Specific immunoadsorption of pathogenic autoantibodies in pemphigus requires the entire ectodomains of desmogleins

Pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are life-threatening autoimmune blistering skin diseases. They are characterized by circulating autoantibodies which bind to the ectodomains of desmoglein (Dsg) 1 and Dsg3. These antibodies induce acantholysis in skin and mucous membranes. In severe cases of pemphigus, immunoadsorption is applied to remove total IgG from patient plasma using protein A or other ligands. To develop a specific adsorber for anti-Dsg antibodies, epitope mapping studies of Dsg1 and Dsg3 ectodomains were conducted. Dsg variants were expressed on the surface of HEK-293 cells and analysed for reactivity with pemphigus and control sera by indirect immunofluorescence technique. For Dsg1, a construct consisting of domain 1 directly fused to domain 5, seemed to be suitable for specific immunoadsorption of anti-Dsg1 antibodies. The recognized epitopes were mainly conformation-dependent. However, adsorption of pemphigus foliaceus IgG using this protein coupled to a Sepharose matrix did not completely remove pathogenicity from the sera, as proven by a keratinocyte dissociation assay. In contrast, full-length Dsg1 and Dsg3 ectodomains were able to specifically adsorb anti-Dsg antibodies and to efficiently eliminate pathogenicity. Therefore, the complete and correctly folded ectodomains of both desmogleins are required for therapeutic immunoadsorption.