CTLA4 — Immune system checkpoint
The CTLA4 gene codes for a protein that is important in the immune system. It acts as a checkpoint that can downregulate your immune system response. CTLA4 is active in regulatory T cells (Tregs), which are the part of the immune system that maintains tolerance to self-antigens.
Basically, you want a powerful response from your immune system when you are exposed to a pathogen that causes a disease — pneumonia, West Nile virus, cholera, measles, flu… But you don’t want an out-of-control immune system.
Your body needs to control your immune response when it isn’t needed. Checks and balances. The Treg cells are the checks that keep your immune system from going out of control and attacking your own cells.
One way in which the body needs to deactivate the immune response is during pregnancy. Think about it — a mother’s body has an organism with foreign DNA growing in it. There has to be a system in place to keep the mother’s body from attacking the fetus. Immune checkpoint molecules (CTLA4 is one of them), keep the maternal immune system from attacking the fetus.