Autoimmunity in bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune blistering disease primarily of the elderly, characterized by the development of urticarial plaques surmounted by subepidermal blisters and the deposition of immunoglobulins and complement at the basement membrane zone (BMZ). Immunologically, it is characterized by the development of autoantibodies targeting two structural proteins of the hemidesmosomes, BP180 (collagen XVII) and BP230. BP230 is intracellular protein of the hemidesmosomal plaque, while BP180 is a transmembrane protein with a collagenous extracellular domain. The weight of experimental evidence indicates that BP180 is the primary target of the pathogenic autoantibodies. Autoantibodies are of both the IgG or IgE class, and their binding in the skin triggers complement activation, mast cell degranulation and the accumulation of inflammatory cells, including eosinophils, mast cells, and neutrophils. Release of proteases from these inflammatory cells results in cleavage of the BMZ and blister formation. While the initial triggers of autoantibody production remain obscure, a better understanding of the pathomechanisms of blister formation will lead to the development of new therapeutic strategies.

Identification of two collagen domains within the bullous pemphigoid autoantigen, BP180.

Bullous pemphigoid (BP) is an autoimmune disease characterized by subepidermal vesicles and the presence of autoantibodies directed against the epidermal basement membrane zone. Previous studies have identified two protein components of the hemidesmosome, BP180 and BP230, as the primary antigenic targets of BP autoantibodies. We have recently reported the isolation of a 1.0-kb BP180 cDNA. Sequence analysis presented in this report reveals that this partial BP180 cDNA encodes two protein domains which have primary structures that are characteristic of the triple helical domains of collagens, i.e., glycine appears at every third position and over one-third of the remaining residues are proline. The two collagen domains have lengths of 242 and 30 amino acids and are separated by a noncollagen stretch of 12 amino acids. Collagenase digestion of the BP180 cDNA-encoded fusion protein generated a peptide fragment with a size that was consistent with the predicted locations of the collagenase digestion sites. A possible physiological function for the collagen domains of the BP180 hemidesmosomal protein may be to form stable interactions with constituents of the extracellular matrix of the cutaneous basement membrane zone. Such interactions may provide the molecular framework for the adhesion between the basal keratinocyte and the basal lamina.

Isolation of a human epidermal cDNA corresponding to the 180-kD autoantigen recognized by bullous pemphigoid and herpes gestationis sera. Immunolocalization of this protein to the hemidesmosome.

Autoantibodies present in the sera of patients with bullous pemphigoid (BP) bind to the basement membrane zone of normal human skin and commonly recognize two epidermal proteins, the BP240 and BP180 antigens. Two BP antigen cDNA clones from a lambda gt11 human keratinocyte library have been identified on the basis of reactivity with a BP serum. The fusion protein (FP) produced by one clone immunoadsorbed autoantibodies, which specifically recognized the BP180 by antigen, showing no cross-reactivity with BP240 by immunoblot analysis. The FP produced by the second clone immunoadsorbed autoantibodies which specifically reacted with the BP240 epidermal antigen. Northern blot analysis demonstrated that the BP180 and BP240 antigens are encoded by distinct RNA transcripts with lengths of 6.0 and 8.5 kb, respectively. Immunoblot analysis of the BP180 lysogen extract identified a 135-kD FP which was recognized by 7 of 16 BP sera and 7 of 8 herpes gestationis sera. A rabbit antiserum prepared against the lysogenic BP180 FP specifically recognized the BP180 antigen from human epidermal extracts by immunoblotting, labeled the BMZ by indirect immunofluorescence, and bound to human epidermal hemidesmosomes by immuno-electron microscopy. These results indicate that the BP180 antigen recognized by BP and herpes gestationis autoantibodies is a unique hemidesmosomal polypeptide, distinguishable from the BP240 antigen.

The role of complement in experimental bullous pemphigoid.

