Major cleavage-dependent epitopes for linear IgA bullous dermatosis are formed at the boundary between the non-collagenous 16A and collagenous 15 domains of BP180

Abstract

BackgroundThe autoantigen for the major type of linear IgA bullous dermatosis (LAD, lamina lucida type) is the shed ectodomain of BP180. However, it is unknown why most LAD sera react with the shed ectodomain but not with the intact BP180/type XVII collagen. ObjectiveThe aim of this study was to characterize the unique cleavage-dependent epitope(s) in the shed ectodomain. MethodsWe used a monoclonal antibody (MAb-1337) and six LAD sera, which reacted preferentially with the shed ectodomain of BP180. The location and characteristics of the epitopes for these antibodies were analyzed mainly by immunoblotting using chimeric bovine–human BP180 mammalian recombinant proteins and variously truncated bacterial recombinant proteins. ResultsLAD sera and MAb-1337 reacted with the plasmin-digested products of full-length BP180. Four of the six LAD sera reacted to a bacterial recombinant protein consisting of the human non-collagenous 16th A (NC16A) and the collagenous 15th (C15) domains, while these sera were negative or only faintly reactive with the NC16A and C15 recombinants. The epitope for MAb-1337 was localized to the COOH-terminal 21 amino acid region within the NC16A domain. ConclusionThe results in this study indicate that the major epitopes for LAD sera are formed or exposed by a cleavage-induced conformational change, but not by a post-translational modification that occurs only in the shed ectodomain, and are located at the boundary between the NC16A and C15 domains.