Curvicircular intracytoplasmic membranous structures in keratinocytes of pemphigus foliaceus

We noticed intracytoplasmic membranous, annular, or circular structures in the lesion of pemphigus foliaceus and studied these by regular transmission electron microscopy and immunoelectron microscopy. These curvicircular bodies were observed in the preacantholytic keratinocytes of the blister wall as well as in acantholytic cells in 6 out of 6 patients with pemphigus foliaceus. They were absent in samples from 3 patients with pemphigus vulgaris. These structures were about 60-70 nm wide and consisted of 4 electron-dense layers. They were continuous with intact desmosomal structures and gap junctions in the periphery of the keratinocytes. These curvicircular membranous bodies were well labeled with immunogold particles for desmoglein, plakoglobin, connexin 43, and IgG. In contrast to pemphigus vulgaris, splitting of desmosomes through dissolution of intercellular desmoglea was seldom observed in all 6 specimens of pemphigus foliaceus. These findings suggest that in pemphigus foliaceus 1) curvicircular bodies are derived from internalized desmosomes and gap junctions, and 2) cell-to-cell adhesions are weakened by this internalization and acantholysis is initiated, while in pemphigus vulgaris the dissolution of desmoglea is the initial event. It is suggested that in pemphigus foliaceus the binding of autoantibody induces internalization of many intact desmosomes and gap junctions rather than splitting them.