Agglutination is an antibody-mediated immune response in which bacteria or viruses are clumped together, effectively neutralized and opsonized. Which option best captures this description?

• A. Phagocytosis alone
• B. Complement activation without clumping
• C. Antibody-mediated clumping of pathogens
• D. Direct lysis by antibodies

Answer: (C)

Agglutination is the antibodies cross-linking pathogens into clumps, which neutralizes them and makes them easier to eliminate. This clumping is the defining feature, because it physically groups multiple microbes together, preventing spread and enhancing their recognition by phagocytes.

The best description reflects this cross-linking of pathogens by antibodies, leading to clump formation and easier clearance. Phagocytosis alone describes the next step after the pathogens are marked but doesn’t capture the clumping action itself. Complement activation without clumping describes a different pathway that does not emphasize the visible clumping. Direct lysis by antibodies isn’t accurate because antibodies themselves don’t lyse pathogens; lysis is usually the result of the complement system or other mechanisms acting after antibody binding.