Herpes gestationis (HG) is a rare pregnancy-associated disease. A 35-year-old G3P2 presented during her third trimester with erythematous pruritic papular eruptions. Electron microscopic immunocytochemical investigations, performed with a peroxidase-antiperoxidase sandwich technique, revealed the in vivo-bound IgG to be localized at the epidermal basal lamina and to exhibit a distribution pattern which is identical to that reported for bullous pemphigoid. Immunoblotting of human epidermal extracts and immunofluorescence of various tissues also suggested that the sera did not recognize any other desmosomal components or paraneoplastic pemphigus antigens. 73% (11/15) of BP sera and 100% (8/8) of HG sera reacted with at least one of three BP180 fusion proteins representing various portions of the NC16A domain. Immunoadsorption analysis identified this region of BP180 as an immunodominant site. In the later blister stage, the basal lamina was usually lost.
These findings confirmed the predicted type II transmembrane orientation of the BP180 Ag. Thus, the long, C-terminal collagenous domain of this basal keratinocyte protein projects into the basal lamina and may function as a site of interaction with an extracellular matrix component. It is proposed that autoantibodies directed against the well-defined antigenic site on the BP180 ectodomain may play an initiatory role in subepidermal blister formation in BP and HG patients.