basal cells was observed, while in normal skin BPAG2 was detected on the whole surface of the basal cells without its internalization. No internalization of BPAG1 was detected in BP and normal epidermis. These results suggest that binding of BP-IgG on the lateral-apical cell surface of basal cells causes internalization of BPAG2 in situ in the epidermis of BP patients similar to that seen in cultured cell systems, and that this internalization of immune complexes of BPAG2 and BP-IgG may play an important part in blister formation in BP.     

Transient translocation of hemidesmosomal bullous pemphigoid antigen 1 from cytosol to membrane fractions by 12-O-tetradecanoylphorbol-13-acetate treatment and Ca2+-switch in a human carcinoma cell line

We previously showed that 12-O-tetradecanoylphorbol-13-acetate (TPA) and Ca2+-switch from low (0.07 mM) to normal (1.87 mM) concentration in culture medium, which were also linked to activation of protein kinase C (PKC), lead to phosphorylation of 180 kDa-bullous pemphigoid antigen (BPAG) 2, but not of 230 kDa-BPAG1, and possibly to its disassembly from hemidesmosomes in a human squamous cell carcinoma cell line (DJM-1). In this study, we examined the effects of TPA and Ca2+-switch on intracellular localization of BPAG1 by immuno-blotting and immuno-fluorescence microscopy with monoclonal antibodies to the antigen after sub-cellular fractionation. In DJM-1 cells cultured in low Ca2+ medium, BPAG1 was detected as phosphate buffered saline-soluble (cytosolic), Triton X-100 soluble (roughly membrane-associated) and Triton X-100 insoluble (cytoskeleton-bound) forms, whereas in normal Ca2+-grown cells only as cytosolic and cytoskeleton-bound forms. In normal Ca2+-cultured cells, TPA (50 nM) caused a complete translocation of BPAG1 from cytosol to membrane fractions within 10 min, that was inhibited by pretreatment with H7 (a selective PKC inhibitor) at 40 microM. After 30 min and 4 h of TPA-treatment, BPAG1 was exclusively detected in cytoskeleton fractions. Morphologically, immuno-fluorescence microscopy showed that treatment caused a marked reduction of BPAG1 from the cytoplasm and generated a linear pattern at cell-cell contacts, suggesting translocation of BPAG1 from the cytosol to the plasma membrane. In contrast, the Ca2+-switch from low to normal caused a prominent increase of BPAG1, both in cytosolic and membrane-associated forms after 4 h, that was inhibited both with H7 and cycloheximide (an inhibitor of protein synthesis) at 70 microM, suggesting a role for PKC and BPAG1 synthesis in these Ca2+-induced effects. These results suggest that TPA and Ca2+-switch induced BPAG1 translocation to membrane fractions possibly mediated by PKC-activation. Furthermore, whereas TPA affects the redistribution of BPAG1 among their pools without inducing their synthesis, Ca2+-switch induces both membrane translocation and synthesis of BPAG1, suggesting involvement of signaling other than PKC pathways in control of BPAG1 synthesis.     

Precise ultrastructural localization of in vivo deposited IgG antibodies in fresh perilesional skin of patients with bullous pemphigoid

Bullous pemphigoid (BP) is a blistering skin disease in which the patient develops autoantibodies to the epidermal basement membrane zone. Using postembedding immunogold electron microscopy, we previously demonstrated that autoantibodies against the 230-kDa BP antigen (BPAG1) bind to the intracellular hemidesmosomal component of normal skin, whereas those against the 180-kDa BP antigen (BPAG2) bind only along the plasma membrane of hemidesmosomes. The purpose of the present study was to elucidate the precise localization of the in vivo deposited IgG antibodies in fresh perilesional skin of patients with BP. Samples of fresh perilesional skin were obtained from three patients with BP whose sera reacted only with BPAG1, only with BPAG2, and with both BPAG1 and BPAG2 upon immunoblotting using epidermal extracts. Cryofixed and cryosubstituted skin samples were used as a substrate for on-surface immunolabelling. In all three cases, most of the gold particles were observed close to the plasma membrane of the basal keratinocytes. A quantitative analysis revealed that most (> 80%) of the in vivo deposited IgG antibodies in the three cases were localized within 10 nm inside to 50 nm outside of the cell membrane, with a single peak observed 0–10 nm outside of the cells (> 50%). This distribution corresponded to the location of BPAG2, but not to that of BPAG1. These findings suggest that most, if not all, of the in vivo deposited IgG antibodies in the perilesional skin of BP are directed against BPAG2, rather than against BPAG1, thus further supporting the crucial role of anti-BPAG2 autoantibody in the initial stage of blister formation in BP.     

