# NK cells (Natural Killer cells)

Natural Killer (NK) cells are part of your innate immune system. They destroy virus-infected and cancerous cells without needing prior 'training' on an antigen. Their action is governed by a balance: activating receptors (NKG2D, NKp46, DNAM-1) versus inhibitory receptors that recognize your own healthy cells (via self-MHC class I). NK cells also help direct the adaptive immune system, by quickly releasing cytokines, especially IFN-γ. With age, your NK-cell numbers in the blood tend to rise. But the cells shift toward a 'terminally differentiated', less proliferative state, with weaker killing per cell and poorer cytokine output. That functional decline means worse tumor surveillance and weaker control of reactivating herpesviruses in older adults.

## Sources

- Brauning A, Rae M, Zhu G, Fulton E, Admasu TD, Stolzing A, Sharma A. (2022). Aging of the Immune System: Focus on Natural Killer Cells Phenotype and Functions. Cells. https://doi.org/10.3390/cells11061017
- Gayoso I, Sanchez-Correa B, Campos C, et al.. (2011). Immunosenescence of Human Natural Killer Cells. Journal of Innate Immunity. https://doi.org/10.1159/000328005

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