Evaluation of intrauterine immune suppression during pregnancy in a species with epitheliochorial placentation.

Cells capable of suppressing the immune response of PBL to the mitogen PHA are associated with the epitheliochorial placenta during normal first pregnancy in the pig. Because placentation in the pig is noninvasive, these suppressor cells are not associated with decidua. Cells with similar activity are also found between the implantation sites and in the uterus of pseudopregnant pigs, suggesting that fetal trophoblast is not essential for recruitment of intrauterine suppressor cells. Cell separation studies demonstrate that two independent populations of suppressor cells are present in the pig uterus on day 28 of gestation, as well as a population of PHA-responsive cells. The inability of unseparated porcine uterine cells to respond to PHA, plus the reconstitution of suppression in remixing experiments, demonstrate directly that a functional, putative T effector cell population is blocked within the uterus during normal mammalian pregnancy.