Preferential distribution of NK cells into uteri of C57Bl/6J mice after adoptive transfer of lymphocytes

Circulating natural killer (NK) cells can migrate into target organs and possess tissue-associated differentiation and function under normal conditions. By adoptive transfer of spleen mononuclear cells (MNC) to C57Bl/6J mice at gestation day (gd) 6.5, it was found that 24 h later both NK1.1+ and CD3+ cell populations migrated to the fetal-maternal interface. Although there was no statistical difference between the relative number of CFDA-SE+ NK1.1+ cells migrated into the decidua (1.13 ± 0.18%) and that into liver (0.96 ± 0.14%) or spleen (0.15 ± 0.08%), it was noted that, by comparing the ratio of CFDA-SE+ NK1.1+ to CFDA-SE+ CD3+ cells in different tissues, peripheral NK1.1+ but not CD3+ cell populations, had preferentially migrated to decidua (1.61 ± 0.08%) compared with that to liver (0.44 ± 0.06%; p < 0.05) or spleen (0.09 ± 0.02%, p < 0.05), respectively. This suggested that implantation sites were a primary site for NK cell homing when undergoing the decidualization reaction. But NK cell homeostasis can be altered when systemic Toll-like receptor (TLR) 3 signaling was evoked. In the case of poly I:C administration, adoptively transferred NK cells accumulated in liver, but not in uteri or spleen. It was concluded that there were different requirements for NK cell trafficking into given tissue niche during the pregnancy; mesometrial decidua render a privileged microenvironment for NK1.1+ cell migration during the normal condition compared with liver or spleen. The constitution of the uterine NK cell pool was revealed not only in a spatiotemporal pattern but also in a stimuli-dependent manner.