Which immune response uses antibodies circulating in body fluids?

• A. Humoral immunity
• B. Cell-mediated immunity
• C. Innate immunity
• D. Fever response

Answer: (A)

Antibodies circulating in body fluids are produced and used through humoral immunity. In this branch, B lymphocytes become plasma cells that secrete antibodies into the bloodstream and lymph. These antibodies travel in body fluids, bind to specific antigens on extracellular pathogens or toxins, neutralize them, and mark them for attack by other immune components. That fluid-based, antibody-driven action is what defines humoral immunity. In contrast, cell-mediated immunity uses T cells to recognize and destroy infected cells without relying on circulating antibodies, innate immunity provides non-specific barriers and responses rather than tailored antibodies, and fever is a general systemic response not itself the antibody-based mechanism.