Bullous pemphigoid (BP) is a blistering skin disease associated with an IgG autoimmune response directed against the ectodomain of the hemidesmosomal protein, BP180. An animal model of BP has recently been developed by our laboratory based on the passive transfer of rabbit antimurine BP180 antibodies into neonatal BALB/c mice. The experimental animals develop a blistering disease that reproduces all of the key immunopathological features of BP. In the present study we have investigated the role of complement in the pathogenesis of subepidermal blistering in the mouse model of BP. We demonstrate the following. (a) Rabbit anti-murine-BP180 IgG was effective in inducing cutaneous blisters in a C5-sufficient mouse strain, but failed to induce disease in the syngeneic C5-deficient strain; (b) neonatal BALB/c mice, pretreated with cobra venom factor to deplete complement, became resistant to the pathogenic effects of the anti-BP180 IgG; (c) F(ab')2 fragments generated from the anti-BP180 IgG exhibited no pathogenic activity in the mouse model; and (d) histologic evaluation of the skin of mice described in points b and c above showed minimal or no neutrophilic cell infiltration in the upper dermis. Thus, anti-BP180 antibodies trigger subepidermal blistering in this BP model via complement activation. This experimental model of BP should greatly facilitate future studies on the pathophysiology of autoantibody-mediated diseases of the dermal-epidermal junction.

A passive transfer model of the organ-specific autoimmune disease, bullous pemphigoid, using antibodies generated against the hemidesmosomal antigen, BP180.

Subepidermal blistering associated with the human skin diseases bullous pemphigoid and herpes gestationis has been thought to be an IgG autoantibody-mediated process; however, previous attempts to demonstrate the pathogenicity of patient autoantibodies have been unsuccessful. An immunodominant and potentially pathogenic epitope associated with these blistering diseases has recently been mapped to the extracellular domain of a human epidermal antigen, BP180. Patient autoantibodies that react with this well-defined antigenic site failed to crossreact with the murine form of this autoantigen and thus could not be assayed for pathogenicity in a conventional passive transfer mouse model. As an alternative, rabbit polyclonal antibodies were generated against a segment of the murine BP180 protein homologous with the human BP180 autoantibody-reactive site and were passively transferred into neonatal BALB/c mice. The injected animals developed a subepidermal blistering disease that closely mimicked bullous pemphigoid and herpes gestationis at the clinical, histological, and immunological levels. Autoantibodies that recognize the human BP180 ectodomain are therefore likely to play an initiatory role in the pathogenesis of bullous pemphigoid and herpes gestationis.

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.

A major role for neutrophils in experimental bullous pemphigoid.

Bullous pemphigoid (BP) is an inflammatory subepidermal blistering disease associated with an IgG autoimmune response to the hemidesmosomal protein, BP180. Using a passive transfer mouse model, our group has shown previously that antibodies to the murine BP180 (mBP180) ectodomain are capable of triggering a blistering skin disease that closely mimics human BP. In this study, we investigated the role of neutrophils in the immunopathogenesis of this disease model. BALB/c mice depleted of circulating neutrophils by treatment with neutrophil-specific antibodies were no longer susceptible to the pathogenic effects of anti-mBP180 IgG. IgG and complement were deposited at the dermal-epidermal junction of these animals, but there was no evidence of inflammatory infiltration or blistering. C5-deficient mice, which are resistant to the pathogenic activity of anti-mBP180 IgG, could be made susceptible to this IgG-mediated blistering disease by intradermal administration of a neutrophil chemoattractant, IL-8 or C5a. Intraperitoneal injection of IL-8, which sequesters neutrophils in the peritoneal cavity, interferes with anti-mBP180-induced neutrophilic infiltration of the skin and prevented the development of BP disease in BALB/c mice. These findings provide the first direct evidence that neutrophils recruited to the skin via a C5-dependent pathway play an essential role in subepidermal blister formation in experimental BP, and suggest new directions for disease intervention.

Desmoglein-1-specific T lymphocytes from patients with endemic pemphigus foliaceus (fogo selvagem).

