The Regulatory Roles of Uterine Natural Killer Cells Acommpanied with Toll-like Receptor Activation at Fetal Maternal Interface

Abstract: The fetus is considered to be an allograft that, paradoxically, survives pregnancy despite the laws of classical transplantation and tumor immunology. The reproductive tract is unique since it hormonally controls expression levels of soluble immune mediators and influx of immune cells to maintain the menstrual cycle, embryo implantation and survival. In primates, including women, and in rodents, natural killer lymphocytes (NK cells) have a unique relationship with the pregnancy process though they are found as a type of lethal lymphocyte and profoundly shaped the immune response, both qualitatively and quantitatively. During the mammal pregnancy, the mucosal lining of the uterus is transformed from endometrium in the non-pregnant state to the decidua of pregnancy. Regarded as a constructive element supporting reproductive development, uterine NK (uNK) cells are massively recruit from peripheral lymphoid tissue in response to specific arrays of adhesion molecules, chemokines, cytokines expressed on endothelium, and present at the fetal maternal interface.The recruitment of uNK precursor cells from peripheral lymphoid tissues appeared to occur in a window promoted by rising plasma estrogen and LH and limited by rising progesterone, which indirectly mediated through the responsiveness of local cell types. By the adoptive transfer of spleen mononuclear cells (MNC) to C57B1/6J (B6) mice at gestation day (gd) 6.5, it was found that 24 hours later, peripheral NK1.1~+, but not CD3~+ population was preferentially trafficked to the fetal maternal interface, and there was more CFDA-SE~+NKL1.1~+ cells migrated into the decidua (1.13±0.18%) than that in liver (0.96±0.14%) or spleen (0.15±0.08%). This phenomenon suggested that implantation sites was a primary site for NK cells homing when the decidualization reaction undergoing. But NK cells homeostasis can be altered when systemic Toll-like receptor (TLR) 3 signaling was evoked. In the case of polyinosinic-polycytidylic acid (poly I:C) administration, adoptive transferred NK cells was accumulated in liver, but not in uteri or spleen. It was concluded that there were very different requirements for NK cells migrating into given niche during the pregnancy, and the constitution of uterine NK pool was not only revealed in spatiotemporal pattern but in a stimuli-dependent manner.The results of this study also indicated that TLR mediated the immune responses to inflammatory stimuli in the endometrium. TLR3 was determined to be a cyclically regulated protein that can mediate antiviral immune responses and alter the cytokine milieu, potentially influencing the outcomes and consequences of infection. Many viruses that infect female reproductive tract either contain or express dsRNA during part of their lifecycle, which could lead to activation of TLR3. Herein, the nontoxic poly I:C (a TLR3 agonist) was applied to the CBA×DBA/2 mating at early gestation day (gd) 6.5, immune response and histological change at maternal-fetal interface were investigated. It was found that all implantation sites appeared viable at gd 7.5 when endometrium was dissected for immunohistological examination, and poly I:C treatment increased fetal losses to 40.2±1.7% at midgestation stage, compared with control animals (11.0±3.0%). It was also observed that the ratio of vessel area to lumen area significantly increased at gd 10.5 and gd 12.5 after poly I:C administration, indicating that the spiral arterial (SA) modification was impaired. Meanwhile, twenty-four hours after poly I:C injection, the expression of TLR3 dramatically elevated within decidua basalis (DB), and content of the endometrial TNF-αincreased 2.7 fold but IFN-γremained unchanged in homogenized endometrium. Moreover, poly I:C-TLR3 action played disparate roles in inducing proinflammatory cytokines such as TNF-αsecretion, and retarding uterine spiral artery remodeling, both of which were closely correlated with pregnancy failure of mice. Herein we suggest that innate antiviral immune response at the maternal-fetal interface was involved in the fetal loss of CBA×DBA/2 mating, and harness the hyper-activation of TLR3 could contribute to the pregnancy health.On the other hand, a novel feature for the decidualization in the process of pregnancy is the influx of distinctive immunocompetent cells, mainly uterine natural killer, which can regulate key developmental process at the fetal-maternal interface. Both immune response of murine uNK cells to TLR3 agonist and histological change at maternal-fetal interface were investigated. It was found the CD69 expression of uNK (DX5~+CD3~-) cells was highly up-regulated to 92.3±0.9%, the percentage of intracellular TNF-α~+ or IFN-γ~+ uNK (DX5~+CD3~-) cells in the implantation sites of CBA×DBA/2 matings were significantly increased, 24 hours after poly I:C injection. Surprisingly, poly I:C treatment significantly decreased the total number of uNK cells (either DX5~+CD3~- or DBA~+) at fetal maternal surface, but had no influence on local NKT cells, T cells and DCs. This investigation will help to explain the central role for hyperactivated uNK cells in the progress of mice pregnancy, and suggest that TLR3 ligands may be utilized to develop treatment and vaccine strategies against viral pathogens in the endometrium.In conclusion, it was addressed that similar to trafficking precursors of uNK cells (pre-uNK), spleen sourced peripheral NK cells can preferentially migrate to fetal maternal interface under the selective pressure of decidualization. With the stimulation of poly I:C, uNK cells were identified as a kind of regulatory population to influence the spiral artery remodeling, by modulating their production of inflammatory cytokines. It was also suggested that TLR3 signal could be render as a possible target for the treatment of endometrial dysfunctions such as endometriosis, preeclampsia, and spontaneous abortion…
Key words: uNK cells; poly I:C; spiral artery; IFN-γ; TNF-α; TLR3

This entry was posted in Doctoral Dissertation. Bookmark the permalink.