Clinical Research Centre, Watford Road, Harrow
(Received 4th October 1974)
One of the most striking features of early pregnancy in the mouse is the development of the decidual cell reaction (DCR). This cellular proliferation is induced in the uterine stroma by the presence of a blastocyst on the 4th day of pregnancy (the day of finding a vaginal plug was designated the 1st day of pregnancy). The significance of the DCR and the interactions between blastocyst and uterus, which result in its induction, are poorly understood.
Kirby, Billington & James (1966) postulated that the DCR might be instrumental in preventing the rejection of the conceptus as foreign tissue. The extent of the DCR on the 7th day of pregnancy is dependent on the genotype of the mother and the genotype of the conceptus (Hetherington, 1971). Antigenic differences between mother and conceptus can apparently reduce the extent of the DCR. It