大疱性类天疱疮抗原2在毛发周期不同阶段的表达情况

目的：研究大疱性类天疱疮抗原2(BPAG2)在毛发周期不同阶段的表达情况及其对毛发生长和毛发周期的影响。方法：间接免疫荧光、免疫组化、透射电镜和原位杂交。结果：BPAG2和其它基底膜相关分子如层粘连蛋白一样，在整个毛发周期中持续表达，不随毛发周期的不同阶段发生周期性变化。透射电镜研究发现在人头发毛囊的玻璃膜位置存在半桥粒结构。结论：BPAG2的持续表达说明它对于毛囊的作用主要是参与半桥粒的组成，维持结构稳定，而不是直接参与毛发周期的调节。     

先天性大疱性表皮松解症基底膜带分子的研究

目的：通过透射电镜和免疫荧光研究先天性大疱性表皮松解症患者的基底膜带分子。方法：分析7个组织病理表现为表皮下疱的先天性大疱性表皮松解症患者的透射电镜和免疫荧光表现。结果：电镜检查1例为基底膜透明板裂隙,即JEB,其余6例为基底膜下裂隙,即DEB,间接免疫荧光检查此例JEB是BPAG2缺陷。结合临床资料诊断为泛发型萎缩性良性大疱性表皮松解症（generalized atrophic benign EB,GABEB),这是我国首例报告;6例DEB患者透射电镜和免疫荧光检查辅助诊断DDEB和RDEB。结论：先天性大疱性表皮松解症是一组疾病,电镜和免疫荧光检查对于分型和明确诊断是必需的,间接免疫荧光检查还可以指导进一步的基因诊断。     

180-kDa bullous pemphigoid antigen defective generalized atrophic benign epidermolysis bullosa: report of four cases with an unusually mild phenotype

Generalized atrophic benign epidermolysis bullosa (GABEB) is a rare variant of non-lethal junctional epidermolysis bullosa characterized by generalized skin blistering healing with atrophy and by atrophic alopecia with onset in childhood. Other features include mild mucosal blistering, dental abnormalities and nail dystrophy. We report four additional cases of GABEB from two families originating from the same isolated village. The patients shared an unusually mild clinical phenotype with cutaneous blisters strictly limited to trauma sites and rare occurrence of oral mucosal lesions. Scalp, eyelash and eyebrow alopecia was present in only two cases. Immunofluorescence studies showed a markedly reduced expression of the 180-kDa bullous pemphigoid antigen (BP180), and northern analysis of cultured keratinocytes indicated that the gene encoding for BP180 is affected in these GABEB patients.     

Large melanocytic nevi in generalized atrophic benign epidermolysis bullosa (epidermolysis bullosa nevi)

Generalized atrophic benign epidermolysis bullosa (GABEB) is a nonlethal form of junctional epidermolysis bullosa. The expression of type XVII collagen (180 kDa bullous pemphigoid antigen) or of laminin 5 is markedly reduced in the skin. A 13-year-old patient with GABEB, developed several large, asymmetric, irregularly pigmented melanocytic nevi with poorly defined borders. They had appeared following blister formation since 8 years of age. Histological examination revealed an irregular proliferation of monomorphous melanocytes at the dermoepidermal junction. Small nests of melanocytes were focally present. This case further emphasizes the difficulty in differentiating nevi appearing in GABEB from malignant melanoma.     

