Developmental regulation of the monoclonally defined IIC3 antigen during primary and secondary trophoblast differentiation in vitro

The monoclonally defined IIC3 antigen has been found to be developmentally regulated during primary and secondary throphoblast differentiation in the mouse. Cell surface expression of the antigen was associated only with diploid and tetraploid trophoblast cell types. Endoreduplication to 8C DNA in differentiating trophoblast giant cells was associated with a loss of IIC3 cell surface expression and appearance of cytoplasmic expression. This developmental change was not temporally regulated, but dependent on the attachment and outgrowth of the trophoblast in vitro. The surface antigen was neither shed into the media nor masked by glycosylation, but was apparently internalized by the trophoblast giant cells.