Bullous eruption associated with scabies: evidence for scabetic induction of true bullous pemphigoid

Some patients with scabies develop bullae concomitantly with, or subsequently after, the occurrence of scabetic lesions. Although several immunofluorescence studies have demonstrated immunoglobulin deposition in the basement membrane zone of bullous lesions, it remained unclear whether these antibodies are directed to bullous pemphigoid antigens. We clearly show that two scabetic patients with bullous eruptions had circulating antibodies against BP180 and/or BP230 as determined by Western blotting analysis. This is the first report to demonstrate that at least some of the bullous eruptions occurring in scabetics are true bullous pemphigoid.

An induction gene trap for identifying a homeoprotein-regulated locus

An important issue in developmental biology is the identification of homeoprotein target genes. We have developed a strategy based on the internalization and nuclear addressing of exogenous homeodomains, using an engrailed homeodomain (EnHD) to screen an embryonic stem (ES) cell gene trap library. Eight integrated gene trap loci responded to EnHD. One is within the bullous pemphigoid antigen 1 (BPAG1) locus, in a region that interrupts two neural isoforms. By combining in vivo electroporation with organotypic cultures, we show that an already identified BPAG1 enhancer/promoter is differentially regulated by homeoproteins Hoxc-8 and Engrailed in the embryonic spinal cord and mesencephalon. This strategy can therefore be used for identifying and mutating homeoprotein targets. Because homeodomain third helices can internalize proteins, peptides, phosphopeptides, and antisense oligonucleotides, this strategy should be applicable to other intracellular targets for characterizing genetic networks involved in a large number of physiopathological states.

Autoantibodies against the processed ectodomain of collagen XVII (BPAG2, BP180) define a canine homologue of linear IgA disease of humans

Linear IgA disease (LAD) is an acquired autoimmune subepidermal blistering dermatosis that affects human children and adults. In contrast to bullous pemphigoid, in which autoantibodies recognize transmembrane type XVII collagen (BP180, BPAG2), LAD is associated with skin-fixed and circulating IgA autoantibodies that target LAD-1, the processed extracellular form of type XVII collagen. An immunologic homologue of LAD in humans was identified in two dogs according to the following criteria: 1) erosive, ulcerative, and crusted lesions seen on the face, in the oral cavity, and on the extremities, 2) dermoepidermal clefting present in the basement membrane lamina lucida without inflammation or with mild neutrophilic infiltration, 3) basement membrane-fixed IgG and/or IgA antibodies, and 4) circulating IgA and IgG autoantibodies that target the 120-kd soluble protein LAD-1. The present study establishes unequivocally the existence of a naturally occurring canine model of LAD of humans.

A disease-associated glycine substitution in BP180 (type XVII collagen) leads to a local destabilization of the major collagen triple helix

BP180 is a homotrimeric transmembrane protein with a carboxy-terminal ectodomain that forms an interrupted collagen triple helix. Null type mutations in the BP180 gene produce a recessive subepidermal blistering disease, non-Herlitz junctional epidermolysis bullosa. Like the null mutations, a glycine substitution (G627V) within the longest BP180 collagenous domain (COL15) is also associated with the recessive skin disease; however, unlike the null mutations, this glycine substitution appears to act in a dominant fashion to give rise to a novel form of random pitting dental enamel hypoplasia. The dominant effects of this mutation were thought to be due to alterations in the assembly and/or stability of this BP180 collagenous region. To further investigate this issue, a structural analysis was performed on recombinant forms of the wild type and G627V mutant BP180 ectodomain. Both proteins were found to form collagen-like triple helices with very similar Stokes radii and melting temperatures and exhibited very similar rates of synthesis, secretion and turn-over. Tryptic digestion analysis revealed that the mutant G627V-sec180e contains an additional highly sensitive proteolytic site that maps within the region of the mutation. Thus, the disease-associated G627V mutation in BP180 does not grossly alter protein structure, but causes a local destabilization of the triple-helix that exposes sensitive residues to the in vitro effects of trypsin and possibly affects its structure-function in vivo.

