White blood cells, or leukocytes, are specialized components of blood integral to the immune system. These cells are responsible for defending the body against pathogens, foreign materials, and abnormal cells. They function through various mechanisms, including phagocytosis, where they engulf and destroy invaders, and by orchestrating targeted immune responses. The types of leukocytes vary significantly in function, including those specialized for immediate engulfment of bacteria and those involved in developing long-term immunological memory and coordinating the adaptive response. The collective action of these cells ensures the body maintains homeostasis by neutralizing threats and initiating repair processes.