The pathogenic role of pemphigus antibodies and proteinase in epidermal acantholysis

Proteases are responsible for blister formation in recessive dystrophic epidermolysis bullosa and epidermolysis bullosa simplex

The specific factors which induce blister formation in recessive dystrophic epidermolysis bullosa (RDEB) and epidermolysis bullosa simplex (EBS) were studied by culturing normal human skin with blister fluid from patients with RDEB and EBS. When skin from a healthy person was cultured with RDEB blister fluid, it developed a clean subepidermal blister with histology similar to that of a RDEB blister. The specific factor(s) which induced this subepidermal blister was inactivated by heat (60 degrees C, 30 min), trypsin digestion and by treating with EDTA, EGTA, alpha 2-macroglobulin, soybean trypsin inhibitor (SBTI) or N-ethylmaleimide (NEM), but was not affected by dialysis. These findings suggest that the active factor(s) in the blister fluid from patients with RDEB might include collagenase, neutral thiol protease and trypsin-like protease. By contrast, when normal skin was cultured with EBS blister fluid, this produced a clean intra-epidermal blister with histology similar to that of an EBS blister. The specific factor(s) inducing the intra-epidermal blister was inactivated by heat (60 degrees C, 30 min), trypsin digestion and by treating with NEM, but was not affected by dialysis, divalent cation chelators (EGTA, EDTA), alpha 2-macroglobulin, SBTI and pepstatin. These results suggest that the active factor(s) inducing the intra-epidermal blister in EBS might be a neutral SH-protease.

High doses of antigen-nonspecific IgG do not inhibit pemphigus acantholysis in skin organ cultures

A patient suffering from severe pemphigus vulgaris was treated using large-volume plasma exchange in combination with an immunosuppressive regimen. As some recent reports have shown evidence that polyclonal, polyspecific human IgG in high doses through the i.v. route (IGIV) protect target platelets in idiopathic thrombocytopenic purpura from attack by antiplatelet autoantibodies and/or immune complexes, we also administered IGIV to this pemphigus-vulgaris patient. In order to test the hypothesis that IGIV might protect in vitro-cultured human skin from acantholysis induced by pemphigus antibodies, studies with skin organ cultures were carried out using plasma from another pemphigus-vulgaris patient who had undergone plasma exchange. The preincubation of either the skin explants or the pemphigus plasma with various concentrations of IGIV (ranging from 0.15 to 15 mg/ml in the culture medium) did not prevent acantholysis induced by the pemphigus plasma nor did it inhibit the binding of the specific antibodies visualized by direct immunofluorescence. Thus, the assumption that IGIV may coat the pemphigus antigens on epidermal cells making them inaccessible to pathogenic autoantibodies was not substantiated by our tests in vitro; likewise, the hypothesis of functionally blocking autoantibody activity by means of anti-idiotype effects of IGIV cannot be supported.

IgM class antibodies to intercellular substance in massive cutaneous hyalinosis: occurrence and relation to antigluten and antihyalin antibodies

High levels of circulating IgM class antibodies to intercellular substance were found in massive cutaneous hyalinosis, a systemic kappa light chain disease characterized by hyalin deposits in skin and gut. A strong humoral immune response to the accumulating mannose-rich hyalin glycoprotein and to wheat gluten was also demonstrated. Both gluten and the hyalin protein, when added to serum, abolished the immunofluorescence staining of the intercellular cement, suggesting that there may exist common antigenic sites in the hyalin protein, gluten, and intercellular substance.

Demonstration of pemphigus antibodies on the cell surface of murine epidermal cell monolayers and their internalization

