Presence of uterine pinopodes at the embryo-endometrial interface during human implantation in vitro

In order to study changes occurring on the surfaces of human endometrial ep ithelial cells in the presence of an implanted blastocyst, we used scanning electron microscopy for investigation of five endometrial biopsies and thr ee human implantation sites obtained in vitro. All specimens showed areas w ith endometrial pinopodes, separated by cells displaying microvilli or cili a at the apical surface. Pinopode formation was more pronounced in endometr ial biopsies than in cell cultures. All blastocysts adhered to pinopode pre senting cells. Endometrial surface changes were not seen around the blastoc ysts. The results of this study demonstrate that cultured endometrial epith elial cells are capable of pinopode formation. Furthermore, endometrial epi thelial pinopodes, generally considered as a marker of endometrial receptiv ity, seem to be directly involved in the adhesion of the blastocyst to the endometrial surface.