A possible cause for implantation failure following embryo transfer is the rejection of pre-embryos by the maternal immune system. To elucidate the mechanisms underlying the rescue of the pre-embryo from maternal rejection, immunosuppressive activity was investigated in culture media containing human oocytes fertilized in vitro by employing the graft-versus-host reaction and the active rosette test. Normal donor lymphocytes were incubated with culture medium containing either fertilized or nonfertilized oocytes. Control experiments were carried out using lymphocytes incubated in culture medium only, as well as in culture medium containing human sperm. In 67% of the tests (12 out of 18), graft-versus-host reaction was inhibited, as compared to 29% of those performed with medium in which oocytes failed to fertilize (p < 03), and 33% with medium in which only sperm was present. The frequency of an inhibitory active rosette test was similar in both groups. It is possible that immunosuppressive properties are acquired by the human pre-embryo as it grows in culture. Detection of such substances, which could contribute to the establishment of pregnancy, may improve monitoring of embryo quality prior to transfer.
- Immunosuppressive factors