Fogo selvagem (FS), the endemic form of pemphigus foliaceus, is a cutaneous autoimmune disease characterized by subcorneal blistering of the epidermis and the production of autoantibodies against the desmosomal antigen desmoglein-1 (Dsg1). Previously, we showed that mice injected with autoantibodies from FS patients develop a skin disease that reproduces the clinical, histological, and immunological features of FS, indicating that autoantibodies play an essential role in the development of this disease. The purpose of this study was to characterize the autoimmune T-cell response associated with FS. We provide here the first evidence, to our knowledge, that the great majority of FS patients have circulating T lymphocytes that specifically proliferate in response to the extracellular domain of Dsg1. Long-term T cells developed from these patients also responded to Dsg1, and this antigen-specific response was shown to be restricted to HLA-DR molecules. These Dsg1-reactive FS T cells exhibited a CD4-positive memory T-cell phenotype and produced a T helper 2-like cytokine profile. These findings represent the initial steps in defining the role of T cells in FS autoimmunity.

Subclass reactivity of pemphigus foliaceus autoantibodies with recombinant human desmoglein.

Pemphigus foliaceus (PF) and its endemic form, Fogo Selvagem (FS), are autoimmune disorders characterized by subcorneal vesicles and IgG4 subclass autoantibodies that recognize a surface antigen of normal epidermal cells. FS and PF autoantibodies have been shown to bind desmoglein (DGI), a desmosomal glycoprotein classified as a member of the cadherin family of calcium-dependent cell adhesion molecules. In the present study we report the isolation of three overlapping cDNA clones representing greater than 90% of the extracellular domain of human DGI. Recombinant proteins encoded by these clones, designated DGI-1, DGI-2, and DGI-3, were produced in bacteria and analyzed for immunoblot (IB) reactivity with a panel of FS, PF, and control sera. FS and PF autoantibodies possessing reactivity with each of the three recombinant fusion proteins (FPs) were identified. FP DGI-3 (containing 123 amino acids of the membrane proximal region of the DGI ectodomain) showed reactivity with the largest number of patient sera--seven FS and one PF. IB reactivity with the DGI-1 FP (encoding 205 amino acids of the N-terminal region of DGI) could be eliminated by truncation of the C-terminal portion of this protein, indicating that autoantibodies were not binding the R-A-L motif. Autoantibodies reactive with two of the three FPs were predominantly restricted to IgG4, the subclass shown to be pathogenic in the passive transfer mouse model. The findings of this study demonstrate that the extracellular domain of DGI contains at least three antigenic sites recognized by FS and PF autoantibodies. The region near the membrane-spanning domain of DGI appears to contain an immunodominant site. This study is the first to document immunoblot reactivity of FS and PF autoantibodies with recombinant forms of DGI. The use of such molecular tools should facilitate the identification and characterization of relevant antigen/antibody systems in FS and PF.

Pemphigus foliaceus sera recognize an N-terminal fragment of bovine desmoglein 1.

It has previously been demonstrated that sera from endemic and nonendemic pemphigus foliaceus patients recognize three immunoreactive fragments of 80, 62, and 45 kilodaltons (kD) from extracts of the envelope fraction of human and bovine epidermis. These polypeptides are also immunoprecipitated by approximately 50% of pemphigus vulgaris sera, but are unreactive with sera from bullous pemphigoid patients or normal controls. The 80-kDa antigen has been shown to be a glycoprotein with N-linked oligosaccharides. Complete removal of the carbohydrate moieties produced a 76-kD polypeptide that continued to react with pemphigus foliaceus autoantibodies in a Ca(++)-dependent manner. To further characterize this antigen/antibody system, the 80-kD pemphigus foliaceus antigen solubilized from a bovine epidermal envelope extract was purified by affinity chromatography using a pemphigus foliaceus patient's immunoglobulin (Ig)G immobilized on agarose. After elution with 0.2 M glycine/HCl, pH 2.8, 5 mM ethylene diaminetetraacetic acid, the polypeptide was mixed with a small amount of 125I-labeled 80-kD antigen, added as a tracer, fractionated by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and electrotransferred onto a polyvinylidene difluoride membrane. The 80-kD band detected by amido black staining and autoradiography was excised and characterized by amino acid sequence analysis. The resulting sequence, EXIKFAAAXREGEXNSKRNPIA, matched perfectly with the N-terminal 22 amino acids of the mature form of bovine desmoglein 1. These findings demonstrate that the 80-kD bovine autoantibody-reactive polypeptide is the glycosylated ectodomain of desmoglein 1, which may contain epitopes recognized by pathogenic autoantibodies.

