Which component of the innate immune system is known for coating pathogens to promote phagocytosis by macrophages?

• A. MHC proteins
• B. Intracellular vesicles
• C. Antibodies
• D. Complement proteins

Answer: (D)

Coating pathogens to flag them for ingestion by phagocytes is called opsonization. In the innate immune system, the complement system provides this tagging. Complement proteins like C3b bind to the surface of microbes, and macrophages have receptors for these tagged molecules. When a pathogen is coated, it’s more readily recognized and engulfed by the macrophage, speeding clearance.

MHC proteins don’t tag pathogens for phagocytosis; they present peptide fragments to T cells. Intracellular vesicles are cellular compartments, not pathogen coatings. Antibodies can opsonize pathogens, but they come from the adaptive immune system, not innate. Therefore, complement proteins best fit the role described.