IMMUNOSUPPRESSION IN HUMAN UTERINE TISSUES THROUGHOUT THE REPRODUCTIVE CYCLE

The purpose of this study was to investigate and compare whether the explant supernatants prepared from endometrial tissues during the proliferative phase, secretory phase and early pregnancy differ in immunosuppressive activity. Specimens of nonpregnant endometrium from hysterectomies and normal first trimester decidua following elective aspiration termination of pregnancy were obtained. Supernatants from culture of endometrium or decidual fragments were prepared after 24, 48 and 72 hours. The effect of the supernatants on mitogeninduced lymphoproliferation in vitro was assessed. The percentage of suppression was calculated and then data were evaluated using Student's t-test. The results confinned that endometrial immunosuppressive activity exists throughout the reproductive cycle and confirm that early pregnancy decidua is a source of immunoregulatory factors. Immunosuppressive activity was increased in early pregnancy decidua compared with secretory phase endometrium but the results did not reach statistical signifIcance. In contrast, the difference in immunosuppressive activity between proliferative endometrium and early pregnancy decidua was highly significant. In conclusion, the high frequency of early embryonic loss before implantation and the low success rate of in vitro fertilization (IVF), embryo transfer and pathological pregnancy in humans can be explained in part by lack of suppressor activity in the endometrium.