Which of the following is an example of humoral immunity?

• A. T cells attacking infected cells
• B. Skin barrier
• C. Antibodies in the blood
• D. Fever response

Answer: (C)

Humoral immunity is antibody-mediated protection carried in body fluids. When B lymphocytes encounter an antigen, they become plasma cells that secrete antibodies. These circulating antibodies in the blood and lymph bind to pathogens or toxins outside cells, neutralizing them and tagging them for attack by other immune components. That makes antibodies in the blood a classic example of humoral immunity.

T cells attacking infected cells illustrate cell-mediated immunity, which uses T lymphocytes rather than antibodies. The skin barrier is an innate physical barrier that prevents entry, and fever is part of the broader inflammatory response rather than humoral immunity.