Autoimmunity against type VII collagen: role of the complement system in the induction and effector phase of the autoimmune response

Type VII collagen is a structural protein of the skin and contributes significantly to the adhesion between the epidermis and dermis. Patients with epidermolysis bullosa acquisita (EBA) suffer from a severe, subepidermal blistering autoimmune dermatosis associated with autoantibodies against type VII collagen. Until now, however, it was unclear whether these autoantibodies are actually pathogenetically relevant. Recently, we succeeded for the first time in inducing dermo-epidermal cleft formation using IgG from EBA patients incubated with frozen sections of human skin. The patients' antibodies had previously been purified against a recombinant form of type VII collagen. In addition to the antibodies, the additional incubation of the frozen sections with leukocytes from healthy donors was a mandatory prerequisite for blistering in this in vitro model. Using this assay, the present project proposal aims to characterize the humoral and cellular mechanisms of blistering in EBA.Overlapping recombinant fragments of the type VII collagen NC1 domain will be expressed in insect cells, purified by affinity chromatography, coupled to a matrix, and used to map the pathogenetically relevant epitopes. In further experiments, we aim to characterize the pathogenetically relevant IgG subclass(es) of autoantibodies and investigate the role of proteases as well as various inflammatory cells and their Fc receptors in blistering in this experimental model. Our work is expected to lead to new insights into the pathogenesis of EBA and provide the basis for the future development of more differentiated therapies for this disease.