In which body system do white blood cells function?

• A. Lymphatic
• B. Circulatory
• C. Digestive
• D. Nervous

Answer: (A)

White blood cells are the immune system’s defenders: they recognize, attack, and help coordinate responses to pathogens. Much of their activity happens in the lymphatic system, which moves immune cells through lymph vessels and filters pathogens in lymph nodes, the spleen, and other lymphoid organs. Lymphocytes, a major type of white blood cell, mature and function primarily within these lymphatic tissues, making this system the best place to describe where their immune actions take place. They do also circulate in the blood as a means of travel, but the core immune activity—the interaction with pathogens and orchestration of defense—occurs within the lymphatic system.