Humoral immunity is described as which of the following?

• A. Immunity mediated by T cells
• B. Immunity that uses NK cells
• C. Specific immunity produced by B cells that produce antibodies that circulate in body fluids
• D. Non-specific defense by the skin

Answer: (C)

Humoral immunity is a component of adaptive immunity in which B lymphocytes produce antibodies that circulate in body fluids. When a matching antigen is encountered, B cells differentiate into plasma cells that secrete antibodies into the bloodstream and other extracellular fluids. These antibodies bind free pathogens or toxins, neutralize them, prevent infection of new cells, promote their removal by phagocytes through opsonization, and can activate the complement system. Some B cells become memory cells for a faster response in the future. This differs from cellular immunity, which is driven by T cells that target infected body cells, and from innate defenses like NK cells and the skin barrier that provide non-specific protection.