The pathogenic effects of pemphigus vulgaris (PV) antibodies on epidermal cells can be demonstrated both in vitro using skin organ culture or primary epidermal cell cultures (PECC) and in vivo by passive transfer of PV antibodies into neonatal BALB/c mice. Although PV antibodies have been localized on the epidermal cell surface by several techniques, little is known about the fate of these autoantibodies subsequent to their surface binding. We have examined this, using murine PECC which express pemphigus antigen on their surface, and followed the fate of the bound antibody molecules. Forty-eight-hour PECC were incubated at 37 degrees C with PV antibodies for 20 min and then with horseradish peroxidase-labelled antihuman IgG. This was considered time 0. The monolayers were fixed with glutaraldehyde after 0, 0.5, 1, 3, 6, 18, and 24 h incubation at 37 degrees C and then processed for electron microscopy. At time 0 hour, PV antibodies is detected bound evenly along the surface of keratinocytes. Within 30 min, the bound PV antibodies becomes clustered, internalized into submembranous vesicles via surface pits, and eventually fused with lysosomes. Widening of the intercellular spaces was also seen in PECC treated with PV antibodies within the first 24 h. PECC treated with normal human IgG in parallel cultures showed no such surface binding, internalization, or cell-cell detachment. Treatment with cytochalasin-D and/or colchicine did not affect the internalization of the PV antibodies, but fusion with lysosomes was not seen in treated cultures. These findings suggest that PV antibodies binds a surface antigen and the complex is internalized and fused with lysosomes in a process that may have pathophysiologic relevance.

Human autoantibodies against a desmosomal core protein in pemphigus foliaceus

Pemphigus foliaceus (PF) is a human autoimmune disease in which antibodies are directed against the cell surface of epidermal cells with resultant blister formation. The histopathology of these blisters indicates that cells have detached from each other, and electron microscopy of early blisters shows diminished numbers, to complete loss, of desmosomes as well as abnormalities of the tonofilament-desmosome complex. In this study we demonstrate that autoantibodies from certain PF patients bind to a desmosomal core glycoprotein called desmoglein (DG) I. Proteins in extracts of normal human epidermis were separated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE), then transferred to nitrocellulose or 2-aminophenylthioether paper for immunoperoxidase staining. Results of these immunoblots indicated that sera from 6 of 13 PF patients specifically and intensely stained an approximately 160,000 mol wt polypeptide, "PF antigen". Such staining was not seen with normal human sera or sera from patients with pemphigus vulgaris or bullous pemphigoid, two autoimmune blistering skin diseases that are clinically, histologically, and immunochemically distinct from PF. However, rabbit antiserum directed against DGI, that was isolated from bovine muzzle desmosomes, stained a polypeptide band which co-migrated with PF antigen. Furthermore, when proteins from extracts of normal human epidermis were electrophoresed in two dimensions (isoelectric focusing, then SDS-PAGE) before transfer to nitrocellulose for immunoperoxidase staining, PF antibodies and antibodies to DGI stained identical spots. Finally, PF sera as well as PF IgG that was affinity purified with PF antigen from normal human epidermis, both selectively bound to DGI extracted from bovine muzzle desmosomes. These studies demonstrate that the human autoantibodies from certain patients with PF, a disease of epidermal cell adhesion, are directed against a desmosomal core protein.

Distinction between epidermal antigens binding pemphigus vulgaris and pemphigus foliaceus autoantibodies

Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are autoimmune blistering diseases in which antibodies develop to the cell surface of epidermal cells. In this study we sought to determine the antigenic specificity of antibodies in the sera of patients with PV and PF. Sera from 12 patients with PV were used to immunoprecipitate extracts of cultured human epidermal cells that were radiolabeled with 14C-amino acids. Immunoprecipitates were identified by SDS polyacrylamide gel electrophoresis (PAGE) and fluorography. All 12 PV sera precipitated a protein which, when reduced, displayed chains of 130,000 and 80,000 mol wt on SDS-PAGE. Electrophoresis under nonreducing conditions identified a 210,000-mol wt molecule, which was presumably formed by disulfide crosslinking of the 130,000 and 80,000-mol wt chains. Immunoprecipitates of epidermal cell extracts that were labeled with 14C-glucosamine indicated that the 130,000-mol wt chain. Seven of eight PF sera, which were run concurrently with the PV sera in this immunoprecipitation assay, did not precipitate this glycoprotein, nor did they specifically precipitate any protein. To determine if a specific molecule which reacted with antibodies in PF sera could be identified, we used immunoblot analysis of extracts of normal human epidermis. The proteins in these extracts were reduced, separated by SDS-PAGE, and electrophoretically transferred to nitrocellulose sheets or to 2-aminophenylthioether paper. Immunoperoxidase staining of the transferred proteins with PF sera indicated that four of eight PF sera contained antibodies that stained a protein band of 160,000 mol wt. Indirect immunofluorescence, using normal human skin as the substrate, indicated that IgG that was eluted from this protein band stained the epidermis in a cell surface pattern. PV sera did not specifically recognize any bands by immunoblot analysis. Immunoblots performed with PV antigen that was immunoprecipitated from cell culture extracts suggested that, once denatured for SDS-PAGE, PV antigen is no longer immunoreactive. Taken together, these data indicate that: autoantibodies contained in PV sera from various patients have a unique molecular specificity; autoantibodies from most PF sera have a specificity different from that of PV autoantibodies; and autoantibodies from various PF patients may not have identical antigenic specificities. These differences in antigenic specificity between PV and PF sera may account for the clinical and histologic differences between these diseases.

