The complement system in bullous pemphigoid. I. Complement and component levels in sera and blister fluids

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

Insights Into the Pathogenesis of Bullous Pemphigoid: The Role of Complement-Independent Mechanisms

Bullous pemphigoid is an autoimmune blistering disease caused by autoantibodies targeting BP180 and BP230. While deposits of IgG and/or complement along the epidermal basement membrane are typically seen suggesting complement -mediated pathogenesis, several recent lines of evidence point towards complement-independent pathways contributing to tissue damage and subepidermal blister formation. Notable pathways include macropinocytosis of IgG-BP180 complexes resulting in depletion of cellular BP180, direct induction of pro-inflammatory cytokines from keratinocytes, as well as IgE autoantibody- and eosinophil-mediated effects. We review these mechanisms which open new perspectives on novel targeted treatment modalities.

Complement Activation in Autoimmune Bullous Dermatoses: A Comprehensive Review

Autoimmune bullous dermatoses (AIBD) are characterized by circulating autoantibodies that are either directed against epidermal antigens or deposited as immune complexes in the basement membrane zone (BMZ). The complement system (CS) can be activated by autoantibodies, thereby triggering activation of specific complement pathways. Local complement activation induces a pathogenic inflammatory response that eventually results in the formation of a sub- or intraepidermal blister. Deposition of complement components is routinely used as a diagnostic marker for AIBD. Knowledge from different animal models mimicking AIBD and deposition of complement components in human skin biopsies provides more insight into the role of complement in the pathogenesis of the different AIBD. This review outlines the role of the CS in several AIBD including bullous pemphigoid, epidermolysis bullosa acquisita, mucous membrane pemphigoid (MMP), pemphigus, linear IgA-disease, and dermatitis herpetiformis. We also discuss potential therapeutic approaches targeting key complement components, pathways and pathogenic complement-mediated events.

Complement-Activating Capacity of Autoantibodies Correlates With Disease Activity in Bullous Pemphigoid Patients

Background: Bullous pemphigoid is a subepidermal blistering skin disease, associated with autoantibodies to hemidesmosomal proteins, complement activation at the dermal-epidermal junction, and dermal granulocyte infiltration. Clinical and experimental laboratory findings support conflicting hypotheses regarding the role of complement activation for the skin blistering induced by pemphigoid autoantibodies. In-depth studies on the pathogenic relevance of autoimmune complement activation in patients are largely lacking. Therefore, the aim of this study was to investigate the pathogenic relevance of complement activation in patients with bullous pemphigoid. Complement activation by autoantibodies in vivo as measured by the intensity of complement C3 deposits in the patients' skin and ex vivo by the complement-fixation assay in serum was correlated with the clinical disease activity, evaluated by Autoimmune Bullous Skin Disorder Intensity Score (ABSIS) and Bullous Pemphigoid Disease Area Index (BPDAI), as well as, with further immunopathological findings in patients with bullous pemphigoid. Results: Complement-activation capacity of autoantibodies ex vivo, but not deposition of complement in the perilesional skin of patients, correlates with the extent of skin disease (measured by ABSIS and BPDAI) and with levels of autoantibodies. Conclusions: Our study provides for the first time evidence in patients for a pathogenic role of complement activation in bullous pemphigoid and should greatly facilitate the development of novel diagnostic tools and of more specific therapies for complement-dependent autoimmune injury.

Complement Activation in Inflammatory Skin Diseases

The complement system is a fundamental part of the innate immune system, playing a crucial role in host defense against various pathogens, such as bacteria, viruses, and fungi. Activation of complement results in production of several molecules mediating chemotaxis, opsonization, and mast cell degranulation, which can contribute to the elimination of pathogenic organisms and inflammation. Furthermore, the complement system also has regulating properties in inflammatory and immune responses. Complement activity in diseases is rather complex and may involve both aberrant expression of complement and genetic deficiencies of complement components or regulators. The skin represents an active immune organ with complex interactions between cellular components and various mediators. Complement involvement has been associated with several skin diseases, such as psoriasis, lupus erythematosus, cutaneous vasculitis, urticaria, and bullous dermatoses. Several triggers including auto-antibodies and micro-organisms can activate complement, while on the other hand complement deficiencies can contribute to impaired immune complex clearance, leading to disease. This review provides an overview of the role of complement in inflammatory skin diseases and discusses complement factors as potential new targets for therapeutic intervention.