Cloning and primary structural analysis of the bullous pemphigoid autoantigen BP180.

Bullous pemphigoid (BP) is an autoimmune skin disease that is characterized by the presence of subepidermal blisters resulting from a disruption of the adhesive interactions between basal keratinocytes and the cutaneous basement membrane. Autoantibodies from patients suffering from this disorder recognize two epidermal antigens, BP180 and BP230, both of which have been localized to the hemidesmosome, a transmembrane structure of stratified, squamous epithelia that functions in cell-matrix adhesion. In the present study we report the primary structural analysis of BP180 based on the sequence of a series of overlapping cDNA clones encompassing 4,669 bases of the BP180 transcript. A polymerase chain reaction-based protocol was used to confirm the contiguity of the cDNA segments. This cloned portion of the BP180 transcript was found to contain one long open reading frame (ORF) 4.596 bases in length. This ORF encodes a polypeptide of 155,000 Daltons with an isoelectric point of 9.7. The carboxy-terminal half of BP180, a stretch of 916 amino acids, consists of 15 collagen domains of variable length (15 to 242 amino acids) that are separated from one another by short stretches of non-collagen sequences. Located 76 amino acids upstream of the collagenous region is a putative transmembrane domain, a structural feature that distinguishes BP180 from all of the well-characterized members of the collagen family. This membrane-spanning domain is predicted to function as a signal-anchor sequence, directing the C-terminal collagenous segment of this protein to the exterior of the cell. The putative intracellular domain is highly basic with an isoelectric point of 10.37. This molecular analysis predicts that the BP180 antigen is an integral membrane protein of the hemidesmosome that contains a long extracellular collagenous tail. This combination of structural features suggests that BP180 may function as a cell-matrix adhesion molecule, with the collagenous region acting as a potential site of interaction with basement membrane components. Autoantibody-mediated disruption of such an adhesive interaction may play a critical role in the development of sub-epidermal blisters in BP patients.

The anti-desmoglein 1 autoantibodies in pemphigus vulgaris sera are pathogenic.

Pemphigus vulgaris and pemphigus foliaceus are two closely related, but clinically and histologically distinct, autoimmune skin diseases. The autoantigens for pemphigus vulgaris and pemphigus foliaceus are desmoglein 3 and desmoglein 1, respectively. The anti-desmoglein 1 antibodies in pemphigus foliaceus and anti-desmoglein 3 antibodies in pemphigus vulgaris are pathogenic as determined by immunoglobulin G passive transfer animal models. More than 50% of pemphigus vulgaris sera also contain anti-desmoglein 1 autoantibodies; however, the pathogenicity of the anti-desmoglein 1 autoantibodies in pemphigus vulgaris remains unknown. In this study, we used soluble recombinant extracellular domains of desmoglein 1 and desmoglein 3 to obtain affinity-purified anti-desmoglein 1 and anti-desmoglein 3 autoantibodies from pemphigus vulgaris sera and examined the pathogenicity of each fraction separately using the passive transfer mouse model. By immunoprecipitation, the purified anti-desmoglein 1 and anti-desmoglein 3 showed no cross-reactivity. The anti-desmoglein 1 autoantibodies in pemphigus vulgaris induced typical pemphigus foliaceus lesions in neonatal mice, whereas the anti-desmoglein 3 fraction induced pemphigus vulgaris-like lesions. In addition, the pathogenic anti-desmoglein 1 and anti-desmoglein 3 autoantibodies in pemphigus vulgaris had predominant IgG4 subclass specificity. These findings suggest that the anti-desmoglein 1 antibodies in pemphigus vulgaris are pathogenic.

