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

Innate immune activation as cofactor in pemphigus disease manifestation

Molecular mechanisms underlying auto-antibody-induced acantholysis in pemphigus vulgaris are subject of current research to date. To decipher the discrepancy between ubiquitous antibody binding to the epidermal desmosomes, but discontinuous disease manifestation, we were able to identify Ultraviolet A (UVA) as a cofactor for acantholysis. UVA induces interleukin (IL)-1 secretion in keratinocytes, mirroring innate immune system activation. In an in vitro keratinocyte dissociation assay increased fragmentation was observed when UVA was added to anti-Desmoglein 3 Immunoglobulins (anti-Dsg3 IgG). These results were confirmed in skin explants where UVA enhanced anti-Dsg3-mediated loss of epidermal adhesion. The UVA-mediated effect was blocked in vitro by the pan-caspase-inhibitor zVAD-fmk. Thus, we introduce UVA as a caspase-dependent exogenous cofactor for acantholysis which suggests that local innate immune responses largely contribute to overt clinical blister formation upon autoantibody binding to epidermal cells in pemphigus vulgaris.

Utility of immunofluorescence in dermatology

Immunofluorescence (IF) tests have redefined our understanding of many immune-mediated skin diseases, especially autoimmune blistering diseases (AIBDs). Nomenclature of certain AIBDs (for example, linear IgA diseases and IgA pemphigus) has been done based solely on the finding of tissue-bound immunoreactants as detected by IF tests. Direct and indirect are the two major types of IF tests; they are not only useful in the diagnosis but also guide the clinician in the treatment at least in certain AIBDs, as the titer of circulating antibodies as detected by IF reflects the disease activity. In this review, we describe techniques, various types of IF, and its modification.

Immunofluorescence in dermatology

The accurate diagnosis of bullous and other immune diseases of the skin requires evaluation of clinical, histologic, and immunofluorescence findings. Immunofluorescence testing is invaluable in confirming a diagnosis that is suspected by clinical or histologic examination. This is especially true in subepidermal bullous diseases that often have overlap in the clinical and histologic findings. Direct immunofluorescence is performed on perilesional skin for patients with bullous diseases and lesional skin for patients with connective tissue diseases and vasculitis.

Antibodies to desmogleins 1 and 3, but not to BP180, induce blisters in human skin grafted onto SCID mice

Pemphigus and bullous pemphigoid (BP) are blistering skin diseases associated with IgG autoantibodies to desmosomal and hemidesmosomal components. When autoantibodies to desmogleins 1 and 3 from patients with pemphigus foliaceus (PF) and pemphigus vulgaris (PV) or rabbit antibodies against the murine hemidesmosomal component BP180 are passively transferred into neonatal mice, they induce blisters in the skin of the mice. To develop an animal model that would duplicate the findings in the skin of the patients more closely, full-thickness human skin from healthy volunteers was grafted onto SCID mice. Injection of the purified IgG fraction from the serum of PF and PV patients led to subcorneal and suprabasal splits in the human grafts and human IgG was deposited intercellularly in the upper and lower layers of the epidermis, respectively. Interestingly, anti-BP180 autoantibodies purified from the serum of BP patients and from a rabbit immunized with recombinant human BP180 strongly bound to the basement membrane zone of the grafts (n=32), fixed murine complement, led to the recruitment of neutrophils to the upper dermis of the graft, but did not induce subepidermal blisters. We report a novel experimental model for PF and PV which should greatly facilitate further studies to dissect the immunopathological mechanisms in these diseases. Specifically, this model can be used to identify pathogenically relevant epitopes on human desmogleins 1 and 3 and to develop novel strategies for the treatment of pemphigus.

Molecular biological aspects of acquired bullous diseases

Bullous diseases of the oral mucosa and skin were originally classified on the basis of clinical and histological criteria. The discovery of autoantibodies in some of these patients and the introduction of molecular biology have resulted in a new understanding of the pathological mechanisms of many of the bullous lesions. In this article, updated topics of the immune-mediated bullous lesions which involve oral mucosa and skin are reviewed. Pemphigus antigens, which are desmosomal-associated proteins and belong to the cadherin superfamily of cell adhesion proteins, have been isolated, and their genes have been cloned. The antigens which react with autoantibodies from patients with bullous pemphigoid, cicatricial pemphigoid, acquired epidermolysis bullosa, and linear IgA disease are all proteins of the hemidesmosome basement membrane complex. Interestingly, most of the antigens also appear to be the target for mutations seen in patients with the inherited type of epidermolysis bullosa in which bullous lesions are a prominent clinical feature.

