To study the expression of plexin-B1 in high- and low-receptive epithelial-endometrial cell lines, and its possible role in endometrial adhesiveness.Controlled, laboratory study.Laboratory for Research in Reproductive Sciences, Department of Obstetrics and Gynecology, Ha'Emek Medical Center, Afula, Israel.None.None.This study was designed to explore and compare the expression and role of plexin-B1 in endometrial cell lines RL95-2 and HEC-1A, used as models of receptive and nonreceptive cells, respectively. The expression of plexin-B1 was analyzed by Western blotting and reverse-transcriptase polymerase chain reaction. The possible role of plexin-B1 in endometrial-trophoblast adhesiveness was studied with attachment and invasion assays. For further validation, we transfected HEC-1A cells with an expressing vector encoded for plexin-B1.Significant differences in spheroid attachment was observed between RL95-2 and HEC-1A cells. Western blotting and reverse-transcriptase polymerase chain reaction revealed that in RL95-2 cells, the expression of plexin-B1 was significantly higher. An attachment assay that used RL95-2 cells in the presence of inhibiting antibodies against plexin-B1 significantly decreased the attachment rates of spheroids. A comparison between HEC-1A and transfected HEC-1A (HEC-1A-2) cells showed significant differences in spheroid attachment. No significant difference was found between HEC-1A-2 and RL95-2. An attachment assay using inhibitory antibodies against plexin-B1 significantly decreased the spheroid-attachment rate.Based on our results, we think that plexin-B1 contributes to trophoblast-endometrium interactions, most likely by enhancing adhesion properties.