Molecules of the early equine trophoblast

Three monoclonal antibodies raised against equine trophoblast cells were tested to determine the characteristics of the identified molecules. First, the antibodies were used to precipitate molecules from radiolabelled equine trophoblast cells of the chorionic girdle. Antibody F71.1 precipitated a molecule of 115 kDa, whereas antibodies 71.8 and 71.10 precipitated a molecule of 66 kDa. Second, 2 of the antibodies were used in an indirect immunoperoxidase assay on frozen sections of equine conceptuses of different gestational ages beginning at Day 8. Antibody F71.1 labelled trophoblast cells from Day 13 onward, whereas antibody F71.8 first labelled trophoblast cells beginning on Day 24. Third, the antibodies were tested for reactivity with first trimester human placental tissues using an indirect immunoperoxidase assay. Antibody F71.1 labelled villous cytotrophoblast cells, whereas antibody F71.8 labelled only the syncytiotrophoblast cells. Neither antibody reacted with extra-villous trophoblast cells. The molecular weight and tissue distribution of the antigen identified by antibody F71.8 suggest that it may be a placental form of alkaline phosphatase. The molecule identified by antibody F71.1 was first detected very close to the time of maternal recognition of pregnancy in the mare.