T reg
Meaning of T reg: The immune system's own restraint, written in shorthand: a cell whose entire purpose is stopping other cells from going too far.
Definition of T reg
A T reg is a type of white blood cell that suppresses the activity of other immune cells, holding the immune response within limits and preventing it from attacking the body's own tissues. It is a subset of T lymphocyte, identified by a control protein called FOXP3 that switches on its suppressive program. The full name is regulatory T cell.
What does it actually suppress?
Almost every arm of the response. A T reg dampens the killer and helper cells of its own family, restrains the cells that present fragments of invaders, and releases signalling molecules that quiet inflammation in the surrounding tissue. It also consumes the growth signal that other lymphocyte populations depend on, starving them of what they need to multiply. Suppression is delivered locally rather than as a general brake, which is what allows a vigorous response in one place while another is being shut down.
Why does the body need cells that block immunity?
Because the selection process that removes self-reactive cells before they leave the thymus is imperfect, and cells capable of attacking the body's own tissue reach the circulation in everyone. T regs are the second line of defense against that. When the FOXP3 gene is faulty, the result is severe autoimmune disease affecting several organs from infancy, which shows how much of ordinary tolerance rests on this population. They also hold back the response to harmless material such as food proteins and to the resident bacteria of the gut, and they moderate the mother's response to a fetus.
Where do they come from?
| Type | Where it develops | Main job |
|---|---|---|
| Thymic | In the thymus, before leaving | Tolerance to the body's own tissues |
| Peripheral | Converted from ordinary T cells in tissue | Tolerance to food and gut bacteria |
What is the interest in cancer?
It is the opposite of what a first reading suggests. Tumors accumulate T regs and use them as a shield, since a suppressed local response leaves the cancer unattacked, and a high density of these cells inside a tumor generally signals a poorer outlook. Research in cancer therefore aims at removing or disabling them, while research in autoimmune disease and transplantation aims at the reverse, expanding them so the immune system tolerates a graft or stops attacking a joint.
Also known as
Used in a sentence
T reg numbers within the tumor were quantified alongside the killer cell count.
Good to know
In cancer the aim is generally to remove or disable these cells, because tumors recruit them to suppress the local immune response, whereas in autoimmune disease and transplantation the aim is to expand them.