Chemokine Profiles and Immunosuppressive Properties of Murine Placental Nucleated Erythroid Cells in Mid- and Late Gestation

Nucleated erythroid cells (NECs) are emerging as important immunoregulators at the feto–maternal interface, yet their chemokine profiles and functional dynamics across pregnancy remain poorly understood. Using a murine allogeneic pregnancy model (CBA × C57Bl/6), we isolated placental and splenic TER-119+ NECs at mid- (E12.5) and late (E19.5) gestation. Chemokine production (13-plex), chemokine receptor expression (qPCR), immunosuppressive molecules (PD-L1, TGF-β, and ROS), T-cell proliferation (CFSE), and immune cell migration (Transwell) were assessed. CD45+ placental NECs were the main producers of PD-L1, TGF-β, and ROS, with maximal expression at E19.5, suggesting their potential contribution to the immunosuppressive functions observed in the total TER-119+ population. Chemokine production showed a striking shift in CCL17 and CXCL9 from the spleen to the placenta as pregnancy advanced (E12.5 → E19.5). Splenic NECs displayed dominant expressions of CCR3 and CXCR4. Unexpectedly, CCL2 and CCL4 blockade enhanced immune cell migration toward placental NECs at E19.5. Placental nucleated erythroid cells potently suppressed T-cell proliferation at E12.5, and this suppressive capacity remained stable until full term. Placental NECs undergo dynamic chemokine reprogramming while maintaining stable T-cell suppression. The paradoxical enhancement of migration after CCL2/CCL4 blockade suggests a complex chemokine network warranting further investigation. These findings provide new insights into the immunobiology of pregnancy and may have implications for understanding pregnancy complications.