Differentiate humoral immunity from cell-mediated immunity.

• A. Humoral immunity uses B cells and antibodies to neutralize pathogens in body fluids; cell-mediated immunity involves T cells to kill infected cells and regulate immune responses.
• B. Humoral immunity uses T cells to kill pathogens; cell-mediated uses B cells and antibodies to neutralize pathogens in body fluids.
• C. Humoral immunity involves phagocytes; cell-mediated involves complement.
• D. Humoral immunity is slower; cell-mediated is faster.

Answer: (A)

The distinction lies in who handles the threat and where the action takes place. Humoral immunity centers on B lymphocytes that become plasma cells and secrete antibodies into body fluids. These antibodies neutralize extracellular pathogens and toxins, prevent their attachment to host cells, tag them for phagocytosis, and can activate the complement system.

Cell-mediated immunity relies on T lymphocytes. Helper T cells coordinate and regulate immune responses, including helping B cells and activating macrophages, while cytotoxic T cells recognize infected cells presenting foreign antigens on MHC I and destroy those cells directly. This arm is essential for intracellular pathogens and abnormal host cells.

Phagocytes and complement are part of the broader immune system and support both arms, but they don’t define the core difference. Timing can vary, but the key idea is that antibodies in body fluids handle extracellular threats, while T cells deal with intracellular challenges and cellular regulation.