How do antibodies neutralize viruses?

• A. Antibodies digest viral RNA inside the virus.
• B. Antibodies stimulate T-cells to kill viruses directly.
• C. Antibodies only mark viruses for destruction but do not prevent entry.
• D. Antibodies can bind to viral particles to block entry into host cells and can neutralize toxins or cause agglutination.

Answer: (D)

Antibodies neutralize viruses mainly by binding to viral surface proteins, which can prevent the virus from attaching to or fusing with host cells. When an antibody coats a virus and blocks its receptors, the virus can’t gain entry, so infection is halted at the earliest step. Antibodies can also cause viruses to clump together, or agglutinate, which makes them easier for phagocytes to remove from the body. This combination of blocking entry and promoting clearance is the core way antibodies neutralize viral infections. While antibodies also have other protective roles, such as neutralizing toxins in general, the essential idea for viruses is the blocking of entry and potential agglutination. The other descriptions don’t fit as well: digesting viral RNA isn’t an antibody action, T-cell–mediated killing is a different arm of the immune response, and antibodies don’t only mark viruses without preventing entry.