Bullous Pemphigoid Blister Fluid Research Articles

27005 Proteomics analysis of blister fluid from patients with bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune disorder characterized by the development of pruritic lesions and/or blisters. Previous research analyzing the blister fluid from BP patients shows proinflammatory cytokines/chemokines, typically at a higher concentration than in serum. We explored the blister fluid proteome of 8 patients with BP to assess the intraepidermal microenvironment. TMT-labeled proteomics identified a total of 339 proteins. Using gene names for these proteins, Gene Ontology was used for analysis, demonstrating marked enrichment of exocytosis pathways, immune response, and platelet degranulation. In light of an abundance of exosomal proteins, we depleted exosomes using ultracentrifugation, to determine which proteins were exosome-bound and increase sensitivity for soluble proteins. Differential protein analysis was performed between these samples. Notable findings in BP blister fluid proteome include eosinophil degranulation proteins (EPX, ECP, EDN, MBP) at greater abundance than neutrophil-related proteins (neutrophil gelatinase-associated lipocalin, myeloperoxidase, neutrophil defensin 3). We identified IgM/IgA/IgG/IgE, 16 SERPIN-family protease inhibitors, heat shock proteins (HSP90AA1, HSP90AB1, HSP90B1, HSPA1b, HSPA5, HSPA8, HSPB1), neutrophil inflammasome mediators (lipopolysaccharide-binding protein, CD14), clotting factors (factors 2,5,9,10-13 (A1,B), VWF, tissue factor, fibrinogen), and complement mediators (C1-9). Neutrophil elastase, MMP9, ECP, and eosinophil derived neurotoxin appear to be bound or contained in fluid exosomes. The results demonstrate the players that may be responsible for the inflammatory/proteolytic environment in BP. Exosomal proteins appear to be derived from eosinophils, keratinocytes, and neutrophils, suggesting that exosomes likely contribute to the propagation of the inflammatory response. The extent of clotting factor presence in fluid confirms prior studies identifying coagulation activation in BP.

Characterizing the proteome of bullous pemphigoid blister fluid utilizing tandem mass tag labeling coupled with LC-MS/MS.

Bullous pemphigoid is an autoimmune blistering disease caused by autoantibodies against components of the cutaneous basement membrane zone. Autoantibodies lead to complement-dependent and -independent inflammation and blistering. Blister fluid is a valuable biologic resource, as it provides insight into both systemic and local microenvironment responses. Here, we utilized liquid chromatography with tandem mass spectrometry to characterize the bullous pemphigoid blister fluid proteome. We then depleted exosomes to better understand the exosomal versus non-exosomal proteome. We identified 339 proteins in the blister fluid of bullous pemphigoid patients. Gene ontology demonstrated enrichment of several key biologic processes including innate immune response, neutrophil degranulation, platelet degranulation, and complement activation. Exosome depletion resulted in a significant decrease in normalized reporter intensities of 192 proteins, consistent with our observation of a large number of exosomal proteins found in the blister fluid. We then compared the bullous pemphigoid blister fluid proteome to prior proteomic datasets in suction blister fluid, snake bites, and thermal burns, identifying 76 proteins unique to bullous pemphigoid. These include major basic protein, eosinophil peroxidase, galectin-10, and the immunoglobulin epsilon heavy constant region, consistent with tissue eosinophilia. We lastly validated several previously reported blister fluid exosomal components. Blister fluid in bullous pemphigoid contains a mixture of numerous biologic processes. While many of these processes are shared with blistering from alternative causes, we have identified several notable features unique to bullous pemphigoid.

Distinct compartmentalization of immune cells and mediators characterizes bullous pemphigoid disease.

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by recruitment of leucocytes into skin and release of damaging enzymes, resulting in epidermal detachment and blister formation. To better understand the role of leukotriene B4 (LTB4) and other inflammatory factors in BP pathophysiology, we conducted microscopic and immunohistochemical analyses of preserved skin biopsy sections and conducted flow cytometry and ELISA analyses of matched blood and blister fluid from BP patients. Neutrophils predominated in BP blister fluid, which also contained monocytes/macrophages and T cells, but few to no eosinophils and B cells. In contrast, BP skin histology showed a different pattern, with abundant neutrophils but eosinophils being the predominant immune cell type. LTB4 pathway and neutrophil activation markers were prevalent in BP skin lesions and strongly associated with perivascular neutrophils. Blister fluid neutrophils, monocytes/macrophages and eosinophils all exhibited increased surface expression of leukotriene A4 hydrolase and neutrophil elastase (P=.002 for both). Blister fluid was also enriched in interleukins (IL)-1α, IL-1β, IL-8, IL-10, IL-18, monocyte colony-stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF). Our findings suggest differential leucocyte recruitment from blood into dermis and from dermis into blister, which correlates with disease activity, and presents potential new treatment opportunities for BP.

