On electron microscopic examination, the most prominent change in a case of herpes gestationis consisted of severe necrosis of the basal cells. The basal lamina usually was located at the floor of the blister. A pronounced cellular infiltrate was found in the dermis and epidermis, consisting mainly of eosinophils and macrophages. It was concluded that the blister formed as the result of disintegration of basal cells and an accumulation of fluid between basal cells and basal lamina.
Schaumburg-Lever G, Saffold OE, Orfanos CE, Lever WF. Herpes GestationisHistology and Ultrastructure. Arch Dermatol. 1973;107(6):888-892. doi:10.1001/archderm.1973.01620210052014