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Activation of the complement cascade via the classical pathway is required for the development of tissue injury in many autoantibody-mediated diseases. It therefore makes sense to block the pathological action of autoantibodies by preventing complement activation through inhibition of autoantibody binding to the corresponding pathogenic autoantigen using targeted Fab antibody fragments. To achieve this, we use bullous pemphigoid (BP) as an example of a typical autoimmune disease. Recombinant Fabs against the non-collagenous 16th-A domain of type XVII collagen, the main pathogenic epitope for autoantibodies in BP, were generated from antibody repertoires of BP patients by phage display. Two Fabs, Fab-B4 and Fab-19, showed marked ability to inhibit the binding of BP autoantibodies and subsequent complement activation in vitro. In the in vivo experiments using type XVII collagen humanized BP model mice, these Fabs protected mice against BP autoantibody-induced blistering disease. Thus, the blocking of pathogenic epitopes using engineered Fabs appears to demonstrate efficacy and may lead to disease-specific treatments for antibody-mediated autoimmune diseases.

All mammal neonates receive maternal Abs for protection against pathogenic organisms in the postnatal environment. However, neonates can experience serious adverse reactions if the Abs transferred from the mother recognize self-molecules as autoAgs. In this study, we describe a novel model for autoimmune disease induced by transferred maternal Abs in genetically transformed Ag-humanized mice progeny. Bullous pemphigoid is the most common life-threatening autoimmune blistering skin disease that affects the elderly, in which circulating IgG autoAbs are directed against epidermal type XVII collagen (COL17). We have established a genetically manipulated experimental mouse model in which maternal Abs against human COL17 are transferred to pups whose skin expresses only human and not mouse COL17, resulting in blistering similar to that seen in patients with bullous pemphigoid. Maternal transfer of pathogenic Abs to humanized neonatal mice is a unique and potential experimental system to establish a novel autoimmune disease model.