Canine pemphigus foliaceus antigen is localized within desmosomes of keratinocyte.

The target antigen of autoantibodies in human pemphigus foliaceus (PF) is a desmosomal cadherin, desmoglein 1 (Dsg1). It was demonstrated by immunoelectron microscopy (IEM) that the location of the binding sites of PF autoantibodies in the human epidermis was the extracellular regions of the desmosomes. Only a limited number of canine PF sera were shown to react with canine Dsg1, and the target proteins have not yet been identified. The purpose of this study was to demonstrate the ultrastructural binding site of canine PF autoantibodies to the canine skin by two kinds of IEM methods. Three canine PF sera, which were shown to react with the keratinocyte cell surface by immunofluorescence, were tested in this study. Using a technique of immunoprecipitation-immunoblotting, one out of the three canine PF sera were shown to react with recombinant canine Dsg1. By post-embedding IEM using cryofixation technique, one serum, which did not react with canine Dsg1 by immunoprecipitation-immunoblotting, bound broadly to the extra- and intracellular regions of the desmosomes of normal canine skin. By pre-embedding IEM using canine cultured keratinocytes (MCA-B1 cells), the autoantibodies of all three canine PF sera were identified to be bound to the cell-cell contact area of the adjacent cytoplasmic projections. When double stained with human PF serum and canine PF sera, the binding sites of both human and canine autoantibodies were co-localized on the MCA-B1 cells where the cytoplasmic projections contacted each other. Therefore, it may be concluded that the serum antibodies of canine PF targeted desmosomal proteins, regardless of whether or not they react with canine Dsg1 by immunoprecipitation-immunoblotting method.