BEEF SPECIES-RUMINANT NUTRITION CACTUS BEEF SYMPOSIUM: Maternal immune modulation prior to embryo arrival in the uterus is important for establishment of pregnancy in cattle1.

In 1953, Sir Peter Medawar first recognized the allogeneic properties of a developing conceptus and rationalized that an "immune-tolerant" physiological state must exist during pregnancy. Early theories speculated that the conceptus evaded the maternal immune system completely, but 40 yr after Medawar's observations, Wegmann proposed that the maternal immune system shifts the cytokine profile away from inflammatory cytokine production when an embryo is present. The economic consequences and production losses of subfertile animals have been well documented in studies evaluating calving distribution. Despite advances in understanding infertility or subfertility, few technologies exist to identify subfertile animals or improve fertility beyond hormonal intervention associated with synchronization protocols. Work in rodents and some livestock species indicates that the uterine immune cell population shifts dramatically after copulation and these early immune-modulated events establish a receptive uterine environment. Clearly, as evident in embryo transfer, the presence of a conceptus is sufficient to establish communication for pregnancy establishment but does not rule out the importance of other physiological events to prime the maternal immune system prior to blastocyst arrival in the uterus. In support of this concept, work in our laboratory and by others has demonstrated that autologous intrauterine transfer of peripheral immune cells prior to embryo transfer can increase pregnancy rates and accelerate conceptus development in women and cattle. Understanding aberrant immune regulation in subfertile animals may provide markers for subfertility or targets for clinical intervention to enhance fertility, particularly when using reproductive technologies.