Morphological demonstration of the failure of Mus caroli trophoblast in the Mus musculus uterus

A histological study of Mus caroli embryos gestating in the Mus musculus uterus was undertaken at Day 8.5 of gestation, 1 day after such embryos are reported to be normal and 1 day before the earliest events associated with death of the xenogeneic embryos. In comparison to control M. caroli embryos recovered from M. caroli and to control M. musculus embryos recovered from M. musculus, the xenogeneically transferred embryos showed intrauterine growth retardation that was associated with trophoblastic insufficiency. Trophoblast cell degeneration was observed, in the absence of lymphocytic infiltration. Therefore, loss of trophoblast cell function rather than lymphocyte-mediated destruction of trophoblast appears to underlie the death of M. caroli embryos in the M. musculus uterus.