Which process describes white blood cells engulfing pathogens and digesting them?

• A. Antibody production
• B. Phagocytosis
• C. Complement activation
• D. Opsonization

Answer: (B)

Phagocytosis is the process by which white blood cells, such as neutrophils and macrophages, engulf and digest pathogens. It starts when receptors on the phagocyte recognize and bind to components of the invader, then the cell wraps around the microbe to form a phagosome. The phagosome fuses with a lysosome to create a phagolysosome, where digestive enzymes and reactive oxygen species break down the pathogen. In macrophages, some of the broken-down pieces can be displayed to other immune cells to help coordinate the response. Other terms listed describe different immune activities: antibody production is making antibodies by B cells; complement activation is a cascade that helps fight infection; and opsonization is tagging pathogens to make them easier to phagocytose, not the eating and digestion step itself.