Immunological studies of the human placenta: functional and morphological analysis of pregnancy-associated plasma protein A (PAPP-A).

A blood protein, pregnancy-associated plasma protein A (PAPP-A), has been isolated from the plasma of pregnant women. An antiserum to this protein has been prepared and used to localize the protein within the placenta by immunofluorescence. It was found to be inconstantly present in the syncytiotrophoblast and intervillous fibrin. Neither antiserum nor antigen exerts a cytotoxic effect on peripheral blood lymphocytes, and neither affected blastogenic responses of lymphocytes to mitogens or in mixed lymphocyte culture reactions.