Cobra venom factor: Structure, function, and humanization for therapeutic complement depletion

Cobra venom factor (CVF) is the complement-activating protein in cobra venom. This manuscript reviews the structure and function of CVF, how it interacts with the complement system, the structural and functional homology to complement component C3, and the use of CVF as an experimental tool to decomplement laboratory animals to study the functions of complement in host defense and immune response as well as in the pathogenesis of diseases. This manuscript also reviews the recent progress in using the homology between CVF and C3 to study C3 structure and function, and to develop human C3 derivatives with the complement-depleting function of CVF. These human C3 derivatives represent humanized CVF, and are a conceptually different concept for pharmacological intervention of the complement system, therapeutic complement depletion. The use of humanized CVF for therapeutic complement depletion in several pre-clinical models of human diseases is also reviewed.

The pathophysiology of bullous pemphigoid

Bullous pemphigoid (BP) is a blistering skin disease characterized by an autoimmune response to 2 hemidesmosomal proteins within the dermal-epidermal junction, designated BP180 and BP230. While BP230 localizes intracellularly and associates with the hemidesmosomal plaque, BP180 is a transmembrane glycoprotein with an extracellular domain. Most BP patients have autoantibodies binding to an immunodominant region of BP180, the noncollagenous 16A domain (NC16A), which is located extracellularly close to the transmembrane domain of the protein. Autoreactive T and B cell responses to BP180 have been found in patients with BP. Passive transfer of antibodies to the murine BP180 ectodomain triggers a blistering skin disease in mice that closely mimics human BP. Lesion formation in this animal model depends upon complement activation, mast cell degranulation and accumulation of neutrophils and eosinophils. Patients' autoantibodies to BP180 induce dermal-epidermal separation in cryosections of human skin when co-incubated with leukocytes. The loss of cell-matrix adhesion is mediated by proteinases released by granulocytes. The increased knowledge of the pathophysiology of BP should facilitate the development of novel therapeutic strategies for this disease.

Role of different pathways of the complement cascade in experimental bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies directed against the hemidesmosomal proteins BP180 and BP230 and inflammation. Passive transfer of antibodies to the murine BP180 (mBP180) induces a skin disease that closely resembles human BP. In the present study, we defined the roles of the different complement activation pathways in this model system. Mice deficient in the alternative pathway component factor B (Fb) and injected with pathogenic anti-mBP180 IgG developed delayed and less intense subepidermal blisters. Mice deficient in the classical pathway component complement component 4 (C4) and WT mice pretreated with neutralizing antibody against the first component of the classical pathway, C1q, were resistant to experimental BP. These mice exhibited a significantly reduced level of mast cell degranulation and polymorphonuclear neutrophil (PMN) infiltration in the skin. Intradermal administration of compound 48/80, a mast cell degranulating agent, restored BP disease in C4(-/-) mice. Furthermore, C4(-/-) mice became susceptible to experimental BP after local injection of PMN chemoattractant IL-8 or local reconstitution with PMNs. These findings provide the first direct evidence to our knowledge that complement activation via the classical and alternative pathways is crucial in subepidermal blister formation in experimental BP.

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.

Granulocyte activation in bullous diseases: release of granular proteins in bullous pemphigoid and pemphigus vulgaris

BACKGROUND

Eosinophil and polymorphonuclear granulocytes may be involved in the formation of blisters in bullous dermatoses, particularly bullous pemphigoid.

OBJECTIVE

Our purpose was to evaluate the role of granulocyte activation in the pathogenesis of pemphigus vulgaris and bullous pemphigoid.

METHODS

Levels of eosinophil cationic protein (ECP) and neutrophil-derived myeloperoxidase (MPO) in blister fluid and serum and levels of serum IgE were determined in patients with bullous pemphigoid (n = 12), those with pemphigus vulgaris (n = 9) and healthy volunteers (n = 12).

RESULTS

In blister fluid and serum of patients with bullous pemphigoid, significantly elevated concentrations of ECP, MPO and IgE were detected as compared with controls. In contrast, ECP, MPO, and IgE levels in blister fluid and serum of patients with pemphigus vulgaris did not significantly differ from controls. Moreover, the MPO/ECP ratio in serum of patients with bullous pemphigoid was significantly decreased as compared with controls, whereas the MPO/ECP ratio in pemphigus vulgaris did not differ from controls, indicating a preferential activation of eosinophils in bullous pemphigoid only. In patients with bullous pemphigoid, serum levels of ECP and MPO significantly decreased during immunosuppressive therapy to levels similar to those of controls.

CONCLUSION

Activated granulocytes, releasing their granular contents such as ECP and MPO, may be of importance for blister formation in bullous pemphigoid and may be useful for monitoring disease activity.

