• Fetal allograft;
  • fertilization;
  • trophoblast cells

ABSTRACT: Early pregnancy factor (EPF) is a factor that has been shown to be involved in the maintenance of the fetal allograft in several mammalian species including man. In that capacity it serves as a link between fertilization and immunomodulation. In the present study we have investigated the secretion of EPF by the human conceptus before and after implantation using rosette inhibition antibody concentration (T11 monocllonal antibody). In isolated trophoblastic cells at gestational week 7–9 there was a significant secretion of EPF. For the first 8 days in culture, secretion was maximal; later, however, at days 13 and 21 these levels declined. Further the EPF content of human embryonal extracts was examined. In various organs, spinal cord, liver, and kidney, significant EPF activity was detected. In women undergoing in vitro fertilization/embryo transfer, a total of 52 preimplantational embryos were cultured for 36 hours. No significant EPF activity was detected in the surrounding media. Two of the 11 patients studied became pregnant during the same cycle after embryo transfer. In conclusion, the preimplantational origin of EPF is maternal, while that of the post-implantational embryo is of embryonal origin.