In a study of twenty-five patients with herpes gestationis we found that 80% possessed the HLA antigen DR3, which confers increased immune responsiveness and a predisposition to 'auto-immune disease'. In five patients the development of herpes gestationis coincided with a change in sexual partner, suggesting that the development of herpes gestationis may depend on exposure to an antigen derived from the father. This might share determinants with a component of the basement membrane zone of skin. Although anti-basement membrane zone antibodies are present in HG it is not clear whether they play a pathogenic role. The infrequency of neonatal involvement and the lack of correlation between immunofluorescence findings and clinical activity in our patients suggested that the antibodies might be a result of tissue damage rather than its cause. Two patients in our study were exceptional in that episodes of herpes gestationis were followed by normal pregnancies. In these patients the relationship of their DR antigens to those of the fetus may have been important in determining whether or not the pregnancy would be affected by herpes gestationis.

We compared the clinical features, histopathology, immunopathology and immunogenetics of 30 patients with toxic erythema of pregnancy and 24 patients with herpes gestationis. Although we found some clinical and histopathological overlap we highlighted several important differences. In toxic erythema of pregnancy prominent striae were frequently present. Herpes gestationis was suggested by the occurrence of periumbilical lesions, acute exacerbations immediately after delivery, and persistence of the eruption for more than 3 weeks post-partum. In herpes gestationis, immunofluorescence studies were consistently positive, there was a high frequency of HLA-B8 and an association with autoimmune thyrotoxicosis. Toxic erythema of pregnancy did not share these immunological features. Therefore we feel that toxic erythema of pregnancy and herpes gestationis should continue to be classified as separate disorders.

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