The role of CTLs in immune responses against viruses is to

• A. neutralize viral activity.
• B. promote destruction of viruses by ADCC.
• C. destroy virus-infected host cells.
• D. attack free virions.

Answer: (C)

Cytotoxic T cells kill cells that have been infected by a virus. They do this by recognizing viral peptides presented on MHC class I molecules on the surface of infected cells. When a CTL binds its target, it releases perforin and granzymes that induce apoptosis, effectively stopping viral replication by eliminating the virus’s production site. This direct destruction of infected host cells is how CTLs curb the spread of the virus and limit disease. They also secrete cytokines to support the broader antiviral response, but their defining action is the targeted killing of infected cells rather than neutralizing free virus particles or mediating ADCC on their own. Therefore, the role of CTLs in antiviral immunity is to destroy virus-infected host cells.