The early stage of pregnancy modulates toll-like receptor signaling in the ovine liver

Toll-like receptors (TLRs) participate in maternal immune regulation at multiple maternal-fetal interfaces. The liver is crucial for innate and adaptive immunity during pregnancy. The objective of this study was to measure the expression of genes and proteins related to TLR signaling. In this study, livers were obtained from ewes on day 16 of the estrous cycle, and on days 13, 16 and 25 of gestation, and RT-qPCR, western blot and immunohistochemistry were employed to measure the expression of genes and proteins related to TLR signaling, including TLR2, TLR3, TLR4, TLR5, TLR7, TLR9, myeloid differentiation primary-response protein 88 (MyD88), tumor necrosis factor receptor associated factor 6 (TRAF6) and interleukin-1-receptor-associated kinase 1 (IRAK1). Our data showed that the expression levels of TLR2, TLR3, TLR5, TLR9 and TRAF6 were increased, but those of TLR4 and TLR7 were decreased in the liver during early pregnancy. In addition, the expression levels of MyD88 and IRAK1 were the highest on days 13 and 16 of pregnancy, respectively, and the MyD88 protein was located in endothelial cells of proper hepatic arteries and portal veins and in hepatocytes. In conclusion, early pregnancy modulates TLR signaling in the maternal liver in sheep, which may participate in maternal immune regulation.