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# T-Cells

T-cells - TEE-selz

## Definition

T-cells are a type of white blood cell that plays a central role in the adaptive immune system - the branch of immunity that learns to recognize and remember specific threats. Named after the thymus gland where they mature, T-cells are responsible for directly killing infected cells, coordinating broader immune responses, and maintaining immunological memory that provides long-lasting protection against previously encountered [pathogens](/glossary/pathogen).

There are several major types of T-cells, each with distinct functions. Cytotoxic T-cells (CD8+ T-cells, or "killer" T-cells) directly destroy cells that have been infected by viruses or have become cancerous. Helper T-cells (CD4+ T-cells) don't kill directly but orchestrate the immune response by releasing cytokines that activate and coordinate other immune cells. Regulatory T-cells (Tregs) suppress immune responses to prevent overreaction and [autoimmunity](/glossary/autoimmune-response). Memory T-cells persist long after an infection is cleared, enabling a rapid and robust response if the same pathogen is encountered again.

T-cells recognize threats through T-cell receptors (TCRs) on their surface that bind to specific [antigens](/glossary/antigen) (molecular signatures) displayed on cell surfaces. This recognition system is extraordinarily specific - each T-cell recognizes one particular antigen - and is the basis for both natural immunity and vaccine-induced immunity.

## Also Known As

T lymphocytes T-lymphocytes Thymus-derived lymphocytes 

## Key Facts

-   • The thymus gland, where T-cells mature, is most active during childhood and gradually shrinks with age (thymic involution). 
-   • CD4+ (helper) T-cells are the primary target of HIV - their destruction is what causes AIDS-related immune deficiency. 
-   • A single person's T-cell repertoire can recognize billions of different antigens. 
-   • CAR-T cell therapy - genetically engineering a patient's T-cells to attack cancer - is one of the most promising developments in cancer treatment. 
-   • Memory T-cells can persist for decades, providing long-lasting immunity to previously encountered pathogens. 
-   • Regular moderate exercise has been shown to improve T-cell function, while chronic intense exercise may temporarily suppress it. 

## How It Relates To Your Health

T-cells are relevant to understanding how your immune system fights infections, how vaccines work, and why immune function changes with age. If you've received a vaccination, T-cells (along with B-cells) are the reason your body can rapidly fight the targeted [pathogen](/glossary/pathogen) if you encounter it later.

For people with autoimmune diseases, understanding that the disease involves T-cells (and other [immune cells](/glossary/white-blood-cells)) attacking the body's own tissues helps explain why immunosuppressive treatments are necessary. For cancer patients, emerging T-cell-based immunotherapies like CAR-T cell therapy represent a revolutionary approach that harnesses the immune system's own power to fight cancer.

## Related Terms

[Antigen](/glossary/antigen)[Cytokines](/glossary/cytokines)[Autoimmune Response](/glossary/autoimmune-response)[Inflammation](/glossary/inflammation)

## Sources

1.  [T Cells](https://www.niaid.nih.gov/research/immune-cells) - National Institute of Allergy and Infectious Diseases (NIH)
2.  [T-cell](https://www.britannica.com/science/T-cell) - Encyclopædia Britannica

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