Further analyses of epitopes for human monoclonal anti-basement membrane zone antibodies produced by stable human hybridoma cell lines constructed with Epstein-Barr virus transformants

We previously established Epstein-Barr virus (EBV)-transformed bullous pemphigoid (BP) patient lymphoblastoid cell lines, which produced human monoclonal anti-basement membrane zone antibodies. In the present study, we established two independent human-human hybridomas by fusion of these EBV transformants with a human B-cell line. These hybridomas, designated 5E-HY-4B and 10D-HY-8B, were very stable and showed a high yield of monoclonal antibody (MoAb) secretion. Each cell line was tetraploid and showed combined rearranged segments of immunoglobulin heavy-chain gene derived from both an EBV transformant and a parent cell. Immunoblot analysis showed that the 5E-HY-4B MoAb recognized the 230-kDa BP antigen but that the 10D-HY-8B MoAb did not show any reactivity. In contrast, both MoAbs precipitated the 230-kDa BP antigen with immunoprecipitation. These results indicate that the two MoAbs reacted with different epitopes on the 230-kDa BP antigen: a continuous epitope for the 5E-HY-4B MoAb and a conformation-dependent epitope for the 10D-HY-8B MoAb. This speculation was confirmed at the molecular level by the result that the fusion protein produced by a partial cDNA for the 230-kDa mouse BP antigen reacted with the 5E-HY-4B MoAb but not with the 10D-HY-8B MoAb. Furthermore, the study of the reactivity with fusion proteins of a series of deleted clones restricted the epitope for the 5E-HY-4B MoAb within the region with 114 amino acid residues in the C-terminal domain of the 230-kDa BP antigen.

Detection of the 170-kDa bullous pemphigoid antigen by immunoprecipitation

There has been controversy concerning the nature of the bullous pemphigoid (BP) antigen: immunoprecipitation identified BP antigen as a single, unique 230-kDa protein, whereas immunoblot analysis showed multiple antigen molecules, mainly 230- and 170-kDa proteins. In this study, to further characterize the 170-kDa protein, we have examined whether the 170-kDa protein is detected by immunoprecipitation. Extracts of human squamous cell carcinoma cells revealed the 170-kDa protein with immunoblot analysis. Although the conventional immunoprecipitation detected only the 230-kDa protein, some BP sera that detected the 170-kDa protein with immunoblotting also precipitated the 170-kDa protein with our modified immunoprecipitation, in which the cells were extracted with 1% sodium dodecylsulfate (SDS) buffer and reacted with the sera under reduced SDS concentration. The 170-kDa protein-specific BP sera clearly showed hemidesmosomal plaque staining with immunofluorescence of cultured cells. These results indicate that the 170-kDa protein is indeed one of the BP antigens and that the 230- and 170-kDa BP antigens are integrated in different ways in hemidesmosomes.

Bullous and cicatricial pemphigoid

Bullous pemphigoid (BP) and cicatricial pemphigoid are blistering mucocutaneous diseases characterized by detachment of the overlying epithelium from its stroma. IgG and complement components are deposited in all affected tissue at the level of blister formation--through the lamina lucida of the epithelium. The primary antibody response is of the IgG 4 subclass, and the antigens recognized by these autoantibodies have been shown to be 230 kD and 180 kD transmembrane proteins unique to the hemidesmosome of stratified squamous epithelial cells. Although it is suspected that these antigens are important in cell-substrate adhesion, this has not been proven. Stanley et al. have recently defined the sequence of a portion of the C terminal end of the 230 kD antigen and Diaz et al. have isolated a cDNA encoding for the 180 kD antigen. Structural data regarding these antigens should prove critical to definition of their presumed function. Therefore, BP is felt to be an autoimmune disease where the cutaneous lesions may solely be a consequence of binding of these antihemidesmosome autoantibodies to the specific antigen, but definitive proof of this assumption is incomplete.

