The immune system differentiates between “self” and “non-self”, and attacks any entity it perceives as foreign. Microorganisms like bacteria and viruses are obviously recognized as foreign, but the immune system also recognizes tissue from different individuals within the same species as foreign, which can cause major problems for organ transplantation. But why doesn’t the maternal immune system attack a developing fetus even though it would clearly be recognized as foreign? A deeper understanding of this mystery could lead to medical advances that reduce birth defects and miscarriages.

Maternal Immune System During Pregnancy