Diagnosis of bullous disease and studies in the pathogenesis of blister formation using immunopathological techniques

Several skin diseases may present as vesicles or bullae. Immunofluorescent studies are very helpful in differentiating the various disease entities. Familiarity with the procedure and the various kinds of patterns that are specific and non-specific is essential for the practicing dermatologist. Immunofluorescent patterns are particularly helpful in differentiating pemphigus, bullous pemphigoid, cicatrical pemphigoid, herpes gestationis, dermatitis herpetiformis, linear IgA dermatosis and porphyria. Immunofluorescent studies of the skin and sera of these patients were vital to an understanding their pathogenesis. Immunoelectron microscopy has further helped in delineating the exact sites of immunoglobulin deposition, and, thus, identifying the location of the antigens. In pemphigus, studies at the molecular level reveal that the basic pathological process is mediated by an anti-cellular cement substance antibody. The binding of this antibody at the cell surface level results in a process that is seen at the light microscopy level in the form of acantholysis. In bullous pemphigoid cells may play an important role. It appears that the mast cell, eosinophil, and the lymphocyte in harmony with the polymorphonuclear leucocyte work together to bring about an enzymatic degradation of the basement membrane. The specific role of the anti-basement membrane zone antibody is also under current study. With advances in molecular immunology, especially monoclonal antibodies and gene technology, it is hoped that these cellular and molecular interactions will be better understood and further defined.

Human autoantibodies against desmosomes: possible causative factors in pemphigus

Pemphigus is a human disease that causes extensive blistering of the skin. This blistering is related to a loss of epidermal cell cohesion and is accompanied by circulating autoantibodies that stain epidermal cell surfaces, as shown by immunofluorescence microscopy. One of the major components involved in epidermal cell cohesion is the desmosome. The pathological changes that accompany pemphigus led us to determine whether the autoantibodies are specific for desmosomes. Incubation of cultured mouse keratinocytes in medium containing pemphigus antiserum leads to cell separation at cell-cell contact sites, which possess desmosomes. Tissue sections of mouse skin processed for indirect immunofluorescence, using pemphigus antiserum or a rabbit antiserum directed against components of desmosomes, show similar punctate cell-surface staining patterns within the epidermis. Cultured mouse keratinocytes possessing well-defined intermediate filament bundles (tonofilaments) and desmosomes were processed for double indirect immunofluorescence, using a monoclonal antibody directed against mouse skin keratin and either pemphigus antiserum or the desmosome antiserum. The keratinocytes exhibit a complex system of keratin-containing tonofilaments. Tonofilaments in contacting cells are separated by thin dark bands at the cell surface, which correspond precisely to desmosomal plaques seen by phase-contrast microscopy. These bands specifically stain with both pemphigus antiserum and the desmosome antiserum. Double indirect immunofluorescence of the cultured mouse keratinocytes, using pemphigus antiserum and the desmosome antiserum, reveals that the pemphigus autoantibodies stain the same areas of cell-cell contact as the desmosome antibodies. Our evidence supports the idea that pemphigus blisters form, at least in part, from a specific antibody-induced disruption of desmosomes in the epidermis.

