The Effects Of Low Dose Mifepristone On The Cytotoxicity Of NK Cells In Human Endometrium During Receptive Phase.

Background:In physiology of gestation,the endometrial receptivity to embryo is one criticality factor for estabilishing pregnancy.The uterus is ready to accept the implanting embryo only during a limited period of time known as the "window of implantation"(days 20-24 of an ideal cycle or day LH+ 7 to LH+ 11),outside of which the endometrium may be indifferent or even hostile to the embryo.During this time,the immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system.There is evidence now that immunological recognition of pregnancy is important for the maintenance of gestation,and that inadequate recognition of fetal antigens might result in failed pregnancy.The immunological recognition between the mother and the fetus is important for the maintenance of gestation,which is regulated by T,B,Natural killer(NK)cells and cytokines in the endometrium.NK cells are a key component of innate immunity, particularly crucial during the early phase of immune responses against certain viruses, parasites,and microbial pathogens.The role of CD56^brightgranulated NK(uNK)cells are the most important lymphocytes in the endometrium and it is now becoming increasingly clear that uNK cells control pregnancy maintenance at several levels, including cytotoxicity,cytokine production,the control of trophoblast invasion,spiral artery remodelling and to keep the immunologic balance between the feto-maternal interface.Many investigations have showed that the disturbance of uterine NK cells during receptive phase may lead to implantation failure and recurrent miscarriage.Mifepristone(RU486)is a synthetic 19-norsteroid that blocks the effect of progesterone at the receptor level.Mifepristone(RU486)is the first progesterone receptor antagonist for clinical use,and widely used in terminating early pregnancy recently.For the past few years,investigations show daily administration of low dose mifepristone can inhibit the development of endometrium to achieve the purpose of contraception,so called "endometrium contraception".Low dose mifepristone is an effective contraceptional regimens with few side effects.Our aim was to determine the effect of low dose mifepristone(65nmol/L,200 nmol/L)on the cytotoxicity of NK cells in human endometrium during receptive phase,in order to investigate the immunologic mechanism of low dose mifepristone as an anti-implantation contraception drug.Methods And Materials:Endometrial biopsies were obtained from twelve normally cycling IVF-ET patients for tubal resection or man infertility.The criteria of study subjects:the patients were reproductive age(aged 25-35 years)with mormal menstrual cycles(26-31 days),and had no hormone or immunosuppressant therapy for the last 3 months.Endometrial biopsies were obtained at the "window of implantation"(days 20-24 of an ideal cycle).Each endometrial tissue was chopped into 1-2mm³ pieces and divided into three equal parts,then assigned to three groups(control group, 65nmol/L group and 200nmol/L group).The first part of the explant was treated with 2ml DMEM/F-12 containing 10^-9mol/L estrin+10^-7mol/L progesterone.The other two parts of the endometrial explant was incubated with the same medium to which 65nmol/L and 200nmol/L mifepristone was added respectively.Incubations were performed in a humidified atmosphere at 37℃in 5%CO₂.the uNK cytotoxicity in endometrium is analysed by using MTT assay;the coexistence of PFP and CD56 cells in endometrium examined with EnVision two step procedure method on adjacent mirror thin section.Results: 1.HE-stained sections show no significantly morphologic distinction between pre-cultured and post-cultured endometrial tissue.2.The variation of uNK cytotoxicity in endometrium:The uNK cytotoxicity was(13.52±3.12)%in control group,(22.33±4.53)%in 65nmol/L group and(30.55±6.09)%in 200nmol/L group.The uNK cytotoxicity in two mifepristone-treated groups were significantly higher when compared to the control group(P＜0.05),significant difference between the two mifepristone-treated groups(P＜0.05).3.The quantitive variation of PFP⁺ CD56⁺ cells in endometrium:PFP staining was brown,localized on the kytoplasm.CD56 staining was brown, localized on the cellular membrane,positive cells was found in endometrial stroma of all three groups and in proximity of the gland and the small blood vessels.The mean number of PFP⁺CD56⁺ cells was 60±7 in control group,80±6 in 65nmol/L group,92±7 in 200nmol/L group.The numbers of PFP⁺CD56⁺ cells in two mifepristone-treated groups were significantly higher when compared to the control group(P＜0.05).There was significantly difference between the two mifepristone-treated groups(P＜0.05).Conclusion:1.Low dose mifepristone increased the uNK cytotoxicity in endometrium during receptive phase.This suggested that low dose mifepristone promote the excessive uNK cytotoxicity,which might result in the disturbance of human endometrial immuno-microenvironment during receptive phase.2.Low dose mifepristone increased the the number of PFP⁺CD56⁺ cells in endometrium during receptive phase.This suggested that low dose mifepristone promote the excessive expression of PFP on the uNK cells,which might relate to the increasing of uNK cytotoxicity in human endometrium during receptive phase.