Regulatory T cell (Treg)

A regulatory T cell, also called a Treg or a suppressor T cell, is a kind of T cell: a type of white blood cell, one of the cells that defend the body. Its job is to keep things in check. It modulates immune responses, which are the body's defensive reactions, and it holds back autoimmunity, which is what happens when those defenses turn on the body's own tissues.

To put on the brakes, it has tools of its own. It releases inhibitory cytokines, IL-10 and IL-35. Cytokines are chemical messengers that immune cells use to talk to each other, and these in particular help turn the response down. It also carries a molecule called CTLA-4 on its surface, which it uses to block B7, a signal found on antigen-presenting cells, the cells that show T cells what to attack. Think of the brake pedal in a car: it isn't the engine, it's what keeps the speed under control. That's what a Treg does for the immune response.

To develop and work properly, a Treg needs FOXP3, a transcription factor, meaning a protein that controls the activity of certain genes. In a disease called IPEX syndrome, there are mutations, or changes, in the FOXP3 gene, and Tregs lose their function. Without that brake, T-cell activation runs unchecked, and inflammation spreads to many parts of the body.