043 A novel tool to analyse the pathogenic impact of IgG binding to extracellular domain 5 of Desmoglein 3

      Pemphigus vulgaris (PV) is a severe autoimmune blistering disease characterized by autoantibodies (auto-ab) against the desmosomal adhesion molecules desmoglein3 (Dsg3) and Dsg1. Binding of Dsg specific auto-ab to target structures induces an interruption of the desmosomal integrity which ultimately results in the clinical manifestation of flaccid blisters and erosions in PV patients. Underlying mechanisms inducing blister formation upon binding of Dsg-specific auto-ab are largely unknown. Numerous studies demonstrated the pathogenicity of auto-ab specific for the amino-terminal region (extracellular domain 1, EC1) of Dsg3. However, the Dsg3 specific auto-ab response in PV patients is polyclonal, including auto-ab directed against both amino- and membrane proximal epitopes. In this study, the pathogenicity of a murine monoclonal antibody directed against the membrane-proximal region (EC5) of the Dsg3 ectodomain was analysed. This Dsg3-specific antibody was isolated from the supernatant of a Dsg3-specific B-cell hybridoma and tested in various specificity and functional assays as well as in-vivo. Results clearly demonstrate that this murine auto-ab specifically binds human Dsg3 and is capable of inhibiting intercellular keratinocyte adhesion accompanied by the activation of the p38 MAPK signal transduction pathway. Here, for the first time, we can demonstrate that a specific auto-ab directed against the membrane-proximal region EC5 of human Dsg3 exhibit pathogenic activity similar to the well characterized EC1-specific antibody AK23 without the Ca2+ dependency. Our results deliver new aspects of a more defined understanding of auto-ab-induced blister formation in PV.