Our immune system is like a defense team that protects our body from germs and infections. It remembers germs it has seen before so it can fight them better next time. Two important types of immune cells are involved in this process:

B cells, which act like the intelligence officers, spotting invaders and calling for backup.

T cells, which are the soldiers that attack and destroy the invaders.

For the immune system to work properly, many proteins have to work together. But when one of these proteins doesn’t work right or is missing, the immune system can go wrong. Sometimes, it attacks the body’s own healthy cells by mistake—this is called autoimmunity.

The researchers noticed that a protein called capicua (CIC) is found in high levels inside many immune cells. They wondered if CIC helps control how the immune system behaves.

To find out, they removed CIC from the early “precursor” cells in mice that grow up to become immune cells. The mice then developed signs of autoimmunity: their immune organs, like the spleen, became swollen and inflamed, and immune cells started invading healthy body tissues.

The researchers focused on special sites in the immune system called Germinal Centers (GCs), where B cells learn to recognize specific germs and mature with help from follicular helper T (TFH) cells. Normally, only certain B cells are chosen here. But in mice without CIC, there were too many TFH cells and B cells in these Germinal Centers. This means the immune system was being too active and less picky, leading it to attack healthy cells by mistake.

Next, the scientists looked specifically at what happens if CIC is missing only in T cells. The results were the same: overactive Germinal Centers and more TFH and B cells, showing that CIC’s role in T cells is crucial to prevent autoimmunity.

They also studied a special group of T cells called regulatory T (Treg) cells, which act as peacekeepers to calm the immune response and stop it from attacking healthy tissues. Without CIC, the number of Treg cells grew abnormally high because certain genes got activated too much. This imbalance also contributes to autoimmune problems.

In conclusion, the researchers found that losing CIC causes the immune system to become overactive and attack the body’s own cells. This happens because of too many TFH and Treg cells and overactive Germinal Centers—all signs of autoimmunity. Understanding how CIC controls these immune cells opens up new possibilities to develop treatments for autoimmune diseases and their complications in the future.