Prenatal onset of axonopathy in Dystonia musculorum mice

Dystonia musculorum (dt) is a recessive hereditary neuropathy of the mouse. Affected animals display loss of limb coordination and twisting of the trunk. Sensory nerve fibers of these mice are severely reduced in number, and the remaining fibers present numerous axonal swellings. The gene defective in dt, dystonin (Dst), encodes a cytoskeletal linker protein that forms the bridge between F-actin and intermediate filaments. Dst is expressed during embryogenesis, whereas overt phenotype in dt mice only appears during the second week after birth. Here we show that axonal swellings are present in sensory nerve fibers of dt embryos as early as E15.5, before myelination and radial axonal growth have begun. Thus disease progression is gradual in dt mice, having begun during embryogenesis. In dt embryos, microtubule network disorganization and cytoplasmic organelle accumulation within axonal swellings were consistently observed. In addition, a few of the axonal swellings presented intermediate filament accumulation. These results demonstrate that dystonin is required for cytoskeleton organization during axonogenesis. They also suggest that axonal transport defects, through microtubule network perturbation, may be the primary mechanism of neurodegeneration in dt mice.

Epithelialization of a synthetic polymer in the feline cornea: a preliminary study

PURPOSE

This study examined the potential of a synthetic polymer to support stable epithelial growth when implanted in the feline cornea.

METHODS

A perfluoropolyether-based polymer was cast into lenticules that were coated with collagen I and implanted in four feline corneas. Epithelial growth onto the lenticules was monitored clinically for 6 weeks, after which time the animals were killed, and three corneas were evaluated histologically. Immunohistochemistry was used to identify proteins associated with the formation of a basement membrane (laminin) and adhesion complexes (bullous pemphigoid antigen and collagen VII). Electron microscopy was used to examine the tissue-polymer interface for evidence of the assembly of these adhesive structures.

RESULTS

Postoperative epithelial growth began on days 2 to 3, and lenticules were fully epithelialized by days 5 to 9. Lenticules were clinically well tolerated and histology showed epithelium consisting of multiple layers adherent to the lenticule's surface. Laminin, bullous pemphigoid antigen and collagen VII were identified at the tissue-polymer interface using immunohistochemistry. Ultrastructural examination showed evidence of assembly of these proteins into a recognizable basement membrane and hemidesmosomal plaques.

CONCLUSIONS

A perfluoropolyether-based polymer coated with collagen I was implanted in the feline cornea and supported epithelial growth that showed signs of persistent adhesion, both clinically and histologically. This polymer shows potential for ophthalmic applications that require sustained epithelialization.

Tyrosine phosphorylation: a critical component in the formation of hemidesmosomes

Our goal was to evaluate the role of tyrosine phosphorylation in the complete formation of hemidesmosomes that occurs during development or during remodeling after injury. A corneal organ culture system was used to study hemidesmosome formation as it would occur in an intact tissue. Phosphorylation of the integrin subunit beta 4 and bullous pemphigoid antigen-1 (BPAG-1) was examined, as these proteins are known to play a role in linking the electron-dense plaques along the basal surface with the intermediate filaments to complete the formation of hemidesmosomes. Corneal epithelial sheets were placed on substrata that contained an intact basal lamina or basal laminae that had been either modified or removed. These constructs were incubated for up to 18 h, and hemidesmosome formation was evaluated by using transmission electron microscopy. When epithelial sheets were placed on intact basal laminae and incubated in the presence of the tyrosine kinase inhibitor genistein (200 microM), hemidesmosome formation was impaired. The formation of electron-dense regions was delayed, and no association of intermediate filaments was detected. Results were confirmed by biochemical studies. When the epithelium and underlying proteins were extracted and immunoprecipitated with beta 4 or BPAG-1, tyrosine phosphorylation decreased in the presence of genistein. In addition, the phosphorylation of beta 4 decreased when epithelial sheets were incubated on substrata from which the basal lamina had been removed or altered. Thus, a reduction in phosphorylation of tyrosine residues impairs the formation of mature hemidesmosomes, and substrata that fail to support hemidesmosome formation also demonstrate decreased phosphorylation of tyrosine residues.

