Which statement describes humoral immunity?

• A. Presence of antibodies in body fluids
• B. Destruction of infected cells by cytotoxic T cells
• C. Phagocytosis independent of antibodies
• D. Immediate non-specific barrier defenses

Answer: (A)

Humoral immunity is the part of the adaptive immune system that uses antibodies circulating in body fluids to defend against pathogens. Antibodies, produced by B cells and released into blood and lymph, bind to antigens on bacteria, viruses, or toxins. This binding can neutralize the threat directly, prevent pathogens from entering host cells, and mark them for attack by other defenses such as complement proteins or phagocytes. Because these protective actions occur in the fluids of the body, the presence of antibodies in body fluids captures the essence of humoral immunity. In contrast, destroying infected cells with cytotoxic T cells is a cell-mediated response; phagocytosis that does not involve antibodies falls under non-specific or innate processes; and immediate barrier defenses are innate, non-specific protections.