Non-Herlitz junctional epidermolysis bullosa without hair involvement associated with BP180 deficiency

Junctional epidermolysis bullosa (JEB) is a clinically and genetically heterogeneous recessively inherited blistering disease of the skin and mucous membranes due to impaired epithelial adhesion. In particular, defective expression of the 180-kD bullous pemphigoid antigen (BP180) has been correlated to a non-lethal (non-Herlitz) form of JEB, generalized atrophic benign epidermolysis bullosa (GABEB), characterized by widespread skin blistering healing with atrophy and by atrophic alopecia with onset in childhood. We report the case of a 33-year-old man suffering from a generalized blistering skin disorder since birth. He also presented nail dystrophy and tooth abnormalities. Mucosal involvement was limited to gingival erosion. Alopecia was absent and body, axillary and pubic hair were normal. Immunofluorescence analysis showed a markedly reduced expression of BP180, electron microscopy studies evidenced hypoplastic hemidesmosomes and Northern blot analysis confirmed a striking decrease in the amount of BP180 mRNA. The clinical features of our patient confirm that BP180 deficiency usually results in a non-Herlitz JEB form. However, the degree of skin, mucous membranes and hair involvement appears more variable and less typical than originally described for GABEB.     

Successful prenatal exclusion of an unspecified subtype of severe epidermolysis bullosa

Background In most cases of prenatal diagnosis of epidermolysis bullosa (EB), the subtype of severe EB from which the fetus is at risk is identified by studying the specimens of the proband. In this study, the parents of a child with an unspecified subtype of severe EB sought prenatal diagnosis for their second and third pregnancies.
Methods The firstborn of a couple (the proband) suffered generalized blistering and erosions of the skin present from delivery, and died on the 11th postnatal day of severe EB of an unspecified type. The only diagnostic specimen available from the first infant was a conventionally stained skin section for light microscopy that showed the dermo–epidermal separation. For prenatal diagnosis in the second and third pregnancies, fetal skin biopsies were performed at 19 weeks of gestation.
Results In both cases, fetal skin showed no ultrastructural abnormalities and no evidence of dermo–epidermal separation. Indirect immunofluorescence was positive for monoclonal antibodies against type VII collagen, laminin 5, uncein, α6 and β4 integrins, BPAG2, and HD1/plectin, which are known to be reduced or absent in specific subsets of severe EB. The pregnancies were therefore continued, and normal healthy second and third children were delivered.
Conclusions Fetal skin biopsy, together with a panel of newly developed monoclonal antibodies, provided reliable prenatal diagnosis in the present family in which preliminary information of the EB proband was limited.     

泛发性萎缩性良性大疱性表皮松解症我国首例报道

目的 报道我国首例泛发性萎缩性良性大疱性表皮松解症家系。方法 对该家系先证者的临床资料、组织病理、透射电镜、间接免疫荧光检查进行分析。结果 该患者除了先天性大疱性表皮松解症的症状外,特征性表现是萎缩性秃发和牙齿发育不良。透射电镜检查裂隙位于基底膜透明板,同时伴半桥粒数目减少和发育不良。间接免疫荧光检查发现患者针对大疱性类天疱疮抗原2的荧光消失,说明本例发病与编码大疱性类天疱疮抗原2的基因COL17A1的缺陷有关。结论 此例为泛发性萎缩性良性大疱性表皮松解症,是交界性大疱性表皮松解症的一种特殊亚型。泛发性萎缩性良性大疱性表皮松解症有一定的临床特点,透射电镜和间接免疫荧光检查对于正确诊断和分型十分重要,并对进一步基因突变位点研究有指导作用。     

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

Abstract To develop a new method to evaluate autoantibodies in various autoimmune bullous skin diseases, we examined reactivity of bullous pemphigoid (BP) and pemphigus vulgaris (PV) patients' sera with partial bacterial fusion proteins of the 230 kD BP antigen (BPAG1) and PV antigen, respectively, by an enzyme-linked immunosorbent assay (ELISA), and compared the results with those of immunoblotting. We used two fusion proteins derived from the mouse BPAG1 and a fusion protein derived from the amino-terminus (EC 1-2) of PV antigen. For both BP and PV sera, the ELISA scores were well correlated with the reactivities on immunoblot assays. The present study indicates that ELISA using recombinant antigen proteins in various autoimmune bullous skin diseases will be a new useful technique to detect the autoantibodies. However, development of recombinant proteins with the entire molecule and correct conformation will be necessary to establish a perfect ELISA system in the future.     