Ultrastructural differentiation of epidermolysis bullosa subtypes and porphyria cutanea tarda

Identifying subtypes of epidermolysis bullosa clinically, particularly at the time of disease onset, can be extremely difficult. In this investigation samples of intact skin from cases of epidermolysis bullosa and porphyria cutanea tarda were examined ultrastructurally and compared with normal tissue. The histological composition of the blister roof and floor surfaces was also evaluated. Three of the ten epidermolysis bullosa subtypes examined revealed specific features. Distinctive, circumscribed, clumped tonofilament bodies were present in basal keratinocytes from epidermolysis bullosa herpetiformis Dowling-Meara. Blister formation in epidermolysis bullosa simplex generalisata gravis occurred immediately above the dermo-epidermal junction aspect of stratum basale cells and thick (30 nm diameter), cross-striated anchoring fibrils were absent in epidermolysis bullosa dystrophica generalisata gravis. Features relating to the lamina densa of the dermo-epidermal junction, dermal capillaries and blister composition were distinctive, but not confined to a particular epidermolysis bullosa subtype or porphyria cutanea tarda.

Bullous systemic lupus erythematosus: revised criteria for diagnosis

Blistering in systemic lupus erythematosus has been divided into three groups. A specific subgroup of 'bullous systemic lupus erythematosus' has been defined by Gammon et al. on the basis of a number of criteria. From our experience of seven patients with bullous systemic lupus erythematosus, and after reviewing the literature, we suggest that the current classification is too narrow. Our patients displayed clinical and immunohistological (based on direct and indirect immunofluorescence and Western immunoblotting) heterogeneity. Sera from two patients bound to epidermal epitopes in sodium chloride-split skin, but immunoblotting was negative. In neither of these patients could the target antigen be type VII collagen, the only antigen identified as pathogenic in this disease. Patients with epidermal binding should not be excluded from a diagnosis of bullous systemic lupus erythematosus. SLE is a disease in which there is a genetic predisposition to form antibodies to type VII collagen, along with other autoantibodies, many of which may be implicated in blistering. We suggest that the criteria for the diagnosis of BSLE should be revised. We define this disease as an acquired subepidermal blistering disease in a patient with SLE, in which immune reactants are present at the basement membrane zone on either direct or indirect immunofluorescence.

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.

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.

Cutaneous IgA deposits in bullous diseases function as ligands to mediate adherence of activated neutrophils

Linear IgA bullous dermatosis and dermatitis herpetiformis are inflammatory subepidermal blistering diseases characterized by IgA deposits at the cutaneous epithelial basement membrane and in dermal papillae, respectively. Inflammation in both disorders localizes to sites of IgA deposition and is characterized by a predominance of neutrophils. From these observations we postulate that IgA deposits in both diseases may contribute to the recruitment and/or localization of neutrophils. In this study we examined the ability of in vitro and in vivo bound IgA anti-basement membrane autoantibodies from patients with linear IgA bullous dermatosis and in vivo bound IgA deposits in dermal papillae from patients with dermatitis herpetiformis to mediate adherence of neutrophils stimulated by granulocyte macrophage colony-stimulating factor. The study showed that stimulated neutrophils adhered to basement membranes and dermal papillae containing IgA deposits. Adherence was IgA anti-basement membrane antibody concentration dependent and correlated with the immunofluorescence staining intensity of IgA deposits in dermal papillae. Adherence to IgA deposits but not IgG deposits could be inhibited by purified exogenous secretory IgA but not IgG and adherence to IgG deposits could be inhibited by purified exogenous IgG but not secretory IgA. These results provide direct experimental evidence that cutaneous IgA deposits in linear IgA bullous dermatosis and dermatitis herpetiformis can function as ligands for neutrophil adherence and have a role in the localization of inflammation in these disorders.

