Pathology and immunology
Histopathologic findings demonstrate subepidermal vesicles, spongiosis, and perivascular lymphocyte, and histiocyte infiltrates with a preponderance of eosinophils.3 The sine qua non of the disease, though, is the demonstration through direct immunofluorescence of complement deposition and IgG in a linear band along the basement membrane.14
There appears to be a genetic predisposition toward the development of pemphigoid gestationis. Associations with human leukocyte antigens (HLAs) DR3 (61%–85%), DR4 (52%), or both (43%–50%) have been reported.3,15,16 Interestingly, 85% of persons with a history of pemphigoid gestationis were found to have anti-HLA antibodies, some of which were directed against paternal HLAs expressed in their placentae.17 These findings raised speculation about a possible immunologic insult against placental antigens during pregnancy. Evidence suggests that circulating autoantibodies in patients with pemphigoid gestationis bind to the dermal-epidermal junction of skin and amnion in which BP180 antigen is also present.18-20
It has been demonstrated that in patients with pemphigoid gestationis the cells of the placenta stroma express abnormal major histocompatibility complex (MHC) class II molecules.21,22 This lead to the proposition of 2 possible mechanisms for the initiation of an autoimmune response in pemphigoid gestationis. The first proposes that placental BP180 is presented to the maternal immune system in association with abnormal MHC molecules, which then trigger the production of autoantibodies that cross-react with the skin. Alternatively, the placental stromal cells may evoke an allogeneic reaction against the BP180 antigen presented by paternal MHC molecules of the placental stroma, which then cross-reacts with the skin.23 The latter theory supports the findings in this patient, who developed pemphigoid gestationis during the 2 pregnancies with her second husband and not during the pregnancies with her first husband.