Ultrastructural immunogold investigation of the function and diversity of binucleate cells in the ovine placenta using a monoclonal antibody.

Ultrastructural immunogold labelling of ovine placentomes demonstrated that the molecule recognized by the monoclonal antibody SBU-3 is restricted to the fetal binucleate cell granules and Golgi body, and granules of similar size in the syncytium. Quantitative examination shows that the percentage of placentomal mature binucleate cells that are SBU-3-positive increases rapidly from a low level at 29 days of pregnancy to a plateau at virtually 100 per cent from 41 days to term, whereas interplacentomal binucleate cells rarely show label at any stage. There were no detectable differences in ultrastructure between SBU-3-positive or -negative binucleate cells. These results corroborate the hypothesis of syncytium formation by migration of binucleate cells and indicate local control of SBU-3 production and its possible role in villus formation.