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.

Pemphigus foliaceus and pemphigus vulgaris autoantibodies react with the extracellular domain of desmoglein-1.

Pemphigus foliaceus is associated with an autoimmune response against desmoglein-1; however, the fine specificity of these autoantibodies and the role that they play in pathogenesis have not yet been elucidated. In an attempt to develop a system to facilitate the detection and characterization of this antigen/antibody system, recombinant human desmoglein-1 was expressed in COS-1 cells, a mammalian epithelial cell line. The desmoglein-1 transgene product was shown to be expressed on the surface of the COS-1 cells in the appropriate transmembrane orientation. All pemphigus foliaceus sera (endemic form, n = 24; nonendemic form, n = 7) reacted strongly with nonpermeabilized desmoglein-1-transfected cells, exhibiting a punctate cell-surface staining pattern. This reactivity against the desmoglein-1 ectodomain was predominantly an IgG4-restricted response and was calcium dependent. Ten of 18 pemphigus vulgaris sera also reacted with the extra-cellular domain of recombinant desmoglein-1. Use of this eukaryotic expression system should greatly facilitate further characterization of the anti-desmoglein-1 autoimmune response associated with pemphigus foliaceus and pemphigus vulgaris and may aid in determining its pathogenic relevance.

Bullous pemphigoid and cicatricial pemphigoid autoantibodies react with ultrastructurally separable epitopes on the BP180 ectodomain: evidence that BP180 spans the lamina lucida.

The BP180 antigen is a hemidesmosomal glycoprotein that is recognized by autoantibodies associated with three autoimmune disorders, bullous pemphigoid (BP), herpes gestationis (HG), and cicatricial pemphigoid (CP). BP and HG sera have been shown to recognize a common extracellular site located near the membrane-spanning domain of this protein, whereas CP sera react predominantly with a distinct site near the C terminus. In the current study, the main immunogenic sites on the BP180 ectodomain were ultrastructurally localized using six BP sera, four CP sera, and two rabbit antisera. The immunolocalization pattern of BP sera was largely restricted to the upper lamina lucida region immediately subjacent to the epidermal hemidesmosome and closely resembled that of a rabbit antiserum directed against the NC16A (membrane-proximal) domain of BP180. CP sera, on the other hand, exhibited a lower lamina lucida/lamina densa labeling pattern that was strikingly similar to that of rabbit antibodies to the BP180 C-terminal region. Finally, antibodies to the BP180 C-terminal region co-localized with an anti-laminin-5 antibody in the anchoring filament zone. These findings strongly suggest that the BP180 extracellular domain exists in an extended conformation, with the C terminus of this protein projecting into the lamina densa. These data support the hypothesis that BP180 contributes to the structure and function of the anchoring filaments. Differences in the ultrastructural mapping of BP and CP autoantibodies appear to correlate with epitope mapping data, which, together, may help to explain the clinical heterogeneity observed in this group of bullous disorders.

Tight clustering of extracellular BP180 epitopes recognized by bullous pemphigoid autoantibodies.

