Reproduction Abstracts

Maternal and embryonic factors integrate to determine the success of embryo implantation and progression to pregnancy, with major impact on later placental and fetal development, and long-term consequences for offspring health. The female immune response is a major force in this peri-conception environment. In contrast to conventional wisdom, the immune response is not passive or suppressed in pregnancy. Instead, immune cells are centrally engaged with all steps of the reproductive process from conception to implantation and placental development. Through an active role in the decision pathway that permits pregnancy progression, the immune system acts in synergy with the reproductive system to ensure healthy reproduction. The biological benefit of a robust immune contribution is to discriminate between good and bad reproductive opportunities and execute an appropriate response at conception – to sustain and nurture an implanting embryo, or alternatively to actively suppress pregnancy. Emerging information is expanding our understanding of the underlying mechanisms – the immune system has an active function in sensing and evaluating parameters of male gamete quality and embryo viability, as well as markers associated with seminal fluid and the embryo that are relevant to embryo-maternal compatibility. This is mediated by immune contributions to pre-implantation embryo development, progesterone synthesis, and endometrial receptivity. Since the immune response is modulated by infectious, inflammatory, stress, nutritional and metabolic status, immune influence on progression or disruption of pregnancy can be disturbed by environmental stressors and resource availability. From an evolutionary perspective, such a ‘quality control’ function ensures appropriate investment of limited female resources and opportunities for reproduction. The challenge now is to define the critical cytokines and seminal fluid signals that control this nexus. Understanding immune decision-making at conception will offer new ways to promote fertility and will shed light on infertility disorders with an immune aetiology.