Rat bladder epithelium: a sensitive substrate for indirect immunofluorescence of bullous pemphigoid

Serological diagnosis of bullous pemphigoid is based on immunoblotting or indirect immunofluorescence on normal human salt-split skin. These methods are expensive or time-consuming and not available as a routine test in all laboratories. We used rat bladder epithelium as substrate for indirect immunofluorescence and compared it with other substrates and with immunoblotting. Twenty-nine bullous pemphigoid sera were studied on rat bladder epithelium, monkey oesophagus, salt-split skin and with immunoblotting on human keratinocyte cultures. Indirect immunofluorescence on rat bladder epithelium proved to be more sensitive (72%) than on monkey oesophagus alone (45%) and less sensitive than on salt-split skin (97%). Rat bladder epithelium, when tested on 41 sera of a control group, showed a very high specificity: 2/41 (95%). In combination with immunoblotting on keratinocyte extracts, indirect immunofluorescence on rat bladder epithelium allowed 93% of sera to be recognized, a value close to the salt-split skin alone. Rat bladder epithelium appears to be a more sensitive substrate than monkey oesophagus for the diagnosis of bullous pemphigoid and, although less specific, it is easier and faster than using salt-split skin, which remains indispensable to distinguish bullous pemphigoid from epidermolysis bullosa acquisita.

IgG autoantibodies from bullous pemphigoid patients recognize multiple antigenic reactive sites located predominantly within the B and C subdomains of the COOH-terminus of BP230

Bullous pemphigoid is a subepidermal bullous disorder characterized by an autoantibody response against the bullous pemphigoid antigen 230 (BP230) and the bullous pemphigoid antigen 180 (BP180), a cytoplasmic component and a transmembrane component, respectively, of hemidesmosomes. Although immunodominant sequences within the extracellular domain of BP180 have been identified, characterization of the antigenic sites on BP230 is still incomplete. To identify autoantibody-reactive sites on BP230 and to examine whether the targeted regions are contained within functionally important domains, recombinant fragments encompassing almost the entire BP230 were used to assess the reactivity of 25 bullous pemphigoid sera by immunoblotting. Our results demonstrate that (i) the region bearing the B and C subdomains of the COOH-terminus of BP230 contains immunodominant sequences recognized by the majority of bullous pemphigoid sera; (ii) additional autoantibody- reactive sites are present over extended regions of the NH2-terminal half of BP230 without evidence for antigenic cross-reactivity between the NH2- and COOH-termini of BP230; and, finally, (iii) autoantibodies reacting with the BP230 tail predominantly belong to the IgG4 and IgG1 subclasses, suggesting that both autoreactive TH2 and autoreactive TH1 cells regulate the autoantibody response to immunodominant sequences of BP230. As the COOH- terminus of BP230 mediates the attachment of keratin intermediate filaments to the hemidesmosomal plaque, whereas its NH2-terminus contains sequences important for its interaction with other constituents of hemidesmosomes, autoantibodies to BP230 might precipitate subepidermal blister formation and perpetuate the disease not only by eliciting an inflammatory reaction but also by interfering with the function of BP230 and thus the stability of hemidesmosomes.

Development of a system for detection of circulating antibodies against hemidesmosomal proteins in patients with bullous pemphigoid

Specific antibodies directed against special hemidesmosomal proteins are involved in the pathogenesis of bullous pemphigoid (BP), and detection of these antibodies is crucial for a correct diagnosis. As the BP autoantigen primary structures are known, the question was addressed as to whether it is possible to demonstrate circulating antibodies against BP autoantigens (BPAG1 and BPAG2) by means of an ELISA system, using antigenic epitopes. With the help of the programs Peptidestructure and Plotstructure, antigenic epitopes of BP antigens were predicted, chemically synthesized and screened using serum from 43 proven BP patients. The coding sequences of the best antigenic epitopes were then chemically synthesized and inserted as monomer and homo- or hetero-oligomer forms into fusion-expression plasmids (PGEX-4T, Pharmacia) in-frame to the C-terminus of glutathione-S-transferase. Fusion products were expressed and purified from Escherichia coli cells by affinity chromatography. The recombinant proteins were used for the detection of antibodies in the serum of 43 BP patients and of 60 controls (including 30 healthy persons, 22 patients with pemphigus vulgaris and 8 patients with other bullous dermatoses). Use of the homo- and hetero-oligomers of the recombinant fusion peptides increased the sensitivity of the disease-specific antibody detection. When a mixture of the best recombinant fusion proteins was used, the sensitivity of the ELISA assays in the case of the BP patients' serum was 0.90. This system could form the basis of a rapid and simple system for the diagnosis of BP.

