Th1, Th2, Th17 and Treg: helper T-cell subsets
Th1, Th2, Th17 and Treg are chosen by the cytokines around a naive CD4 T cell. Each has an inducer, a master transcription factor, a product and a target.
Match the helper T-cell subsets Th1, Th2, Th17 and Treg to their inducing cytokines, their master transcription factor and signature cytokines, and the pathogens or diseases they drive or control.
The short version
- The cytokines around a naive CD4 T cell, mostly released by the antigen-presenting cell, decide which helper subset it becomes.
- Th1: IL-12 with IFN-γ switches on T-bet; Th1 cells make IFN-γ, which activates macrophages against intracellular microbes such as mycobacteria; Th1 cells also help the response to viruses.
- Th2: IL-4 switches on GATA3; Th2 cells make IL-4, IL-5 and IL-13 for worms and allergy. Th17: IL-6 with TGF-β switches on RORγt; Th17 cells make IL-17 and IL-22 for extracellular bacteria and fungi.
- Treg: IL-2 with TGF-β switches on FOXP3; Treg cells make IL-10 and TGF-β to calm the response, and FOXP3 loss causes IPEX syndrome.
- Read the chain forwards or backwards: inducer, master factor, product, target. A failed subset leaves its target enemy unchecked.
One naive T cell, three enemies
A mycobacterium hides inside a macrophage. A worm sits in the gut. A fungus grows on the skin. The same kind of cell, a naive CD4 T cell, has to fight all three, and it has to know which weapons to build. The answer is that the cell does not choose alone.
After the two activation signals, the cell chooses a job. The choice is made by the cytokines around it, mostly released by the antigen-presenting cell.[1][3] This is the logic behind Th1, Th2, Th17 and Treg, the helper T-cell subsets.
How helper T-cell subsets are defined
Each subset is defined by two things: a signature cytokine and a master transcription factor.[1][2] Reading each subset as a chain makes the list easy to hold: inducer, then master factor, then product, then target.
| Subset | Inducer | Master factor | Product | Target |
|---|---|---|---|---|
| Th1 | IL-12 (from the APC) with IFN-γ | T-bet | IFN-γ | Macrophages; intracellular microbes such as mycobacteria, and viruses |
| Th2 | IL-4 | GATA3 | IL-4, IL-5, IL-13 | Eosinophils, basophils, mast cells; B cells toward IgE; worms and allergy |
| Th17 | IL-6 with TGF-β | RORγt | IL-17, IL-22 | Neutrophils; barrier tissues; extracellular bacteria and fungi |
| Treg | IL-2 with TGF-β | FOXP3 | IL-10, TGF-β | Calms the response |
Th1: IL-12, T-bet and interferon gamma
Interleukin-12 from the antigen-presenting cell, together with interferon gamma (IFN-γ), switches on the master factor T-bet.[1][2]
So the Th1 chain reads: IL-12 and IFN-γ, then T-bet, then IFN-γ as the product, then macrophages as the target.
Th1 cells make IFN-γ. It activates macrophages to kill what they have swallowed, such as mycobacteria, and Th1 cells also help cytotoxic T cells and NK cells against viruses.[1][3]
Th2: IL-4, GATA3 and the worm and allergy response
Interleukin-4 switches on GATA3. Th2 cells then make IL-4, IL-5 and IL-13. They recruit eosinophils, basophils and mast cells, and IL-4 pushes B cells toward IgE.[1][3][9]
That is the response to worms, and it is also the machinery of allergy.[1]
So the Th2 chain reads: IL-4, then GATA3, then IL-4, IL-5 and IL-13, then eosinophils, basophils and mast cells, with B cells pushed toward IgE.
Th17 and Treg: bacteria, fungi and restraint
Th17. Interleukin-6 with TGF-β switches on RORγt (the exam pairing; IL-23 and IL-1β also support Th17 cells). Th17 cells make IL-17 and IL-22, which recruit neutrophils and make barrier tissues release antimicrobial peptides. That is the response to extracellular bacteria and fungi.[1][3][7]
Regulatory T cells. Interleukin-2 and TGF-β switch on FOXP3. Treg cells make IL-10 and TGF-β to calm the response.[1][3][8]
Without FOXP3, boys develop X-linked IPEX syndrome, with severe autoimmunity.[1][8]
The chains for these two subsets read the same way. Th17: IL-6 with TGF-β, then RORγt, then IL-17 and IL-22, then neutrophils and barrier tissues. Treg: IL-2 with TGF-β, then FOXP3, then IL-10 and TGF-β, then a calmer response.
The three enemies matched to their subsets
The same chain can be read backwards, from an enemy to the subset that is needed, and from a failed subset to the infection it will allow.
