Which of the following are the three main functions of antibodies?

• A. Neutralization, Phagocytosis, Complement activation
• B. Neutralization, Opsonization, Complement activation
• C. Neutralization, Phagocytosis, Cytotoxicity
• D. Opsonization, Antigen presentation, Cytokine production

Answer: (B)

Antibodies protect the body mainly through three key actions. First, neutralization blocks pathogens or toxins from infecting cells by binding to them and preventing attachment or entry. Second, opsonization coats the microbe so phagocytes with Fc receptors can recognize and engulf it more efficiently. Third, antibody-bound pathogens can trigger the classical complement pathway, starting a cascade that enhances inflammation, promotes opsonization (via C3b), and can lead to lysis of the microbe. Together, these functions account for the primary protective roles of antibodies. While antigen presentation and cytokine production are important immune activities, they are carried out by other cells, and cytotoxicity via antibody interactions (ADCC) is a distinct Fc-mediated process, not one of the three defining antibody functions.