The Ability of the Murine Placenta to Absorb Monoclonal Anti-Fetal H-2K antibody from the Maternal Circulation

Abstract

One of the major unresolved questions in transplantation immunology is the mechanism that prevents the mother from rejecting her allogeneic offspring in utero (1). A number of investigators have proposed that the placenta could serve as a histocompatibility antigen-containing immunoabsorbent barrier between mother and fetus, preventing potentially harmful maternal antibodies from reaching the fetus (2–7). We have recently obtained direct evidence for this by injecting partially-purified radiolabeled antibodies directed against the paternal strain H-2 haplotype into the maternal circulation during pregnancy (6, 7). We found that the antibody differentially accumulated in the placenta exclusively, and only when the fetus bore the target H-2 haplotype, although the exact component(s) of H-2 being recognized was not defined. Fetectomy experiments ruled out the fetal circulation as an immediate source for the immunoabsorbent effect.In this communication we report confirmation of these findings by using a highly purified monoclonal antibody directed solely against a K region antigen coded for by the fetal H-2 haplotype. We have also determined that Fc receptor binding is not a necessary precondition for this differential binding, because the F(ab')2 portion of this monoclonal antibody shows a similar differential uptake in the placenta.