IgG subclasses of intercellular and basement membrane zone antibodies: the relationship to the capability of complement fixation

There are four main subclasses of human IgG: IgG1, IgG2, IgG3, and IgG4, among which IgG1-IgG3 activate complement, but IgG4 does not. We studied the IgG subclasses of anti-intercellular (IC) antibodies in pemphigus patients and anti-basement membrane zone (BMZ) antibodies in bullous pemphigoid (BP) patients by immunofluorescent staining using mouse monoclonal antibodies against human IgG1-IgG4. At the same time, the capability of complement fixation of each serum was determined by means of complement immunofluorescence. In both pemphigus and BP autoantibodies, various distributions of IgG subclass were shown, but specific patterns were not observed. In BP, all of the complement fixing antibodies had at least one of IgG1-IgG3 subclasses, while noncomplement fixing antibodies only possessed IgG4. This result agreed well with the biologic characteristics of IgG subclasses in respect of complement fixing capability. On the contrary, in pemphigus, the circulating antibodies showed a distribution of IgG subclass which did not correlate with the biologic characteristics in terms of complement activation. This discrepancy may further dispute the roles of the complement system on the bulla formation in pemphigus.

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.

Activation of the alternative pathway of complement by skin immune deposits

Skin immune deposits at the basement membrane zone have been demonstrated by functional assays to activate complement. This important biologic function has not yet been explored for immune deposits present in other locations mainly because many cytoplasmic structures in the skin have the capacity to activate the complement cascade by the classical pathway. In this study the capacity of immune deposits to activate directly the alternative pathway was examined using a functional guinea pig C3 binding test. This test was devised so as to avoid complement activation by normal cutaneous structures, thus it did not examine the capacity of immune reactants to activate the classical pathway. The main findings were that alternative pathway activation could be demonstrated only when human C3 deposits were seen by direct immunofluorescence, but not all C3 deposits were found to activate the alternative pathway; such activation was restricted to vascular deposits; the phlogistic potential of the immune deposits correlated with serologic evidence of ongoing immune reactions, i.e., hypocomplementemia and circulating immune complexes. It is suggested that this test provides data on one aspect of the phlogistic potential of skin immune deposits not detectable by direct immunofluorescence.

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.

Oral pemphigoid

Forty-six patients were seen over a four-year period because of oral blistering. Of these 26 were thought to have pemphigoid affecting the oral mucosa. The clinical features in these patients are compared with the commonly accepted descriptions and some differences noted. The nomenclature is reviewed and the term 'intermittent mucosal pemphigoid' is suggested to describe a clinical variant in which lesions are few and widely separated in time and which heal without scar formation. The relationship between oral pemphigoid and oral 'blood blisters' is discussed.

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.

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.

Junctional blisters in acquired bullous disorders of the dermal-epidermal junction zone: role of the lamina lucida as the mechanical locus minoris resistentiae

The level of cleavage was determined in a variety of acquired bullous diseases of the dermal-epidermal junction zone (bullous pemphigoid, dermatitis herpetiformis, porphyria cutanea tarda and epidermolysis bullosa acquisita). We used an indirect immunofluorescence technique to examine the basal membrane zone with anti-type IV collagen and anti-laminin antisera and bullous pemphigoid sera. The majority of blisters examined proved to be junctional, including those from disorders hitherto considered to be dermolytic. Dermolytic cleavage was encountered only sporadically in microvesicles of dermatitis herpetiformis, in one small vesicle and in one out of five large blisters of porphyria cutanea tarda and in a large lesion of epidermolysis bullosa acquisita. We conclude that in acquired bullous disorders of the dermal-epidermal junction zone the preferential site of split formation is the lamina lucida which appears to act as a locus minoris resistentiae; dermolytic split formation of substantial extent occurs only when the sublaminal fibrillar apparatus is mechanically compromised.

Evidence supporting a role for immune complex-mediated inflammation in the pathogenesis of bullous lesions of systemic lupus erythematosus

Evidence supporting an immune complex pathogenesis of bullous lesions in systemic lupus erythematosus includes immune deposits, acute inflammation, and blister formation at the cutaneous basement membrane zone. Since cutaneous immune deposits are a general feature of lupus, an attempt has been made to determine whether deposits in lupus patients with blisters are functionally different from those in patients without blisters. Skin was obtained from 4 consecutive patients with blisters and 14 controls. The groups were matched for clinical and serologic features, duration and activity of disease, and treatment. Skin was examined by direct immunofluorescence for immune deposits and by the leukocyte attachment assay for quantification of complement-activating immune complexes. Clinically normal, viable skin from 1 patient with blisters and 1 patient without blisters was incubated in organ culture with normal human leukocytes and serum complement. All patients in both groups had immune deposits at the basement membrane zone with an equivalent incidence of the major Ig classes. Deposits in patients with blisters were slightly more intense and a linear pattern of fluorescence seen in 75% of these patients was not seen in controls. The leukocyte attachment assay showed significantly greater (p less than .02) cell attachment in patients with blisters (mean = 167) than in patients without blisters (mean = 64) and greater cell attachment in peribullous than normal skin from the same patient. Organ culture showed complement-dependent migration of leukocytes and histologic features similar to those in spontaneous lesions in skin from the patient with blisters but not in skin from the patient without blisters. These results provide evidence supporting immune complex and complement-dependent inflammation in the pathogenesis of bullous lesions in systemic lupus erythematosus.