Back to the opening puzzle. The mycobacterium meets Th1, the worm meets Th2, and the fungus meets Th17.[1][3]
- Mycobacterium inside a macrophage → Th1 → IFN-γ activates the macrophage
- Worm in the gut → Th2 → IL-4, IL-5, IL-13 recruit eosinophils, basophils and mast cells
- Fungus on the skin → Th17 → IL-17 and IL-22 recruit neutrophils and induce antimicrobial peptides
When a subset fails
Because each subset has a target, a failure shows up as a pattern of infection. Weak Th1 function leaves mycobacteria unchecked.[1][6]
Each failure follows from the subset's target. Th1 cells activate macrophages against intracellular microbes, so losing them leaves those microbes unchecked. Th17 cells recruit neutrophils and drive barrier-tissue antimicrobial peptides against extracellular bacteria and fungi, so losing them leaves those infections unchecked.
Impaired Th17 cells, as in STAT3 hyper-IgE syndrome, mean recurrent Staphylococcus aureus and Candida infections.[1][4]
Practice question
Original · USMLE styleA 4-year-old boy has had repeated disseminated infections with Mycobacterium avium complex. His serum immunoglobulin levels, CD4+ T-cell count and neutrophil oxidative burst are normal. Genetic testing shows a loss-of-function mutation in the gene encoding the interleukin-12 receptor beta-1 chain.
Common questions
What do Th1, Th2, Th17 and Treg cells do?
Th1 cells activate macrophages against intracellular microbes such as mycobacteria and help the response to viruses. Th2 cells drive the response to worms and allergy. Th17 cells recruit neutrophils against extracellular bacteria and fungi, and Treg cells calm the response.
Which cytokines induce each helper T-cell subset?
IL-12 with IFN-γ induces Th1, IL-4 induces Th2, IL-6 with TGF-β induces Th17, and IL-2 with TGF-β induces Treg.
Which master transcription factor belongs to each subset?
T-bet for Th1, GATA3 for Th2, RORγt for Th17 and FOXP3 for Treg.
What happens if FOXP3 is missing?
Without FOXP3, boys develop X-linked IPEX syndrome, with severe autoimmunity, because regulatory T cells cannot calm the response.
Why do Th1 and Th2 responses tend to commit to one path?
Th1 and Th2 suppress one another, so a response tends to commit to one path.
Transcript
Read the full narration, by chapter624 words
0:00The puzzle: one naive T cell, three enemies
One naive CD four T cell, three very different enemies. A mycobacterium hiding inside a macrophage. A worm in the gut. A fungus on the skin. The same kind of cell has to fight all three. How does it know which weapons to build? Today: match each helper T cell subset to its inducing cytokines, its own cytokines, and what it fights.
0:25The cytokines around the cell choose its job
Last lesson, a T cell received signal one and signal two. Now it chooses a job. The choice is made by the cytokines around it, mostly released by the antigen-presenting cell. Each subset is defined by a signature cytokine and a master transcription factor.
0:44Th1: IL-12, T-bet, interferon gamma, macrophages
Th one. Interleukin 12 from the antigen-presenting cell, with interferon gamma, switches on T-bet. Th one cells make interferon gamma, which activates macrophages to kill what they have swallowed: intracellular microbes such as mycobacteria, and viruses too.
1:04Th2: IL-4, GATA3, eosinophils, mast cells, IgE
Th two. Interleukin four switches on GATA three. Th two cells make interleukin four, 18. They recruit eosinophils, basophils and mast cells, and interleukin four pushes B cells toward I g E. That is the response to worms, and also the machinery of allergy. Th 17.
1:28Th17: IL-6 + TGF-beta, RORgt, neutrophils
Interleukin six with TGF beta switches on ROR gamma T. Th 17 cells make interleukin 17 and 22, which recruit neutrophils and make barrier tissues release antimicrobial peptides. That is the response to extracellular bacteria and fungi.
1:50Treg: IL-2 + TGF-beta, FOXP3, IL-10, IPEX
Regulatory T cells. Interleukin two and TGF beta switch on FOX P three. They make interleukin 10 and TGF beta to calm the response. Without FOX P three, boys develop IPEX syndrome, with severe autoimmunity.
2:08Th1 and Th2 oppose each other; the pattern to hold
The subsets also oppose each other: Th one and Th two suppress one another, so a response tends to commit to one path. Here is the pattern to hold. Inducer, then master factor, then product, then target.
2:24The three enemies matched, and what fails
Back to our three enemies: the mycobacterium meets Th one, the worm meets Th two, and the fungus meets Th 17. Now watch what happens when a subset fails. Weak Th one function leaves mycobacteria unchecked. Impaired Th 17 cells, as in ST AT three hyper I g E syndrome, mean recurrent Staphylococcus aureus and Candida infections.
