text: Reactivity of rat placental cells with alloantisera.
  The nature of the protection afforded the placental structure against the immunologic consequences that could result from maternal exposure to paternal alloantigens remains obscure. One problem has been difficulty in antigenically defining the individual cellular components of the intact placenta. These studies were designed to examine serologically, with specific antisera, five cell types isolated from the rat placenta. The results indicate that non-Ag-B antigens are present on the cytotrophoblast cells, while Ag-G antigens are absent on all the cells except an undefined population of fibroblasts. Of particular significance is the obvious absence of detectable surface antigens on the cells directly in contact with the maternal tissues, the trophoblast mononuclear giant cells.