Specific antigens of rat embryonic serum.

Three s|>ecifieembryonic constituents were revealed in the rat serum using rabbit immune sera. These were: a globulin palled Antigen LA, an a2-glycoprotein, and a lipoprotein-esterase. All three antigens were found in embryonic serum, while low titers of the lipoprotein-esterase were found in adult sera. The titers of Antigen LA and the <*2-glycoproteinwere followed in the female rat during gestation and in the newborn after birth. Antigen LA was purified from amniotic fluid by an immunoabsorption technic which employs an insoluble polymer of rabbit immune serum prepared against adult rat serum. It was shown to be a protein of euglobulin nature, sedimenting at 2.9 S.