Subclass reactivity of pemphigus foliaceus autoantibodies with recombinant human desmoglein

Pemphigus foliaceus (PF) and its endemic form, Fogo Selvagem (FS), are autoimmune disorders characterized by subcorneal vesicles and IgG4 subclass autoantibodies that recognize a surface antigen of normal epidermal cells. FS and PF autoantibodies have been shown to bind desmoglein (DGI), a desmosomal glycoprotein classified as a member of the cadherin family of calcium-dependent cell adhesion molecules. In the present study we report the isolation of three overlapping cDNA clones representing greater than 90% of the extracellular domain of human DGI. Recombinant proteins encoded by these clones, designated DGI-1, DGI-2, and DGI-3, were produced in bacteria and analyzed for immunoblot (IB) reactivity with a panel of FS, PF, and control sera. FS and PF autoantibodies possessing reactivity with each of the three recombinant fusion proteins (FPs) were identified. FP DGI-3 (containing 123 amino acids of the membrane proximal region of the DGI ectodomain) showed reactivity with the largest number of patient sera--seven FS and one PF. IB reactivity with the DGI-1 FP (encoding 205 amino acids of the N-terminal region of DGI) could be eliminated by truncation of the C-terminal portion of this protein, indicating that autoantibodies were not binding the R-A-L motif. Autoantibodies reactive with two of the three FPs were predominantly restricted to IgG4, the subclass shown to be pathogenic in the passive transfer mouse model. The findings of this study demonstrate that the extracellular domain of DGI contains at least three antigenic sites recognized by FS and PF autoantibodies. The region near the membrane-spanning domain of DGI appears to contain an immunodominant site. This study is the first to document immunoblot reactivity of FS and PF autoantibodies with recombinant forms of DGI. The use of such molecular tools should facilitate the identification and characterization of relevant antigen/antibody systems in FS and PF.