Identification of chemoattractant activity for lymphocytes in blister fluid of patients with bullous pemphigoid: evidence for the presence of a lymphokine

Bullous pemphigoid is characterized by the dermal infiltration of lymphocytes, which precedes the striking influx of eosinophils as the lesion evolves into the bullous phase. This finding prompted a search for chemoattractant activity for lymphocytes in the blister fluid of untreated individuals with bullous pemphigoid. We found such activity in the bullous fluids of 6 consecutive patients but not in a patient with pemphigus vulgaris. This lymphocyte chemoattractant activity separates into 4 peaks upon Sephadex G-100 chromatography and the peak of 56,000 daltons was further evaluated. Upon quaternary aminoethyl Sephadex-anion exchange chromatography this peak elutes at 4-8 ms and with preparative isoelectric focusing it demonstrates an isoelectric point of 8.6-9.0. This activity was susceptible to degradation by trypsin and neuraminidase, but was stable upon heating to 56 degrees C for 30 min. Its chemoattractant activity is predominantly chemokinetic by checkerboard analysis. As defined by chromatography, stability, and functional characteristics, this activity is similar to a recently described human lymphocyte chemoattractant lymphokine. This finding suggests that products of activated lymphocytes are present in blister fluids of patients with bullous pemphigoid and may contribute to the early influx of lymphocytes in this disease.

Complement-activating immune deposits in systemic lupus erythematosus skin

Immune deposits at the cutaneous basement membrane zone are a characteristic feature of systemic lupus erythematosus. Previous studies using immunofluorescent methods to detect complement components have provided evidence that some deposits contain immune complexes capable of activating complement. However, this important biologic property of complexes has not been detected or measured using functional assays, and it has not been determined whether immune deposits can activate complement at the basement membrane zone. In this study immune deposits in biopsies of lupus skin have been examined using direct immunofluorescence for the third component of complement (C3) to detect complement deposited in vivo. In addition, the deposits have been studied using the leukocyte attachment assay and indirect C3 binding immunofluorescence to detect and measure complement activation at the basement membrane zone in vitro. The results show that complement activation occurs at the basement membrane in some but not all lupus skin containing immunoglobulin deposits, that deposits differ quantitatively in their ability to activate complement, and that direct C3 immunofluorescence is a relatively insensitive method for detecting complement-activating complexes. The results provide functional evidence suggesting that immune deposits in some lupus skin are complement-activating complexes and potentially capable of activating complement at the basement membrane in vivo. Furthermore, the results suggest functional assays for evaluating complement-activating complexes may be valuable supplements to immunofluorescence in exploring the relationship between immune deposits and systemic and cutaneous disease.

Bullous systemic lupus erythematosus

Two patients with established systemic lupus erythematosus developed bullous dermatoses clinically suggestive of bullous pemphigoid (BP). Direct immunofluorescence demonstrated linear staining at the dermoepidermal junction for IgG and C3 in a pattern typical for BP. However, immunoelectron microscopy demonstrated deposits of IgG largely below the basal lamina, with little if any deposit present within the lamina lucida. These findings are consistent with systemic lupus erythematosus (SLE) and effectively rule out BP. In addition, the leukocyte attachment assay, an in vitro assay of the functional activity of tissue-deposited immune complexes, demonstrated strong attachment of leukocytes to the dermoepidermal junction of patients' skin, suggesting that the immune reactants were functional immune complexes of possible importance to the pathogenesis of the bullous lesions. To our knowledge, this is the first time that immunoelectron microscopy has been performed on skin from patients suspected of manifesting concurrent SLE and BP. Our findings cast doubt on previous such reports by demonstrating the existence of a bullous form of SLE resembling BP both clinically and by direct immunofluorescence.

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.

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.