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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.

Epidermolysis bullosa acquisita (EBA) is an immunologically distinctive disease with characteristic clinical features. These include extreme skin fragility, trauma-induced blisters and erosions, and healing with scars and milia. These clinical features are currently the major means of routinely distinguishing EBA from bullous pemphigoid (BP) and cicatricial pemphigoid (CP). In this study we describe five patients with EBA who presented with or developed clinical as well as histologic and immunohistologic features indistinguishable from those characteristic of BP or CP. At different times during the course of their disease, it closely resembled classic BP or CP and cases of BP or CP with atypical features or evolving features of EBA. To determine how often EBA might present and be misdiagnosed as BP, we reviewed our experience with bullous diseases and screened eighty-five "BP" sera for EBA antibodies. The results of this study show EBA can mimic the clinical, histologic, and immunohistologic features of BP and CP, suggest that a BP-like clinical presentation occurs in as many as 50% of EBA patients, and suggest that 10% of patients referred to medical centers and diagnosed as BP have EBA.

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.

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.

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.