The role of carbohydrates in embryo implantation in the mouse was investigated using an embryo transfer model and a blastocyst-uterine epithelial cell co-culture system. The monoclonal antibody (mAb) AH 6 directed to Le Y oligosaccharide (Fuc α1-2 Gal β 1-4 [Fuc α1-3] GlcNAc) and other three mAbs directed to carbohydrates whose structures are closely related to Le Y were used to show the effect of carbohydrate specificity on implantation. In the embryo transfer model, donor blastocysts (4 days

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... ost-coitus) were pretreated with mAb AH 6 (experimental) or other mAbs (control) and transferred into one uterine horn of a recipient. The implantation rate was checked after 5 days. Implantation was significantly inhibited by mAb AH 6 pretreatment, and inhibition was not observed in control groups. In the co-culture system, the attachment and outgrowth rate of blastocysts on the surface of uterine epithelial cells was significantly inhibited when monolayer epithelial cells or blastocysts were pretreated with mAb AH 6 . The most obvious effect of mAb AH 6 was obtained during 2-4 h co-incubation. No inhibition was observed in the control groups. It was, therefore, concluded that oligosaccharide Le Y recognized by mAb AH 6 plays an essential role at the initial stage of implantation. It may act as a mediator molecule for adhesion between the surface of blastocyst and epithelial cell, and its function is carbohydrate-specific.