Production of blister in normal human skin in vitro by blister fluids from epidermolysis bullosa

Pathogenic mechanisms involved in the blister formation of epidermolysis bullosa (EB) are not clearly understood at present. In this paper, we attempted to produce experimental blistering in vitro similar to the histologic picture of EB simplex (EBS) and recessive dystrophic EB (RDEB). It was demonstrated by light and electron microscopy that the medium containing fresh blister fluids from the patients with EBS or RDEB could produce similar histologic features in normal human skin (in vitro) to those of the skin lesions of patients (in vivo). This observation may open new avenues of approach to studying these diseases.

Epidermolysis bullosa simplex blister fluid induces an intra-epidermal blister in cultured normal skin

Organ cultures of normal human skin incubated with blister fluid from a patient with epidermolysis bullosa simplex (EBS) produced a clean intra-epidermal blister with histology similar to that of an EBS blister.

Specificity and inhibition of the epidermal cell detachment induced by pemphigus IgG in vitro

IgG isolated from sera of patients with pemphigus vulgaris (PV) has been shown to induce cell detachment when added to primary epidermal cell cultures (PECC). We studied the specificity of this phenomenon. IgG fractions were purified from the sera of five patients with PV and control IgG fractions from the sera of normal donors and patients with bullous pemphigoid (BP), systemic lupus erythematosus (SLE), and anti-AB blood group sera (anti-AB). IgG fractions were added to PECC either at initial plating (0 hours), at media change (48 hours), or sequentially at both times, and cell detachment was quantitated at 72 and 96 hours. Significant cell detachment occurred only when PV IgG was added to the growth media sequentially at 0 and 48 hours (p = 0.001), and this effect was dose-dependent for either dose. Substitution of an unrelated IgG (BP, SLE, or anti-AB) at either time points reduced cell detachment to near control values. Furthermore, cell detachment was inhibited by the addition of the proteinase inhibitors alpha 2 macroglobulin (70% inhibition of detachment), aprotinin (63% inhibition), soybean and lima bean trypsin inhibitor (62 and 64%, respectively), and pepstatin (49%), but not by the inhibitors chymostatin, leupeptin, or antipain. These data confirm that PV IgG induces increased cell detachment in PECC and shows that this effect is specific for PV IgG, is dose-dependent, and may be inhibited by certain proteinase inhibitors.

Desmosomal antigens are not recognized by the majority of pemphigus autoimmune sera

Sera from 7 patients with pemphigus vulgaris and both mouse and rabbit antisera against bovine epidermal desmosomes contained antibodies that bound to cell surface components of the spinous layer of bovine epidermis. The antidesmosomal sera showed significant binding to purified desmosomal proteins in an enzyme-linked immunosorbent assay (ELISA). Two of 7 pemphigus sera bound to desmosomal protein-coated microtiter plates at low dilution titers. Two of 6 normal human sera also bound to desmosomal protein-coated microtiter plates at titers comparable to those of the pemphigus sera. Indirect immunofluorescent labeling of frozen sections of monkey esophagus revealed striking differences in the distribution of pemphigus antigens and desmosomal constituents. Pemphigus antisera produced rather uniform fluorescence around the borders of spinous cells of the esophageal epithelium, while anti-desmosomal antibodies bound in a punctate pattern. Anti-desmosomal antibodies labeled cells of the basal layer in a strongly punctate pattern. Only 1 pemphigus serum appreciably labeled basal cells. Two of 3 anti-desmosomal antisera bound avidly in the upper differentiating layers of the epithelium. Pemphigus antibodies did not. Pemphigus sera that reacted with desmosomal proteins in ELISA were absorbed by affinity chromatography on immobilized desmosomal proteins. This treatment did not alter the immunofluorescent labeling patterns produced by these sera. From these results we conclude that the pemphigus autoantibodies studied here bind to epithelial cell surface antigens which are distinguishable from the structural components of desmosomes.