Partial cDNA cloning of the 230-kD mouse bullous pemphigoid antigen by use of a human monoclonal anti-basement membrane zone antibody

A cDNA clone with the coding sequence for the 230-kD bullous pemphioid (BP) antigen was isolated from a mouse cDNA expression library by using an anti-basement membrane zone human monoclonal antibody (MoAb-5E). The lambda gt11 cDNA expression library was constructed from poly(A)+RNA from the mouse epidermal cell line, Pam cells, by random priming. 1.5 X 10(5) recombinant clones were screened by immunostaining with MoAb-5E and one positive clone (BPM1) was obtained. All of the ten BP sera but none of the five normal or seven pemphigus sera tested reacted with the fusion protein produced by BPM1. The size of the cDNA was 3.2 kb. Northern blot analysis indicated that BPM1 cDNA hybridized to a mRNA of about 9 kb, which is large enough to encode for a 230-kD protein. DNA sequencing demonstrated a 2,991-bp open reading frame encoding a peptide of 115 kD. Sequence comparison between mouse and human cDNA clones revealed that the 230-kD BP antigen was well conserved during evolution except for the carboxyl terminus. Highly conserved and hydrophilic regions in the molecule were considered to be good candidates for antigenic determinants. This cDNA clone will be useful not only for diagnosis of BP, e.g., enzyme-linked immunosorbent assay using recombinant proteins or synthetic peptides as antigens, but also for pathophysiologic study in which mouse models of BP might be used.

Production of human monoclonal anti-basement membrane zone (BMZ) antibodies from a patient with bullous pemphigoid (BP) by Epstein-Barr virus transformation. Analyses of the heterogeneity of anti-BMZ antibodies in BP sera using them

We established three lymphoblastoid cell lines from a bullous pemphigoid (BP) patient's peripheral blood by means of EBV transformation, which produced human monoclonal anti-basement membrane zone (BMZ) IgG antibodies. A blocking immunofluorescence test using these MAbs, designated 5A, 5E, and 10D, revealed that 5A and 5E recognized the same or a closely associated epitope, but the epitope for 10D was completely different, 18 of 30 BP sera blocked the reactivity of 10D MAb and 17 sera blocked 5E, while 9 sera did not block the staining of either antibody. Immunoblot analysis demonstrated that both 5A and 5E MAbs reacted exclusively with a protein band of approximately 230 kD in normal human epidermal extracts. However, 10D did not show any protein band. 22 of 30 BP sera strongly reacted with the same 230-kD protein, while none of control sera showed such reactivity. These results clearly demonstrated the heterogeneity of anti-BMZ antibodies in terms of epitopes. These MAbs should be useful in future investigations concerning not only the immunopathology but also the biochemial and molecular analyses of the BP antigen.

Absence of specific histologic changes in guinea pig skin treated with bullous pemphigoid antibodies

Previous studies have reported that intradermal injections of bullous pemphigoid antibodies into guinea pigs can reproduce the histologic and immunohistologic features of bullous pemphigoid lesions. In this study we examined this model to determine its reproducibility and suitability for testing other types of anti-BMZ antibodies. Twenty guinea pigs were injected intradermally with 0.1, 0.3, or 0.5 ml of either bullous pemphigoid serum or IgG fraction containing high-titer complement-binding anti-BMZ antibodies or an equivalent volume of normal human serum or IgG fraction as control. Sites were biopsied at intervals after injection and were examined by routine histology and direct immunofluorescence. The results showed (a) no difference in the incidence of dermal epidermal separation or type of inflammation in experimental and control sites; (b) no evidence of an eosinophil-rich inflammatory reaction typical of bullous pemphigoid; (c) an absence of linear BMZ deposits of IgG and complement in the majority of sites injected with bullous pemphigoid antibodies; and (d) no correlation between dermal-epidermal separation and deposition of immune reactants at the BMZ. These results suggest the histologic changes seen in guinea pigs that are administered intradermal injections of bullous pemphigoid antibodies are nonspecific and that the model is not suitable for testing the pathogenicity of anti-BMZ antibodies in sera or IgG fractions.

Circulating anti-skin basement membrane zone antibodies in a patient with Goodpasture's syndrome

We report the case of a patient with atypical bullous pemphigoid and haemoptysis in whom circulating IgG skin basement membrane zone antibodies were demonstrated. Six years later she developed acute renal failure due to Goodpasture's syndrome. This is the first case to raise the possibility of a link between epidermal and glomerular basement membrane antibodies.

Bullous pemphigoid

Bullous pemphigoid is an autoimmune blistering dermatologic disease characterized clinically by tense bullae that may develop on normal or erythematous skin. The major histologic feature is a subepidermal blister with variable degrees of dermal inflammation. Other immunologically mediated blistering skin diseases may mimic bullous pemphigoid, including herpes gestationis, cicatricial pemphigoid, dermatitis herpetiformis, and epidermolysis bullosa acquisita. These diseases will be discussed. Most patients with bullous pemphigoid demonstrate circulating autoantibodies reactive with an antigen located in the lamina lucida region of the basement membrane zone. Complement activation by these autoantibodies initiates influx and activation of mast cells along with other inflammatory cells. Tissue injury with damage and eventual destruction of the basement membrane occurs as a result of the release of inflammatory mediators. The final result is subepidermal blister formation. The course of bullous pemphigoid tends to be self-limited, and successful treatment is usually effected with systemic glucocorticosteroids.

