A Monoclonal Antibody to an Early Pregnancy Factor-Induced Suppressor Factor (EPF-S1) Disrupts Implantation in Mice


University of Queensland, Department of Surgery, Clinical Sciences Building, Royal Brisbane Hospital, Herston Qld 4029, Australia.


PROBLEM: The importance of EPF during pregnancy has been established previously but the importance of the EPF-induced suppressor factor EPF-S1 in pregnancy has to date been unaddressed. Investigations were therefore conducted in order to study this.

METHOD: Monoclonal antibodies to EPF-S1 were produced, and one antibody, designated R2Tγ, was characterized. Mated mice were passively immunized with R2Tγ and the effect on implantation determined.

RESULTS: Characterization of anti-EPF-S1 R2Tγ revealed that it cross-reacted with EPF-S1 of different MHC restriction but not with EPF or EPF-S2. When injected into mated mice on days 1 to 4, R2Tγ had no effect on pregnancy but when injections continued to day 5, pregnancy was affected; the number of embryos implanted on day 7 were significantly less than the number of corpora lutea counted, signifying embryonic loss.

CONCLUSION: These studies show that anti-EPF-S1 R2Tγ disrupts implantation in mice when injected on days 1 to 5 of pregnancy but not when injected on days 1 to 4, demonstrating that EPF-S1 exerts its effects around the time of implantation.