What is the role of B cells in the immune response?

• A. Present antigen to T cells
• B. Phagocytose pathogens
• C. Activate complement
• D. Produce antibodies

Answer: (D)

B cells drive the humoral immune response by producing antibodies. When a B cell encounters its specific antigen, it internalizes and presents fragments to helper T cells, receiving signals to become activated. It then proliferates into plasma cells that secrete large quantities of antibodies and memory B cells that provide quicker responses later. These antibodies circulate and bind to pathogens or toxins, neutralizing them, blocking entry into cells, tagging invaders for destruction by other immune cells (opsonization), and, when bound to antigen, helping to activate the classical pathway of the complement system. This antibody-mediated defense is the primary function of B cells in defending against extracellular pathogens. While B cells can present antigen to T cells as part of the collaboration with helper T cells, and antibodies can engage complement, the central role of B cells themselves is antibody production.