Detection of early pregnancy factor in human sera.

The rosette inhibition titers (RIT) for sera from 94 women at various stages of gestation were detected with a standardized rosette inhibition test. The results showed that an immunosuppressive substance, named early pregnancy factor (EPF), did exist in the pregnancy sera. We confirmed that the EPF activity was very high in the early pregnant stage (the mean RIT = 6.30), gradually decreased with the continuance of gestation, and disappeared at 8 weeks before delivery when the mean RIT for sera (less than 4) had fallen in the RIT nonpregnant range. In addition, observations for the EPF dynamic changes before and at varying stages after the induced abortion in 21 pregnant women showed that the mean RIT was 5.9 +/- 0.25 (SE) before the abortion and dropped below 4 (EPF activity could not be detected) at 3-5 days after the abortion.