Which statement best distinguishes humoral immunity from cell-mediated immunity?

• A. Humoral immunity uses antibodies produced by B cells; cell-mediated immunity uses T cells and does not rely on antibodies.
• B. Humoral immunity uses antibodies produced by T cells; cell-mediated uses antibodies.
• C. Humoral immunity is not antigen-specific; cell-mediated is highly antigen-specific.
• D. Humoral immunity is restricted to mucosal surfaces only.

Answer: (A)

Humoral immunity centers on antibodies circulating in body fluids, produced by B cells that differentiate into plasma cells. These antibodies specifically recognize extracellular pathogens and toxins, neutralize them, promote opsonization, and can activate the complement system. This arm operates without requiring T cells to generate the antibodies themselves, though T helper cells can help boost the B cell response.

Cell-mediated immunity, on the other hand, relies on T cells to control infections, especially those inside host cells. Cytotoxic T cells recognize infected cells presenting antigen with MHC I and kill those cells directly, while helper T cells secrete cytokines to activate other immune cells, such as macrophages. No antibodies are the central mediators in this pathway.

So the distinguishing feature is that humoral immunity uses antibodies produced by B cells, whereas cell-mediated immunity relies on T cells and does not depend on antibodies for its primary actions.

For completeness: antibodies are produced by B cells, not T cells; both arms are antigen-specific, so humoral immunity is not non-specific; and humoral immunity is not limited to mucosal surfaces but functions systemically with antibodies in blood, lymph, and secretions.