Progress in Characterization of Pre‐Implantation Factor in Embryo Cultures and In Vivo

Abstract

PROBLEM: Pre‐implantation factor (PIF), a small, embryo‐derived peptide is detected in the maternal serum prior to implantation and is associated with successful pregnancy outcome. However, its identity is not known.METHOD OF STUDY: PIF was isolated from mouse embryo conditioned media and from pregnant porcine sera, using high‐performance liquid chromatography (HPLC) followed by mass spectrometry.RESULTS: Conditioned culture media was separated by gel filtration chromatography followed by reversed phase chromatography. At each step, PIF activity was determined by the lymphocyte/platelet binding autorosette assay (LPBA). Mass spectrometry yielded a single peak with a mass of 1300 Da. The peptide is, however, present in very low concentrations (fM), which has so far precluded complete identification. Pregnant porcine sera that exhibit potent PIF activity were deproteinated by acetone and further fractionated by reversed phase HPLC. Active fractions contain peptides of molecular masses 523 and 551 Da.CONCLUSION: PIF, likely to be peptides, represents a novel substance related to pregnancy initiation and maintenance.