Characteristic Pattern of IL-17RA, IL-17RB, and IL-17RC in Monocytes/Macrophages and Mast Cells From Patients With Bullous Pemphigoid.

Inflammation is largely implicated in bullous pemphigoid (BP), the most frequent skin auto-immune blistering disease. IL-17, essentially IL-17A/F, has been involved in blister formation through regulation of protease production, and its specific serum profile within BP was related to disease outcome. However, relationships between IL-17 family ligands and receptors are quite complex with six different IL-17 isoforms, and five different receptors. We here aimed at clarifying the contribution of the IL-17 axis in BP by characterizing not only the expression of IL-17 receptor (IL-17R) members within immune cells isolated from BP patients (PMNs, n = 9; T-lymphocytes, n = 10; and monocytes, n = 10) but also the expression of IL-17 isoforms in sera (n = 83), and blister fluid (n = 31) of BP patients. We showed that at diagnosis, IL-17RA and IL-17RC expression were significantly increased in monocytes isolated from BP patients as compared to those from control subjects (p = 0.006 and p = 0.016, respectively). Notably, both IL-17RA and IL-17RC mRNA expression remained elevated in BP monocytes at time of relapse. We further demonstrated a significant increase of all IL-17 isoforms tested in BP blister fluid compared with BP serum (IL-17A, p < 0.0001; IL-17A/F, p < 0.0001; IL-17B, p = 0.0023; IL-17C, p = 0.0022; IL-17E, p < 0.0001). Among all, IL-17B was the only cytokine for which a significant decreased concentration within blister fluid was observed in BP patients with severe disease compared to patients with moderate disease (p = 0.012). We further evidenced a significant negative correlation between IL-17B levels and blister/erosion BPDAI subscore (r = −0.52, p = 0.003). We finally identified mast cells as a potential target of IL-17B in lesional skin of BP patients. In conclusion, we showed here that IL-17RA and IL-17RC expression in monocyte was associated with disease activity and evidenced in situ a negative correlation between BP disease activity and IL-17B, whose effects could be mediated by IL-17RB expressed by mast cell in BP lesional skin.

Semaphorin 4D from CD15+ Granulocytes via ADAM10-Induced Cleavage Contributes to Antibody Production in Bullous Pemphigoid

Autoreactive B-cell activation and antibody production are critical events for the development of bullous pemphigoid (BP). However, the mechanism that is involved in the modulation of B-cell activation and autoantibody generation has not been fully understood. Semaphorin 4D (Sema4D, or CD100) plays important roles in immune regulation related to B cells, but its implications in BP remain obscure. The aim of our study was to characterize Sema4D and the underlying mechanism contributing to the autoimmune features of BP. We found that soluble Sema4D (sSema4D) levels were elevated and correlated with disease severity and activity in serum and blister fluids from patients with BP. Additionally, Sema4D-expressing cells accumulated in subepidermal blisters of BP lesions. In patient-derived peripheral blood mononuclear cells, by promoting the differentiation of B cells into plasmablasts, sSema4D boosted anti-BP180/anti-BP230 antibody production in a time- and dose-dependent manner, which may be attributed to CD72-mediated activation of Akt/NF-κB phosphorylated (p-)65/ERK cascades in B cells. We determined that a disintegrin and metalloproteinase 10 is a proteolytic enzyme for the cleavage of sSema4D from CD15+ granulocytes instead of T cells, which is probably responsible for the high concentration of sSema4D in BP blister fluid and serum. These findings suggest that Sema4D is a crucial participant in BP pathogenesis.