Re-epithelialization rate and protein expression in the suction-induced wound model: comparison between intact blisters, open wounds and calcipotriol-pretreated open wounds

We have investigated re-epithelialization following induction of suction blisters in humans in intact blisters, open wounds, i.e. blister roofs removed immediately after blister induction, and calcipotriol-pretreated open wounds. Intact blisters simulate blister healing in bullous disease, while open wounds simulate re-epithelialization during wound healing. Re-epithelialization was clearly faster in open wounds than in intact blisters, and was not affected by calcipotriol pretreatment. Bullous pemphigoid antigen 2 (BP180), bullous pemphigoid antigen 1 (BP230), plectin/hemidesmosomal 1 protein (HD1), laminin 5, laminin alpha5, laminin beta1, type VII collagen, tenascin-C, beta4, alphavbeta5, alpha5 and alpha9 integrins were studied in intact blisters and open wounds by immunohistochemistry. Hemidesmosomal plaque proteins BP230 and plectin/HD1, which connect the keratin cytoskeleton to the hemidesmosome, appeared earlier at the leading edge in intact blisters than in open wounds. Band-like immunostaining in the basement membrane for laminin 5, alpha5 and beta1 chains was continuous in blister bases, but partially discontinuous in open wound bases. The other antigens studied showed similar expression in intact blisters and open wounds. BP180, BP230, plectin/HD1, beta4 integrin, laminin 5 and tenascin-C expression were further studied in calcipotriol-pretreated open wounds. Calcipotriol did not affect the expression of these antigens. The immunohistochemical results suggest that the keratin cytoskeleton is linked to the basal plasma membrane of migrating basal cells via BP230 and plectin/HD1 earlier in the more slowly re-epithelializing blisters than in open wounds. An intact laminin sheath may inhibit keratinocyte migration in intact blisters.

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.

Human bronchial epithelial cells secrete laminin 5, express hemidesmosomal proteins, and assemble hemidesmosomes

Epithelial cells attach to the basement membrane through adhesive contacts between the basal cells of the epithelium and the proteins of the extracellular matrix (ECM). The hemidesmosome (HD) is a specialized cell-ECM contact, that mediates the attachment of the epithelial cell basal surface to the ECM. In bronchial epithelial cells, the protein components that constitute the HD have not been demonstrated. Using immunohistochemical techniques, we determined that normal human bronchial epithelial (NHBE) cells express the HD cell surface integrin alpha6beta4 and produce laminin 5, the ECM protein associated with HDs. Furthermore, expression of the HD-associated structural proteins, bullous pemphigoid antigens 1 (BPAG 1) and 2 (BPAG 2), was demonstrated in NHBE cells by immunofluorescence microscopy and immunoblot analyses. In addition, we confirmed the presence of laminin 5 in the basement membrane (BM) of bronchial epithelial biopsy specimens and of BP230, BP180, and the alpha6beta4 integrin heterodimer at the site of bronchial epithelial cell-ECM interaction in vivo. Finally, using electron microscopy, we were able to demonstrate intact HDs in a glutaraldehyde-fixed NHBE cell monolayer. These findings suggest that bronchial epithelium forms HDs and that the laminin 5-alpha6beta4 integrin interaction may be important in stabilizing epithelial cell adhesion to the BM in the lung.

Bullous pemphigoid and amyotrophic lateral sclerosis: a new clue for understanding the bullous disease?

BACKGROUND

Bullous pemphigoid (BP) occurs in many patients with multiple sclerosis. Isolated cases of BP in patients with other neurological disorders further support a pathogenic association between cutaneous and neurological diseases. Any description of BP in patients with amyotrophic lateral sclerosis is lacking.

