[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Immune cells](https://durgical.com/en/immunology/#a-cells) › CD8⁺ cytotoxic T cell [Immunology](https://durgical.com/en/immunology/) · [Immune cells](https://durgical.com/en/immunology/#a-cells) # CD8⁺ cytotoxic T cell - Cell Cytotoxic T cells recognize viral or tumor peptides on MHC class I and kill the cell that shows them. Updated 2026-11-01 ## Key points - CD8 binds MHC class I, which presents peptides from the cell's own cytosol (viral or tumor proteins). - Kill with perforin and granzymes, or with Fas ligand binding Fas on the target; one CD8 cell can kill several targets. - Also secrete interferon-γ and TNF-α. - Naive CD8 activation usually needs a dendritic cell that cross-presents antigen, plus CD4 help for good memory. - Key effectors in viral hepatitis damage, acute cellular transplant rejection and type IV contact reactions. ## What it is CD8⁺ T cells recognize peptides from inside a cell presented on MHC class I, which almost every nucleated cell expresses. When a cell shows a foreign peptide, such as from a virus or a mutated tumor protein, the activated CD8 cell binds it and triggers its death by apoptosis. They are central to clearing viruses, controlling tumors and rejecting transplanted organs. ## Key facts - Origin: lymphoid progenitor in the marrow; selected in the thymus on MHC class I. - Memory CD8 cells persist for years and respond faster on re-exposure. - Viruses and tumors can lower MHC class I to escape them, which is when NK cells take over. ## Step by step - A virus makes proteins inside an infected cell. - The proteasome cuts them into peptides, which TAP carries into the endoplasmic reticulum. - Peptides load onto MHC class I and travel to the cell surface. - An activated CD8 T cell with a matching receptor binds the complex. - It releases perforin and granzymes (or uses Fas ligand) and the infected cell dies by apoptosis. ## Markers - CD3 - CD8 - TCR αβ - Perforin and granzymes - PD-1 when exhausted ## Clinical notes - Atypical lymphocytes in infectious mononucleosis are mostly activated CD8 T cells responding to EBV-infected B cells. - Persistent infections and tumors exhaust CD8 cells (PD-1, CTLA-4); checkpoint inhibitors release this brake and can cause autoimmune side effects. - HLA class I (for example HLA-B27) presents peptides to CD8 cells and is linked to some diseases. - Low CD8 function contributes to severe viral infections in combined immunodeficiencies. ## Memory aid MHC class I is the window every cell has: the CD8 cell looks through it, and if it sees a stranger inside, it ends the house. ## Test yourself Think of the answer, then tap the question to see it. ## Which MHC class presents antigen to CD8 T cells, and where do those peptides come from? MHC class I, presenting peptides made inside the cell, such as viral or tumor proteins. ## What are two ways a CD8 T cell kills its target? Perforin and granzymes, and Fas ligand binding Fas on the target cell; both induce apoptosis. ## What are the atypical lymphocytes of infectious mononucleosis? Mostly activated CD8 T cells responding to Epstein-Barr virus-infected B cells. ## Why do NK cells complement CD8 T cells? When a virus or tumor lowers MHC class I to escape CD8 cells, NK cells kill the cells that lack MHC class I. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/immunology/cd8-cytotoxic-t-cell/) ## Related - [CD4⁺ helper T cell](https://durgical.com/en/immunology/cd4-helper-t-cell/) - [Natural killer cell](https://durgical.com/en/immunology/natural-killer-cell/) - [MHC/HLA class I and II](https://durgical.com/en/immunology/mhc-hla-class-i-and-ii/) - [Antigen processing and presentation](https://durgical.com/en/immunology/antigen-processing-and-presentation/) - [Transplant rejection: hyperacute, acute, chronic](https://durgical.com/en/immunology/transplant-rejection-hyperacute-acute-chronic/) - [Tumor immunology and checkpoint inhibitors](https://durgical.com/en/immunology/tumor-immunology-and-checkpoint-inhibitors/) ## Related conditions - [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/) [← All of immunology](https://durgical.com/en/immunology/) 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: [21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types](https://openstax.org/books/anatomy-and-physiology-2e/pages/21-3-the-adaptive-immune-response-t-lymphocytes-and-their-functional-types) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); [Natural Killer Cells](https://www.immunology.org/public-information/bitesized-immunology/cells/natural-killer-cells) (British Society for Immunology, 2024); [18.4 Leukocytes and Platelets](https://openstax.org/books/anatomy-and-physiology-2e/pages/18-4-leukocytes-and-platelets) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/