The first 7 days post-insemination are critical for establishment of pregnancy. The pre-ovulatory luteinizing hormone (LH) surge induces ovulation through disruption of the follicle structure that elucidates pro-inflammatory (Th1) responses. Various types of immune cells are recruited into the corpus luteum (CL) to regulate luteal angiogenesis and progesterone (P4) secretion into the circulation to establish pregnancy. The active sperm-uterine crosstalk also induces Th1 responses, mainly via Toll-like receptor (TLR) 2/4 signaling pathway in vitro. The endometrial glands serve as sensors for sperm signals, which trigger Th1 responses. Conversely, the sperm-oviduct binding generates anti-inflammatory (Th2) responses to support sperm survival until fertilization. It is well-established that embryo-maternal crosstalk starts after the embryo hatches out from the zona pellucida (ZP). However most recently, it was shown that the 16-cell stage bovine embryo starts to secrete interferon-tau (IFNT) that induces Th2 immune responses in the oviduct. Once developing embryos descend into the uterine horn, they induce Th2 responses with interferon-stimulated genes (ISGs) expression in the uterine epithelium and local immune cells mainly via IFNT release. Likewise, multiple embryos in the uterus of superovulated donor cows on D7 post-insemination induce Th2 immune responses with ISGs expressions in circulating immune cells. These findings strongly suggest that the maternal immune system reacts to the embryo during the first 7 days post-insemination to induce fetal tolerance. It became evident that the innate immunity of the developing CL, oviduct, and uterus works together to provide optimal conditions for fertilization and early embryonic development during the first 7 days post-insemination.

中文翻译：

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母牛受精后前 7 天怀孕的路线图：黄体、输卵管和子宫中的免疫串扰

受精后的前 7 天对于确定怀孕至关重要。排卵前促黄体生成素 (LH) 激增通过破坏卵泡结构来诱导排卵，从而阐明促炎 (Th1) 反应。各种类型的免疫细胞被募集到黄体 (CL) 中以调节黄体血管生成和黄体酮 (P4) 分泌到循环中以建立妊娠。活跃的精子 - 子宫串扰还诱导 Th1 反应，主要通过体外 Toll 样受体 (TLR) 2/4 信号通路。子宫内膜腺体作为精子信号的传感器，触发 Th1 反应。相反，精子与输卵管的结合会产生抗炎 (Th2) 反应以支持精子存活直至受精。众所周知，胚胎-母体串扰在胚胎从透明带 (ZP) 中孵化出来后就开始了。然而最近，显示 16 细胞阶段的牛胚胎开始分泌干扰素 - tau (IFNT)，在输卵管中诱导 Th2 免疫反应。一旦发育中的胚胎下降到子宫角，它们主要通过 IFNT 释放在子宫上皮细胞和局部免疫细胞中通过干扰素刺激基因 (ISG) 表达诱导 Th2 反应。同样，在受精后第 7 天，超排卵母牛子宫中的多个胚胎诱导 Th2 免疫反应，并在循环免疫细胞中表达 ISG。这些发现有力地表明，母体免疫系统在受精后的前 7 天内对胚胎作出反应以诱导胎儿耐受。