Bullous pemphigoid: elution of in vivo-fixed antibody

In situ-bound antibodies eluted from the skin of patients with bullous pemphigoid are preferentially directed against the 230-kD bullous pemphigoid antigen

Two bullous pemphigoid antigens (BPAs) have been identified: a 230-kD intracellular hemidesmosome-associated molecule and a 180-kD transmembrane hemidesmosome-associated molecule. Although patients with bullous pemphigoid (BP) have been shown to have circulating antibodies directed against one or both BPAs, the antigenic specificity of tissue-bound BP autoantibodies has not been studied. Because these skin-bound antibodies may play an important role in disease initiation, we sought to determine their antigenic specificity. In situ-bound BP antibodies were eluted with glycine from salt-split perilesional skin biopsy specimens and subjected to immunoprecipitation. Ten of 13 patients had glycine-eluted antibodies that recognized the 230-kD BPA, whereas four of 13 patients had glycine-eluted antibodies that recognized the 180-kD BPA. When these glycine-eluted BP skin specimens were sequentially eluted with urea, we found either antibodies of the same specificity or loss of reactivity to one of the BPAs, but no reactivity to any BPAs previously undetected with glycine elution. Sequential elution with sodium dodecylsulfate revealed no detectable BP antibodies. The heavy- and light-chain isotypes of the circulating, tissue-bound, and eluted BP antibodies were very similar, suggesting that we are not eluting certain subsets of BP antibodies. Sera from these patients contained circulating antibodies that recognized either one or both BPAs. Our observations demonstrate that in situ-bound antibodies eluted from the skin of patients with BP are preferentially directed against the 230-kD BPA.

Pathogenetic studies in bullous pemphigoid--review of the literature and our own results

Bullous pemphigoid (bP) is a blister‐forming disease, probably of autoimmune nature. Its genetic background has not been established yet. Associations with other autoimmune diseases and, to some extend, with malignant tumors are noteworthy. The blisters are located subepidermally in the lamina lucida between the cytoplasmic membrane of the basal cells and the lamina densa of the basement membrane. The bP antigen, which is produced by basal cells, serves as an attachment factor and can be liberated into the blister fluid, probably by serine proteases from leucocytes. The formation of antigen‐antibody complexes is favoured afterwards. Freely circulating bP antibodies, mostly of the IgG class, are fixed in the skin tissue in vivo and in vitro and bind complement. Components of the classical complement pathway as well as of the amplification loop are activated locally in the skin tissue and fixed. The content of immune complexes is increased in the serum and in the blister fluid. They partially consist of specific bP antigen‐antibody complexes. The determination of the entire bP antibody titer (after immune complex splitting) correlates well with the clinical course of the disease.

Chemotactic factors for neutrophils and eosinophils are released into the blister fluid after complement activation, so that leucocyte attraction is mediated. Deviations of humoral and cellular immune reactivity have not been studied sufficiently. There might be an immune modulating effect of immune complexes and other serum factors on T‐lymphocytes due to steric hindrance of surface receptors. In vivo and in vitro models in rabbit cornea, skin explants, and frozen sectioned skin tissue suggest that the interaction of circulating bP antibodies with the bP antigen followed by complement activation and attraction of neutrophils might be the primary immunopathological mechanism, producing an immune complex mediated inflammation.

Binding of bullous pemphigoid antibodies to basal cells

Eight out of 12 serum samples from patients with bullous pemphigoid having basement membrane zone antibodies gave positive binding not only to the basement membrane zone but also to the basal cell membrane and/or cytoplasm as observed by complement immunofluorescence. Reaction of fluorescein labeled pemphigus vulgaris gamma-globulins, binding mainly to the lower intercellular spaces of the epidermis, was greatly reduced by the prior incubation of high-titered bullous pemphigoid sera having the reactivity to the basal cells, while that of fluorescein labeled pemphigus foliaceus gamma-globulins binding mainly to the upper and middle intercellular spaces, was not influenced by the prior application of these bullous pemphigoid sera. These results indicate that bullous pemphigoid antibodies are heterogenous and can be classified into 2 types and that some cross reaction is present between pemphigus antibodies and bullous pemphigoid antibodies having the reactivity to the basal cells.

Cutaneous immunopathology: recent observations

Immunofluorescent studies are currently being done on patients with pemphigus, pemphigoid, dermatitis, lupus erythematosus and its variants, the cutaneous prophyrias, scarring alopecia, erosive mouth lesions, light-sensitive disorders, and cutaneous vasculitis. In this paper I shall review some of the recent advances in immunopathology and report the results that have been obtained in our laboratory.

Complement activation in bullous skin diseases

Pemphigus, bullous pemphigoid, cicatricial pemphigoid, dermatitis herpetiformis, and herpes gestationis are members of the chronic vesiculobullous skin diseases of man. The complement system, including both the classical and alternative pathways, may be important in the pathogenesis of these diseases. In pemphigus, early complement components (C1, C4, and C2) appear to be activated in addition to later components (C3 and C5), suggestive of classical pathway activation. Participation of properdin in addition to early complement components suggests local activation of both complement pathways in bullous pemphigoid and cicatricial pemphigoid. Herpes gestationis and dermatitis herpetiformis may be bullous skin diseases entirely mediated by the alternate or properdin pathway. The specific immunopathologic findings in these diseases are discussed.