What is the primary function of antibodies?

What is the primary function of antibodies?

• A. They directly lyse infected cells.
• B. They act as chemotactic signals to recruit neutrophils.
• C. They inhibit the activity of phagocytes.
• D. Neutralization, precipitation, complement fixation, activation of NK cells, agglutination, and opsonization.

Answer: (D)

Antibodies recognize specific antigens and coordinate several defense actions. Their main role is to mark and neutralize invaders, including neutralizing toxins or pathogens by blocking their activity, and promoting precipitation or agglutination to keep antigens in clumps for easier removal. They also fix complement through the classical pathway, which can directly lyse pathogens and boost phagocytosis. The Fc portion of antibodies binds to receptors on natural killer cells to trigger antibody-dependent cellular cytotoxicity, and it tags microbes for phagocytes to engulf (opsonization). The other options describe mechanisms antibodies do not directly perform, such as directly lysing infected cells, acting as chemotactic signals, or inhibiting phagocytes. So the comprehensive set of functions—neutralization, precipitation, complement fixation, NK cell activation, agglutination, and opsonization—best captures how antibodies work.

Antibodies recognize specific antigens and coordinate several defense actions. Their main role is to mark and neutralize invaders, including neutralizing toxins or pathogens by blocking their activity, and promoting precipitation or agglutination to keep antigens in clumps for easier removal. They also fix complement through the classical pathway, which can directly lyse pathogens and boost phagocytosis. The Fc portion of antibodies binds to receptors on natural killer cells to trigger antibody-dependent cellular cytotoxicity, and it tags microbes for phagocytes to engulf (opsonization). The other options describe mechanisms antibodies do not directly perform, such as directly lysing infected cells, acting as chemotactic signals, or inhibiting phagocytes. So the comprehensive set of functions—neutralization, precipitation, complement fixation, NK cell activation, agglutination, and opsonization—best captures how antibodies work.