Identification of two species of suppressive factor of differing molecular weight released by in vitro fertilized human oocytes*

Preimplantation human embryos have been shown to release factors that have immunosuppressive activity and that are highly correlated with successful implantation. The present study was undertaken to determine the molecular weight of these factors using HPLC. Two peaks of suppressive activity were found associated with molecular weights of 3.7 +/- 0.3 and 1.2 +/- 0.1 kd, respectively. The potential significance of low molecular weight immunosuppressor factors in avoiding maternal inflammatory and immunologic responses is discussed.