Bullous pemphigoid is a blistering skin disease associated with autoantibodies against the BP180 antigen, a transmembrane component of the hemidesmosome. Anti-BP180 antibodies have been demonstrated to be pathogenic in a passive transfer mouse model. One extracellular site on human BP180 (MCW-1) was previously shown to be recognized by 50-60% of bullous pemphigoid sera. To facilitate the identification of additional autoantibody-reactive epitopes, recombinant forms of the BP180 ectodomain were generated using both bacterial and mammalian expression systems. One recombinant protein, sec180e, that was expressed in COS-1 cells and that contained the entire BP180 ectodomain, provided us with a tool to detect conformational epitopes. Bullous pemphigoid sera immunoadsorbed against the major noncollagenous NC16A domain no longer reacted with sec180e, indicating that autoantibody reactivity to the BP180 ectodomain is restricted to the NC16A region. Immunoblot analysis of bullous pemphigoid sera immunoadsorbed with a series of recombinant NC16A peptides revealed the presence of three novel autoantigenic sites that, along with the MCW-1 epitope, are clustered within the N-terminal 45 amino acid stretch of NC16A. All 15 bullous pemphigoid sera tested reacted with a recombinant protein containing this BP180 segment. No disease-associated epitopes were detectable within the remaining 28 amino acids of NC16A. Thus, bullous pemphigoid patient autoantibodies react with a set of epitopes on the BP180 ectodomain that are highly clustered. This autoantibody-reactive region on human BP180 shows overlap with the corresponding murine BP180 site that is targeted by antibodies that are pathogenic in the mouse model of bullous pemphigoid. These findings suggest new directions for the development of diagnostic and therapeutic tools for this disease.

A highly sensitive enzyme-linked immunosorbent assay for the detection of circulating anti-BP180 autoantibodies in patients with bullous pemphigoid.

The BP180 antigen, a component of the epidermal anchoring complex, has been identified as one of the major antigenic targets of autoantibodies associated with the blistering skin disease, bullous pemphigoid. Our research group has recently demonstrated that reactivity of bullous pemphigoid autoantibodies to the BP180 ectodomain is almost entirely restricted to a set of four antigenic sites clustered within the membrane-proximal noncollagenous stretch (NC16A). Using a passive transfer mouse model, antibodies to the corresponding noncollagenous region of murine BP180 were shown to trigger an inflammatory subepidermal blistering disease that closely mimics bullous pemphigoid. We now report the development of an enzyme-linked immunoabsorbent assay system that is extremely sensitive in detecting disease-specific autoantibodies in the sera of bullous pemphigoid patients. The target antigen in this assay is a recombinant form of the BP180 NC16A domain that contains all four of the well-defined bullous pemphigoid-associated antigenic sites. Of 50 randomly selected bullous pemphigoid sera tested, 47 (94%) were positive in this assay, whereas no specific reactivity was detected in any of the 107 controls. Interestingly, all three of the bullous pemphigoid sera that were negative in this assay had been obtained from patients who were already undergoing treatment. The NC16A enzyme-linked immunosorbent assay is more sensitive than any of the standard techniques for detecting circulating bullous pemphigoid autoantibodies, including other enzyme-linked immunosorbent assays, immunoblotting, and indirect immunofluorescence. Finally, the NC16A enzyme-linked immunosorbent assay provides immunologic information that cannot be obtained from direct immunofluorescence studies of skin biopsies, and that may well be relevant in the diagnosis and treatment of bullous pemphigoid.

Autoantibodies to BP180 associated with bullous pemphigoid release interleukin-6 and interleukin-8 from cultured human keratinocytes.

Bullous pemphigoid is an inflammatory subepidermal blistering disease that is associated with auto- antibodies to the keratinocyte surface protein, BP180. In addition to the binding of autoantibodies, the infiltration of inflammatory cells is necessary for blister formation. Cytokines, including interleukin-6 and interleukin-8, have been implicated in the disease process of both human and experimental murine bullous pemphigoid. This study was aimed at testing the hypothesis that the binding of anti-BP180 antibodies to their target antigen triggers a signal transduction event that results in the secretion of these pro-inflammatory cytokines. Consistent with this hypothesis, treatment of cultured normal human epidermal keratinocytes with bullous pemphigoid IgG, but not control IgG, led to increased levels of interleukin-6 and interleukin-8, but not interleukin-1alpha, interleukin-1beta, tumor necrosis factor-alpha, interleukin-10, or monocyte chemoattractant protein-1, in the culture medium. This effect was concentration- and time-dependent and was abolished by depleting the bullous pemphigoid IgG of reactivity to two distinct epitopes on the BP180 NC16A domain. Upregulation of interleukin-6 and interleukin-8 was found at both protein and mRNA levels. In addition, bullous pemphigoid IgG did not induce the release of interleukin-6 and interleukin-8 from BP180-deficient keratinocytes obtained from a patient with generalized atrophic benign epidermolysis bullosa. These data indicate that bullous pemphigoid-associated autoantibodies to the human BP180 ectodomain trigger a signal transducing event that leads to expression and secretion of interleukin-6 and interleukin-8 from human keratinocytes.