OBSERVATIONS

We studied a French population of 168 patients with typical amyotrophic lateral sclerosis. Among these, 3 had clinical and histological features of BP. The mean age of the patients was 54 years. None was known to have autoimmune disorders. Results of immunoblot analysis disclosed both anti-BP antigen 1 and anti-BP antigen 2 antibodies.

CONCLUSIONS

Bullous pemphigoid seems to be unexpectedly associated with amyotrophic lateral sclerosis. On the basis of the cases presented herein, we discuss the epidemiological significance of the association and the possible interrelation between BP antigen 1 and neurofilaments in the pathogenesis of both disorders.

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.

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.

Plasmapheresis as a steroid saving procedure in bullous pemphigoid

BACKGROUND

Bullous pemphigoid is an immunobullous disease affecting predominantly older patients. In severe cases, high-dose corticosteroids and/or other immunosuppressants are often needed long term to control the disease. These can be associated with serious side-effects in this patient population. Objective To evaluate the benefit of plasmapheresis as a steroid saving agent in a cohort of 10 patients.

RESULTS

Plasmapheresis was effective as a steroid saving therapy. All patients went into remission with a lower daily dosage of oral prednisone at 3 and 6 months postplasmapheresis. Two patients had side-effects from therapy that, while significant, did not interfere with long-term improvement in their disease. Eight patients had circulating immunoglobulin G (IgG) antibodies reactive with bullous pemphigoid antigen 1, and three of these had circulating antibodies reactive with bullous pemphigoid antigen 2 on Western immunoblot.

CONCLUSIONS

Plasmapheresis was an effective steroid sparing therapy in these patients. Due to its high cost and potential morbidity, plasmapheresis should not be recommended as routine therapy for bullous pemphigoid, but it is a useful adjunct in resistant cases.

Collagen XVII is destabilized by a glycine substitution mutation in the cell adhesion domain Col15

Collagen XVII is a hemidesmosomal transmembrane molecule important for epithelial adhesion in the skin. It exists in two forms, as a full-length protein and as a soluble ectodomain that is shed from the keratinocyte surface by furin-mediated proteolysis. To obtain information on the conformation and the functions of this unusual collagen, its largest collagenous domain, Col15, was expressed in a eukaryotic episomal expression system and purified by DEAE and fast protein liquid- Mono S chromatography. The protein was triple-helical (T(m) of 26.5 degrees C) when produced in cultures containing ascorbic acid. When the vitamin supply was limited, the 4-hydroxyproline content was reduced from 74 to 9%, which, in turn, resulted in a drastic reduction of the stability of the triple helix. The glycine substitution mutation G627V associated with junctional epidermolysis bullosa, a human blistering skin disease, also had a striking effect on thermal stability of rCol15 causing partial unfolding already at 4 degrees C. Col15 promoted cell adhesion of epithelial and fibroblastic cell lines with a beta1 integrin-mediated mechanism. In concert with this, in acquired autoimmune blistering skin diseases, circulating IgG and IgA autoantibodies were found to target rCol15r.

The shed ectodomain of collagen XVII/BP180 is targeted by autoantibodies in different blistering skin diseases

Collagen XVII/BP180, an epidermal adhesion molecule, exists as a full-length transmembrane protein and as a soluble 120-kd ectodomain that is shed from the keratinocyte surface by furin-mediated proteolysis. Despite a number of studies on autoantibody targets in blistering skin diseases, it has remained unclear whether the physiologically shed ectodomain of collagen XVII plays a role as an autoantigen. Here we isolated the authentic, soluble form of human collagen XVII and showed that it is an autoantigen recognized by IgG and IgA autoantibodies in different blistering skin diseases and is, in some cases, the preferential target. The ectodomain was isolated from the epidermis, keratinocyte media, amniotic fluid, and pemphigoid blister fluid, and autoantibodies affinity-purified with this ectodomain bound to the proximal surface of the epidermis in normal skin but not in collagen XVII-deficient skin. The antibody reactivity was not dependent on the native conformation or the N-glycosylation of the soluble ectodomain, but was abolished by collagenase treatment. Sera of 81 patients with a clinically active blistering skin disease were reacted with full-length collagen XVII, the authentic soluble ectodomain, and recombinant fragments. In bullous and cicatricial pemphigoid, IgG reactive with full-length collagen XVII also recognized the soluble ectodomain. In linear IgA dermatosis and chronic bullous dermatosis of childhood, IgA targeted the soluble ectodomain more efficiently than the full-length protein. The use of recombinant fragments demonstrated that epitopes were present in several noncollagenous and collagenous subdomains of the molecule, and that a significant portion of the sera targeted Col15 domain, a hitherto unrecognized epitope region.

