regulatory T cell
Meaning of regulatory T cell: Tolerance is not the absence of an immune response but an actively maintained one, and this is the cell that maintains it.
Definition of regulatory T cell
A regulatory T cell is a lymphocyte that suppresses the activity of other immune cells, keeping the immune response proportionate and preventing attacks on the body's own tissues. It is distinguished from other T cells by a master control protein, FOXP3, which drives its suppressive behavior. Abbreviated to T reg in most writing, it is central to what immunologists call self-tolerance.
Why is tolerance an active process?
It would be simpler if the body ignored itself by default, but that is not how it works. Every person carries lymphocytes capable of recognizing their own tissue, because the process that generates receptors is random and the screening that follows lets some through. Something must continuously restrain them, and this population is the main thing doing it. Tolerance is therefore a state that has to be maintained, and when the maintenance fails, autoimmune disease follows.
How is suppression delivered?
| Mechanism | Effect on neighboring cells |
|---|---|
| Consuming the shared growth signal | Other cells cannot multiply |
| Releasing damping molecules | Inflammation subsides locally |
| Stripping signals off presenting cells | The activating handshake never completes |
| Direct killing | Activated cells are removed |
Several mechanisms run at once and the mix varies with the tissue, which is one reason a single drug has not been able to switch the whole population on or off cleanly.
What happens when they fail or dominate?
Too little activity and the immune system turns on its host. A faulty FOXP3 gene causes a severe multi-organ autoimmune syndrome beginning in infancy, and reduced or dysfunctional populations are described in several common autoimmune conditions. Too much activity in the wrong place and useful responses are suppressed: chronic infections persist partly because these cells are drawn to the site, and a tumor that attracts them gains a local shelter from attack. Balance, not quantity, is what matters.
How does it relate to the other T cells?
All arise from the same precursor and all carry the T cell receptor, but their instructions diverge. A killer T cell destroys infected cells. A helper cell coordinates and amplifies. A regulatory cell restrains both. Most carry the surface marker CD4, like helper cells, so the two cannot be separated by that marker alone, and identifying them reliably means looking for the internal FOXP3 protein rather than anything on the surface. The shorthand T reg refers to exactly the same cell.
Also known as
Used in a sentence
Regulatory T cell counts were measured before and after the transplant.
Good to know
Regulatory T cells share the CD4 surface marker with helper T cells, so they cannot be distinguished by surface staining alone and are identified by the internal FOXP3 protein.