PEMPHIGUS-FOLIACEUS SERA RECOGNIZE AN N-TERMINAL FRAGMENT OF BOVINE DESMOGLEIN-1

It has previously been demonstrated that sera from endemic and nonendemic pemphigus foliaceus patients recognize three immunoreactive fragments of 80, 62, and 45 kilodaltons (kD) from extracts of the envelope fraction of human and bovine epidermis. These polypeptides are also immunoprecipitated by approximately 50% of pemphigus vulgaris sera, but are unreactive with sera from bullous pemphigoid patients or normal controls. The 80-kD antigen has been shown to be a glycoprotein with N-linked oligosaccharides. Complete removal of the carbohydrate moieties produced a 76-kD polypeptide that continued to react with pemphigus foliaceus autoantibodies in a Ca++-dependent manner. To further characterize this antigen/antibody system, the 80-kD pemphigus foliaceus antigen solubilized from a bovine epidermal envelope extract was purified by affinity chromatography using a pemphigus foliaceus patient's immunoglobulin (Ig)G immobilized on agarose. After elution with 0.2 M glycine/HCl, pH 2.8, 5 mM ethylene diaminetetraacetic acid, the polypeptide was mixed with a small amount of I-125-labeled 80-kD antigen, added as a tracer, fractionated by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and electrotransferred onto a polyvinylidene difluoride membrane. The 80-kD band detected by amido black staining and autoradiography was excised and characterized by amino acid sequence analysis. The resulting sequence, EXIKFAAAXREGEXNSKRNPIA, matched perfectly with the N-terminal 22 amino acids of the mature form of bovine desmoglein 1. These findings demonstrate that the 80-kD bovine autoantibody-reactive polypeptide is the glycosylated ectodomain of desmoglein 1, which may contain epitopes recognized by pathogenic autoantibodies.