Question: what changes does the immune system make when a female turns pregnant?

Craig O'Hare answered on 6 Mar 2017:

When a woman becomes pregnant the immune system is actually really important in ensuring that the pregnancy is successful.

Cells of the immune system start behaving differently and start forming what is known as the placenta. The placenta serves as a link for food between the mother and baby while it’s in the womb. Special cells which normally kill viruses called Natural Killer cells make molecules that promote the growth of blood vessals so that the placenta can form properly. They also make lots of immune suppressing signals and recruit other special cells called T cells to help with this. This is to stop the mother’s body recognising the baby as a foreign object because to the immune system it looks like half of the mother, and half of the father. If the immune system doesn’t function correctly here the mother can miscarry the baby.

Scientists who work on the immunology of pregnancy are trying to find out more about how to manipulate these cells do that we can use them to help stop organ transplant rejections.