[Studies of early pregnancy factor by rosette inhibition test using monoclonal antibody]

We established a new stable rosette inhibition test using anti-human T-cell and anti-mouse Thy-1 monoclonal antibody, instead of antilymphocyte serum for the testing of immunosuppressive early pregnancy factor (EPF). The results obtained with this experimental system are as follows. Serum of pregnant mouse and woman indicated the immunosuppressive activity as inhibition of rosette formation. Serum of pregnant mouse inhibited rosette formation between human lymphocytes and heterologous erythrocytes as well as mouse spleen cells. It indicated that EPF, at least partially, is species-independent. In mouse serum, EPF became evident within 8 hours after mating, and declined at 4 days before term. In human pregnancy, EPF was detected in the 1st and 2nd trimesters but the rosette inhibition declined to the nonpregnant range in the 3rd trimester. In patients with threatened miscarriage and poor prognosis, the rosette inhibition declined. Surgical abortion led to normalization of the rosette formation within 18 to 24 hours. To investigate the origin of EPF, an in vitro fertilization system for mouse was employed. Immunosuppression was demonstrated in the culture medium of a two cell-stage embryo.