# CD4/CD8 ratio

The CD4/CD8 ratio compares two kinds of T cell in your blood: CD4+ helper T cells versus CD8+ killer T cells. A healthy ratio is usually cited as about 1.5 to 2.5. In young, healthy adults, CD4+ cells outnumber the rest and coordinate the immune response, while CD8+ cells patrol for infected or cancerous cells. With age, especially if you carry the common CMV virus, certain CD8+ cells expand in large clones. That squeezes the ratio, and can even flip it below 1.0. An inverted ratio is tied to frailty, weak vaccine responses, and higher all-cause death in elderly groups and in people with HIV. So it is increasingly used as part of immune-risk profiling, in the context of immune aging (immunosenescence).

## Sources

- Nikolich-Žugich J. (2018). The twilight of immunity: emerging concepts in aging of the immune system. Nature Immunology. https://doi.org/10.1038/s41590-017-0006-x
- Pawelec G. (2012). Hallmarks of human 'immunosenescence': adaptation or dysregulation?. Immunity and Ageing. https://doi.org/10.1186/1742-4933-9-15

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_Canonical: https://longevity-switzerland.com/en/glossary/cd4-cd8-ratio · Part of Longevity Cities · Updated 2026-06-22_