Distinguish humoral 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 cytotoxic T cells to kill infected cells.
• C. Humoral immunity is not specific; cell-mediated immunity is specific.
• D. Humoral immunity relies on innate immune cells.

Answer: (A)

Humoral immunity and cell-mediated immunity are two arms of the adaptive immune response with different mediators and roles. In humoral immunity, B lymphocytes become plasma cells that secrete antigen-specific antibodies into the circulation. These antibodies bind extracellular pathogens and toxins, neutralize them, tag pathogens for phagocytosis (opsonization), and can activate the classical complement pathway. This makes humoral immunity especially effective against extracellular bacteria and viruses outside cells.

Cell-mediated immunity is driven by T lymphocytes. Helper T cells coordinate the response, while cytotoxic T cells recognize infected cells presenting antigen on MHC I and kill those cells to stop intracellular pathogens from replicating. This arm operates without antibodies.

So the best distinguishing statement is that humoral immunity uses antibodies produced by B cells, whereas cell-mediated immunity relies on T cells and does not depend on antibodies.