Association of KM genotype with bullous pemphigoid

Association of kappa light chain immunoglobulin allotypes with bullous pemphigoid was examined in 101 Caucasian patients. Km alleles were determined by polymerase chain reaction amplification followed by restriction enzyme digestion. The frequency of Km(3)/Km(1,2)kappa light-chain genotype was found to be significantly associated with the disease, while that of the Km(3)homozygous genotype was significantly higher in patients with both anti-BPAG1 and anti-BPAG2 autoantibodies.

Equine bullous pemphigoid IgG autoantibodies target linear epitopes in the NC16A ectodomain of collagen XVII (BP180, BPAG2)

Bullous pemphigoid (BP) is an autoimmune subepithelial blistering dermatosis of humans, dogs, cats and pigs. It is characterized by skin-fixed and circulating IgG autoantibodies that target one or both BP antigens. An immunological homologue of BP in humans was diagnosed in two horses with cutaneous and mucosal ulcerations as well as microscopic subepithelial vesiculation. Immunological investigations revealed similar findings for both the horses. Direct immunofluorescence demonstrated the presence of IgG deposited linearly at the dermoepidermal junction in mucosal and skin biopsy specimens. Indirect immunofluorescence testing confirmed the existence of circulating basement membrane-specific IgG autoantibodies. Using intact and salt-split epithelial substrates, serum IgG were shown to target antigens situated not only at the basal, but also at the lateral and apical aspects of stratum basale keratinocytes. Immunoblotting and ELISA corroborated that the IgG from affected horses, but not those from normal controls, exhibited high immunoreactivity against the NC16A extracellular domain of type XVII collagen (BPAG2, BP180). Equine BP could be proposed, therefore, as another spontaneous model of this most common basement membrane autoimmune dermatosis of humans.

Molecular cloning of canine bullous pemphigoid antigen 2 cDNA and immunomapping of NC16A domain by canine bullous pemphigoid autoantibodies

The autoantibody-mediated subepidermal blistering skin disease bullous pemphigoid affects both humans and dogs. We previously demonstrated that canine bullous pemphigoid patient's autoantibodies targeted skin basement membrane component and a 180-kDa keratinocyte protein. We extend our works to partially isolate the cDNA encoding canine bullous pemphigoid antigen 2 (BPAg2, BP180). Total RNA extracted from a papillomavirus-immortalized canine keratinocyte cell line and a cultured canine squamous carcinoma cell line SCC 2/88 were used to isolate fragments of cDNA encoding BPAg2 by reverse transcription-PCR and 5'-rapid amplification of cDNA end. The isolated sequence included the 5'-untranslated region, the entire intracellular, transmembranous, and extracellular NC16A autoantigenic domains, plus a small segment of the collagenous domain. Sequence analyses of the isolated cDNA showed 87 and 85% identities between canine and human at the nucleotide sequence and at the deduced amino acid sequence levels, respectively. The canine BPAg2 sequence was confirmed by a rabbit antibody raised against a 18-amino acid peptide deduced from the canine NC16A nucleotide sequence. Autoantibodies from canine bullous pemphigoid patients' sera recognized epitopes within the human NC16A domain. The cloning of the cDNA encoding this disease-associated protein may allow us to develop a canine model in dissecting the immunopathologic mechanism underlying bullous pemphigoid.

