Pemphigus foliaceus antigen: characterization of an immunoreactive tryptic fragment from BALB/c mouse epidermis recognized by all patients' sera and major autoantibody subclasses

The pemphigus foliaceus antigen (PF Ag) is a 160-kDa desmosomal core glycoprotein, desmoglein I. A 50-kDa soluble immunoreactive fragment of the PF Ag was recently prepared from trypsinized cornified cell envelope preparations by papain treatment (R.S. Labib et al. 1989, J. Invest. Dermatol. 93, 272-279). This papain fragment (pf-PF) is associated with upper cell layers of the epidermis and appears to be trypsin resistant in situ. The present work describes the preparation of another fragment by trysinization of the viable lower cells of the epidermis of neonatal BALB/c mice. This tryptic fragment (tf-PF) is a 45-kDa glycoprotein that is partially purified by concanavalin A affinity chromatography of the trypsinization medium. The partially purified tf-PF preparation is capable of completely blocking the indirect immunofluorescence of high titer PF sera. The tf-PF is immunoprecipitated by all PF sera tested (n = 19) and by the two major subclasses of PF autoantibodies, IgG1 and IgG4. Autoantibodies of both the predominant IgG4 and the less prevalent IgG1 subclasses precipitate the same tf-PF as demonstrated by a single compact spot of pI 5.5 by two-dimensional polyacrylamide gel electrophoresis. Chemical and immunological comparison of the tf-PF and pf-PF may explain why the acantholytic lesions of PF appear only in the upper epidermis, despite the presence of the PF Ag throughout all layers of the epidermis. The availability of these two soluble immunoreactive fragments of the PF Ag will be of great value for the further immunochemical characterization of the antigenic epitopes and their role in cell-cell adhesion.