The Leukotriene B4 and its Receptor BLT1 Act as Critical Drivers of Neutrophil Recruitment in Murine Bullous Pemphigoid-Like Epidermolysis Bullosa Acquisita

Recruitment of neutrophils and eosinophils into the skin is a hallmark of pemphigoid diseases. The molecular cues regulating granulocyte recruitment into the skin and the individual contributions of neutrophils and eosinophils to pemphigoid diseases are, however, poorly understood. The lipid mediator leukotriene B4 (LTB4) is a potent granulocyte chemoattractant and is abundant in the skin blister fluid of bullous pemphigoid (BP) patients, but its pathogenic significance is unknown. Using mouse models of BP-like epidermolysis bullosa acquisita and of BP, we show that LTB4 and its receptor BLT1 act as critical drivers of neutrophil entry into the skin upon antibody deposition at the dermal-epidermal junction. Mice deficient in 5-lipoxygenase, a key enzyme in LTB4 biosynthesis, or in BLT1 exhibited dramatic resistance to neutrophil recruitment and, consequently, skin inflammation. Accordingly, liquid chromatography-mass spectrometry, used to comprehensively profile lipid mediator generation in the first 48 hours after antibody deposition, showed a pronounced parallel increase in LTB4 and in neutrophils in the skin. Subsequent mechanistic studies in BP-like epidermolysis bullosa acquisita uncovered that neutrophils are necessary for skin inflammation, whereas eosinophils are dispensable, thus identifying neutrophils as major culprits of blister formation. Our results highlight LTB4/BLT1 as absolutely critical drivers of murine pemphigoid disease-like skin inflammation.

Increased Activity and Apoptosis of Eosinophils in Blister Fluids, Skin and Peripheral Blood of Patients with Bullous Pemphigoid.

Bullous pemphigoid (BP) is an autoimmune blistering skin disease that is more common in elderly individuals. The aim of this study was to determine the functional activity of eosinophils in patients with BP compared with healthy donors. Blood, skin and blister-derived eosinophils were strongly activated in patients with BP, seen by increased surface expression of CD69 compared with controls. CD11b was also increased in BP blood eosinophils, which may explain the striking accumulation of eosinophils in BP (1×106 per ml blister fluid). Furthermore, CCL26 was expressed by activated eosinophils in BP skin and in blister fluid. BP eosinophils also released IL-6, IL-8 and IL-1α in BP blister fluids. Apoptosis in cultivated BP eosinophils was increased and accompanied by enhanced surface externalization of CD95. Caspase 3 positive eosinophils in lesional BP skin and blister fluid also showed the initiation of apoptosis. These results reveal novel pathophysiological aspects of BP, with a strong activation pattern and increased apoptosis of eosinophils in the peripheral blood, skin and blister fluids.

CCL18 is expressed in patients with bullous pemphigoid and parallels disease course

The autoimmune skin disease bullous pemphigoid (BP) is characterized by subepidermal blister formation and a strong dermal infiltrate of mononuclear cells and eosinophils as well as a T-helper (Th) 2-dominated cytokine milieu. CCL18 is a chemokine, with unknown receptor counterpart, frequently associated with inflammatory Th2-type responses. The study was performed to investigate an association of CCL18 with BP. CCL18 was determined by enzyme-linked immunosorbent assay in serum and blister fluid of patients with BP, pemphigus vulgaris and healthy individuals. In vitro chemotaxis assays were performed to demonstrate migration of peripheral blood mononuclear cells to BP blister fluid. Immunohistology and immunofluorescence staining were used to evaluate CCL18 expression in skin. We have found that the levels of CCL18 in sera from patients with BP are 84% higher than those normally observed in healthy individuals. In addition, blister fluid of patients with BP is extremely rich in CCL18, reaching concentrations which are fivefold and sevenfold higher than those found in the sera of patients with BP and healthy individuals, respectively. Using immunofluorescence techniques we identified Langerhans cells, antigen-presenting cells of the dermis and eosinophils as producers of CCL18 in BP skin. We studied the possibility of using CCL18 expression as a biomarker linked to BP by monitoring the serum levels of CCL18 and the disease course of nine patients with BP over a maximum period of 54 months. In this study, CCL18 levels correlated with the disease course in most of the patients. Our data implicate CCL18 as a functionally relevant chemokine in BP, mediating recruitment of blood mononuclear cells into the hallmark infiltrated skin lesion. The high correlation of CCL18 expression and BP disease suggests that blood levels of this chemokine can be used as an easy method to monitor disease progression and/or efficacy of therapeutic interventions.

