During embryo implantation, trophinin mediates cell adhesion by homophilic binding at the apical surfaces of trophectoderm and endometrium. Trophinin is expressed on the human endometrial epithelia in rare occasions. We developed hCG-coated agarose beads that mimic the physical and physiological features of an implantation-stage human blastocyst. When hCG-coated beads were applied to human endometrial epithelial cells in the presence of IL-1β, endometrial cells acquired strong trophinin expression and the ability for apical cell adhesion with trophinin-expressing human trophoblastic cells. These results provide a mechanism for trophinin-mediated adhesion of human blastocyst to endometrium by a spatially and temporally restricted paracrine effect of hCG derived from the blastocyst.
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