Nonprofessional phagocytosis in trophectoderm cells of human preimplantation blastocysts

Trophoblast phagocytosis has been considered important in pregnancy. However, whether human preimplantation blastocysts possess phagocytic activity is still unclear. In this study, we determined the phagocytosis potential in human trophectoderm cells of blastocysts prior to implantation. Fluorescent microspheres were used as markers for phagocytic analysis under transmission electron microscope (TEM) and fluorescence microscopy. Phagocytosis of 1 m fluorescent microspheres was observed in most (9/11) day-6 and even some (2/9) day-5 blastocysts. More effective phagocytosis occurred in blastocysts at the morula-blastocyst stage of day-6. Furthermore, we observed an increased trend of phagocytic acitivities in polar trophectoderm. Our findings indicated phagocytic ability exists in human blastocysts prior to implantation and the differentiation between polar and mural trophectoderm may be associated with blastocyst implantation.