Anti-cell surface pemphigus autoantibody stimulates plasminogen activator activity of human epidermal cells. A mechanism for the loss of epidermal cohesion and blister formation

Binding of anti-cell surface pemphigus autoantibodies to cultured human epidermal cells stimulates synthesis and secretion of plasminogen activator (PA). Increases in PA activity were detected within 6 h of the addition of IgG and stimulation was dependent upon IgG concentration. Stimulation of PA activity was inhibited by cycloheximide, which indicates that synthesis of protein was necessary. Pharmacological doses of dexamethasone also prevented IgG-induced stimulation of PA. Electrophoretic profiles of PA secreted by cultured human epidermal cells in the presence or absence of pemphigus IgG were similar. The majority of the PA activity comigrated with the higher-molecular-weight species of human urokinase (approximately 55,000). Explants of normal human skin incubated with pemphigus vulgaris IgG displayed loss of epidermal cohesion similar to that observed in patient biopsies. The histologic changes were potentiated by the inclusion of human plasminogen. Loss of epidermal cohesion in normal skin explants incubated with pemphigus foliaceous IgG was dependent upon the addition of plasminogen and was inhibited by aprotinin or lima bean trypsin inhibitor, which indicated that plasmin is the active enzyme in producing acantholysis. These data support the hypothesis that stimulation of PA by the anti-cell surface autoantibodies of pemphigus results in a localized increase in plasmin, which through proteolysis produces the loss of epidermal cohesion characteristic of pemphigus.

Autodegradation of 125I-labeled human epidermal cell surface proteins

Triton X-100 extracts of cultured human epidermal cells exhibited proteolytic activity as measured by the hydrolysis of [3H]-casein at neutral pH. The majority of endogenous proteolytic activity was inhibited by parahydroxy mercuribenzoate and by mersalyl acid, indicating the enzyme(s) was a thiol class proteinase(s). Crude Triton X-100 extracts were prepared from epidermal cells following labeling of proteins with 125I. Autodegradation of labeled proteins at 37 degrees C was detected as early as 1 hr and reached a plateau level by 4 hr. Degradation was inhibited by thiol class proteinase inhibitors. Among the detergent-solubilized radiolabeled proteins a polypeptide chain of Mr 155,000 was particularly sensitive to degradation by endogenous thiol proteinase(s).

The pathogenic mechanisms of blister formation in bullous pemphigoid

Normal human skin was cultured with sera, IgG fractions, and blister fluids (BF) from patients with bullous pemphigoid. Antibody binding (IgG) was observed by immunofluorescence techniques at the dermal-epidermal junction of all skin explants culture with sera, IgG fractions, and BF. Dermal-epidermal separation was observed only in the skin explants cultured with BF. Dermal-epidermal separation was observed in 19 out of 20 explants cultured with BF obtained from fresh bullae. In addition, dermal-epidermal separation can be produced in vivo 6 hr after the injection of BF into the dorsal skin of Hartley guinea pigs. Dermal-epidermal separation was not observed in skin explants cultured with heat-inactivated (56 degrees, C 30 min) BF, although antibody binding was observed. In addition, dermal-epidermal separation did not occur when the BF were preincubated with rabbit antihuman C1, C3, C4, and C5 antibodies. These observations suggested that both antibody and complement were essential for the production of dermal-epidermal separation. Since patient sera failed to produce dermal-epidermal separation, other factor(s) present in BF but absent from serum might be necessary for the production of dermal-epidermal separation. The addition of the proteinase inhibitors, pepstatin, EDTA, and soy bean trypsin inhibitor, did not inhibit the formation of dermal-epidermal separation. In contrast, the presence of alpha 2-macroglobulin inhibited dermal-epidermal separation.

Pemphigus antibodies identify a cell surface glycoprotein synthesized by human and mouse keratinocytes