2:51Your turn: a practice question
Your turn. A 4-year-old boy has had repeated disseminated infections with Mycobacterium avium complex. His immunoglobulin levels, CD four count and neutrophil oxidative burst are normal. Genetic testing shows a loss of function mutation in the gene for the interleukin 12 receptor beta one chain. Production of which of the following cytokines is most likely decreased? A, interferon gamma. B, interleukin four. C, interleukin five. D, interleukin 10. E, transforming growth factor beta. Pause here and decide.
3:36The options, one at a time
B is out: interleukin four comes from Th two cells, which are induced by interleukin four itself, not by interleukin 12. C is out: interleukin five is also a Th two product, part of the worm and allergy response. D is out: interleukin 10 comes from regulatory T cells, which need interleukin two and TGF beta. E is out: transforming growth factor beta comes from regulatory T cells and many other cells, not from the Th one pathway that interleukin 12 drives.
4:12The answer: IL-12 receptor, Th1 and interferon gamma
So the answer is A. Interleukin 12 induces Th one cells, so without its receptor they make little interferon gamma, and macrophages cannot kill mycobacteria.
4:25Recap pocket card and next lesson
Three things to keep. One: interleukin 12 makes Th one, interleukin four makes Th two, interleukin six with TGF beta makes Th 17, interleukin two with TGF beta makes regulatory T cells. Two: Th one makes interferon gamma for mycobacteria and viruses; Th two makes four, 18 for worms and allergy; Th 17 makes 17 for bacteria and fungi. Three: regulatory T cells run on FOX P three and make interleukin 10 and TGF beta. Next, antibody classes and how B cells switch between them.
Sources
Numbers in the text, e.g. [1], point here- Zhu X, Zhu J. CD4 T Helper Cell Subsets and Related Human Immunological Disorders. Int J Mol Sci 2020. europepmc.org/article/PMC/PMC7663252
- Raphael I, et al. T cell subsets and their signature cytokines in autoimmune and inflammatory diseases. Cytokine 2015. europepmc.org/article/PMC/PMC4637008
- OpenStax Microbiology, 18.3 T Lymphocytes and Cellular Immunity. openstax.org/books/microbiology/pages/18-3-t-lymphocytes-and-cellular-immunity
- Tsilifis C, et al. STAT3 hyper-IgE syndrome. 2021. europepmc.org/article/PMC/PMC8249299
- IL-12 receptor beta-1 deficiency and Th1 and Th17 immunity. Clin Rev Allergy Immunol 2026. europepmc.org/article/PMC/PMC13375957
- Mendelian susceptibility to mycobacterial disease review. Front Immunol 2026. europepmc.org/article/PMC/PMC13193987
- TGF-beta in Treg and Th17 biology. Cell Mol Immunol 2023. europepmc.org/article/PMC/PMC10468540
- Regulatory T cells and FOXP3 (IPEX). europepmc.org/article/PMC/PMC2784904
- Snapper CM, et al. IL-4 and isotype switching to IgE (1988). europepmc.org/article/PMC/PMC2189023
The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.
Image credits. Illustrations: Servier Medical Art (smart.servier.com), CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/), adapted (recoloured, outlined, resized): ancylostoma (worm), intestine, Candida albicans, skin, eosinophil, neutrophil, child. NIAID NIH BioArt (public domain): T cell, dendritic cell, macrophage, tuberculosis (mycobacteria and lung), dendritic cell bound to Tregs. Bioicons: mast cell degranulation by Sebastian Reinig and B cell by El-Jayawant (CC BY 4.0); IgE immunoglobulin by Servier (CC BY 3.0). The fork table, cytokine dots, basophil, see-saw, receptor sketch, question card, pocket card and all handwriting are drawn in code (original). No AI-generated teaching images.
Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-IMM-010.
For exam study only, not medical advice. Read the medical disclaimer.
In this series
Playlist on YouTube- EP 01MHC I vs MHC II: how antigen presentation works5:03
- EP 02T-cell activation: the two-signal model4:58
- EP 03Th1, Th2, Th17 and Treg: helper T-cell subsets5:13
- EP 04Antibody isotypes and class switching5:13
- EP 05Central vs peripheral tolerance: how lymphocytes learn self-tolerance5:26
- EP 06Complement system explained: three pathways, one ending5:24
- EP 07Complement deficiencies: C1q, C3, C5–C9 and C1 inhibitor5:15
- EP 08Hypersensitivity types I to IV: the four effectors5:20
- EP 09B-cell vs T-cell immunodeficiency: predict the infections5:24
- EP 10Hyper IgM syndrome: CD40 ligand and class switching5:19
- EP 11Chronic granulomatous disease: NADPH oxidase and the respiratory burst5:20
- EP 12Leukocyte adhesion deficiency: CD18 and neutrophil extravasation5:01
- EP 13Transplant rejection explained: hyperacute, acute, chronic and GVHD5:51
- EP 14Vaccine types explained: live, inactivated, conjugate and mRNA5:41