What is the primary mechanism by which humoral antibodies protect against reinfection by viruses?

• A. Activation of macrophages
• B. Blocking viral attachment to cell receptors
• C. Killing of intracellular virus
• D. Prevention of release of virions from infected cells

Answer: (B)

The primary mechanism by which humoral antibodies protect against reinfection by viruses is through the blocking of viral attachment to cell receptors. When antibodies bind to viral particles, they can neutralize the virus by preventing it from attaching to and entering host cells. This blocking action is crucial, as it stops the virus from initiating the infection process in the first place, thereby protecting the host from illness.

When antibodies are produced in response to a viral infection or through vaccination, they specifically recognize and bind to various viral antigens, such as proteins on the virus's surface. This interaction not only inhibits the virus's ability to adhere to and penetrate the host cells but also marks the virus for destruction by other components of the immune system, such as phagocytes.

The effectiveness of antibodies in preventing viral entry is a cornerstone of the adaptive immune response, highlighting how vaccination strategies often aim to elicit strong humoral responses to avert future infections.