Pemphigus is an antibody-mediated autoimmune skin disease in which loss of cell-to-cell contacts in the epidermis results in blister formation. Patients with pemphigus develop antibodies that bind to the keratinocyte cell surface, the site of primary pathology. The purpose of this study was to characterize the antigen(s) to which pemphigus antibodies bind. Because we could detect pemphigus antigen by indirect immunofluorescence on the surface of multiply-passaged cells in cultures of both a spontaneously transformed mouse keratinocyte cell line (Pam) and normal human epidermal cells, we used these cells as a source of antigen. In order to demonstrate biosynthesis of antigen and to characterize the antigen(s), we radiolabeled cell cultures with [(14)C]glucosamine or d-[2-(3)H]mannose and used different pemphigus sera to immunoprecipitate antigen from nonionic detergent extracts of these labeled cells. Specifically precipitated radiolabeled molecules were identified using sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) and fluorography. Sera from five of seven pemphigus patients specifically precipitated (from extracts of both Pam cells and human epidermal cells) a molecule that, when reduced, was approximately 130 kD, whereas seven normal human sera and two pemphigoid sera did not precipitate this molecule. The findings that (a) these precipitated molecules comigrated on SDS-PAGE and that (b) the 130-kD molecule could no longer be precipitated from cell extracts that had been previously reacted with a pemphigus serum, indicate that reactive pemphigus sera bind the same molecule. The molecule was not detected in the culture medium of these cells. This finding, along with the cell surface immunofluorescence pattern, suggests that the antigen is bound to the cell surface. Cultured mouse and human fibroblasts do not synthesize the antigen. The antigen contains protein because it was degraded by V8 protease and chymotrypsin, and it could also be labeled with [(14)C]amino acids. It is probably not a sulfated proteoglycan because it did not label with (35)SO(4). Taken together, these data indicate that some, but not all, pemphigus sera bind a specific cell surface glycoprotein that is synthesized by keratinocytes.

Induction of pemphigus in neonatal mice by passive transfer of IgG from patients with the disease

We examined the role of circulating autoantibodies in the pathogenesis of pemphigus vulgaris by passively transferring IgG fractions from five patients with pemphigus vulgaris into neonatal Balb/c mice, in doses of 1.5 to 16 mg per gram of body weight per day. Cutaneous blisters and erosions with the histologic, ultrastructural, and immunofluorescence features of pemphigus occurred in 39 to 55 mice given intraperitoneal injections of IgG from patients with pemphigus and in none of 58 control mice given normal human IgG. IgG fractions with high titers of pemphigus antibodies were most effective in inducing disease, and this effect was dose dependent. Titers of circulating IgG in mouse serum closely correlated with the extent of disease induced (P less than 0.002). This study strongly supports the proposed role of pemphigus autoantibodies in the pathogenesis of pemphigus vulgaris in human beings and demonstrates that pemphigus can be passively transferred to laboratory animals.

Mechanism of lesion production in pemphigus and pemphigoid

Current evidence strongly supports the theory that the lesions of pemphigus are due to binding of pemphigus antibody to an antigen in or near the epidermal cell membrane, which causes a release of at least one enzyme which results in dissolution of the intercellular attachments and acantholysis. Similarly, strong evidence supports the hypothesis that pemphigoid blisters are due to binding of antibody at the basement membrane, followed by activation of complement and release of anaphylatoxins which activate tissue mast cells to release eosinophil chemotactic factor. These eosinophils then release tissue-destructive enzymes and reactive oxygen intermediates directly onto the basement membrane zone, with loss of dermoepidermal adherence and formation of blisters.

Antibody-induced proteinase activation: a proposed mechanism for pemphigus

The current state of understanding of pemphigus includes the following: 1. Pemphigus is an autoimmune disease. In all variants a circulating autoantibody is found which binds to epidermal cells. In vivo antibody may be found deposited in the epidermis of patients. 2. The autoantibody levels generally correlate with disease activity indicating a relationship between antibody and clinical disease. 3. Although complement components are found in lesional skin, complement does not appear to be necessary for dissolution of the epidermal cement substance. 4. The treatment of pemphigus with corticosteroids has drastically reduced mortality rates. 5. Three different groups have presented results in two different experimental systems which indicate that subsequent to binding of pemphigus antibody to epidermal cells a proteinase is activated. This proteinase(s) degrades the intercellular cement substance of epidermis which results in loss of cellular adhesion and acantholysis. There are numerous questions still remaining. What is the nature of the proteinase(s) and the surface protein(s) it cleaves? Does the binding of pemphigus antibody to the cell surface induce enzyme synthesis, specific enzyme activation, or generalized lysosomal secretion? The answers to these questions will have broad biologic relevance since they may elucidate the role of anticell surface antibodies in disease states.