Cloning of canine desmoglein 3 and immunoreactivity of serum antibodies in human and canine pemphigus vulgaris with its extracellular domains

Background: Pemphigus vulgaris (PV) is an antibody-mediated autoimmune blistering disease of the skin and mucous membrane recognized in humans and several domestic animals, including dogs. The autoimmune target in human PV has been identified as desmoglein (Dsg) 3, a desmosomal cell-cell adhesion molecule, whereas the autoimmune target in canine PV has not yet been identified clearly. Objective: To obtain and sequence the mRNA for the entire coding region of canine Dsg3, and to investigate whether the serum antibodies in human and canine PV recognize the extracellular domains of canine Dsg3. Methods: The cDNA clones for canine Dsg3 were obtained from cultured-canine keratinocytes by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of the cDNA ends (RACE) and were sequenced. Immunoprecipitation-immunoblotting (IP-IB) was performed with nine human PV sera, a canine PV serum and six normal canine sera using canine keratinocyte extracts as well as the entire extracellular domain of canine Dsg3 produced by baculovirus as the substrates. Results: The open reading frame of canine Dsg3 consists of 993 amino acids, and shares 81.2 and 72.6% amino acid identities with human and mouse Dsg3, respectively. IP-IB demonstrated that all of the human and canine PV sera, but none of the normal canine sera tested, immunoprecipitated a 130-kDa protein in canine keratinocyte extracts as well as the recombinant extracellular domains of canine Dsg3. Conclusion: The cDNA sequence and the baculovirus recombinant protein of canine Dsg3 will be useful to characterize the serum autoantibodies in canine PV.