Immunological factors responsible for pathogenetic cell degeneration in pregnancy.

The placenta has an important role as an immunological barrier during pregnancy. When the placental barrier is disrupted, materno-embryonic transfusion takes place. Several clinical reports relate congenital malformations or abortion to intrauterine bleeding or transplacental transfusion. In an earlier experiment, pathogenetic cell degeneration was induced using an in vitro whole rat embryo culture. Transplacental transfusion was simulated by intracardiac injection of an allogeneic rat-antirat serum directed against the blood group antigens. The present study examines the morphological and immunological effects on the development of rat embryos 9 to 10 days old (stages 8-10 somites) of the separate administration of primary allogeneic antisera, obtained 10-17 days after immunization, and secondary allogeneic antisera, obtained after booster immunization on day 45-52. Rat-antirat alloantibodies were directed against the blood group antigens. Transplacental transfusion was simulated by the embryonic intracardiac microinjection of approximately 0.5 microliters serum enriched with either primary or secondary obtained allogeneic antibodies. After 48 hours' incubation, the embryos were examined microscopically, and it appeared that the secondary antisera, which had hemolytic activity, was more potent (P less than 0.005) in the induction of pathogenetic cell degeneration. It is well known that IgG antibodies display hemolytic activity. This finding was confirmed by direct immunofluorescence performed on rat embryos 2, 4, and 6 hours after injection, where incubation with rabbit-antirat anti-IgG antibodies gave a strong reaction. The hypothesis discussed is whether or not pathogenetic cell degeneration subsequent to transplacental transfusion of maternal antibodies can be initiated by similar immunological events.