What is opsonization?

• A. The coating of an antigen or particle by antibodies and complement components that facilitate uptake by phagocytes.
• B. The destruction of a cell by enzymes.
• C. The transport of antigens to lymph nodes.
• D. The initiation of an immune response by T cells.

Answer: (A)

Opsonization is marking a microbe for phagocytosis. Antibodies bind to the pathogen and complement components, especially C3b, coat its surface. Phagocytes have receptors for the antibodies’ Fc region and for complement fragments, so these tags greatly enhance uptake and digestion by cells like macrophages and neutrophils. This tagging speeds and improves clearance by linking the antibody response to innate phagocytic killing. Other processes described—enzymatic destruction, antigen transport to lymph nodes, or initiation of T cell responses—are separate immune functions and do not define opsonization.