One gene but different proteins and diseases: the complexity of dystonin and bullous pemphigoid antigen 1

Since the immunochemical identification of the bullous pemphigoid antigen 230 (BP230) as one of the major target autoantigens of bullous pemphigoid (BP) in 1981, our understanding of this protein has significantly increased. Cloning of its gene, development and characterization of animal models with engineered gene mutations or spontaneous mouse mutations have revealed an unexpected complexity of the gene encoding BP230. The latter, now called dystonin (DST), is composed of at least 100 exons and gives rise to three major isoforms, an epithelial, a neuronal and a muscular isoform, named BPAG1e (corresponding to the original BP230), BPAG1a and BPAG1b, respectively. The various BPAG1 isoforms play a key role in fundamental processes, such as cell adhesion, cytoskeleton organization, and cell migration. Genetic defects of BPAG1 isoforms are the culprits of epidermolysis bullosa and complex, devastating neurological diseases. In this review, we summarize recent advances of our knowledge about several BPAG1 isoforms, their role in various biological processes and in human diseases.     

Human bullous pemphigoid antigen 2 transgenic skin elicits specific IgG in wild-type mice

Bullous pemphigoid antigen 2 (BPAG2) is targeted by autoantibodies in patients with bullous pemphigoid (BP), and absent in patients with one type of epidermolysis bullosa (OMIM #226650). A keratin 14 promoter construct was used to produce transgenic (Tg) mice appropriately expressing human BPAG2 (hBPAG2) in murine epidermal basement membrane (BM). Grafts of Tg skin placed on gender-matched, syngeneic wild type (Wt) or major histocompatibility complex I (MHC I)-/- mice elicited IgG that bound human epidermal BM and BPAG2. Production of such IgG in grafted mice was prompt (detectable within 16+/-2 days), robust (titer > or = 1,280), durable (present > or = 380 days), and correlated with the involution and loss of Tg skin grafts. MHC II-/- mice grafted with Tg skin did not develop anti-hBPAG2 IgG or graft loss indicating that MHC II:CD4+ T cell interactions were crucial for these responses. Tg skin grafts on Wt mice developed neutrophil-rich infiltrates, dermal edema, subepidermal blisters, and deposits of immunoreactants in epidermal BM. This model shows fidelity to alterations seen in patients with BP, has relevance to immune responses that may arise in patients with epidermolysis bullosa following BPAG2 gene replacement, and can be used to identify interventions that may block production of IgG against proteins in epidermal BM.     

The presence of anti–basement membrane zone antibodies in the sera of patients with non–bullous lupus erythematosus

We performed indirect immunofluorescence (IF) studies using 1 mol/1 sodium chloride split skin to determine whether or not a positive IF is specific to patients with bullous lupus erythematosus (LE). We examined the sera from 21 patients with systemic LE (SLE), three of which were obtained from two SLE patients and one subacute cutaneous LE (SCLE) patient with bullous eruptions. As a comparison, we also studied the sera from patients with discoid LE (DLE,n= 7). SCLE (n= 1), systemic sclerosis (SSc, n= 20), bullous pemphigoid (n= 2) and normal individuals (n= 10). Sera from 16 SLE, four DLE and two SSc revealed a linear deposition of IgG isotype antibody at the epidermal side and/or the dermal side on indirect IF of split skin. The sera from three patients with bullous eruption and from 12 patients of SLE, SCLE, DLE without bullous eruption or SSc were further analysed by immunoblotting using five defined antigens, i.e, dermal extract, epidermal extract, three fusion proteins of 230 kDa bullous pemphigoid antigen (BPAG), 180 kDa BPAG, and human epidermolysis bullosa acquisita (EBA) antigen. Two SLE sera as well as one of the SCLE and the DLE serum reacted with 230 kDa BPAG in epidermal extract, and one of the SCLE and the DLE serum also reacted with the fusion protein of 180 kDa BPAG, No serum reacted with the dermal extract or the fusion protein of 230 kDa BPAG or EBA antigen. There was no consistent correlation between split–skin IF results and immunoblotting results. These results may suggest that even non–bullous LE patients often have autoantibodies to the basement membrane zone antigens, most of which are less pathogenic. Although we rarely examine the sera from non–bullous LE patients, we should keep this phenomenon in mind to avoid overestimating the results of split–skin test and immunoblotting.