High levels of interleukin-8, soluble CD4 and soluble CD8 in bullous pemphigoid blister fluid. The relationship between local cytokine production and lesional T-cell activities.

Bullous pemphigoid (BP) is an inflammatory subepidermal blistering disease associated with autoantibodies that recognize hemidesmosomal proteins. In addition to autoantibodies, the cell-mediated immune reaction is considered to play an important part in blister formation. Objectives To investigate some T-cell activation markers and inflammatory cytokines in the blister fluid and sera of patients with BP. We measured soluble CD4 (sCD4) and soluble CD8 (sCD8), which have been, respectively, associated with CD4 and CD8 T-cell activation. Enzyme-linked immunosorbent assays were also used to quantify the production of the leucocyte chemoattractant interleukin (IL) -8 and of the cytokines IL-1alpha, IL-1beta, IL-6, IL-10 and tumour necrosis factor-alpha in the blister fluid and sera of 11 patients with BP. The mean +/- SD level of sCD4 in patients' blisters (42.4 +/- 25.0 units mL-1) was significantly elevated (P < 0.005) compared with that in their sera (11.2 +/- 8.9) and that in the suction blisters of 10 healthy people (11.4 +/- 5.4; P < 0.005). Mean +/- SD IL-8 concentrations in BP blisters (4683.6 +/- 3878.1 pg mL-1) were much higher than those in their sera (17.1 +/- 18.9; P < 0.001), and were very significantly elevated (P < 0.005) in comparison with those in suction blisters of healthy persons (512 +/- 292). sCD4 levels in BP blisters were inversely related to IL-10 levels (P = 0. 03, r2 = 0.85), IL-8 levels were positively related to sCD8 levels (P = 0.01, r2 = 0.54), and IL-1beta levels were positively related to sCD8 concentrations (P < 0.005, r2 = 0.65). The correlations suggest that there is a delicately orchestrated network of cytokines and cell-mediated immunity operating in BP blisters.

Elevated levels of eotaxin and interleukin-5 in blister fluid of bullous pemphigoid: correlation with tissue eosinophilia.

Bullous pemphigoid (BP) often provokes blood and tissue eosinophilia, which suggests that some chemoattractants modulate the eosinophil infiltration in BP. Eotaxin, a CC chemokine, strongly attracts eosinophils, and interleukin (IL)-5 induces eosinophil differentiation, proliferation and colony formation in vitro. To examine the correlation between levels of eotaxin and IL-5 and the number of lesional eosinophils, and the expression of eotaxin in BP lesions. In this study we measured eotaxin and IL-5 levels in blister fluid of BP by enzyme-linked immunosorbent assay. We also examined the expression of eotaxin in BP lesions by immunohistochemistry. Both eotaxin and IL-5 were detected at high levels in BP blister fluid. Blister fluid eotaxin, but not IL-5 levels, correlated significantly with the number of dermal infiltrating eosinophils. By immunohistochemistry, eotaxin was strongly expressed in epidermal keratinocytes around BP blisters. These findings suggest that eotaxin and IL-5 are strongly associated with the tissue eosinophilia of BP. Therapies which aim to inhibit production of eotaxin and IL-5 may improve the inflammation and blister formation in BP.

Gelatinase B-deficient mice are resistant to experimental bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease characterized by deposition of autoantibodies at the basement membrane zone. In an experimental BP model in mice, the subepidermal blistering is mediated by antibodies directed against the hemidesmosomal protein BP180 (collagen XVII, BPAG2), and depends on complement activation and neutrophil infiltration. Gelatinase B is present in BP blister fluid and can cleave BP180. In this study we investigated the role of gelatinase B in the immunopathogenesis of experimental BP using mice containing targeted disruption of the gelatinase B (MMP-9, 92 kD gelatinase) gene. Gelatinase B-deficient mice were resistant to the blistering effect of intracutaneous anti-mBP180 antibodies, although these mice showed deposition of autoantibodies at the basement membrane zone and neutrophil recruitment to the skin comparable to that observed in the control mice. Interleukin 8 given intradermally concomitantly with pathogenic anti-mBP180 elicited a significant neutrophil recruitment into the skin in gelatinase B-deficient mice, but blistering did not occur. However, gelatinase B-deficient mice reconstituted with neutrophils from normal mice developed blistering in response to anti-mBP180 antibodies. These results implicate neutrophil-derived gelatinase B in the pathogenesis of experimental BP and might lead to novel therapeutic strategies for BP.

