Detection of a pregnancy-associated protein

Monospecific antiserum was produced with the use of a placental extract showing high activity of a proteinase which hydrolyses a synthetic substrate, N-benzoyl-D,L-arginine p-nitroanilide, used for measuring tryptic activity. An immunological study showed that antibodies were not generated against the component with this activity but against an antigen which was not related to several well-known pregnancy-associated proteins. Pregnancy sera contained an antigen which immunologically was completely identical to the antigen of placental origin. Single radial immunodiffusion showed an elevated level of reactive antigen in pregnant subjects: 70% of 333 cases were positive. Cross-reacting antigen was also detected in sera as well as ascitic fluid from cases of advanced ovarian cancer. Sephadex G-200 gel filtration indicated that the antigen has an apparent molecular weight of 94000, and immunoelectrophoresis showed the molecule to be of beta-mobility. These properties suggest that the substance may represent an additional pregnancy-associated protein entity. Partial purification and some immunological properties of this antigen are described.