Which of the following describes the sequence of phagocytosis?

Which of the following describes the sequence of phagocytosis?

• A. A phagocyte secretes antibodies to neutralize a pathogen before engulfing it.
• B. A phagocyte detects a pathogen, engulfs it to form a phagosome, fuses with a lysosome to digest contents, and presents antigens via MHC if needed.
• C. A phagocyte engulfs pathogens and immediately releases them back without digestion.
• D. Phagocytosis occurs only after a pathogen has been coated with complement.

Answer: (B)

Phagocytosis proceeds in a clear sequence: a phagocyte first detects and binds to a pathogen, then engulfs it to form a phagosome. The phagosome then fuses with a lysosome, producing a phagolysosome where digestive enzymes break down the pathogen. If needed, the resulting fragments are loaded onto MHC molecules and presented on the cell surface to activate T cells, linking innate and adaptive immunity. This sequence is exactly what describes engulfment into a vesicle, fusion with a lysosome for digestion, and antigen presentation. Antibodies aren’t secreted by phagocytes to neutralize pathogens before engulfing them—antibodies are produced by B cells. Phagocytosis also doesn’t involve releasing the ingested pathogen intact after grabbing it. And while coating a pathogen with complement can enhance uptake (opsonization), it’s not an absolute requirement for phagocytosis to occur.

Phagocytosis proceeds in a clear sequence: a phagocyte first detects and binds to a pathogen, then engulfs it to form a phagosome. The phagosome then fuses with a lysosome, producing a phagolysosome where digestive enzymes break down the pathogen. If needed, the resulting fragments are loaded onto MHC molecules and presented on the cell surface to activate T cells, linking innate and adaptive immunity. This sequence is exactly what describes engulfment into a vesicle, fusion with a lysosome for digestion, and antigen presentation.

Antibodies aren’t secreted by phagocytes to neutralize pathogens before engulfing them—antibodies are produced by B cells. Phagocytosis also doesn’t involve releasing the ingested pathogen intact after grabbing it. And while coating a pathogen with complement can enhance uptake (opsonization), it’s not an absolute requirement for phagocytosis to occur.