Natural killer (NK) cells are a type of white blood cell that play a crucial role in the body's immune system. They are part of the innate immune response, meaning they can act quickly to identify and destroy infected or cancerous cells without prior exposure. NK cells recognize stressed or abnormal cells through specific receptors and release substances that induce cell death. These cells are essential for maintaining the body's defense against infections and tumors. They can also produce cytokines, which are signaling molecules that help regulate immune responses. Overall, NK cells are vital for early detection and elimination of threats to the body, contributing to overall health and immunity.