What is the primary function of humoral immunity?

• A. Antibody-mediated neutralization, opsonization, and complement activation against extracellular pathogens.
• B. Activation of macrophages to kill intracellular pathogens.
• C. Destruction of virus-infected cells via cytotoxic T cells.
• D. Regulation of immune responses by cytokines.

Answer: (A)

Humoral immunity is the antibody-mediated defense of the immune system. B cells differentiate into plasma cells that produce antibodies, which bind to extracellular pathogens and their toxins. This binding can neutralize pathogens directly, block toxins, and prevent infection. Antibodies also tag microbes for destruction by phagocytes in a process called opsonization, making them easier to engulf. Additionally, antibody–antigen complexes can activate the classical complement pathway, leading to lysis of some microbes and further recruitment of immune cells. These actions together constitute the primary function of humoral immunity against extracellular threats.

Other aspects of immunity involve cell-mediated responses, such as macrophage activation to kill intracellular pathogens or cytotoxic T cells destroying infected cells, and cytokine regulation, which coordinates the broader immune response.