Regulatory T cell (Treg, FOXP3) !
- Cell
Regulatory T cells are the brakes of the immune system: they calm other lymphocytes and protect the body from autoimmunity.
Updated 2026-11-01
What it is
Regulatory T cells are a subset of CD4⁺ T cells defined by high CD25 (the IL-2 receptor α chain) and the transcription factor FOXP3. They suppress the activation and expansion of other T cells, and probably B cells and dendritic cells, through IL-10, TGF-β, CTLA-4 and by consuming IL-2. Without them, self-reactive cells that escape the thymus cause severe autoimmune disease, as in IPEX syndrome.
Key facts
- FOXP3 is the master transcription factor for Treg development and function.
- CTLA-4 is not unique to Tregs; activated conventional T cells also express it.
- Their balance with Th17 cells is shaped by TGF-β and the cytokine context.
Function
- Limit the size and length of immune responses.
- Keep self-reactive T cells in check (peripheral tolerance).
- Help maintain tolerance to food and to the normal gut flora.
- Contribute to tolerance of the fetus during pregnancy.
Markers
- CD4
- CD25 (IL-2Rα)
- FOXP3
- CTLA-4 (CD152)
Clinical notes
- IPEX: boys with diarrhea from the first months of life, eczema, early type 1 diabetes, thyroiditis and autoimmune cytopenias.
- CTLA-4 deficiency causes autoimmunity and immune dysregulation.
- Checkpoint inhibitors against CTLA-4 remove a brake and can cause colitis, hepatitis and endocrine autoimmunity.
- Increasing Treg function is a research strategy for autoimmunity and transplant tolerance.
Test yourself
Think of the answer, then tap the question to see it.
Which three markers define regulatory T cells?
CD4, high CD25 (IL-2 receptor α chain) and the transcription factor FOXP3.
Which gene is mutated in IPEX syndrome, and how is it inherited?
FOXP3; it is X-linked recessive, so it mainly affects boys.
Which two cytokines do Tregs use to suppress other cells?
IL-10 and TGF-β.
Why can a CTLA-4 blocking drug cause colitis?
It removes an inhibitory checkpoint used by Tregs and activated T cells, so self-reactive responses can attack the gut.
Related
- CD4⁺ helper T cell
- Immune tolerance and how autoimmunity begins
- IL-10 and TGF-β (the brakes)
- Th1, Th2, Th17, Tfh and Treg
- Tumor immunology and checkpoint inhibitors
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: Regulatory T Cells (Tregs) (British Society for Immunology, 2024); 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); Immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (MedlinePlus Genetics, U.S. National Library of Medicine, 2024).
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Representative model, for educational purposes only.