In vitro synthesis of the foetal alpha 1-globulin in man.

Abstract

Synthesis of fetal alpha-1-globulin (AFP) during fetal life was investigated to obtain information on the level of this protein in fetal sera. Tissues and sera were obtained from fetuses born alive but who died immediately after delivery. Short-term cultures of fetal and adult tissues were carried out. The anti-AFP serum was prepared in a rabbit by immunization with serum from a 20-week-old fetus. De novo synthesis of proteins was detected and analyzed by autoradiography of the immunoelectrophoretic pattern. Synthesis of AFP was found in 28/30 fetal liver cultures. During the 10-20 weeks of gestation synthesis of AFP was greater than after this period. Culture fluids of fetal spleen thymus and lung did not contain any newly synthesized AFP. Cultures of adult liver lymph nodes and bone marrow showed no AFP production. AFP synthesis was also studied in placental tissues from 7 fetuses aged from 11-18 weeks. 2 placental cultures contained newly synthesized AFP. Levels of AFP and albumin in serum of 16 6-22 week old fetuses were determined by radial diffusion. The 6- and 7-week-old fetuses contained only traces of AFP. Protein level increased steadily to a maximum at 14-16 weeks but then decreased. In 39 cord sera the AFP level was between 3 and 17 mg/100 ml (5.5 mg average). Albumin in fetal serum increased gradually with age; after Week 20 of gestation the ratio of AFP to albumin fell below 1:10. Therefore the greatest amounts of AFP were synthesized during gestation Weeks 10-20. Synthesis then diminished--in humans as well as other mammals--possibly as a result either of the disappearance of cells exclusively producing AFP or of a regulatory mechanism at the intracellular level.