Immunopathologic mechanisms in pemphigus and bullous pemphigoid

Pemphigus and bullous pemphigoid are autoimmune bullous diseases of the skin. Pemphigus, an intraepidermal blistering disease, is characterized by autoantibodies reactive with antigens located in the intercellular spaces or on the surfaces of epidermal cells. These antibodies, which have recently been shown to activate complement, appear to be the cause of the basic pathologic process of pemphigus, acantholysis. The complement system and the plasminogen-plasmin system may be important mediators in the detachment of epidermal cells. Bullous pemphigoid, a subepidermal blistering disease, is characterized by autoantibodies reactive with an antigen located in the lamina lucida region of the basement membrane zone. These autoantibodies, which will avidly fix complement, appear to mediate subepidermal separation by attraction of a variety of inflammatory cells. Anaphylatoxins, released by activation of C4 and C3, or specific IgE antibodies, may activate mast cells with release of ECF-A attracting eosinophils. With activation of C5, C5a is released which could attract polymorphonuclear leukocytes. Antigen-specific lymphocytes, which can also contribute histamine releasing substances, may also be involved. The exact mechanism by which the epidermis separates from the dermis in bullous pemphigoid, however, remains unresolved.

Differences in complement-dependent chemotactic activity generated by bullous pemphigoid and epidermolysis bullosa acquisita immune complexes: demonstration by leukocytic attachment and organ culture methods

Bullous pemphigoid (BP) and epidermolysis bullosa acquisita (EBA) are chronic blistering diseases associated with circulating complement (C)-binding anti-basement membrane zone (BMZ) antibodies and tissue-deposited immune complexes at the BMZ. Experimental evidence supporting a role for C-activating immune complexes in the pathogenesis of dermal inflammation and blisters has been reported in BP but not in EBA. In this study tissue-deposited immune complexes composed of EBA or BP antibodies were tested for generation of C-dependent chemotactic activity and the capacity to cause dermal leukocyte infiltration and dermal-epidermal separation (DES). Chemotactic activity was measured by the leukocyte attachment (LA) method. The capacity of complexes to mediate leukocyte infiltration and DES was examined in vitro using a newly described organ culture method. The results of LA showed immune complexes formed in vivo in EBA skin or in vitro by treating normal human skin with EBA antibodies were significantly more active in mediating C-dependent chemotaxis than complexes in BP skin or those formed with BP antibodies of equivalent or higher C-binding titers. Furthermore EBA antibodies and C caused leukocyte infiltration and DES in organ culture while BP antibodies did not. These results support a role for C-binding anti-BMZ antibodies in the pathogenesis of EBA lesions and demonstrate differences in the capacity of BP and EBA immune complexes to generate C-dependent chemotactic activity. These results suggest factors in addition to C-binding titers are important in the activation of C by BP and EBA immune complexes and suggest chemotactic factors other than those derived from C activation may be important in the recruitment of leukocytes in BP.

Circulating immune complexes: their immunochemistry, biology, and detection in selected dermatologic and systemic diseases

Circulating immune complexes (CICs) are a heterogeneous group of immunoreactants formed by the noncovalent union of antigen and antibody. Many factors influence the formation, immunochemistry, biology, and clearance of these soluble reactants. The recent development of sensitive assays for the detection of CICs and the capability to assess immune complex (IC) clearance mechanisms in humans in vivo have expanded our understanding of these mediators. CICs influence both the afferent and efferent limbs of the immune response and can mediate tissue damage in certain pathologic states. ICs probably play an important role in the pathogenesis of serum sickness, systemic lupus erythematosus, and cutaneous necrotizing vasculitis. Recent investigations have raised the possibility that CICs may be of significance in other types of vasculitis as well. In other instances, ICs may form in response to tissue injury and subsequently modify the immune response of the host. A review of this material with special emphasis on diseases of relevance to dermatologists is presented.

Deposition of the membrane attack complex of complement in bullous pemphigoid

Bullous pemphigoid is associated with deposition of IgG and C3 at the dermal-epidermal junction. In order to see whether complement activation in bullous pemphigoid resulted in deposition of membrane attack complex (MAC) at the basement membrane zone, skin biopsies from patients with bullous pemphigoid were examined using a direct immunofluorescence technique. By employing a monoclonal antibody to a neoantigen of C9, the MAC was demonstrated in linear pattern at the basement membrane zone. These deposits were seen in both involved and uninvolved skin but the amount of MAC was greater in involved skin as judged by intensity of staining. Stippled deposits of MAC were also present in or around epidermal basal cells. The MAC could be generated in vitro by reaction of normal plasma with antibasement membrane antibody bound to sections of monkey esophagus. The IgG antibody activated complement and this complement activation proceeded all the way to the terminal step.