Cytokine pattern in blister fluid and serum of patients with bullous pemphigoid: relationships with disease intensity.

Few and contrasting data are available in the literature concerning the levels of various cytokines in blister fluid (BF) and in the serum of patients affected with bullous pemphigoid (BP). Using commercially available ELISA kits, this study reports the levels of 11 cytokines detected both in BF and sera of 15 BP patients and compares them with those of 15 control subjects' sera. Generally, no significant differences were observed in BP and control sera. In contrast, interleukin (IL) 1 beta, IL-2, IL-4, IL-5, IL-6, IL-8, tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) showed increased BF levels as compared with BP sera. Two cytokines, IL-11 and IL-12 did not show significant differences between BP BF and sera, while an opposite behaviour was observed for transforming growth factor beta 1 (TGF-beta 1), whose serum levels were higher than the concentrations in BF. Using the number of lesions of the patients as a possible disease intensity marker, significant correlations were found with the BF levels of IL-1 beta, IL-8, TNF-alpha and, most closely, IL-5. These data may have pathogenetic relevance and suggest the possibility that these biological modulators may be used as a quantitative marker of disease intensity.

Detection of elevated levels of IL-4, IL-6, and IL-10 in blister fluid of bullous pemphigoid

Detection of elevated levels of IL-4, IL-6, and IL-10 in blister fluid of bullous pemphigoid

Detection of elevated levels of IL-4, IL-6, and IL-10 in blister fluid of bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease with autoantibodies directed against antigens associated with hemidesmosomes of basal keratinocytes. In addition to autoantibodies and activated complement, cellular mechanisms are crucial for blister formation in this disease. Mononuclear cells, which are the first cells infiltrating BP lesions, mainly belong to CD3, CD4+ T-helper (Th) cells. Elevated concentrations of IL-2, IFN gamma, TNF beta, and IL-5 have been recently demonstrated in BP blister fluid. In this study, we were interested in levels of other Th-type cytokines, including IL-3, IL-4, IL-6, IL-10, and GM-CSF in blister fluid of BP. Cytokines were determined by ELISA or bioassay. Levels in the blister fluid from ten BP patients were compared with those in serum samples taken at the time of blister puncture and with those in suction blister fluid of ten healthy volunteers. In blister fluid of BP, we found significantly elevated concentrations of IL-4, IL-6, and IL-10 relative to both concurrent serum samples and suction blister fluid from controls. No differences were detected for either IL-3 or GM-CSF. Our results suggest that IL-4, IL-6, and IL-10 are released at the site of blister formation in BP.

Detection of IL-1α, IL-1β and IL-1 receptor antagonist in blister fluid of bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease. In addition to autoantibodies, complement activation and inflammatory cells are necessary for lesion formation. In this study, we investigated the potential involvement of IL-1, secreted by various inflammatory and non-inflammatory cells, in BP lesions. We determined IL-1α IL-1β and IL-1 receptor antagonist in both blister fluid and concurrent serum samples of 10 BP patients by ELISAs. For comparison, we assayed experimentally generated suction blisters from 10 healthy volunteers. IL-1β levels were significantly elevated in BP blisters, whereas levels of IL-1α were decreased relative to those in controls. In concurrent serum samples, no IL-1α or IL-1β were detected in patients or controls. Levels of IL-1 receptor antagonist were significantly higher in BP blisters in relation to both concurrent sera and suction blisters. Our data indicate the release of IL-1β, IL-1 receptor antagonist, and to a lesser extent, of IL-1α, at the site of blister formation in BP and support the notion that cell-mediated immune mechanisms may contribute to blister formation in this disease.

92-kD gelatinase is produced by eosinophils at the site of blister formation in bullous pemphigoid and cleaves the extracellular domain of recombinant 180-kD bullous pemphigoid autoantigen.

