The current estimation is that there are likely more than 2 billion natural killer (NK) cells circulating in an adult human body at any given time.
NK cells are a type of cytotoxic lymphocyte crucial to the innate immune system. They provide rapid responses to viral-infected cells and tumor formation. Unlike T cells, NK cells can recognize and kill infected or cancerous cells without prior sensitization. Because they are relatively short-lived, the body needs to produce a vast number of them to maintain homeostasis.
Key characteristics of Natural Killer Cells:
- Innate Immunity: NK cells are part of the innate immune system, providing immediate defense against pathogens and tumors.
- Cytotoxicity: They kill target cells by releasing cytotoxic granules containing perforin and granzymes.
- Regulation: NK cell activity is tightly regulated by a balance of activating and inhibitory signals.
- Development: Their development is still under investigation, but is crucial to understanding how such high numbers are maintained.
While the exact number can vary from person to person and depend on factors such as age, health status, and immune system activity, 2 billion serves as an accepted approximation. Further research may refine this estimate.
