Which cells are central to humoral immunity?

• A. T lymphocytes
• B. Natural killer cells
• C. B lymphocytes
• D. Macrophages

Answer: (C)

Humoral immunity is the antibody-mediated arm of the adaptive immune system, and its cellular driver is the B lymphocyte. When a B cell’s receptor binds its specific antigen, it becomes activated, proliferates, and differentiates into antibody-secreting plasma cells and memory B cells. The antibodies it produces circulate in blood and body fluids, neutralizing pathogens, tagging them for destruction, and activating complement. T lymphocytes mainly govern cell-mediated immunity, coordinating responses and killing infected cells. Natural killer cells contribute to early innate defense against infected or malignant cells, not antibody production. Macrophages are phagocytes and antigen-presenting cells that help initiate the response, but the hallmark activity of humoral immunity is antibody production by B lymphocytes.