Epidermolysis bullosa acquisita (EBA) is a subepidermal blistering disorder associated with tissue-bound and circulating autoantibodies specific to type VII collagen, a major constituent of the dermal-epidermal junction. Previous attempts to transfer the disease by injection of patient autoantibodies into mice have been unsuccessful. To study the pathogenic relevance of antibodies specific to type VII collagen in vivo, we generated and characterized rabbit antibodies specific to a murine form of this antigen and passively transferred them into adult nude, BALB/c, and C57BL/6 mice. Immune rabbit IgG bound to the lamina densa of murine skin and immunoblotted type VII collagen. Mice injected with purified IgG specific to type VII collagen, in contrast to control mice, developed subepidermal skin blisters, reproducing the human disease at the clinical, histological, electron microscopical, and immunopathological levels. Titers of rabbit IgG in the serum of mice correlated with the extent of the disease. F(ab′) 2 fragments of rabbit IgG specific to type VII collagen were not pathogenic. When injected into C5-deficient mice, antibodies specific to type VII collagen failed to induce the disease, whereas C5-sufficient mice were susceptible to blister induction. This animal model for EBA should facilitate further dissection of the pathogenesis of this disease and development of new therapeutic strategies.

"Nagashima-type" palmoplantar keratosis (NPPK) is an autosomal recessive nonsyndromic diffuse palmoplantar keratosis characterized by well-demarcated diffuse hyperkeratosis with redness, expanding on to the dorsal surfaces of the palms and feet and the Achilles tendon area. Hyperkeratosis in NPPK is mild and nonprogressive, differentiating NPPK clinically from Mal de Meleda. We performed whole-exome and/or Sanger sequencing analyses of 13 unrelated NPPK individuals and identified biallelic putative loss-of-function mutations in SERPINB7, which encodes a cytoplasmic member of the serine protease inhibitor superfamily. We identified a major causative mutation of c.796C>T (p.Arg266(∗)) as a founder mutation in Japanese and Chinese populations. SERPINB7 was specifically present in the cytoplasm of the stratum granulosum and the stratum corneum (SC) of the epidermis. All of the identified mutants are predicted to cause premature termination upstream of the reactive site, which inhibits the proteases, suggesting a complete loss of the protease inhibitory activity of SERPINB7 in NPPK skin. On exposure of NPPK lesional skin to water, we observed a whitish spongy change in the SC, suggesting enhanced water permeation into the SC due to overactivation of proteases and a resultant loss of integrity of the SC structure. These findings provide an important framework for developing pathogenesis-based therapies for NPPK.

Experimental models reproducing an autoimmune response resulting in skin blistering in immunocompetent animals are lacking. Epidermolysis bullosa acquisita (EBA) is a bullous skin disease caused by autoantibodies to type VII collagen. In this study, we describe an active disease model of EBA by immunizing mice of different strains with murine type VII collagen. All mice developed circulating IgG autoantibodies that recognized type VII collagen and bound to the lamina densa of the dermal-epidermal junction. Importantly, subepidermal blisters developed in 82% of SJL-1, 56% of BALB/c mice, and 45% of FcγRIIb-deficient mice, but not in SKH-1 mice. In susceptible animals, deposits of IgG1, IgG2, and complement C3 were detected at the dermal-epidermal junction. In contrast, in the nondiseased mice, tissue-bound autoantibodies were predominantly of the IgG1 subclass and complement activation was weak or absent. This active disease model reproduces in mice the clinical, histopathological, and immunopathological findings in EBA patients. This robust experimental system should greatly facilitate further studies on the pathogenesis of EBA and the development of novel immunomodulatory therapies for this and other autoimmune diseases.

Epidermolysis bullosa acquisita (EBA) is a subepidermal blistering disorder associated with tissue-bound and circulating autoantibodies specific to type VII collagen, a major constituent of the dermal-epidermal junction. Previous attempts to transfer the disease by injection of patient autoantibodies into mice have been unsuccessful. To study the pathogenic relevance of antibodies specific to type VII collagen in vivo, we generated and characterized rabbit antibodies specific to a murine form of this antigen and passively transferred them into adult nude, BALB/c, and C57BL/6 mice. Immune rabbit IgG bound to the lamina densa of murine skin and immunoblotted type VII collagen. Mice injected with purified IgG specific to type VII collagen, in contrast to control mice, developed subepidermal skin blisters, reproducing the human disease at the clinical, histological, electron microscopical, and immunopathological levels. Titers of rabbit IgG in the serum of mice correlated with the extent of the disease. F(ab′) 2 fragments of rabbit IgG specific to type VII collagen were not pathogenic. When injected into C5-deficient mice, antibodies specific to type VII collagen failed to induce the disease, whereas C5-sufficient mice were susceptible to blister induction. This animal model for EBA should facilitate further dissection of the pathogenesis of this disease and development of new therapeutic strategies.

Several components of the basement membrane zone (BMZ) have been identified as antigenic targets in autoimmune bullous diseases. We report a novel disease with autoantibodies to a BMZ antigen that is different from the targets described so far. The patient suffering from this disorder showed tense bullae and severe mucous membrane involvement rapidly responding to oral tetracyclines and colchicine. Histopathologic findings resembled those of dermatitis herpetiformis. Direct immunofluorescence microscopy showed linear deposits of IgG and C3 at the BMZ. By indirect immunofluorescence studies on split human skin, using both 1 M NaCl and suction blistering for dermal-epidermal separation, IgG antibodies localized exclusively to the dermal side of the split. The antibodies were mainly of the IgG4 sub-class. By Western blot analysis of epidermal and dermal extracts, the patient's serum unequivocally reacted with a dermal antigen of 200 kDa. It did not recognize bullous pemphigoid antigens (the autoantigen of epidermolysis bullosa acquisita), purified preparations of laminin-1 and laminin-5, or the recently described 105-kDa BMZ antigen. By immunoblotting of concentrated conditioned SCC-25 medium, the patient's antibodies reacted with a band of 200 kDa and several bands of lower molecular weight. No reactivity was seen with extracts of cultured human fibroblasts. By indirect immunogold electron microscopy, immunoreactants localized to the lower lamina lucida. After clearance of skin lesions, both indirect immunofluorescence and Western blot analysis became negative. This patient suffers from a novel autoimmune bullous disease with autoantibodies to a 200-kDa antigen of the BMZ.