An immunohistological survey of 28 full-term human placentas has demonstrated deposits of IgG, ß1C, ß1E, and fibrinogen/fibrin in areas of fibrinoid necrosis and on the trophoblast basement membrane in approximately 35% of placental villi. Traces of IgM were detected at similar sites in 18 of 28 full-term placentas. In 11 specimens of immature placentas (10–18 wk gestation) traces of IgG and ß1C and deposits of fibrinogen/fibrin were also present, but IgM was not detected in this material.
IgG was recovered in acidic eluates from an homogenized placenta which behaved as an antibody reactive with unidentified material present in fibrinoid deposits and on the thickened trophoblast basement membrane of some villi. It could not be determined whether this IgG was derived from the maternal or fetal circulation.