The placenta as an immunological environment

In the UK, there are approximately 650,000 babies born each year. The pregnancy journey is not only unique to each woman, but for each individual pregnancy that may be experienced. Pregnancy complications, miscarriage, and stillbirths are still a huge problem with maternity services, highlighting the need for more research to understand the underlying causes, earlier detection or even prevention of conditions such as preeclampsia, gestational diabetes, restricted fetal growth and the impact of infection during pregnancy. One area of interest which transcends these conditions is the functioning of the placenta. The placenta is the lifeline for the fetus to the mother. It is a unique organ, crucial for survival, but also known to have impacts on the lifelong health of the fetus. Aberrant development, as well as in utero exposure to infections and environmental chemicals are known to have multiple impacts on the functioning of the placenta, and the fetus it supports. The placental environment is a fascinating organ to study with much still to be learned about its development, role in pregnancy complications, as well as its impact on long term offspring health. The placental environment is abundant with immune cells and mediators. There is a need within medical and biomedical practice for a good understanding of the complex relationship between immune cells, the decidua and placenta, and doing so will aid in development of better diagnostic tests and treatments for placenta-driven pregnancy complications and infections. This review will summarise the placenta as an immunological environment through description of key decidual immune cells, the expression of innate recognition receptors and it will provide an update on the placental immune response to infections of importance during pregnancy.