Circulating levels of pregnancy proteins and depression of lymphoblastogenesis during pregnancy.

Plasma was obtained from 287 normal pregnant women at different times of gestation. Alpha-foetoprotein (AFP), human chorionic gonadotrophin (hCG), human placental lactogen (hPL) and pregnancy associated plasma protein-A (PAPP-A) were measured by radioimmunoassay. The capacity of those plasmas to inhibit phytohaemagglutinin (PHA) induced lymphocyte transformation was also tested. Between the 7th and the 12th week, pregnancy plasma has a relatively small inhibitory effect on lymphoblastogenesis. Plasmas taken between the 13th week and term pregnancy inhibit much more lymphocyte transformation. The factor which increases this inhibition is unknown. None of the proteins measured were significantly correlated with the inhibitory effect. Two explanations are proposed: either AFP, hCG, hPL and PAPP-A are not responsible for the in vitro inhibition of lymphoblastogenesis or else these factors exert a combined effect so that the concentration of each protein taken separately cannot account for the overall inhibitory effect observed with pregnancy plasma.