Which body system regulates immunity?

• A. Endocrine system
• B. Lymphatic system
• C. Circulatory system
• D. Nervous system

Answer: (B)

Lymphatic system is the body’s main coordinator of immune responses. It houses key immune organs—lymph nodes, spleen, and thymus—and circulates lymph, which carries white blood cells to sites of infection. In lymph nodes, immune cells meet antigens, triggering activation and proliferation of T and B cells to fight pathogens. The thymus is where T cells mature, and the spleen filters blood and stores immune cells, helping mount rapid responses. Because these tissues organize detection, activation, and deployment of immune defenses, this system directly regulates immunity. The other systems can influence immunity—hormones from the endocrine system can modulate responses, the circulatory system transports immune cells, and the nervous system can affect immune function—but the lymphatic system best fits the role of regulating immunity.