The N terminus of the transmembrane protein BP180 interacts with the N-terminal domain of BP230, thereby mediating keratin cytoskeleton anchorage to the cell surface at the site of the hemidesmosome

In epidermal cells, the keratin cytoskeleton interacts with the elements in the basement membrane via a multimolecular junction called the hemidesmosome. A major component of the hemidesmosome plaque is the 230-kDa bullous pemphigoid autoantigen (BP230/BPAG1), which connects directly to the keratin-containing intermediate filaments of the cytoskeleton via its C terminus. A second bullous pemphigoid antigen of 180 kDa (BP180/BPAG2) is a type II transmembrane component of the hemidesmosome. Using yeast two-hybrid technology and recombinant proteins, we show that an N-terminal fragment of BP230 can bind directly to an N-terminal fragment of BP180. We have also explored the consequences of expression of the BP230 N terminus in 804G cells that assemble hemidesmosomes in vitro. Unexpectedly, this fragment disrupts the distribution of BP180 in transfected cells but has no apparent impact on the organization of endogenous BP230 and alpha6beta4 integrin. We propose that the BP230 N terminus competes with endogenous BP230 protein for BP180 binding and inhibits incorporation of BP180 into the cell surface at the site of the hemidesmosome. These data provide new insight into those interactions of the molecules of the hemidesmosome that are necessary for its function in integrating epithelial and connective tissue types.

[Pemphigoid gestationis without blisters]

BACKGROUND AND OBJECTIVE

Pemphigoid gestationis (PG) is a rare pregnancy-associated autoimmune bullous disease characterized by autoantibodies to the 180 kD bullous pemphigoid antigen (BP180). The clinical spectrum of PG is polymorphic and for diagnostic purposes, a skin biopsy is usually taken demonstrating the deposition of autoantibodies.

PATIENTS AND METHODS

From 2 patients, skin biopsies were obtained for histopathologic and immunofluorescence studies. Circulating autoantibodies were characterized by immunoblotting and ELISA using a recombinant form of the immunodominant BP180 NC16 A domain.

RESULTS

The 2 PG patients described here did not show blisters but complained about severe itching. In the first case, PG presented in the first trimester of the second pregnancy as an erythema-multiforme-like disease. The second patient developed urticarial plaques a few days after delivery. PG was diagnosed by the detection of autoantibodies against recombinant BP180 NC16 A by immunoblot and ELISA analysis and confirmed by linear deposits of C3 at the cutaneous basement membrane zone on direct immunofluorescence microscopy. Skin lesions healed with oral prednisolone.

CONCLUSIONS

In our two patients, non-bullous PG could be diagnosed by serological tests. Immunoblotting and ELISA might be sensitive and specific tools when screening sera of patients with pruritic skin lesions in pregnancy for the presence of autoantibodies to BP180. In some cases, these newer techniques may make a skin biopsy unnecessary.

A critical role for neutrophil elastase in experimental bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune skin disease characterized by subepidermal blisters and autoantibodies against 2 hemidesmosome-associated proteins, BP180 and BP230. The immunopathologic features of BP can be reproduced in mice by passive transfer of anti-BP180 antibodies. Lesion formation in this animal model depends upon complement activation and neutrophil recruitment. In the present study, we investigated the role of neutrophil elastase (NE) in antibody-induced blister formation in experimental BP. Abnormally high levels of caseinolytic activity, consistent with NE, were detected in extracts of lesional skin and blister fluid of mice injected with anti-BP180 IgG. The pathogenic anti-BP180 IgG failed to induce subepidermal blistering in NE-null (NE(-/-)) mutant mice. NE(-/-) mice reconstituted with neutrophils from wild-type mice became susceptible to experimental BP. Wild-type mice given NE inhibitors (alpha1-proteinase inhibitor and Me-O-Suc-Ala-Ala-Pro-Val-CH(2)Cl), but not mice given cathepsin G/chymase inhibitors (alpha1-antichymotrypsin or Z-Gly-Leu-Phe-CH(2)Cl), were resistant to the pathogenic activity of anti-BP180 antibodies. Incubation of murine skin with NE induced BP-like epidermal-dermal detachment. Finally, NE cleaved BP180 in vitro and in vivo. These results implicate NE directly in the dermal-epidermal cleavage induced by anti-BP180 antibodies in the experimental BP model.