Summary
Cells that mature in the thymus; helper T cells coordinate immunity and cytotoxic T cells kill infected cells.
In depth
CD4 helper cells (Th1, Th2, Th17) direct responses; CD8 cytotoxic cells kill infected or cancerous cells; regulatory T cells suppress. T cells recognise peptide on MHC through their TCR. Positive and negative selection in the thymus removes unresponsive and self-reactive cells.
T cells need antigen presented on MHC. Regulatory T cells maintain tolerance. Exhausted T cells appear in chronic infection and tumours.
Example: CD8 T cells recognise virus peptides on MHC I of infected cells.
T cells mature in the thymus, where they are selected to recognise self-MHC (positive selection) but not self-peptides strongly (negative selection). Helper T cells activate B cells and macrophages through CD40L and cytokines. Cytotoxic T cells recognise peptide-MHC I and release perforin and granzymes to induce apoptosis; they also use Fas ligand. Memory T cells respond faster on re-exposure.
Subsets include Th1 (against intracellular microbes, secrete IFN gamma), Th2 (parasites and allergy), Th17 (fungi and extracellular bacteria, linked to autoimmunity), Tfh (help B cells) and Tregs (suppress). HIV destroys CD4 T cells, crippling immunity. DiGeorge syndrome has no thymus and so few T cells.
Key idea: T cells need antigen presented on MHC, they cannot detect free antigen.
Frequently asked questions
What is T Lymphocytes?
Cells that mature in the thymus; helper T cells coordinate immunity and cytotoxic T cells kill infected cells.
Which area of biology covers T Lymphocytes, and how advanced is it?
T Lymphocytes is one of the 52 topics in Immunology & Disease. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Adaptive Immunity, Immunological Tolerance, Innate Lymphoid Cells.
Can you give an example of T Lymphocytes?
DiGeorge syndrome (no thymus) causes severe immunodeficiency.
What should I learn before T Lymphocytes?
Work through the Beginner topics in Immunology & Disease first, such as Immune System, Viruses, Innate Immunity, then return to T Lymphocytes. Intermediate topics assume the Beginner vocabulary.
What topics are related to T Lymphocytes?
The closest topics to T Lymphocytes are Adaptive Immunity, Immunological Tolerance, Innate Lymphoid Cells, Immunosenescence. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand T Lymphocytes?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for T Lymphocytes. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is T Lymphocytes different from Adaptive Immunity?
T Lymphocytes: Cells that mature in the thymus; helper T cells coordinate immunity and cytotoxic T cells kill infected cells. Adaptive Immunity: Slower, specific defence involving lymphocytes that remember pathogens. Read both side by side and note what each one explains.
How should I study T Lymphocytes step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Adaptive Immunity and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.