Consequences of interactions between the maternal immune system and the preimplantation embryo in cattle

Abstract

Summary. Using the cow, three questions related to the importance of the maternal immune system for the developing embryo are addressed: role of semen-induced inflammation for pregnancy establishment, regulation of preimplantation development by molecules that function as soluble mediators of immune cells, and immunological aspects of embryonic signaling by interferon-τ. Unlike rodents, there is no indication that semen modifies the physiology of the mother in a way that promotes embryonic survival. Bulls without seminal vesicles are fertile, artificial insemination results in pregnancy rates similar to natural mating and intrauterine deposition of seminal plasma at the time of insemination does not improve fertility. Regulatory molecules associated with the immune system can be important for development of the embryo. Among the molecules implicated in embryonic growth and survival are colony stimulating factor 2, which can enhance embryo competence to establish and maintain pregnancy, and tumor necrosis factor α, which induces apoptosis and blocks development. Elongation of the trophoblast beginning at Day 14 of development results in large-scale changes in the transcriptome of the embryo, including many genes involved in immune responses. Signaling by interferon-τ and other embryo-derived molecules does not, however, lead to a large-scale change in accumulation of lymphocytes in the endometrium. In contrast, numbers of macrophages and dendritic cells do increase and there is increased expression of genes associated with macrophage activation. Perhaps these antigen-presenting and immunoregulatory cells play an important role in continued survival and development of the conceptus.