Sero-immunological studies of the specific protein contained in human placenta

Rabbits were immunized repeatedly (ten times) with the extract of human placenta, and with these rabbits' anti-sera the precipitin reaction was investigated, the following are the results: 1) These anti-sera contained the precipitins reacting on human, fetal and umbilical cord blood sera as well as human placental extract, fetal hemoglobin and amnion water. 2) After absorption of these anti-sera with human, they contained yet some precipitins reacting on human placental extract, fetal, umbilical cord blood sera, amnion water and fetal hemoglobin. They reacted on some pregnant women's sera, and did not on the others. 3) After the absorption of the anti-sera, which were already absobed anti-human sera precipitin, with fetal blood sera or fetal hemoglobin, they did not react on the above mentioned reaction antigens in the former case, but they reacted on them in the latter, though it was weak. 4) It was considered from these data that some specific protein fractions, which were not contained in the adult human sera, were contained in the human placental extract. As J. HIRASE in our laboratory confirmed that the fetal blood sera contained some specific protein fractions, it was also considered that these two fractions were the same. It was suggested by this author that the specific antibody was not the same with the reacting antigen of fetal hemoglobin.