Ruthenium red staining demonstrated the intercellular cement substance more distinctly and specifically than staining with uranyl acetate and lead citrate. The intercellular cement substance was seen in direct contact with the outer leaflet of the plasma membrane. In the acantholysis of pemphigus vulgaris the cement substance underwent dissolution first in nondesmosomal areas and later in desmosomal areas and at intermediate junctions where the cement substance was present as a thicker layer and appeared condensed. Occluding zonules persisted even in degenerated acantholytic cells, indicating a high degree of resistance against separation. In separated desmosomal areas and separated intermediate junctions, the trilaminar structure of the plasma membrane remained intact. In early acantholyzed cells, the attachment plaques and tonofilaments appeared normal. Thus, acantholysis in pemphigus is initially an extracellular phenomenon.
Fine fibrillar structures were found crisscrossing the space between the basal plasma membrane of the basal cell and the basal lamina. The presence of these fibrils partially explained why acantholysis does not occur in this space.
Hashimoto K, Lever WF. An Ultrastructural Study of Cell Junctions in Pemphigus Vulgaris. Arch Dermatol. 1970;101(3):287-298. doi:10.1001/archderm.1970.04000030031005