Bullous pemphigoid blister fluid stimulates eosinophil colony formation and activates eosinophils

An eosinophil stimulating material (ESM) is described in the blister fluids (BF) of six patients with bullous pemphigoid (BP). This ESM is similar in function to a subspecies of human colony stimulating factor (CSF), CSF-alpha, since (i) it stimulated the production from bone marrow cells of day 14 colonies (31 +/- 15, arithmetic mean +/- 1 s.e.m. colonies, n = 5) in semi-solid agar, (ii) a large proportion (47 +/- 12%, n = 5) of these colonies were eosinophilic and (iii) it activated purified peripheral eosinophils as judged by increased autofluorescence (a mean increase of 23.6 +/- 6.6 units measured by flow cytometry, n = 10). BF from patients with four other blistering diseases, burn blisters, suction blisters from normal, eosinophilic or BP patients, various sera, histamine and eosinophil chemotactic factor (ECF-A) lacked activities in these assays. This description of a tissue accumulation of a CSF like substance suggests that there exists a physiological role for CSF in the periphery. In addition it supports the concept that local activation of eosinophils contributes to the pathogenesis of BP.

Bullous pemphigoid: a correlative study of autoantibodies, circulating immune complexes and dermo-epidermal deposits

Twenty bullous pemphigoid (BP) patients were studied to establish any correlation between free anti-basement membrane zone (BMZ) antibodies, circulating immune complexes (CIC) and dermo-epidermal junction deposits. CIC levels were evaluated by 2% polyethylene glycol (PEG) precipitation. The twenty patients were found to have IgG and/or C3 deposited in the BMZ. Eight of the twelve patients who had no free anti-BMZ antibodies displayed a positive in vivo C4 and/or CIq staining and high levels of CIC. Moreover, CIC were detected in only one patient with positive circulating free anti-BMZ antibodies. The presence of free anti-BMZ antibodies was generally found to correlate with the absence of cutaneous deposits of CIq and /or C4 and with negative CIC; on the other hand, the absence of free anti-BMZ antibodies was generally found to correlate with high levels of CIC and with deposits of C3 and CIq and/or C4. The absence of circulating free anti-BMZ antibodies in BP patients, could be explained by the formation of CIC. It is possible that BMZ antigens released from damaged tissue could combine with free antibodies and form complexes in the blood. The release could involve locally formed immune complexes. Elevated CIC levels were generally found to correlate with the presence of active disease.

Production of anti-basement membrane-zone antibody by peripheral blood leukocytes of pemphigoid patients

Peripheral blood leukocytes (PBL) from patients with bullous pemphigoid stimulated by pokeweed mitogen (PWM) produce an anti-basement membrane-zone(BMZ) antibody. the antibody produced in vitro was biosynthetically radiolabeled, and its binding to the BMZ was histologically demonstrated by autoradiography. The IgG nature of the antibody was evidence by the fact that it was absorbed by rabbit anti-human IgG antiserum immunoabsorbents. The peak antibody production in vitro occurred after 6 days of culture. Antibody produced in vitro did not bind to the BMZ of human skin, but it did bind to the BMZ of the monkey esophagus. Normal human volunteers and control patients did not produce such an antibody. In other experiments the effects of adding serum containing anti-BMZ antibody to the synthesis of Ig by cells of patients and normal subjects were studied. Although serum from patients with bullous pemphigoid stimulated Ig production with either normal or BP-patient PBL, the difference was not statistically significant. The availability of the assay system allows for studying the immunoregulatory mechanism of autoantibody production in bullous pemphigoid.

