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B ullous pemphigoid (BP) is an autoimmune skin disease characterized by subepidermal blisters and autoantibodies against 2 hemidesmosome-associated proteins, BP180 and BP230. The immunopathologic features of BP can be reproduced in mice by passive transfer of anti-BP180 antibodies. Lesion formation in this animal model depends upon complement activation and neutrophil recruitment. In the present study, we investigated the role of neutrophil elastase (NE) in antibody-induced blister formation in experimental BP. Abnormally high levels of caseinolytic activity, consistent with NE, were detected in extracts of lesional skin and blister fluid of mice injected with anti-BP180 IgG. The pathogenic anti-BP180 IgG failed to induce subepidermal blistering in NE-null (NE^–/–) mutant mice. NE^–/– mice reconstituted with neutrophils from wild-type mice became susceptible to experimental BP. Wild-type mice given NE inhibitors (α1-proteinase inhibitor and Me-O-Suc-Ala-Ala-Pro-Val-CH₂Cl), but not mice given cathepsin G/chymase inhibitors (α1-antichymotrypsin or Z-Gly-Leu-Phe-CH₂Cl), were resistant to the pathogenic activity of anti-BP180 antibodies. Incubation of murine skin with NE induced BP-like epidermal-dermal detachment. Finally, NE cleaved BP180 in vitro and in vivo. These results implicate NE directly in the dermal-epidermal cleavage induced by anti-BP180 antibodies in the experimental BP model.