How are natural killer cells activated and what role do they play in the immune response?

Natural killer cells are activated by recognizing abnormal cells, such as infected or cancerous cells, through specific receptors on their surface. Once activated, they release toxic substances to destroy these target cells. Natural killer cells play a crucial role in the immune response by providing rapid and non-specific defense against infected or abnormal cells, helping to prevent the spread of pathogens and tumors in the body.