An in vitro model of immune complex-mediated basement membrane zone separation caused by pemphigoid antibodies, leukocytes, and complement

In this study, an in vitro model of immune complex-mediated basement membrane zone separation caused by periphigoid antibodies, serum complement, and peripheral blood leukocytes is described. When cryostat sections of fresh-frozen normal human skin were treated with either of 4 bullous pemiphigoid sera containing complement-activating anti-basement membrane zone antibodies and subsequently incubated at 37 degrees C with normal human peripheral blood leukocytes and fresh human serum, leukocytes attached to 96% of the basement membrane zone in 100% of sections. Sixty-seven percent of the sections developed focal areas of basement membrane zone separation resembling dermal-epidermal separation described in early pemphigoid lesions. In control sections in which either leukocytes, pemphigoid antibody or fresh human serum were omitted, significantly less leukocyte attachment and basement membrane zone separation occurred. Evidence that leukocytes caused separation was supported by an absolute requirement for viable leukocytes during incubation, a high correlation between leukocyte attachment and separation and experiments showing that leukocytes attached to the basement membrane zone were activated. This study provides the first in vitro evidence directly supporting a functional role for immune-complex mediated inflammation in the pathogenesis of basement membrane zone separation and blisters in bullous pemphigoid.

Bullous pemphigoid, an ultrastructural study of the inflammatory response: eosinophil, basophil and mast cell granule changes in multiple biopsies from one patient

We have studied by electron and light microscopy the inflammatory reaction in lesions at various stages of clinical development from a patient with bullous pemphigoid. The evolution of clinical lesions was associated with a sequence of histopathologic events which began with alterations of mast cells and proceeded to infiltration, first with lymphocytes and later with eosinophils and basophils. Mast cells in the papillary and reticular dermis demonstrated a unique, focal, irregular loss of granule contents. Intact eosinophils demonstrated intracytoplasmic losses of granule contents and karyorrhectic and karyolytic eosinophils had released membranebound granules. Partially and completely degranulated basophils were present within a fibrin gel which formed in the dermis. Thus, the sequence of histopathologic events in the pathogenesis of bullous pemphigoid includes mast cell granule alterations and release of granule contents from eosinophils which are undergoing nuclear and cytoplasmic damage.

Functional evidence for complement-activating immune complexes in the skin of patients with bullous pemphigoid

Previous immunofluorescent studies showing deposits of immunoglobulin and complement at the cutaneous basement membrane zone have provided evidence supporting a role for immune complexes in the pathogenesis of bullous pemphigoid. In this study the functional activity of the deposits has been examined using leukocyte attachment, a method for detecting and quantitating the biological activity of complement-activating immune complexes in tissues. When peripheral blood leukocytes suspended in serum complement were incubated with cryostat sections of lesional and adjacent normal-appearing skin from 9 patients with pemphigoid, skin from 11 normal controls and lesional skin from 14 nonpemphigoid disease controls there was significantly greater attachment of leukocytes to the basement membrane zone of lesional bullous pemphigoid skin compared to normal-appearing pemphigoid skin and skin of both control groups. A significant reduction in attachment in the absence of serum complement suggested the reaction was dependent on activation of complement by tissue-deposited complexes. Although leukocyte attachment was greater in lesional than normal-appearing pemphigoid skin, a comparison of the incidence and intensity of cutaneous IgG and complement immunofluorescence between the 2 groups showed no significant differences. Furthermore, no correlation between leukocyte attachment and serum titers of immunoglobulin G or complement-binding anti-basement membrane zone antibodies was observed. These results suggest that immune reactants in lesional pemphigoid skin are functional complement-activating immune complexes, that differences exist between the activity of complexes in lesional and normal-appearing pemphigoid skin and may explain why lesions develop at some sites and not others.

Serum and blister fluid immune complexes in bullous pemphigoid: detection with C1q and monoclonal rheumatoid factor

Eighty serum samples and 24 blister fluids from 51 patients with active bullous pemphigoid were tested for the presence of immune complexes by both a monoclonal rheumatoid factor (mRF) inhibition radioassay and a C1q-binding radioassay. Forty-two of the 80 serum samples were positive by the mRF assay, while 27 were positive by the C1q-binding assay. Antibody titres to the basement membrane zone did not correlate with levels of circulating immune complexes. Thirteen of 24 blister fluids had detectable immune complexes by the C1q assay, while only seven of 24 blister fluids were positive by the mRF assay. Sucrose density-gradient ultracentrifugation studies suggest that the mRF- and C1q-reactive substances in both bullous pemphigoid sera and blister fluids are of a size compatible with immune complexes. Although immune complexes are detectable in a high percentage of bullous pemphigoid patients, their role in this disease may be epiphenomenal rather than pathogenetic, merely reflecting the presence of autoantibody and soluble antigen.

