Background Pemphigus foliaceus (PF) is a chronic cutaneous autoimmune blistering disease that is characterized by superficial blistering of the skin, and according to the current perspective is caused by autoantibodies directed against desmoglein 1 (Dsg1).
Objectives To examine early acantholysis in skin of PF patients at an ultrastructural level.
Methods Two Nikolsky negative (N-), five Nikolsky positive (N+) and two lesional skin biopsies of immunoserological defined PF patients were studied by light and electron microscopy.
Results We found no abnormalities in N- PF skin, whereas all N+ skin biopsies displayed intercellular widening between desmosomes, a decreased number of desmosomes, and hypoplastic desmosomes in the lower epidermal layers. Acantholysis was present in two of five N+ biopsies, but only in the upper epidermal layers. The lesional skin biopsies displayed acantholysis in the higher epidermal layers. Hypoplastic desmosomes were partially (pseudo-half-desmosomes) or completely torn off from the opposing cell.
Conclusion We propose the following mechanism for acantholysis in PF: initially PF IgG causes a depletion of non-junctional Dsg1, leading to intercellular widening between desmosomes starting in the lower layers and spreading upwards. Depletion of non-junctional Dsg1 impairs the assembly of desmosomes, resulting in hypoplastic and a decreased number of desmosomes. In addition antibodies might promote disassembly of desmosomes. In the upper layers of the epidermis, where Dsg3 is not expressed and cannot compensate for Dsg1 loss, ongoing depletion of Dsg1 will finally result in a total disappearance of desmosomes and subsequent acantholysis.