Immunoadsorption against two distinct eiptopes on human type XVII collagen abolishes dermal-epidermal separation induced in vitro by autoantibodies from pemphigoid gestationis patients

Pemphigoid gestationis (PG) is a subepidermal autoimmune blistering disease characterized by self-reactive T and B cells specific for the transmembrane hemidesmosomal protein type XVII collagen/BP180. Major T and B cell epitopes are located within the immunodominant 16th non-collagenous domain A (NC16A) of type XVII collagen. The aim of the present study was to map the pathogenically relevant epitopes targeted by blister-inducing patients' autoantibodies. For this purpose, we used an in vitro model of autoantibody-induced leukocyte-dependent dermal-epidermal separation. Pre-adsorption against a recombinant form of the NC16A region abolished the blister-inducing potential of autoantibodies from all PG patients. Using overlapping synthetic peptides, we demonstrated that PG autoantibodies bind to two defined epitopes within the NC16A region (aa 500-514 and as 511-523). Importantly, pre-adsorption using an affinity matrix containing these epitopes completely abolished dermal-epidermal separation induced by PG autoantibodies. This study identifies the epitopes relevant for blister induction in PG and should facilitate the development of an antigen-specific immunoadsorption therapy for this disease.