Eosinophils are prominent in bullous pemphigoid (BP), and proteases secreted from these and other inflammatory cells may induce disruption of the basement membrane. We used in situ hybridization and immunohistochemistry to localize the sites of 92-kD gelatinase expression in BP lesions. In all samples (20/20), a strong signal for gelatinase mRNA was detected only in eosinophils and was most pronounced where these cells accumulated at the floor of forming blisters. No other cells were positive for enzyme mRNA. Both eosinophils and neutrophils, however, contained immunoreactive 92-kD gelatinase indicating that active expression occurred only in eosinophils. Degranulated eosinophils were also seen near blisters, and as demonstrated by gelatin zymography, immunoblotting, and ELISA, 92-kD gelatinase protein was prominent in BP blister fluid. No other gelatinolytic activity was specifically detected in BP fluid, and only small amounts of 92-kD gelatinase were present in suction blister fluids. As demonstrated in vitro, 92-kD gelatinase cleaved the extracellular, collagenous domain of recombinant 180-kD BP autoantigen (BP180, BPAG2, HD4, type XVII collagen), a transmembrane molecule of the epidermal hemidesmosome. Our results suggest that production and release 92-kD gelatinase by eosinophils contributes significantly to tissue damage in BP.

The autoimmune blistering skin disease bullous pemphigoid. The presence of plasmin/alpha 2-antiplasmin complexes in skin blister fluid indicates plasmin generation in lesional skin.

Plasminogen activators produced locally in the skin have been implicated in blistering skin diseases. To explore whether plasminogen activators convert their substrate plasminogen into plasmin locally in the lesional skin we have analyzed the autoimmune blistering skin disease bullous pemphigoid. Enzyme activity was detected in bullous pemphigoid skin blister fluid by using a low molecular weight chromogenic substrate for plasmin. Enzyme activity was detected neither in suction blister fluid raised on normal skin nor in normal plasma. Immunoprecipitation or fractionation by molecular sieve chromatography of bullous pemphigoid skin blister fluid followed by testing in immunoassays disclosed putative plasmin/alpha 2-macroglobulin complexes and plasmin/alpha 2-antiplasmin complexes. Enzyme activity detected in bullous pemphigoid skin blister fluid by the low molecular weight chromogenic peptide assay was ascribed to the putative plasmin pha 2-macroglobulin complexes. Because formation of plasmin-inhibitor complexes requires the active plasmin, our findings indicate previous activation of plasminogen to plasmin in skin lesions. There was no evidence for free plasmin (i.e., plasmin not complexed to inhibitors) in bullous pemphigoid blister fluid, suction blister fluid, or plasma.

Alteration in the density, morphology, and biological properties of eosinophils produced by bullous pemphigoid blister fluid

Bullous pemphigoid blister fluid (BP-BF) was examined for its effects on the density, morphology, and biological properties of eosinophils. Normodense eosinophils (NEo) were prepared from guinea pig peritoneal exudates by Nycodenz density gradient centrifugation. After culturing with BP-BF, NEo were converted into hypodense eosinophils (HEo) in a time-dependent manner. HEo were morphologically different from NEo in that HEo had spheroidal granules each with a lytic crystalloid core and a significantly increased cell volume. These HEo showed an enhanced antibody- and/or complement-dependent helminthotoxic activity to Schistosoma mansoni larvae, amplified chemiluminescence response to opsonized zymosan, and augmented expression of both FcR+ and CR+. These results suggest that BP-BF contains an activity that may not only induce an eosinophil hypodensity as a consequence of increasing cell volume, but simultaneously enhance an eosinophil cytotoxic potential through augmenting cell-surface receptors and receptor-linked oxidative metabolism. In addition, observed tissue accumulation of this activity suggests that eosinophils may be regulated by their phenotypic change in the skin lesions of bullous pemphigoid and be involved in blister formation.

Detection of basement membrane zone antigens and C3 fragments in the blister fluid of bullous pemphigoid.

In polyacrylamide gel gradient electrophoresis, serum and blister fluid of patients with bullous pemphigoid showed a nearly identical protein distribution pattern except for one more concentrated fraction in the blister fluid. This fraction could be isolated by several gel chromatographic steps and then be characterized as a protein with a molecular weight of 240,000 (BFP 240,000) consisting of several subunits. Two of these subunits could be identified as C3 fragments and two other ones as basement membrane zone antigens (BMZ-Ag) by means of a modified Laurell technique. The molecular weight of the BFP 240,000 may be small enough to allow it to penetrate through the vessel wall into the blood circulation where, with the BMZ-antibodies (BMZ-Ag-BMZ-Ab-complexes can be formed. The occurrence of such immune complexes in the serum has been shown in a previous paper.