What is the role of opsonization in innate and adaptive immunity?

• A. Opsonization marks pathogens for phagocytosis by binding antibodies and complement components to their surface.
• B. Opsonization neutralizes toxins produced by pathogens.
• C. Opsonization causes direct lysis of pathogens.
• D. Opsonization prevents phagocytosis.

Answer: (B)

Opsonization is about marking pathogens so phagocytes can recognize and engulf them more easily. It involves coating the microbe with opsonins such as antibodies bound to its surface (mainly IgG) and complement fragments like C3b. Phagocytes have receptors for the antibody’s Fc region and for C3b, so when these tags are present, binding is stronger and uptake is triggered more efficiently. This concept spans both innate and adaptive immunity: the complement system is an innate mechanism that helps tag invaders, while antibodies are produced by the adaptive immune system to target specific pathogens. It’s important to differentiate this from neutralizing toxins or directly lysing pathogens; opsonization specifically enhances phagocytosis, not toxin neutralization or membrane attack complex–mediated lysis.