Preliminary characterization of two types of suppressor cells in the human uterus *

Survival of the mammalian fetus in an immunologically hostile host has been shown to be determined by the properties of the tissue at the maternal-fetal interface. Suppressor cells have been found in the decidua in both murine and human systems. This study was carried out to further characterize these cells and to determine whether they were present in abnormal early pregnancies and in the endometrium at the time of implantation. Suppressor cells appear in the endometrium after ovulation, and their activity is present in the decidua of successful pregnancies but is absent in missed abortions. Two types of cells have been identified. An early phase large cell appears to be hormone dependent, and later phase small cell appears to be trophoblast dependent. This would suggest that suppressor cells may play a role in protecting the fetal allograft, from the time of implantation, against maternal immunity, thereby allowing a pregnancy to succeed.