Fate of antipaternal H-2 antibodies bound to the placenta in vivo.

We have previously demonstrated that the placental spongiotrophoblast and yolk sac venous plexus express paternally derived H-2K and D (class I) antigens in a manner accessible to maternal circulation, and that the placenta serves to prevent antipaternal antibodies from reaching the fetus. Kinetic studies indicated that the placenta is capable of reexpressing its H-2 antigens after having been bound by anti-H-2 antibodies, suggesting that the placental cells somehow have the ability to eliminate the bound antibodies. In order to investigate the fate of the antibodies, we have followed the uptake and fate of radiolabeled anti-H-2Kk monoclonal antibody in the placentas of target allogeneic and control syngeneic pregnancies. Chromatographic analyses indicate that most of the intercellular radiolabel is associated with fragments smaller than IgG, and similar degradation was not observed with syngeneic control placentas. We conclude that the placenta is capable of binding, ingesting, and then digesting antipaternal H-2 antibodies, further substantiating the immunoabsorbent barrier hypothesis of allogeneic fetal survival.