The complement system in bullous pemphigoid: VII. Fixation of the regulatory protein beta 1H globulin by pemphigoid antibody

Using in vitro complement immunofluorescent staining methods, serum samples from 5 active cases of bullous pemphigoid, with pemphigoid antibody titers of 320 or greater, were tested for their ability to fix the regulatory protein beta 1H globulin in addition to C4 and C3. All 5 samples yielded positive C3, C4 and beta 1H staining reactions in a linear fashion along the basement membrane zone. Heat inactivation or treatment of the complement source (fresh normal human serum) with EDTA, Mg2-EGTA abolished all 3 staining reactions. Substitution of C2-deficient serum as the source of complement inhibited both C3 and beta 1H staining but had no effect on C4 staining. Use of serum devoid of beta 1H (R beta 1H) minimally enhanced C3 staining while no beta 1H staining was observed. The addition of beta 1H to R beta 1H restored positive beta 1H staining. Skin biopsies of perilesional skin from 6 patients with bullous pemphigoid demonstrated heavy in vivo deposition of beta 1H in addition to C3. These studies suggest that pemphigoid antibodies will fix the regulatory protein beta 1H in addition to other complement components, a phenomenon which requires activation of the classical complement pathway and generation of the C3b amplification convertase.

Pemphigoid antibody mediated attachment of peripheral blood leukocytes at the dermal-epidermal junction of human skin

It has been proposed that cutaneous inflammation and blister formation in bullous pemphigoid is caused by antibodies to the cutaneous basement membrane zone which active complement, thereby, attracting leukocytes to the dermal-epidermal junction. There is, however, no functional evidence which supports a role for pemphigoid antibodies in complement activation or leukocyte activity in skin. This study describes the in vitro attachment of human peripheral blood leukocytes to the dermal-epidermal junction of cryostat skin sections treated with 9/13 pemphigoid sera containing antibodies to the cutaneous basement membrane zone. A requirement for complement in the reaction was supported by the findings that only complement-fixing pemphigoid sera mediated the leukocyte response, a strong correlation existed between complement-fixation titers and leukocyte attachment titers and only leukocytes suspended in fresh serum but not buffer or heat inactivated serum attached at the junction. A requirement for antibody was supported by the observation that IgG fractions of 4 pemphigoid sera were as effective as whole sera in mediating leukocyte attachment. The leukocyte response was shown to be specific for complement-fixing pemphigoid sera since it was not observed with noncomplement-fixing sera or sera from 15 normal human and 22 nonpemphigoid disease controls. This study offers functional evidence for an interaction between pemphigoid antibody, complement and leukocytes in the immunopathogenesis of bullous pemphigoid and demonstrates that complement-fixing antibasement membrane zone antibodies may be important in initiating the cellular inflammatory events observed near the dermal-epidermal junction in vivo.

Demonstration of the complement regulating protein, beta 1H, in skin biopsies from patients with bullous pemphigoid

beta 1H-globulin is a recently characterized plasma protein which regulates the biologic activities of the major fragment of the third complement component, C3b. The major function of this protein is to act as a co-factor for C3b Inactivator (C3bINA) in the cleavage of C3b to an intermediate molecule, C3b', consisting of an intact beta-chain covalently bound by disulfide bridges to 2 alpha-chain fragments of 40,000 and 67,000 daltons. Final cleavage of C3b' to the C3c and C3d fragments requires an additional protease such as plasmin or elastase. Additionally, beta 1H interferes with the activity of the alternative pathway convertases, C3bBb and C3bBbP, by displacing or competing with the binding of factor B. In this study, perilesional skin biopsies from 10 patients with active bullous pemphigoid were examined for the presence of beta 1H at the dermal-epidermal junction by immunofluorescent methods. The protein was found in 8 of 9 biopsies in which C3 also was deposited. In a single case where C3 was not found, beta 1H was not seen. These findings suggest that beta 1H plays a role in the in vivo control of C3b and provides additional evidence for the participation of the complement system in the pathogenesis of bullous pemphigoid.

Morphologic and functional evidence for release of mast-cell products in bullous pemphigoid

We studied nine patients with bullous pemphigoid, a generalized cutaneous eruption- for evidence of mast-cell involvement during development of lesions. As in other reports, six of nine patients demonstrated a serum antibody directed against the epidermal basement-membrane zone. Direct immunofluorescence studies of lesions revealed depostion of immunoglobulin and complement proteins at the basement-membrane zone in six of nine and nine of nine patients, respectively. Participation of mast cells was suggested by a sequence of pathologic alterations in which there was progressive mast-cell degranulation and late eosinophil infiltration. In addition, a factor chemotactic for human eosinophils with the size and charge characteristics of the eosinophil chemotactic factor of anaphylaxis was identified in blullous fluid. The data indicate that, in addition to activation of the complement system, involvement of mast cells is an early and continuing event in the development of the cutanenous lesions of bullous pemphigoid.