Suprresion of in vitro lymphocyte stimulation in mice by uterine and placental extracts.

The effects of uterine extracts from virgin mice and uterine and placental extracts from mice at various stages of gestation on lymphocyte stimulation in vitro were compared. Placental and uterine extracts from mice in gestation, at 1% final concentration by volume, caused marked depression of lymphocyte reactivity to phytohemagglutinin-P (PHA) and to allogeneic cells in two-way mixed leukocyte cultures (MLC). An equivalent concentration of uterine extract from virgin mice caused slight depression of uterine extract from virgin mice caused slight depression of lymphocyte reactivity. Suppression was most of lymphocyte reactivity. Suppression was most marked with uterine extracts of mice at 15 days of gestation. At least two factors of different m.w. in uterine and placental extracts were responsible for suppression of lymphocyte reactivity. The higher m.w. fraction, present in small amounts in the uteri of virgin mice, was markedly increased in uteri of pregnant mice. This fraction contained immunoglobulin G (IgG). These factors may be involved in a protective role for the fetus from rejection by the mother as an allograft, thus assuring successful pregnancy.