Development of an ELISA to detect anti-BP180 autoantibodies in bullous pemphigoid and herpes gestationis.

Autoantibodies associated with the subepidermal blistering disorders bullous pemphigoid and herpes gestationis react with a 180-kD transmembrane hemidesmosomal protein, designated BP180. The BP180 ectodomain is composed of a series of interrupted collagen triple helical domains. Located on one of the noncollagenous extracellular segments of this protein is an immunodominant epitope, designated MCW-1, recognized by patient autoantibodies. In this investigation we have developed an enzyme-linked immunosorbent assay system to detect antibody reactivity against the MCW-1 epitope with the use of a bacterial fusion protein containing the BP180 autoantibody-reactive site. The following sera were assayed for reactivity with this recombinant protein: bullous pemphigoid (n = 62), herpes gestationis (n = 28), endemic pemphigus foliaceus (n = 17), lupus erythematosus (n = 15), and normal human sera (n = 22). This enzyme-linked immunosorbent assay-based protocol was shown to be highly specific (98.3%) in detecting autoantibody activity in bullous pemphigoid and herpes gestationis patients. Fifty-three percent of bullous pemphigoid sera and 71% of herpes gestations sera, but none of the control sera, yielded positive results in this assay. Of the patient sera that were known to react with full-length BP180, almost all showed reactivity with the MCW-1 antigenic site of this protein. Autoantibodies detected in this assay were predominantly of the immunoglobulin G class. The results presented here lend support to the hypothesis that this well-defined antigen/antibody system may be relevant in pathogenesis.

Autoantibodies in lichen planus pemphigoides react with a novel epitope within the C-terminal NC16A domain of BP180.

Lichen planus pemphigoides is an autoimmune subepidermal blistering disease. The finding of immunoglobulin G antibodies directed against the basement membrane zone differentiates it from bullous lichen planus. The aim of this study was to identify the target antigen of lichen planus pemphigoides autoantibodies. Sera from lichen planus pemphigoides patients (n = 4) stained the epidermal side of NaCl-split human skin in a pattern indistinguishable from that produced by bullous pemphigoid sera. In bullous pemphigoid, the autoimmune response is directed against BP180, a hemidesmosomal transmembrane collagenous glycoprotein. We previously demonstrated that bullous pemphigoid sera predominantly react with a set of four epitopes (MCW-0 through MCW-3) clustered within a 45 amino acid stretch of the major noncollagenous extracellular domain (NC16A) of BP180. By immunoblotting and enzyme-linked immunosorbent assay, lichen planus pemphigoides sera were also strongly reactive with recombinant bullous pemphigoid 180 NC16A. The lichen planus pemphigoides epitopes were further mapped using a series of overlapping recombinant segments of the NC16A domain. All lichen planus pemphigoides sera reacted with amino acids 46-59 of domain NC16A, a protein segment that was previously shown to be unreactive with bullous pemphigoid sera. Two lichen planus pemphigoides sera, in addition, reacted with the immunodominant antigenic region associated with bullous pemphigoid. In conclusion, there are now five bullous diseases that are associated with an autoimmune response to BP180: bullous pemphigoid; pemphigoid/herpes gestationis; cicatricial pemphigoid; linear immunoglobulin A disease; and lichen planus pemphigoides. In addition, we have identified a novel epitope within the BP180 NC16A domain, designated MCW-4, that appears to be uniquely recognized by sera from patients with lichen planus pemphigoides.