Pregnant mice are not primed but can be primed to fetal alloantigens.

Abstract

Evidence was presented from various stages of murine pregnancy indicating that pregnant females have no demonstrable immune effector function directed against their semiallogeneic fetuses. Spefifically, cytotoxic lymphocytes were not present in pregnant mice, and pregnant mice challenged with radiolabeled paternal strain leukemia cells showed no evidence of immune elimination, as demonstrated by in vitro assays. Nonetheless, immunity measurable in vitro and in vivo was readily induced by priming with the paternal strain cells. No harm to the fetus was observed in primed mothers. These results cast doubt on the relevance of mechanisms proposed that involve systemic active suppression during pregnancy. The results are compatible with the hypothesis that the placenta acts as a barrier, preventing fetal cells from priming the mother.