Which antibody function enhances phagocytosis by tagging pathogens for engulfment?

• A. Opsonization
• B. Neutralization
• C. Complement activation
• D. Agglutination

Answer: (A)

Opsonization is the process of tagging a pathogen with antibodies (and sometimes complement fragments) to promote recognition and engulfment by phagocytes. When an antibody binds a microbe, its Fc region is available to interact with Fc receptors on macrophages and neutrophils. This Fc–receptor engagement signals the phagocyte to ingest and destroy the tagged pathogen. IgG is particularly effective for this tagging, and complement component C3b can also serve as an opsonin, helping phagocytes recognize and take up the invader.

Neutralization blocks a pathogen from attaching or entering host cells and isn’t primarily about enhancing uptake by phagocytes. Complement activation can lead to lysis or inflammation and, through C3b, can contribute to opsonization, but the direct mechanism of marking for engulfment by antibodies is known as opsonization. Agglutination clumps pathogens together to limit spread and can aid clearance, but it’s not the main process by which antibody tagging enhances phagocytosis.