Herpes gestationis associated with the C3 nephritic factor.

Herpes gestationis (HG) is a rare, blistering disease of pregnancy and the puerperium that has immunologic findings of C3 with or without IgG deposited in a linear, band-like distribution along the dermoepidermal basement membrane zone (BMZ). A circulating IgG factor has been demonstrated that will fix complement by the classic pathway in vitro. This study involves a patient who had classic HG with C3 at the BMZ, and who had a circulating factor with activity via the alternative complement pathway similar to the previously described C3 nephritic factor found in patients with partial lipodystrophy, systemic lupus erythematosus, and membranoproliferative glomerulonephritis. Like the C3 nephritic factor, the activity was detected in IgG fractions of serum samples.